全文获取类型
收费全文 | 8834篇 |
免费 | 685篇 |
国内免费 | 562篇 |
专业分类
化学 | 1843篇 |
晶体学 | 16篇 |
力学 | 613篇 |
综合类 | 184篇 |
数学 | 5512篇 |
物理学 | 1913篇 |
出版年
2023年 | 92篇 |
2022年 | 119篇 |
2021年 | 172篇 |
2020年 | 191篇 |
2019年 | 222篇 |
2018年 | 152篇 |
2017年 | 249篇 |
2016年 | 274篇 |
2015年 | 158篇 |
2014年 | 381篇 |
2013年 | 631篇 |
2012年 | 383篇 |
2011年 | 403篇 |
2010年 | 347篇 |
2009年 | 498篇 |
2008年 | 549篇 |
2007年 | 516篇 |
2006年 | 481篇 |
2005年 | 408篇 |
2004年 | 295篇 |
2003年 | 302篇 |
2002年 | 311篇 |
2001年 | 268篇 |
2000年 | 262篇 |
1999年 | 242篇 |
1998年 | 219篇 |
1997年 | 200篇 |
1996年 | 163篇 |
1995年 | 121篇 |
1994年 | 111篇 |
1993年 | 98篇 |
1992年 | 96篇 |
1991年 | 70篇 |
1990年 | 67篇 |
1989年 | 47篇 |
1988年 | 51篇 |
1987年 | 65篇 |
1986年 | 29篇 |
1985年 | 122篇 |
1984年 | 111篇 |
1983年 | 61篇 |
1982年 | 98篇 |
1981年 | 105篇 |
1980年 | 70篇 |
1979年 | 68篇 |
1978年 | 56篇 |
1977年 | 38篇 |
1976年 | 30篇 |
1974年 | 19篇 |
1973年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
A. Deptuła T. Olczak W. Łada B. Sartowska A.G. Chmielewski C. Alvani P.L. Carconi A. Di Bartolomeo F. Pierdominici S. Casadio 《Journal of Sol-Gel Science and Technology》2003,26(1-3):207-212
Microspheres of Li2TiO3 were fabricated by a classical, inorganic sol-gel process from commercially available TiCl4. Elaborated process consists of the following main steps: (1) dissolving of TiCl4 in concentrated aqueous HCl and addition of LiOH; (2) formation of sol emulsion in 2-ethylhexanol-1 containing the surfactant SPAN-80 (EH); (3) gelation of emulsion drops by extraction of water with partially dehydrated EH; (4) impregnation of gel to Li:Ti molar ratio MR = 2; (5) thermal treatment at 1200°C in order to receive chloride free product. This temperature can be significantly lowered (to 750°C) by dechlorination starting solution TiCl4 by chemical treatment of the with nitric acid to form of nitrate-stabilized titania sols. Tritium release from sol-gel made Li2TiO3 microspheres were found very close to that observed for other traditional materials, however for the first sample process starts slightly earlier. 相似文献
122.
Correlated multivariate processes have a dependence structure which must be taken into account when estimating the covariance matrix. The natural estimator of the covariance matrix is introduced and is shown that to be biased under the dependence structure. This bias is studied under two different asymptotic models, namely increasing the domain by increasing the number of observations, and increasing the number of observations in the fixed domain. Using the first asymptotic model, we quantify the convergence rate of the bias and of the covariance between the components of the estimated covariance matrix. The second asymptotic model serves to derive a fast and accurate bias correction. As shown, under mild hypotheses, the asymptotic normality of the estimated covariance matrix holds and can be used to test whether the bias is significant, for example, in the sense that the eigenvectors of the estimated and true covariance matrices are significantly different. 相似文献
123.
The best-r-point-average (BRPA) estimator of the maximizer of a regression function, proposed in Changchien (in: M.T. Chao, P.E. Cheng (Eds.), Proceedings of the 1990 Taipei Symposium in Statistics, June 28–30, 1990, pp. 63–78) has certain merits over the estimators derived through the estimation of the regression function. Some of the properties of the BRPA estimator have been studied in Chen et al. (J. Multivariate Anal. 57 (1996) 191) and Bai and Huang (Sankhya: Indian J. Statist. Ser. A. 61 (Pt. 2) (1999) 208–217). In this article, we further study the properties of the BRPA estimator and give its convergence rate under some quite general conditions. Simulation results are presented for the illustration of the convergence rate. Some comparisons with existing estimators such as the Müller estimator are provided. 相似文献
124.
For the purpose of testing the spherical uniformity based on i.i.d. directional data (unit vectors) zi, i=1,…,n, Anderson and Stephens (Biometrika 59 (1972) 613–621) proposed testing procedures based on the statistics Smax=maxu S(u) and Smin=minu S(u), where u is a unit vector and nS(u) is the sum of squares of u′zi's. In this paper, we also consider another test statistic Srange=Smax−Smin. We provide formulas for the P-values of Smax, Smin, Srange by approximating tail probabilities of the limiting null distributions by means of the tube method, an integral-geometric approach for evaluating tail probability of the maximum of a Gaussian random field. Monte Carlo simulations for examining the accuracy of the approximation and for the power comparison of the statistics are given. 相似文献
125.
线性规划的符号跟踪算法 总被引:2,自引:1,他引:1
分析了只含一个约束条件的线性规划最优基变量的特征,将其运用到搜寻含m个约束条件的线性规划的最优基变量,从而提出了线性规划的符号跟踪算法,为线性规划求解提供了新途径。 相似文献
126.
Non-compact generalized variational inequalities for quasi-monotone and hemi-continuous operators with applications 总被引:1,自引:0,他引:1
Some results are obtained for non-compact cases in topological vector spaces for the existence problem of solutions for some
set-valued variational inequalities with quasi-monotone and lower hemi-continuous operators, and with quasi-semi-monotone
and upper hemi-continuous operators. Some applications are given in non-reflexive Banach spaces for these existence problems
of solutions and for perturbation problems for these set-valued variational inequalities with quasi-monotone and quasi-semi-monotone
operators.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
127.
Stefan Jaschke Claudia Klüppelberg Alexander Lindner 《Journal of multivariate analysis》2004,88(2):252-273
We derive results on the asymptotic behavior of tails and quantiles of quadratic forms of Gaussian vectors. They appear in particular in delta–gamma models in financial risk management approximating portfolio returns. Quantile estimation corresponds to the estimation of the Value-at-Risk, which is a serious problem in high dimension. 相似文献
128.
129.
给出模糊半群上的模糊同余的概念,并进一步研究它的一些基本代数性质。同时研究带有模糊半群上的模糊同余扩张性质(FCEPF)的半群类,得到一个半群有模糊半群上的模糊同余扩张性质、有模糊同余扩张性质(FCEP)、有同余扩张性质(CEP)三个条件是等价的。 相似文献
130.
This paper considers the estimation problem for a trigonometric regression model with the noise specified by the Ornstein–Uhlenbeck
process with unknown parameter. We propose a sequential procedure which ensures a prescribed mean square precision uniformly
in the nuisance parameter. The asymptotic behaviour of the procedure duration mean has been studied.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献