全文获取类型
收费全文 | 6505篇 |
免费 | 440篇 |
国内免费 | 3篇 |
出版年
2022年 | 35篇 |
2021年 | 68篇 |
2020年 | 34篇 |
2019年 | 58篇 |
2018年 | 62篇 |
2017年 | 53篇 |
2016年 | 96篇 |
2015年 | 190篇 |
2014年 | 224篇 |
2013年 | 302篇 |
2012年 | 337篇 |
2011年 | 363篇 |
2010年 | 293篇 |
2009年 | 249篇 |
2008年 | 337篇 |
2007年 | 366篇 |
2006年 | 361篇 |
2005年 | 338篇 |
2004年 | 356篇 |
2003年 | 347篇 |
2002年 | 356篇 |
2001年 | 92篇 |
2000年 | 76篇 |
1999年 | 103篇 |
1998年 | 126篇 |
1997年 | 84篇 |
1996年 | 83篇 |
1995年 | 96篇 |
1994年 | 76篇 |
1993年 | 88篇 |
1992年 | 68篇 |
1991年 | 62篇 |
1990年 | 74篇 |
1989年 | 54篇 |
1988年 | 54篇 |
1987年 | 38篇 |
1986年 | 50篇 |
1985年 | 34篇 |
1984年 | 63篇 |
1983年 | 53篇 |
1982年 | 66篇 |
1981年 | 73篇 |
1980年 | 60篇 |
1979年 | 54篇 |
1978年 | 45篇 |
1977年 | 41篇 |
1976年 | 34篇 |
1975年 | 34篇 |
1974年 | 36篇 |
1973年 | 18篇 |
排序方式: 共有6948条查询结果,搜索用时 31 毫秒
61.
62.
63.
64.
65.
66.
Short- and Long-Term Alterations of Gene Expression in Limbic Structures by Repeated Electroconvulsive-Induced Seizures 总被引:4,自引:2,他引:2
Vincent Leviel Catherine Fayada Bernard Guibert Michel Chaminade Georges Machek Jacques Mallet Nicole Faucon Biguet† 《Journal of neurochemistry》1990,54(3):899-904
Rats were submitted to a series of 10 daily electroconvulsive shocks (ECS). A first group of animals was killed 1 day after the last seizure and a second group 30 days later. Tyrosine hydroxylase (TH) activity was measured using an in vitro assay in the nucleus caudatus, anterior cortex, amygdala, substantia nigra, ventral tegmental area, and locus ceruleus. The mRNA corresponding to this enzyme (TH-mRNA) was evaluated using a cDNA probe at the cellular level in the ventral tegmental area, substantia nigra, and locus ceruleus. Met-enkephalin (MET)-immunoreactivity and the mRNA coding for the preproenkephalin (PPE-mRNA) were assayed in striatum and the central nucleus of the amygdala. The day after the last ECS an increase of TH activity was observed in the ventral tegmental area, locus ceruleus, and substantia nigra in parallel with a similar increase in the amygdala and striatum; in the anterior cortex TH activity remained unchanged. TH-mRNA was increased in the locus ceruleus, evidencing the presence in this structure of a genomic activation. The amounts of MET and PPE-mRNA were unaffected in the striatum but increased in the amygdala. Thirty days after the last ECS we observed a decrease of TH activity in the amygdala and of TH-mRNA amount in the ventral tegmental area. In the locus ceruleus TH-mRNA remained higher in treated animals than in controls whereas TH activity returned to control levels. These results demonstrate that a series of ECS induces an initial increase of the activity of mesoamygdaloid catecholaminergic neurons followed by a sustained decrease through alterations of TH gene expression which could mediate the clinical effect of the treatment. 相似文献
67.
We have isolated from the ovine rumen eight bacterial strains belonging to the speciesButyrivibrio fibrisolvens. DNA hybridization studies showed that the eight strains could be divided into four homology groups, of which none was closely related to the type strain ATCC 19171. Measurement of cross-hybridization between selected pairs of bacterial strains showed that DNA types which produced low, but significant, cross-hybridization on dot-blots were able to form heteroduplexes with between 8.4% and 32.9% of the efficiency of homoduplex formation. Thermal denaturation of the same heteroduplexes resulted in Tm values 6.4–7.5°C lower than those of the homologous duplexes formed under the same conditions. In some cases, hybridization between strains was below the level of reliable measurement. Similar experiments with ten recently isolated strains ofBacteroides ruminicola sub-sp.brevis revealed a similar degree of genetic divergence between isolates. 相似文献
68.
A defined growth medium (designated AP11), in which the concentrations of Na+ and K+ could be altered independently of one another, was developed for Streptococcus salivarius ATCC 25975. The addition of 100 mM-Na+ to AP11-medium containing 25 mM-K+ initially reduced the rate of expression of extracellular glucosyltransferase (GTFe). However, once S. salivarius had adaptated to grow in the presence of 100 mM-Na+, the rate of GTFe expression was stimulated. In fact once adapted to the presence of Na+ in the environment the same increase in the rate of enzyme expression was observed in all batch cultures irrespective of the K+ concentration (2-50 mM). At 2 mM-K+ there was no change in the level of saturation of the membrane lipids when the Na+ concentration was increased from 0 mM to 100 mM. Na+-stimulation of GTFe expression was confirmed in non-proliferating cell suspensions at different K+ concentrations. In non-proliferating cell suspensions, GTFe expression outlined a rectangular hyperbola with respect to K+ concentration when the K+ concentration was stepped up from 2 mM. The increase in GTFe synthesis and secretion was transient and was similar to that previously reported by us in Na+-rich medium, though it did not reach the same high levels. The reduced transient stimulation of GTFe expression correlated both with an enrichment in the saturated fatty acids of the membrane lipids of S. salivarius, and with the fact that the degree of saturation was only slightly reduced when the K+ concentration was stepped up from 2 mM to 50 mM. Needless to say, the final octadecenoic to octadecanoic (C18:1/C18:0) fatty acid ratio retained its direct correlation with the transient increase in GTFe production following the step up in K+ concentration, giving rise to an apparent biphasic plot when combined with that previously reported. 相似文献
69.
Glycine metabolism by plant mitochondria 总被引:3,自引:0,他引:3
David J. Oliver Michel Neuburger Jacques Bourguignon Roland Douce 《Physiologia plantarum》1990,80(3):487-491
70.
Beverly A. Mock Marianne Krall Christine A. Kozak Muriel N. Nesbitt O. Wesley McBride Jean-Christophe Renauld Jacques Van Snick 《Immunogenetics》1990,31(4):265-270
Mouse and human cDNA clones encoding the T-cell and mast cell growth factor P40, now designated IL-9, were used to identify DNA restriction fragment length polymorphisms (RFLPs) in sets of somatic cell hybrids and between inbred strains of mice and interspecific backcross progeny. Segregation of mouse and human chromosomes among somatic cell hybrids indicated a location on mouse chromosome 13 and human chromosome 5. RFLPs were identified among inbred strains of mice. Analysis of chromosome 13 alleles for Tcrg, Dhfr, and Il-9 in an interspecific cross between Mus musculus and NFS/N or C58/J mice indicates that IL-9 is distal to Tcrg and Proximal to Dhfr. 相似文献