全文获取类型
收费全文 | 25536篇 |
免费 | 547篇 |
国内免费 | 104篇 |
专业分类
化学 | 14327篇 |
晶体学 | 161篇 |
力学 | 785篇 |
综合类 | 9篇 |
数学 | 3508篇 |
物理学 | 7397篇 |
出版年
2023年 | 117篇 |
2022年 | 326篇 |
2021年 | 395篇 |
2020年 | 372篇 |
2019年 | 322篇 |
2018年 | 409篇 |
2017年 | 370篇 |
2016年 | 631篇 |
2015年 | 532篇 |
2014年 | 616篇 |
2013年 | 990篇 |
2012年 | 1279篇 |
2011年 | 1451篇 |
2010年 | 815篇 |
2009年 | 765篇 |
2008年 | 1221篇 |
2007年 | 1215篇 |
2006年 | 1093篇 |
2005年 | 1530篇 |
2004年 | 1558篇 |
2003年 | 1092篇 |
2002年 | 732篇 |
2001年 | 616篇 |
2000年 | 562篇 |
1999年 | 351篇 |
1998年 | 294篇 |
1997年 | 299篇 |
1996年 | 366篇 |
1995年 | 322篇 |
1994年 | 320篇 |
1993年 | 337篇 |
1992年 | 331篇 |
1991年 | 271篇 |
1990年 | 226篇 |
1989年 | 213篇 |
1988年 | 185篇 |
1987年 | 181篇 |
1986年 | 182篇 |
1985年 | 239篇 |
1984年 | 226篇 |
1983年 | 195篇 |
1982年 | 197篇 |
1981年 | 187篇 |
1980年 | 174篇 |
1979年 | 157篇 |
1978年 | 178篇 |
1977年 | 146篇 |
1976年 | 136篇 |
1974年 | 141篇 |
1973年 | 127篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Hubert de Fraysseix 《Discrete Applied Mathematics》2007,155(9):1079-1095
Using a general resolution of barycentric systems we give a generalization of Tutte's theorem on convex drawing of planar graphs. We deduce a characterization of the edge coverings into pairwise non-crossing paths which are stretchable: such a system is stretchable if and only if each subsystem of at least two paths has at least three free vertices (vertices of the outer face of the induced subgraph which are internal to none of the paths of the subsystem). We also deduce that a contact system of pseudo-segments is stretchable if and only if it is extendible. 相似文献
103.
Ivan Nunes da Silva Wagner Caradori do AmaralLucia Valeria de Arruda 《Applied Mathematical Modelling》2007
This paper presents an efficient approach based on recurrent neural network for solving nonlinear optimization. More specifically, a modified Hopfield network is developed and its internal parameters are computed using the valid subspace technique. These parameters guarantee the convergence of the network to the equilibrium points that represent an optimal feasible solution. The main advantage of the developed network is that it treats optimization and constraint terms in different stages with no interference with each other. Moreover, the proposed approach does not require specification of penalty and weighting parameters for its initialization. A study of the modified Hopfield model is also developed to analyze its stability and convergence. Simulation results are provided to demonstrate the performance of the proposed neural network. 相似文献
104.
Detection of hepatocarcinoma in rats by integration of the fluorescence spectrum: Experimental model
J. C. Marcassa J. Ferreira S. Zucoloto O. de Castro e Silva Jr. L. G. Marcassa V. S. Bagnato 《Laser Physics》2006,16(5):827-832
The incorporation of spectroscopic techniques into diagnostic procedures may greatly improve the chances for precise diagnostics. One promising technique is fluorescence spectroscopy, which has recently been used to detect many different types of diseases. In this work, we use laser-induced tissue fluorescence to detect hepatocarcinoma in rats using excitation light at wavelengths of 443 and 532 nm. Hepatocarcinoma was induced chemically in Wistar rats. The collected fluorescence spectrum ranges from the excitation wavelength up to 850 nm. A mathematical procedure carried out on the spectrum determines a figure of merit value, which allows the detection of hepatocarcinoma. The figure of merit involves a procedure which evaluates the ratio between the backscattered excitation wavelength and the broad emission fluorescence band. We demonstrate that a normalization allowed by integration of the fluorescence spectra is a simple operation that may allow the detection of hepatocarcinoma. 相似文献
105.
In this paper, we study the central limit theorem and its weak invariance principle for sums of a stationary sequence of random
variables, via a martingale decomposition. Our conditions involve the conditional expectation of sums of random variables
with respect to the distant past. The results contribute to the clarification of the central limit question for stationary
sequences.
Magda Peligrad is supported in part by a Charles Phelps Taft research support grant at the Univeristy of Cincinnati and the
NSA grant H98230-05-1-0066. 相似文献
106.
107.
Vanessa de Freitas Cunha Lins Geraldo Francisco de Andrade Reis Carlos Roberto de Araujo 《Applied Surface Science》2006,253(5):2875-2884
In this work, electrochemical impedance spectroscopy and linear polarization are used in determining porosity of zinc phosphates, and of nickel and manganese modified zinc phosphates on electrogalvanized steel. The porosity of the phosphate layers ranges from 0.1% for the manganese-modified hopeite to 8% for hopeite, using the linear polarization and the electrochemical impedance spectroscopy techniques. The porosity values measured using the two techniques were in agreement. All impedance spectra of coated samples showed two steps, with two capacitive arcs and an inductive looping. 相似文献
108.
Rafael Tiedra de Aldecoa 《Annales Henri Poincare》2006,7(1):105-124
Although many physical arguments account for using a modified definition of time delay in multichannel-type scattering processes,
one can hardly find rigorous results on that issue in the literature. We try to fill in this gap by showing, both in an abstract
setting and in a short-range case, the identity of the modified time delay and the Eisenbud-Wigner time delay in waveguides.
In the short-range case we also obtain limiting absorption principles, state spectral properties of the total Hamiltonian,
prove the existence of the wave operators and show an explicit formula for the S-matrix. The proofs rely on stationary and commutator methods.
Communicated by Yosi Avron
submitted 12/04/05, accepted 13/05/05 相似文献
109.
110.
Venzo de Sabbata P. I. Pronin C. Sivaram 《International Journal of Theoretical Physics》1991,30(12):1671-1678
We consider the possibility of finding experimental evidence of the fifth force with the measurement of a phase shift of neutron beams via an interferometric apparatus and also a possible rotation of the polarization plane of polarized neutron beams when torsion is introduced in a gravitational field. 相似文献