全文获取类型
收费全文 | 4553篇 |
免费 | 339篇 |
专业分类
4892篇 |
出版年
2021年 | 31篇 |
2020年 | 19篇 |
2019年 | 32篇 |
2018年 | 41篇 |
2017年 | 43篇 |
2016年 | 75篇 |
2015年 | 110篇 |
2014年 | 128篇 |
2013年 | 195篇 |
2012年 | 238篇 |
2011年 | 231篇 |
2010年 | 154篇 |
2009年 | 161篇 |
2008年 | 246篇 |
2007年 | 235篇 |
2006年 | 246篇 |
2005年 | 242篇 |
2004年 | 229篇 |
2003年 | 288篇 |
2002年 | 301篇 |
2001年 | 80篇 |
2000年 | 40篇 |
1999年 | 83篇 |
1998年 | 95篇 |
1997年 | 82篇 |
1996年 | 73篇 |
1995年 | 60篇 |
1994年 | 57篇 |
1993年 | 62篇 |
1992年 | 78篇 |
1991年 | 52篇 |
1990年 | 33篇 |
1989年 | 45篇 |
1988年 | 48篇 |
1987年 | 33篇 |
1986年 | 27篇 |
1985年 | 41篇 |
1984年 | 42篇 |
1983年 | 35篇 |
1982年 | 56篇 |
1981年 | 53篇 |
1980年 | 47篇 |
1979年 | 42篇 |
1978年 | 40篇 |
1977年 | 36篇 |
1976年 | 41篇 |
1975年 | 23篇 |
1974年 | 19篇 |
1973年 | 19篇 |
1971年 | 18篇 |
排序方式: 共有4892条查询结果,搜索用时 0 毫秒
21.
Robert L. Wykle Craig H. Miller Jon C. Lewis Jeffrey D. Schmitt Jennie A. Smith Jefferson R. Surles Claude Piantadosi Joseph T. OFlaherty 《Biochemical and biophysical research communications》1981,100(4):1651-1658
1-O-Hexadecyl-2-O-acetyl--glycero-3-phosphocholine (platelet activating factor) stimulated the degranulation of rabbit platelets and human neutrophils, whereas the enantiomer, 3-O-hexadecyl-2-O-acetyl--glycero-1-phosphocholine, was inactive. The analogs compared had the following relative potencies in degranulating platelets and neutrophils: 1-O-hexadecyl-2-O-acetyl--glycero-3-phosphocholine > 1-O-hexadecyl-2-O-ethyl--glycero-3-phosphocholine >-1-O-octadecyl-2-O-ethylglycero-3-phosphocholine = 1-O-hexadecyl-2-O-methyl--glycero-3-phosphocholine >-1-O-dodecyl-2-O-ethyl-glycero-3-phosphocholine. The deacetylated compound, 1-O-hexadecyl-2-lyso--glycero-3-phosphocholine, and 1-O-hexadecyl-2,2-dimethylpropanediol-3-phosphocholine were inactive. The active analogs selectively desensitized the response to each other in the neutrophils. It is suggested that these compounds may activate cells through interaction with a stereospecific receptor. 相似文献
22.
Claude E. Boyd 《Hydrobiologia》1981,80(1):91-93
Ion-pairing has little effect on ionic activity calculations for weakly mineralized natural water (ionic strength < 2 mM). However, for more strongly mineralized freshwaters, corrections for ion-pairing are necessary if highly accurate ionic activities are required. 相似文献
23.
24.
25.
Cypka Mazurek Claude Stiffel Huguette Chalvet Guido Biozzi 《Cancer immunology, immunotherapy : CII》1979,7(2):85-91
Summary The antitumour activity of C. parvum against two different tumours, a lymphosarcoma grafted in XVII mice and a mammary carcinoma grafted in C3H mice, was a radiosensitive phenomenon. A dose of X-rays as low as 100 rads was sufficient to abrogate the C. parvum-induced protection. The duration of this inhibition increased with augmentation of the X-ray dose. The stimulation of macrophage-phagocytic activity induced by C. parvum was not inhibited by a dose of 500 rads. A chronological parallelism has been demonstrated in the recovery of the C. parvum antitumour effect and the restoration of antibody responsiveness after the suppression of these two activities by 500 rads of X-rays in the case of the C3H mice grafted with mammary carcinoma cells. No such concomitant recovery has been observed in XVII mice. In these mice, the recovery of C. parvum antitumour activity took place before the restoration of antibody responsiveness. 相似文献
26.
27.
28.
29.
Marie-Odile Parat Marie-Jeanne Richard Marie Th r se Leccia Pierre Amblard Alain Favier Jean Claude B ani 《Free radical research》1995,23(4):339-351
Reactive oxygen species (ROS) are involved in the mechanism of photoaging and carcinogenesis. Skin is endowed with antioxidant enzymes including superoxide dismutases (SOD): cytosolic copper zinc SOD and mitochondrial manganese SOD. The aim of our study was to estimate the protective effect of manganese against oxidative injury on cultured human skin fibroblasts. Dithranol, hydrogen peroxide and UV-A radiation (375 nm) were employed as oxidative stressors. The supply of manganese chloride produced an increase in cellular content of this element up to 24 fold without concomitant elevation of MnSOD activity. Nevertheless, manganese protects cells against two of the three ROS generating systems assessed, namely hydrogen peroxyde and UV-A. This protective effect depends on the concentration of manganese in the medium, 0.1 mM and 0.2 mM protect against UVA cytotoxicity, only 0.2 mM protects against H2O2 cytotoxicity. 相似文献
30.
Gruber Véronique Berna Patrick P. Arnaud Thierry Bournat Philippe Clément Christèle Mison Dominique Olagnier Béatrice Philippe Laurence Theisen Manfred Baudino Sylvie Bénicourt Claude Cudrey Claire Bloës Carole Duchateau Nathalie Dufour Sylvie Gueguen Catherine Jacquet Séverine Ollivo Catherine Poncetta Christine Zorn Nathalie Ludevid Dolores Van Dorsselaer Alain Verger Robert Doherty Annette Mérot Bertrand Danzin Charles 《Molecular breeding : new strategies in plant improvement》2001,7(4):329-340
A recombinant dog gastric lipase with therapeutic potential for the treatment of exocrine pancreatic insufficiency was expressed in transgenic tobacco plants. We targeted the protein using two different signal sequences for either vacuolar retention or secretion. In both cases, an active glycosylated recombinant protein was obtained. The recombinant enzymes and the native enzyme displayed similar properties including acid resistance and acidic optimum pH. The proteolytic maturation and the specific activity of the recombinant proteins, however, were found to be dependent on subcellular compartmentalization. Expression levels of recombinant dog gastric lipase were about 5% and 7% of acid extractable plant proteins for vacuolar retention and secretion respectively. This expression system already has allowed the production of tens of grams of purified lipase through open-field culture of transgenic tobacco plants. 相似文献