全文获取类型
收费全文 | 26877篇 |
免费 | 3581篇 |
国内免费 | 13789篇 |
专业分类
化学 | 29712篇 |
晶体学 | 631篇 |
力学 | 1081篇 |
综合类 | 752篇 |
数学 | 3820篇 |
物理学 | 8251篇 |
出版年
2024年 | 242篇 |
2023年 | 898篇 |
2022年 | 1084篇 |
2021年 | 1154篇 |
2020年 | 1072篇 |
2019年 | 1226篇 |
2018年 | 776篇 |
2017年 | 1127篇 |
2016年 | 1263篇 |
2015年 | 1378篇 |
2014年 | 2039篇 |
2013年 | 2176篇 |
2012年 | 2280篇 |
2011年 | 2193篇 |
2010年 | 2150篇 |
2009年 | 2288篇 |
2008年 | 2687篇 |
2007年 | 2504篇 |
2006年 | 2725篇 |
2005年 | 2395篇 |
2004年 | 2595篇 |
2003年 | 1621篇 |
2002年 | 765篇 |
2001年 | 754篇 |
2000年 | 716篇 |
1999年 | 813篇 |
1998年 | 432篇 |
1997年 | 320篇 |
1996年 | 267篇 |
1995年 | 256篇 |
1994年 | 240篇 |
1993年 | 325篇 |
1992年 | 338篇 |
1991年 | 334篇 |
1990年 | 250篇 |
1989年 | 234篇 |
1988年 | 183篇 |
1987年 | 80篇 |
1986年 | 27篇 |
1985年 | 15篇 |
1984年 | 13篇 |
1983年 | 6篇 |
1982年 | 2篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
2H-1,2,3-Diazaphospholes 3a-3h were prepared from various ketone acylhydrazones and phosphorus trichloride in the presence of triethylamine. Compounds 3 underwent feasible hetero-Diels-Alder reactions with cyclopentadiene to afford the respective anellated [1,2,3]diazaphospholes 4a--4d as well as 4a‘--4d‘ in moderate yields. The endo rule in the reaction was observed under kinetic control conditions. 相似文献
62.
5,6-Dihydro-OSW-1 (1) was synthesized following our previous procedure for the total synthesis of OSW-1. This compound demonstrated slightly stronger potency than that of OSW-1 against the growth of cancer cells. 相似文献
63.
NianYuanTAN XiaoMingXIAO ZeLinLI TakekoMATSUMURA-INOUE 《中国化学快报》2004,15(6):687-690
A new cobalt(Ⅱ) complex with tridentate ligand 2, 6-bis (benzimidazol-2-yl)pyridine has been synthesized by microwave irradiation method and characterized by elemental analysis,electrochemical and spectral methods. The binding of the complex with calf thymus DNA has also been investigated by absorption and fluorescence spectra. 相似文献
64.
WeiMingXU LuLingWU XianHUANG 《中国化学快报》2004,15(11):1279-1280
A mild, regioselective 1, 3-dipolar cycloaddition protocol for the preparation ofphenylselenomethyl isoxazolines through substituted allyl phenyl selenides and nitrile oxides wasreported. 相似文献
65.
JiangMinCHEN LuLingWU XianHUANG 《中国化学快报》2004,15(2):143-144
2,5-Disubstituted oxazoles were prepared conveniently by treatment of aromatic α-methyl ketones and nitriles with poly[styrene(iodosodiacetate)] in one-pot process. 相似文献
66.
The First Intramolecular Charge Transfer Transition Based on 2-Ureido-4[1H]-pyrimidinone Binding Module 总被引:1,自引:0,他引:1
The first intramolecular charge transfer transition based on 2-ureido-4[1H]-pyrimidinone binding module was reported. 相似文献
67.
Solid Phase Synthesis of 2-Substituted 1,3-Oxazin-6-ones Using Resin-bound Cyclic Malonic Acid Ester
A facile solid phase synthesis of 2-substituted 1,3-oxazin-6-ones using polymer-supported Meldrum‘s acid has been reported. Reaction of the resin-bound cyclic malonic acid ester with triethyl orthoformate and subsequent double substitution with amide, afforded the corresponding polymer-supported acylaminomethylene cyclic malonic acid ester, which upon thermal treatment led to 1, 3-oxazin-6-ones in good yields and with high purity. 相似文献
68.
The adsorption of asymmetrical triblock copolymers from a non-selective solvent on solid surface has been studied by using Scheutjens-Fleer mean-field theory and Monte Carlo simulation method on lattice model. The main aim of this paper is to provide detailed computer simulation data, taking A8-kB20Ak as a key example, to study the influence of the structure of copolymer on adsorption behavior and make a comparison between MC and SF results. The simulated results show that the size distribution of various configurations and density-profile are dependent on molecular structure and adsorption energy. The molecular structure will lead to diversity of adsorption behavior. This discrepancy between different structures would be enlarged for the surface coverage and adsorption amount with increasing of the adsorption energy. The surface coverage and the adsorption amount as well as the bound fraction will become larger as symmetry of the molecular structure becomes gradually worse. The adsorption layer becomes thicker with increasing of symmetry of the molecule when adsorption energy is smaller but it becomes thinner when adsorption energy is higher. It is shown that SF theory can reproduce the adsorption behavior of asymmetrical triblock copolymers. However, systematic discrepancy between the theory and simulation still exists.The approximations inherited in the mean-filed theory such as random mixing and the allowance of direct back folding may be responsible for those deviations. 相似文献
69.
Ming Zhao WANG Guan Liang CAI Ling XIA Jun Jian YAO Hong Yan CHEN Zhao Xing MENG Bo Li LIUDepartment of Chemistry Beijing Normal University Beijing Chemical Defense Institute PLA Beijing 《中国化学快报》2004,15(4):495-497
The crystal structures of two potential tumor imaging agents and therapeutic agents -copper(Ⅱ) complexes with salicylidene-tyrosinato Schiff base and nitrogen-donor chelating Lewis base, [Cu(sal-tyr)(bipy)] 1 and [Cu(sal-tyr)(phen)]2CH3OH 2 are presented. Our work is helpful to get deep understanding of novel 64Cu tumor imaging agents and therapeutic agents. 相似文献
70.