全文获取类型
收费全文 | 13014篇 |
免费 | 979篇 |
国内免费 | 852篇 |
专业分类
化学 | 9516篇 |
晶体学 | 118篇 |
力学 | 365篇 |
综合类 | 66篇 |
数学 | 2355篇 |
物理学 | 2425篇 |
出版年
2024年 | 10篇 |
2023年 | 133篇 |
2022年 | 146篇 |
2021年 | 373篇 |
2020年 | 384篇 |
2019年 | 373篇 |
2018年 | 312篇 |
2017年 | 312篇 |
2016年 | 596篇 |
2015年 | 524篇 |
2014年 | 609篇 |
2013年 | 886篇 |
2012年 | 1123篇 |
2011年 | 1233篇 |
2010年 | 839篇 |
2009年 | 760篇 |
2008年 | 964篇 |
2007年 | 943篇 |
2006年 | 835篇 |
2005年 | 687篇 |
2004年 | 617篇 |
2003年 | 394篇 |
2002年 | 343篇 |
2001年 | 164篇 |
2000年 | 144篇 |
1999年 | 143篇 |
1998年 | 91篇 |
1997年 | 88篇 |
1996年 | 94篇 |
1995年 | 62篇 |
1994年 | 59篇 |
1993年 | 54篇 |
1992年 | 58篇 |
1991年 | 41篇 |
1990年 | 55篇 |
1989年 | 32篇 |
1988年 | 30篇 |
1987年 | 32篇 |
1986年 | 27篇 |
1985年 | 44篇 |
1984年 | 41篇 |
1983年 | 23篇 |
1982年 | 14篇 |
1981年 | 20篇 |
1980年 | 18篇 |
1979年 | 16篇 |
1978年 | 10篇 |
1977年 | 7篇 |
1975年 | 7篇 |
1974年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 640 毫秒
991.
We propose a novel approach for solving polynomial programs over compact domains with equality constraints. By means of a generic transformation, we show that existing solution schemes for the, typically simpler, problem without equalities can be used to address the problem with equalities. 相似文献
992.
There are infinitely many ways of representing a d.c. function as a difference of convex functions. In this paper we analyze
how the computational efficiency of a d.c.optimization algorithm depends on the representation we choose for the objective
function, and we address the problem of characterizing and obtaining a computationally optimal representation. We introduce
some theoretical concepts which are necessary for this analysis and report some numerical experiments.
相似文献
993.
Razvan Gabriel Iagar Ariel Sánchez Juan Luis Vázquez 《Journal de Mathématiques Pures et Appliquées》2008,89(1):1-24
In this paper we prove that there exists an explicit correspondence between the radially symmetric solutions of two well-known models of nonlinear diffusion, the porous medium equation and the p-Laplacian equation. We establish exact correspondence formulas between these solutions. We also study in detail the application of the results in the important case of self-similar solutions. In particular, we derive the existence of new self-similar solutions for the evolution p-Laplacian equation. 相似文献
994.
995.
996.
Juan C. Castillo Rodrigo Abonía Michael B. Hursthouse Justo Cobo Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2009,65(10):o495-o497
In the title compound, C23H22N4O, there is evidence for some bond fixation in the aryl component of the quinolinone unit. Pairs of molecules related by inversion are linked into R22(8) dimers by almost linear N—H...O hydrogen bonds, and dimers related by inversion are linked into chains by a single aromatic π–π stacking interaction. 相似文献
997.
998.
Nickel and potassium co-medified β-Mo2C catalysts were prepared and used for CO hydrogenation reaction. The major products over β-Mo2C were C1-C4 hydrocarbons, only few alcohols were obtained. Addition of potassium resulted in remarkable selectivity shift from hydrocarbons to alcohols at the expense of CO conversion over β-Mo2C. Moreover, it was found that potassium enhanced the ability of chain propagation with a higher C2+OH production. Modified by nickel, β-Mo-2C showed a relatively high CO conversion, however, the products were similar to those of pure β-Mo2C. When co-modified by nickel and potassium,β-Mo2C exhibited high activity and selectivity towards mixed alcohols synthesis, and also the whole chain propagation to produce alcohols especially for the stage of C1OH to C2OH was remarkably enhanced. It was concluded that the Ni and K had, to some extent, synergistic effect on CO conversion. 相似文献
999.
Francisca Zamora Khalid Hakkou Abdelillah Alla Manuel Rivas Antxón Martínez De Ilarduya Sebastián Muñoz‐Guerra Juan A. Galbis 《Journal of polymer science. Part A, Polymer chemistry》2009,47(4):1168-1177
The synthesis, characterization, and some properties of new copolyesters analogous to poly(butylene terephthalate) (PBT), based on L ‐arabinaric and galactaric acids, are described. These copolyesters were obtained by polycondensation reaction in the melt of mixtures of methyl 2,3,4‐tri‐O‐methyl‐L ‐arabinarate or methyl 2,3,4,5‐tetra‐O‐methyl‐galactarate and dimethyl terephthalate with 1,4‐butanediol. Their weight‐average molecular weights ranged between 10,000 and 34,000, with polydispersities ranging from 1.4 to 2.2. The composition of all the copolymers was analyzed by NMR, and was found to have a statistical microstructure. All these copolyesters were thermally stable, with degradation temperatures well above 300 °C. The melting temperature and crystallinity decreased in both series, and the glass transition temperature increased and decreased respectively, for the PBTGa and PBTAr series with increasing amounts of aldaric units in the copolyester chain. Only PBT‐derived copolyesters containing a maximum of 30% aldaric units showed discrete scattering characteristic of crystalline material. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1168–1177, 2009 相似文献
1000.