全文获取类型
收费全文 | 1160753篇 |
免费 | 131896篇 |
国内免费 | 705篇 |
出版年
2018年 | 10226篇 |
2016年 | 13989篇 |
2015年 | 19386篇 |
2014年 | 22819篇 |
2013年 | 32611篇 |
2012年 | 36285篇 |
2011年 | 36697篇 |
2010年 | 24860篇 |
2009年 | 22829篇 |
2008年 | 32604篇 |
2007年 | 33729篇 |
2006年 | 31744篇 |
2005年 | 30669篇 |
2004年 | 30426篇 |
2003年 | 29228篇 |
2002年 | 28259篇 |
2001年 | 50510篇 |
2000年 | 50998篇 |
1999年 | 40973篇 |
1998年 | 15007篇 |
1997年 | 15585篇 |
1996年 | 14746篇 |
1995年 | 14022篇 |
1994年 | 13736篇 |
1993年 | 13551篇 |
1992年 | 34540篇 |
1991年 | 33722篇 |
1990年 | 33078篇 |
1989年 | 32283篇 |
1988年 | 30101篇 |
1987年 | 28427篇 |
1986年 | 26652篇 |
1985年 | 26778篇 |
1984年 | 22456篇 |
1983年 | 19202篇 |
1982年 | 14892篇 |
1981年 | 13535篇 |
1980年 | 12747篇 |
1979年 | 21315篇 |
1978年 | 16635篇 |
1977年 | 15193篇 |
1976年 | 14103篇 |
1975年 | 15755篇 |
1974年 | 16627篇 |
1973年 | 16489篇 |
1972年 | 14998篇 |
1971年 | 13452篇 |
1970年 | 11699篇 |
1969年 | 11175篇 |
1968年 | 10183篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
In the course of studies on the oxygenation of steroids by purified P-450 cytochromes, particularly rabbit liver microsomal cytochrome P-450 form 3b, a rapid and reliable radiometric assay has been devised for progesterone 16 alpha-hydroxylation. In view of the lack of a commercially available, suitably tritiated substrate, [1,2,6,7,16,17-3H]progesterone was treated with alkali to remove the label from potential hydroxylation sites other than the 16 alpha position. The resulting [1,7,16-3H]progesterone was added to a reconstituted enzyme system containing cytochrome P-450 form 3b, NADPH-cytochrome P-450 reductase, and NADPH, and the rate of 16 alpha-hydroxylation was measured by the formation of 3H2O. This reaction was shown to be linear with respect to time and to the cytochrome P-450 concentration. An apparent tritium isotope effect of 2.1 was observed by comparison of the rates of formation of tritium oxide and 16 alpha-hydroxyprogesterone, and the magnitude of the isotope effect was confirmed by an isotope competition assay in which a mixture of [1,7,16-3H]progesterone and [4-14C]progesterone was employed. 相似文献
993.
A C Srivastava A J Pinching M W Adler R Robertson R Higgs 《BMJ (Clinical research ed.)》1987,294(6570):495-496
Dr A C Srivastava has written to us to describe a case that raises the suggestion that people infected with the human immuno-deficiency virus (HIV) should carry identity cards. We asked two physicians, a general practitioner working with patients with the acquired immune deficiency syndrome (AIDS), and a general practitioner with a special interest in medical ethics to respond to the broad issues raised by Dr Srivastava''s letter. 相似文献
994.
Verapamil is a calcium-channel blocking agent, commonly used for chronic treatment of heart conditions. We have previously demonstrated that verapamil acts as a co-mutagen in a bacterial mutagenicity test for some experimental anilinoacridine antitumour drugs. Within the anilinoacridines series there are several compounds which are apparently non-mutagenic (or very weak mutagens) in the absence of verapamil, but strong mutagens in its presence. We have now tested a wider range of materials for verapamil enhancement of mutagenicity, to include some of those to which persons on verapamil therapy might be exposed through life-style or occupation. Some verapamil enhancement of mutagenicity was seen with most mutagenic compounds including anticancer drugs, antiparasitic agents, one biological stain and one hair dye. A number of tricyclic antidepressants and biological stains were tested and found to be non-mutagenic. If these results extrapolate to mammalian cells, long-term verapamil therapy could potentially increase the effects of certain environmental mutagens. 相似文献
995.
996.
997.
998.
999.
1000.
R. Milne Murray 《BMJ (Clinical research ed.)》1887,2(1401):1020-1021