全文获取类型
收费全文 | 14128篇 |
免费 | 409篇 |
国内免费 | 13篇 |
专业分类
化学 | 7442篇 |
晶体学 | 116篇 |
力学 | 290篇 |
综合类 | 1篇 |
数学 | 3149篇 |
物理学 | 3552篇 |
出版年
2021年 | 135篇 |
2020年 | 181篇 |
2019年 | 166篇 |
2018年 | 312篇 |
2017年 | 315篇 |
2016年 | 586篇 |
2015年 | 430篇 |
2014年 | 490篇 |
2013年 | 1155篇 |
2012年 | 714篇 |
2011年 | 904篇 |
2010年 | 542篇 |
2009年 | 480篇 |
2008年 | 605篇 |
2007年 | 539篇 |
2006年 | 469篇 |
2005年 | 345篇 |
2004年 | 337篇 |
2003年 | 274篇 |
2002年 | 274篇 |
2001年 | 219篇 |
2000年 | 185篇 |
1999年 | 161篇 |
1998年 | 156篇 |
1997年 | 147篇 |
1996年 | 138篇 |
1995年 | 133篇 |
1994年 | 120篇 |
1993年 | 117篇 |
1992年 | 133篇 |
1991年 | 107篇 |
1990年 | 112篇 |
1989年 | 121篇 |
1988年 | 122篇 |
1987年 | 118篇 |
1986年 | 117篇 |
1985年 | 161篇 |
1984年 | 159篇 |
1983年 | 144篇 |
1982年 | 137篇 |
1981年 | 117篇 |
1980年 | 136篇 |
1979年 | 121篇 |
1978年 | 157篇 |
1977年 | 132篇 |
1976年 | 129篇 |
1975年 | 102篇 |
1974年 | 127篇 |
1973年 | 121篇 |
1965年 | 84篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
121.
Summary Kinetics of dehydration of equilibrium swollen poly(acrylic acid) hydrogel was investigated using methods of non-isothermal
thermal analysis. Methods of Kissinger, Coats-Redfern, Van Krevelen and Horowitz-Metzger were applied for determination the
kinetics parameters: activation energy (E), pre-exponent (lnA) as well as the kinetics model ƒ(69) for the process of hydrogel dehydration under different heating rates. An existence
of good agreement between determined values of kinetic parameters (Eand A), which were obtained applying different methods under the same heating rate. Functional relationship between changes of
kinetic parameters of dehydration and changes of heating rate was established. An existence of compensation effect is accepted
and explanation of compensation effect appearance during the hydrogel dehydration is suggested. 相似文献
122.
J. Málek J. šesták F. Rouquerol J. Rouquerol J. M. Criado A. Ortega 《Journal of Thermal Analysis and Calorimetry》1992,38(1-2):71-87
The applicability of both conventional Thermal Analysis (TA) and Controlled Rate Thermal Analysis (CRTA) for kinetic analysis is discussed. It is shown that TA method can give a reliable kinetic information and meaningful kinetic parameters especially for solid state transformation. On the other hand the CRTA method is more suitable for decomposition process where one or more gasses are evolved. A consistent and reliable method of kinetic analysis is proposed for both techniques. This method is illustrated to analyze the crystallization process of chalcogenide glass and the decomposition of dolomite. 相似文献
123.
Yu Gui Gu Xiaolin Zhang Richard F. Clark Stevan W. Djuric Zhenkun Ma 《Tetrahedron letters》2004,45(15):3051-3053
An intramolecular 1,3-dipolar cycloaddition of azomethine ylide, generated in situ via the reaction of C12-glycinate derivative of macrolide with formaldehyde, provided a novel tricyclic macrolide. The high stereoselectivity of this [2+3] reaction was achieved by introducing a suitable directing group at C-6 position of macrolide. 相似文献
124.
D. Reichardt V. Bonačić-Koutecký P. Fantucci J. Jellinek 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1997,40(1):486-489
An ab-initio molecular dynamics procedure without precalculation of the Born-Oppenheimer energy surface based on an iterative non-local density functional method employing Gaussian atomic basis has been developed. Analytical gradients are calculated and used for the propagation of nuclei. Sufficiently long trajectories can be calculated at an acceptable computational cost, allowing for analysis of dynamical behaviour of small metallic clusters. This is illustrated on an example of the Li8 cluster. Temperature behaviour of different type of isomers has been investigated. Calculated power spectra allow to identify the presence of more than one isomeric forms along the given trajectories. 相似文献
125.
I. Kúdelka P.K. Misro J. Pospíšil H. Korbanka T. Riedel G. Pfahler 《Polymer Degradation and Stability》1985,12(4):303-313
The hydroperoxide decomposing efficiencies of dioctadecylsulfide (I), dioctadecyldisulfide (IV) and dioctadecyl 3,3-thio-dipropionate (VII) have been compared at 75°C and 85°C. The formation of oxidation products from (I) and (IV) has been checked. Experimental evidence is given of the important rôle of the activation of the molecule of (IV) by the presence of two sulfidic sulfur atoms compared with the activation of the sulfur atom in (VII) by the alkoxycarbonyl group in the beta position. The explanation of the high efficiency of disulfide has been based on the formation of thiosulfinate—the key intermediate for the generation of peroxidolytic species—in the first reaction step. 相似文献
126.
The paper deals with the problem of the outpatient administration of186Re-HEDP and153Sm-EDTMP for palliative therapy of bone metastases. The subsequent 6 hours stay of the treated patients in a department of nuclear medicine appears to be in compliance with regulations proposed in the Czech Republic as well as with ICRP recommendations. 相似文献
127.
Due to the high safety risks, chemistry instructors avoid demonstrating many remarkable experiments based on the addition of a liquid to a solid. Well-known examples of such demonstrations are various pyrotechnic mixtures of potassium chlorate and sugar (sucrose), which are usually activated with a drop of concentrated sulfuric acid. Other attractive demonstrations are the addition of water to freshly prepared magnesium phosphide and addition of water to burning magnesium. In all of these demonstrations the reaction that takes place immediately is very vigorous and can be hazardous for the instructor. Because chemistry teachers and instructors usually try to avoid performing experiments that include a hazard, a number of highly attractive experiments may remain unknown to the public. Using a simple homemade device called a safety dropper, one can perform all of these experiments with complete safety, both for the audience and the demonstrator. Details for performing some of these experiments as well as for the construction of the safety dropper are given in this paper. Video clips of demonstrations are included as an aid for inexperienced instructors. 相似文献
128.
129.
Data on the structures and reactions of heterocyclic diazo compounds that lead to the formation of new heterocyclic systems as a result of intra- or intermolecular cyclization and rearrangements are systematized.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 579–603, May, 1980. 相似文献
130.
R.R. Adžić D.N. Simić A.R. Despić D.M. Dražić 《Journal of Electroanalytical Chemistry》1975,65(2):587-601
It was demonstrated that some foreign metal monolayers formed by underpotential deposition have pronounced catalytic effects on the oxidation of formic acid on platinum. The explanation of these effects was sought within the framewor of existing data on the formic acid oxidation and the underpotential deposition. It was found that the catalytic effect of foreign metal monolayers originates in the decrease of hydrogen adsorption thus preventing the formation of the main poisoning species COH. At the same time these experiments confirm the previously postulated mechanism of formation of the poisoning species involving adsorbed hydrogen. 相似文献