全文获取类型
收费全文 | 24608篇 |
免费 | 1979篇 |
国内免费 | 1321篇 |
出版年
2024年 | 35篇 |
2023年 | 230篇 |
2022年 | 306篇 |
2021年 | 922篇 |
2020年 | 742篇 |
2019年 | 851篇 |
2018年 | 910篇 |
2017年 | 705篇 |
2016年 | 1005篇 |
2015年 | 1516篇 |
2014年 | 1839篇 |
2013年 | 1893篇 |
2012年 | 2264篇 |
2011年 | 2021篇 |
2010年 | 1322篇 |
2009年 | 1135篇 |
2008年 | 1331篇 |
2007年 | 1235篇 |
2006年 | 1184篇 |
2005年 | 1028篇 |
2004年 | 908篇 |
2003年 | 862篇 |
2002年 | 708篇 |
2001年 | 453篇 |
2000年 | 392篇 |
1999年 | 332篇 |
1998年 | 198篇 |
1997年 | 159篇 |
1996年 | 163篇 |
1995年 | 163篇 |
1994年 | 124篇 |
1993年 | 81篇 |
1992年 | 136篇 |
1991年 | 99篇 |
1990年 | 100篇 |
1989年 | 81篇 |
1988年 | 60篇 |
1987年 | 51篇 |
1986年 | 54篇 |
1985年 | 53篇 |
1984年 | 36篇 |
1983年 | 23篇 |
1982年 | 28篇 |
1981年 | 15篇 |
1980年 | 12篇 |
1979年 | 21篇 |
1978年 | 17篇 |
1976年 | 12篇 |
1974年 | 14篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
天名精倍半萜内酯化合物 总被引:2,自引:0,他引:2
从菊科天名精全草中分得天名精内酯酮,特勒内酯,11(13)-二氢特勒内酯和异埃瓦内酯。其中11(13)-二氢特勒内酯和异埃瓦内酯为新的天然产物。 相似文献
42.
43.
猪肺炎支原体膜上ATP酶为Mg~(2+)激活,乌巴因不抑制。DCCD和寡霉素对该酶也无抑制作用,只有NBD与Quercetin才有一定的抑制效果。用梯度凝胶电泳可获均一的具有活性的酶蛋白带。 相似文献
44.
45.
Bacterial quinones were analysed by two-dimensional thin-layer chromatography with ready-made, multi-phase silica gel plates which allowed good separation of complicated quinone mixtures. A combination of this method and silver-ion-modified thin-layer chromatography made it possible to identify partially hydrogenated quinones. 相似文献
46.
47.
Dr. Jian Wen Chen Lanping Zhang Jiantao Song Fen Hwang Qinghua Dong Jian Liu Yumin Qian 《Current microbiology》1992,24(4):189-192
The glycoproteins and glycolipids from membranes of virulent strain Z and avirulent strain M ofMycoplasma hyopneumoniae have been compared. The proteins and the glycoproteins were identified by SDS-polyacrylamide gel electrophoresis and concanavalin A-biotin labeling, respectively. The membrane preparation contained approximately 34 protein bands with molecular weights between 20 KD and 100 KD. The concanavalin A-biotin system reacted with a glycoprotein of a molecular weight of approximately 28,000 from avirulent strain M and did not react with the correspondent band from virulent strain Z. The membrane glycolipids of both strains consisted of monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG), and the percentages of 160, 180, and 181 fatty acids comprised more than 80% of the total fatty acids of membrane glycolipids. The 180 fatty acid of MGDG in avirulent strain M was twofold higher than that of virulent strain Z. 相似文献
48.
49.
Maternal care in the red-headed spruce web-spinning sawfly,Cephalcia isshikii (Hymenoptera: Pamphiliidae) 总被引:1,自引:0,他引:1
We describe oviposition and maternal behavior in the sawfly Cephalcia isshikiiand examine the adaptive significance of this behavior. Females deposited eggs in a single but loose cluster on needles of terminal twigs of spruces, Piceaspp., and remained with the eggs usually on the underside of the twig facing toward the tip. The female attended her eggs until death without taking food but did not follow the first-instar larvae that moved from natal needles even if she survived until then. When the female was disturbed, she usually moved toward the source and attempted to bite it. Though at much lower frequencies, this aggressive behavior was also observed in gravid females and even in males. Field observations and female removal experiments indicated that the female enhanced the survival of the eggs through the reduction of arthropod prédation. 相似文献
50.
Expression of an enhancer-binding protein in insect cells transfected with the Autographa californica nuclear polyhedrosis virus IE1 gene. 总被引:10,自引:10,他引:0
The baculovirus Autographa californica nuclear polyhedrosis virus contains an element known as homologous region 5 (hr5) which is an enhancer of delayed-early viral gene expression. To begin to identify proteins that interact with hr5, DNA-protein interactions were analyzed by using extracts from Spodoptera frugiperda cells and a fragment of DNA containing the left half of the hr5 enhancer. This 252-bp DNA fragment contains two copies of a 30-bp direct repeat (DR30) and two copies of a 24-bp imperfect palindrome contained within a 60-bp direct repeat (DR60). Extracts prepared from normal S. frugiperda cells and cells transfected with pUC8 lacked enhancer-binding proteins. However, when gel shift assays were performed with extracts from cells transfected with a plasmid containing the viral trans-activator IE1 gene, two DNA-protein complexes were formed. Both DNA-protein complexes were specifically inhibited by competition with a 60-bp oligonucleotide corresponding to DR60 but not by competition with a different oligonucleotide corresponding to DR30. Formation of the two complexes did not appear to involve cooperative interactions between binding proteins. When DR60 was used as a probe, a single complex was formed. To measure the enhancer activity of DR60, a reporter plasmid was constructed that contained DR60 cloned upstream of the reporter chloramphenicol acetyltransferase gene under the control of the delayed-early 39K promoter. Transient expression analysis indicated that the oligonucleotide increased expression of this gene 300-fold over the level obtained in the absence of any enhancer sequences. 相似文献