全文获取类型
收费全文 | 9193篇 |
免费 | 284篇 |
国内免费 | 41篇 |
专业分类
化学 | 4639篇 |
晶体学 | 68篇 |
力学 | 224篇 |
综合类 | 2篇 |
数学 | 1941篇 |
物理学 | 2644篇 |
出版年
2021年 | 91篇 |
2020年 | 123篇 |
2019年 | 118篇 |
2018年 | 169篇 |
2017年 | 165篇 |
2016年 | 353篇 |
2015年 | 303篇 |
2014年 | 341篇 |
2013年 | 611篇 |
2012年 | 447篇 |
2011年 | 584篇 |
2010年 | 352篇 |
2009年 | 284篇 |
2008年 | 346篇 |
2007年 | 295篇 |
2006年 | 229篇 |
2005年 | 131篇 |
2004年 | 168篇 |
2003年 | 187篇 |
2002年 | 166篇 |
2001年 | 163篇 |
2000年 | 143篇 |
1999年 | 128篇 |
1998年 | 116篇 |
1997年 | 112篇 |
1996年 | 102篇 |
1995年 | 88篇 |
1994年 | 103篇 |
1993年 | 104篇 |
1992年 | 99篇 |
1991年 | 79篇 |
1990年 | 97篇 |
1989年 | 85篇 |
1988年 | 79篇 |
1987年 | 75篇 |
1986年 | 70篇 |
1985年 | 113篇 |
1984年 | 114篇 |
1983年 | 81篇 |
1982年 | 100篇 |
1981年 | 102篇 |
1980年 | 84篇 |
1979年 | 101篇 |
1978年 | 91篇 |
1977年 | 83篇 |
1976年 | 109篇 |
1975年 | 103篇 |
1974年 | 99篇 |
1973年 | 73篇 |
1968年 | 75篇 |
排序方式: 共有9518条查询结果,搜索用时 15 毫秒
941.
Iztok Fister Marjan Mernik Bogdan Filipič 《Computational Optimization and Applications》2013,54(3):741-770
This paper proposes a hybrid self-adaptive evolutionary algorithm for graph coloring that is hybridized with the following novel elements: heuristic genotype-phenotype mapping, a swap local search heuristic, and a neutral survivor selection operator. This algorithm was compared with the evolutionary algorithm with the SAW method of Eiben et al., the Tabucol algorithm of Hertz and de Werra, and the hybrid evolutionary algorithm of Galinier and Hao. The performance of these algorithms were tested on a test suite consisting of randomly generated 3-colorable graphs of various structural features, such as graph size, type, edge density, and variability in sizes of color classes. Furthermore, the test graphs were generated including the phase transition where the graphs are hard to color. The purpose of the extensive experimental work was threefold: to investigate the behavior of the tested algorithms in the phase transition, to identify what impact hybridization with the DSatur traditional heuristic has on the evolutionary algorithm, and to show how graph structural features influence the performance of the graph-coloring algorithms. The results indicate that the performance of the hybrid self-adaptive evolutionary algorithm is comparable with, or better than, the performance of the hybrid evolutionary algorithm which is one of the best graph-coloring algorithms today. Moreover, the fact that all the considered algorithms performed poorly on flat graphs confirms that graphs of this type are really the hardest to color. 相似文献
942.
Task specific ionic liquids and onium salts have been used as soluble supports for peptide synthesis. These new supports combine easy monitoring, high loading capacities, large scale preparation, and homogeneous kinetics characteristics while keeping advantages of solid-phase synthesis including easy purification and workup. Careful structural design of these supports allowed for fine tuning of physical properties leading to better yields, kinetics, and purities. 相似文献
943.
Inspired by a problem in steel metallurgy, we prove the existence, regularity, uniqueness, and continuous data dependence
of solutions to a coupled parabolic system in a smooth bounded 3D domain, with nonlinear and nonhomogeneous boundary conditions.
The nonlinear coupling takes place in the diffusion coefficient. The proofs are based on anisotropic estimates in tangential
and normal directions, and on a refined variant of the Gronwall lemma. 相似文献
944.
945.
Tomáš Roubíček Giuseppe Tomassetti 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2010,61(1):1-20
Phase transformation in shape-memory alloys is known to cause electric resistivity variation that, under electric current, may conversely influence Joule heat production and thus eventually the martensitic transformation itself. A thermodynamically consistent general continuum-mechanical model at large strains is presented. In special cases, a proof of the existence of a weak solution is outlined, using a semidiscretization in time. 相似文献
946.
The aim of the present research work was to investigate the possibilities of designing surface texturing for different lubrication regimes and to evaluate its effectiveness, especially under starved, boundary and mixed lubrication regimes. This was achieved by combining an experimental tribological investigation with a surface-roughness analysis, a 2D FEM simulation and fluid dynamic modelling. The tribological investigation under unidirectional and reciprocating sliding was focused on the effect of the laser-texturing parameters—including the dimple depth and size, the dimple area density and the contact size—on the coefficient of friction under different lubrication regimes, achieved by varying the sliding speed, the normal load and the lubricant viscosity. 相似文献
947.
948.
Masashi Shiotsuki Atsushi Nakagawa Jesus Rodriguez Castañon Naoya Onishi Tatsurou Kobayashi Fumio Sanda Toshio Masuda 《Journal of polymer science. Part A, Polymer chemistry》2010,48(23):5549-5556
End‐functionalized poly(phenylacetylene)s were synthesized by the polymerization of phenylacetylene (PA) using the well‐defined palladium catalysts represented as [(dppf)PdBr(R)] {dppf = 1,1′‐bis(diphenylphosphino)ferrocene}. The Pd catalysts having a series of R groups such as o‐tolyl, mesityl, C(Ph)?CPh2, C6H4‐o‐CH2OH, C6H4‐p‐CN, and C6H4‐p‐NO2 in conjunction with silver triflate polymerized PA to give end‐functionalized poly(PA)s bearing the corresponding R groups in high yields. The results of IR and NMR spectroscopies and MALDI‐TOF mass analyses proved the introduction of these R groups at one end of each polymer chain. The poly(PA) bearing a hydroxy end group was applied as a macroinitiator to the synthesis of a block copolymer composed of poly(PA) and poly(β‐propiolactone) moieties. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 相似文献
949.
T. Bantan R. Milačič B. Mitrović B. Pihlar 《Analytical and bioanalytical chemistry》1999,365(6):545-552
The possibilities for speciation of low molecular weight aluminium organic acid complexes (LMW-Al) in plant sap were investigated by applying a combination of various chromatographic and spectroscopic techniques. The behavior of different LMW-Al complexes was investigated in synthetic aqueous solutions on anion and cation exchange fast protein liquid chromatography (FPLC) columns with inductively coupled plasma – atomic emission spectrometry (ICP-AES) or electrothermal atomic absorption spectrometry (ETAAS) detection. Plant sap of Sempervivum tectorum with a high concentration of Al (9.3 μg cm–3) and Sansevieria trifasciata with an appreciably lower Al concentration (0.065 μg cm–3) were analyzed. The speciation study in plant sap indicated that the species present in these samples, existed as negatively charged LMW-Al complexes which were eluted at the retention time typical for Al-citrate and Al-aconitate. In order to identify Al binding ligands eluted under the chromatographic peak analysis by electrospray ionization (ESI)-MS technique using Z spray ion source were also applied. The predominant LMW-Al negatively charged complexes in Sempervivum tectorum and Sansevieria trifasciata were found to be Al-citrate and Al-aconitate. It was shown that other LMW organic acids do not form complexes with Al in the samples studied. 相似文献
950.