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81.
用ab initio方法研究NaN_3的几何构型、电子结构和热力学、动力学性质 总被引:2,自引:0,他引:2
用abinitioMO方法,在MP2(ful)/6311G水平下,全优化计算了叠氮化钠(NaN3)分子的线状和环状两种稳定构型及其转化过渡态的几何参数、电荷分布、分子总能量和振动频率,并研究了它们的热力学性质及转化速率常数和平衡常数.结果表明,线状比环状构型稍稳定(能量低6.04kJ/mol);两者相互转化的能垒分别为13.15kJ/mol(线型→环状)和7.11kJ/mol(环状→线型).热力学和动力学计算均表明:NaN3通常主要以线型结构存在(占85%以上),且随温度升高而增多(在1000K大于91%). 相似文献
82.
New equations are derived and implemented for efficient and accurate computation of solvation energy derivatives for the conductor-like polarizable continuum model (C-PCM) and the isotropic integral equation formalism polarizable continuum model (IEF-PCM). Two new molecular surface tessellation procedures GEPOL-RT and GEPOL-AS that generate near continuous potential energy surfaces are proposed for PCM geometry optimization. The combined use of these new techniques leads to efficient and convergent geometry optimizations with the PCMs. 相似文献
83.
84.
Schlegel HB 《Journal of computational chemistry》2003,24(12):1514-1527
Potential energy surfaces form a central concept in the application of electronic structure methods to the study of molecular structures, properties, and reactivities. Recent advances in tools for exploring potential energy surfaces are surveyed. Methods for geometry optimization of equilibrium structures, searching for transition states, following reaction paths and ab initio molecular dynamics are discussed. For geometry optimization, topics include methods for large molecules, QM/MM calculations, and simultaneous optimization of the wave function and the geometry. Path optimization methods and dynamics based techniques for transition state searching and reaction path following are outlined. Developments in the calculation of ab initio classical trajectories in the Born-Oppenheimer and Car-Parrinello approaches are described. 相似文献
85.
A variational method for solving the time-independent single-particle Dirac equation in the Coulomb field of two nuclei is
described. A minimax variational principle and basis functions that have the proper analytic behavior, i.e. behave like r
γ,γ non-integer, in the neighborhood of a nucleus, are used. A momentum space integration scheme for computing the necessary
two-center integrals is described. Results are given for a standard test problem on two nuclei with Z=90 with an internuclear separation of 2.0/Z. The results confirm those of a previous calculation [F.A. Parpia and A.K. Mohanty, Chem Phys Lett 238: 209 (1995)].
Received: 13 May 1998 / Accepted: 22 June 1998 / Published online: 28 August 1998 相似文献
86.
Mauricio Alcolea Palafox Nerea Iza Manuel Gil Jos Luís Núez 《International journal of quantum chemistry》2002,89(1):25-47
A quantum chemical study of several complex monocyclic 4‐benzoyl‐4‐phenyl‐β‐lactam derivatives was carried out using cyclobutane, azetidine, 2‐azetidinone, 1‐methyl‐2‐azetidinone, and 3‐methyl‐2‐azetidinone as model compounds. The optimum geometry was obtained for the different conformations. The planarity of the ring was discussed in terms of the influence of the substituents on the amide resonance. To better analyze the amide resonance and the activity of the β‐lactam ring, a vibrational study was also carried out. To examine the influence of solvent polarity on the carbonyl bands, the Fourier transform–infrared (FT‐IR) spectra of the β‐lactam monocyclic derivatives were recorded in CCl4, C6H6, and CHCl3 solutions. The normal vibrations of the β‐lactam ring in the model compounds were characterized and used in the analysis of the β‐ring of more complex derivatives. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 相似文献
87.
四唑及其衍生物的理论研究Ⅷ: 硝氨四唑衍生物的从头算 总被引:3,自引:0,他引:3
运用从头计算法,在HF/6-31G^*水平下,全优化计算了7种硝氨四唑衍生物的分子几何和电子结构。结果表明,标题物的四唑环近似为平面构型;2H式中性分子的芳香性大于相应的1H式异构体。5-硝氨-1H四唑分子内氢键使硝氨基与环共面;其余标题物中硝氨基与环垂直。不同水平下的总能量计算表明,标题物中电子相关效应显著;1H式中性分子较2H式的能量高,5-硝氨四唑负离子在三个负离子中最稳定。根据电荷分布阐明了四唑环质子化位置和标题物与金属的配位方式。此外还计算了各标题物的红外光谱及热力学性质。 相似文献
88.
E. T. Denisov 《Russian Chemical Bulletin》2005,54(4):914-923
Interatomic distances in the reaction centers of the addition reactions of (i) H· to the C=C, C=O, N≡C, and C≡C bonds, (ii) ·CH3 radical to the C=C, C=O, and C≡C bonds, and (iii) alkyl, aminyl, and alkoxyl radicals to olefin C=C bonds were determined
using a new semiempirical method for calculating transition-state geometries of radical reactions. For all reactions of the
type X· + Y=Z → X— Y—Z· the r
#
X...Y distance in the transition state is a linear function of the enthalpy of reaction. Parameters of this dependence were determined
for seventeen classes of radical addition reactions. The bond elongation, Δr
#
X...Y, in the transition state decreases as the triplet repulsion, electronegativity difference between the atoms X and Y in the
reaction center, and the force constant of the attacked multiple bond increase.
__________
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 894–902, April, 2005. 相似文献
89.
Michael Aizenman FranÇois Delyon Bernard Souillard 《Journal of statistical physics》1980,23(3):267-280
We rigorously prove that the probabilityP
n
that the origin of ad-dimensional lattice belongs to a cluster of exactlyn sites satisfiesP
n
> exp(–n
(d–1)/d
) whenever percolation occurs. This holds for the usual (noninteracting) percolation models for any concentrationp > p
c
, as well as for the equilibrium states of lattice spin systems with quite general interactions. Such a lower bound applies also if no percolation occurs, but if it appears in some other phase of the system. 相似文献
90.
Crystal structure of the title compound, Cu(phen)(H2O)2·ClO4(phen=1,10-phenanthroline), was deter-mined by X-ray crystallography. It crystallizes in the monoclinic system, space group C2/c with lattice parameters a=1.49071(4)nm, b=1.38594(4)nm, c=0.70292(1)nm, β=108.509(1)° and Z=4; The Cu(Ⅰ) ion is chelated by a phen ligand and two aqua ligands in cis arrangement and assumes a C2 symmetric square-planar geometry with the CuN2O2 core. Eight Cu(phen)(H2O)2·ClO4 molecules are interconnected by strong hydrogen bonds between coordinated water molecules and uncoordinated perchlorate anions to form a molecular scale cavities along c axis. The bond distances of Cu-N and Cu-O are 0.2003(4)nm and 0.1973(3)nm, respectively. CCDC: 197600. 相似文献