全文获取类型
收费全文 | 30813篇 |
免费 | 1922篇 |
国内免费 | 5078篇 |
专业分类
化学 | 26661篇 |
晶体学 | 1221篇 |
力学 | 335篇 |
综合类 | 261篇 |
数学 | 4090篇 |
物理学 | 5245篇 |
出版年
2023年 | 265篇 |
2022年 | 375篇 |
2021年 | 927篇 |
2020年 | 751篇 |
2019年 | 754篇 |
2018年 | 621篇 |
2017年 | 790篇 |
2016年 | 841篇 |
2015年 | 762篇 |
2014年 | 1071篇 |
2013年 | 2440篇 |
2012年 | 1733篇 |
2011年 | 1915篇 |
2010年 | 1834篇 |
2009年 | 2109篇 |
2008年 | 2080篇 |
2007年 | 2099篇 |
2006年 | 2007篇 |
2005年 | 1786篇 |
2004年 | 1774篇 |
2003年 | 1449篇 |
2002年 | 1273篇 |
2001年 | 964篇 |
2000年 | 966篇 |
1999年 | 735篇 |
1998年 | 686篇 |
1997年 | 623篇 |
1996年 | 492篇 |
1995年 | 556篇 |
1994年 | 498篇 |
1993年 | 451篇 |
1992年 | 413篇 |
1991年 | 302篇 |
1990年 | 196篇 |
1989年 | 222篇 |
1988年 | 178篇 |
1987年 | 113篇 |
1986年 | 99篇 |
1985年 | 88篇 |
1984年 | 111篇 |
1983年 | 32篇 |
1982年 | 57篇 |
1981年 | 83篇 |
1980年 | 69篇 |
1979年 | 56篇 |
1978年 | 44篇 |
1977年 | 29篇 |
1976年 | 21篇 |
1975年 | 15篇 |
1974年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
61.
62.
报道了新合成的二氰基二硫纶·菲咯啉-5,6-二酮合铜(Ⅱ)配合物CuLL′(L=mnt2-, 1,2-dicyano-1,2-ethylenedithiolate; L′=phen-5,6-dione, 1,10-phenanthroline-5,6-dione)的变温磁化率和电子顺磁共振波谱表征结果. 发现微晶粉体型的标题配合物CuLL′具有一定的顺磁性,形成四配位的近似于方形的结构. 探讨了这种配合物磁学特性与结构的关系. 相似文献
63.
The title compound is a bifunctional receptors including a thiourea group and a crown ether ring. Due to many possible potentials as a new class of reagents for membrane transports,ion-selective electrodes as well as reaction catalysts, the design and synthesis of bifunctional receptors for simultaneous binding of cations and anions is of ongoning interest in srprarnolecular chemistry1-5. In bifunctional receptors, the binding sites for anions and cations are covalently linked so as to exhibit allosteric or cooperative complexation where the binding affinity for anions(cations)is modified as a result of the cation(anion) complexation.Literature[6] reported that the ability of the thiourea group to bind anions is significantly enhanced when Na+ is bound to the crown moiety. To date, however only a few receptors of this class have been reported.6-8In this paper, we report an improved procedure under microwave irradiation that gives higher yields of title compound and needs fewer reaction times than traditional method.The structure of this compound was determined by IR ,element analysis and X-ray analysis.Scheme 1 The reaction equationThe crystal belongs to triclinic crystal system, P-1 space group, a=0.9547(0)nm, b=1.3637(3)nm,c=1.6029(3)nm, α =75.33(3) , β =83.62(3) , γ =70.99(3) ,Z=4,Dc=1.335g/cm3,F(000)=816,R1= 0.0557 ,wR2=0.1281. It is assembled into a three-dimensionalsupramolecule by intermolecular hydrogen bonds. 相似文献
64.
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
65.
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
66.
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
67.
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
68.
Qing An WU Zhen Yuan XU Mei ZHENG Dan Qian XU Jun XU Yin Chu SHENCollege of Chemical Engineering Materials Zhejiang University of Technology Hangzhou 《中国化学快报》2004,(7)
Six new 13-O-acylavermectin Bl aglycones(3-8) were synthesized from avermectin B1 aglycone and their bioactivities were evaluated against Spodoptera exigua, Spodoptera eridania, Tetranychus urticae and Aphis fabae. 相似文献
69.
Ri Cheng XUAN* Wei Xiao HU Zhong Yu YANG Ya Ping LU College of Pharmaceutical Sciences Zhejiang University of Technology Hangzhou 《中国化学快报》2004,(2)
2-Chloro-5-methylpyridine is an important intermediate for the preparation of biological active compounds, especially insecticides1, e.g. imidacloprid2, and is usually manufac- tured from 3-methylpyridine N-oxide. However, the manufacturing process also forms the by-products: 3-methylpyridine and its isomer 2-chloro-3-methylpyridine3. The pro- perties of the isomers are similar, it is difficult to separate by ordinary methods, such as distillation. Scheme 1 79.4%13.6%5.2%NClCH3NCH3ClNC… 相似文献
70.
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