全文获取类型
收费全文 | 2825篇 |
免费 | 405篇 |
专业分类
3230篇 |
出版年
2022年 | 24篇 |
2021年 | 58篇 |
2020年 | 40篇 |
2019年 | 39篇 |
2018年 | 49篇 |
2017年 | 44篇 |
2016年 | 73篇 |
2015年 | 99篇 |
2014年 | 126篇 |
2013年 | 131篇 |
2012年 | 189篇 |
2011年 | 174篇 |
2010年 | 98篇 |
2009年 | 82篇 |
2008年 | 136篇 |
2007年 | 124篇 |
2006年 | 127篇 |
2005年 | 119篇 |
2004年 | 111篇 |
2003年 | 95篇 |
2002年 | 89篇 |
2001年 | 67篇 |
2000年 | 38篇 |
1999年 | 39篇 |
1998年 | 28篇 |
1997年 | 28篇 |
1996年 | 26篇 |
1995年 | 22篇 |
1992年 | 41篇 |
1991年 | 36篇 |
1990年 | 41篇 |
1989年 | 37篇 |
1988年 | 29篇 |
1987年 | 35篇 |
1986年 | 39篇 |
1985年 | 33篇 |
1984年 | 42篇 |
1983年 | 24篇 |
1982年 | 23篇 |
1981年 | 25篇 |
1980年 | 27篇 |
1979年 | 37篇 |
1978年 | 31篇 |
1977年 | 34篇 |
1976年 | 29篇 |
1975年 | 34篇 |
1974年 | 32篇 |
1973年 | 31篇 |
1971年 | 41篇 |
1970年 | 28篇 |
排序方式: 共有3230条查询结果,搜索用时 0 毫秒
991.
Brendan W. Wren Susan M. Colby Rachel R. Cubberley Mark J. Pallen 《FEMS microbiology letters》1992,99(2-3):287-291
Many bacterial responses to environmental stimuli are mediated by response regulators which coordinately regulate genes involved in particular adaptive responses. Degenerate oligonucleotide primers were used to amplify by the polymerase chain reaction (PCR), fragments from genes encoding eleven novel response regulators. Sequence and phylogenetic analysis revealed that phoB, phoP and creB gene fragments had been amplified from Yersinia enterocolitica and Yersinia pseudotuberculosis, and that a creB sequence had been amplified from Campylobacter jejuni. Four amplified fragments from C. jejuni, Listeria monocytogenes, Mycobacterium tuberculosis and Escherichia coli clearly came from response regulator genes, but were not closely related to any of the known genes. Mutagenesis of the newly identified genes should allow us to determine their function and the genes under their control. 相似文献
992.
Properties of selectively starved euglena 总被引:3,自引:0,他引:3
993.
Oocytes at several stages of growth were isolated by enzymatic digestion of ovaries from infant mice. These oocytes were free of follicle cells and were obtained in sufficient numbers to permit direct biochemical analysis of glucose-6-phosphate dehydrogenase (G6PD) and lactate dehydrogenase (LDH) activities. Both enzymes increase in total activity as the oocyte grows. However, while the specific activity of G6PD remains constant up to an oocyte diameter of 80–85 μm, the specific activity of LDH increases four-fold. The specific activity of G6PD and especially LDH declines in oocytes over 80–85 μm in diameter, suggesting that the synthesis of these enzymes is almost completed at this stage of growth. 相似文献
994.
995.
Scanning electron microscopy reveals microvilli on all preimplantation stages, indicates that their number and length may be dependent on embryo size, and provides examples of regional alterations in their number. Cellular adherence, as evidence by interactions of microvilli, migration of cellular processes, and junctional complexes, increases during development and is accompanied by changes in the shapes of cells and embryos. Cell surfaces bordering the blastocoel differ markedly from the outer cell surfaces of the embryo. 相似文献
996.
The C-glycosylflavone pigments found in wheat leaves are a varied mixture of compounds in the luteolin and apigenin series; iso-orientin, lutonarin, lucenin-1, lucenin-3, vicenin-2, and an unreported C-glycoside, wyomin, an iso-orientin derivative with rutinose at the 7-position. In addition, a 4′-O-glucosyl derivative of iso-swertisin was identified along with the previously reported flavone, tricin. 相似文献
997.
Here we show that the frequency of mutant isolation by two-step allele exchange can be improved by increasing the length of homologous DNA and the opportunity for recombination, obviating the need for counterselection markers. These principles are demonstrated in Clostridium difficile and Streptococcus suis but are likely to be generally applicable. 相似文献
998.
999.
1000.