全文获取类型
收费全文 | 9840篇 |
免费 | 31篇 |
国内免费 | 47篇 |
专业分类
系统科学 | 42篇 |
丛书文集 | 72篇 |
教育与普及 | 8篇 |
理论与方法论 | 21篇 |
现状及发展 | 4613篇 |
研究方法 | 479篇 |
综合类 | 4588篇 |
自然研究 | 95篇 |
出版年
2013年 | 73篇 |
2012年 | 164篇 |
2011年 | 247篇 |
2010年 | 51篇 |
2008年 | 183篇 |
2007年 | 223篇 |
2006年 | 199篇 |
2005年 | 189篇 |
2004年 | 218篇 |
2003年 | 162篇 |
2002年 | 187篇 |
2001年 | 312篇 |
2000年 | 302篇 |
1999年 | 204篇 |
1992年 | 191篇 |
1991年 | 134篇 |
1990年 | 137篇 |
1989年 | 119篇 |
1988年 | 116篇 |
1987年 | 137篇 |
1986年 | 124篇 |
1985年 | 210篇 |
1984年 | 159篇 |
1983年 | 138篇 |
1982年 | 117篇 |
1981年 | 111篇 |
1980年 | 130篇 |
1979年 | 295篇 |
1978年 | 259篇 |
1977年 | 232篇 |
1976年 | 230篇 |
1975年 | 254篇 |
1974年 | 281篇 |
1973年 | 222篇 |
1972年 | 212篇 |
1971年 | 280篇 |
1970年 | 402篇 |
1969年 | 278篇 |
1968年 | 279篇 |
1967年 | 275篇 |
1966年 | 248篇 |
1965年 | 175篇 |
1964年 | 85篇 |
1959年 | 105篇 |
1958年 | 149篇 |
1957年 | 125篇 |
1956年 | 90篇 |
1955年 | 80篇 |
1954年 | 99篇 |
1948年 | 66篇 |
排序方式: 共有9918条查询结果,搜索用时 0 毫秒
1.
西文期刊回溯建库中几个重要项目的著录 总被引:4,自引:0,他引:4
在实践的基础上,从期刊的出版日期、出版周期、卷、期、年、月及其他标识、ISSN、增刊、出版者以及期刊的历史发展等方面对西文期刊机读目录的标准化著录问题进行了探讨。 相似文献
2.
复数,实数及实对称数据下Bruun FFT算法的实现 总被引:3,自引:0,他引:3
本文在复数、实数以及实对称数据下研究和实现了Bruun FFT算法。文章分析和评价了各种数据下BruunFFT的运算量和特点,提出了算法的实现结构和方法。最后给了TMS320C30上的运算时间,我们实现的算法比基2FFT速度提高35%。 相似文献
3.
V.A.帕瑟根 《国外科技新书评介》2007,(2):7-7
分子间的范德华力是十分微弱的,但可以说普遍的存在着,在很多体系中起着巨大的作用,在物理学、化学、生物学等学科中得到了广泛的研究。但怎样计算范德华力?如何考虑各种条件对范德华力的影响? 相似文献
4.
5.
6.
Y Y He T McNally I Manfield O Navratil I G Old S E Phillips I Saint-Girons P G Stockley 《Nature》1992,359(6394):431-433
The three-dimensional crystal structure of the Escherichia coli methionine repressor, MetJ, complexed with a DNA operator fragment is described in an accompanying article. The complex exhibits several novel features of DNA-protein interaction. DNA sequence recognition is achieved largely by hydrogen-bond contacts between the bases and amino-acid side chains located on a beta-ribbon, a mode of recognition previously hypothesized on the basis of modelling of idealized beta-strands and DNA, and mutagenesis of the Salmonella phage P22 repressors Arc and Mnt. The complex comprises a pair of MetJ repressor dimers which bind to adjacent met-box sites on the DNA, and contact each other by means of a pair of antiparallel alpha-helices. Here we assess the importance of these contacts, and also of contacts that would be made between the C-helices of the protein and DNA in a previous model of the complex, by studying mutations aimed at disrupting them. The role of the carboxy-terminal helix face in operator binding was unclear, but we demonstrate that recognition of operator sequences occurs through side chains in the beta-strand motif and that dimer-dimer interactions are required for effective repression. 相似文献
7.
M. Lazzari V. Franceschini G. Minelli F. Ciani 《Cellular and molecular life sciences : CMLS》1993,49(4):277-281
The corrosion cast technique provided for the first time an excellent three-dimensional visualization of the vascular pattern of the choroid and iris in the newt eye. The results show the presence of a single arterial afference to the choroidal and iris capillaries: the ophthalmic artery is the origin fo both ciliary arteries and the long posterior ciliary artery. Slightly behind the equatorial circumference of the eyeball the venous drainage consists of a single vessel on the dorsal side and two distinct vessels on the ventral one. It receives blood from both iris and choroid. The surface of the plastic endocasts shows some details of fine luminal structures of the endothelial cells. Shallow depressions may be regarded as imprints of endothelial cell nuclei, and they are distinctly different for arteries and capillaries. The angioarchitecture of the newt eye differs from that of brain in that hairpin-shaped capillary loops are not observed at all. 相似文献
8.
R. Poggioli A. V. Vergoni A. Bertolini 《Cellular and molecular life sciences : CMLS》1985,41(2):265-266
Summary Hydrochlorothiazide, acutely injected in rats, has a weak analgesic activity per se and potentiates and prolongs the antinociceptive effect of morphine.This work was supported in part by grants from Consiglio Nazionale delle Ricerche, and by Ministero della Pubblica Istruzione, Roma. 相似文献
9.
Nuclear localization and signalling activity of phosphoinositidase C beta in Swiss 3T3 cells. 总被引:14,自引:0,他引:14
The hydrolysis of phosphatidylinositol 4,5-bisphosphate (PtdInsP2) is a widespread receptor-coupled signalling system at the plasma membrane of most eukaryotic cells. The existence of an entirely separate nuclear phosphoinositide signalling system is suggested from evidence that purified nuclei synthesize PtdInsP2 and phosphatidylinositol 4-phosphate (PtdInsP) in vitro and that a transient decrease in the mass of these lipids occurs when Swiss 3T3 cells are cultured in the presence of insulin-like growth factor-1 (IGF-1). These IGF-1-dependent changes in inositol lipids coincide with an increase in nuclear diacyglycerol and precede translocation to the nucleus and activation of protein kinase C (refs 5, 6). Circumstantial evidence that links these changes with mitosis comes from the isolation of a 3T3 clone that expresses the type-1 IGF receptor and binds IGF-1 peptide but does not respond mitogenically or show transient mass changes in nuclear inositol lipids. A key question is how IGF-1 initiates the rapid breakdown of PtdInsP and PtdInsP2 in the nucleus. Here we present evidence that nuclei of 3T3 cells contain the beta-isozyme of phosphoinositidase C, whereas the gamma-isozyme is confined to the cytoplasm and that IGF-1 treatment stimulates exclusively the activity of nuclear phosphoinositidase C. 相似文献
10.
Growth hormone signal transduction 总被引:1,自引:0,他引:1
Growth hormone (GH) promotes animal growth by stimulating bone and cartilage cell proliferation, and influences carbohydrate and lipid metabolism. Some of these effects are brought about indirectly via somatomedin induction in hepatocytes, others by acting directly on the target cells. In either case, GH first binds to specific receptors on cells to trigger a sequence of biochemical events culminating in a biological response. Recently much has been learnt about the molecular structure of GH receptor, its binding to ligand, and the ensuing signal transduction events. 相似文献