全文获取类型
收费全文 | 17721篇 |
免费 | 2011篇 |
国内免费 | 984篇 |
专业分类
化学 | 8511篇 |
晶体学 | 70篇 |
力学 | 1435篇 |
综合类 | 79篇 |
数学 | 5692篇 |
物理学 | 4929篇 |
出版年
2024年 | 29篇 |
2023年 | 181篇 |
2022年 | 269篇 |
2021年 | 373篇 |
2020年 | 586篇 |
2019年 | 458篇 |
2018年 | 468篇 |
2017年 | 431篇 |
2016年 | 699篇 |
2015年 | 650篇 |
2014年 | 858篇 |
2013年 | 1557篇 |
2012年 | 990篇 |
2011年 | 977篇 |
2010年 | 757篇 |
2009年 | 1052篇 |
2008年 | 1026篇 |
2007年 | 1108篇 |
2006年 | 955篇 |
2005年 | 758篇 |
2004年 | 758篇 |
2003年 | 722篇 |
2002年 | 599篇 |
2001年 | 567篇 |
2000年 | 523篇 |
1999年 | 429篇 |
1998年 | 416篇 |
1997年 | 332篇 |
1996年 | 330篇 |
1995年 | 259篇 |
1994年 | 197篇 |
1993年 | 191篇 |
1992年 | 136篇 |
1991年 | 129篇 |
1990年 | 100篇 |
1989年 | 90篇 |
1988年 | 82篇 |
1987年 | 63篇 |
1986年 | 97篇 |
1985年 | 55篇 |
1984年 | 64篇 |
1983年 | 23篇 |
1982年 | 45篇 |
1981年 | 38篇 |
1980年 | 23篇 |
1979年 | 33篇 |
1978年 | 49篇 |
1977年 | 48篇 |
1976年 | 47篇 |
1974年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
221.
The Balancing Domain Decomposition algorithm uses in each iteration solution of local problems on the subdomains coupled with a coarse problem that is used to propagate the error globally and to guarantee that the possibly singular local problems are consistent. The abstract theory introduced recently by the first-named author is used to develop condition number bounds for conforming linear elements in two and three dimensions. The bounds are independent of arbitrary coefficient jumps between subdomains and of the number of subdomains, and grow only as the squared logarithm of the mesh size . Computational experiments for two- and three-dimensional problems confirm the theory.
222.
An energy-transport model is rigorously derived from the Boltzmann transport equation of semiconductors under the hypothesis that the energy gain or loss of the electrons by the phonon collisions is weak. Retaining at leading order electron-electron collisions and elastic collisions (i.e., impurity scattering and the elastic part of phonon collisions), a rigorous diffusion limit of the Boltzmann equation can be carried over, which leads to a set of diffusion equations for the electron density and temperature. The derivation is given in both the degenerate and nondegenerate cases. 相似文献
223.
For the multidimensional heat equation in a parallelepiped, optimal error estimates inL
2(Q) are derived. The error is of the order of +¦h¦2 for any right-hand sidef L
2(Q) and any initial function
; for appropriate classes of less regularf andu
0, the error is of the order of ((+¦h¦2
), 1/2<1.Translated fromMatematicheskie Zametki, Vol. 60, No. 2, pp. 185–197, August, 1996. 相似文献
224.
Olavi Nevanlinna 《BIT Numerical Mathematics》1996,36(4):775-785
We discuss the convergence of Krylov subspace methods for equationsx =Tx +f whereT is a sum of two operators,T =B +K, whereB is bounded andK is nuclear. Bounds are given for inf Q
k
(B+K) and for inf p
k
(B+K), where the infimum is over all polynomials of degreek, such thatQ
k
is monic andp
k
is normalized:p
k
(1) = 1. 相似文献
225.
In this paper, we present a general scheme for bundle-type algorithms which includes a nonmonotone line search procedure and for which global convergence can be proved. Some numerical examples are reported, showing that the nonmonotonicity can be beneficial from a computational point of view.This work was partially supported by the National Research Program on Metodi di ottimizzazione per le decisioni, Ministero dell' Universitá e della Ricerca Scientifica e Tecnologica and by ASI: Agenzia Spaziale Italiana. 相似文献
226.
A sensitive kinetic method for determining low levels of hydrazine has been described. The method is based on the measurement of the rate of the reaction between hydrazine and Mo(VI) in the presence of hydrochloric acid. The redox reaction was monitored spectrophotometrically at 710 nm. The variable-time and fixed-time methods were used. The calibration graph was linear for hydrazine concentrations of 1.0 × 10−4-1.4 × 10−2 M, using the fixed-time method of analysis. The method is simple, rapid, precise, sensitive and widely applicable. 相似文献
227.
228.
Burton A Elomari S Chen CY Medrud RC Chan IY Bull LM Kibby C Harris TV Zones SI Vittoratos ES 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(23):5737-5748
The syntheses, structure solutions, and physicochemical and catalytic characterizations of the novel zeolites SSZ-53 and SSZ-59 are described. SSZ-53 and SSZ-59 were synthesized under hydrothermal conditions with the [1-(4-fluorophenyl)cyclopentylmethyl]trimethyl ammonium cation and 1-[1-(4-chlorophenyl)cyclopentylmethyl]-1-methyl azocanium cation, respectively, as structure-directing agents. The framework topology of SSZ-53 was solved with the FOCUS method, and the structure of SSZ-59 was determined by model building. Rietveld refinement of synchrotron X-ray powder diffraction data confirms each proposed model. SSZ-53 and SSZ-59 each possess a one-dimensional channel system delimited by 14-membered rings. Results from transmission electron microscopy, electron diffraction, catalytic experiments (spaciousness index and constraint index tests), and argon and hydrocarbon adsorption experiments are consistent with the proposed structures. 相似文献
229.
Omar Deeb Prof. Monika Leibscher Dr. Jörn Manz Prof. Wulf von Muellern Tamar Seideman Prof. 《Chemphyschem》2007,8(2):322-328
We propose an approach for separating nuclear spin isomers with coherent light and illustrate it by numerical calculations using fulvene as a model system. The scheme employs the equivalence of torsion and interchange of equivalent H-atoms in a class of molecules of which fulvene is a simple example. The exchange symmetry couples with the rotational symmetry to produce a spatial distinction between the two photo-excited nuclear spin isomers, and wavepacket interferometry is applied to separate the species. 相似文献
230.
Dulal C. Ghosh 《Journal of Chemical Sciences》1984,93(1):33-46
A cndo/2D study of the charge distribution obtained through Mulliken population analysis in the ground state of the title
compounds shows that the features of charge distribution found by severalab initio calculations are fairly well reproduced by this method. The one-particle density, the interference density at the mid-point
of the bond axis and the kinetic part of the interference energy calculated through the deorthogonalized density matrices
over a wide range of intermolecular separation between the donor and the acceptor show that the one-particle density and the
interference density steadily grow with decreasing internuclear separation, while the kinetic interference energy starts with
negative value at large distance, then decreases and passes through a minima near but above the equilibrium distance and then
increases rapidly below it conforming to the characteristic general behaviour of the kinetic component of Morse curve. The
orbital pairwise interference density and the corresponding kinetic energy components reveal that the orbitals involved in
the covalent binding are σ2p AO of B and 2S and σ2p AO of N and C atoms in H3B-NH3 and H3B-CO respectively. 相似文献