全文获取类型
收费全文 | 5041篇 |
免费 | 393篇 |
国内免费 | 499篇 |
专业分类
化学 | 1551篇 |
晶体学 | 18篇 |
力学 | 368篇 |
综合类 | 47篇 |
数学 | 2255篇 |
物理学 | 1694篇 |
出版年
2024年 | 7篇 |
2023年 | 95篇 |
2022年 | 116篇 |
2021年 | 110篇 |
2020年 | 99篇 |
2019年 | 127篇 |
2018年 | 110篇 |
2017年 | 133篇 |
2016年 | 139篇 |
2015年 | 103篇 |
2014年 | 227篇 |
2013年 | 396篇 |
2012年 | 229篇 |
2011年 | 289篇 |
2010年 | 265篇 |
2009年 | 284篇 |
2008年 | 301篇 |
2007年 | 356篇 |
2006年 | 307篇 |
2005年 | 255篇 |
2004年 | 252篇 |
2003年 | 219篇 |
2002年 | 182篇 |
2001年 | 140篇 |
2000年 | 131篇 |
1999年 | 147篇 |
1998年 | 118篇 |
1997年 | 94篇 |
1996年 | 78篇 |
1995年 | 95篇 |
1994年 | 64篇 |
1993年 | 55篇 |
1992年 | 50篇 |
1991年 | 48篇 |
1990年 | 29篇 |
1989年 | 28篇 |
1988年 | 35篇 |
1987年 | 32篇 |
1986年 | 18篇 |
1985年 | 26篇 |
1984年 | 17篇 |
1983年 | 13篇 |
1982年 | 13篇 |
1981年 | 17篇 |
1980年 | 17篇 |
1979年 | 14篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1975年 | 8篇 |
1973年 | 7篇 |
排序方式: 共有5933条查询结果,搜索用时 15 毫秒
21.
潘继斌 《数学的实践与认识》2006,36(2):182-185
研究了基于支持向量机的后验概率的应用,提出了对样本集进行分解,以产生局部后验概率,根据模式的稳健性对局部后验概率进行凸组合融合的方法. 相似文献
22.
We analyze the statistical behavior of signals in nonlinear circuits with delayed feedback in the presence of external Markovian noise. For the special class of circuits with intense phase mixing we develop an approach for the computation of the probability distributions and multitime correlation functions based on the random phase approximation. Both Gaussian and Kubo-Andersen models of external noise statistics are analyzed and the existence of the stationary (asymptotic) random process in the long-time limit is shown. We demonstrate that a nonlinear system with chaotic behavior becomes a noise amplifier with specific statistical transformation properties. 相似文献
23.
Thomas Marlow 《International Journal of Theoretical Physics》2006,45(7):1247-1257
We attempt a justification of a generalisation of the consistent histories programme using a notion of probability that is valid for all complete sets of history propositions. This consists of introducing Cox's axioms of probability theory and showing that our candidate notion of probability obeys them. We also give a generalisation of Bayes' theorem and comment upon how Bayesianism should be useful for the quantum gravity/cosmology programmes.
PACS: 02.50.Cw;03.65.Ta;04.60.-m. 相似文献
24.
B—模糊集合代数和广义互信息公式 总被引:1,自引:0,他引:1
基于两种概率的区分,推导出了一个广义Shannon熵公式和一个广义互信息公式。后者和模糊性有关,并且柯用于语言和感觉中的信息度量。为了由原子语句为真的条件概率求出合语句为真的条件概率,提出了一个遵循存尔运算的模糊集合代数。所谓的模糊信息被还原为概率信息。新的理论在经典理论-概率论,集合论及Shannon信息论-的基础上容易理解。 相似文献
25.
This paper presents detailed information on the experience gained during the attempts to model a set of transitional flows
due to boundary layer separation. These flows are developed on a flat plate with a semi-circular leading edge and they have
been coded by the ERCOFTAC Special Interest Group on Transition, as T3L flows. Different freestream velocities and turbulence
intensities configure these transitional flows and, by consequence, govern the transition mechanism, resulting in larger or
smaller transitional regions. The modeling of the T3L flows has been performed by adopting a low-Reynolds number second-moment
closure turbulence model. The results showed satisfactory agreement with the experimental measurements, although some difficulties
regarding successful convergence have been faced. The final conclusion is that turbulence modeling can present quite accurate
results for transitional flows without any additional use of ad-hoc modifications or additional equations based on various
transition models and intermittency transport modeling. 相似文献
26.
Stochastic mechanism of relaxation, in which a dipole waits until a favourable condition for reorientation exists, is discussed. Assuming that an imposed direction of a dipole moment may be changed when a migrating defect reaches the dipole, we present a mathematically rigorous scheme relating the local random characteristics of a macroscopic system to its effective relaxation behaviour. We derive a relaxation function (the Burr survival probability) that is characterized by the stretched exponential or the power-law behaviour. 相似文献
27.
Summary Multiconfigurational second order perturbation theory (CASSCF/CASPT2) has been used to investigate the dependence of computed valence excitation energies and transition moments on the basis sets. Pyrazine has been selected as the test molecule. Atomic normal orbital (ANO) type basis sets are used throughout. Contractions of the structure (4s3p1d/2s) are found to be an optimal compromise between the quality and the size of the calculations and are capable of yielding results virtually identical to more extended basis sets. 相似文献
28.
有序分组资料的线性趋势检验主要用于检验几个二项总体反应率的线性趋势;在医学与生物学中最典型的用途是研究剂量和反应的关系. 如果用Z检验来代替通常在本检验中所用的卡方检验,就可容易地导出本检验的确切概率计算方法,和其他2×C有序列联表有着相同的形式.本文给出了该检验的确切概率计算方法. 相似文献
29.
Marko D. Mihovilovic Bernhard Müller Markus Spina Arjumand I. Durrani Peter Stanetty Georg Dazinger Karl Kirchner 《Monatshefte für Chemie / Chemical Monthly》2006,137(6):785-794
Summary. Recombinant Escherichia coli overexpressing Pseudomonas sp. NCIMB 9872 cyclopentanone monooxygenase (CPMO, EC 1.14.13.16) and Acinetobacter sp. NCIMB 9871 cyclohexanone monooxygenase (CHMO, EC 1.14.13.22) have been utilized in whole-cell Baeyer-Villiger biotransformations of prochiral bicycloketones. A significant difference in substrate acceptance and stereoselectivity was
observed for bicyclo[3.3.0] and bicyclo[4.3.0] substrates. A plausible mechanism of these transformations was established
by means of high level DFT/B3LYP calculations suggesting an essential difference in electronic requirements for a successful
enzymatic conversion, which was similarly encountered in recombinant whole-cell mediated biooxidations. Some of the lactones
produced in the biocatalytic Baeyer-Villiger oxidation represent key intermediates for the synthesis of indole alkaloids. 相似文献
30.
In survival or reliability studies, the mean residual life or life expectancy is an important characteristic of the model. Whereas the failure rate can be expressed quite simply in terms of the mean residual life and its derivative, the inverse problem—namely that of expressing the mean residual life in terms of the failure rate—typically involves an integral of a complicated expression. In this paper, we obtain simple expressions for the mean residual life in terms of the failure rate for certain classes of distributions which subsume many of the standard cases. Several results in the literature can be obtained using our approach. Additionally, we develop an expansion for the mean residual life in terms of Gaussian probability functions for a broad class of ultimately increasing failure rate distributions. Some examples are provided to illustrate the procedure. 相似文献