全文获取类型
收费全文 | 54667篇 |
免费 | 2321篇 |
国内免费 | 4071篇 |
专业分类
系统科学 | 4103篇 |
丛书文集 | 1704篇 |
教育与普及 | 265篇 |
理论与方法论 | 173篇 |
现状及发展 | 736篇 |
研究方法 | 1篇 |
综合类 | 54024篇 |
自然研究 | 53篇 |
出版年
2024年 | 102篇 |
2023年 | 367篇 |
2022年 | 893篇 |
2021年 | 1001篇 |
2020年 | 979篇 |
2019年 | 798篇 |
2018年 | 721篇 |
2017年 | 936篇 |
2016年 | 1121篇 |
2015年 | 1636篇 |
2014年 | 1949篇 |
2013年 | 1710篇 |
2012年 | 3163篇 |
2011年 | 3383篇 |
2010年 | 2756篇 |
2009年 | 2849篇 |
2008年 | 3028篇 |
2007年 | 4364篇 |
2006年 | 4098篇 |
2005年 | 3667篇 |
2004年 | 3407篇 |
2003年 | 2791篇 |
2002年 | 2262篇 |
2001年 | 1915篇 |
2000年 | 1723篇 |
1999年 | 1508篇 |
1998年 | 1046篇 |
1997年 | 1023篇 |
1996年 | 893篇 |
1995年 | 765篇 |
1994年 | 707篇 |
1993年 | 643篇 |
1992年 | 555篇 |
1991年 | 584篇 |
1990年 | 457篇 |
1989年 | 438篇 |
1988年 | 356篇 |
1987年 | 228篇 |
1986年 | 128篇 |
1985年 | 64篇 |
1984年 | 13篇 |
1982年 | 2篇 |
1981年 | 10篇 |
1980年 | 1篇 |
1955年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
281.
提出了一种利用两台以串口互相连接的计算机来实现对GPS全球定位系统定位信息的模拟发送和接收的方法。 相似文献
282.
肖枚英 《首都师范大学学报(自然科学版)》1996,17(4):43-46
本文报导了DNA与顺铂相互作用下的CD谱的测试过程及实验结果,并对作用机理做了初步分析. 相似文献
283.
P. Levy G. Cherqui A. Robert D. Wicek J. Picard 《Cellular and molecular life sciences : CMLS》1989,45(6):588-591
Summary During the spontaneous differentiation (day 5 to day 15 of the culture) of Caco-2 cells, the sulfation of cell layer glycosaminoglycans increased, whereas protein kinase C activity was concomitantly redistributed from the membrane to the cytosol. The protein kinase C activators, 4-phorbol 12-myristate, 13-acetate and 1,2-dioctanoyl-glycerol inhibited glycosaminoglycan sulfation. By contrast, 4-phorbol 12, 13 didecanoate was ineffective.These results suggest that membrane-bound PKC may exert a modulatory effect on glycosaminoglycan sulfation, and this effect is gradually attenuated as Caco-2 cell differentiation progresses. 相似文献
284.
T. Hatano Y. Kato M. Katayama S. Marumo 《Cellular and molecular life sciences : CMLS》1989,45(4):400-402
Summary A new potent antiauxin, -(5,7-dichloroindole-3-)isobutyric acid has been synthesized and shown to inhibit auxin-mediated elongation ofAvena coleoptiles and to stimulate root growth of rice seedlings. Its activity is stronger than -(p-chlorophenoxy)isobutyric acid and is comparable to that of 2,3,5-triiodobenzoic acid, which are typical antiauxins. 相似文献
285.
Summary Apart from cancer and mutation induction, radiobiological effects on mammals are mostly attributable to cell death, defined as loss of proliferative capacity. Survival curves relate retention of that capacity to radiation dose, and often manifest a quasi-threshold (shoulder). The shoulder is attributable to an initial mechanism of repair (Q-repair) which is gradually depleted as dose increases. Another form of repair, which is not depleted (P-repair), increases the dose required to deliver an average of one lethal event per cell (dose D0). Neither form of repair can unambiguously be linked with repair of defects in isolated DNA. An important initial lesion may well be disruption of the complex structural relationship between the DNA, nuclear membrane and associated proteins. One form of P-repair may be restoration of that structural relationship. 相似文献
286.
287.
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
288.
Feller—Trotter算子的局部饱和定理 总被引:1,自引:1,他引:0
利用Bajsanski-Bajanic抛物线引理建立Feller-Trotter算子的局部小“ο”饱和定理,进一步地应用所得到结论建立了(C_)类算子半群概率表示的局部饱和定理。 相似文献
289.
V. Ralevic P. Milner K. A. Kirkpatrick G. Burnstock 《Cellular and molecular life sciences : CMLS》1992,48(1):31-34
Adenosine 5-triphosphate (ATP) was released into the perfusate of rat isolated mesenteric arterial beds during each of two consecutive increases in flow. There was no significant difference between the amounts of ATP released on each occasion. Substance P was also released into the perfusate by increased flow, although its release was more variable. Removal of the endothelium of the mesenteric vessels with sodium deoxycholate led to a significant reduction (74%) in the amount of ATP released compared with the release before the endothelium had been removed. This suggests that the ATP released into the mesenteric arterial perfusate during increased flow arises from endothelial cells. 相似文献
290.
为了消除应用焓法进行含有相变的有限元传热计算结果呈台阶形的现象,本文作者提出“焓计算单元”和“固相分数”的概念,并将几种一维有限元实施方案的计算结果与精确解对比,说明采用所提出的概念,可以使有限元计算得出更为合理的结果。 相似文献