全文获取类型
收费全文 | 1221篇 |
免费 | 27篇 |
国内免费 | 4篇 |
专业分类
化学 | 798篇 |
晶体学 | 33篇 |
力学 | 43篇 |
数学 | 87篇 |
物理学 | 291篇 |
出版年
2023年 | 7篇 |
2022年 | 35篇 |
2021年 | 29篇 |
2020年 | 23篇 |
2019年 | 38篇 |
2018年 | 32篇 |
2017年 | 35篇 |
2016年 | 33篇 |
2015年 | 31篇 |
2014年 | 48篇 |
2013年 | 66篇 |
2012年 | 71篇 |
2011年 | 73篇 |
2010年 | 56篇 |
2009年 | 52篇 |
2008年 | 46篇 |
2007年 | 46篇 |
2006年 | 50篇 |
2005年 | 39篇 |
2004年 | 26篇 |
2003年 | 24篇 |
2002年 | 22篇 |
2001年 | 17篇 |
2000年 | 19篇 |
1999年 | 17篇 |
1998年 | 15篇 |
1997年 | 13篇 |
1996年 | 12篇 |
1995年 | 12篇 |
1994年 | 10篇 |
1993年 | 14篇 |
1992年 | 19篇 |
1991年 | 13篇 |
1990年 | 10篇 |
1989年 | 11篇 |
1988年 | 8篇 |
1987年 | 9篇 |
1985年 | 17篇 |
1984年 | 8篇 |
1983年 | 11篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1977年 | 13篇 |
1976年 | 13篇 |
1975年 | 6篇 |
1974年 | 9篇 |
1967年 | 5篇 |
排序方式: 共有1252条查询结果,搜索用时 15 毫秒
1.
2.
Guanidinium nitrate: a novel reagent for aryl nitrations 总被引:1,自引:0,他引:1
Nitration of various aromatic compounds utilising guanidinium nitrate in 85% sulfuric acid as a nitrating agent has been studied. 相似文献
3.
This article studies some geometrical aspects of the semidefinite linear complementarity problem (SDLCP), which can be viewed as a generalization of the well-known linear complementarity problem (LCP). SDLCP is a special case of a complementarity problem over a closed convex cone, where the cone considered is the closed convex cone of positive semidefinite matrices. It arises naturally in the unified formulation of a pair of primal-dual semidefinite programming problems. In this article, we introduce the notion of complementary cones in the semidefinite setting using the faces of the cone of positive semidefinite matrices and show that unlike complementary cones induced by an LCP, semidefinite complementary cones need not be closed. However, under R0-property of the linear transformation, closedness of all the semidefinite complementary cones induced by L is ensured. We also introduce the notion of a principal subtransformation with respect to a face of the cone of positive semidefinite matrices and show that for a self-adjoint linear transformation, strict copositivity is equivalent to strict semimonotonicity of each principal subtransformation. Besides the above, various other solution properties of SDLCP will be interpreted and studied geometrically. 相似文献
4.
5.
6.
7.
Polarographic reduction of 4-arylhydrazono-1-guanylnitrate-3-methyl-2-pyrazoline-5-ones takes place in a single 4-electron transfer, giving a diffusion controlled irreversible wave in B.R. buffers of pH range 2.0–10.0. The reduction in these compounds takes place at the ?NH?N=C-bond. Effect of various cations, anions and solvent percentage on the reduction has been discussed. The effect of substituents and its correlation with the Hammett substituent constant (δ) have also been studied. 相似文献
8.
Summary The chromatographic performance of newly developed dicyanobiphenyl polysiloxane stationary phases were evaluated and compared
with the performance of other polar stationary phases, including the previously reported monocyanobiphenyl polysiloxanes.
Due to the unique combination of polarizable biphenyl and polar cyano functionalities in the side chains of the flexible polysiloxane
backbone, and by virtue of their mild liquid crystalline properties, the new stationary phases provide excellent resolution
of a wide variety of analytes, both polar and nonpolar, in both GC and SFC. They can be easily coated and cross-linked in
open tubular columns, and the resultant columns demonstrate excellent efficiency and performance at temperatures up to 280–300°C.
The new stationary phases exhibit enhanced selectivities for various types of isomeric compounds. 相似文献
9.
10.
Abstract— The binding of hematoporphyrin derivated (Hpd) to lipid vesicles and bacterial membranes was determined by fluorescence spectroscopy. The fluorescence measurements of Hpd in aqueous solutions showed two bands at 613 and 677 nm. In lipid environments of lecithin vesicles the fluorescence spectrum was shifted to 631 and 692 nm, respectively. Hpd was rapidly bound to the cell membrane of Staphylococcus aureus while much less binding occurred in the presence of Escherichia coli. At the same time, spheroplasts of both bacteria were shown to bind Hpd to a similar extent. These results are well correlated with the photoinactivation of the gram positive bacteria with Hpd while the gram negative cells were shown to be resistant. The pH dependence of both Hpd binding to S. aureus as well as the photodynamic inhibitory effect of the same bacteria are similar. It is concluded that the segregation of Hpd to the cell membrane is a prerequisite for its photodynamic effect. 相似文献