全文获取类型
收费全文 | 17342篇 |
免费 | 1930篇 |
国内免费 | 2917篇 |
出版年
2024年 | 82篇 |
2023年 | 314篇 |
2022年 | 695篇 |
2021年 | 987篇 |
2020年 | 748篇 |
2019年 | 923篇 |
2018年 | 889篇 |
2017年 | 669篇 |
2016年 | 861篇 |
2015年 | 1079篇 |
2014年 | 1330篇 |
2013年 | 1313篇 |
2012年 | 1600篇 |
2011年 | 1479篇 |
2010年 | 930篇 |
2009年 | 878篇 |
2008年 | 955篇 |
2007年 | 860篇 |
2006年 | 733篇 |
2005年 | 656篇 |
2004年 | 625篇 |
2003年 | 635篇 |
2002年 | 581篇 |
2001年 | 522篇 |
2000年 | 393篇 |
1999年 | 290篇 |
1998年 | 175篇 |
1997年 | 136篇 |
1996年 | 143篇 |
1995年 | 88篇 |
1994年 | 97篇 |
1993年 | 75篇 |
1992年 | 77篇 |
1991年 | 80篇 |
1990年 | 59篇 |
1989年 | 39篇 |
1988年 | 37篇 |
1987年 | 35篇 |
1986年 | 21篇 |
1985年 | 29篇 |
1984年 | 13篇 |
1983年 | 10篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1975年 | 6篇 |
1972年 | 6篇 |
1950年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
44.
45.
46.
47.
Structure of phosphate-free ribonuclease A refined at 1.26 A 总被引:21,自引:0,他引:21
The structure of phosphate-free bovine ribonuclease A has been refined at 1.26-A resolution by a restrained least-squares procedure to a final R factor of 0.15. X-ray diffraction data were collected with an electronic position-sensitive detector. The final model consists of all atoms in the polypeptide chain including hydrogens, 188 water sites with full or partial occupancy, and a single molecule of 2-methyl-2-propanol. Thirteen side chains were modeled with two alternate conformations. Major changes to the active site include the addition of two waters in the phosphate-binding pocket, disordering of Gln-11, and tilting of the imidazole ring of His-119. The structure of the protein and of the associated solvent was extensively compared with three other high-resolution, refined structures of this enzyme. 相似文献
48.
Earlier observations in our laboratory indicated that i.v. infusion of human/rat corticotropin-releasing hormone (hCRH) suppresses pulsatile luteinizing hormone (LH) and follicle-stimulating hormone (FSH) release in ovariectomized rhesus monkeys. Since cortisol secretion increased significantly as well, it was not possible to exclude the possibility that this inhibitory effect of hCRH on gonadotropins was related to the activation of the pituitary/adrenal axis. The purpose of the present study was to determine the role of pituitary/adrenal activation in the effect of hCRH on LH and FSH secretion. We compared the effects of 5-h i.v. infusions of hCRH (100 micrograms/h, n = 7) and of human adrenocorticotropic hormone (ACTH) (1-24) (5 micrograms/h, n = 3; 10 micrograms/h, n = 3, 20 micrograms/h, n = 3) to ovariectomized monkeys on LH, FSH, and cortisol secretion. As expected, during the 5-h ACTH infusions, cortisol levels increased by 176-215% of baseline control, an increase similar to that observed after CRH infusion (184%). However, in contrast to the inhibitory effect observed during the CRH infusion, LH and FSH continued to be released in a pulsatile fashion during the ACTH infusions, and no decreases in gonadotropin secretion were observed. The results indicated that increases in ACTH and cortisol did not affect LH and FSH secretion and allowed us to conclude that the rapid inhibitory effect of CRH on LH and FSH pulsatile release was not mediated by activation of the pituitary/adrenal axis. 相似文献
49.
玉米螟触角电位反应的专一性 总被引:1,自引:1,他引:0
我国的玉米螟曾被记载为欧洲玉米螟(European corn borer,Ostrinia nubilalis),在研究性信息素的过程中,曾按照Klun等(1970)鉴定的欧洲玉米螟性信息素顺-和反-11-十四碳烯醇乙酸酯这两种异构体进行合成,但未发现该两种异构体的任何配比在田间有诱蛾活性。程志青等(1980)鉴定出我国玉米螟的性信息素是顺-和反-12-十四碳烯醇乙酸酯,并根据Mutuura等(1970)作的分类鉴定,认为我国的玉米螟应为亚洲玉米螟(Asiatic corn borer,Ostrinia furnacalis)。因此,近年来国内有关玉米螟的研究报告(程志青等,1980;1982;姜仲雪等,1981;任自立等,1983)都称我国的玉米螟为亚洲玉米螟。但 相似文献
50.