全文获取类型
收费全文 | 46230篇 |
免费 | 814篇 |
国内免费 | 324篇 |
专业分类
化学 | 22030篇 |
晶体学 | 424篇 |
力学 | 1953篇 |
综合类 | 16篇 |
数学 | 11401篇 |
物理学 | 11544篇 |
出版年
2023年 | 127篇 |
2022年 | 298篇 |
2021年 | 397篇 |
2020年 | 364篇 |
2019年 | 371篇 |
2018年 | 1573篇 |
2017年 | 1770篇 |
2016年 | 1400篇 |
2015年 | 1071篇 |
2014年 | 1042篇 |
2013年 | 1852篇 |
2012年 | 4201篇 |
2011年 | 3565篇 |
2010年 | 2538篇 |
2009年 | 2251篇 |
2008年 | 1693篇 |
2007年 | 1753篇 |
2006年 | 1540篇 |
2005年 | 5272篇 |
2004年 | 4611篇 |
2003年 | 2941篇 |
2002年 | 1015篇 |
2001年 | 599篇 |
2000年 | 364篇 |
1999年 | 361篇 |
1998年 | 267篇 |
1997年 | 196篇 |
1996年 | 221篇 |
1995年 | 179篇 |
1994年 | 162篇 |
1993年 | 145篇 |
1992年 | 270篇 |
1991年 | 236篇 |
1990年 | 219篇 |
1989年 | 191篇 |
1988年 | 162篇 |
1987年 | 113篇 |
1986年 | 100篇 |
1985年 | 151篇 |
1984年 | 128篇 |
1983年 | 87篇 |
1982年 | 105篇 |
1981年 | 102篇 |
1980年 | 105篇 |
1979年 | 103篇 |
1978年 | 105篇 |
1976年 | 156篇 |
1975年 | 111篇 |
1974年 | 95篇 |
1973年 | 98篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
通过数值求解一维瞬态受激布里渊散射(SBS)声光耦合波方程,从理论上分析了泵浦激光参数及光学材料参数对SBS过程发生阈值的影响。以SBS过程中建立起来的应力场抗拉(压)强度和散射场的反射率为判据,分析了激光脉宽及作用区域长度对激光超声破坏材料效果的影响,探讨了短脉冲激光(约ns)引起的激光超声对材料的破坏机理;讨论了通过参数配置有效遏制SBS过程激光超声对光学材料的破坏问题。 相似文献
92.
A closed microwave digestion method followed by inductively coupled plasma spectrometric (ICP-MS) analysis was evaluated for the determination of trace impurities in photoresist. To optimize the digestion procedure, several digestion parameters such as acid, heating temperature and heating time were evaluated. Besides, the digestion efficiency of used photoresist material and the recovery of analyte elements obtained by the use of gravimetric method and ICP-MS measurement, individually, were also compared to clarify the completeness of digestion. According to our experiments, the gravimetric method was found to be not so relevant to the completeness of digestion, because the remaining sample matrix could cause suppression effect in the subsequent ICP-MS measurement. In view of minimizing blank value and working time, a simple single-step heating program was proposed to mineralize 0.25 ml of photoresist material with 5 ml of nitric acid at 180 °C for 10 min. Based on the comparative study of the analytical results obtained by instrumental neutron activation analysis (INAA) and proposed method, the reliability of proposed method for the determination of trace metallic impurities in photoresist material has been confirmed. 相似文献
93.
Ewa Stró?yna 《Journal of Differential Equations》2003,193(1):239-259
We solve completely the problem of classification of germs of complex planar vector fields with nilpotent singularity with respect to formal orbital equivalence. 相似文献
94.
Jean-François Burnol 《Comptes Rendus Mathematique》2003,336(11):919-924
Dyson has associated with the Fredholm determinants of the even (resp. odd) Dirichlet kernels a Schrödinger equation on the half-axis and has used, in tandem, the Gel'fand–Levitan and Marchenko methods of inverse scattering theory to study the asymptotics of these determinants. We have proposed following our unearthing of the conductor operator to seek to realize the Fourier transform itself as a scattering, and we obtain here to this end two Dirac systems on the entire real axis which are intrinsically associated, respectively, to the cosine and to the sine transforms. To cite this article: J.-F. Burnol, C. R. Acad. Sci. Paris, Ser. I 336 (2003). 相似文献
95.
Formation of p-type ZnO film on InP substrate by phosphor doping 总被引:3,自引:0,他引:3
Kyu-Hyun Bang Deuk-Kyu Hwang Min-Chul Park Young-Don Ko Ilgu Yun Jae-Min Myoung 《Applied Surface Science》2003,210(3-4):177-182
ZnO thin film was initially deposited on InP substrate by radio frequency (rf) magnetron sputtering and the diffusion process was performed using the closed ampoule technique where Zn3P2 was used as the dopant source. To verify the junction formation of ZnO thin films, the electrical properties were measured, and the effects of Zn3P2 diffusion on ZnO thin films were investigated. It is observed that the electrical property of the film is changed from n-type to p-type by dopant diffusion effect. Based on the results, it is confirmed that ZnO thin films can be a potential candidate for ultraviolet (UV) optical devices. 相似文献
96.
Parameters of Gaussian multivariate models are often estimated using the maximum likelihood approach. In spite of its merits, this methodology is not practical when the sample size is very large, as, for example, in the case of massive georeferenced data sets. In this paper, we study the asymptotic properties of the estimators that minimize three alternatives to the likelihood function, designed to increase the computational efficiency. This is achieved by applying the information sandwich technique to expansions of the pseudo-likelihood functions as quadratic forms of independent normal random variables. Theoretical calculations are given for a first-order autoregressive time series and then extended to a two-dimensional autoregressive process on a lattice. We compare the efficiency of the three estimators to that of the maximum likelihood estimator as well as among themselves, using numerical calculations of the theoretical results and simulations. 相似文献
97.
In this paper, by using elementary analysis, we establish some new Lyapunov-type inequalities for nonlinear systems of differential equations, special cases of which contain the well-known equations such as Emden-Fowler-type and half-linear equations. The inequalities obtained here can be used as handy tools in the study of qualitative behaviour of solutions of the associated equations. 相似文献
98.
99.
René Meziat Diego Patiño Pablo Pedregal 《Computational Optimization and Applications》2007,38(1):147-171
We propose an alternative method for computing effectively the solution of non-linear, fixed-terminal-time, optimal control
problems when they are given in Lagrange, Bolza or Mayer forms. This method works well when the nonlinearities in the control
variable can be expressed as polynomials. The essential of this proposal is the transformation of a non-linear, non-convex
optimal control problem into an equivalent optimal control problem with linear and convex structure. The method is based on
global optimization of polynomials by the method of moments. With this method we can determine either the existence or lacking
of minimizers. In addition, we can calculate generalized solutions when the original problem lacks of minimizers. We also
present the numerical schemes to solve several examples arising in science and technology. 相似文献
100.
E. Beinrohr M. Németh P. Tsch?pel G. T?lg 《Fresenius' Journal of Analytical Chemistry》1992,344(3):93-99
Summary Flow-through electrochemical cells with porous working electrodes made of crushed reticulated vitreous carbon and plated with mercury were used for absolute analysis of trace amounts of lead by anodic stripping coulometry with collection (ASCWC) in a flow system. The role of mercury coating, flow rate and pH were investigated. The coulombic content of the collection peak corresponded to the theoretical values calculated by Faraday's law in a concentration range from about 10–9 to 10–6 mol/l. The relative error and the relative standard deviation was +0.15% and 0.8%, respectively for 2×10–6 mol/l analyte concentration. The absolute detection limit (3 s) was 0.1 ng of Pb, the linear response range 7×104.
One leave from: Department of Analytical Chemistry, Slovak Technical University, CS-812 37 Bratislava, Czechoslovakia 相似文献