全文获取类型
收费全文 | 221067篇 |
免费 | 2976篇 |
国内免费 | 1325篇 |
专业分类
化学 | 123025篇 |
晶体学 | 3230篇 |
力学 | 8890篇 |
综合类 | 61篇 |
数学 | 24427篇 |
物理学 | 65735篇 |
出版年
2020年 | 1761篇 |
2019年 | 1903篇 |
2018年 | 2486篇 |
2017年 | 2535篇 |
2016年 | 3652篇 |
2015年 | 2428篇 |
2014年 | 3553篇 |
2013年 | 8893篇 |
2012年 | 7711篇 |
2011年 | 9415篇 |
2010年 | 6673篇 |
2009年 | 6458篇 |
2008年 | 8807篇 |
2007年 | 8918篇 |
2006年 | 8398篇 |
2005年 | 7715篇 |
2004年 | 6878篇 |
2003年 | 6062篇 |
2002年 | 5993篇 |
2001年 | 6710篇 |
2000年 | 5079篇 |
1999年 | 3673篇 |
1998年 | 3040篇 |
1997年 | 3010篇 |
1996年 | 3017篇 |
1995年 | 2625篇 |
1994年 | 2722篇 |
1993年 | 2582篇 |
1992年 | 2838篇 |
1991年 | 2897篇 |
1990年 | 2709篇 |
1989年 | 2619篇 |
1988年 | 2561篇 |
1987年 | 2498篇 |
1986年 | 2528篇 |
1985年 | 3305篇 |
1984年 | 3371篇 |
1983年 | 2808篇 |
1982年 | 3049篇 |
1981年 | 2816篇 |
1980年 | 2612篇 |
1979年 | 2796篇 |
1978年 | 3004篇 |
1977年 | 3037篇 |
1976年 | 3063篇 |
1975年 | 2800篇 |
1974年 | 2914篇 |
1973年 | 2964篇 |
1972年 | 2323篇 |
1971年 | 1846篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
241.
Stable aminoxyls and an iminoxyl were observed by spin trapping and EPR techniques during the nitration of coumarins containing a hydroxy group by nitric oxide. The trapped free radicals are deduced to be the resonance stabilized phenoxy-like radicals. The mechanisms for the nitrations are suggested. 相似文献
242.
J. Saunier F. Alloin J. Y. Sanchez L. Maniguet 《Journal of Polymer Science.Polymer Physics》2004,42(12):2308-2317
Microporous poly(vinylidene fluoride) (PVdF) separators for lithium-ion batteries, used in liquid organic electrolytes, have been characterized with respect to the swelling phenomena on dense PVdF membranes (obtained through hot pressing). In the first and second parts of this study, we have described the swelling equilibria and swelling kinetics of dense PVdF. Here the thermal properties of PVdF gels and their irreversible modifications induced by swelling are characterized. Particular attention is paid to crystallinity modifications, polymer plasticization, and membrane degradation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2308–2317, 2004 相似文献
243.
L. A. Utracki 《Journal of Polymer Science.Polymer Physics》2004,42(15):2909-2915
The Simha and Somcynsky (S–S) statistical thermodynamics theory was used to compute the solubility parameters as a function of temperature and pressure [δ = δ(T, P)], for a series of polymer melts. The characteristic scaling parameters required for this task, P*, T*, and V*, were extracted from the pressure–temperature–volume (PVT) data. To determine the potential polymer–polymer miscibility, the dependence of δ versus T (at ambient pressure) was computed for 17 polymers. Close proximity of the δ versus T curves for four miscible polymer pairs: PPE/PS, PS/PVME, and PC/PMMA signaled the usefulness of this approach. It is noteworthy, that the tabulated solubility parameters (derived from the solution data under ambient conditions) propounded the immiscibility of the PVC/PVAc pair. The computed values of δ also suggested miscibility for polymer pairs of unknown miscibility, namely PPE/PVC, PPE/PVAc, and PET/PSF. In recognizing the limitations of the solubility parameter approach (the omission of several thermodynamic contributions), these preliminary results are auspicious because they indicate a new route for estimating the miscibility of any polymeric material at a given temperature and pressure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2909–2915, 2004 相似文献
244.
Data on the adsorption of kryptates of alkali metals on a mercury electrode are obtained for the first time by a method of the measurement of the differential capacitance as a function of potential and are compared to one another. Shown is that there takes place a deep mutual relationship between the structure of a complex and the regularities of its adsorption. An assumption is put forth about the possibility of adsorption of a free ligand in solutions of lithium kryptate, which possesses relatively low strength. The co-adsorption of sodium kryptate with 1-adamantanol, which forms a two-dimensional condensed layer, is investigated. Established is that the C vs. E curves, obtained in 1 M Na2SO4 at a constant activity of 1-adamantanol and a varying concentration of KryptofixR 222, exhibit two distinctly pronounced portions, each of which corresponds to predominant adsorption of one of the surface-active components. The region of predominant adsorption of KryptofixR 222 expands with its concentration. 相似文献
245.
For vector quasivariational inequalities involving multifunctions in topological vector spaces, an existence result is obtained without a monotonicity assumption and with a convergence assumption weaker than semicontinuity. A new type of quasivariational inequality is proposed. Applications to quasicomplementarity problems and traffic network equilibria are considered. In particular, definitions of weak and strong Wardrop equilibria are introduced for the case of multivalued cost functions. 相似文献
246.
247.
A carousel is a dynamical system that describes the movement of an equilateral linkage in which the midpoint of each rod travels parallel to it. They are closely related to the floating body problem. We prove, using the work of Auerbach, that any figure that floats in equilibrium in every position is drawn by a carousel. Of special interest are such figures with rational perimetral density of the floating chords, which are then drawn by carousels. In particular, we prove that for some perimetral densities the only such figure is the circle, as the problem suggests. 相似文献
248.
Periodica Mathematica Hungarica - 相似文献
249.
250.
Many real problems can be modelled as robust shortest path problems on interval digraphs, where intervals represent uncertainty about real costs and a robust path is not too far from the shortest path for each possible configuration of the arc costs.A branch and bound algorithm for this problem is presented. 相似文献