全文获取类型
收费全文 | 235041篇 |
免费 | 2365篇 |
国内免费 | 813篇 |
专业分类
化学 | 118561篇 |
晶体学 | 4017篇 |
力学 | 10815篇 |
综合类 | 1篇 |
数学 | 25797篇 |
物理学 | 79028篇 |
出版年
2020年 | 1834篇 |
2019年 | 2102篇 |
2018年 | 2771篇 |
2017年 | 2676篇 |
2016年 | 4001篇 |
2015年 | 2462篇 |
2014年 | 4043篇 |
2013年 | 10226篇 |
2012年 | 7707篇 |
2011年 | 9561篇 |
2010年 | 6774篇 |
2009年 | 6708篇 |
2008年 | 8832篇 |
2007年 | 8882篇 |
2006年 | 8369篇 |
2005年 | 7613篇 |
2004年 | 7031篇 |
2003年 | 6182篇 |
2002年 | 6183篇 |
2001年 | 7117篇 |
2000年 | 5394篇 |
1999年 | 4259篇 |
1998年 | 3581篇 |
1997年 | 3503篇 |
1996年 | 3312篇 |
1995年 | 3028篇 |
1994年 | 2965篇 |
1993年 | 3060篇 |
1992年 | 3159篇 |
1991年 | 3347篇 |
1990年 | 3096篇 |
1989年 | 3041篇 |
1988年 | 3072篇 |
1987年 | 2964篇 |
1986年 | 2812篇 |
1985年 | 3820篇 |
1984年 | 4019篇 |
1983年 | 3206篇 |
1982年 | 3417篇 |
1981年 | 3344篇 |
1980年 | 3237篇 |
1979年 | 3343篇 |
1978年 | 3434篇 |
1977年 | 3357篇 |
1976年 | 3452篇 |
1975年 | 3141篇 |
1974年 | 3152篇 |
1973年 | 3197篇 |
1972年 | 2236篇 |
1971年 | 1850篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
121.
Chromatographia - A theoretical model is used to predict retention times of divalent metal cations in single-column ion chromatography using one or more ligands in the eluent. Stability constants... 相似文献
122.
123.
124.
Separation of 23 dansylated amino acids by micellar electrokinetic chromatography at low temperature
Summary The baseline separation of 23 dansylated amino acids (including 3 didansylated species) is reported. Lowering of the analysis
temperature and fine control of the surfactant concentration were essential in obtaining this result. Calibration graphs with
good linearity were obtained. 相似文献
125.
Synthesis of optically active sesquiterpenes with a eudesmane C-skeleton from the chiral starting material thujone involves transformation of a tricyclic intermediate (1R,2R,4S)-1,7-dimethyl-4-(1-methylethyl)tricyclo[4.4.0.02,4]dec-6-en-8-one ( 2 ) into the bicyclic compound β -cyperone ( 5 ). Hydroxylation of 2 at C(5) or C(11) permits subsequent opening of the cyclopropane ring and rearrangement to β -cyperone. In this publication, studies involving hydroxylation of 2 by fungal cultures are presented. The resultant products are useful intermediates in efficient synthesis of eudesmane sesquiterpenes. Of five fungi tested, Rhizopus oryzae ATCC 11145 proved most versatile. It hydroxylates at the exocyclic C(11) position in high yield (70%) and, to a lesser extent, at C(5) (5%). Enzymatic activity appears at the end of growth phase and at least 2.2 g of 2 per liter can be metabolized without significant loss of product yield. A second fungus, Cunninghamella echinulata ATCC 9244, proved most useful for hydroxylation of derivatives of 2 for the preparation of derivatives of β -cyperone, although product yields were low (2–20%), some derivatives were nonreactive, and hydroxylation at C(9) occurred. The relationship between precursor structure and enzyme affinity is discussed. 相似文献
126.
A set of exact conditions is compiled for the purpose of developing and testing approximations for the exchange-correlation energy as a functional of the electron density. Special emphasis is placed upon recently developed density-scaling relationships. Commonly used generalized gradient approximations are compared against several of these conditions. A direct tabular comparison of these functionals (not of calculated properties) with one another is also made. © 1994 John Wiley & Sons, Inc. 相似文献
127.
128.
129.
E. N. Yurchenko G. E. Kramareva N. G. Zubritskaya T. P. Gaidei 《Reaction Kinetics and Catalysis Letters》1995,55(2):425-432
In the Russian Scientific Center Applied Chemistry catalysts have been developed for the gas-phase fluorination of organics, including chlorine-containing substances, hydrogenation and reductive amination of organic substances, decomposition of liquid substances to gases, complete oxidation and reduction, suitable for environment at protection. 相似文献
130.