全文获取类型
收费全文 | 14464篇 |
免费 | 2622篇 |
国内免费 | 2706篇 |
专业分类
化学 | 11000篇 |
晶体学 | 50篇 |
力学 | 225篇 |
综合类 | 126篇 |
数学 | 4957篇 |
物理学 | 3434篇 |
出版年
2024年 | 53篇 |
2023年 | 211篇 |
2022年 | 406篇 |
2021年 | 495篇 |
2020年 | 628篇 |
2019年 | 644篇 |
2018年 | 484篇 |
2017年 | 568篇 |
2016年 | 904篇 |
2015年 | 877篇 |
2014年 | 992篇 |
2013年 | 1386篇 |
2012年 | 1098篇 |
2011年 | 1095篇 |
2010年 | 927篇 |
2009年 | 1100篇 |
2008年 | 1076篇 |
2007年 | 1136篇 |
2006年 | 1012篇 |
2005年 | 801篇 |
2004年 | 645篇 |
2003年 | 603篇 |
2002年 | 401篇 |
2001年 | 343篇 |
2000年 | 354篇 |
1999年 | 245篇 |
1998年 | 230篇 |
1997年 | 234篇 |
1996年 | 121篇 |
1995年 | 105篇 |
1994年 | 94篇 |
1993年 | 70篇 |
1992年 | 54篇 |
1991年 | 46篇 |
1990年 | 42篇 |
1989年 | 31篇 |
1988年 | 32篇 |
1987年 | 28篇 |
1986年 | 17篇 |
1985年 | 29篇 |
1984年 | 24篇 |
1983年 | 9篇 |
1982年 | 23篇 |
1981年 | 21篇 |
1980年 | 17篇 |
1979年 | 14篇 |
1978年 | 22篇 |
1977年 | 15篇 |
1976年 | 9篇 |
1974年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 765 毫秒
91.
本文证明了:(1)Exchange环R的K0群的正向凸子群格同构于R的稳定余有限半本原理想格;(2)稳定有限、半本原的exchange环R是单的当且仅当它是K0-单的并且满足逼近弱s^*—可比性,推广了Goodearl,Ara等人的结果。 相似文献
92.
运用多种密度泛函理论 (DFT)和从头算 (abinitio)方法研究了草酰胺顺、反异构体的分子几何构型 ,结果表明Beck88交换函数与LYP非局域相关函数形成杂化的DFT方法B3LYP与MP2方法计算结果比较吻合。在此基础上选择B3LYP方法对草酰胺分子电子结构、红外光谱和前线分子轨道组成进行了系统研究 ;与实验事实对比分析了气态草酰胺分子中配位原子的反应活性 相似文献
93.
In this paper, we examine a class of convex problems of Bolza type, involving a time delay in the state. It encompasses a variety of time-delay problems arising in the calculus of variations and optimal control. A duality analysis is carried out which, among other things, leads to a characterization of minimizers in terms of the Euler-Lagrange inclusion. The results obtained improve in significant respects on what is achievable by techniques previously employed, based on elimination of the time delay by introduction of an infinite-dimensional state space or on the method of steps. 相似文献
94.
Considering a plane hyperbolic system with time-periodic coefficients, we construct a version of the direct Lyapunov method with the condition on the derivative of the Lyapunov functional along the trajectories of the system which is weakened by use of periodicity of the coefficients. We exhibit an illustrative example. 相似文献
95.
We propose objectives consisting of two mirrors with central holes for passage of a light beam. The optical layout ensures
multiple reflection of rays from both mirrors. We consider several approaches to calculating the design parameters for which
three and four aberrations do not occur. The objectives can be used in optical devices operating in the UV and IR regions
of the spectrum.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 267–270, March–April, 2007. 相似文献
96.
New variants of the generalized level method for minimization of convex nondifferentiable functions taking infinite values 总被引:1,自引:1,他引:0
N. A. Sokolov 《Computational Mathematics and Mathematical Physics》2007,47(12):1952-1969
New variants of the generalized level method for minimization of convex Lipschitz functions on a compact set with a nonempty interior are proposed. These variants include the well-known generalized and classical level methods. For the new variants, an estimate of the convergence rate is found, including the variants in which the auxiliary problems are solved approximately. 相似文献
97.
V. S. Klimov 《Mathematical Notes》2007,81(1-2):61-71
We study homology characteristics of critical values and extremals of Lipschitz functionals defined on bounded closed convex subsets of a reflexive space that are invariant under deformations. Sufficient conditions for the existence of a bifurcation point of a multivalued potential operator (the switch principle for the typical number of an extremal) are established. 相似文献
98.
Xin Tao YE Chong LI 《数学学报(英文版)》2007,23(1):65-76
The BCQ and the Abadie CQ for infinite systems of convex inequalities in Banach spaces are characterized in terms of the upper semi-continuity of the convex cones generated by the subdifferentials of active convex functions. Some relationships with other constraint qualifications such as the CPLV and the Slate condition are also studied. Applications in best approximation theory are provided. 相似文献
99.
Mihai V. Putz 《International journal of quantum chemistry》2006,106(2):361-389
A unified Mulliken valence with Parr ground‐state electronegativity picture is presented. It provides a useful analytical tool on which the absolute hardness as well ionization potential and electron affinity functionals are based. For all these chemical reactivity indices, systematic approximate density functionals are formulated within density functional softness theory and are applied to atomic systems. For the absolute hardness, a special relationship with the new electronegativity ansatz and a particular atomic trend paralleling the absolute electron affinity are established that should complement and augment the earlier finite‐difference energetic approach. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 相似文献
100.
Orotic acid (vitamin B13) is a key intermediate in biosynthesis of the pyrimidine nucleotides in living organisms, moreover, it may serve as the biological carrier for some metal ions. cis-Diammine(orotato)platinum(II), cis-[Pt(C5H2N2O4)(NH3)2] can be considered as a new potential cisplatin analogue. The FT-Raman and FT-IR spectra of the title complex are reported, for the first time. The molecular structure, vibrational frequencies, and the theoretical infrared and Raman intensities have been calculated by the density functional mPW1PW91 method. The detailed vibrational assignment has been made on the basis of the calculated potential energy distribution. The theoretically predicted IR and Raman spectra show very good agreement with experiment. Natural bond orbital (NBO) analyses were performed for cisplatin, carboplatin and the title complex. The results provided new data on the nature of platinum–ligand bonding in these compounds. Strong intramolecular hydrogen bond between the orotate ligand and the coordinated ammonia group stabilizes the structure of the platinum(II) complex. Thus, it is suggested that the orotate ligand in the title complex is more inert to the substitution reactions than the chloride ligands in cisplatin. 相似文献