全文获取类型
收费全文 | 26563篇 |
免费 | 732篇 |
国内免费 | 146篇 |
专业分类
化学 | 18095篇 |
晶体学 | 140篇 |
力学 | 613篇 |
数学 | 4762篇 |
物理学 | 3831篇 |
出版年
2022年 | 161篇 |
2021年 | 302篇 |
2020年 | 355篇 |
2019年 | 369篇 |
2018年 | 257篇 |
2017年 | 225篇 |
2016年 | 553篇 |
2015年 | 514篇 |
2014年 | 559篇 |
2013年 | 1422篇 |
2012年 | 1286篇 |
2011年 | 1571篇 |
2010年 | 806篇 |
2009年 | 789篇 |
2008年 | 1383篇 |
2007年 | 1424篇 |
2006年 | 1371篇 |
2005年 | 1315篇 |
2004年 | 1149篇 |
2003年 | 997篇 |
2002年 | 902篇 |
2001年 | 391篇 |
2000年 | 309篇 |
1999年 | 276篇 |
1998年 | 302篇 |
1997年 | 334篇 |
1996年 | 378篇 |
1995年 | 258篇 |
1994年 | 306篇 |
1993年 | 287篇 |
1992年 | 264篇 |
1991年 | 258篇 |
1990年 | 196篇 |
1989年 | 238篇 |
1988年 | 244篇 |
1987年 | 209篇 |
1986年 | 205篇 |
1985年 | 307篇 |
1984年 | 347篇 |
1983年 | 234篇 |
1982年 | 381篇 |
1981年 | 349篇 |
1980年 | 328篇 |
1979年 | 325篇 |
1978年 | 335篇 |
1977年 | 308篇 |
1976年 | 292篇 |
1975年 | 265篇 |
1974年 | 263篇 |
1973年 | 240篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Physical aging in amorphous poly(ethylene furanoate): Enthalpic recovery,density, and oxygen transport considerations 下载免费PDF全文
Steven K. Burgess Christopher R. Mubarak Robert M. Kriegel William J. Koros 《Journal of Polymer Science.Polymer Physics》2015,53(6):389-399
The current work utilizes three separate techniques to study the physical aging process in amorphous poly(ethylene furanoate) (PEF), which is a recently introduced engineering thermoplastic with enhanced properties compared to petroleum‐sourced poly(ethylene terephthalate). Differential scanning calorimetry aging experiments were conducted at multiple aging temperatures and times, and the resultant enthalpic recovery values compared to the theoretical maximum enthalpy loss evaluated from calculations involving extrapolation of the equilibrium liquid line. Density measurements reveal densification of the matrix for the aged versus unaged samples, and provide an estimate for the reduction in free volume for the aged samples. Complementary oxygen permeation and pressure‐decay sorption experiments provide independent verification of the free volume reduction mechanism for physical aging in glassy polymers. The current work provides the first detailed aging study for PEF. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 389–399 相似文献
12.
13.
14.
Pan Huang Dawen Xu Robert M. Reich Felix Kaiser Boping Liu Fritz E. Kühn 《Tetrahedron letters》2019,60(24):1574-1577
A first example of an Et2Zn mediated silylation of 1-aklynes is reported. A series of functional groups are tolerated in this reaction. Mechanistic studies support Zn alkynilides as intermediates in the reaction. This reaction protocol provides a practical method for the preparation of alkynylsilanes and expands the application of organometallic zinc in organic synthesis. 相似文献
15.
Robert G. Parr 《International journal of quantum chemistry》1994,49(3):135-144
The helium atom in its ground state, subject to strong magnetic fields, is treated using a variational method. Trial functions consisting of Gaussians with nonlinear parameters variationally optimized are used. The form of these functions is a generalized s-symmetry-state properly modified to admit spatial deformation along the direction on which the magnetic field is applied. © 1994 John Wiley & Sons, Inc. 相似文献
16.
17.
18.
The Cauchy Problem for the relativistic Vlasov-Maxwell equations is studied in three space dimensions. It is assumed that the initial data satisfy the required constraints and have compact support. If in addition the data have sufficiently smallC
2 norm, then a uniqueC
1 solution to this system is shown to exist on all of spacetime.Research supported in part by NSF DMS 85-20662 and NSF DMS 84-20957 相似文献
19.
A practical access to alkyl- and aryl-substituted (E)-2-(azidomethyl)alkenoates and related azido compounds from the corresponding allylic bromides in aqueous acetone is described. An alternative method to obtain the starting bromides based on heterogeneous catalysis under mild conditions was also investigated. 相似文献
20.
Robert S. Strichartz 《Proceedings of the American Mathematical Society》2002,130(3):805-817
Harmonic mappings from the Sierpinski gasket to the circle are described explicitly in terms of boundary values and topological data. In particular, all such mappings minimize energy within a given homotopy class. Explicit formulas are also given for the energy of the mapping and its normal derivatives at boundary points.