全文获取类型
收费全文 | 7298篇 |
免费 | 191篇 |
国内免费 | 160篇 |
专业分类
化学 | 1336篇 |
晶体学 | 68篇 |
力学 | 41篇 |
综合类 | 19篇 |
数学 | 5446篇 |
物理学 | 739篇 |
出版年
2023年 | 35篇 |
2022年 | 58篇 |
2021年 | 53篇 |
2020年 | 66篇 |
2019年 | 160篇 |
2018年 | 142篇 |
2017年 | 88篇 |
2016年 | 80篇 |
2015年 | 105篇 |
2014年 | 202篇 |
2013年 | 340篇 |
2012年 | 232篇 |
2011年 | 462篇 |
2010年 | 374篇 |
2009年 | 430篇 |
2008年 | 443篇 |
2007年 | 503篇 |
2006年 | 386篇 |
2005年 | 248篇 |
2004年 | 197篇 |
2003年 | 212篇 |
2002年 | 196篇 |
2001年 | 141篇 |
2000年 | 136篇 |
1999年 | 178篇 |
1998年 | 195篇 |
1997年 | 168篇 |
1996年 | 163篇 |
1995年 | 209篇 |
1994年 | 158篇 |
1993年 | 164篇 |
1992年 | 154篇 |
1991年 | 92篇 |
1990年 | 92篇 |
1989年 | 112篇 |
1988年 | 63篇 |
1987年 | 49篇 |
1986年 | 53篇 |
1985年 | 76篇 |
1984年 | 72篇 |
1983年 | 55篇 |
1982年 | 67篇 |
1981年 | 43篇 |
1980年 | 41篇 |
1979年 | 43篇 |
1978年 | 44篇 |
1977年 | 17篇 |
1976年 | 17篇 |
1975年 | 11篇 |
1974年 | 10篇 |
排序方式: 共有7649条查询结果,搜索用时 15 毫秒
121.
Kullback-Leibler divergence and the Neyman-Pearson lemma are two fundamental concepts in statistics. Both are about likelihood ratios: Kullback-Leibler divergence is the expected log-likelihood ratio, and the Neyman-Pearson lemma is about error rates of likelihood ratio tests. Exploring this connection gives another statistical interpretation of the Kullback-Leibler divergence in terms of the loss of power of the likelihood ratio test when the wrong distribution is used for one of the hypotheses. In this interpretation, the standard non-negativity property of the Kullback-Leibler divergence is essentially a restatement of the optimal property of likelihood ratios established by the Neyman-Pearson lemma. The asymmetry of Kullback-Leibler divergence is overviewed in information geometry. 相似文献
122.
New tools are introduced for the study of homogeneous continua. The subcontinua of a given continuum are classified into three types: filament, non-filament, and ample, with ample being a subcategory of non-filament. The richness of the collection of ample subcontinua of a homogeneous continuum reflects where the space lies in the gradation from being locally connected at one extreme to indecomposable at another. Applications are given to the general theory of homogeneous continua and their hyperspaces. 相似文献
123.
T. Radul 《Topology and its Applications》2007,154(8):1794-1798
R. Pol has shown that for every countable ordinal number α there exists a universal space for separable metrizable spaces X with trindX?α. W. Olszewski has shown that for every countable limit ordinal number λ there is no universal space for separable metrizable space with trIndX?λ. T. Radul and M. Zarichnyi have proved that for every countable limit ordinal number there is no universal space for separable metrizable spaces with dimWX?α where dimW is a transfinite extension of covering dimension introduced by P. Borst. We prove the same result for another transfinite extension dimC of the covering dimension.As an application, we show that there is no absorbing sets (in the sense of Bestvina and Mogilski) for the classes of spaces X with dimCX?α belonging to some absolute Borel class. 相似文献
124.
The non-resonant third-order non-linear optical properties of amorphous Ge20As25Se55 films were studied experimentally by the method of the femtosecond optical heterodyne detection of optical Kerr effect. The real and imaginary parts of complex third-order optical non-linearity could be effectively separated and their values and signs could be also determined, which were 6.6 × 10−12 and −2.4 × 10−12 esu, respectively. Amorphous Ge20As25Se55 films showed a very fast response in the range of 200 fs under ultrafast excitation. The ultrafast response and large third-order non-linearity are attributed to the ultrafast distortion of the electron orbitals surrounding the average positions of the nucleus of Ge, As and Se atoms. The high third-order susceptibility and a fast response time of amorphous Ge20As25Se55 films makes it a promising material for application in advanced techniques especially in optical switching. 相似文献
125.
The subject of this paper is a characterization of the -definable set functions of Kripke-Platek set theory with infinity and a uniform version of axiom of choice: . This class of functions is shown to coincide with the collection of set functionals of type 1 primitive recursive in a
given choice functional and . This goal is achieved by a G?del Dialectica-style functional interpretation of and a computability proof for the involved functionals.
Received October 9, 1996 相似文献
126.
127.
We study the large-time behavior and rate of convergence to the invariant measures of the processes dX
(t)=b(X)
(t)) dt + (X
(t)) dB(t). A crucial constant appears naturally in our study. Heuristically, when the time is of the order exp( – )/2 , the transition density has a good lower bound and when the process has run for about exp( – )/2, it is very close to the invariant measure. LetL
=(2/2) – U · be a second-order differential operator on d. Under suitable conditions,L
z has the discrete spectrum
- \lambda _2^\varepsilon ...and lim \varepsilon ^2 log \lambda _2^\varepsilon = - \Lambda \hfill \\ \varepsilon \to 0 \hfill \\ \end{gathered} $$
" align="middle" vspace="20%" border="0"> 相似文献
128.
Jenó Szigeti 《Order》1990,7(1):77-81
Given a linearly ordered set (A,
R
) and an R-monotone function f: AA, we give a necessary and sufficient condition on A, f,
R
, involving generating sets and forbidden subalgebras, for
R
to be a well-ordering.Partially supported by Hungarian National Foundation for Scientific Research Grant nr. 1813. 相似文献
129.
Martin Schlichenmaier 《Letters in Mathematical Physics》1990,19(2):151-165
Krichever-Novikov algebras of meromorphic vector fields with more than two poles on higher genus Riemann surfaces are introduced. The structure of these algebras and their induced modules of forms of weight is studied. 相似文献
130.
In this paper, we describe an algorithm to stably sort an array ofn elements using only a linear number of data movements and constant extra space, albeit in quadratic time. It was not known previously whether such an algorithm existed. When the input contains only a constant number of distinct values, we present a sequence ofin situ stable sorting algorithms makingO(n lg(k+1)
n+kn) comparisons (lg(K) means lg iteratedk times and lg* the number of times the logarithm must be taken to give a result 0) andO(kn) data movements for any fixed valuek, culminating in one that makesO(n lg*n) comparisons and data movements. Stable versions of quicksort follow from these algorithms.Research supported by Natural Sciences and Engineering Research Council of Canada grant No.A-8237 and the Information Technology Research Centre of Ontario.Supported in part by a Research Initiation Grant from the Virginia Engineering Foundation. 相似文献
|