全文获取类型
收费全文 | 4623篇 |
免费 | 415篇 |
国内免费 | 609篇 |
出版年
2023年 | 82篇 |
2022年 | 91篇 |
2021年 | 144篇 |
2020年 | 158篇 |
2019年 | 190篇 |
2018年 | 164篇 |
2017年 | 148篇 |
2016年 | 176篇 |
2015年 | 161篇 |
2014年 | 247篇 |
2013年 | 388篇 |
2012年 | 198篇 |
2011年 | 209篇 |
2010年 | 182篇 |
2009年 | 227篇 |
2008年 | 256篇 |
2007年 | 298篇 |
2006年 | 225篇 |
2005年 | 233篇 |
2004年 | 183篇 |
2003年 | 159篇 |
2002年 | 144篇 |
2001年 | 123篇 |
2000年 | 116篇 |
1999年 | 101篇 |
1998年 | 84篇 |
1997年 | 80篇 |
1996年 | 74篇 |
1995年 | 69篇 |
1994年 | 68篇 |
1993年 | 68篇 |
1992年 | 55篇 |
1991年 | 55篇 |
1990年 | 51篇 |
1989年 | 47篇 |
1988年 | 29篇 |
1987年 | 32篇 |
1986年 | 35篇 |
1985年 | 46篇 |
1984年 | 32篇 |
1983年 | 41篇 |
1982年 | 38篇 |
1981年 | 27篇 |
1980年 | 19篇 |
1979年 | 27篇 |
1978年 | 17篇 |
1977年 | 14篇 |
1976年 | 4篇 |
1975年 | 9篇 |
1974年 | 9篇 |
排序方式: 共有5647条查询结果,搜索用时 15 毫秒
1.
2.
王世荣 《中国微生态学杂志》2015,27(5)
本文阐述了中药防治病毒病的历史及其应用概况,中药联合微生态制剂防治呼吸、消化系统病毒病的理论依据、临床应用和发展前景。 相似文献
3.
《Bioorganic & medicinal chemistry》2020,28(9):115437
NDM-1 can hydrolyze nearly all available β-lactam antibiotics, including carbapenems. NDM-1 producing bacterial strains are worldwide threats. It is still very challenging to find a potent NDM-1 inhibitor for clinical use. In our study, we used a metal-binding pharmacophore (MBP) enriched virtual fragment library to screen NDM-1 hits. SPR screening helped to verify the MBP virtual hits and identified a new NDM-1 binder and weak inhibitor A1. A solution NMR study of 15N-labeled NDM-1 showed that A1 disturbed all three residues coordinating the second zinc ion (Zn2) in the active pocket of NDM-1. The perturbation only happened in the presence of zinc ion, indicating that A1 bound to Zn2. Based on the scaffold of A1, we designed and synthesized a series of NDM-1 inhibitors. Several compounds showed synergistic antibacterial activity with meropenem against NDM-1 producing K. pneumoniae. 相似文献
4.
6.
Molecular genetics of peripheral populations of Nova Scotian Unionidae (Mollusca: Bivalvia) 总被引:1,自引:0,他引:1
PIETER W. KAT GEORGE M. DAVIS 《Biological journal of the Linnean Society. Linnean Society of London》1984,22(2):157-185
Peripheral populations of eight species of freshwater bivalves (Unionidae.) extending their geographic ranges into Nova Scotia, Canada, were examined electrophoretically to determine both the extent of genetic variability within such populations, and whether the hypothesized pathway of colonization across the Isthmus of Chignecto is reflected in patterns of genetic resemblance among these populations. The Nova Scotian species examined could be separated into two groups based on levels of observed heterozygosity and levels of variability in allele frequencies. The first group is characterized by low levels of heterozygosity and polymorphism compared with north-eastern American populations, and in the case of one species, Elliptio complanala, considerable variability in allele frequencies among populations occurring in similar habitats in different drainages. Populations of E. complanata from Nova Scotia can be differentiated from conspecific populations on the southern Atlantic Slope by possession of fast alleles at two loci. Multivariate analyses define subgroups within populations of E. complanata consistent with hypothesis that the species invaded Nova Scotia by way of the Isthmus of Chignecto, and then split into two groups, one of which colonized Cape Breton to the north and the other of which colonized southern areas of the Province. The second group of Nova Scotian species is characterized by little reduction in heterozygosity and polymorphism compared with values observed among north-eastern American conspecifics or congeners, little variability in allele frequencies from population to population, and little evidence to suggest that these species were dependent on the land bridge to invade the Province. The type of dispersal is hypothesized to be responsible, in part, for these differences: larvae of species in the first group rely on a parasitic attachment to fish with territorial habits limited to fresh water, and are thus likely to invade new drainages separated by salt water by chance, in small numbers, and in stepping-stone fashion. Species in the second group parasitize anadromous or saltwater tolerant hosts, are likely to be introduced into new habitats in greater numbers and/or receive greater amounts of gene flow subsequent to colonization, and seem less dependent on land-bridges to colonize new habitats. 相似文献
7.
Ascorbate caused a dose-dependent increase in sister-chromatid exchanges (SCEs) in Chinese hamster ovary (CHO) cells and in human lymphocytes. Moreover, in the DNA synthesis inhibition test with HeLa cells, ascorbate gave results typical of DNA-damaging chemicals. Catalase reduced SCE induction by ascorbate, prevented its cytotoxicity in CHO cells, and prevented its effect on HeLa DNA synthesis. Ascorbate reduced induction of SCE in CHO cells by N-methylN′-nitrosoguanidine (MNNG) by direct inactivation of MNNG. 相似文献
8.
We describe the development of DNA markers for the fungal pathogen of Eucalyptus, Cryphonectria cubensis. These markers originated from cloned intershort sequence repeat polymerase chain reactions, which enrich for medium to highly repetitive DNA sequences. In total, 10 markers were isolated, eight of which were polymorphic, and these can subsequently be applied to study populations of C. cubensis. 相似文献
9.
Two new compounds, derriscoumaronochromone (1) and cis-3,4′-dihydroxy- 5,7-dimethoxyflavan (2), as well as trans-4'-O-methylcatechin (3) were isolated from Derris laxiflora, The structures of these compounds were determined by analysis of their spectroscopic data. 相似文献
10.
The overall density of 17 large herbivore species encountered during the study differed among species and habitat types, but not between seasons. There were clear seasonal patterns of association among species, which were more pronounced during wet than dry seasons, suggesting greater habitat selectivity and increased ecological separation. The defassa waterbuck (Kobus ellypsiprymnus defassa Ruppel) showed ecological separation from other species, possibly because it competitively displaced them. 相似文献