全文获取类型
收费全文 | 130212篇 |
免费 | 3467篇 |
国内免费 | 1008篇 |
专业分类
134687篇 |
出版年
2022年 | 277篇 |
2021年 | 558篇 |
2020年 | 374篇 |
2019年 | 497篇 |
2018年 | 12319篇 |
2017年 | 11054篇 |
2016年 | 8195篇 |
2015年 | 1899篇 |
2014年 | 1769篇 |
2013年 | 2338篇 |
2012年 | 6497篇 |
2011年 | 14861篇 |
2010年 | 13356篇 |
2009年 | 9430篇 |
2008年 | 11510篇 |
2007年 | 13025篇 |
2006年 | 2012篇 |
2005年 | 2054篇 |
2004年 | 2540篇 |
2003年 | 2526篇 |
2002年 | 2348篇 |
2001年 | 1327篇 |
2000年 | 1112篇 |
1999年 | 925篇 |
1998年 | 521篇 |
1997年 | 503篇 |
1996年 | 397篇 |
1995年 | 397篇 |
1994年 | 316篇 |
1993年 | 384篇 |
1992年 | 650篇 |
1991年 | 586篇 |
1990年 | 525篇 |
1989年 | 469篇 |
1988年 | 404篇 |
1987年 | 376篇 |
1986年 | 356篇 |
1985年 | 397篇 |
1984年 | 379篇 |
1983年 | 349篇 |
1982年 | 260篇 |
1981年 | 257篇 |
1979年 | 292篇 |
1978年 | 253篇 |
1977年 | 288篇 |
1976年 | 265篇 |
1975年 | 261篇 |
1974年 | 252篇 |
1972年 | 443篇 |
1971年 | 461篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
Effects of antimicrotubular agents in cAMP production and in steroidogenic response of isolated rat Leydig cells 总被引:1,自引:0,他引:1
D Saltarelli M P De la Llosa-Hermier C Tertrin-Clary C Hermier 《Biology of the cell / under the auspices of the European Cell Biology Organization》1984,52(3):259-266
In dispersed rat Leydig cells, colchicine was found to stimulate basal cAMP production and testosterone secretion in a dose and time-dependent manner, but to a lesser extent than LH. However, these drugs are unable to stimulate adenylate cyclase activity in plasma membranes isolated from these cells. The amount of testosterone secreted at 150 min under the influence of colchicine and LH added simultaneously was not different from the amount produced during stimulation by LH alone. It is only after exposure of the cells for 1 hr to colchicine that the accumulation of cAMP in response to LH was inhibited; furthermore, both intracellular and medium testosterone accumulation in response to the hormone were reduced. Similar effects were observed with two other alkaloids, vinblastine and podophyllotoxin. The three drugs also inhibited the stimulation of testosterone secretion by 8-Br-cAMP or choleratoxin. These studies suggest that the state of microtubule polymerization and/or tubulin can influence the process of steroidogenesis in rat Leydig cells. 相似文献
32.
Andrew Leask 《Journal of cell communication and signaling》2010,4(1):71-72
Connective tissue growth factor (CTGF/CCN2) is overexpressed in diabetes. Diabetic rats possess myocardial and cardiomyocyte
hypertrophy. In a recent report, Wang and colleagues (Am J Physiol Cell Physiol. 2009 Jul 22. [Epub ahead of print]) show
that CCN2 directly mediates cardiomyocyte hypertrophy as well as that induced by high glucose and fatty acid. CCN2 acted via
the TrkA receptor. These data are the subject of this commentary, and emphasize that CCN2 may be an excellent target for therapy
in diabetes. 相似文献
33.
Summary A 20.5-month study was undertaken to determine detrital processing of the halophytesSpartina anglica, Elytrigia pungens, andHalimione portulacoides in three different habitats of an estuarine salt marsh in the South-West Netherlands. Decomposition was measured using litter-bags of three different mesh sizes to partition the effects of different faunal groups on decomposition. From April 1980 through October 1981 litter-bags were sampled regulary from a creek, the upper marsh, and from a plant-debris belt on the higher marsh. Dry weights and nutritive values were measured and animals were counted. Mainly rates of loss are reported here. Zonal differences were significant. At first, decomposition in the creek was most rapid. After two months the processes in the creek slowed down because of the trapping of silt by the bags, which probably simulated the natural course of the decomposition process in the water. Decomposition on the marsh followed the most regular pattern, while in the plant-debris belt the pattern was very irregular. Population dynamics of microfaunal organisms supported these findings. In the plant-debris belts loss rates seem to be higher than on the marsh, because of the influence of detritivorous macrofaunal organisms. The loss rates of the three plant species differed significantly.Halimione decomposed fastest, especially in the beginning, and in the plant-debris habitat. On the upper marsh and in the plant-debris belt the loss rates ofSpartina seem to be a little higher than those ofElytrigia.Communication No. 233, Delta Institute for Hydrobiological Research, Yerseke, The Netherlands. 相似文献
34.
The ability of an invasive plant to occupy new areas is often attributed to both morphological and physiological plasticities
that allow them to remain viable over a wide range of environmental conditions. Studies addressing the ecological requirements
of Microstegium vimineum often consider soil moisture or soil moisture along with other factors as important explanatory components for the establishment
and persistence of this invasive monocot. However, controlled studies specifically targeting water relations in M. vimineum are needed. Therefore, the purpose of this study was to determine how different water availabilities influence the growth
and physiological performance of M. vimineum. This study utilized experimental microcosms to achieve different water availabilities including low soil moisture (<15%
water), moderate soil moisture (ca. 20–30%), and flooded conditions. While both flooded and low soil moisture resulted in
diminished growth, M. vimineum still survived under these conditions. Physiological processes including C4 metabolism, minimum stress under low water conditions, and the ability to increase tissue rigidity may confer some advantages
to M. vimineum during periods of limiting water conditions. Similarly, the proportionally low root biomass, shallow root structure, and
its ability to maintain stable water relations during flooding and/or soil waterlogging may facilitate M. vimineum’s ability to invade mesic habitats. It is likely, therefore, that the capacity to tolerate both low soil moistures and flooded
conditions has enhanced the ability of M. vimineum to populate disturbed systems in central North Carolina. 相似文献
35.
36.
37.
38.
David Skelly 《BMC biology》2010,8(1):136
A new study of divergence in freshwater fish provides strong evidence of rapid, temperature-mediated adaptation. This study
is particularly important in the ongoing debate over the extent and significance of evolutionary response to climate change
because divergence has occurred in relatively few generations in spite of ongoing gene flow and in the aftermath of a significant
genetic bottleneck, factors that have previously been considered obstacles to evolution. Climate change may thus be more likely
to foster contemporary evolutionary responses than has been anticipated, and I argue here for the importance of investigating
their possible occurrence. 相似文献
39.
Transcriptional regulatory network triggered by oxidative signals configures the early response mechanisms of japonica rice to chilling stress 总被引:3,自引:0,他引:3
40.
C T Lago G Sannia G Marino C H Squires J M Calvo M De Felice 《Biochimica et biophysica acta》1985,824(1):74-79
The ilvI and ilvH gene products were identified physically by electrophoretic analysis of in vivo-labelled polypeptides produced in minicells from plasmids carrying the wild-type ilvIH operon of Escherichia coli K-12 and derivatives of it. An analysis of the distribution of methionine residues in the amino-terminal portion of micro-quantities of the ilvI product eluted from gel showed that the translational start of the ilvI gene is the promoter-proximal one of three putative methionine codons predicted from the DNA sequence. 相似文献