全文获取类型
收费全文 | 2571篇 |
免费 | 176篇 |
国内免费 | 4篇 |
出版年
2021年 | 37篇 |
2020年 | 29篇 |
2019年 | 21篇 |
2018年 | 28篇 |
2017年 | 25篇 |
2016年 | 42篇 |
2015年 | 63篇 |
2014年 | 103篇 |
2013年 | 121篇 |
2012年 | 157篇 |
2011年 | 147篇 |
2010年 | 100篇 |
2009年 | 100篇 |
2008年 | 146篇 |
2007年 | 149篇 |
2006年 | 129篇 |
2005年 | 126篇 |
2004年 | 126篇 |
2003年 | 106篇 |
2002年 | 92篇 |
2001年 | 23篇 |
2000年 | 30篇 |
1999年 | 35篇 |
1998年 | 40篇 |
1997年 | 23篇 |
1996年 | 34篇 |
1995年 | 26篇 |
1994年 | 23篇 |
1993年 | 33篇 |
1992年 | 36篇 |
1991年 | 29篇 |
1990年 | 24篇 |
1989年 | 27篇 |
1988年 | 27篇 |
1987年 | 18篇 |
1986年 | 19篇 |
1985年 | 27篇 |
1984年 | 33篇 |
1983年 | 17篇 |
1982年 | 18篇 |
1981年 | 26篇 |
1980年 | 18篇 |
1979年 | 15篇 |
1978年 | 21篇 |
1977年 | 18篇 |
1976年 | 19篇 |
1975年 | 22篇 |
1974年 | 19篇 |
1973年 | 14篇 |
1971年 | 11篇 |
排序方式: 共有2751条查询结果,搜索用时 203 毫秒
101.
The biosynthesis of aspartate-ammonium lyase, the enzyme which is induced by aspartic acid, is specifically repressed by fumaric acid. In the presence of aspartate, the enzyme permits the deamination of this compound by the cell. Aspartic acid is converted into fumaric acid which is an intermediate in the Krebs'cycle. The reaction may be considered as an anaplerotic sequence. In the absence of aspartic acid in the culture medium, its role is anabolic; the enzyme catalyses the biosynthesis of this amino acid. Therefore it appears that the reversible reaction fumarate+NH3=aspartate catalysed by aspartase is included in amphibolic processes. 相似文献
102.
103.
104.
E Devinoy C Hubert E Schaerer L M Houdebine J P Kraehenbuhl 《Nucleic acids research》1988,16(16):8180
105.
106.
107.
Hui Liu Xiang Li Matthew D. Dun Sam Faulkner Chen Chen Jiang Hubert Hondermarck 《Proteomics》2020,20(10)
Pancreatic cancer has a dismal prognosis and to date there are no targeted therapies for this malignancy. Using shotgun proteomics, the mRNA binding protein cold shock domain containing E1 (CSDE1), also called upstream‐of‐N‐Ras, is detected in pancreatic cancer cell lines but not in normal pancreatic epithelial cells. The expression of CSDE1 in pancreatic cancer cells is confirmed by Western blotting and immunohistochemistry of human pancreatic tumors. In vitro functional assays show that siRNA downregulation of CSDE1 or gene knockout using CRISPR‐Cas9 significantly reduce the invasiveness of pancreatic cancer cells. Together, this study reveals that CSDE1 is overexpressed in pancreatic cancer and is a potential therapeutic target to inhibit pancreatic cancer cell invasion. 相似文献
108.
Emma Bell Angela Sherry Giovanni Pilloni Ana Suárez-Suárez Margaret A. Cramm Guillermo Cueto Ian M. Head Casey R. J. Hubert 《Environmental microbiology》2020,22(1):456-465
Thermophilic endospores are widespread in cold marine sediments where the temperature is too low to support growth and activity of thermophiles in situ. These endospores are likely expelled from warm subsurface environments and subsequently dispersed by ocean currents. The endospore upper temperature limit for survival is 140°C, which can be tolerated in repeated short exposures, potentially enabling transit through hot crustal fluids. Longer-term thermal tolerance of endospores, and how long they could persist in an environment hotter than their maximum growth temperature, is less understood. To test whether thermophilic endospores can survive prolonged exposure to high temperatures, sediments were incubated at 80–90°C for 6, 12 or 463 days. Sediments were then cooled by 10–40°C, mimicking the cooling in subsurface oil reservoirs subjected to seawater injection. Cooling the sediments induced sulfate reduction, coinciding with an enrichment of endospore-forming Clostridia. Different Desulfofundulus, Desulfohalotomaculum, Desulfallas, Desulfotomaculum and Desulfofarcimen demonstrated different thermal tolerances, with some Desulfofundulus strains surviving for >1 year at 80°C. In an oil reservoir context, heat-resistant endospore-forming sulfate-reducing bacteria have a survival advantage if they are introduced to, or are resident in, an oil reservoir normally too hot for germination and growth, explaining observations of reservoir souring following cold seawater injection. 相似文献
109.
Júlia R. de Rezende Thomas B. P. Oldenburg Tetyana Korin William D. L. Richardson Milovan Fustic Carolyn M. Aitken Bernard F. J. Bowler Angela Sherry Alexander Grigoryan Gerrit Voordouw Stephen R. Larter Ian M. Head Casey R. J. Hubert 《Environmental microbiology》2020,22(8):3049-3065
Most of the oil in low temperature, non-uplifted reservoirs is biodegraded due to millions of years of microbial activity, including via methanogenesis from crude oil. To evaluate stimulating additional methanogenesis in already heavily biodegraded oil reservoirs, oil sands samples were amended with nutrients and electron acceptors, but oil sands bitumen was the only organic substrate. Methane production was monitored for over 3000 days. Methanogenesis was observed in duplicate microcosms that were unamended, amended with sulfate or that were initially oxic, however methanogenesis was not observed in nitrate-amended controls. The highest rate of methane production was 0.15 μmol CH4 g−1 oil d−1, orders of magnitude lower than other reports of methanogenesis from lighter crude oils. Methanogenic Archaea and several potential syntrophic bacterial partners were detected following the incubations. GC–MS and FTICR–MS revealed no significant bitumen alteration for any specific compound or compound class, suggesting that the very slow methanogenesis observed was coupled to bitumen biodegradation in an unspecific manner. After 3000 days, methanogenic communities were amended with benzoate resulting in methanogenesis rates that were 110-fold greater. This suggests that oil-to-methane conversion is limited by the recalcitrant nature of oil sands bitumen, not the microbial communities resident in heavy oil reservoirs. 相似文献
110.
Hubert du Pontavice Didier Gascuel Gabriel Reygondeau Aurore Maureaud William W. L. Cheung 《Global Change Biology》2020,26(3):1306-1318
Sea water temperature affects all biological and ecological processes that ultimately impact ecosystem functioning. In this study, we examine the influence of temperature on global biomass transfers from marine secondary production to fish stocks. By combining fisheries catches in all coastal ocean areas and life‐history traits of exploited marine species, we provide global estimates of two trophic transfer parameters which determine biomass flows in coastal marine food web: the trophic transfer efficiency (TTE) and the biomass residence time (BRT) in the food web. We find that biomass transfers in tropical ecosystems are less efficient and faster than in areas with cooler waters. In contrast, biomass transfers through the food web became faster and more efficient between 1950 and 2010. Using simulated changes in sea water temperature from three Earth system models, we project that the mean TTE in coastal waters would decrease from 7.7% to 7.2% between 2010 and 2100 under the ‘no effective mitigation’ representative concentration pathway (RCP8.5), while BRT between trophic levels 2 and 4 is projected to decrease from 2.7 to 2.3 years on average. Beyond the global trends, we show that the TTEs and BRTs may vary substantially among ecosystem types and that the polar ecosystems may be the most impacted ecosystems. The detected and projected changes in mean TTE and BRT will undermine food web functioning. Our study provides quantitative understanding of temperature effects on trophodynamic of marine ecosystems under climate change. 相似文献