全文获取类型
收费全文 | 2510篇 |
免费 | 320篇 |
国内免费 | 503篇 |
专业分类
化学 | 2086篇 |
晶体学 | 25篇 |
力学 | 77篇 |
综合类 | 42篇 |
数学 | 382篇 |
物理学 | 721篇 |
出版年
2024年 | 5篇 |
2023年 | 23篇 |
2022年 | 44篇 |
2021年 | 63篇 |
2020年 | 66篇 |
2019年 | 98篇 |
2018年 | 56篇 |
2017年 | 82篇 |
2016年 | 98篇 |
2015年 | 97篇 |
2014年 | 107篇 |
2013年 | 179篇 |
2012年 | 161篇 |
2011年 | 167篇 |
2010年 | 146篇 |
2009年 | 138篇 |
2008年 | 169篇 |
2007年 | 146篇 |
2006年 | 133篇 |
2005年 | 132篇 |
2004年 | 138篇 |
2003年 | 162篇 |
2002年 | 203篇 |
2001年 | 160篇 |
2000年 | 89篇 |
1999年 | 74篇 |
1998年 | 43篇 |
1997年 | 40篇 |
1996年 | 43篇 |
1995年 | 41篇 |
1994年 | 27篇 |
1993年 | 25篇 |
1992年 | 39篇 |
1991年 | 26篇 |
1990年 | 19篇 |
1989年 | 19篇 |
1988年 | 30篇 |
1987年 | 6篇 |
1986年 | 13篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1957年 | 1篇 |
排序方式: 共有3333条查询结果,搜索用时 93 毫秒
81.
This paper reports a successful development of a group of efficient soluble polymer-supported chiral tartrate ligands by liquid-phase synthesis for Sharpless epoxidation of a variety of allylic alcohols through ligand diversity. The influence of substituent in chiral tartrate ligands on the enantioselectivities of the reaction was disclosed. Moderate chemical yields and good enantiomeric excesses were obtained by using soluble polymer-supported tartrate ester in the epoxidation of allylic alcohols with Ti(O-i-Pr)(4)/tert-butyl hydroperoxide. 相似文献
82.
Determination of Partial Molar Volumes of EPA and DHA Ethyl Esters in Supercritical Carbon Dioxide 总被引:4,自引:0,他引:4
Mei HUANG Xian Da WANG Ren Tian XIONG Ping Dong WU Qi Long REN* National Laboratory of Secondary Resources Chemical Engineering Zhejiang University Hangzhou 《中国化学快报》2002,13(1)
The use of supercritical fluids (SCFs) as solvents has been attracting widespread interest in the research and commercial applications. The study of partial molar volumes of solutes at infinite dilution in the near-critical region is of considerable fundamental importance, as these data reflects the interactions occurring between the solute and the solvent. Experimental measurements of partial molar volumes may be divided into two categories: direct and indirect methods. The direct methods… 相似文献
83.
Zhu H Pan S Gu S Bradbury EM Chen X 《Rapid communications in mass spectrometry : RCM》2002,16(22):2115-2123
84.
Tetra-Schiff base macrocyclic compound containing benzo-12-crown-4 was synthesized via condensation of 2,6-diformyl-4-methyl-phenol with 4′,5′-diaminobenzo-12-C-4 promoted by proton. The compound was characterized by MS,IR ^1HNMR spectroscopy and elemental analysis. 相似文献
85.
A Pt microelectrode modified with nickel(II) polytetramethyldibenzo[b,i]tetraaza[14]annulene was prepared by electropolymerization of nickel(II) tetramethyldibenzo[b,i]tetraaza[14]annulene monomers and applied to determine sulfur dioxide in vitriol plant wastewater. For determination of SO2 with this electrochemically modified Pt microelectrode, the linear range was from 9.6 x 10(-6) to 2.4 x 10(-4) mol L-1, the sensitivity was 1.8 x 10(-4) A L mol-1, the detection limit was calculated to be 4.8 x 10(-6) mol L-1 (S/N = 3), the response time was less than 20 s and the relative standard deviation was found to be 2.1% on analyzing 4.8 x 10(-5) mol L-1 SO2 solution repeatedly (n = 7). These results demonstrated good accuracy compared with those obtained by the conventional iodimetric method. 相似文献
86.
87.
The atom transfer radical polymerization(ARP)of (-)-menthyl methacrylatc((-)-MnMA) mediated by CuCl/bipyridine and ethy1 2-bromopropionate or 1-phenylethyl bromide in THF system has been studied.The dependence of the specific rotation on molecular weight and the CD of Poly((-)-MnMA) thus obatined was investigated. 相似文献
88.
89.
Wei Ming XU Yu Guang WANG Zhen Hua CHEN Xian HUANG 《中国化学快报》2005,16(8):995-996
The development of organoselenium chemistry1 has been expanding rapidly during the last decades. Among them, organic selenides are key intermediates, for that they can be efficiently introduced, manipulated, and removed through selenoxide syn-elimination2. Our research group3 has been interested in the application of selenium in organic synthesis for several years. Isoxazolinyl substituted phenyl selenide 13a, although a β-H exists in the molecule, did not undergo selenoxide syn-elimination e… 相似文献
90.
In the present paper, Na_2SO_4-Al_2(SO_4)_3-H_2O system has been studied by ~(23)Na and ~(27)Al NMR quantitative method. It has been shown that the existence of double salt can be easily identified by this method. 相似文献