全文获取类型
收费全文 | 2114篇 |
免费 | 23篇 |
专业分类
化学 | 1039篇 |
晶体学 | 9篇 |
力学 | 44篇 |
数学 | 269篇 |
物理学 | 776篇 |
出版年
2018年 | 24篇 |
2017年 | 34篇 |
2016年 | 39篇 |
2015年 | 39篇 |
2014年 | 43篇 |
2013年 | 94篇 |
2012年 | 58篇 |
2011年 | 109篇 |
2010年 | 46篇 |
2009年 | 32篇 |
2008年 | 118篇 |
2007年 | 99篇 |
2006年 | 104篇 |
2005年 | 55篇 |
2004年 | 65篇 |
2003年 | 57篇 |
2002年 | 50篇 |
2001年 | 36篇 |
2000年 | 46篇 |
1999年 | 28篇 |
1998年 | 19篇 |
1995年 | 28篇 |
1994年 | 22篇 |
1993年 | 23篇 |
1992年 | 20篇 |
1989年 | 28篇 |
1988年 | 18篇 |
1987年 | 22篇 |
1986年 | 34篇 |
1985年 | 40篇 |
1984年 | 32篇 |
1983年 | 28篇 |
1982年 | 29篇 |
1981年 | 20篇 |
1980年 | 25篇 |
1979年 | 22篇 |
1978年 | 33篇 |
1977年 | 24篇 |
1976年 | 29篇 |
1975年 | 28篇 |
1974年 | 20篇 |
1972年 | 24篇 |
1969年 | 22篇 |
1968年 | 26篇 |
1967年 | 20篇 |
1966年 | 29篇 |
1965年 | 16篇 |
1963年 | 19篇 |
1961年 | 18篇 |
1960年 | 16篇 |
排序方式: 共有2137条查询结果,搜索用时 15 毫秒
31.
Infrared laser ablation study of pressed soil pellets with inductively coupled plasma atomic emission spectrometry 总被引:1,自引:0,他引:1
Mikolás J Musil P Stuchliková V Novotný K Otruba V Kanický V 《Analytical and bioanalytical chemistry》2002,374(2):244-250
Potential of infrared laser ablation (LA) coupled with ICP-AES as a technique suitable for the determination of trace elements (Zn, Cu, Ni, Cr, and V) in agricultural soils was studied. Operating parameters such as laser beam energy, laser beam focusing with respect to the sample surface, and velocity of the sample translation in the plane perpendicular to the laser beam were optimized. Soil samples were mixed with powdered Ag as a binder, and an internal standard (GeO(2)), and pressed into pellets. Calibration samples were prepared by adding known amounts of oxides of elements of interest into soils of known elemental composition and then processed in the same way as the analyzed samples. Calibration curves were found to be linear at least up to several hundreds of mg kg(-1) for the elements of interest. The elemental contents obtained by using LA-ICP-AES were compared with those obtained by analysis using wet chemistry followed by ICP-AES with pneumatic nebulization (PN). The results were in good agreement. Accuracy was also tested using certified reference soils with a bias not exceeding 10% relative. 相似文献
32.
Jaroslav Koutecký 《Theoretical chemistry accounts》1967,8(3):244-248
Approximate pairing properties are proved for the Hartree-Fock solutions for highly symmetric heteroatomic molecules. These molecules have an alternant topology and are built from two kinds of atoms in such a way that by an operation the atoms of one kind go over into the atoms of the second kind and vice versa.
Supported in part by a grant to The Johns Hopkins University from the Petroleum Research Fund of the American Chemical Society. 相似文献
Zusammenfassung Es werden genäherte alternierende Eigenschaften für Hartree-Fock-Lösungen hochsymmetrischer heterocyclischer Moleküle abgeleitet. Diese Moleküle haben eine alternierende Topologie, sie sind aus zwei Sorten von Atomen in solcher Weise aufgebaut, daß die Atome der ersten Sorte in die Atome der zweiten Sorte — und umgekehrt — transformiert werden können.
Résumé Des propriétés d'accouplement orbital approché sont prouvées pour les solutions de type Hartree-Fock des molécules hétéroatomiques hautement symétriques. Ces molécules ont une topologie alternante et sont formées de deux classes d'atomes de telle sorte qu'il existe une opération interchangeant les atomes des deux classes.
Supported in part by a grant to The Johns Hopkins University from the Petroleum Research Fund of the American Chemical Society. 相似文献
33.
The solubility products for some rare earth hydroxides and their temperature dependence have been shown. Greater solubility is shown for larger atomic radii and for lower temperature. 相似文献
34.
Maprotiline determination in blood serum samples was investigated by the use of both capillary isotachophoresis and spectrofluorimetric techniques. The analyte had to be enriched before determination and extraction with n-heptane was used for this purpose. The preliminary separation enabled the determination of maprotiline in blood serum at therapeutic concentration levels. 相似文献
35.
Teplý F Stará IG Starý I Kollárovic A Saman D Vyskocil S Fiedler P 《The Journal of organic chemistry》2003,68(13):5193-5197
A nonphotochemical synthetic route to 3-hexahelicenol is reported. It involves a key [2+2+2] cycloisomerization of CH(3)O-substituted triyne that is readily available from 1-methoxy-3-methylbenzene and 1-bromo-2-(bromomethyl)naphthalene. Further functional group transformations led to 3-CO(2)CH(3), 3-NH(2), 3-PPh(2), and 3-SC(O)N(CH(3))(2) substituted hexahelicenes. 相似文献
36.
Ludvík Beneš Klára Melánová Vítězslav Zima Jaroslava Kalousová Jiří Votinský 《Journal of inclusion phenomena and macrocyclic chemistry》1998,31(3):275-286
Recent knowledge of the kinetics and intercalation mechanisms are summarized and accompanied by examples of intercalation reactions of water and ethanol into anhydrous vanadyl phosphate and redox intercalation of alkali metal cations into vanadyl phosphate dihydrate. Three possible mechanisms of intercalation are presented which are based on: (i) a concept of exfoliation of layers; (ii) the formation of stages and randomly stacked layers; (iii) co-existence of intercalated and non-intercalated parts of crystals of the host separated by an advancing phase boundary. The corresponding kinetic curves are ascribed to mechanisms (ii) and (iii). 相似文献
37.
Stará IG Alexandrová Z Teplý F Sehnal P Starý I Saman D Budesínský M Cvacka J 《Organic letters》2005,7(13):2547-2550
[reaction: see text] A new approach to nonracemic [7]helicene-like molecules has been developed. Stereoselective Co(I)-mediated [2 + 2 + 2] cycloisomerization of aromatic triynes containing an asymmetric carbon atom produces [7]helicene-like scaffolds in diastereomeric ratios up to 100:0. This central-to-helical chirality transfer can be controlled by the absolute configuration at the asymmetric center and by the presence of carbon substituents. 相似文献
38.
The viscosity interaction coefficient, kAB, for the system poly(vinylalcohol)-polyacrylamide-water was determined at 25° by two methods: (a) estimation of the Huggins slope coefficients for mixtures of polymers in different proportions; (b) determination of the intrinsic viscosity of polymer (A) in aqueous solutions of polymer (B). The result, kAB = 0.3, indicates a low degree of overlapping of unlike polymer molecules. 相似文献
39.
A mathematical model of capillary zone electrophoresis (CZE) based on the conception of eigenmobilities, which are the eigenvalues of a matrix M tied to the linearized governing equations is presented. The model considers CZE systems, where constituents, either analytes or components of the background electrolyte (BGE), are weak electrolytes--acids, bases, or ampholytes. There is no restriction on the number of components nor on the valence of the constituents nor on pH of the BGE. An electrophoretic system with N constituents has N eigenmobilities. In most BGEs one or two eigenmobilities are very close to zero so their corresponding eigenzones move very slowly. However, there are BGEs where no eigenmobility is close to zero. The mathematical model further provides: the transfer ratio, the molar conductivity detection response, and the relative velocity slope. This allows the assessment of the indirect detection, conductivity detection and peak broadening (distortion) due to electromigration dispersion. Also, we present a spectral decomposition of the matrix M to matrices allowing the assessment of the amplitudes of system eigenpeaks (system peaks). Our model predicted the existence of BGEs having no stationary injection zone (or water zone, gap, peak, dip). A common practice of using the injection zone as a marker of the electroosmotic flow must fail in such electrolytes. 相似文献
40.
The gas phase basicities of a series of carbofunctional derivatives H3M(CH2)nX (M = C, Si, Ge; X = NH2, OH, F; n = 1–3) were investigated by the semiempirical CNDO/2 method. The calculations indicate that the electronic effects of silyl- and germyl-substituents differ greatly from the effect of simple alkyls. Moreover, in contrast to simple carbon derivatives, the overall nature of the electronic effects of siliyl- and germyl-substituents is crucially influenced by the molecular conformation. 相似文献