全文获取类型
收费全文 | 5951篇 |
免费 | 477篇 |
国内免费 | 6篇 |
专业分类
6434篇 |
出版年
2023年 | 51篇 |
2022年 | 83篇 |
2021年 | 149篇 |
2020年 | 96篇 |
2019年 | 96篇 |
2018年 | 171篇 |
2017年 | 147篇 |
2016年 | 266篇 |
2015年 | 294篇 |
2014年 | 340篇 |
2013年 | 475篇 |
2012年 | 367篇 |
2011年 | 363篇 |
2010年 | 314篇 |
2009年 | 229篇 |
2008年 | 264篇 |
2007年 | 211篇 |
2006年 | 270篇 |
2005年 | 222篇 |
2004年 | 184篇 |
2003年 | 192篇 |
2002年 | 171篇 |
2001年 | 77篇 |
2000年 | 65篇 |
1999年 | 67篇 |
1998年 | 82篇 |
1997年 | 54篇 |
1996年 | 64篇 |
1995年 | 57篇 |
1994年 | 66篇 |
1993年 | 67篇 |
1992年 | 38篇 |
1991年 | 38篇 |
1990年 | 26篇 |
1989年 | 31篇 |
1988年 | 35篇 |
1987年 | 29篇 |
1985年 | 35篇 |
1984年 | 34篇 |
1983年 | 31篇 |
1982年 | 26篇 |
1981年 | 30篇 |
1980年 | 36篇 |
1978年 | 29篇 |
1975年 | 28篇 |
1974年 | 35篇 |
1973年 | 26篇 |
1971年 | 23篇 |
1969年 | 24篇 |
1966年 | 23篇 |
排序方式: 共有6434条查询结果,搜索用时 15 毫秒
81.
ARTEMIS stabilizes the genome and modulates proliferative responses in multipotent mesenchymal cells
Background
Unrepaired DNA double-stranded breaks (DSBs) cause chromosomal rearrangements, loss of genetic information, neoplastic transformation or cell death. The nonhomologous end joining (NHEJ) pathway, catalyzing sequence-independent direct rejoining of DSBs, is a crucial mechanism for repairing both stochastically occurring and developmentally programmed DSBs. In lymphocytes, NHEJ is critical for both development and genome stability. NHEJ defects lead to severe combined immunodeficiency (SCID) and lymphoid cancer predisposition in both mice and humans. While NHEJ has been thoroughly investigated in lymphocytes, the importance of NHEJ in other cell types, especially with regard to tumor suppression, is less well documented. We previously reported evidence that the NHEJ pathway functions to suppress a range of nonlymphoid tumor types, including various classes of sarcomas, by unknown mechanisms. 相似文献82.
Heiko F. Stahl Tanja Fauti Nina Ullrich Tobias Bopp Jan Kubach Werner Rust Paul Labhart Vassili Alexiadis Christian Becker Mathias Hafner Andreas Weith Martin C. Lenter Helmut Jonuleit Edgar Schmitt Detlev Mennerich 《PloS one》2009,4(9)
Background
In humans and mice naturally occurring CD4+CD25+ regulatory T cells (nTregs) are a thymus-derived subset of T cells, crucial for the maintenance of peripheral tolerance by controlling not only potentially autoreactive T cells but virtually all cells of the adaptive and innate immune system. Recent work using Dicer-deficient mice irrevocably demonstrated the importance of miRNAs for nTreg cell-mediated tolerance.Principal Findings
DNA-Microarray analyses of human as well as murine conventional CD4+ Th cells and nTregs revealed a strong up-regulation of mature miR-155 (microRNA-155) upon activation in both populations. Studying miR-155 expression in FoxP3-deficient scurfy mice and performing FoxP3 ChIP-Seq experiments using activated human T lymphocytes, we show that the expression and maturation of miR-155 seem to be not necessarily regulated by FoxP3. In order to address the functional relevance of elevated miR-155 levels, we transfected miR-155 inhibitors or mature miR-155 RNAs into freshly-isolated human and mouse primary CD4+ Th cells and nTregs and investigated the resulting phenotype in nTreg suppression assays. Whereas miR-155 inhibition in conventional CD4+ Th cells strengthened nTreg cell-mediated suppression, overexpression of mature miR-155 rendered these cells unresponsive to nTreg cell-mediated suppression.Conclusion
Investigation of FoxP3 downstream targets, certainly of bound and regulated miRNAs revealed the associated function between the master regulator FoxP3 and miRNAs as regulators itself. miR-155 is shown to be crucially involved in nTreg cell mediated tolerance by regulating the susceptibility of conventional human as well as murine CD4+ Th cells to nTreg cell-mediated suppression. 相似文献83.
Alexandru Paraschiv Thibaut J. Lagny Christian Vanhille Campos Evelyne Coudrier Patricia Bassereau Anđela Šarić 《Biophysical journal》2021,120(4):598-606
The cell membrane is an inhomogeneous system composed of phospholipids, sterols, carbohydrates, and proteins that can be directly attached to underlying cytoskeleton. The protein linkers between the membrane and the cytoskeleton are believed to have a profound effect on the mechanical properties of the cell membrane and its ability to reshape. Here, we investigate the role of membrane-cortex linkers on the extrusion of membrane tubes using computer simulations and experiments. In simulations, we find that the force for tube extrusion has a nonlinear dependence on the density of membrane-cortex attachments: at a range of low and intermediate linker densities, the force is not significantly influenced by the presence of the membrane-cortex attachments and resembles that of the bare membrane. For large concentrations of linkers, however, the force substantially increases compared with the bare membrane. In both cases, the linkers provided membrane tubes with increased stability against coalescence. We then pulled tubes from HEK cells using optical tweezers for varying expression levels of the membrane-cortex attachment protein Ezrin. In line with simulations, we observed that overexpression of Ezrin led to an increased extrusion force, while Ezrin depletion had a negligible effect on the force. Our results shed light on the importance of local protein rearrangements for membrane reshaping at nanoscopic scales. 相似文献
84.
Matić Ivana Z. Ergün Sercan Đorđić Crnogorac Marija Misir Sema Aliyazicioğlu Yüksel Damjanović Ana Džudžević-Čančar Hurija Stanojković Tatjana Konanç Kalbiye Petrović Nina 《Cytotechnology》2021,73(3):373-389
Cytotechnology - Six extracts were obtained from plant species Hypericum perforatum L., collected at Samsun in Turkey. The aim of this study was to examine the mechanisms of the anticancer activity... 相似文献
85.
A. Soteriou M. D. Carr T. A. Frenkiel J. E. McCormick C. J. Bauer D. Šali B. Birdsall J. Feeney 《Journal of biomolecular NMR》1993,3(5):535-546
Summary
13C-based three-dimensional 1H–1H correlation experiments have been used to determine essentially complete 13C and 1H resonance assignments for the amino acid side chains of uniformly 13C/15N labelled L. casei dihydrofolate reductase in a complex with the drug methotrexate. Excellent agreement is observed between these assignments and an earlier set of partial assignments made on the basis of correlating nuclear Overhauser effect and crystal structure data, indicating that the tertiary structure of the enzyme is similar in solution and in the crystal state.To whom correspondence should be addressed. 相似文献
86.
Nina Forsgren Richard J. Lamont Karina Persson 《Protein science : a publication of the Protein Society》2009,18(9):1896-1905
The Antigen I/II (AgI/II) family of proteins are cell wall anchored adhesins expressed on the surface of oral streptococci. The AgI/II proteins interact with molecules on other bacteria, on the surface of host cells, and with salivary proteins. Streptococcus gordonii is a commensal bacterium, and one of the primary colonizers that initiate the formation of the oral biofilm. S. gordonii expresses two AgI/II proteins, SspA and SspB that are closely related. One of the domains of SspB, called the variable (V‐) domain, is significantly different from corresponding domains in SspA and all other AgI/II proteins. As a first step to elucidate the differences among these proteins, we have determined the crystal structure of the V‐domain from S. gordonii SspB at 2.3 Å resolution. The domain comprises a β‐supersandwich with a putative binding cleft stabilized by a metal ion. The overall structure of the SspB V‐domain is similar to the previously reported V‐domain of the Streptococcus mutans protein SpaP, despite their low sequence similarity. In spite of the conserved architecture of the binding cleft, the cavity is significantly smaller in SspB, which may provide clues about the difference in ligand specificity. We also verified that the metal in the binding cleft is a calcium ion, in concurrence with previous biological data. It was previously suggested that AgI/II V‐domains are carbohydrate binding. However, we tested that hypothesis by screening the SspB V‐domain for binding to over 400 glycoconjucates and found that the domain does not interact with any of the carbohydrates. 相似文献
87.
Nina Mironenko Elena Timopheeva Ludmila Mikhailova Doris Kopahnke Ilona Krämer Frank Ordon 《Archives Of Phytopathology And Plant Protection》2013,46(6):431-440
Abstract Random amplified polymorphic DNAs (RAPDs) were used to study the genetic variation of Pyrenophora tritici-repentis isolates causing wheat tan spot. Two independent experiments were conducted in 2002 – 2003. In 2002, 40 isolates collected in Russia (Krasnodar region, Bashkiria), Germany, and the Czech Republic were studied and 35 unique RAPD genotypes were identified. Most of the genetic variation (72%) was observed within populations and 28% between them. In 2003, 69 new isolates from Russia (Dagestan, North Osetia, Bashkiria), Germany, and the Czech Republic were studied and 47 unique RAPD genotypes were identified. As in 2002, most of the genetic variation (75%) was observed within populations and 25% between them. Total gene diversity in each group ranged from 0.67 – 1.00 for 2002 and was 1.00 for 2003. The average gene diversity was estimated between 0.13 and 0.20 in 2002 and between 0.07 and 0.18 in 2003. A dendrogramme based on genetic distances between isolates illustrates that the variation is distributed on a small scale (0.3 – 4.0%). Estimated FST values and clustering of isolates on dendrogrammes suggest that groups of isolates from Bashkiria and groups of isolates from Dagestan and North Osetia are separated from others and may be considered as different geographical populations. No clear differentiation between isolates from other sites was revealed. 相似文献
88.
Ivana Šagud Nikolina Maček Hrvat Ana Grgičević Tena Čadež Josipa Hodak Milena Dragojević 《Journal of enzyme inhibition and medicinal chemistry》2013,28(1):460-467
Abstract The enzymes acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) are primary targets in attenuating the symptoms of neurodegenerative diseases. Their inhibition results in elevated concentrations of the neurotransmitter acetylcholine which supports communication among nerve cells. It was previously shown for trans-4/5-arylethenyloxazole compounds to have moderate AChE and BChE inhibitory properties. A preliminary docking study showed that elongating oxazole molecules and adding a new NH group could make them more prone to bind to the active site of both enzymes. Therefore, new trans-amino-4-/5-arylethenyl-oxazoles were designed and synthesised by the Buchwald-Hartwig amination of a previously synthesised trans-chloro-arylethenyloxazole derivative. Additionally, naphthoxazole benzylamine photoproducts were obtained by efficient photochemical electrocyclization reaction. Novel compounds were tested as inhibitors of both AChE and BChE. All of the compounds exhibited binding preference for BChE over AChE, especially for trans-amino-4-/5-arylethenyl-oxazole derivatives which inhibited BChE potently (IC50 in µM range) and AChE poorly (IC50?100?µM). Therefore, due to the selectivity of all of the tested compounds for binding to BChE, these compounds could be applied for further development of cholinesterase selective inhibitors.
- HIGHLIGHTS
-
Series of oxazole benzylamines were designed and synthesised
-
The tested compounds showed binding selectivity for BChE
-
Naphthoxazoles were more potent AChE inhibitors
89.
Shinichi Sunagawa Jens Roat Kultima Paul I Costea Aurélien Amiot Jürgen Böhm Francesco Brunetti Nina Habermann Rajna Hercog Moritz Koch Alain Luciani Daniel R Mende Martin A Schneider Petra Schrotz‐King Christophe Tournigand Jeanne Tran Van Nhieu Takuji Yamada Jürgen Zimmermann Vladimir Benes Matthias Kloor Cornelia M Ulrich Magnus von Knebel Doeberitz Iradj Sobhani Peer Bork 《Molecular systems biology》2014,10(11)
Several bacterial species have been implicated in the development of colorectal carcinoma (CRC),
but CRC-associated changes of fecal microbiota and their potential for cancer screening remain to be
explored. Here, we used metagenomic sequencing of fecal samples to identify taxonomic markers that
distinguished CRC patients from tumor-free controls in a study population of 156 participants.
Accuracy of metagenomic CRC detection was similar to the standard fecal occult blood test (FOBT) and
when both approaches were combined, sensitivity improved > 45% relative to the FOBT,
while maintaining its specificity. Accuracy of metagenomic CRC detection did not differ
significantly between early- and late-stage cancer and could be validated in independent patient and
control populations (N = 335) from different countries. CRC-associated
changes in the fecal microbiome at least partially reflected microbial community composition at the
tumor itself, indicating that observed gene pool differences may reveal tumor-related
host–microbe interactions. Indeed, we deduced a metabolic shift from fiber degradation in
controls to utilization of host carbohydrates and amino acids in CRC patients, accompanied by an
increase of lipopolysaccharide metabolism. 相似文献
90.
Crop yield determines economy by influencing prices on the trade market, and so accurate forecasts of the yield are important for planning various aspects of agricultural production. The main aim of this study is to construct a model for predicting walnut yield in an important walnut production area (the region of Novi Sad in Northern Serbia). Relationships between the amount of walnuts produced annually (2000–2011) and abiotic (e.g. meteorological) and biotic (e.g. airborne pollen data) factors were examined using Pearson correlation analysis. Walnut yield data were then entered into linear regression models with variables that had the highest correlations. The models were constructed using 10 years of data, and tested using 2 years of data not included in constructing the model. This paper has shown that walnut yield is greatly dependent on weather conditions, particularly during fertilisation and seed growth, but the amount of available airborne pollen also plays an important role. The introduction of the seasonal pollen index, as a proxy for the amount of pollen available for fertilisation, improved the performance of models predicting walnut yield. 相似文献