全文获取类型
收费全文 | 5616篇 |
免费 | 445篇 |
国内免费 | 445篇 |
专业分类
化学 | 549篇 |
晶体学 | 12篇 |
力学 | 717篇 |
综合类 | 114篇 |
数学 | 4324篇 |
物理学 | 790篇 |
出版年
2024年 | 8篇 |
2023年 | 68篇 |
2022年 | 83篇 |
2021年 | 76篇 |
2020年 | 122篇 |
2019年 | 143篇 |
2018年 | 158篇 |
2017年 | 166篇 |
2016年 | 188篇 |
2015年 | 169篇 |
2014年 | 255篇 |
2013年 | 434篇 |
2012年 | 281篇 |
2011年 | 303篇 |
2010年 | 231篇 |
2009年 | 332篇 |
2008年 | 358篇 |
2007年 | 356篇 |
2006年 | 318篇 |
2005年 | 298篇 |
2004年 | 254篇 |
2003年 | 243篇 |
2002年 | 224篇 |
2001年 | 176篇 |
2000年 | 175篇 |
1999年 | 159篇 |
1998年 | 137篇 |
1997年 | 108篇 |
1996年 | 103篇 |
1995年 | 68篇 |
1994年 | 81篇 |
1993年 | 43篇 |
1992年 | 57篇 |
1991年 | 41篇 |
1990年 | 35篇 |
1989年 | 32篇 |
1988年 | 23篇 |
1987年 | 25篇 |
1986年 | 21篇 |
1985年 | 18篇 |
1984年 | 28篇 |
1983年 | 8篇 |
1982年 | 20篇 |
1981年 | 14篇 |
1980年 | 10篇 |
1979年 | 15篇 |
1978年 | 9篇 |
1977年 | 13篇 |
1976年 | 14篇 |
1973年 | 2篇 |
排序方式: 共有6506条查询结果,搜索用时 0 毫秒
101.
An expectation value approach to calculations of first-order properties using the non-iterative, triple-excitation amplitudes
in the coupled cluster wave function is exploited. Three methods are suggested and analysed using the many body perturbation
theory (MBPT) expansion arguments. The first method, in which non-iterative triple-excitation amplitudes are used in the expression
for the expectation values, makes the wave function accurate through the second order of MBPT. In the second method, which
is an extension of the first, effects of triple-excitation amplitudes are coupled with single- and double-excitation amplitudes.
The correlated density matrix equivalent through the fourth order to that obtained when CCSDT-la amplitudes are used is employed
in the third method. The suggested methods are tested on dipole moment and polarizability calculations for several diatomic
closed-shell molecules and are compared to other related approaches.
Received: 15 May 1997 / Accepted: 5 June 1997 相似文献
102.
Summary Analytical peak-shape equations were derived for first-order reversible reactions occurring in a chromatographic reactor by
treating the reversible reactions as consecutive reactions with alternating products. The results of the analytical peak-shape
equations were compared with those from a numerical solution of the partial differential equation system modeling the chromatographic
reactor. For small to medium conversions the correspondence was found to be sufficiently close to enable substitution of the
numerical solution in fitting procedures for the determination of rate constants.
Presented at the 21st ISC held in Stuttgart, Germany, 15th–20th September, 1996 相似文献
103.
计算机辅助高效液相色谱(HPLC)分离条件优化可以低成本、快速地得到优化的分离条,因而已较为广泛地用于复杂样品的分离分析。基于移动重叠分离图方法,又发展了一种新型的多台阶梯度分离条件的优化方法可调移动重叠分离图法。该方法通过预测不同流动相条件下各组分的保留时间、峰宽和分离度,绘制出对于样品中各组分的重叠分离区域图。在对当前台阶流动相组成进行优化的同时,考虑其对后面一到两个台阶上流出组分保留的影响,实时地重新绘制对于后面台阶上流出组分的重叠分离区域图。通过观察当前台阶流动相条件对当前台阶和后面台阶上流出组分分离的影响,综合考虑样品中所有组分的分离情况,找到更接近全局最优的分离条件。通过扫描的方法对优化得到的分离条件进行微调,能够进一步提高分离效果。采用文献数据对可调移动重叠分离图法的应用加以说明,在二元流动相体系下,证明了该方法在HPLC方法建立方面的优越性。 相似文献
104.
Christian Borgs Roman Kotecký Salvador Miracle-Solé 《Journal of statistical physics》1991,62(3-4):529-551
Recently, Borgs and Kotecký developed a rigorous theory of finite-size effects near first-order phase transitions. Here we apply this theory to the ferromagneticq-state Potts model, which (forq large andd2) undergoes a first-order phase transition as the inverse temperature is varied. We prove a formula for the internal energy in a periodic cube of side lengthL which describes the rounding of the infinite-volume jumpE in terms of a hyperbolic tangent, and show that the position of the maximum of the specific heat is shifted by
m
(L)=(Inq/E)L
–d
+O(L
–2d
) with respect to the infinite-volume transition point
t
. We also propose an alternative definition of the finite-volume transition temperature
t
(L) which might be useful for numerical calculations because it differs only by exponentially small corrections from
t
. 相似文献
105.
C. I. J. M. Stuart 《Foundations of Physics Letters》1991,4(5):479-492
Aprediction puzzle leads to a form ofnecessary realism which forces the rejection of a central tenet of the Copenhagen interpretation. This leads to reconsidering conceptual difficulties related to Bell's locality premise. It is shown that aparadox of elementary probability theory puts new light on Bell's assumption that causality and statistical independence are mutually incompatible.
Nemo dat quod non habet : No one can offer more than he has ability to give; in that spirit, this paper is dedicated to the memory of J.S. Bell. 相似文献
106.
Chu-In Charles Lee 《Annals of the Institute of Statistical Mathematics》1992,44(1):107-120
The Laplace continued fraction is derived through a power series. It provides both upper bounds and lower bounds of the normal tail probability % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbqefm0B1jxALjhiov2D% aebbfv3ySLgzGueE0jxyaibaiGc9yrFr0xXdbba91rFfpec8Eeeu0x% Xdbba9frFj0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs% 0dXdbPYxe9vr0-vr0-vqpWqaaeaabiGaciaacaqabeaadaqaaqGaaO% qaaiqbfA6agzaaraaaaa!3DC0!\[\bar \Phi\](x), it is simple, it converges for x>0, and it is by far the best approximation for x3. The Laplace continued fraction is rederived as an extreme case of admissible bounds of the Mills' ratio, % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbqefm0B1jxALjhiov2D% aebbfv3ySLgzGueE0jxyaibaiGc9yrFr0xXdbba91rFfpec8Eeeu0x% Xdbba9frFj0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs% 0dXdbPYxe9vr0-vr0-vqpWqaaeaabiGaciaacaqabeaadaqaaqGaaO% qaaiqbfA6agzaaraaaaa!3DC0!\[\bar \Phi\](x)/(x), in the family of ratios of two polynomials subject to a monotone decreasing absolute error. However, it is not optimal at any finite x. Convergence at the origin and local optimality of a subclass of admissible bounds are investigated. A modified continued fraction is proposed. It is the sharpest tail bound of the Mills' ratio, it has a satisfactory convergence rate for x1 and it is recommended for the entire range of x if a maximum absolute error of 10-4 is required.The efforts of the author were supported by the NSERC of Canada. 相似文献
107.
We present a study of finite-size effects in a model exhibiting a first-order temperature-driven symmetry-breaking structural phase transition in theL
× cylindrical geometry in theL
limit. Exact studies demonstrate the applicability of our scaling ansatz even in the one-dimensional limit, making this model ideal for studying finite-size effects. The scaling ansatz, similar to the previously developed ansatz for field-driven transitions, demonstrates that latent heat is crucial in driving these transitions. This ansatz is supported by a 2×2 phenomenological transfer matrix based upon the symmetries of the system; this produces an analytic free energy which has the scaling form. Order parameter probability distributions show that the high- and low-temperature phases coexist only in a small finite-size-affected regime near the bulk transition temperature; this regime vanishes exponentially fast asL
diverges. 相似文献
108.
A. Linnemann 《Journal of Optimization Theory and Applications》1982,38(4):483-511
In this paper, we present a unified theory of first-order and higher-order necessary optimality conditions for abstract vector optimization problems in normed linear spaces. We prove general multiplier rules, from which nearly all known first-order, second-order, and higher-order necessary conditions can be derived. In the last section, we prove higher-order necessary conditions for semi-infinite programming problems.This work was developed within the Forschungsschwerpunkt Dynamische Systeme, Universität Bremen, Bremen, West Germany.The author wishes to thank Prof. Dr. D. Hinrichsen for his helpful remarks and discussions during the preparation of this work. 相似文献
109.
同分布NA列Jamison型加权和强稳定的充要条件 总被引:3,自引:1,他引:3
本文将Jamison等(1965)关于iid列加权和强稳定的充分性结果推广到NA列的场合并且得到了NA列Jamison型加权和强稳定的必要性结果。 相似文献
110.