全文获取类型
收费全文 | 11253篇 |
免费 | 285篇 |
国内免费 | 319篇 |
出版年
2023年 | 241篇 |
2022年 | 105篇 |
2021年 | 154篇 |
2020年 | 229篇 |
2019年 | 418篇 |
2018年 | 357篇 |
2017年 | 261篇 |
2016年 | 254篇 |
2015年 | 310篇 |
2014年 | 645篇 |
2013年 | 1151篇 |
2012年 | 644篇 |
2011年 | 594篇 |
2010年 | 353篇 |
2009年 | 538篇 |
2008年 | 555篇 |
2007年 | 580篇 |
2006年 | 424篇 |
2005年 | 425篇 |
2004年 | 368篇 |
2003年 | 328篇 |
2002年 | 284篇 |
2001年 | 241篇 |
2000年 | 201篇 |
1999年 | 238篇 |
1998年 | 226篇 |
1997年 | 187篇 |
1996年 | 212篇 |
1995年 | 191篇 |
1994年 | 144篇 |
1993年 | 100篇 |
1992年 | 96篇 |
1991年 | 93篇 |
1990年 | 106篇 |
1989年 | 71篇 |
1988年 | 46篇 |
1987年 | 46篇 |
1986年 | 44篇 |
1985年 | 52篇 |
1984年 | 49篇 |
1983年 | 33篇 |
1982年 | 60篇 |
1981年 | 41篇 |
1980年 | 31篇 |
1979年 | 36篇 |
1978年 | 22篇 |
1977年 | 15篇 |
1976年 | 23篇 |
1975年 | 10篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Efforts were taken to synthesis and characterize 2-amino-1-methyl-1H-imidazole-4(5H)-one derivatives (4a-u) through a four-step reaction. The achieved compounds in remarkable yield have characterized through standard analytical techniques such as FTIR, LC-MS, NMR, HRMS, and elemental analysis. Present study mainly aimed to evaluate 4a-u as G protein-coupled receptors (GPCR). In the mechanism, stimulation of phosphoinositide 3-kinase (PI3K) and Akt (protein kinase B) is a general reaction activated by a series of membrane-bound receptors such as GPCR. Protease-activated receptor-1 (PAR1) is a subfamily of related GPCR, which triggered by the division of fragment of its extracellular domain. Therefore, molecular docking is done to ensure the inhibition of PAR1 and PI3Kinase. PI3Kinase is a chief enzyme in the development of breast cancer via the Akt/mTOR pathway. Thus, in vitro PI3Kinase inhibition and anti-breast cancer studies has also done to screen medicinally important compounds among (4a-u). Based on the best binding affinity, in vitro relative % activity and IC50 values, compounds 4a, 4g, 4i, 4n, and 4u were screened for further preclinical studies in animal model evaluations. 相似文献
42.
Santiago F. Elena Fernando González-Candelas Andrés Moya 《Journal of molecular evolution》1992,35(3):223-229
Summary We have carried out a phylogenetic study of the evolution of the VP1 gene sequence from different serological types and subtypes of foot-and-mouth disease virus (FMDV). The maximum-likelihood method developed by Hasegawa and co-workers (Hasegawa et al. 1985) for the estimation of evolutionary parameters and branching dates has been used to decide between alternative models of evolution: constant versus variable rates. The results obtained indicate that a constant rate model, i.e., a molecular clock, seems to be the most plausible one. However, additional information suggests the possibility that the appearance of serotype CS has been accompanied by an episode of rapid evolution (Villaverde et al. 1991). We discuss the possibility that this evolution of RNA viruses was due to episodic positive Darwinian selection, which would have helped the new variant to escape the immunogenic pressure from the hosts.
Offprint requests to: A. Moya 相似文献
43.
Maurice Jay Bernard Voirin Aurangzeb Hasan Jean-François Gonnet Marie-Rose Viricel 《Biochemical Systematics and Ecology》1980,8(2):127-132
A survey of the leaves and flowers of 62 representatives of the tribe Loteae (Leguminosae) showed the presence of several classes of flavonoids: flavonol 7-methyl ethers (rhamnocitrin, rhamnetin), 8-O-substituted flavonols (gossypetin, limocitrin, sexangularetin, corniculatusin), 3′,4′,5′-tri-O-substituted flavonols (myricetin, mearnsetin, syringetin, laricitrin), proanthocyanidins and flavone-C-glycosides. The trisubstitution of the B-ring and the 8-O-substitution of the A-ring allow the definition of a major group including the genera Dorycnium, Bonjeania, Lotus and Tetragonolobus. The presence of proanthocyanidins and 7-O-methylation determine a second group consisting of the genus Anthyllis. Finally, Securigera, on the basis of its flavonoid chemistry, appears to be rather remote from other members of the tribe. 相似文献
44.
A.V. Kuznetsov 《Mathematical biosciences》2010,226(2):147-155
The purpose of this paper is to develop a model for simulation of the formation of organelle traps in fast axonal transport. Such traps may form in the regions of microtubule polar mismatching. Depending on the orientation of microtubules pointing toward the trap region, these traps can accumulate either plus-end or minus-end oriented vesicles. The model predicts that the maximum concentrations of organelles occur at the boundaries of the trap regions; the overall concentration of organelles in the axon with traps is greatly increased compared to that in a healthy axon, which is expected to contribute to mechanical damages of the axon. The organelle traps induce hindrance to organelle transport down the axon; the total organelle flux down the axon with traps is found to be significantly reduced compared to that in a healthy axon. 相似文献
45.
46.
Puerto Rican populations of two species of sea anemones (Bunodosoma cavernata and B. granulifera) which had previously been considered one were assayed electrophoretically for enzymes encoded by 12 loci. The two species shared no common allozymes at 6 of the 12 loci. Genetic distance and identity values based on these allozymes were computed for the Puerto Rican populations and for B. cavernata from Florida and B. granulifera from Panama. The Puerto Rican populations of both species had much higher genetic identities for their geographically distant conspecifics than for each other. These results indicate that the two species are reproductively isolated and should be considered as separate valid species. Average heterozygosities are presented which are the first published for coelenterate species. 相似文献
47.
The l-thyroxine binding site in human serum thyroxine-binding globulin was investigated by affinity labeling with N-bromoacetyl-l-thyroxine (BrAcT4). Competitive binding studies showed that, in the presence of 100 molar excess of BrAcT4, binding of thyroxine to thyroxine-binding globulin was nearly totally abolished. The reaction of BrAcT4 to form covalent binding was inhibited in the presence of thyroxine and the affinity-labeled thyroxinebinding globulin lost its ability to bind thyroxine. These results indicate BrAcT4 and thyroxine competed for the same binding site. Affinity labeling with 2 mol of BrAcT4/mol of thyroxine-binding globulin resulted in the covalent attachment of 0.7 mol of ligand. By amino acid analysis and high voltage paper electrophoresis, methionine was identified as the major residue labeled (75%). Lysine, tyrosine, and histidine were also found to be labeled to the extent of 8, 8, and 5%, respectively. 相似文献
48.
49.
50.