全文获取类型
收费全文 | 3309篇 |
免费 | 892篇 |
国内免费 | 318篇 |
专业分类
化学 | 680篇 |
晶体学 | 7篇 |
力学 | 231篇 |
综合类 | 56篇 |
数学 | 768篇 |
物理学 | 2777篇 |
出版年
2024年 | 3篇 |
2023年 | 29篇 |
2022年 | 68篇 |
2021年 | 59篇 |
2020年 | 86篇 |
2019年 | 81篇 |
2018年 | 87篇 |
2017年 | 109篇 |
2016年 | 121篇 |
2015年 | 123篇 |
2014年 | 206篇 |
2013年 | 259篇 |
2012年 | 202篇 |
2011年 | 267篇 |
2010年 | 202篇 |
2009年 | 201篇 |
2008年 | 272篇 |
2007年 | 244篇 |
2006年 | 203篇 |
2005年 | 193篇 |
2004年 | 152篇 |
2003年 | 154篇 |
2002年 | 168篇 |
2001年 | 145篇 |
2000年 | 133篇 |
1999年 | 138篇 |
1998年 | 105篇 |
1997年 | 69篇 |
1996年 | 62篇 |
1995年 | 42篇 |
1994年 | 32篇 |
1993年 | 43篇 |
1992年 | 33篇 |
1991年 | 31篇 |
1990年 | 30篇 |
1989年 | 21篇 |
1988年 | 25篇 |
1987年 | 19篇 |
1986年 | 15篇 |
1985年 | 11篇 |
1984年 | 16篇 |
1983年 | 10篇 |
1982年 | 14篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1973年 | 2篇 |
排序方式: 共有4519条查询结果,搜索用时 15 毫秒
71.
3d‐Metal mononitrides are studied using the density functional theory method. The lowest spin state for these dimers is obtained using the B3LYP hybrid functional with the 6‐311+G* basis set. The equilibrium geometries, vibrational frequencies, binding energies, Mulliken, and natural orbital population analysis charges, natural orbital electronic configuration, electron affinity, and ionization potential are obtained. Mulliken as well as natural orbital population analysis charges indicate that for all dimers, in cations most of the positive charge localized on the transition metal atom where in anions most of the negative charge localized on nitrogen atom. The binding energies for 3d‐metal mononitrides are higher than those for monocarbides and monoxides. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
72.
73.
Frank J.S. Wang 《Stochastic Processes and their Applications》1977,5(2):173-193
Consider a population consisting of one type of individual living in a fixed region with area A. In [8], we constructed a stochastic population model in which the death rate is affected by the age of the individual and the birth rate is affected by the population density PA(t), i.e., the population size divided by the area A of the given region. In [8], we proposed a continuous deterministic model which in general is a nonlinear Volterra type integral equation and proved that under appropriate conditions the sequence PA(t) would converge to the solution P(t) of our integral equation in the sense that .In this paper, we obtain a “central limit theorem” for the random element √A(PA(t)?P(t)). We prove that under appropriate conditions √A(PA(t)?P(t)) will converge to a Gaussian process. (See Theorem 3.4 for the explicit formula of this Gaussian process.) 相似文献
74.
Diaminocarboxylic acid carrier ampholytes, such as L-histidine, 2,3-diaminopropionic acid, L-ornithine, and L-lysine, were reacted with glycerol-1,3-diglycidyl ether (GDGE) and poly(vinyl alcohol) (PVA) in the presence of sodium hydroxide to produce hydrolytically and mechanically stable hydrogels, supported on a PVA substrate, for use as buffering membranes in isoelectric trapping (IET) separations. The pH values of the DACAPVA membranes were determined with the help of small-molecule pI markers and proteins and were found to be in the 6 < pH < 8.5 range. The membranes were successfully used to isoelectrically trap small ampholytes, desalt ampholyte solutions in IET mode, and effect the binary separation of chicken egg white proteins. 相似文献
75.
邻位吡啶自由基多通道分解反应的动力学和反应机理研究 总被引:1,自引:0,他引:1
Utilizing Gaussian94 program package, all species involved in decomposition reactions of o-pyridyl radical were optimized fully at B3LYP/6-311++G^** level. Intrinsic reaction coordinate calculations were employed to confirm the connections of the transition states and products, and transition states were ascertained by the number of imaginary frequency (0 or 1). The reaction mechanism was elucidated by the vibrational mode analysis and electronic population analysis, and the reaction rate constants were calculated with transition state theory. 相似文献
76.
N. M. Avram Gh. E. Drgnescu M. R. Kibler 《International journal of quantum chemistry》2002,88(3):303-309
The coupling between doubly degenerate electronic states and doubly degenerate vibrations is analyzed for an octahedral system on the basis of the introduction of an anharmonic Morse potential for the vibronic part. The vibrations are described by anharmonic coherent states and their linear coupling with the electronic states is considered. The matrix elements of the vibronic interaction are built and the energy levels corresponding to the interaction Hamiltonian derived. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 相似文献
77.
本文评述了近年来4-氧-2,2,6,6-四甲基哌啶-1-氧自由基(TMPO)和2,2,5,5-四甲基吡咯啉-1-氧自由基(TMPRO)及其衍生物在合成和应用方面的进展,着重讨论了这些氮氧自由基的合成方法和作为自旋标记试剂的应用。 相似文献
78.
The capillary gas chromatography of the C2-C5 lower aliphatic aldehydes (e.g.,acetaldehyde, propionaldehyde, n- and i-butyraldehydes, n- and i-valeraldehydes) which, in the free form in air, have unpleasant odors and low threshold odor values, has been studied using cold-trap preconcentration with liquid oxygen. The capillary column outlet was connected to enable simultaneous detection by FID, ECD, FPD AND FTD (SID). 相似文献
79.
Mild methods for controlled C- and N-alkylation of 3-benzyloxycarbonylpiperazine-2,5-diones are reported. The benzyloxylcarbonyl substituent can also serve as latent functionality for N-acyliminium ion formation and subsequent trapping enables installation of new carbon and/or heteroatom substituents. 相似文献
80.
For lattices with two kinds of points (black and white), distributed according to a translation-invariant joint probability distribution, we study statistical properties of the sequence of consecutive colors encountered by a random walker moving through the lattice. The probability distribution for the single steps of the walk is considered to be independent of the colors of the points. Several exact results are presented which are valid in any number of dimensions and for arbitrary probability distributions for the coloring of the points and the steps of the walk. They are used to derive a few general properties of random walks on lattices containing traps.Presented at the Symposium on Random Walks, Gaithersburg, MD, June 1982. 相似文献