全文获取类型
收费全文 | 41598篇 |
免费 | 1435篇 |
国内免费 | 1616篇 |
专业分类
化学 | 19611篇 |
晶体学 | 551篇 |
力学 | 1845篇 |
综合类 | 136篇 |
数学 | 10680篇 |
物理学 | 11826篇 |
出版年
2023年 | 113篇 |
2022年 | 214篇 |
2021年 | 230篇 |
2020年 | 294篇 |
2019年 | 421篇 |
2018年 | 1463篇 |
2017年 | 1721篇 |
2016年 | 1112篇 |
2015年 | 957篇 |
2014年 | 970篇 |
2013年 | 1621篇 |
2012年 | 3886篇 |
2011年 | 3073篇 |
2010年 | 2466篇 |
2009年 | 2091篇 |
2008年 | 1239篇 |
2007年 | 1231篇 |
2006年 | 1170篇 |
2005年 | 4932篇 |
2004年 | 4378篇 |
2003年 | 2830篇 |
2002年 | 1131篇 |
2001年 | 831篇 |
2000年 | 462篇 |
1999年 | 412篇 |
1998年 | 261篇 |
1997年 | 189篇 |
1996年 | 172篇 |
1995年 | 157篇 |
1994年 | 147篇 |
1993年 | 118篇 |
1992年 | 288篇 |
1991年 | 273篇 |
1990年 | 228篇 |
1989年 | 225篇 |
1988年 | 189篇 |
1987年 | 132篇 |
1986年 | 128篇 |
1985年 | 168篇 |
1984年 | 153篇 |
1983年 | 124篇 |
1982年 | 118篇 |
1981年 | 120篇 |
1979年 | 127篇 |
1978年 | 98篇 |
1977年 | 119篇 |
1976年 | 158篇 |
1975年 | 124篇 |
1974年 | 132篇 |
1973年 | 145篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
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
83.
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
84.
The SmF_(2.01)was synthesized by reducing SmF_3 in H_2 stream.As it was doped inKM_gF_3 and KCaF_3.there was emission of Sm~(2+) in KMgF_3 but no emission of Sm~(2+) inKCaF_3 was observed. 相似文献
85.
86.
Chu-Li Fu Xiang-Tuan Xiong Zhi Qian 《Journal of Mathematical Analysis and Applications》2007,331(1):472-480
In this paper a simple and convenient new regularization method for solving backward heat equation—Fourier regularization method is given. Meanwhile, some quite sharp error estimates between the approximate solution and exact solution are provided. A numerical example also shows that the method works effectively. 相似文献
87.
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
88.
Celik Tarimci Anda? Karamustafa Kutalmi? Güven Mehmet Kabak Akgül Ye?ilada 《Analytical sciences》2003,19(9):1347-1348
The crystal structure of 1-[3-(3,4-dimethoxyphenyl)-2-propenoyl]pyrrolidine (C15H19NO3) (I) has been determined by X-ray analysis. It crystallizes orthorhombic space group Pbca with a = 24.295(3), b = 15.086(3), c = 7.552(3)A, V = 2768(1)A3, Z = 8, Dcalc = 1.254 g/cm3, mu = (Mo K(alpha)) = 0.87 cm(-1). The title compound has analgesic activity of cycloaliphatic amine part. The molecule is deviated from planar configuration. 相似文献
89.
设H为复的可分无限维Hilbert空间,称有界线性算子T为强不可约的,如果与T可交换的幂等算子只有0和I.王宗尧、蒋春澜、纪有清等人证明了在任何一个套的套代数中都存在大量的强不可约算子,并且找到了它们的酉轨道闭包.本文考虑有限个套的张量积的代数中强不可约算子的存在性问题。证明了:对复平面上任何一个连通完备集σ、总存在一个对角算子N和它的一个范数可以任意小的紧摄动T=X+K,使得T是一个强不可约算子、T在有限个良序套的张量积的代数中,并且σ(T)=σlre(T)=σ(N)=σlre(N)=σ进一步,文章还对具有单点谱的算子和良序套与正交补为良序套的张量积的代数进行了讨论,得到了一些结果. 相似文献
90.
We introduce and investigate the properties of Hochschild cohomology of algebras in an abelian monoidal category M. We show that the second Hochschild cohomology group of an algebra in M classifies extensions of A up to an equivalence. We characterize algebras of Hochschild dimension 0 (separable algebras), and of Hochschild dimension ≤1 (formally smooth algebras). Several particular cases and applications are included in the last section of the paper. 相似文献