全文获取类型
收费全文 | 445篇 |
免费 | 15篇 |
专业分类
化学 | 342篇 |
晶体学 | 8篇 |
力学 | 3篇 |
数学 | 33篇 |
物理学 | 74篇 |
出版年
2023年 | 4篇 |
2022年 | 13篇 |
2021年 | 15篇 |
2020年 | 9篇 |
2019年 | 9篇 |
2018年 | 8篇 |
2017年 | 5篇 |
2016年 | 9篇 |
2015年 | 13篇 |
2014年 | 19篇 |
2013年 | 32篇 |
2012年 | 61篇 |
2011年 | 62篇 |
2010年 | 21篇 |
2009年 | 19篇 |
2008年 | 22篇 |
2007年 | 24篇 |
2006年 | 29篇 |
2005年 | 13篇 |
2004年 | 10篇 |
2003年 | 2篇 |
2002年 | 13篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1956年 | 1篇 |
1935年 | 1篇 |
排序方式: 共有460条查询结果,搜索用时 15 毫秒
1.
Anirudh Pradhan Sudhir Kumar Srivastav Kanti R. Jotania 《Czechoslovak Journal of Physics》2004,54(2):255-272
Some cylindrically symmetric inhomogeneous viscous-fluid cosmological models with electromagnetic field are obtained. To get
a solution a supplementary condition between metric potentials is used. The viscosity coefficient of bulk viscous fluid is
assumed to be a power function of mass density. Without assuming anyad hoc law, we obtain a cosmological constant as a decreasing function of time. The behaviour of the electromagnetic field tensor
together with some physical aspects of the model are also discussed. 相似文献
2.
K. P. Madhusudanan Shubhra Mittal Susheel Durani R. S. Kapil 《Journal of mass spectrometry : JMS》1985,20(5):323-326
Stereospecific adduct ion formation has been observed in the chemical ionization mass spectra (positive and negative) of certain E- and Z-1,2,3-triaryl-2-propen-1-ones. The Z isomers are found to give higher relative abundances of adduct ions than the E isomers. This has been interpreted in terms of the differences in the proton affinities of the isomers originating from their different degrees of enone resonance. Halide ion (CI? and Br?) attachment spectra of these compounds also show stereochemical differences in the relative abundances of [M]?˙ and [M+halide]? ions, though the effect is not as pronounced as in the case of the positive ion spectra. 相似文献
3.
The reduction of triphenyltin piperidyl dithiocarbamate in acetone has been investigated using d.c. polarography and cyclic
voltammetry. Polarographic reduction yielded four well-defined waves, two of which were diffusion-controlled and two of which
appear to represent adsorption processes. The cyclic voltammetric study yielded results in close agreement with the polarographic
data. Results appear to indicate the release of the dithiocarbamate moiety, followed by reduction to form the triphenyltin
radical, which undergoes dimerization, as well as reduction to the triphenyltin anion. For comparison, the polarographic reduction
of triphenyltinchloride was investigated. A mechanism similar to that proposed by earlier authors for the polarographic behaviour
of tributyltin oxide was found.
For convenience, the more commonly used terminology of piperidyl dithiocarbamate is used throughout the paper, in place of
(piperidine-1-carbodithioato) triphenyltin (IV). 相似文献
4.
Dimers of the pyrrole amino acid (Paa), 5-(aminomethyl)pyrrole-2-carboxylic acid, and its derivatives having Lys anchored on N- and C-termini bind in the minor groove of DNA with considerable apparent binding affinities. When the Lys unit is attached to the C-terminus, the resulting ligand binds to ds-DNA with twice the affinity, of the order of 105, than the one carrying two positive charges at the same end. 相似文献
5.
Ghosh SK Khatua PK Ghosh JK Bhattacharya SC 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(3):395-401
This paper has explored the quenching of fluorescence of the dye safranine T (ST) by the inorganic cations viz Cu2+, Co2+, Ni2+ and Mn2+ in micellar solutions of the surfactant dioxyethylene nonyl phenol (Igepal CO-210), pentaoxyethylene nonyl phenol (Igepal CO-520) and dodecaoxyethylene nonyl phenol (Igepal CO-720). The quenching results have been calculated in light of stern volmer equation (SV) to evaluate the extent of interaction between the fluorophore (ST) and quencher. The average concentration of the quencher ions in the micelle have been determined. The quenching efficiency of ST by inorganic ions in micellar medium is lower than that in aqueous medium. The results show that the ions get partitioned in the micellar medium. The values of the partition coefficient of the ions decrease with increase in HLB value and number of oxyethylene groups in Igepal. 相似文献
6.
7.
Syntheses of Boc-protected 4-amino- and 5-amino-pyrrole-2-carboxylic acid methyl esters have been achieved and the structures of these compounds have been fully characterized by detailed NMR studies. 相似文献
8.
Tarun Kanti Pradhan 《Tetrahedron letters》2005,46(9):1493-1495
One-pot syntheses of (3-hydroxybenzo[b]thiophen-2-yl) aryl methanones from ortho-methylsulfanylaryl N,N-diethyl amides and of 1-(3-hydroxybenzo[b]thiophen-2-yl)ethanone and 1-(3-hydroxybenzo[b]thiophen-2-yl)propan-1-one via an anionic ortho-Fries rearrangement are described. The hydroxy ketones were used as key intermediates in the synthesis of benzothienopyranones. 相似文献
9.
Preparation and properties of the salts of the series MVO2F4, where M = NH, Na+, K+, 1/2 Ni2+, and 1/3 [Co(NH3)6]3+ are described. Molecular conductivity of Na3VO2F4 at different dilutions indicates that Na3VO2F4 dissociates into 3 Na+ and VOaF ions. Ion exchange study of (NH4)3VO2F4 solution through cation exchange resin (H+ form) suggests that the corresponding acid decomposes partly to vanadium pentoxide. Reaction between (NH4)3VO2F4 with BaCl2 and AgNO3 solutions shows the formation of BaVO2F3 and AgVO3 respectively. Thermogravimetric study of (NH4)3VO2F4 shows the formation of impure vanadium pentoxide as the ultimate product on heating up to 450°C. X-ray powder diffraction data are given for (NH4)3VO2F4 and Na3VO2F4. 相似文献
10.
Ujjal Kanti Roy 《Tetrahedron》2006,62(4):678-683
A simple and highly efficient one-pot procedure for allylation and propargylation of arylepoxides has been developed. A combination of SnCl2 and catalytic Pd(0) or Pd(II) promotes the reaction of organic halides and epoxides in DMSO with controlled water addition, leading to the regioselective formation of the corresponding homoallyl and homopropargyl alcohols in good yields. 相似文献