全文获取类型
收费全文 | 1898篇 |
免费 | 153篇 |
国内免费 | 1篇 |
专业分类
2052篇 |
出版年
2023年 | 8篇 |
2022年 | 13篇 |
2021年 | 36篇 |
2020年 | 25篇 |
2019年 | 27篇 |
2018年 | 21篇 |
2017年 | 31篇 |
2016年 | 50篇 |
2015年 | 73篇 |
2014年 | 63篇 |
2013年 | 134篇 |
2012年 | 131篇 |
2011年 | 141篇 |
2010年 | 108篇 |
2009年 | 98篇 |
2008年 | 130篇 |
2007年 | 103篇 |
2006年 | 100篇 |
2005年 | 101篇 |
2004年 | 108篇 |
2003年 | 104篇 |
2002年 | 108篇 |
2001年 | 30篇 |
2000年 | 20篇 |
1999年 | 26篇 |
1998年 | 20篇 |
1997年 | 14篇 |
1996年 | 16篇 |
1995年 | 18篇 |
1994年 | 12篇 |
1993年 | 13篇 |
1992年 | 16篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 17篇 |
1988年 | 9篇 |
1987年 | 8篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1974年 | 9篇 |
1973年 | 4篇 |
1955年 | 3篇 |
1954年 | 3篇 |
1943年 | 5篇 |
1942年 | 7篇 |
1898年 | 3篇 |
排序方式: 共有2052条查询结果,搜索用时 15 毫秒
991.
Effect of exposure to fluoride,nitrogen compounds and SO2 on the numbers of spruce shoot aphids on Norway spruce seedlings 总被引:1,自引:0,他引:1
Summary Development of spruce shoot aphid (Cinara pilicornis Hartig) populations was monitored in natural and artificial infestations of Norway spruce (Picea abies Karst.) seedlings, exposed to air pollutants in an experimental field. The pollutants, applied both singly and in mixtures, were gaseous sulphur dioxide, NaF (30 mg l-1 F) and Ca(NO3)2 or (NH4)2SO4 in aqueous solutions (200 mg l-1 N). Aphid numbers on 10 seedlings in each treatment and two control plots were counted at 2-week intervals. At the beginning of the experiment aphid numbers did not differ between treatments. Aphid populations peaked in late June and early July. All the pollutants and their combinations significantly increased the numbers of aphids per seedling. Four apterous females were transferred to spruce seedlings which were growing in containers in the same plots. After 4–5 weeks aphid numbers were significantly higher in the fluoride treatment and in the combined treatment of fluoride, nitrogen and SO2. The pollution treatments did not have a significant effect on shoot growth. Concentrations of F and S in needles were higher in treatments involving these pollutants. There were no significant differences in the concentrations of free amino acids in shoot stems between control and fluoride treatment. However, the relatively low concentration of arginine in the F treatment at the end of the growing season might indicate disturbances in the nitrogen metabolism of spruce seedlings. 相似文献
992.
Mycosporine‐like amino acids (MAAs) are found in a variety of prokaryotic and eucaryotic algae, as well as higher plants, fungi, and animals. These compounds function as a photoprotective sunscreen to prevent ultra‐violet light damage. MAAs may thus be one of the competitive advantages that facilitated development of ozone (by oxytrophs), and thereby may be a competitive advantage for the proliferation of cyanobacteria and other harmful algal species. Numerous difficulties exist with assessment of MAAs, including identification of the compounds, conversion of isomers during HPLC preparation as a result of pH shifts, as well as the ecological implications of the presence, concentration, and forms of these compounds (see J Phycology 1999; 35, for relevant papers). This symposium will provide opportunities for intercalibration of laboratories involved in MAA analyses, suggestions regarding standardization of extraction protocols, as well as results from field‐ and laboratory‐based studies. 相似文献
993.
Sue Sha Damayanthi Devineni Atalanta Ghosh David Polidori Marcus Hompesch Sabine Arnolds Linda Morrow Heike Spitzer Keith Demarest Paul Rothenberg 《PloS one》2014,9(8)
Introduction
This randomized, double-blind, placebo-controlled, single and multiple ascending-dose study evaluated the pharmacodynamic effects and safety/tolerability of canagliflozin, a sodium glucose co-transporter 2 inhibitor, in patients with type 2 diabetes.Methods
Patients (N = 116) discontinued their antihyperglycemic medications 2 weeks before randomization. Patients received canagliflozin 30, 100, 200, or 400 mg once daily or 300 mg twice daily, or placebo at 2 study centers in the United States and Germany, or canagliflozin 30 mg once daily or placebo at 1 study center in Korea, while maintaining an isocaloric diet for 2 weeks. On Days –1, 1, and 16, urinary glucose excretion (UGE), plasma glucose (PG), fasting PG (FPG), and insulin were measured. The renal threshold for glucose (RTG) was calculated from UGE, PG, and estimated glomerular filtration rate. Safety was evaluated based on adverse event (AE) reports, vital signs, electrocardiograms, clinical laboratory tests, and physical examinations.Results
Canagliflozin increased UGE dose-dependently (∼80–120 g/day with canagliflozin ≥100 mg), with increases maintained over the 14-day dosing period with each dose. Canagliflozin dose-dependently decreased RTG, with maximal reductions to ∼4–5 mM (72–90 mg/dL). Canagliflozin also reduced FPG and 24-hour mean PG; glucose reductions were seen on Day 1 and maintained over 2 weeks. Plasma insulin reductions with canagliflozin were consistent with observed PG reductions. Canagliflozin also reduced body weight. AEs were transient, mild to moderate in intensity, and balanced across groups; 1 canagliflozin-treated female reported an episode of vaginal candidiasis. Canagliflozin did not cause hypoglycemia, consistent with the RTG values remaining above the hypoglycemia threshold. At Day 16, there were no clinically meaningful changes in urine volume, urine electrolyte excretion, renal function, or routine laboratory test values.Conclusions
Canagliflozin increased UGE and decreased RTG, leading to reductions in PG, insulin, and body weight, and was generally well tolerated in patients with type 2 diabetes.Trial Registration
ClinicalTrials.gov NCT00963768相似文献994.
Makoto Fukuta Yoshinori Nakai Kosuke Kirino Masato Nakagawa Kazuya Sekiguchi Sanae Nagata Yoshihisa Matsumoto Takuya Yamamoto Katsutsugu Umeda Toshio Heike Naoki Okumura Noriko Koizumi Takahiko Sato Tatsutoshi Nakahata Megumu Saito Takanobu Otsuka Shigeru Kinoshita Morio Ueno Makoto Ikeya Junya Toguchida 《PloS one》2014,9(12)
Neural crest cells (NCCs) are an embryonic migratory cell population with the ability to differentiate into a wide variety of cell types that contribute to the craniofacial skeleton, cornea, peripheral nervous system, and skin pigmentation. This ability suggests the promising role of NCCs as a source for cell-based therapy. Although several methods have been used to induce human NCCs (hNCCs) from human pluripotent stem cells (hPSCs), such as embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), further modifications are required to improve the robustness, efficacy, and simplicity of these methods. Chemically defined medium (CDM) was used as the basal medium in the induction and maintenance steps. By optimizing the culture conditions, the combination of the GSK3β inhibitor and TGFβ inhibitor with a minimum growth factor (insulin) very efficiently induced hNCCs (70–80%) from hPSCs. The induced hNCCs expressed cranial NCC-related genes and stably proliferated in CDM supplemented with EGF and FGF2 up to at least 10 passages without changes being observed in the major gene expression profiles. Differentiation properties were confirmed for peripheral neurons, glia, melanocytes, and corneal endothelial cells. In addition, cells with differentiation characteristics similar to multipotent mesenchymal stromal cells (MSCs) were induced from hNCCs using CDM specific for human MSCs. Our simple and robust induction protocol using small molecule compounds with defined media enabled the generation of hNCCs as an intermediate material producing terminally differentiated cells for cell-based innovative medicine. 相似文献
995.
Thomas Heilskov-Hansen Susanne Wulff Svendsen Jane Fr?lund Thomsen Sigurd Mikkelsen Gert-?ke Hansson 《PloS one》2014,9(11)
Objectives
Sex differences in occupational biomechanical exposures may be part of the explanation why musculoskeletal complaints and disorders tend to be more common among women than among men. We aimed to determine possible sex differences in task distribution and task-specific postures and movements of the upper extremities among Danish house painters, and to establish sex-specific task exposure matrices.Methods
To obtain task distributions, we sent out a questionnaire to all members of the Painters'' Union in Denmark (N = 9364), of whom 53% responded. Respondents reported their task distributions in a typical week. To obtain task exposures, postures and movements were measured in 25 male and 25 female house painters for one whole working day per person. We used goniometers on the wrists, and inclinometers on the forehead and the upper arms. Participants filled in a logbook allowing task-specific exposures to be identified. Percentiles and % time with non-neutral postures were used to characterise postures. Velocity, range of motion, repetitiveness, and variation were used as measures of movement. Cochran-Mantel-Haenszel statistics and unpaired double-sided t-tests with post-hoc Bonferroni correction were used to evaluate sex differences.Results
Statistically significant (p<0.05) sex differences were revealed in task proportions, but the proportions differed by less than 4%. For task exposures, no statistically significant sex differences were found.Conclusions
Only minor sex differences were found in task distribution and task exposures regarding postures and movements among Danish house painters. Sex-specific task exposure matrices were established. 相似文献996.
Catalysed by members of the adenosine deaminase acting on RNA (ADAR) family of enzymes, adenosine-to-inosine (A-to-I) editing converts adenosines in RNA molecules to inosines, which are functionally equivalent to guanosines. Recently, global approaches to studying this widely conserved phenomenon have emerged. The use of bioinformatics, high-throughput sequencing and other approaches has increased the number of known editing sites by several orders of magnitude, and we now have a greater understanding of the control and the biological significance of editing. This Progress article reviews some of these recent global studies and their results. 相似文献
997.
Lorenz HM Schmitt WH Tesar V Müller-Ladner U Tarner I Hauser IA Hiepe F Alexander T Woehling H Nemoto K Heinzel PA 《Arthritis research & therapy》2011,13(2):R36-12
Introduction
As the immunosuppressive potency of 15-deoxyspergualin (DSG) has been shown in the therapy of renal transplant rejection and Wegener's granulomatosis, the intention of this study was to evaluate the safety of DSG in the therapy of lupus nephritis (LN).Methods
Patients with histologically proven active LN after prior treatment with at least one immunosuppressant were treated with 0.5 mg/kg normal body weight/day DSG, injected subcutaneously for 14 days, followed by a break of one week. These cycles were repeated to a maximum of nine times. Doses of oral corticosteroids were gradually reduced to 7.5 mg/day or lower by cycle 4. Response was measured according to a predefined decision pattern. The dose of DSG was adjusted depending on the efficacy and side effects.Results
A total of 21 patients were included in this phase-I/II study. After the first DSG injection, one patient was excluded from the study due to renal failure. Five patients dropped out due to adverse events or serious adverse events including fever, leukopenia, oral candidiasis, herpes zoster or pneumonia. Eleven out of 20 patients achieved partial (4) or complete responses (7), 8 were judged as treatment failures and 1 patient was not assessable. Twelve patients completed all nine cycles; in those patients, proteinuria decreased from 5.88 g/day to 3.37 g/day (P = 0.028), Selena-SLEDAI (Safety of Estrogens in Lupus Erythematosus - National Assessment - systemic lupus erythematosus disease activity index) decreased from 17.6 to 11.7. In 13 out of 20 patients, proteinuria decreased by at least 50%; in 7 patients to less than 1 g/day.Conclusions
Although the number of patients was small, we could demonstrate that DSG provides a tolerably safe treatment for LN. The improvement in proteinuria encourages larger controlled trials.Trial registration
ClinicalTrials.gov: NCT00709722 相似文献998.
Obligate biotrophic pathogens like the rust fungi are important plant pathogens causing enormous losses on food, forage and biomass crops. The analysis of the molecular details underlying obligate biotrophic host-parasite interactions is mainly hampered by the fact that no system for transformation is available for most obligate biotrophic organisms. Here we report the transient transformation of Uromyces fabae, an obligate biotrophic rust fungus using a biolistic approach. Biolistic bombardment of U. fabae urediospores was used to deliver different color markers (β-glucuronidase (GUS), intron green fluorescent protein (iGFP) and red fluorescent protein (DsRed) and/or a selection marker. Endogenous regulatory elements from U. fabae plasma membrane ATPase (Uf-PMA1) were used to drive expression of the transgenes. In addition to the delivery of color markers, an in planta selection procedure using the fungicide Carboxin was established allowing the propagation of transformants. In addition to mere cytoplasmic expression of the color markers, a nuclear localization signal was fused to DsRed (pRV115-NLS) targeting the fluorescent marker protein to the nuclei. A?procedure for the genetic modification of U. fabae was established. The method can be easily adapted for use with other obligate biotrophic fungi. This provides the basis for a more in depth analysis of the molecular principles governing the obligate biotrophic lifestyle. 相似文献
999.
Kato I Niwa A Heike T Fujino H Saito MK Umeda K Hiramatsu H Ito M Morita M Nishinaka Y Adachi S Ishikawa F Nakahata T 《PloS one》2011,6(11):e27042
In acute lymphoblastic leukemia (ALL) patients, the bone marrow niche is widely known to be an important element of treatment response and relapse. Furthermore, a characteristic liver pathology observed in ALL patients implies that the hepatic microenvironment provides an extramedullary niche for leukemic cells. However, it remains unclear whether the liver actually provides a specific niche. The mechanism underlying this pathology is also poorly understood. Here, to answer these questions, we reconstituted the histopathology of leukemic liver by using patients-derived primary ALL cells into NOD/SCID/Yc (null) mice. The liver pathology in this model was similar to that observed in the patients. By using this model, we clearly demonstrated that bile duct epithelial cells form a hepatic niche that supports infiltration and proliferation of ALL cells in the liver. Furthermore, we showed that functions of the niche are maintained by the SDF-1/CXCR4 axis, proposing a novel therapeutic approach targeting the extramedullary niche by inhibition of the SDF-1/CXCR4 axis. In conclusion, we demonstrated that the liver dissemination of leukemia is not due to nonselective infiltration, but rather systematic invasion and proliferation of leukemic cells in hepatic niche. Although the contribution of SDF-1/CXCR4 axis is reported in some cancer cells or leukemic niches such as bone marrow, we demonstrated that this axis works even in the extramedullary niche of leukemic cells. Our findings form the basis for therapeutic approaches that target the extramedullary niche by inhibiting the SDF-1/CXCR4 axis. 相似文献
1000.
Hannemann J Meyer-Staeckling S Kemming D Alpers I Joosse SA Pospisil H Kurtz S Görndt J Püschel K Riethdorf S Pantel K Brandt B 《PloS one》2011,6(11):e26362
During cancer progression, specific genomic aberrations arise that can determine the scope of the disease and can be used as predictive or prognostic markers. The detection of specific gene amplifications or deletions in single blood-borne or disseminated tumour cells that may give rise to the development of metastases is of great clinical interest but technically challenging. In this study, we present a method for quantitative high-resolution genomic analysis of single cells. Cells were isolated under permanent microscopic control followed by high-fidelity whole genome amplification and subsequent analyses by fine tiling array-CGH and qPCR. The assay was applied to single breast cancer cells to analyze the chromosomal region centred by the therapeutical relevant EGFR gene. This method allows precise quantitative analysis of copy number variations in single cell diagnostics. 相似文献