全文获取类型
收费全文 | 241509篇 |
免费 | 16746篇 |
国内免费 | 642篇 |
专业分类
化学 | 152339篇 |
晶体学 | 3357篇 |
力学 | 10266篇 |
综合类 | 5篇 |
数学 | 23533篇 |
物理学 | 69397篇 |
出版年
2023年 | 4444篇 |
2022年 | 2482篇 |
2021年 | 3941篇 |
2020年 | 6237篇 |
2019年 | 4094篇 |
2018年 | 4962篇 |
2017年 | 3169篇 |
2016年 | 9043篇 |
2015年 | 7526篇 |
2014年 | 8295篇 |
2013年 | 13890篇 |
2012年 | 10106篇 |
2011年 | 9619篇 |
2010年 | 9209篇 |
2009年 | 8962篇 |
2008年 | 8843篇 |
2007年 | 8697篇 |
2006年 | 7802篇 |
2005年 | 6931篇 |
2004年 | 6454篇 |
2003年 | 5679篇 |
2002年 | 5503篇 |
2001年 | 6447篇 |
2000年 | 4944篇 |
1999年 | 3806篇 |
1998年 | 3049篇 |
1997年 | 3087篇 |
1996年 | 2833篇 |
1995年 | 2711篇 |
1994年 | 2522篇 |
1993年 | 2511篇 |
1992年 | 2748篇 |
1991年 | 2723篇 |
1990年 | 2633篇 |
1989年 | 2438篇 |
1988年 | 2516篇 |
1987年 | 2499篇 |
1985年 | 3004篇 |
1984年 | 3267篇 |
1983年 | 2693篇 |
1982年 | 2866篇 |
1981年 | 2848篇 |
1980年 | 2732篇 |
1979年 | 2815篇 |
1978年 | 2906篇 |
1977年 | 2974篇 |
1976年 | 3056篇 |
1975年 | 2847篇 |
1974年 | 2820篇 |
1973年 | 2884篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
本文讨论圆形区域内芽虫分布模型,特别研究了芽虫与天敌接触时产生与避免outbreak状态的可能性。 相似文献
143.
F. D. Saccone C. E. Rodrí guez Torres F. H. S nchez O. Gutfleisch 《Physica B: Condensed Matter》2002,320(1-4):312-315
In the present work, a quantitative analysis of the phase compositions by Mössbauer effect spectroscopy of solid and conventional hydrogen disproportionated Pr13.7Fe80.3B6.0 and Pr13.7Fe63.5Co16.7Zr0.1B6.0 alloys was carried out. Significant amounts of intermediate borides t-Fe3B and Pr(Fe, Co)12B6 were detected after solid hydrogen disproportionation treatment in Pr13.7Fe80.3B6.0 and Pr13.7Fe63.5Co16.7Zr0.1B6.0 alloys, respectively. After conventional hydrogenation–disproportionation–desorption–recombination treatment these phases were not detected and in no case residual Pr2Fe14B-phase was found. It was observed that the amount of intermediate borides after disproportionation can be correlated with the degree of texture after recombination at various temperatures. 相似文献
144.
145.
The Gelfand-Zetlin basis is adapted toSU(N)
q
forq a root of unit. Extra parameters are incorporated in the matrix elements of the generators to obtain all the invariants corresponding to the augmented center. A crucial identity is derived and proved, which guarantees the periodicity of the action of the generators. Full periodicity is relaxed by stages, some raising and lowering operators remaining injective while others become nilpotent with corresponding changes in the dimension of the representation. In the extreme case of highest weight representations. all the raising and lowering operators are nilpotent. As an alternative approach an auxiliary algebra giving all the periodic representations is presented. An explicit solution of this system forN=3, while fully equivalent to the G.-Z. basis, turns out to be much simpler. 相似文献
146.
V. N. Volynets D. I. Slovetskii A. Ya. Strochkov V. N. Trofimov 《Journal of Applied Spectroscopy》1991,54(6):613-619
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 6, pp. 1004–1010, June, 1991. 相似文献
147.
148.
Numerical methods for ordinary initial value problems that do not depend on special properties of the system are usually found in the class of linear multistage multivalue methods, first formulated by J.C. Butcher. Among these the explicit methods are easiest to implement. For these reasons there has been considerable research activity devoted to generating methods of this class which utilize independent function evaluations that can be performed in parallel. Each such group of concurrent function evaluations can be regarded as a stage of the method. However, it turns out that parallelism affords only limited opportunity for reducing the computing time with such methods. This is most evident for the simple linear homogeneous constant-coefficient test problem, whose solution is essentially a matter of approximating the exponential by an algebraic function. For a given number of stages and a given number of saved values, parallelism offers a somewhat enlarged set of algebraic functions from which to choose. However, there is absolutely no benefit in having the degree of parallelism (number of processors) exceed the number of saved values of the method. Thus, in particular, parallel one-step methods offer no speedup over serial one-step methods for the standard linear test problem. Although the implication of this result for general nonlinear problems is unclear, there are indications that dramatic speedups are not possible in general. Also given are some results relevant to the construction of methods.Work supported in part by National Science Foundation grants DMS 89 11410 and DMS 90 15533 and by US Department of Energy grant DOE DEFG02-87ER25026. Work of the second author was completed while at the University of Illinois. 相似文献
149.
150.
The elastic constants of dilute alloys based on bcc metals have been calculated using the Green’s function method obtaining
explicit expressions for change in elastic constants in terms oft-matrix. The crystal impurity problem is discussed within an impurity model containing central and non-central force constant
changes extended up to second neighbours of the impurity. The effect of volume change on elastic constants and a contribution
from electron pressure term are considered. Numerical results for changes in three elastic moduli have been presented for
a number of dilute alloys based on Mo, Nb, W, Ta and V. 相似文献