全文获取类型
收费全文 | 1036篇 |
免费 | 51篇 |
国内免费 | 2篇 |
专业分类
化学 | 745篇 |
晶体学 | 13篇 |
力学 | 13篇 |
数学 | 61篇 |
物理学 | 257篇 |
出版年
2024年 | 2篇 |
2023年 | 16篇 |
2022年 | 36篇 |
2021年 | 34篇 |
2020年 | 44篇 |
2019年 | 60篇 |
2018年 | 52篇 |
2017年 | 34篇 |
2016年 | 57篇 |
2015年 | 41篇 |
2014年 | 100篇 |
2013年 | 108篇 |
2012年 | 68篇 |
2011年 | 71篇 |
2010年 | 38篇 |
2009年 | 29篇 |
2008年 | 41篇 |
2007年 | 31篇 |
2006年 | 27篇 |
2005年 | 22篇 |
2004年 | 27篇 |
2003年 | 17篇 |
2002年 | 20篇 |
2001年 | 14篇 |
2000年 | 7篇 |
1999年 | 10篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 8篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 8篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1939年 | 1篇 |
排序方式: 共有1089条查询结果,搜索用时 15 毫秒
111.
Dansyl-anthracene dyads 1 and 2 in CH(3)CN-H(2)O (7:3) selectively recognize Cu(2+) ions amongst alkali, alkaline earth and other heavy metal ions using both absorbance and fluorescence spectroscopy. In absorbance, the addition of Cu(2+) to the solution of dyads 1 or 2 results in appearance of broad absorption band from 200 nm to 725 nm for dyad 1 and from 200 nm to 520 nm for dyad 2. This is associated with color change from colorless to blue (for 1) and fluorescent green (for 2). This bathochromic shift of the spectrum could be assigned to internal charge transfer from sulfonamide nitrogen to anthracene moiety. In fluorescence, under similar conditions dyads 1 and 2 on addition of Cu(2+) selectively quench fluorescence due to dansyl moiety between 520-570 nm (for 1)/555-650 nm (for 2) with simultaneous fluorescence enhancement at 470 nm and 505 nm for dyads 1 and 2, respectively. Hence these dyads provide opportunity for ratiometric analysis of 1-50 μM Cu(2+). The other metal ions viz. Fe(3+), Co(2+), Ni(2+), Cd(2+), Zn(2+), Hg(2+), Ag(+), Pb(2+), Li(+), Na(+), K(+), Mg(2+), Ca(2+), Ba(2+) do not interfere in the estimation of Cu(2+) except Cr(3+) in case of dyad 1. The coordination of dimethylamino group of dansyl unit with Cu(2+) causes quenching of fluorescence due to dansyl moiety between 520-600 nm and also restricts the photoinduced electron transfer from dimethylamino to anthracene moiety to release fluorescence between 450-510 nm. This simultaneous quenching and release of fluorescence respectively due to dansyl and anthracene moieties emulates into Cu(2+) induced ratiometric change. 相似文献
112.
One of the results generalizing Eisenstein Irreducibility Criterion states that if ${\phi(x) = a_nx^n\,{+} \,a_{n-1}x^{n-1} \,{+} \,\cdots\,{+} \,a_0}$ is a polynomial with coefficients from the ring of integers such that a s is not divisible by a prime p for some ${s \, \leqslant \, n}$ , each a i is divisible by p for ${0 \, \leqslant \, i \, \leqslant \, s-1}$ and a 0 is not divisible by p 2, then ${\phi(x)}$ has an irreducible factor of degree at least s over the field of rational numbers. We have observed that if ${\phi(x)}$ is as above, then it has an irreducible factor g(x) of degree s over the ring of p-adic integers such that g(x) is an Eisenstein polynomial with respect to p. In this paper, we prove an analogue of the above result for a wider class of polynomials which will extend the classical Sch?nemann Irreducibility Criterion as well as Generalized Sch?nemann Irreducibility Criterion and yields irreducibility criteria by Akira et?al. (J Number Theory 25:107?C111, 1987). 相似文献
113.
Compound 4 removes cyanide from water and human serum in the form of compound 7 (cyano-derivative of 4) and experiments show its suitability as an antidote of CN(-) poisoning. 相似文献
114.
The present paper reports that TL glow curve and kinetic parameter of Eu3+ doped SrY2O4 phosphor irradiated by beta source. Sample was prepared by solid state preparation method. Sample was characterized by XRD analysis and particle size was calculated by Debye–Scherrer formula. The sample was irradiated with Sr-90 beta source giving a dose of 10 Gy and the heating rate used for TL measurements are 6.7 °C/s. The samples display good TL peaks at 106 °C, 225 °C and 382 °C. The corresponding kinetic parameters are calculated. The photoluminescence excitation spectrum at 247 and 364 nm monitored with 400 nm excitation and the corresponding emission peaks at 590, 612 and 624 nm are reported. 相似文献
115.
The dissociation energy of twelve diatomic molecules has been determined by fitting four-parameter potential functionU(r)=D
e[[1−exp{−b(r−r
e)}]/ [1−Cexp{−b(r−r
e)}]]2 to the true Rydberg-Klein-Rees (RKR) curves for their fifteen electronic states using the mean square deviation as the criterion
for the selection of the best fit. Average deviation ofD
e has been found to be 2.7% as compared to 20.5% obtained with Lippincott’s potential function for these molecules. In addition
the anharmonocity constantω
exe has also been calculated for the same electronic states yielding average mean deviation 8.9%. 相似文献
116.
117.
Vazid Ali Raminder Kaur Sukhmehar Singh H.P.S. Kang M. Husain 《Journal of Physics and Chemistry of Solids》2006,67(4):659-664
The structural modification and properties of polymeric materials are of utmost importance in deciding their applications. In the present study, the synthesis of polyaniline (PANI) has been carried out via chemical oxidation in acidic medium by potassium-dichromate and the yield of synthesized polyaniline was found to be 75-80%. The copper per chlorate tetrabenzonitrile salt (CuClO4·4BN) used for chemical doping in synthesized polyaniline is stable in organic solvent like acetonitrile (AN) and benzonitrile (BN). The effect of Cu+1 oxidation state (dopant) in polyaniline has been characterized by FTIR. Electrical and dielectric measurements show the decrease in the intensity of the Cu+1 salt signal and the appearance of a radical signal due to the formation of oxidative coupled in polymeric species. Electrical and dielectric properties of doped polyaniline samples show significant changes due to the effect of dopant (CuClO4·4BN). It is observed that the conductivity is contributing both by formation of ionic complex and particularly dominated by electronic due to the mobility of charge carriers along the polyaniline chain. 相似文献
118.
A. Reginiv R. Kaur N. Sudha S. C. Menon H. B. Singh 《Journal of Chemical Sciences》1995,107(4):431-442
A range of novel bi-, tri- and multidentate organotellurium ligands containing Te and N donor atoms and their derivatives
have been synthesised. The synthetic strategy involves telluration of orthochelating, monoanionic substrates derived from
the following arylamines: N,N-dimethylbenzylamine, (S)-(-)-N,Ndimethyl-1-phenethylamine, N,N-dimethylnaphthylamine, (N,N-di-methylaminomethy
l) ferrocene, tricarbony1(N, N-dimethylbenzenemethanamine) chromium and 2-(3-thienyl)-pyridine. In addition novel chiral hybrid
Schiff base ligands have been prepared by the condensation reaction of bis(o-formylphenyl) telluride ando-butyltellurobenzaldehyde with (R)-(+)-l-phenethylamine and (1R, 2S)-(-)-norephedrine. 相似文献
119.
120.
Summary Sorption of iso-propyl, iso-butyl, sec-butyl, tert-butyl and iso-amyl alcohols on egg albumin has been studied at 35 °C by using quartz fiber spring technique. Sorption is related inversely to the molar volume of the sorbate. The specific surface area of egg albumin has been calculated by the BET method. The thermodynamic functions have also been evaluated.With 3 figures and 2 tables 相似文献