全文获取类型
收费全文 | 7505篇 |
免费 | 1044篇 |
出版年
2023年 | 39篇 |
2022年 | 89篇 |
2021年 | 174篇 |
2020年 | 109篇 |
2019年 | 142篇 |
2018年 | 158篇 |
2017年 | 120篇 |
2016年 | 233篇 |
2015年 | 376篇 |
2014年 | 429篇 |
2013年 | 472篇 |
2012年 | 663篇 |
2011年 | 649篇 |
2010年 | 440篇 |
2009年 | 358篇 |
2008年 | 455篇 |
2007年 | 506篇 |
2006年 | 512篇 |
2005年 | 526篇 |
2004年 | 466篇 |
2003年 | 378篇 |
2002年 | 413篇 |
2001年 | 53篇 |
2000年 | 39篇 |
1999年 | 65篇 |
1998年 | 74篇 |
1997年 | 51篇 |
1996年 | 45篇 |
1995年 | 42篇 |
1994年 | 41篇 |
1993年 | 42篇 |
1992年 | 46篇 |
1991年 | 22篇 |
1990年 | 24篇 |
1989年 | 26篇 |
1988年 | 17篇 |
1987年 | 27篇 |
1986年 | 24篇 |
1985年 | 19篇 |
1984年 | 18篇 |
1983年 | 11篇 |
1982年 | 19篇 |
1981年 | 17篇 |
1980年 | 20篇 |
1979年 | 15篇 |
1978年 | 13篇 |
1977年 | 9篇 |
1976年 | 11篇 |
1975年 | 9篇 |
1974年 | 9篇 |
排序方式: 共有8549条查询结果,搜索用时 547 毫秒
191.
There is a lack of standardized country-specific environmental data to combine with nutritional and dietary data for assessing the environmental impact of individual diets in epidemiology surveys, which are consequently reliant on environmental food datasets based on values retrieved from a heterogeneous literature. The aim of this study was to compare and assess the relative strengths and limits of a database of food greenhouse gas emissions (GHGE) values estimated with a hybrid method combining input/output and LCA approaches, with a dataset of GHGE values retrieved from the literature. France is the geographical perimeter considered in this study, but the methodology could be applied to other countries. The GHGE of 402 foodstuffs, representative of French diet, were estimated using the hybrid method. In parallel, the GHGE of individual foods were collected from existing literature. Median per-food-category GHGE values from the hybrid method and the reviewed literature were found to correlate strongly (Spearman correlation was 0.83), showing similar rankings of food categories. Median values were significantly different for only 5 (out of 29) food categories, including the ruminant meats category for which the hybrid method gave lower estimates than those from existing literature. Analysis also revealed that literature values came from heterogeneous studies that were not always sourced and that were conducted under different LCA modeling hypotheses. In contrast, the hybrid method helps build reliably-sourced, representative national standards for product-based datasets. We anticipate this hybrid method to be a starting point for better environmental impact assessments of diets. 相似文献
192.
Socioeconomic status and anthropometric changes—A meta‐analytic approach from seven German cohorts
下载免费PDF全文
![点击此处可从《Obesity (Silver Spring, Md.)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Johannes Haerting Saskia Hartwig Daniel Tiller Daniel Medenwald Susanne Vogt Barbara Thorand Rolf Holle Ursula Bachlechner Heiner Boeing Benedikt Merz Ute Nöthlings Sabrina Schlesinger Sabine Schipf Till Ittermann Nicole Aumann Anja Schienkiewitz Marjolein Haftenberger Karin H. Greiser Jasmine Neamat‐Allah Verena Katzke Alexander Kluttig 《Obesity (Silver Spring, Md.)》2016,24(3):710-718
193.
Astrid Grottke Florian Ewald Tobias Lange Dominik N?rz Christiane Herzberger Johanna Bach Nicole Grabinski Lareen Gr?ser Frank H?ppner Bj?rn Nashan Udo Schumacher Manfred Jücker 《PloS one》2016,11(1)
Background
Treatment of breast cancer patients with distant metastases represents one of the biggest challenges in today’s gynecological oncology. Therefore, a better understanding of mechanisms promoting the development of metastases is of paramount importance. The serine/threonine kinase AKT was shown to drive cancer progression and metastasis. However, there is emerging data that single AKT isoforms (i.e. AKT1, AKT2 and AKT3) have different or even opposing functions in the regulation of cancer cell migration in vitro, giving rise to the hypothesis that inhibition of distinct AKT isoforms might have undesirable effects on cancer dissemination in vivo.Methods
The triple negative breast cancer cell line MDA-MB-231 was used to investigate the functional roles of AKT in migration and metastasis. AKT single and double knockdown cells were generated using isoform specific shRNAs. Migration was analyzed using live cell imaging, chemotaxis and transwell assays. The metastatic potential of AKT isoform knockdown cells was evaluated in a subcutaneous xenograft mouse model in vivo.Results
Depletion of AKT3, but not AKT1 or AKT2, resulted in increased migration in vitro. This effect was even more prominent in AKT2,3 double knockdown cells. Furthermore, combined downregulation of AKT2 and AKT3, as well as AKT1 and AKT3 significantly increased metastasis formation in vivo. Screening for promigratory proteins revealed that downregulation of AKT3 increases the expression of S100A4 protein. In accordance, depletion of S100A4 by siRNA approach reverses the increased migration induced by knockdown of AKT3.Conclusions
We demonstrated that knockdown of AKT3 can increase the metastatic potential of triple negative breast cancer cells. Therefore, our results provide a rationale for the development of AKT isoform specific inhibitors. 相似文献194.
Megan A. Greischar Nicole Mideo Andrew F. Read Ottar N. Bj?rnstad 《PLoS computational biology》2016,12(2)
Many microparasites infect new hosts with specialized life stages, requiring a subset of the parasite population to forgo proliferation and develop into transmission forms. Transmission stage production influences infectivity, host exploitation, and the impact of medical interventions like drug treatment. Predicting how parasites will respond to public health efforts on both epidemiological and evolutionary timescales requires understanding transmission strategies. These strategies can rarely be observed directly and must typically be inferred from infection dynamics. Using malaria as a case study, we test previously described methods for inferring transmission stage investment against simulated data generated with a model of within-host infection dynamics, where the true transmission investment is known. We show that existing methods are inadequate and potentially very misleading. The key difficulty lies in separating transmission stages produced by different generations of parasites. We develop a new approach that performs much better on simulated data. Applying this approach to real data from mice infected with a single Plasmodium chabaudi strain, we estimate that transmission investment varies from zero to 20%, with evidence for variable investment over time in some hosts, but not others. These patterns suggest that, even in experimental infections where host genetics and other environmental factors are controlled, parasites may exhibit remarkably different patterns of transmission investment. 相似文献
195.
Sheila N. Balinda Pascale Ondoa Ekwaro A. Obuku Aletta Kliphuis Isaac Egau Michelle Bronze Lordwin Kasambula Rob Schuurman Nicole Spieker Tobias F. Rinke de Wit Cissy Kityo ART–A consortium 《PloS one》2016,11(1)
Background
WHO recommends regular viral load (VL) monitoring of patients on antiretroviral therapy (ART) for timely detection of virological failure, prevention of acquired HIV drug resistance (HIVDR) and avoiding unnecessary switching to second-line ART. However, the cost and complexity of routine VL testing remains prohibitive in most resource limited settings (RLS). We evaluated a simple, low–cost, qualitative viral–failure assay (VFA) on dried blood spots (DBS) in three clinical settings in Uganda.Methods
We conducted a cross–sectional diagnostic accuracy study in three HIV/AIDS treatment centres at the Joint Clinical Research Centre in Uganda. The VFA employs semi-quantitative detection of HIV–1 RNA amplified from the LTR gene. We used paired dry blood spot (DBS) and plasma with the COBASAmpliPrep/COBASTaqMan, Roche version 2 (VLref) as the reference assay. We used the VFA at two thresholds of viral load, (>5,000 or >1,000 copies/ml).Results
496 paired VFA and VLref results were available for comparative analysis. Overall, VFA demonstrated 78.4% sensitivity, (95% CI: 69.7%–87.1%), 93% specificity (95% CI: 89.7%–96.4%), 89.3% accuracy (95% CI: 85%–92%) and an agreement kappa = 0.72 as compared to the VLref. The predictive values of positivity and negativity among patients on ART for >12 months were 72.7% and 99.3%, respectively.Conclusions
VFA allowed 89% of correct classification of VF. Only 11% of the patients were misclassified with the potential of unnecessary or late switch to second–line ART. Our findings present an opportunity to roll out simple and affordable VL monitoring for HIV–1 treatment in RLS. 相似文献196.
Stephan Rudolph Antonia Nicole Klein Markus Tusche Christine Schlosser Anne Elfgen Oleksandr Brener Charlotte Teunissen Lothar Gremer Susanne Aileen Funke Janine Kutzsche Dieter Willbold 《PloS one》2016,11(2)
Alzheimer´s disease is the most prominent type of dementia and currently no causative treatment is available. According to recent studies, oligomeric species of the amyloid beta (Aβ) peptide appear to be the most toxic Aβ assemblies. Aβ monomers, however, may be not toxic per se and may even have a neuroprotective role. Here we describe a competitive mirror image phage display procedure that allowed us to identify preferentially Aβ1–42 monomer binding and thereby stabilizing peptides, which destabilize and thereby eliminate toxic oligomer species. One of the peptides, called Mosd1 (monomer specific d-peptide 1), was characterized in more detail. Mosd1 abolished oligomers from a mixture of Aβ1–42 species, reduced Aβ1–42 toxicity in cell culture, and restored the physiological phenotype in neuronal cells stably transfected with the gene coding for human amyloid precursor protein. 相似文献
197.
Achim von Bomhard Alexander Els?sser Lucas Maximilian Ritschl Silke Schwarz Nicole Rotter 《PloS one》2016,11(2)
Vitrification of endothelial cells (MHECT-5) has not previously been compared with controlled slow freezing methods under standardized conditions. To identify the best cryopreservation technique, we evaluated vitrification and standardized controlled-rate -1°C/minute cell freezing in a -80°C freezer and tested four cryoprotective agents (CPA), namely dimethyl sulfoxide (DMSO), ethylene glycol (EG), propylene glycol (PG), and glycerol (GLY), and two media, namely Dulbecco''s modified Eagle medium Ham’s F-12 (DMEM)and K+-modified TiProtec (K+TiP), which is a high-potassium-containing medium. Numbers of viable cells in proliferation were evaluated by the CellTiter 96® AQueous One Solution Cell Proliferation Assay (Promega Corporation, Mannheim, Germany). To detect the exact frozen cell number per cryo vial, DNA content was measured by using Hoechst 33258 dye prior to analysis. Thus, results could be evaluated unconstrained by absolute cell number. Thawed cells were cultured in 25 cm2 cell culture flasks to confluence and examined daily by phase contrast imaging. With regard to cell recovery immediately after thawing, DMSO was the most suitable CPA combined with K+TiP in vitrification (99 ±0.5%) and with DMEM in slow freezing (92 ±1.6%). The most viable cells in proliferation after three days of culture were obtained in cells vitrificated by using GLY with K+TiP (308 ±34%) and PG with DMEM in slow freezing (280 ±27%). 相似文献
198.
Marc Tebruegge Anastasia Pantazidou Duncan MacGregor Gena Gonis David Leslie Luigi Sedda Nicole Ritz Tom Connell Nigel Curtis 《PloS one》2016,11(1)
Background
There are limited data on the epidemiology, diagnosis and optimal management of nontuberculous mycobacterial (NTM) disease in children.Methods
Retrospective cohort study of NTM cases over a 10-year-period at a tertiary referral hospital in Australia.Results
A total of 140 children with NTM disease, including 107 with lymphadenitis and 25 with skin and soft tissue infections (SSTIs), were identified. The estimated incidence of NTM disease was 0.6–1.6 cases / 100,000 children / year; no increasing trend was observed over the study period. Temporal analyses revealed a seasonal incidence cycle around 12 months, with peaks in late winter/spring and troughs in autumn. Mycobacterium-avium-complex accounted for most cases (77.8%), followed by Mycobacterium ulcerans (14.4%) and Mycobacterium marinum (3.3%). Polymerase chain reaction testing had higher sensitivity than culture and microscopy for acid-fast bacilli (92.0%, 67.2% and 35.7%, respectively). The majority of lymphadenitis cases underwent surgical excision (97.2%); multiple recurrences in this group were less common in cases treated with clarithromycin and rifampicin compared with clarithromycin alone or no anti-mycobacterial drugs (0% versus 7.1%; OR:0.73). SSTI recurrences were also less common in cases treated with two anti-mycobacterial drugs compared with one or none (10.5% versus 33.3%; OR:0.23).Conclusions
There was seasonal variation in the incidence of NTM disease, analogous to recently published observations in tuberculosis, which have been linked to seasonal variation in vitamin D. Our finding that anti-mycobacterial combination therapy was associated with a reduced risk of recurrences in patients with NTM lymphadenitis or SSTI requires further confirmation in prospective trials. 相似文献199.
Dylan Alexander Carlin Ryan W. Caster Xiaokang Wang Stephanie A. Betzenderfer Claire X. Chen Veasna M. Duong Carolina V. Ryklansky Alp Alpekin Nathan Beaumont Harshul Kapoor Nicole Kim Hosna Mohabbot Boyu Pang Rachel Teel Lillian Whithaus Ilias Tagkopoulos Justin B. Siegel 《PloS one》2016,11(1)
The use of computational modeling algorithms to guide the design of novel enzyme catalysts is a rapidly growing field. Force-field based methods have now been used to engineer both enzyme specificity and activity. However, the proportion of designed mutants with the intended function is often less than ten percent. One potential reason for this is that current force-field based approaches are trained on indirect measures of function rather than direct correlation to experimentally-determined functional effects of mutations. We hypothesize that this is partially due to the lack of data sets for which a large panel of enzyme variants has been produced, purified, and kinetically characterized. Here we report the kcat and KM values of 100 purified mutants of a glycoside hydrolase enzyme. We demonstrate the utility of this data set by using machine learning to train a new algorithm that enables prediction of each kinetic parameter based on readily-modeled structural features. The generated dataset and analyses carried out in this study not only provide insight into how this enzyme functions, they also provide a clear path forward for the improvement of computational enzyme redesign algorithms. 相似文献
200.
Kristin Clift Kimberly Guthrie Eric W. Klee Nicole Boczek Margot Cousin Patrick Blackburn 《朊病毒》2016,10(6):502-506
Here we present a case of an asymptomatic 53-year-old woman who sought genetic testing for Familial Creutzfeldt-Jakob Disease (fCJD) after learning that her mother had fCJD. The patient's mother had a sudden onset of memory problems and rapidly deteriorating mental faculties in her late 70s, which led to difficulties ambulating, progressive non-fluent aphasia, dysphagia and death within ~1 y of symptom onset. The cause of death was reported as “rapid onset dementia.” The patient's family, unhappy with the vague diagnosis, researched prion disorders online and aggressively pursued causation and submitted frozen brain tissue from the mother to the National Prion Disease Surveillance Center, where testing revealed a previously described 5-octapeptide repeat insertion (5-OPRI) in the prion protein gene (PRNP) that is known to cause fCJD. The family had additional questions about the implications of this result and thus independently sought out genetic counseling. ?While rare, fCJD is likely underdiagnosed due to clinical heterogeneity, rapid onset, early non-specific symptomatology, and overlap in the differential diagnosis of Alzheimer disease and Lewy body dementias. When fCJD is identified, a multidisciplinary approach to return of results that includes the affected patient's provider, genetics professionals, and mental health professionals is key to the care of the family. We present an example case which discusses the psychosocial issues encountered and the role of genetic counseling in presymptomatic testing for incurable neurodegenerative conditions. Ordering physicians should be aware of the basic issues surrounding presymptomatic genetic testing and identify local genetic counseling resources for their patients. 相似文献