全文获取类型
收费全文 | 4749篇 |
免费 | 342篇 |
专业分类
5091篇 |
出版年
2023年 | 26篇 |
2022年 | 45篇 |
2021年 | 80篇 |
2020年 | 60篇 |
2019年 | 60篇 |
2018年 | 70篇 |
2017年 | 79篇 |
2016年 | 111篇 |
2015年 | 242篇 |
2014年 | 263篇 |
2013年 | 309篇 |
2012年 | 426篇 |
2011年 | 377篇 |
2010年 | 230篇 |
2009年 | 199篇 |
2008年 | 303篇 |
2007年 | 313篇 |
2006年 | 304篇 |
2005年 | 230篇 |
2004年 | 226篇 |
2003年 | 221篇 |
2002年 | 230篇 |
2001年 | 43篇 |
2000年 | 47篇 |
1999年 | 56篇 |
1998年 | 50篇 |
1997年 | 30篇 |
1996年 | 36篇 |
1995年 | 48篇 |
1994年 | 20篇 |
1993年 | 35篇 |
1992年 | 21篇 |
1991年 | 22篇 |
1990年 | 23篇 |
1989年 | 15篇 |
1988年 | 15篇 |
1987年 | 15篇 |
1986年 | 19篇 |
1985年 | 17篇 |
1984年 | 20篇 |
1983年 | 19篇 |
1982年 | 21篇 |
1981年 | 10篇 |
1979年 | 10篇 |
1978年 | 14篇 |
1977年 | 20篇 |
1976年 | 9篇 |
1975年 | 10篇 |
1974年 | 11篇 |
1971年 | 6篇 |
排序方式: 共有5091条查询结果,搜索用时 15 毫秒
81.
82.
Johan Zakrisson Krister Wiklund Ove Axner Magnus Andersson 《Biophysical journal》2013,104(10):2137-2148
Type 1 fimbriae mediate adhesion of uropathogenic Escherichia coli to host cells. It has been hypothesized that due to their ability to uncoil under exposure to force, fimbriae can reduce fluid shear stress on the adhesin-receptor interaction by which the bacterium adheres to the surface. In this work, we develop a model that describes how the force on the adhesin-receptor interaction of a type 1 fimbria varies as a bacterium is affected by a time-dependent fluid flow mimicking in vivo conditions. The model combines in vivo hydrodynamic conditions with previously assessed biomechanical properties of the fimbriae. Numerical methods are used to solve for the motion and adhesion force under the presence of time-dependent fluid profiles. It is found that a bacterium tethered with a type 1 pilus will experience significantly reduced shear stress for moderate to high flow velocities and that the maximum stress the adhesin will experience is limited to ∼120 pN, which is sufficient to activate the conformational change of the FimH adhesin into its stronger state but also lower than the force required for breaking it under rapid loading. Our model thus supports the assumption that the type 1 fimbria shaft and the FimH adhesin-receptor interaction are optimized to each other, and that they give piliated bacteria significant advantages in rapidly changing fluidic environments. 相似文献
83.
Julien Gonzalez Sofia Mouttalib Christine Delage Denis Calise Jean-José Maoret Jean-Philippe Pradère Julie Klein Bénédicte Buffin-Meyer Betty Van der Veen Israel F. Charo Peter Heeringa Johan Duchene Jean-Loup Bascands Joost-Peter Schanstra 《Biochemical and biophysical research communications》2013
Most end-stage renal disease kidneys display accumulation of extracellular matrix (ECM) in the renal tubular compartment (tubular interstitial fibrosis – TIF) which is strongly correlated with the future loss of renal function. Although inflammation is a key event in the development of TIF, it can also have a beneficial anti-fibrotic role depending in particular on the stage of the pathology. Chemokines play an important role in monocyte extravasation in the inflammatory process. CCL2 has already been shown to be involved in the development of TIF but CCL7, a close relative of CCL2 and able to bind to similar receptors, has not been studied in renal disease. We therefore studied chemokine CCL7 in a model of unilateral ureteral obstruction (UUO)-induced TIF. We observed that the role of CCL7 differs depending on the stage of the pathology. In early stages (0–8 days), CCL7 deficient (CCL7-KO) mice displayed attenuated TIF potentially involving two mechanisms: an early (0–3 days) decrease of inflammatory cell infiltration followed (3–8 days) by a decrease in tubular ECM production independent of inflammation. In contrast, during later stages of obstruction (10–14 days), CCL7-KO mice displayed increased TIF which was again associated with reduced inflammation. Interestingly, the switch between this anti- to profibrotic effect was accompanied by an increased influx of immunosuppressive regulatory T cells. In conclusion, these results highlight for the first time a dual role for CCL7 in the development of renal TIF, deleterious in early stages but beneficial during later stages. 相似文献
84.
Laleh Khodaparast Ladan Khodaparast Mohammad Shahrooei Benoit Stijlemans Rita Merckx Pieter Baatsen James P. O’Gara Elaine Waters Lieve Van Mellaert Johan Van Eldere 《PloS one》2016,11(1)
Staphylococcus epidermidis is the most common cause of device-associated infections. It has been shown that active and passive immunization in an animal model against protein SesC significantly reduces S. epidermidis biofilm-associated infections. In order to elucidate its role, knock-out of sesC or isolation of S. epidermidis sesC-negative mutants were attempted, however, without success. As an alternative strategy, sesC was introduced into Staphylococcus aureus 8325–4 and its isogenic icaADBC and srtA mutants, into the clinical methicillin-sensitive S. aureus isolate MSSA4 and the MRSA S. aureus isolate BH1CC, which all lack sesC. Transformation of these strains with sesC i) changed the biofilm phenotype of strains 8325–4 and MSSA4 from PIA-dependent to proteinaceous even though PIA synthesis was not affected, ii) converted the non-biofilm-forming strain 8325–4 ica::tet to a proteinaceous biofilm-forming strain, iii) impaired PIA-dependent biofilm formation by 8325–4 srtA::tet, iv) had no impact on protein-mediated biofilm formation of BH1CC and v) increased in vivo catheter and organ colonization by strain 8325–4. Furthermore, treatment with anti-SesC antibodies significantly reduced in vitro biofilm formation and in vivo colonization by these transformants expressing sesC. These findings strongly suggest that SesC is involved in S. epidermidis attachment to and subsequent biofilm formation on a substrate. 相似文献
85.
By converting biomass residue to biochar, we could generate power cleanly and sequester carbon resulting in overall greenhouse gas emissions (GHG) savings when compared to typical fossil fuel usage and waste disposal. We estimated the carbon dioxide (CO2) abatements and emissions associated to the concurrent production of bioenergy and biochar through biomass gasification in an organic walnut farm and processing facility in California, USA. We accounted for (i) avoided-CO2 emissions from displaced grid electricity by bioenergy; (ii) CO2 emissions from farm machinery used for soil amendment of biochar; (iii) CO2 sequestered in the soil through stable biochar-C; and (iv) direct CO2 and nitrous oxide (N2O) emissions from soil. The objective of these assessments was to pinpoint where the largest C offsets can be expected in the bioenergy-biochar chain. We found that energy production from gasification resulted in 91.8% of total C offsets, followed by stable biochar-C (8.2% of total C sinks), offsetting a total of 107.7 kg CO2-C eq Mg-1 feedstock. At the field scale, we monitored gas fluxes from soils for 29 months (180 individual observations) following field management and precipitation events in addition to weekly measurements within three growing seasons and two tree dormancy periods. We compared four treatments: control, biochar, compost, and biochar combined with compost. Biochar alone or in combination with compost did not alter total N2O and CO2 emissions from soils, indicating that under the conditions of this study, biochar-prompted C offsets may not be expected from the mitigation of direct soil GHG emissions. However, this study revealed a case where a large environmental benefit was given by the waste-to-bioenergy treatment, addressing farm level challenges such as waste management, renewable energy generation, and C sequestration. 相似文献
86.
Strong invaders are strong defenders – implications for the resistance of invaded communities 下载免费PDF全文
Anna Henriksson David A. Wardle Johan Trygg Sebastian Diehl Göran Englund 《Ecology letters》2016,19(4):487-494
Many ecosystems receive a steady stream of non‐native species. How biotic resistance develops over time in these ecosystems will depend on how established invaders contribute to subsequent resistance. If invasion success and defence capacity (i.e. contribution to resistance) are correlated, then community resistance should increase as species accumulate. If successful invaders also cause most impact (through replacing native species with low defence capacity) then the effect will be even stronger. If successful invaders instead have weak defence capacity or even facilitative attributes, then resistance should decrease with time, as proposed by the invasional meltdown hypothesis. We analysed 1157 introductions of freshwater fish in Swedish lakes and found that species’ invasion success was positively correlated with their defence capacity and impact, suggesting that these communities will develop stronger resistance over time. These insights can be used to identify scenarios where invading species are expected to cause large impact. 相似文献
87.
88.
89.
Johan Decelle Hryhoriy Stryhanyuk Benoit Gallet Giulia Veronesi Matthias Schmidt Sergio Balzano Sophie Marro Clarisse Uwizeye Pierre-Henri Jouneau Josselin Lupette Juliette Jouhet Eric Maréchal Yannick Schwab Nicole L. Schieber Rémi Tucoulou Hans Richnow Giovanni Finazzi Niculina Musat 《Current biology : CB》2019,29(6):968-978.e4
90.
Sebolai OM Pohl CH Botes PJ Strauss CJ van Wyk PW Botha A Kock JL 《Canadian journal of microbiology》2007,53(6):809-812
Using immunofluorescence confocal laser scanning microscopy, immunogold transmission electron microscopy and gas chromatography--mass spectrometry, we demonstrated the presence of 3-hydroxy fatty acids in Cryptococcus neoformans. Our results suggest that these oxylipins accumulate in capsules where they are released as hydrophobic droplets through tubular protuberances into the surrounding medium. 相似文献