全文获取类型
收费全文 | 107565篇 |
免费 | 8275篇 |
国内免费 | 8795篇 |
出版年
2024年 | 171篇 |
2023年 | 1347篇 |
2022年 | 3135篇 |
2021年 | 5631篇 |
2020年 | 3867篇 |
2019年 | 4793篇 |
2018年 | 4686篇 |
2017年 | 3426篇 |
2016年 | 4744篇 |
2015年 | 6925篇 |
2014年 | 8163篇 |
2013年 | 8569篇 |
2012年 | 10129篇 |
2011年 | 9252篇 |
2010年 | 5470篇 |
2009年 | 4967篇 |
2008年 | 5694篇 |
2007年 | 4963篇 |
2006年 | 4224篇 |
2005年 | 3430篇 |
2004年 | 2771篇 |
2003年 | 2466篇 |
2002年 | 2032篇 |
2001年 | 1711篇 |
2000年 | 1559篇 |
1999年 | 1597篇 |
1998年 | 953篇 |
1997年 | 1016篇 |
1996年 | 930篇 |
1995年 | 867篇 |
1994年 | 773篇 |
1993年 | 641篇 |
1992年 | 769篇 |
1991年 | 593篇 |
1990年 | 516篇 |
1989年 | 382篇 |
1988年 | 315篇 |
1987年 | 247篇 |
1986年 | 210篇 |
1985年 | 235篇 |
1984年 | 141篇 |
1983年 | 130篇 |
1982年 | 70篇 |
1981年 | 29篇 |
1980年 | 25篇 |
1979年 | 28篇 |
1978年 | 4篇 |
1976年 | 10篇 |
1975年 | 8篇 |
1950年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 803 毫秒
61.
62.
A food-producing role for cephalic exocrine glands has arisen independently in both taxa of highly eusocial bees, Apis and Meliponini. With several exceptions, there is little evidence that food is produced by glands of solitary bees or by most bees at lower levels of sociality. We suggest that this association with sociality is due to four adaptive features of these glands: (1) food from the glands allows feces from queens and larvae to have a small volume, (2) the queen's fecundity can be increased, (3) nutrient recovery via cannibalism can be facilitated, and (4) rearing of emergency replacement queens is accelerated. Acceleration of the rearing of other castes and of queens in the normal process of colony fission is not clearly an advantage ascribed to these glands. Trophic eggs produced by meliponine colony workers are analogous to the secretions from food-producing glands in Meliponini and Apis workers. 相似文献
63.
64.
65.
Mengmeng Zhuang Yuequ Deng Wenwen Zhang Bo Zhu Hao Yan Jiaqi Lou Pan Zhang Qingwei Cui Hao Tang Han Sun Yong Sun 《Cell death & disease》2021,12(6)
Intestinal mucosal injuries are directly or indirectly related to many common acute and chronic diseases. Long non-coding RNAs (lncRNAs) are expressed in many diseases, including intestinal mucosal injury. However, the relationship between lncRNAs and intestinal mucosal injury has not been determined. Here, we investigated the functions and mechanisms of action of lncRNA Bmp1 on damaged intestinal mucosa. We found that Bmp1 was increased in damaged intestinal mucosal tissue and Bmp1 overexpression was able to alleviate intestinal mucosal injury. Bmp1 overexpression was found to influence cell proliferation, colony formation, and migration in IEC-6 or HIEC-6 cells. Moreover, miR-128-3p was downregulated after Bmp1 overexpression, and upregulation of miR-128-3p reversed the effects of Bmp1 overexpression in IEC-6 cells. Phf6 was observed to be a target of miR-128-3p. Furthermore, PHF6 overexpression affected IEC-6 cells by activating PI3K/AKT signaling which was mediated by the miR-128-3p/PHF6 axis. In conclusion, Bmp1 was found to promote the expression of PHF6 through the sponge miR-128-3p, activating the PI3K/AKT signaling pathway to promote cell migration and proliferation.Subject terms: Cell growth, Cell migration 相似文献
66.
67.
68.
ATPase-defective derivatives of Escherichia coli DnaK that behave differently with respect to ATP-induced conformational change and peptide release. 下载免费PDF全文
We have characterized the effects of the T199S, T199A, and K70A mutations on the biochemical activity and in vivo functioning of Escherichia coli DnaK. Threonine-199 is the site of autophosphorylation of DnaK, and the lysine residue of bovine Hsc70 corresponding to K70 of DnaK has been shown to be essential for the hydrolysis of ATP. The dnaK alleles T199A and K70A are completely unable, and the T199S allele is only partially able, to complement the defects of a DeltadnaK mutant. The ATPase activities of the DnaK T199A and DnaK K70A proteins are nearly abolished, while the ATPase activity of the DnaK T199S protein has a steady-state rate similar to that of wild-type DnaK. The DnaK T199S protein also retains approximately 13% of the autophosphorylation activity of wild-type DnaK, while the autophosphorylation activities of the T199A and K70A derivatives are completely abolished. All four DnaK proteins bind a model peptide substrate, and the wild-type, T199A, and T199S DnaK proteins release the peptide with similar kinetics upon the addition of ATP. The DnaK K70A protein, in contrast, does not release the peptide upon the addition of ATP. ATP induces a conformational change in the wild-type, T199A, and T199S DnaK proteins but not in the DnaK K70A protein. The T199A and K70A mutations both disrupt the ATPase activity of DnaK but have profoundly different effects on the ATP-induced conformational change and peptide release activities of DnaK, implying that the two mutations affect different steps in the functional cycle of DnaK. The DnaK T199S protein represents a new class of DnaK mutant, one which has near-normal levels of ATPase activity and undergoes an ATP-induced conformational change that results in the release of peptide but which is not able to fully complement loss of DnaK function in the cell. 相似文献
69.
70.
Wenjun Geng Jinggong Xiangyu Xiuzhen Li Zhongning Zhang Deyuan Han Yongwei Li 《Insect Science》1997,4(4):364-368
Abstract Field trials by sex pheromone of aphid to trap peach aphids Myzus persicae have been carried out in 1995 and in 1996. Suitable time and the effect of ratio of two components nepetalactone and nepetalactol to apply the lure have been observed. 相似文献