全文获取类型
收费全文 | 818篇 |
免费 | 47篇 |
出版年
2022年 | 7篇 |
2021年 | 8篇 |
2020年 | 3篇 |
2019年 | 13篇 |
2018年 | 24篇 |
2017年 | 17篇 |
2016年 | 15篇 |
2015年 | 30篇 |
2014年 | 44篇 |
2013年 | 48篇 |
2012年 | 63篇 |
2011年 | 50篇 |
2010年 | 44篇 |
2009年 | 33篇 |
2008年 | 53篇 |
2007年 | 50篇 |
2006年 | 46篇 |
2005年 | 36篇 |
2004年 | 41篇 |
2003年 | 45篇 |
2002年 | 30篇 |
2001年 | 18篇 |
2000年 | 14篇 |
1999年 | 12篇 |
1998年 | 5篇 |
1997年 | 9篇 |
1996年 | 5篇 |
1995年 | 6篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1992年 | 4篇 |
1991年 | 8篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1979年 | 3篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1974年 | 3篇 |
1968年 | 3篇 |
1966年 | 3篇 |
1943年 | 2篇 |
1941年 | 2篇 |
1939年 | 2篇 |
排序方式: 共有865条查询结果,搜索用时 31 毫秒
51.
Leonarda Troiano Antonio R.M. Granata Andrea Cossarizza Galina Kalashnikova Rita Bianchi Gabriella Pini Franco Tropea Cesare Carani Claudio Franceschi 《Experimental cell research》1998,241(2):384
Sperm cells from control donors of proven fertility and men from barren couples were studied by conventional procedures, i.e., light microscopy as well as flow cytometry. Light microscopy analysis of semen included the measurement of spermatozoa concentration, morphology, and motility. All the men from barren couples were asthenozoospermic at the conventional analysis of semen samples. Flow cytometry was applied to study two important parameters of sperm cells: mitochondrial membrane potential (MMP) assessed by the cationic dye JC-1 and DNA stainability with propidium iodide (PI). JC-1 staining was more reliable than the classical procedure used for this purpose, i.e., rhodamine 123 (Rh123) staining, and allowed us to show a positive correlation between MMP and spermatozoa motility. Regarding DNA analysis, a higher relative percentage of immature spermatozoa, showing a high accessibility of DNA to the intercalating PI fluorochrome, was found in men from barren couples compared to donors of proven fertility. The relative percentage of immature spermatozoa was significantly higher in semen from oligoasthenozoospermic subjects. Moreover, a positive correlation was found between immature spermatozoa, as evaluated by PI staining, and cells with depolarized mitochondria, as evaluated by JC-1 staining, suggesting that spermatozoa defective for nuclear maturity could be functionally defective cells. No correlation between immature spermatozoa determined by FCM and immature spermatozoa determined by light microscopy was found, suggesting that these two techniques assess sperm cell maturity at different levels. 相似文献
52.
Jessica Lebenberg Alain Lalande Patrick Clarysse Irene Buvat Christopher Casta Alexandre Cochet Constantin Constantinidès Jean Cousty Alain de Cesare Stephanie Jehan-Besson Muriel Lefort Laurent Najman Elodie Roullot Laurent Sarry Christophe Tilmant Frederique Frouin Mireille Garreau 《PloS one》2015,10(8)
This work aimed at combining different segmentation approaches to produce a robust and accurate segmentation result. Three to five segmentation results of the left ventricle were combined using the STAPLE algorithm and the reliability of the resulting segmentation was evaluated in comparison with the result of each individual segmentation method. This comparison was performed using a supervised approach based on a reference method. Then, we used an unsupervised statistical evaluation, the extended Regression Without Truth (eRWT) that ranks different methods according to their accuracy in estimating a specific biomarker in a population. The segmentation accuracy was evaluated by estimating six cardiac function parameters resulting from the left ventricle contour delineation using a public cardiac cine MRI database. Eight different segmentation methods, including three expert delineations and five automated methods, were considered, and sixteen combinations of the automated methods using STAPLE were investigated. The supervised and unsupervised evaluations demonstrated that in most cases, STAPLE results provided better estimates than individual automated segmentation methods. Overall, combining different automated segmentation methods improved the reliability of the segmentation result compared to that obtained using an individual method and could achieve the accuracy of an expert. 相似文献
53.
Mario Di Staso Giovanni Luca Gravina Luigi Zugaro Pierluigi Bonfili Lorenzo Gregori Pietro Franzese Francesco Marampon Francesca Vittorini Roberto Moro Vincenzo Tombolini Ernesto Di Cesare Carlo Masciocchi 《PloS one》2015,10(6)
Purpose
aim of this study was to identify outcomes in pain relief and quality of life in patients with a solitary painful osseous metastasis treated by radiotherapy, cryoablation or the combination using a propensity score matching study design.Materials and Methods
175 patients with painful bone metastases were included in the study. Twenty-five of them underwent a radiation course (20 Gy in five daily fractions) 15 days after the cryoablation. These subjects were retrospectively matched by propensity analysis with a group of subjects treated by radiotherapy (125 subjects) and with a group treated byCryoablation (25 subjects). The pain relief in terms of complete response, rate of subjects requiring analgesics after treatments and the changes in self-rated quality of life were measured. Informed consent was obtained from the subject and the study was approved by the local Ethical Committee.Results
An higher proportion of subjects treated by cryoablation (32%) or cryoablation followed by RT (72%;) experienced a complete response compared with patients treated by radiotherapy alone (11.2%). After Bonferroni correction strategy, the addition of radiotherapy to cryoablation significantly improved the rate of complete response compared with cryoablation alone (p = 0.011) and this paralleled with an improved self-rated quality of life. Seventeen subjects (13.6%) of patients in the radiotherapy group, 9 (36%) in the cryoablation group, and 19 (76)% in the cryoablation- radiotherapy group did not require narcotic medications.Conclusions
The addition of radiotherapy to cryoablation favorably impacts on perceived pain, with a favorable toxicity profile. However, our data should be interpreted with caution and could serve as a framework around which to design future trials. 相似文献54.
Diego Bellavia Alessandro Cataliotti Francesco Clemenza Cesar Hernandez Baravoglia Angelo Luca Marcello Traina Bruno Gridelli Tullio Bertani John C. Burnett Cesare Scardulla 《PloS one》2015,10(11)
Background and Aims
Compensatory renal hypertrophy following unilateral nephrectomy (UNX) occurs in the remaining kidney. However, the long-term cardiac adaptive process to UNX remains poorly defined in humans. Our goal was to characterize myocardial structure and function in living kidney donors (LKDs), approximately 12 years after UNX.Methods and Results
Cardiac function and structure in 15 Italian LKDs, at least 5 years after UNX (median time from donation = 8.4 years) was investigated and compared to those of age and sex matched U.S. citizens healthy controls (n = 15). Standard and speckle tracking echocardiography (STE) was performed in both LKDs and controls. Plasma angiotensin II, aldosterone, atrial natriuretic peptide (ANP), N terminus pro B-type natriuretic peptide (NT-proBNP), cyclic guanylyl monophosphate (cGMP), and amino-terminal peptide of procollagen III (PIIINP) were also collected. Median follow-up was 11.9 years. In LKDs, LV geometry and function by STE were similar to controls, wall thickness and volumes were within normal limits also by CMR. In LKDs, CMR was negative for myocardial fibrosis, but apical rotation and LV torsion obtained by STE were impaired as compared to controls (21.4 ± 7.8 vs 32.7 ± 8.9 degrees, p = 0.04). Serum creatinine and PIIINP levels were increased [1.1 (0.9–1.3) mg/dL, and 5.8 (5.4–7.6)] μg/L, respectively), while urinary cGMP was reduced [270 (250–355) vs 581 (437–698) pmol/mL] in LKDs. No LKD developed cardiovascular or renal events during follow-up.Conclusions
Long-term kidney donors have no apparent structural myocardial abnormalities as assessed by contrast enhanced CMR. However, myocardial deformation of the apical segments, as well as apical rotation, and LV torsion are reduced. The concomitant increase in circulating PIIINP level is suggestive of fibrosis. Further studies, focused on US and EU patients are warranted to evaluate whether these early functional modifications will progress to a more compromised cardiac function and structure at a later time. 相似文献55.
Andrei Belitski Stefano Panzeri Cesare Magri Nikos K. Logothetis Christoph Kayser 《Journal of computational neuroscience》2010,29(3):533-545
Studies analyzing sensory cortical processing or trying to decode brain activity often rely on a combination of different
electrophysiological signals, such as local field potentials (LFPs) and spiking activity. Understanding the relation between
these signals and sensory stimuli and between different components of these signals is hence of great interest. We here provide
an analysis of LFPs and spiking activity recorded from visual and auditory cortex during stimulation with natural stimuli.
In particular, we focus on the time scales on which different components of these signals are informative about the stimulus,
and on the dependencies between different components of these signals. Addressing the first question, we find that stimulus
information in low frequency bands (<12 Hz) is high, regardless of whether their energy is computed at the scale of milliseconds
or seconds. Stimulus information in higher bands (>50 Hz), in contrast, is scale dependent, and is larger when the energy
is averaged over several hundreds of milliseconds. Indeed, combined analysis of signal reliability and information revealed
that the energy of slow LFP fluctuations is well related to the stimulus even when considering individual or few cycles, while
the energy of fast LFP oscillations carries information only when averaged over many cycles. Addressing the second question,
we find that stimulus information in different LFP bands, and in different LFP bands and spiking activity, is largely independent
regardless of time scale or sensory system. Taken together, these findings suggest that different LFP bands represent dynamic
natural stimuli on distinct time scales and together provide a potentially rich source of information for sensory processing
or decoding brain activity. 相似文献
56.
Elisa Vescovi Brigitta Ammann Cesare Ravazzi Willy Tinner 《Vegetation History and Archaeobotany》2010,19(3):219-233
Detailed Late-glacial and Holocene palaeoenvironmental records from the northern Apennines with a robust chronology are still
rare, though the region has been regarded as a main area of potential refugia of important trees such as Picea abies and Abies alba. We present a new high-resolution pollen and stomata record from Lago del Greppo (1,442 m a.s.l., Pistoia, northern Apennines)
that has been dated relying on 12 terrestrial plant macrofossils. Late-glacial woodlands became established before 13000 cal
b.p. and were dominated by Pinus and Betula, although more thermophilous taxa such as Quercus, Tilia and Ulmus were already present in the Greppo area, probably at lower altitudes. Abies and Picea expanded locally at the onset of the Holocene at ca. 11500 cal b.p. Fagus sylvatica was the last important tree to expand at ca. 6500 cal b.p., following the decline of Abies. Human impact was generally low throughout the Holocene, and the local woods remained rather closed until the most recent
time, ca. a.d. 1700–1800. The vegetational history of Lago del Greppo appears consistent with that of previous investigations in the study
region. Late-glacial and Holocene vegetation dynamics in the northern Apennines are very similar to those in the Insubrian
southern Alps bordering Switzerland and Italy, across the Po Plain. Similarities between the two areas include the Late-glacial
presence of Abies alba, its strong dominance during the Holocene across different vegetation belts from the lowlands to high elevations, as well
as its final fire and human-triggered reduction during the mid Holocene. Our new data suggest that isolated and minor Picea abies populations survived the Late-glacial in the foothills of the northern Apennines and that at the onset of the Holocene they
moved upwards, reaching the site of Lago del Greppo. Today stands of Picea abies occur only in two small areas in the highest part of the northern Apennines, and they have become extinct elsewhere. Given
the forecast global warming, these relict Picea abies stands of the northern Apennines, which have a history of at least 13,000 years, appear severely endangered. 相似文献
57.
Marielle C. Gold Stefania Cerri Susan Smyk-Pearson Meghan E. Cansler Todd M. Vogt Jacob Delepine Ervina Winata Gwendolyn M. Swarbrick Wei-Jen Chua Yik Y. L. Yu Olivier Lantz Matthew S. Cook Megan D. Null David B. Jacoby Melanie J. Harriff Deborah A. Lewinsohn Ted H. Hansen David M. Lewinsohn 《PLoS biology》2010,8(6)
Control of infection with Mycobacterium tuberculosis (Mtb) requires Th1-type immunity, of which CD8+ T cells play a unique role. High frequency Mtb-reactive CD8+ T cells are present in both Mtb-infected and uninfected humans. We show by limiting dilution analysis that nonclassically restricted CD8+ T cells are universally present, but predominate in Mtb-uninfected individuals. Interestingly, these Mtb-reactive cells expressed the Vα7.2 T-cell receptor (TCR), were restricted by the nonclassical MHC (HLA-Ib) molecule MR1, and were activated in a transporter associated with antigen processing and presentation (TAP) independent manner. These properties are all characteristics of mucosal associated invariant T cells (MAIT), an “innate” T-cell population of previously unknown function. These MAIT cells also detect cells infected with other bacteria. Direct ex vivo analysis demonstrates that Mtb-reactive MAIT cells are decreased in peripheral blood mononuclear cells (PBMCs) from individuals with active tuberculosis, are enriched in human lung, and respond to Mtb-infected MR1-expressing lung epithelial cells. Overall, these findings suggest a generalized role for MAIT cells in the detection of bacterially infected cells, and potentially in the control of bacterial infection. 相似文献
58.
The objectives of these studies were to evaluate the efficacy of a PGF(2alpha) (PGF) analog given through different routes on causing luteal regression in lactating dairy cows. In Experiment 1, lactating Holstein cows (n=118) at random stages of lactation were blocked by parity and days in milk (DIM) and, within each block, randomly assigned to receive PGF as an intra-muscular (IM) injection in the semimembranous/semitendinous muscle (CON), subcutaneous (SC) injection in the cervical area (SCN), or SC injection in the ischio-rectal fossa (IRF). Blood was sampled at 0, 12, 24, 36, and 48 h after treatment for assessment of progesterone concentration. In Experiment 2, a total of 379 lactating Holstein cows, 46+/-7 DIM, were blocked by DIM and, within each block, randomly assigned to receive treatment similar to CON or IRF groups from Experiment 1. Blood was sampled 0 and 48 h after treatment for assessment of progesterone concentration. Cows were classified as experiencing luteal regression when progesterone concentration was <1.0 ng/mL or <40% of initial concentration (0 h=100%). In Experiment 1, there was no effect of route of PGF treatment on decline in progesterone concentration and on the proportion of cows experiencing luteal regression by 12, 24, 36, and 48 h after treatment. Similarly, in Experiment 2, route of treatment did not affect either the decline in progesterone concentration or the proportion of cows that had luteal regression by 48 h after treatment. Treatment of lactating dairy cows with 25mg of PGF given SC in the ischio-rectal fossa did not affect either the decline in progesterone concentration or the proportion of cows that experienced luteal regression by 12, 24, 36, and 48 h after PGF treatment. 相似文献
59.
Self-renewing osteoprogenitors in bone marrow sinusoids can organize a hematopoietic microenvironment 总被引:13,自引:0,他引:13
Sacchetti B Funari A Michienzi S Di Cesare S Piersanti S Saggio I Tagliafico E Ferrari S Robey PG Riminucci M Bianco P 《Cell》2007,131(2):324-336
The identity of cells that establish the hematopoietic microenvironment (HME) in human bone marrow (BM), and of clonogenic skeletal progenitors found in BM stroma, has long remained elusive. We show that MCAM/CD146-expressing, subendothelial cells in human BM stroma are capable of transferring, upon transplantation, the HME to heterotopic sites, coincident with the establishment of identical subendothelial cells within a miniature bone organ. Establishment of subendothelial stromal cells in developing heterotopic BM in vivo occurs via specific, dynamic interactions with developing sinusoids. Subendothelial stromal cells residing on the sinusoidal wall are major producers of Angiopoietin-1 (a pivotal molecule of the HSC "niche" involved in vascular remodeling). Our data reveal the functional relationships between establishment of the HME in vivo, establishment of skeletal progenitors in BM sinusoids, and angiogenesis. 相似文献
60.
Calabrese V Mancuso C Ravagna A Perluigi M Cini C De Marco C Butterfield DA Stella AM 《Journal of neurochemistry》2007,101(3):709-717
Increasing evidence suggests a critical role for oxidative and nitrosative stress in the pathogenesis of most important neurodegenerative disorders. Parkinson's disease (PD) is a neurodegenerative disease characterized by a severe depletion in number of dopaminergic cells of the substantia nigra (SN). Administration of L-DOPA (LD) is the more effective treatment for patients with PD. However, the vast majority of patients suffer LD-related complications, which represent the major problem in the clinical management of PD. In the present study, LD administration to rats resulted in a significant dose-dependent increase in Hsp70 synthesis which was specific for the SN. The amount of 70 kDa protein increased after 6 h treatment reaching the maximal induction after 24-48 h. Induction of Hsp70 in the SN was associated with a significant increase in constitutive Hsc70 and mitochondrial Hsp60 stress proteins, and with increased expression of mitochondrial complex I whereas no significant changes were found in the activity of complex IV. In the same experimental conditions, a significant decrease in reduced glutathione was observed, which was associated with an increased content of oxidized glutathione content as well as nitric oxide (NO) synthase activity, NO metabolites and nitrotyrosine immunoreactivity. Interestingly, Hsp70 induction, iNOS up-regulation and nitrotyrosine formation have been confirmed also in SN and striatum of rats treated with LD and carbidopa, this latter being an inhibitor of the peripheral DOPA decarboxylase. Our data are in favor of the importance of the heat shock signal pathway as a basic mechanism of defense against neurotoxicity elicited by free radical oxygen and nitrogen species produced in aging and neurodegenerative disorders. 相似文献