全文获取类型
收费全文 | 8397篇 |
免费 | 350篇 |
国内免费 | 53篇 |
专业分类
化学 | 5780篇 |
晶体学 | 74篇 |
力学 | 217篇 |
综合类 | 1篇 |
数学 | 960篇 |
物理学 | 1170篇 |
无线电 | 598篇 |
出版年
2023年 | 70篇 |
2022年 | 79篇 |
2021年 | 169篇 |
2020年 | 165篇 |
2019年 | 136篇 |
2018年 | 111篇 |
2017年 | 100篇 |
2016年 | 226篇 |
2015年 | 200篇 |
2014年 | 253篇 |
2013年 | 434篇 |
2012年 | 580篇 |
2011年 | 623篇 |
2010年 | 355篇 |
2009年 | 288篇 |
2008年 | 535篇 |
2007年 | 561篇 |
2006年 | 568篇 |
2005年 | 545篇 |
2004年 | 461篇 |
2003年 | 373篇 |
2002年 | 298篇 |
2001年 | 132篇 |
2000年 | 96篇 |
1999年 | 78篇 |
1998年 | 76篇 |
1997年 | 96篇 |
1996年 | 132篇 |
1995年 | 78篇 |
1994年 | 85篇 |
1993年 | 76篇 |
1992年 | 61篇 |
1991年 | 41篇 |
1990年 | 29篇 |
1989年 | 37篇 |
1988年 | 47篇 |
1987年 | 29篇 |
1986年 | 35篇 |
1985年 | 71篇 |
1984年 | 48篇 |
1983年 | 29篇 |
1982年 | 56篇 |
1981年 | 34篇 |
1980年 | 29篇 |
1979年 | 28篇 |
1978年 | 37篇 |
1977年 | 32篇 |
1976年 | 25篇 |
1975年 | 24篇 |
1974年 | 24篇 |
排序方式: 共有8800条查询结果,搜索用时 17 毫秒
991.
Absintholide is a new guaianolide dimer whose structure and stereochemistry has been elucidated on the basis of high resolution n.m.r. 相似文献
992.
Eric Foxley 《BIT Numerical Mathematics》1968,8(2):104-121
In the early days of computing, special machines were built for solving logical (as opposed to numerical) problems. Experience in several significant problems of Mathematical logic has indicated that a general purpose machine can be used simply and effectively, provided a powerful programming language is available. 相似文献
993.
The cyclic-shift tensor-factorization interpolation method recently described by de Boor can be used in particular for least-squares fitting of multivariate data on a rectangular grid and for evaluation of the resulting tensor-product splines, taking advantage of existing linear algebra and univariate spline software. We discuss the computational details of this method, pointing out variants and suggesting techniques for dealing with ill-conditioned least-squares problems. 相似文献
994.
995.
Patrick W. O'Connor Steven Tomsovic Eric J. Heller 《Journal of statistical physics》1992,68(1-2):131-152
We review some of the issues facing semiclassical methods in classically chaotic systems, then demonstrate the long-time accuracy of semiclassical propagation of a nonstationary wave packet using the quantum baker's map of Balazs and Voros. We show why some of the standard arguments against the efficacy of semiclassical dynamics for long-time chaotic motion are incorrect. 相似文献
996.
997.
998.
999.
1000.
Dry chitosan is an excellent candidate for facilitated transport membranes that can be utilized in industrial applications, such as fuel cell operations and other purification processes. This article is the first to report temperature effects on transport properties of CO2, H2, and N2 in a gas mixture typical of such applications. At a feed pressure of 1.5 atm, CO2 permeabilities increased (0.381–26.1 barrers) at temperatures of 20–150 °C with decreasing CO2/N2 (19.7–4.55) and CO2/H2 (3.14–1.71) separation factors. The pressure effect on solubilities and permeabilities were fitted to the extended dual mode model and its corresponding mixed gas permeation model. The dual mode and transport parameters, the sorption heats and the activation energies of Henry's and Langmuir's regimes and their pre‐exponential parameters were determined. The Langmuir's capacity constants were utilized to estimate chitosan's glass transition temperature (CO2: 172 °C, N2: 175 °C, and H2: 171 °C). The activation energies of diffusion in the Henry's law and Langmuir regimes were dependent on the collision diameter of the gases. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2620–2631, 2007 相似文献