全文获取类型
收费全文 | 2501篇 |
免费 | 65篇 |
国内免费 | 9篇 |
专业分类
化学 | 2003篇 |
晶体学 | 33篇 |
力学 | 46篇 |
数学 | 74篇 |
物理学 | 419篇 |
出版年
2020年 | 21篇 |
2019年 | 34篇 |
2018年 | 18篇 |
2017年 | 21篇 |
2016年 | 35篇 |
2015年 | 49篇 |
2014年 | 59篇 |
2013年 | 92篇 |
2012年 | 115篇 |
2011年 | 141篇 |
2010年 | 71篇 |
2009年 | 81篇 |
2008年 | 153篇 |
2007年 | 141篇 |
2006年 | 161篇 |
2005年 | 145篇 |
2004年 | 145篇 |
2003年 | 99篇 |
2002年 | 126篇 |
2001年 | 62篇 |
2000年 | 54篇 |
1999年 | 33篇 |
1998年 | 22篇 |
1997年 | 29篇 |
1996年 | 29篇 |
1995年 | 19篇 |
1994年 | 39篇 |
1993年 | 23篇 |
1992年 | 34篇 |
1991年 | 24篇 |
1990年 | 27篇 |
1989年 | 18篇 |
1988年 | 23篇 |
1987年 | 22篇 |
1986年 | 23篇 |
1985年 | 28篇 |
1984年 | 36篇 |
1983年 | 23篇 |
1982年 | 33篇 |
1981年 | 22篇 |
1980年 | 26篇 |
1979年 | 16篇 |
1978年 | 19篇 |
1977年 | 29篇 |
1976年 | 14篇 |
1975年 | 21篇 |
1974年 | 19篇 |
1973年 | 14篇 |
1971年 | 15篇 |
1968年 | 13篇 |
排序方式: 共有2575条查询结果,搜索用时 15 毫秒
71.
Tsujita H Ura Y Wada K Kondo T Mitsudo TA 《Chemical communications (Cambridge, England)》2005,(40):5100-5102
2-(1-Alkoxycarbonyl)alkylidenetetrahydrofurans were readily synthesized by the codimerization of 2,3- or 2,5-dihydrofurans with alpha,beta-unsaturated esters using a zerovalent Ru catalyst, Ru(cod)(cot), with high regio- and stereoselectivity. 相似文献
72.
Ishikawa A Takata T Kondo JN Hara M Kobayashi H Domen K 《Journal of the American Chemical Society》2002,124(45):13547-13553
A Ti-based oxysulfide, Sm(2)Ti(2)S(2)O(5), was studied as a visible light-driven photocatalyst. Under visible light (440 nm < or = lambda < or = 650 nm) irradiation, Sm(2)Ti(2)S(2)O(5) with a band gap of approximately 2 eV evolved H(2) or O(2) from aqueous solutions containing a sacrificial electron donor (Na(2)S-Na(2)SO(3) or methanol) or acceptor (Ag(+)) without any noticeable degradation. This oxysulfide is, therefore, a stable photocatalyst with strong reduction and oxidation abilities under visible-light irradiation. The electronic band structure of Sm(2)Ti(2)S(2)O(5) was calculated using the plane-wave-based density functional theory (DFT) program. It was elucidated that the S3p orbitals constitute the upper part of the valence band and these orbitals make an essential contribution to the small band gap energy. The conduction and valence bands' positions of Sm(2)Ti(2)S(2)O(5) were also determined by electrochemical measurements. It indicated that conduction and valence bands were found to have satisfactory potentials for the reduction of H(+) to H(2) and the oxidation of H(2)O to O(2) at pH = 8. This is consistent with the results of the photocatalytic reactions. 相似文献
73.
74.
Masahiko Miyauchi Yoshinori Kawaguchi Akira Harada 《Journal of inclusion phenomena and macrocyclic chemistry》2004,50(1-2):57-62
-Cyclodextrin having cinnamamide at 6- or 3-positions (6-CiNH--CD, 3-CiNH--CD) and -cyclodextrin with cinnamamide on 6-position (6-CiNH--CD) have been prepared. Supramolecular structures were formed in the solid state or aqueous solutions and characterized by measurements of NMR and vapor pressure osmometry (VPO). The results indicate that 6-CiNH--CD formed insoluble supramolecular polymers in the solid state, while 6-CiNH--CD and 3-CiNH--CD formed supramolecular complexes in aqueous solutions. 6-CiNH--CD was found to form a dimer in an aqueous solution. 3-CiNH--CD formed intermolecular complexes to give supramolecular polymers. The differences of the position of guest part on cyclodextrins caused to give a variety of supramolecular structures in aqueous solutions. 相似文献
75.
Photolysis of perfluoroazooctane with diamond powders led to chemical modification of the surface with the introduction of perfluorooctyl ester and ether functional groups, the presence of which was confirmed by means of FT-IR, XPS and 19F NMR measurements. 相似文献
76.
A capillary electrophoretic method for the simultaneous determination of sulfamethoxazole and trimethoprim in plasma was developed. Sulfamethoxazole and trimethoprim extracted from human plasma with ethyl acetate were analyzed at 20 kV and 25 degrees C using 15 mm phosphate buffer (pH 6.2) as the electrolyte. The detection was by UV at 220 nm. The run time was 8.0 min and the limit of quantification was 10.00 microg/mL for sulfamethoxazole and 2.00 microg/mL for trimethoprim. The recovery was >99% for both compounds. This method enabled the detection of sulfamethoxazole and trimethoprim in plasma of patients after oral ingestion of their combined formulation. The present simple and rapid method is applicable to drug monitoring in immunocompromised patients who are taking the combined formulation of these compounds for the treatment or prophylaxis of Pneumocystis carinii pneumonia. 相似文献
77.
78.
Yoshinori Tominaga Syuichirou Ohno Shinya Kohra Hiroshi Fujito Hisako Mazurae 《Journal of heterocyclic chemistry》1991,28(4):1039-1042
N-Bis(methylthio)methylenecyanamide ( 1 ) was allowed to react with active methylene compounds (methyl cyanoacetate, dimethyl malonate, ethyl acetoacetate, ethyl phenylacetate) in the presence of potassium carbonate or potassium hydroxide in dimethyl sulfoxide followed by the treatment using appropriate a base or an acid to give the corresponding 6-methylthiouracil derivatives in 15–80% yields. These uracil derivatives are found to be useful intermediates for the synthesis of 6-aminouracils and fused pyrimidine derivatives. 相似文献
79.
80.
A bioassay-directed fractionation of the cytotoxic constituents of the Japanese sea hare Dolabella auricularia resulted in the isolation of two 35-membered depsipeptides dolastatin G (1) and nordolastatin G (2), which showed cytotoxicity against HeLa S(3) cells with IC(50) values of 1.0 and 5.3 &mgr;g/mL, respectively. The gross structures of these substances were established by spectroscopic analysis including 2D NMR techniques. The absolute stereostructure of 1 was determined by chiral HPLC analysis of amino acid components obtained from acid hydrolysis of 1 and by the enantioselective syntheses of two degradation products arising from polyketide portions. Nordolastatin G (2) is a congener that has the same absolute stereochemistry as that of 1. 相似文献