全文获取类型
收费全文 | 10933篇 |
免费 | 752篇 |
国内免费 | 12篇 |
出版年
2023年 | 103篇 |
2022年 | 320篇 |
2021年 | 502篇 |
2020年 | 212篇 |
2019年 | 291篇 |
2018年 | 420篇 |
2017年 | 309篇 |
2016年 | 418篇 |
2015年 | 615篇 |
2014年 | 613篇 |
2013年 | 810篇 |
2012年 | 803篇 |
2011年 | 817篇 |
2010年 | 519篇 |
2009年 | 437篇 |
2008年 | 483篇 |
2007年 | 503篇 |
2006年 | 386篇 |
2005年 | 326篇 |
2004年 | 301篇 |
2003年 | 246篇 |
2002年 | 234篇 |
2001年 | 179篇 |
2000年 | 176篇 |
1999年 | 129篇 |
1998年 | 95篇 |
1997年 | 62篇 |
1996年 | 57篇 |
1995年 | 55篇 |
1994年 | 36篇 |
1993年 | 41篇 |
1992年 | 74篇 |
1991年 | 58篇 |
1990年 | 64篇 |
1989年 | 72篇 |
1988年 | 52篇 |
1987年 | 45篇 |
1986年 | 53篇 |
1985年 | 44篇 |
1984年 | 63篇 |
1983年 | 56篇 |
1982年 | 54篇 |
1981年 | 48篇 |
1980年 | 74篇 |
1979年 | 46篇 |
1978年 | 54篇 |
1977年 | 44篇 |
1975年 | 26篇 |
1974年 | 34篇 |
1973年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Ahmed Hasbi Jocelyne Polastron Stéphane Allouche Laura Stanasila Dominique Massotte Philippe Jauzac 《Journal of neurochemistry》1998,70(5):2129-2138
Abstract: Phosphorylation of G protein-coupled receptors is considered an important step during their desensitization. In SK-N-BE cells, recently presented as a pertinent model for the studies of the human δ-opioid receptor, pretreatment with the opioid agonist etorphine increased time-dependently the rate of phosphorylation of a 51-kDa membrane protein. Immunological characterization of this protein with an antibody, raised against the amino-terminal region of the cloned human δ-opioid receptor, revealed that it corresponded to the δ-opioid receptor. During prolonged treatment with etorphine, phosphorylation increased as early as 15 min to reach a maximum within 1 h. Phosphorylation and desensitization of adenylyl cyclase inhibition paralleled closely and okadaic acid inhibited the resensitization, a result strongly suggesting that phosphorylation of the δ-opioid receptor plays a prominent role in its rapid desensitization. The increase in phosphorylation of the δ-opioid receptor, as well as its desensitization, was not affected by H7, an inhibitor of protein kinase A and protein kinase C, but was drastically reduced by heparin or Zn2+ , known to act as G protein-coupled receptor kinase (GRK) inhibitors. These results are the first to show, on endogenously expressed human δ-opioid receptor, that a close link exists between receptor phosphorylation and agonist-promoted desensitization and that desensitization involves a GRK. 相似文献
3.
Pierre Beuchet Laïla El kihel Michel Dherbomez Georges Charles Yves Letourneux 《Bioorganic & medicinal chemistry letters》1998,8(24):931
Δ7-5-Desaturase catalyses one of the last steps in ergosterol biosynthesis in fungi. Moreover Δ5-unsaturation is necessary for the sparking function. Synthesis of three pairs of C-6 epimeric cholestanol derivatives are described as potential growth inhibitors. Preliminary results suggest that 6β-aminocholestanol is a potent antifungal agent. 相似文献
4.
Branchingprocess(BP)isusedtomodeltheearlystagesofthespreadofasexuallytransmitteddisease.TheearlystagesofAIDSspreadwhichistransmittedbothhomosexuallyandheterosexuallyarestudiedasaBP. 相似文献
5.
6.
Camera trapping studies have become increasingly popular to produce population estimates of individually recognisable mammals. Yet, monitoring techniques for rare species which occur at extremely low densities are lacking. Additionally, species which have unpredictable movements may make obtaining reliable population estimates challenging due to low detectability. Our study explores the effectiveness of intensive camera trapping for estimating cheetah (Acinonyx jubatus) numbers. Using both a more traditional, systematic grid approach and pre-determined, targeted sites for camera placement, the cheetah population of the Northern Tuli Game Reserve, Botswana was sampled between December 2012 and October 2013. Placement of cameras in a regular grid pattern yielded very few (n = 9) cheetah images and these were insufficient to estimate cheetah density. However, pre-selected cheetah scent-marking posts provided 53 images of seven adult cheetahs (0.61 ± 0.18 cheetahs/100km²). While increasing the length of the camera trapping survey from 90 to 130 days increased the total number of cheetah images obtained (from 53 to 200), no new individuals were recorded and the estimated population density remained stable. Thus, our study demonstrates that targeted camera placement (irrespective of survey duration) is necessary for reliably assessing cheetah densities where populations are naturally very low or dominated by transient individuals. Significantly our approach can easily be applied to other rare predator species. 相似文献
7.
Energy is one of the most important factors in the socioeconomic development of a country. In a developing country like Malaysia, the development of islands is mostly related to the availability of electric power. Power generated by renewable energy sources has recently become one of the most promising solutions for the electrification of islands and remote rural areas. But high dependency on weather conditions and the unpredictable nature of these renewable energy sources are the main drawbacks. To overcome this weakness, different green energy sources and power electronic converters need to be integrated with each other. This study presents a battery storage hybrid standalone photovoltaic-wind energy power supply system. In the proposed standalone hybrid system, a DC-DC buck-boost bidirectional converter controller is used to accumulates the surplus hybrid power in the battery bank and supplies this power to the load during the hybrid power shortage by maintaining the constant dc-link voltage. A three-phase voltage source inverter complex vector control scheme is used to control the load side voltage in terms of the voltage amplitude and frequency. Based on the simulation results obtained from MATLAB/Simulink, it has been found that the overall hybrid framework is capable of working under variable weather and load conditions. 相似文献
8.
9.
Ahmed Imrul Mosaddek Nadira Umme Aktari Cao Fangbin He Xiaoyan Zhang Guoping Wu Feibo 《Planta》2016,243(4):973-985
Planta - The drought-stimulated gene expression of NCED, SUS, and KS - DHN and ABA signal cross-talk with other phytohormones maintains barley root growth under drought stress at pH 4.0 plus... 相似文献
10.