全文获取类型
收费全文 | 575473篇 |
免费 | 63990篇 |
国内免费 | 299篇 |
专业分类
639762篇 |
出版年
2021年 | 4523篇 |
2018年 | 7071篇 |
2017年 | 6538篇 |
2016年 | 9546篇 |
2015年 | 14042篇 |
2014年 | 15010篇 |
2013年 | 20862篇 |
2012年 | 24461篇 |
2011年 | 23810篇 |
2010年 | 15562篇 |
2009年 | 13439篇 |
2008年 | 20377篇 |
2007年 | 20662篇 |
2006年 | 18845篇 |
2005年 | 17993篇 |
2004年 | 17511篇 |
2003年 | 16498篇 |
2002年 | 15638篇 |
2001年 | 23910篇 |
2000年 | 23941篇 |
1999年 | 19299篇 |
1998年 | 7145篇 |
1997年 | 7164篇 |
1996年 | 6929篇 |
1995年 | 6343篇 |
1994年 | 6355篇 |
1993年 | 6079篇 |
1992年 | 14900篇 |
1991年 | 14082篇 |
1990年 | 13678篇 |
1989年 | 13478篇 |
1988年 | 12093篇 |
1987年 | 11574篇 |
1986年 | 10593篇 |
1985年 | 10474篇 |
1984年 | 8962篇 |
1983年 | 7703篇 |
1982年 | 6041篇 |
1981年 | 5480篇 |
1980年 | 5103篇 |
1979年 | 8322篇 |
1978年 | 6459篇 |
1977年 | 5868篇 |
1976年 | 5477篇 |
1975年 | 5868篇 |
1974年 | 6352篇 |
1973年 | 6213篇 |
1972年 | 5534篇 |
1971年 | 5114篇 |
1970年 | 4309篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
932.
The hydroosmotic responses induced by oxytocin and 8-bromo-cyclic AMP, in frog and toad urinary bladders, were recorded minute by minute. 3HHO and 45Ca unidirectional fluxes as well as prostaglandin B2 liberation were also measured. It was observed that: (1) Addition of the calcium ionophore A23187 or quinidine to the serosal bath inhibited the response to oxytocin, but not to 8-bromo-cyclic AMP, while increasing prostaglandin E1 liberation into the serosal but not into the mucosal bath. (2) Addition of A23187 to the mucosal bath induced a transient and temperature-dependent inhibition of the response elicited by 8-bromo-cyclic AMP. The time-course of this reduction in water permeability and its sensitivity to medium temperature were similar to those observed after the withdrawal of agonist, but clearly different of those observed after intracellular acidification. (3) The hydroosmotic response was also transitorily inhibited when the Ca2+ concentration was step-changed in the mucosal bath. (4) When added to the mucosal or to the serosal baths, the ionophore increased either the apical or the laterobasal Ca2+ permeabilities. It is concluded that manipulation of intracellular Ca2+ interferes with the hydroosmotic response at two different levels. (1) A first target point located 'pre-cyclic-AMP production'. This effect would be mediated by prostaglandin liberation. (2) A second target point located after cyclic AMP production and before the 'temperature-dependent rate-limiting step'. This effect is probably related to the mechanism controlling the insertion and removal of water channels. 相似文献
933.
The influence of contact guidance on the orientation of colonies of subcultured vascular smooth muscle cells 总被引:1,自引:0,他引:1
Robert C. Buck 《In vitro cellular & developmental biology. Plant》1982,18(9):783-788
Summary Subcultures of smooth muscle cells derived from rat thoracic aorta were grown on plane plastic substrata and on plastic substrata
having ridges molded in them by a heated, ruled template. The cells were found to have a very high degree of contact guidance
when distributed sparsely on the ridged substrata. When the cell density increased multilayered, elongated colonies formed.
On plane substrata these were irregular, curved, and disposed in all directions. On the ridged substrata, however, the colonies
were straight, evenly spaced, and positioned at right angles to the ridges.
Supported by Grant MT1011 from the Medical Research Council of Canada. 相似文献
934.
935.
Charles E. Wenner John C. Cheney L. David Tomei 《Journal of cellular biochemistry》1981,15(2):161-168
The introduction of either PGF2α (10?7 M) or TPA (10?7 M) stimulated, ouabain-sensitive 86Rb+ influx at 30 min in postconfluent 3T3-4 mouse fibroblast cultures by 117% and 124%, respectively. Both TPA and PGF2α at these concentrations stimulated the incorporation of 3H-TdR into DNA. TPA had the greatest stimulatory effect, which was similar to that obtained with 10% fetal calf serum. In accord with the idea that modulation of membrane processes such as Na+/K+ pump activity in fibroblasts may reflect important events related to the initiation of DNA synthesis, it was observed that in both 3T3-4 and C3H-1 0T½ cells there were parallel increases in 3H-TdR incorporation and ouabain-sensitive 86Rb+ influxes with 10?7 M TPA, whereas PGF2α stimulated a significant increase in 3H-TdR incorporation in 3T3-4 but not C3H-10T½ cells and only marginal increases in ouabain-sensitive 86Rb+ influx in both. Therefore, although there appears to be a close correlation between Na+/K+ pump activation and subsequent S-phase entry following TPA stimulation, a similar correlation for PGF2α cannot be confirmed. 相似文献
936.
937.
Using a solid-phase radioimmunoassay, serum IgE level was determined in 46 normal subjects, 53 patients with bronchial asthma, 44 patients with chronic bronchitis and / or emphysema, and 19 patients with restrictive lung disease. Sputum IgE was measured simultaneously in 51 of the subjects. The range of serum IgE concentration in the normal subjects was wide. It varied between 15 and 750 ng/ml with a mean of 135 ng. Asthmatic patients had significantly higher levels of serum IgE with a mean of 579 ng/ml, but only 30% fell outside the normal 95% confidence limits. Patients with chronic bronchitis, emphysema and restrictive lung diseases had normal IgE levels. There was a significant correlation between serum and sputum IgE levels. 相似文献
938.
The Devonian cemented brachiopod Schuchertellopsis durbutensis has proved difficult to classify and its possible taxonomic relationships are unknown. Morphologically Schuchertellopsis resembles more closely members of the Orthotetidina than the Davidsoniidina. Examination of the shell structure, a key diagnostic feature of the Orthotetidina, shows that Schuchertellopsis has the cross laminar secondary shell typical of all orthotetidines. However, the presence of both pseudopunctate and incipient an extropunctate fabric within the ventral valve is unique amongst orthotetidine brachiopods and is thought to represent a phase of shell fabric experimentation. Schuchertellopsis probably fits most comfortably within the Schuchertellidae, and is the earliest representative of that family. 相似文献
939.
S. H. Habib S.-E. Ooi Ond?ej Novák Danu?e Tarkowská Jakub Rol?ík Karel Dole?al S. S. R. Syed-Alwee C.-L. Ho P. Namasivayam 《Plant Growth Regulation》2012,68(2):313-317
Comparative mineral and hormonal analyses were made on tissue culture derived truncated leaf syndrome and wild type oil palm seedlings. Mineral analysis confirmed that Boron, Zinc and chlorophyll levels were significantly lower in truncated leaf syndrome leaves than those of wild type. Hormonal analysis also revealed various cytokinin derivatives such as trans-zeatin, trans-zeatin riboside, trans-zeatin O-glucoside and trans-zeatin riboside 5??mono phosphate were significantly higher in truncated leaf syndrome leaves compared to wild type leaves. Brassinolide level was also significantly higher in truncated leaf syndrome leaves than those of the wild type. These observations suggest that the truncated leaf syndrome abnormality could be associated to high cytokinin and brassinosteroid production which affects the uptake of Boron and Zinc. 相似文献
940.