全文获取类型
收费全文 | 1098篇 |
免费 | 27篇 |
国内免费 | 14篇 |
专业分类
化学 | 872篇 |
晶体学 | 7篇 |
力学 | 8篇 |
数学 | 76篇 |
物理学 | 176篇 |
出版年
2022年 | 3篇 |
2021年 | 4篇 |
2020年 | 17篇 |
2019年 | 13篇 |
2018年 | 3篇 |
2017年 | 5篇 |
2016年 | 19篇 |
2015年 | 20篇 |
2014年 | 34篇 |
2013年 | 82篇 |
2012年 | 50篇 |
2011年 | 64篇 |
2010年 | 27篇 |
2009年 | 37篇 |
2008年 | 62篇 |
2007年 | 61篇 |
2006年 | 74篇 |
2005年 | 53篇 |
2004年 | 59篇 |
2003年 | 50篇 |
2002年 | 35篇 |
2001年 | 27篇 |
2000年 | 31篇 |
1999年 | 18篇 |
1998年 | 11篇 |
1997年 | 17篇 |
1996年 | 9篇 |
1995年 | 11篇 |
1994年 | 11篇 |
1993年 | 6篇 |
1992年 | 10篇 |
1991年 | 16篇 |
1990年 | 18篇 |
1989年 | 16篇 |
1988年 | 17篇 |
1987年 | 12篇 |
1986年 | 4篇 |
1985年 | 15篇 |
1984年 | 16篇 |
1983年 | 8篇 |
1982年 | 19篇 |
1981年 | 12篇 |
1980年 | 10篇 |
1979年 | 7篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1974年 | 5篇 |
1973年 | 7篇 |
1968年 | 3篇 |
1966年 | 4篇 |
排序方式: 共有1139条查询结果,搜索用时 31 毫秒
91.
Tsuyoshi Satoh Takayuki Kuramoto Shingo Ogata Hiroyuki Watanabe Takahito Saitou Makoto Tadokoro 《Tetrahedron: Asymmetry》2010,21(1):1-5
Treatment of enantiomerically pure 1-chlorovinyl p-tolyl sulfoxides, derived from cyclic ketones and (R)-chloromethyl p-tolyl sulfoxide, with the lithium enolate of tert-butyl carboxylates gave adducts in quantitative yields as single diastereomers. The adducts were treated with i-PrMgCl in toluene to afford optically active bicyclo[n.1.0]alkanes bearing a tert-butyl carboxylate moiety in up to 99% enantiomeric excess through the enantioselective 1,3-CH insertion reaction of the generated chiral magnesium carbenoids. This is the first example of the enantioselective 1,3-CH insertion reaction of magnesium carbenoid. 相似文献
92.
93.
Secondary 2-thiophenecarboxamides efficiently undergo unique triarylation accompanied by formal decarbamoylation under palladium catalysis. 3-Substituted thiophenes, especially having an electron-withdrawing group, can also be triarylated. 相似文献
94.
Treatment of 2-(2'-bromo-beta-phenethyl)isocarbostyrils 7 with AIBN-Bu(3)SnH in boiling benzene gave 8-oxoberbines 3 in good yields. A similar treatment of 2-(2'-bromo-beta-phenethyl)isoquinolinium bromides 6 and their nor- and homoanalogues (10,11) induced 6-, 5-, and 7-exo radical closures in a one-pot manner to give protoberberines 2, dibenzo[b,g]indolizidine 14a and, dibenzo[a, h]-1-azabicyclo[5.4.0]undecane 15a, respectively. A one-pot radical cyclization of 1-(2'-bromobenzyl)isoquinoline methiodide 18a gave a pavine alkaloid, (+/-)-algemonine (19a). 相似文献
95.
96.
Masaharu Tanemura 《Annals of the Institute of Statistical Mathematics》1979,31(1):351-365
Summary A computational algorithm for random complete packing by discs is proposed. Monte Carlo simulations using this algorithm give
the value 0.5473 for random packing density of discs. It greatly improves the Solomon's result, 04756.
The Institute of Statistical Mathematics 相似文献
97.
98.
99.
alpha,beta,gamma,delta-Tetrakis(1-methylpyridinium-3-yl)porphine [T(3-MPy)P] and alpha,beta,gamma,delta-tetrakis(1-methylpyridinium-4-yl)porphine [T(4-MPy)P] have been found to react rapidly with cadmium to give coloured complexes in weakly alkaline media at room temperature. Simple and practical methods for the determination of cadmium at ng/ml levels by conventional and analogue derivative spectrophotometry have been proposed. The analogue method gives higher sensitivity. T(3-MPy)P gives higher sensitivity than T(4-MPy)P. The interference of various foreign cations and anions has also been examined and in many cases eliminated or reduced. Adsorption of the porphyrins and their cadmium complexes onto the glassware, which is usually observed under the conditions of reaction and causes significant errors in the determination, can be suppressed almost completely by addition of fairly large amounts of a salt such as sodium chloride. 相似文献
100.
The effect of MCM-41 on the ESR spectrum of an aqueous spin probe solution was observed. The sharp ESR spectrum turns into a rather broad characteristic one leaving a sharper signal as the minor component, immediately after the addition of MCM-41 powder to the system. This observation indicates that MCM-41 traps the solute molecule into the nanochannel by letting the solvent water form a rather stable molecular cage, since the ESR line shape indicates that the nitroxide radical undergoes anisotropic rotation without being adsorbed on the wall. Thermodynamic parameters for this process are estimated from the temperature dependencies of the trapping efficiency. This process is explained in terms of the surface enthalpy of the liquid specifically intensified in the nanospace. 相似文献