全文获取类型
收费全文 | 56500篇 |
免费 | 250篇 |
国内免费 | 549篇 |
专业分类
系统科学 | 1242篇 |
丛书文集 | 357篇 |
教育与普及 | 291篇 |
理论与方法论 | 516篇 |
现状及发展 | 32523篇 |
研究方法 | 911篇 |
综合类 | 19269篇 |
自然研究 | 2190篇 |
出版年
2013年 | 804篇 |
2012年 | 635篇 |
2011年 | 2674篇 |
2009年 | 617篇 |
2008年 | 819篇 |
2007年 | 921篇 |
2006年 | 1032篇 |
2005年 | 1195篇 |
2004年 | 2290篇 |
2003年 | 1895篇 |
2002年 | 1594篇 |
2001年 | 1447篇 |
2000年 | 957篇 |
1999年 | 981篇 |
1998年 | 641篇 |
1997年 | 774篇 |
1996年 | 534篇 |
1994年 | 687篇 |
1993年 | 689篇 |
1992年 | 917篇 |
1991年 | 785篇 |
1990年 | 850篇 |
1989年 | 669篇 |
1988年 | 627篇 |
1987年 | 666篇 |
1986年 | 744篇 |
1985年 | 861篇 |
1984年 | 785篇 |
1983年 | 668篇 |
1982年 | 790篇 |
1981年 | 832篇 |
1980年 | 940篇 |
1979年 | 1431篇 |
1978年 | 1285篇 |
1977年 | 1287篇 |
1976年 | 1089篇 |
1975年 | 1088篇 |
1974年 | 1020篇 |
1973年 | 1247篇 |
1972年 | 1324篇 |
1971年 | 1366篇 |
1970年 | 1480篇 |
1969年 | 1273篇 |
1968年 | 1172篇 |
1967年 | 1123篇 |
1966年 | 921篇 |
1965年 | 731篇 |
1964年 | 480篇 |
1958年 | 564篇 |
1957年 | 486篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
171.
Summary Zn2+ (10–100 M) elevated the frequency of miniature end-plate potentials (MEPPs) in the mouse diaphragm. The effect did not depend on external Ca2+. Botulinum type A toxin (BTXA, 50 ng/ml) abolished MEPPs almost completely within 30 min. Zn2+ (100 M) restored MEPPs and increased their frequency after they had been abolished by BTXA in Ca2+-free solutions. The antagonistic effect of Zn2+ in the Ca2+-free solution was reduced by exposing the diaphragm to the toxin in the Ca2+-free solutions containing high K+. Thus, the action of BTXA is probably enhanced by depolarization of the motor nerve terminals. 相似文献
172.
E. Habermann 《Cellular and molecular life sciences : CMLS》1988,44(3):224-226
Summary Rat brain homogenate was preloaded with [3H]noradrenaline or [3H]GABA and stimulated with high K+. Tetanus toxin and botulinum A neurotoxin partially prevent the evoked [3H]noradrenaline release in the same range of toxin concentrations starting below 10–10M. In contrast, release of -amino butyric acid (GABA) is much more sensitive to tetanus than to botulinum A toxin. 相似文献
173.
174.
H. J. Bestmann J. Erler O. Vostrowsky 《Cellular and molecular life sciences : CMLS》1988,44(9):797-799
Summary By means of closed-loop-stripping and subsequent GC analyses the diel periodicity of release of (Z)-11-hexadecenyl acetate, (E)-8-dodecenyl acetate, and (Z)-9-tetradecenyl acetate, the main constituents of the respective sex pheromone blends ofMamestra brassicae, Cryptophlebia leucotreta andSpodoptera sunia females, was determined.Pheromones, 64. For the 63rd contribution we have taken from: Szöcs, G., Toth, M., Bestmann, H. J., Vostrowsky, O., Heath, R. R., and Tumlinson, J. H., Z. Naturforsch.42c (1987) 165; Pheromones, 62: Bestmann et al.13. 相似文献
175.
M. Caron G. Cherqui D. Wicek J. Capeau J. Bertrand J. Picard 《Cellular and molecular life sciences : CMLS》1988,44(1):34-37
Summary Insulin stimulation of glycogen synthesis was nearly abolished in hepatoma cells shortly treated with 4 ß-phorbol 12 \-myristate, 13 -acetate (protein kinase C activation) but remained unmodified in cells chronically treated with the phorbol ester (protein kinase C depletion). Thus, although exogenous activation of protein kinase C results in an inhibition of insulin action, protein kinase C depletion has no influence on this process. The results suggest that, in hepatoma cells, no endogenous activation of protein kinase C may occur in response to the signal triggered by insulin. 相似文献
176.
E. Flückiger U. Briner B. Clark A. Closse A. Enz P. Gull A. Hofmann R. Markstein L. Tolcsvai H. R. Wagner 《Cellular and molecular life sciences : CMLS》1988,44(5):431-436
Summary The profile of action in animals of CQP 201-403, a novel 8-amino-ergoline, is in most aspects that of a very potent dopaminomimetic, both as a prolactin secretion inhibitor, and at the levels of the CNS and the cardiovascular system. Qualitatively CQP 201-403 differs slightly from bromocriptine and apomorphine in its effects on the CNS (no influence on serotonin metabolism in the rat cortex; induction of masculine mounting behavior in rats) and the cardiovascular system of the dog (reflex tachycardia in response to a blood-pressure fall). In man the new compound proved to be highly active in lowering prolactin serum levels and to be more potent than bromocriptine (Parlodel®).In memory of Dr Annemarie Closse, who died 14 June 1987. 相似文献
177.
本文对使用谱带模型理论方法计算尾喷焰光辐射特性所出现的等价宽度问题进行了较为详细的讨论,研究了几种形式等价宽度的有效性,并提出了计算尾喷焰辐射的“穿截尾喷焰小气柱”方法,回避了四重积分的计算,得到了良好效果。 相似文献
178.
A number of neuropeptides were isolated from the ganglia and muscles of molluscs, and their actions were examined. Diverse neuropeptides, in addition to several classical neurotransmitters, were suggested to be involved in the regulation of the anterior byssus retractor muscle ofMytilus. A wide structural variety of members of theMytilus inhibitory peptide family was observed in each of the generaMytilus, Achatina andHelix. Gly-Trp-NH2, the C-terminal dipeptide fragment of the neuropeptide AGPWamide, showed a more potent action than the parent peptide in all of the muscles examined. Peptides related to some molluscan neuropeptides were found to be distributed interphyletically. Some neuropeptides containing ad-amino acid residue were found inAchatina andMytilus. These aspects of molluscan neuropeptides are thought not to be exceptional. 相似文献
179.
M. T. Santini R. Masella A. Cantafora S. W. Peterson 《Cellular and molecular life sciences : CMLS》1992,48(1):36-39
We have recently demonstrated, using electron paramagnetic resonance (EPR) spectroscopy, that insulin receptor internalization in response to insulin incubation (down-regulation) in human erythrocytes is accompanied by a transient decrease in membrane order, as measured by the 2T order parameter. Since membrane lipids play such an important role in receptor internalization, we investigated the possible effects that an alteration of the normally-occurring lipid profile might have on down-regulation and the concomitant transient decrease in membrane order. Consequently, human erythrocytes enriched with cholesterol and erythrocytes from cirrhotic patients were examined, because both of these groups of cells have a higher cholesterol/phospholipid molar ratio (CH/PL) than controls. The 5-nitroxystearate spin label, which inserts into the lipid bilayer of cell membranes, was used to monitor changes in 2T for a 3-h period at 37°C. We report here that both cholesterol-enriched and cirrhotic erythrocytes do not down-regulate, as demonstrated by binding assays, and that they do not show the typical transient decrease in membrane order observed in controls. The results seem to indicate that a more ordered membrane inhibits internalization of the insulin receptor in erythrocytes, and that an increase in membrane disorder is necessary for insulin receptor down-regulation. 相似文献
180.
We demonstrate for the first time a hair cycle-dependent gene and protein expression of proopiomelanocortin in mouse skin in vivo. Northern blot detected POMC mRNA with an apparent size of 0.9 kb in anagen but not telogen skin. Western blot emphasized a specific protein of 30–33 kDa recognized by anti -endorphin in late but not early anagen or telogen skin. By immunocytochemistry, -endorphin antigen was localized in the sebaceous gland in a hair cycle dependent manner. 相似文献