全文获取类型
收费全文 | 5833篇 |
免费 | 110篇 |
专业分类
化学 | 3187篇 |
晶体学 | 30篇 |
力学 | 128篇 |
数学 | 1348篇 |
物理学 | 1250篇 |
出版年
2021年 | 35篇 |
2020年 | 42篇 |
2019年 | 50篇 |
2018年 | 140篇 |
2017年 | 128篇 |
2016年 | 197篇 |
2015年 | 143篇 |
2014年 | 193篇 |
2013年 | 474篇 |
2012年 | 291篇 |
2011年 | 391篇 |
2010年 | 214篇 |
2009年 | 182篇 |
2008年 | 330篇 |
2007年 | 327篇 |
2006年 | 305篇 |
2005年 | 221篇 |
2004年 | 197篇 |
2003年 | 140篇 |
2002年 | 133篇 |
2001年 | 94篇 |
2000年 | 78篇 |
1999年 | 56篇 |
1998年 | 48篇 |
1997年 | 48篇 |
1996年 | 46篇 |
1995年 | 46篇 |
1994年 | 28篇 |
1993年 | 41篇 |
1992年 | 54篇 |
1991年 | 42篇 |
1990年 | 47篇 |
1989年 | 51篇 |
1988年 | 47篇 |
1987年 | 46篇 |
1986年 | 40篇 |
1985年 | 60篇 |
1984年 | 66篇 |
1983年 | 64篇 |
1982年 | 61篇 |
1981年 | 41篇 |
1980年 | 53篇 |
1979年 | 47篇 |
1978年 | 68篇 |
1977年 | 39篇 |
1976年 | 52篇 |
1975年 | 40篇 |
1974年 | 48篇 |
1973年 | 40篇 |
1972年 | 33篇 |
排序方式: 共有5943条查询结果,搜索用时 15 毫秒
91.
V. Dondur D. Fidler B. Adnadjević V. Rakić 《Journal of Thermal Analysis and Calorimetry》1987,32(2):613-622
The kinetics of water desorption from porous glasses silica gel and porous aluminosilicates were followed through the TG and DTG methods. In all cases only one thermodesorption peak appeared. The kinetic parameters were determined by standard nonisothermal methods. The activation energy is constant and independent of the coverage degree and pore diameter in the system porous glass-water. The functionE(θ) were determined for the silica gel and porous aluminosilicatesE=E 0+a exp (-bθ). The parametersE 0,a andb depend on the SiO2/Al2O3 ratio and on the distribution of active centers on the surface. 相似文献
92.
Komorsky-Lovrić S 《Analytical and bioanalytical chemistry》1996,356(3-4):306-309
Kinetics of the surface redox reaction of alizarine red S adsorbed on mercury is measured by square-wave voltammetry. In 1 mol/l KNO3 buffered to pH 9.22, the standard reaction rate constant of the redox couple anthraquinone/anthrahydroquinone in the adsorbed alizarine red S molecule is ks=100 ±10 s-1 and the cathodic transfer coefficient is =0.4. At pH 2 in this medium ks is greater than 500 s-1. 相似文献
93.
Holclajtner-Antunović Raspopović Z Georgijević Tripković M Georgijević J 《Analytical and bioanalytical chemistry》1996,356(8):471-475
A systematic parametric study of an LTE (local thermodynamic equilibrium) mathematical model of pure inductively coupled argon plasma (ICAP) used for spectrochemical purposes was performed by means of computer simulations. The spatial distributions of temperature, gas velocity, magnetic field and energy losses were investigated under typical plasma operating conditions as function of the ICAP geometrical dimensions and dynamic parameters. These theoretical calculations can be used to predict the properties of the applied plasma in the course of practical work, to choose the optimal conditions by changing the operating parameters and to interpret existing analytical results. 相似文献
94.
Tomislav P. Živković 《Theoretical chemistry accounts》1988,73(2-3):207-219
A new method for the calculation of bond orders in alternant hydrocarbons is presented. The method requires a summation over the contributions of various superposition diagrams. Quantitatively, the method is almost as reliable as PPP, and due to its simplicity it can be used for fast and relatively accurate calculation of bond orders. In addition some simple rules are derived, which in many cases can be used to predict the signs of bond orders between nonbonded atoms.Dedicated to Professor J. Koutecký on the occasion of his 65th birthdayResearch supported by the Robert A. Welch Foundation of Houston, Texas 相似文献
95.
Summary
UV Densitometric Method for the Determination of Estrogens and Androgens in Pharmaceutical Preparations
A convenient method for the determination of estradiol benzoate/testosterone propionate and of ethynylestradiol/methyltestosterone mixtures from ampoules and lingualets, is described. The procedure is simple since the method involves direct reading from the thin-layer plate, avoiding thus the elution of the spot.After TL Chromatographie separation of active substances, densitometric measurements were performed with a HPTL scanner at 254 nm, whereby good and precise results were obtained. The standard deviation was found to range from 0.022 to 0.183, whereas the relative standard deviation ranged from 0.93 to 2.7%.The results obtained show that the method is applicable to routine analysis. 相似文献
96.
Metal-catalyzed di-tert-butylsilylene transfer was developed as a mild, operationally simple, functional-group-tolerant method for silacyclopropane formation. Di-tert-butylsilylene was transferred from cyclohexene silacyclopropane 1 to an alkene through the use of a metal salt. Silacyclopropanation occurred at temperatures as low as -27 degrees C when AgOTf or AgOC(O)CF(3) were used as catalysts. Complex silacyclopropanes were formed stereospecifically and diastereoselectively from functionalized alkenes. Silacyclopropanes reacted with various carbonyl compounds, including aldehydes, ketones, formate esters, and formamides, in an overall process that efficiently converts alkenes into oxasilacyclopentanes with defined stereochemistry. 相似文献
97.
Djordje Vlaović Gordana Ćetković Ivan Juranić Jelica Balaž Stevan Lajšić Dejan Djoković 《Monatshefte für Chemie / Chemical Monthly》1990,121(11):931-939
Summary The syntheses andin vitro antibacterial and antifungal evaluation of certain (5-nitro-2-furyl)azomethines with different heterocyclic nuclei are described.
Die Anwendung von Lävulinsäure und 5-Nitro-2-furylmethylendiacetat in der Totalsynthese einiger neuer biologisch aktiver (5-Nitro-2-furyl)azomethine
Zusammenfassung Es wird die Synthese und diein-vitro-antibakterielle und antifungale Wirksamkeit für bestimmte (5-Nitro-2-furyl)azomethine mit verschiedenen heterocyclischen Kernen beschrieben.相似文献
98.
P. Fantucci S. Polezzo V. Bonačić-Koutecký J. Koutecký 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1989,13(4):355-361
The core-valence correlation potential has been derived for Na and K employing atomic calculations which make use of the density functional formula worked out by Lee, Yang and Parr based on Colle-Salvetti approach. The numerical potential is fitted with a small number of Gaussians leading to a very simple expression for an one-electron corevalence correlation operator? cv . The core-valence correlation corrections can be computed by applying? cv on a quite general class of wavefunctions. Applications of the? cv operator within the framework of valence-electron-only calculations using effective Hamiltonians are presented for Na and K atoms, for Na2, K2, NaK and their cations. Almost all the corrections calculated for the physical properties due to the core-valence correlation lead to results which are in good agreement with those obtained from much more sophisticated treatments and experimental data. 相似文献
99.
Dž. Belkić 《Zeitschrift für Physik A Hadrons and Nuclei》1984,317(2):131-138
We examine a general Dalitz integral containing the usual Feynman-type two-denominator term together with the Fourier transform \(\tilde \phi _{nlm} (q)\) of the hydrogenlike wave-function. A single closed formula is obtained for an arbitrary set {nlm} of quantum numbers, which is expressed in terms of the multivariable Lauricella hypergeometric functionF D . The result is useful in a variety of calculations within the second Born approximation. 相似文献
100.
Silica gel impregnated with poly(ethylene glycol) of different molecular mass (400, 1000, 1540, 4000, and 5500) was investigated for salting-out thin-layer chromatography of 15 mixed aminocarboxylato Co(III) complexes using eight ammonium sulphate solutions as mobile phases. Regularities established earlier for non-impregnated adsorbents are also valid in this work. Poly(ethylene glycol) of high molecular mass increases the hydrophobicity of the adsorbent. Positive linear dependence of RM values and of salting-out efficiency on average poly(ethylene glycol) molecular mass was usually observed. In contrast with non-impregnated silica gel, separation was achieved between complexes with the smallest hydrocarbon groups. 相似文献