全文获取类型
收费全文 | 18835篇 |
免费 | 1973篇 |
国内免费 | 635篇 |
出版年
2023年 | 122篇 |
2022年 | 250篇 |
2021年 | 580篇 |
2020年 | 379篇 |
2019年 | 481篇 |
2018年 | 485篇 |
2017年 | 431篇 |
2016年 | 589篇 |
2015年 | 785篇 |
2014年 | 942篇 |
2013年 | 1002篇 |
2012年 | 1216篇 |
2011年 | 1101篇 |
2010年 | 688篇 |
2009年 | 718篇 |
2008年 | 838篇 |
2007年 | 744篇 |
2006年 | 653篇 |
2005年 | 551篇 |
2004年 | 545篇 |
2003年 | 506篇 |
2002年 | 405篇 |
2001年 | 1250篇 |
2000年 | 1092篇 |
1999年 | 839篇 |
1998年 | 293篇 |
1997年 | 290篇 |
1996年 | 249篇 |
1995年 | 213篇 |
1994年 | 210篇 |
1993年 | 135篇 |
1992年 | 424篇 |
1991年 | 364篇 |
1990年 | 320篇 |
1989年 | 239篇 |
1988年 | 219篇 |
1987年 | 164篇 |
1986年 | 162篇 |
1985年 | 141篇 |
1984年 | 70篇 |
1983年 | 68篇 |
1982年 | 30篇 |
1981年 | 31篇 |
1979年 | 40篇 |
1976年 | 37篇 |
1975年 | 35篇 |
1973年 | 39篇 |
1972年 | 50篇 |
1971年 | 45篇 |
1970年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
121.
122.
The TIS11 primary response gene is a member of a gene family that encodes proteins with a highly conserved sequence containing an unusual Cys-His repeat. 总被引:8,自引:1,他引:7 下载免费PDF全文
B C Varnum Q F Ma T H Chi B Fletcher H R Herschman 《Molecular and cellular biology》1991,11(3):1754-1758
The TIS11 primary response gene is rapidly and transiently induced by both 12-O-tetradecanoylphorbol-13-acetate and growth factors. The predicted TIS11 protein contains a 6-amino-acid repeat, YKTELC. We cloned two additional cDNAs, TIS11b and TIS11d, that contain the YKTELC sequence. TIS11, TIS11b, and TIS11d proteins share a 67-amino-acid region of sequence similarity that includes the YKTELC repeat and two cysteine-histidine containing repeats. TIS11 gene family members are not coordinately expressed: (i) unlike TIS11, the TIS11b and TIS11d mRNAs are detectable in quiescent Swiss 3T3 cells and are not dramatically induced by 12-O-tetradecanoylphorbol-13-acetate; (ii) cycloheximide superinduction does not occur for TIS11b and TIS11d; and (iii) unlike TIS11, TIS11b expression is extinguished in PC12 pheochromocytoma cells. 相似文献
123.
The three-dimensional structure of the aspartyl protease from the HIV-1 isolate BRU. 总被引:6,自引:0,他引:6
The crystal structure of the aspartyl protease encoded by the gene pol of the human immunodeficiency virus (HIV-1, isolate BRU) has been determined to 2.7 A resolution. The enzyme, expressed as an insoluble denatured polypeptide in inclusion bodies of Escherichia coli has been renatured and crystallized. It differs by several amino acid replacements from the homologous enzymes of other HIV-1 isolates. A superposition of the C alpha-backbone of the BRU protease with that of the SF2 protease gives a roots mean square positional difference of 0.45 A. Thus, neither the denaturation/renaturation process nor the amino acid replacements have a noticeable effect on the three-dimensional structure of the BRU protease or on the detailed conformation of the catalytic site, which is very similar to that of other aspartyl proteases. 相似文献
124.
Actinomycin D induced DNase I hypersensitivity and asymmetric structure transmission in a DNA hexadecamer. 总被引:1,自引:1,他引:0
DNase I cleavage rates and nmr chemical shifts are shown to change for DNA sequences distal to an intercalated actinomycin D molecule in a duplex hexadecamer upon drug binding. Both sets of observations suggest that the source of these changes is a DNA-mediated structural response. The nmr results imply the response is transmitted preferentially in a 5'-to-3' direction from the drug binding site. An inequivalent response of the two strands to a ligand-induced conformational change immediately suggests a mechanism for distinguishing the sense and antisense strands of DNA. 相似文献
125.
126.
The effect of fluorosis on lactation, lactotroph function and ultrastructure were studied in lactating rats. The results were as follows: 1) Inhibition of lactation in lactating rats with chronic fluorosis was assessed by stunting growth of pups and decrease in the amount of milk suckled by pups in 30 min. Metoclopramide, a blocker of dopamine receptor, could improve lactation in these rats. 2) During chronic fluorosis serum PRL level was decreased, however, PRL content in pituitary was increased. Electronmicroscopic examination showed accumulation of large mature secretory granules and appearance of extremely large abnormal secretory granules in lactotroph cytoplasma. These findings indicate that hormone release of pituitary lactotrophs is obstructed in lactating rats with fluorosis, and the toxic effect of fluoride is mediated by an enhanced function of dopaminergic system in hypothalamus. 相似文献
127.
The effect of alpha-hANF on contractile force and action potential duration (APD) of isolated myocardium in guinea pig was investigated. At the level of 20 nmol/L and 40 nmol/L alpha-hANF, the contraction amplitude and rate of contraction phase decreased to a remarkable extent. And at 40 nmol/L, APDs were shortened significantly 20 min after alpha-hANF. The results suggest that there exists a direct inhibitory effect of alpha-hANF on myocardial contractile force and action potential duration. 相似文献
128.
129.
130.