全文获取类型
收费全文 | 32759篇 |
免费 | 1091篇 |
国内免费 | 249篇 |
专业分类
化学 | 22723篇 |
晶体学 | 223篇 |
力学 | 770篇 |
数学 | 5447篇 |
物理学 | 4936篇 |
出版年
2022年 | 283篇 |
2021年 | 420篇 |
2020年 | 514篇 |
2019年 | 484篇 |
2018年 | 376篇 |
2017年 | 373篇 |
2016年 | 837篇 |
2015年 | 739篇 |
2014年 | 810篇 |
2013年 | 1732篇 |
2012年 | 1866篇 |
2011年 | 2358篇 |
2010年 | 1144篇 |
2009年 | 1005篇 |
2008年 | 2017篇 |
2007年 | 2026篇 |
2006年 | 2003篇 |
2005年 | 1868篇 |
2004年 | 1589篇 |
2003年 | 1384篇 |
2002年 | 1284篇 |
2001年 | 403篇 |
2000年 | 392篇 |
1999年 | 360篇 |
1998年 | 335篇 |
1997年 | 357篇 |
1996年 | 490篇 |
1995年 | 346篇 |
1994年 | 299篇 |
1993年 | 273篇 |
1992年 | 270篇 |
1991年 | 239篇 |
1990年 | 203篇 |
1989年 | 205篇 |
1988年 | 235篇 |
1987年 | 199篇 |
1986年 | 181篇 |
1985年 | 348篇 |
1984年 | 343篇 |
1983年 | 243篇 |
1982年 | 314篇 |
1981年 | 325篇 |
1980年 | 298篇 |
1979年 | 285篇 |
1978年 | 259篇 |
1977年 | 228篇 |
1976年 | 208篇 |
1975年 | 208篇 |
1974年 | 211篇 |
1973年 | 210篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
91.
Cun Feng Fan David A. Waldman Shaw Ling Hsu 《Journal of Polymer Science.Polymer Physics》1991,29(2):235-246
Raman mechanical spectroscopy was used to examine interfacial effects on the stress distribution in model polydiacetylene fiber/epoxy composites. Epoxy release agents were coated on fiber surfaces to modify the interfacial adhesion properties. The modified fiber surfaces were then characterized by scanning electron microscopy and x-ray photoelectron spectroscopy as well as optical microscopy. No difference in the maximum stress value or stress distribution was observed for the two types of fibers, coated or uncoated, used in composites. This suggests that adhesion properties at the composite interface do not affect tensile stress transfer efficiency nor, therefore, the composite tensile modulus along the fiber axis direction in uniaxial composites. Experimental data were also compared with theoretical calculations assuming perfect bonding between fiber and matrix, and idealized frictional force transfer mechanism at the fiber–matrix interface. 相似文献
92.
Future pathways for combinatorial chemistry 总被引:1,自引:0,他引:1
David Brown 《Molecular diversity》1997,2(4):217-222
Summary Investment in combinatorial chemistry (combichem) in the pharmaceutical industry is being driven by the need for increased efficiency. Results from pioneers in the field have demonstrated where mixture or discrete compound synthesis is useful, and what mixture sizes and compound concentrations are appropriate. To make the techniques of combichem of general utility in drug discovery, a broad range of advances is still required. Conversion of organic chemistry to solid phase conditions is key, as are developments in linkers and resins. Library design methodology requires further development. Combinatorial biosynthesis of focused libraries of natural products holds great promise for capitalising on hardwon natural product leads. Miniaturisation of screens is required to reduce the cost of screening combinatorial libraries. Developments in the processes preceding and following synthesis are required to enable the flow of increased numbers of compounds without new bottlenecks developing. The impact of combinatorial chemistry will be greatly enhanced by synergy with ongoing parallel developments in genetic technologies, screening technologies and bioinformatics. 相似文献
93.
94.
Asymptotics in the random assignment problem 总被引:1,自引:0,他引:1
David Aldous 《Probability Theory and Related Fields》1992,93(4):507-534
Summary We show that, in the usual probabilistic model for the random assignment problem, the optimal cost tends to a limit constant in probability and in expectation. The method involves construction of an infinite limit structure, in terms of which the limit constant is defined. But we cannot improve on the known numerical bounds for the limit.Research supported by NSF Grant MCS90-01710 相似文献
95.
96.
Eschweiler-Clarke methylations of both acyclic and cyclic polyamines can lead to methylation products of fragments of the original polyamine; thus 1,5,9,13-tetra-azatridecane yields 1,1,3,3-tetramethylpropanediamine exclusively and 1,5,9-triazacyclododecane gives 45% 1,5,9-trimethyl-1,5,9-triazacyclodecane and 45% 2,6,10-trimethyl-2,6,10-triazaundecane. 相似文献
97.
98.
99.
David Ruelle 《Communications in Mathematical Physics》2007,270(1):233-265
We analyze the dynamics of a simple but nontrivial classical Hamiltonian system of infinitely many coupled rotators. We assume
that this infinite system is driven out of thermal equilibrium either because energy is injected by an external force (Case
I), or because heat flows between two thermostats at different temperatures (Case II). We discuss several possible definitions
of the entropy production associated with a finite or infinite region, or with a partition of the system into a finite number
of pieces. We show that these definitions satisfy the expected bounds in terms of thermostat temperatures and energy flow. 相似文献
100.
Huayang Zhu Robert J. Kee Jeffrey R. Engel David T. Wickham 《Proceedings of the Combustion Institute》2007,31(2):1965-1972
This paper reports the results of experimental and modeling efforts to characterize partial oxidation of methane to produce synthesis gas (H2 and CO) using metal-substituted hexaaluminate catalysts in short-contact-time reactors. Hexaaluminate catalysts offer excellent high-temperature stability compared to the equivalent metal-based catalysts. The hexaaluminates are synthesized by a metal-exchange process using alumoxane precursors that enable a wide range of metal substitutions. Of all the combinations tested, RhSr-substituted hexaaluminates yielded the best performance. The catalysts are supported on alumina porous-foam structures, which are positioned within a tube furnace to control the operating temperature. Two-stage combinations of RhSr- and Ni-substituted hexaaluminates are shown to improve conversion activity and selectivity compared to a single-catalyst system. 相似文献