全文获取类型
收费全文 | 47528篇 |
免费 | 1652篇 |
国内免费 | 165篇 |
专业分类
化学 | 31806篇 |
晶体学 | 342篇 |
力学 | 855篇 |
综合类 | 4篇 |
数学 | 7319篇 |
物理学 | 9019篇 |
出版年
2023年 | 332篇 |
2022年 | 259篇 |
2021年 | 728篇 |
2020年 | 778篇 |
2019年 | 785篇 |
2018年 | 938篇 |
2017年 | 884篇 |
2016年 | 1675篇 |
2015年 | 1381篇 |
2014年 | 1439篇 |
2013年 | 2925篇 |
2012年 | 3125篇 |
2011年 | 3454篇 |
2010年 | 2109篇 |
2009年 | 1869篇 |
2008年 | 2977篇 |
2007年 | 2891篇 |
2006年 | 2601篇 |
2005年 | 2362篇 |
2004年 | 1927篇 |
2003年 | 1558篇 |
2002年 | 1325篇 |
2001年 | 1017篇 |
2000年 | 898篇 |
1999年 | 696篇 |
1998年 | 516篇 |
1997年 | 436篇 |
1996年 | 549篇 |
1995年 | 407篇 |
1994年 | 410篇 |
1993年 | 443篇 |
1992年 | 415篇 |
1991年 | 308篇 |
1990年 | 296篇 |
1989年 | 236篇 |
1988年 | 232篇 |
1987年 | 247篇 |
1986年 | 233篇 |
1985年 | 312篇 |
1984年 | 291篇 |
1983年 | 220篇 |
1982年 | 219篇 |
1981年 | 195篇 |
1980年 | 171篇 |
1979年 | 172篇 |
1978年 | 143篇 |
1977年 | 145篇 |
1976年 | 131篇 |
1975年 | 113篇 |
1973年 | 131篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Mattias Edn Jekabs Grins Zhijian Shen Zheng Weng 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,169(2):1
Using enhancement of the 27Al central-transition magnetization by applying RAPT prior to 27Al → 29Si cross-polarization, we demonstrate fast acquisition of 29Si one-dimensional MAS and two-dimensional 27Al–29Si HETCOR spectra on a new sialon phase Ba2Al3Si9N13O5. 相似文献
82.
Compared with linear polymers, more factors may affect the glass‐transition temperature (Tg) of a hyperbranched structure, for instance, the contents of end groups, the chemical properties of end groups, branching junctions, and the compactness of a hyperbranched structure. Tg's decrease with increasing content of end‐group free volumes, whereas they increase with increasing polarity of end groups, junction density, or compactness of a hyperbranched structure. However, end‐group free volumes are often a prevailing factor according to the literature. In this work, chain‐end, free‐volume theory was extended for predicting the relations of Tg to conversion (X) and molecular weight (M) in hyperbranched polymers obtained through one‐pot approaches of either polycondensation or self‐condensing vinyl polymerization. The theoretical relations of polymerization degrees to monomer conversions in developing processes of hyperbranched structures reported in the literature were applied in the extended model, and some interesting results were obtained. Tg's of hyperbranched polymers showed a nonlinear relation to reciprocal molecular weight, which differed from the linear relation observed in linear polymers. Tg values decreased with increasing molecular weight in the low‐molecular‐weight range; however, they increased with increasing molecular weight in the high‐molecular‐weight range. Tg values decreased with increasing log M and then turned to a constant value in the high‐molecular‐weight range. The plot of Tg versus 1/M or log M for hyperbranched polymers may exhibit intersecting straight‐line behaviors. The intersection or transition does not result from entanglements that account for such intersections in linear polymers but from a nonlinear feature in hyperbranched polymers according to chain‐end, free‐volume theory. However, the conclusions obtained in this work cannot be extended to dendrimers because after the third generation, the end‐group extents of a dendrimer decrease with molecular weight. Thus, it is very possible for a dendrimer that Tg increases with 1/M before the third generation; however, it decreases with 1/M after the third generation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1235–1242, 2004 相似文献
83.
84.
M. A. Diniz-Ehrhardt M. A. Gomes-Ruggiero J. M. Martínez S. A. Santos 《Journal of Optimization Theory and Applications》2004,123(3):497-517
The spectral projected gradient method SPG is an algorithm for large-scale bound-constrained optimization introduced recently by Birgin, Martínez, and Raydan. It is based on the Raydan unconstrained generalization of the Barzilai-Borwein method for quadratics. The SPG algorithm turned out to be surprisingly effective for solving many large-scale minimization problems with box constraints. Therefore, it is natural to test its perfomance for solving the sub-problems that appear in nonlinear programming methods based on augmented Lagrangians. In this work, augmented Lagrangian methods which use SPG as the underlying convex-constraint solver are introduced (ALSPG) and the methods are tested in two sets of problems. First, a meaningful subset of large-scale nonlinearly constrained problems of the CUTE collection is solved and compared with the perfomance of LANCELOT. Second, a family of location problems in the minimax formulation is solved against the package FFSQP. 相似文献
85.
86.
Paramagnetic pyrroline and 1,2,3,6-tetrahydropyridine derivatives of BODIPY and their diamagnetic analogs have been synthesized and characterized as novel redox double sensor and cation sensitive reagents. 相似文献
87.
88.
In this paper, space adaptivity is introduced to control the error in the numerical solution of hyperbolic systems of conservation laws. The reference numerical scheme is a new version of the discontinuous Galerkin method, which uses an implicit diffusive term in the direction of the streamlines, for stability purposes. The decision whether to refine or to unrefine the grid in a certain location is taken according to the magnitude of wavelet coefficients, which are indicators of local smoothness of the numerical solution. Numerical solutions of the nonlinear Euler equations illustrate the efficiency of the method. 相似文献
89.
V. Petržílka 《Czechoslovak Journal of Physics》1997,47(2):183-196
Test particle motion and acceleration has been explored in strong radio frequency (RF) fields, for which quasilinear ponderomotive force approximation is not valid. By nonlinear acceleration in spatially varying wave amplitude of RF travelling wave, electrons may be accelerated to time averaged velocities significantly larger than the RF wave phase velocity, and than the boundary plasma thermal velocity, in RF fields of several Volts per centimeter at wave frequency of 7 MHz. It is also demonstrated that even weak spatial gradients, much weaker than those expected in experiments, of the RF wave field amplitude, have significant consequences for the particle motion. Estimates are presented of the total energy transferred from the near antenna RF field to the plasma due to the nonlinear electron acceleration effects. 相似文献
90.
We study condensation of ethanol-hexanol vapour by numerical solution of kinetic equations. The number of droplets formed
in unit volume is computed within self-consistent classical model. It is shown that formation of ethanol-rich droplets prevails
at the initial stage of nucleation process, but in the stationary state formation of droplets near the saddle point (on cluster
formation energy surface) plays the dominant role.
Presented at the 6th Joint Seminar “Development of Materials Science in Research and Education”, Karlštejn, Czech Republic,
17–19 September 1996.
This work was supported by Grant No. A1010615 of the Grant Agency of the Academy of Sciences of the Czech Republic. 相似文献