全文获取类型
收费全文 | 41936篇 |
免费 | 15797篇 |
国内免费 | 66篇 |
专业分类
化学 | 53919篇 |
晶体学 | 23篇 |
力学 | 1207篇 |
数学 | 1707篇 |
物理学 | 943篇 |
出版年
2024年 | 424篇 |
2023年 | 4258篇 |
2022年 | 1478篇 |
2021年 | 2498篇 |
2020年 | 4714篇 |
2019年 | 2282篇 |
2018年 | 2426篇 |
2017年 | 640篇 |
2016年 | 5615篇 |
2015年 | 5565篇 |
2014年 | 5009篇 |
2013年 | 5177篇 |
2012年 | 3210篇 |
2011年 | 1172篇 |
2010年 | 3415篇 |
2009年 | 3313篇 |
2008年 | 1154篇 |
2007年 | 817篇 |
2006年 | 239篇 |
2005年 | 205篇 |
2004年 | 146篇 |
2003年 | 139篇 |
2002年 | 106篇 |
2001年 | 62篇 |
1997年 | 70篇 |
1996年 | 67篇 |
1995年 | 125篇 |
1994年 | 82篇 |
1993年 | 198篇 |
1992年 | 71篇 |
1991年 | 58篇 |
1988年 | 76篇 |
1987年 | 60篇 |
1984年 | 64篇 |
1983年 | 72篇 |
1982年 | 74篇 |
1981年 | 89篇 |
1980年 | 108篇 |
1979年 | 97篇 |
1978年 | 99篇 |
1977年 | 164篇 |
1976年 | 183篇 |
1975年 | 187篇 |
1974年 | 197篇 |
1973年 | 111篇 |
1972年 | 153篇 |
1971年 | 122篇 |
1970年 | 207篇 |
1969年 | 125篇 |
1968年 | 133篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
Günter Graumann Prof. Dr. 《ZDM》2005,37(3):190-198
Problem fields with one or two generating problems and possibilities of varying existing problems give a good chance for self-activities of students and can be used for reaching different general aims. In this paper some topics concerning quadrilaterals will be presented. I hope they will animate teachers for more problem orientation in mathematics education. First we will reflect about different types of convex and non-convex quadrilaterals and possibilities of ordering them. Then we focus on middle-quadrilaterals and types of quadrilaterals with special middle-quadrilaterals as well as their logical ordering. Finally we investigate the analogies in space to the parallelogram and its sub-types and order them in the “house of parallelepipeds”. 相似文献
12.
13.
14.
15.
16.
Prof. Dr. Leszek Stoch 《Journal of Thermal Analysis and Calorimetry》1992,38(9):1947-1948
17.
18.
19.
Suchada Suntornchashwej Dr. Khanit Suwanborirux Dr. Kazushi Koga Minoru Isobe Prof. Dr. 《化学:亚洲杂志》2007,2(1):114-122
Malyngamide X ( 1 ), the first (7R)‐lyngbic acid connected to a new tripeptide backbone, was isolated from the Thai sea hare Bursatella leachii. The gross structure of 1 was established on the basis of 1D and 2D NMR and mass spectroscopic data. Combination of the NMR spectroscopic experiments with α‐methoxy‐α‐(trifluoromethyl)phenylacetic acid esters, 2,2,2‐trifluoro‐1‐(9‐anthryl)ethanol chiral solvating agent, and molecular mechanics of 1 and the synthetic molecular fragments allowed us to determine the absolute stereochemistry of all six stereogenic centers without hydrolytic degradation of the compound. Compound 1 displayed moderate cytotoxic, antitubercular, and antimalarial properties. 相似文献
20.
Blundell Tom L. Bolanos-Garcia Victor Chirgadze Dimitri Y. Harmer Nicholas J. Lo Thomas Pellegrini Luca Sibanda B. Lynn 《Structural chemistry》2002,13(3-4):405-412
Signaling in living systems needs to achieve high specificity, to be reversible, and to achieve high signal to noise. Signaling mediated by multiprotein systems has evolved that avoids the requirement for high-affinity binary complexes that would be difficult to reverse and which, in the overcrowded cell, would lead to excessive noise in the system. Symmetrical structures are only occasionally formed. When they are, it is principally to colocate components, for example, the tyrosyl kinases of growth factors, where dimers form. Symmetry is, however, often broken, presumably to create more sensitivity and specificity in the signaling system by assembling other components, into higher-order multiprotein systems. The binding of a single heparin to two 1:1 FGF:FGFR complexes is an example, as is the binding of a single ligase to the Xrcc4 dimer, perhaps so creating a further DNA-binding site. 相似文献