全文获取类型
收费全文 | 13189篇 |
免费 | 769篇 |
国内免费 | 5篇 |
出版年
2023年 | 84篇 |
2022年 | 127篇 |
2021年 | 227篇 |
2020年 | 184篇 |
2019年 | 259篇 |
2018年 | 485篇 |
2017年 | 402篇 |
2016年 | 527篇 |
2015年 | 535篇 |
2014年 | 674篇 |
2013年 | 943篇 |
2012年 | 834篇 |
2011年 | 1033篇 |
2010年 | 631篇 |
2009年 | 487篇 |
2008年 | 681篇 |
2007年 | 730篇 |
2006年 | 690篇 |
2005年 | 610篇 |
2004年 | 509篇 |
2003年 | 546篇 |
2002年 | 429篇 |
2001年 | 285篇 |
2000年 | 284篇 |
1999年 | 203篇 |
1998年 | 120篇 |
1997年 | 58篇 |
1996年 | 49篇 |
1995年 | 50篇 |
1994年 | 33篇 |
1993年 | 37篇 |
1992年 | 47篇 |
1991年 | 64篇 |
1990年 | 40篇 |
1989年 | 49篇 |
1988年 | 48篇 |
1987年 | 46篇 |
1986年 | 50篇 |
1985年 | 66篇 |
1984年 | 61篇 |
1983年 | 43篇 |
1982年 | 43篇 |
1981年 | 36篇 |
1980年 | 51篇 |
1979年 | 62篇 |
1978年 | 51篇 |
1977年 | 44篇 |
1976年 | 30篇 |
1973年 | 28篇 |
1952年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Nathalie Le Floc'h Céline Deblanc Roland Cariolet Anne V. Gautier-Bouchardon Elodie Merlot Ga?lle Simon 《PloS one》2014,9(8)
As nutritional status and inflammation are strongly connected, feeding and nutritional strategies could be effective to improve the ability of pigs to cope with disease. The aims of this study were to investigate the impact of a feed restriction on the ability of pigs to resist and be tolerant to a coinfection with Mycoplasma hyopneumoniae (Mhp) and the European H1N1 swine influenza virus, and the consequences for nutrient metabolism, with a focus on amino acids. Two groups of specific pathogen-free pigs were inoculated with Mhp and H1N1 21 days apart. One group was fed ad libitum, the other group was subjected to a two-week 40% feed restriction starting one week before H1N1 infection. The two respective mock control groups were included. Three days post-H1N1 infection, 200 g of feed was given to pigs previously fasted overnight and serial blood samples were taken over 4 hours to measure plasma nutrient concentrations. Throughout the study, clinical signs were observed and pathogens were detected in nasal swabs and lung tissues. Feed-restricted pigs presented shorter hyperthermia and a positive mean weight gain over the 3 days post-H1N1 infection whereas animals fed ad libitum lost weight. Both infection and feed restriction reduced postprandial glucose concentrations, indicating changes in glucose metabolism. Post-prandial plasma concentrations of the essential amino acids histidine, arginine and threonine were lower in co-infected pigs suggesting a greater use of those amino acids for metabolic purposes associated with the immune response. Altogether, these results indicate that modifying feeding practices could help to prepare animals to overcome an influenza infection. Connections with metabolism changes are discussed. 相似文献
3.
4.
M Kh Ga?nutdinov S I Mirmakhmudova N M Mullagalieva Ia Kh Turakulov 《Biulleten' eksperimental'no? biologii i meditsiny》1984,97(3):293-295
Addition of a thermostable cytoplasmic fraction leads to the uncoupling of oxidative phosphorylation of the mitochondria. In hyperthyrosis such an effect manifests itself more powerfully than in the control. Addition of the thermostable cytoplasmic fraction induces electrogenic phosphate transport via the mitochondrial membrane. In hyperthyrosis, the activity of the thermostable inducer of phosphate transport in the cytoplasm increases. The functioning of the phosphate cycle may be the cause of the uncoupling of oxidative phosphorylation of the mitochondria during the disease in question. 相似文献
5.
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
6.
7.
8.
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
9.
10.
Cultured cells from the anterior pituitary glands of adult rats were treated with the tripeptide aldehyde proteinase inhibitor, BOC-DPhe-Phe-Lys-H. The addition of this tripeptide aldehyde decreased the in vitro release of prolactin to 25% of the control value, while the release of growth hormone in the same cultures decreased to 33% of the control value. Prolactin immunostaining was stronger in semithin sections of proteinase-inhibitor-treated cultures than in control sections. After 2 h treatment with the inhibitor, prolactin- and growth hormone-containing secretory granules were numerous, and the number of crinophagic vacuoles had increased. In the presence of the inhibitor, the overall cytoarchitecture of parenchymal cells was well preserved, and the pathway of the uptake of cationic ferritin appeared to be unaffected. 相似文献