首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   433800篇
  免费   48659篇
  国内免费   171篇
  482630篇
  2018年   4126篇
  2016年   5553篇
  2015年   7412篇
  2014年   8655篇
  2013年   11786篇
  2012年   13535篇
  2011年   13997篇
  2010年   9523篇
  2009年   8848篇
  2008年   12670篇
  2007年   13131篇
  2006年   12248篇
  2005年   11701篇
  2004年   11753篇
  2003年   11056篇
  2002年   10820篇
  2001年   17490篇
  2000年   17470篇
  1999年   13970篇
  1998年   5115篇
  1997年   5322篇
  1996年   4966篇
  1995年   4672篇
  1994年   4533篇
  1993年   4582篇
  1992年   11659篇
  1991年   11584篇
  1990年   11329篇
  1989年   10940篇
  1988年   10515篇
  1987年   10101篇
  1986年   9394篇
  1985年   9292篇
  1984年   7789篇
  1983年   6750篇
  1982年   5200篇
  1981年   4653篇
  1980年   4492篇
  1979年   7447篇
  1978年   5894篇
  1977年   5425篇
  1976年   5224篇
  1975年   5620篇
  1974年   6326篇
  1973年   6192篇
  1972年   5782篇
  1971年   5242篇
  1970年   4651篇
  1969年   4594篇
  1968年   4437篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
143.
Sullivantia species were found to produce quercetin 3-O-glycosides, several of which contain glucuronic acid, as well as pedalitin (6-hydroxy-7-O-methyl luteolin), pedalitin 6-O-glycosides, and small amounts of luteolin. Sullivantia has a unique combination of compounds that distinguishes it from other genera in the Saxifraginae for which flavonoid data are available. The nature of the flavonoid compounds is in accordance with a general trend within the Saxifragaceae of reduction and replacement of flavonols by flavones.  相似文献   
144.
Cytochrome b5 holoenzyme was bound asymmetrically in the tightly bound form to small unilamellar dimyristoylphosphatidylcholine vesicles. [3H]Taurine, a membrane-impermeant nucleophile, was added to the external medium and was then cross-linked to cytochrome carboxyl residues by the addition of a water-soluble carbodiimide. Nonpolar peptide was isolated after trypsin digestion of taurine-labeled apocytochrome b5 and contained 1.7-1.9 residues of taurine. The C-terminal tetrapeptide containing residues Thr130-Asn133 was generated by chymotryptic hydrolysis of radiolabeled nonpolar peptide and was purified by gel filtration and ion exchange chromatography. Amino acid analysis of the C-terminal tetrapeptide showed that about 1.6 mol of taurine was cross-linked per mol of peptide. When the experiment was performed with taurine trapped inside the vesicles, no cross-linking was observed. The results suggest that when cytochrome b5 holoenzyme is bound to vesicles in the tight binding form, the C terminus is located on the external surface of the vesicles.  相似文献   
145.
146.
147.
148.
Summary Eicosapentaenoic acid (EPA) volumetric productivity from an outdoor chemostat culture ofPhaeodactylum tricornutum UTEX 640 in a 50-l tubular photobioreactor varies with dilution rate, reaching a maximum of 47.8 mg l–1 d–1 at D=0.36 d–1. Continuous culture at high dilution rates' is proposed as the most adequate operating mode to maximize polyunsaturated fatty acid production.  相似文献   
149.
A crude extract of human placenta has been demonstrated to stimulate growth, motility and the production of the proteases plasminogen activator and collagenase in cultured bovine capillary endothelial cells. These data are in keeping with the presence of an angiogenic factor(s) in human placenta.  相似文献   
150.
The authors studies the effects of blood serum and IgG fraction from dogs immunized with brain and blood sera from patients with multiple sclerosis and schizophrenia on lipid peroxidation in rat brain homogenates. Measured the content of diene conjugates (DC) and malonic dialdehyde (MDA) in the rat brain after administering the IgG fraction. It was established that antioxidant activity of blood sera and IgG fraction from control animals and donors was significantly higher as compared to experimental. Administration of the IgG fraction brought about an increase in the content of DC and MDA in the brain of experimental animals. It is concluded that complement-dependent brain antibodies present in the blood serum of patients with schizophrenia and multiple sclerosis potentiate lipid peroxidation in the cerebral tissue and that the unsophisticated and informative method for antibody determination may be used in clinical practice.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号