全文获取类型
收费全文 | 23185篇 |
免费 | 614篇 |
国内免费 | 1170篇 |
专业分类
系统科学 | 868篇 |
丛书文集 | 840篇 |
教育与普及 | 244篇 |
理论与方法论 | 62篇 |
现状及发展 | 444篇 |
综合类 | 22503篇 |
自然研究 | 8篇 |
出版年
2024年 | 30篇 |
2023年 | 65篇 |
2022年 | 113篇 |
2021年 | 148篇 |
2020年 | 170篇 |
2019年 | 157篇 |
2018年 | 167篇 |
2017年 | 197篇 |
2016年 | 232篇 |
2015年 | 334篇 |
2014年 | 721篇 |
2013年 | 603篇 |
2012年 | 1013篇 |
2011年 | 1187篇 |
2010年 | 965篇 |
2009年 | 1134篇 |
2008年 | 1192篇 |
2007年 | 1490篇 |
2006年 | 1376篇 |
2005年 | 1235篇 |
2004年 | 1088篇 |
2003年 | 1139篇 |
2002年 | 1082篇 |
2001年 | 882篇 |
2000年 | 868篇 |
1999年 | 735篇 |
1998年 | 601篇 |
1997年 | 615篇 |
1996年 | 599篇 |
1995年 | 830篇 |
1994年 | 651篇 |
1993年 | 653篇 |
1992年 | 646篇 |
1991年 | 567篇 |
1990年 | 577篇 |
1989年 | 406篇 |
1988年 | 216篇 |
1987年 | 143篇 |
1986年 | 77篇 |
1985年 | 45篇 |
1984年 | 13篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1955年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
D. Porquet M. Appel T. Fournier O. Bertaux D. Biou J. Féger 《Cellular and molecular life sciences : CMLS》1992,48(3):257-261
Both in vivo and in vitro models have certain disadvantages for the study of the chronic hepatotoxicity of drugs. The aim of this work was to evaluate a new approach based on an in vivo/in vitro model. After chronic in vivo treatment of rats with Vincamine and Vindeburnol (an eburnamenine derivative which exhibits hepatotoxic properties in man) liver cells were isolated, and functional and metabolic disorders (metabolic utilization of fructose and protein biosynthesis) were studied to determine injury. The results showed no modification of blood parameters, but a direct relationship between the dose of Vindeburnol administered in vivo and the metabolic disorders observed in vitro, evidencing the high sensitivity and reliability of this model. 相似文献
92.
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
93.
J. Y. Toullec M. Chikhi A. van Wormhoudt 《Cellular and molecular life sciences : CMLS》1992,48(3):272-277
In crustaceans, all the steps in the assimilation of food take place in the hepatopancreas. To facilitate the study of this organ, a method for the dissociation of cell types was developed. The hepatopancreas of the prawnPalaemon serratus was mechanically dissociated and the cells separated by Percoll density-gradient centrifugation. The E and R cells had similar densities of around 1.05 g/ml. The F cells were separated into two distinct fractions with densities of 1.075 and 1.082 g/ml. The B cells sedimented at a density of 1.12 g/ml. The ratio between the two populations of F cells was found to vary during the intermolt cycle while B cells disappeared after the molt. When the density gradient fractions were incubated with3H-leucine, incorporation was highest in the F cell fractions. Measurements of -amylase activity, indicated that the two populations of F cells may be derived from the same cell type. 相似文献
94.
龚斌 《石河子大学学报(自然科学版)》1992,(2)
本文对影响柴油用转子流量计测量精度的主要因素进行了试验研究。研究结果表明,柴没的粘度、密度以及测试温度不同,对测量精度将造成不可忽视的影响。根据流体力学的基本原理,利用试验优化方法提出的薄壁量孔校正方法,能够对柴油用转子流量计各标定值进行快速有效的校正。该方法具有较好的油品和温度适应性,其校正精度达2%。 相似文献
95.
本文用“等效长度”的概念研究并计算了铁路信号技术进步在换算周转量增长中的贡献.依据有关数据,分析并提出了具体的计算方法,算出了铁路信号技术进步的贡献占铁路运输各部门技术进步总贡献的16.49%~20.77%.其中,还未包括为确保行车安全所作出的贡献. 相似文献
96.
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
97.
G. L. Mendz C. R. Middlehurst P. W. Kuchel P. A. Crossie 《Cellular and molecular life sciences : CMLS》1986,42(9):1016-1018
Summary A technique to assay erythrocyte pyrimidine 5-nucleotidase activity in situ using31P nuclear magnetic resonance spectroscopy is presented. The assay is chemically specific, simple and applicable to untreated lysates. A comparison of enzyme levels in normal controls and in multiple sclerosis patients employing the assay yielded no significant differences between both groups. Difficulties encountered in the quantitative analysis of the assay using1H-NMR spectroscopy are briefly discussed. 相似文献
98.
A. M. Landolt V. Osterwalder T. A. Landolt 《Cellular and molecular life sciences : CMLS》1985,41(5):640-642
Summary Adenomatous prolactin cells lose 39% of their cytoplasm volume within 7 days after the beginning of bromocriptine treatment. A simultaneous reduction of the rough-surfaced endoplasmic reticulum and the Golgi apparatus occurs. Their membranes are removed by rapid transport along the secretory pathway to the cell surface and to lysosomal destruction.We thank Prof. E. del Pozo, Sandoz Ltd, Basle, for the generous gift of injectable bromocriptine, Prof. E.R. Weibel, Dept. of Anatomy, University of Bern, for his technical advice, Dr U. Helfenstein, Institute of Biostatistics, University of Zürich, for his help in the statistical evaluation of the results and the EMDO-Foundation, Zürich, for financial support. 相似文献
99.
100.
Yu. Yu. Chirkov A. R. Kazarov M. A. Malatsidze A. S. Sobolev 《Cellular and molecular life sciences : CMLS》1985,41(11):1430-1432
Summary In mixed culture of Chinese hamster fibroblatst, clone 431, and transformed murine L fibroblasts, clone B-82, isoproterenol was found to protect only 431 cells against ionizing radiation. It was shown that 431 cells, in contrast to B-82 cells, possess-adrenoreceptors, and the radioprotective effect of isoproterenol can be realized only if this agent interacts with-adrenoreceptors coupled with the cAMP system. Since malignization often causes the disappearance of-adrenergic and other hormone receptors, the combined culturing and irradiation of the cells studied can be regarded as a model of the growth of malignant cells (B-82) among normal tissue cells (431 cells) under conditions of radiation therapy. A possibility of selective protection against radiation damage of normal tissue cells, with retention of the former radiosensitivity of tumor cells, is discussed. 相似文献