全文获取类型
收费全文 | 42163篇 |
免费 | 1546篇 |
国内免费 | 1305篇 |
专业分类
化学 | 19545篇 |
晶体学 | 455篇 |
力学 | 1905篇 |
综合类 | 122篇 |
数学 | 10709篇 |
物理学 | 12278篇 |
出版年
2023年 | 190篇 |
2022年 | 271篇 |
2021年 | 371篇 |
2020年 | 409篇 |
2019年 | 396篇 |
2018年 | 1489篇 |
2017年 | 1776篇 |
2016年 | 1269篇 |
2015年 | 1046篇 |
2014年 | 1119篇 |
2013年 | 1548篇 |
2012年 | 4085篇 |
2011年 | 3356篇 |
2010年 | 2466篇 |
2009年 | 2157篇 |
2008年 | 1272篇 |
2007年 | 1243篇 |
2006年 | 1119篇 |
2005年 | 4881篇 |
2004年 | 4335篇 |
2003年 | 2678篇 |
2002年 | 906篇 |
2001年 | 623篇 |
2000年 | 336篇 |
1999年 | 454篇 |
1998年 | 311篇 |
1997年 | 233篇 |
1996年 | 243篇 |
1995年 | 199篇 |
1994年 | 196篇 |
1993年 | 180篇 |
1992年 | 303篇 |
1991年 | 281篇 |
1990年 | 239篇 |
1989年 | 215篇 |
1988年 | 180篇 |
1987年 | 159篇 |
1986年 | 113篇 |
1985年 | 126篇 |
1984年 | 103篇 |
1983年 | 93篇 |
1982年 | 93篇 |
1981年 | 86篇 |
1979年 | 97篇 |
1976年 | 138篇 |
1975年 | 100篇 |
1974年 | 88篇 |
1973年 | 89篇 |
1969年 | 85篇 |
1966年 | 88篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
通过保持非耗散介观LC电路的固有频率不变,而使电路参数作阶跃函数变化,就可将介观LC电路由初始的偶相干态制备到压缩偶相干态;在压缩偶相干态下,介观电路系统不仅有非经典的量子压缩效应,而且有非经典的反聚束效应.
关键词:
介观LC电路
单位阶跃函数
压缩算符
压缩偶相干态 相似文献
92.
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
93.
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
94.
95.
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
96.
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
97.
Single-crystalline layered lithium manganese oxide nanorods were prepared via a low-temperature molten salt synthesis method. The material was investigated by a variety of techniques, including X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectrum (XPS). 相似文献
98.
The kinetics of the hydrolysis of p-nitrophenyl esters of three types of single-chain carboxylic acids, namely, saturated, olefinic and acetylenic, was investigated in two aquiorgano binary solvent systems, DMSO-H2O and dioxane (DX)-H2O. The ester probes used are: octanoic (C8), dodecanoic (C12) , stearic (C18) , oleic (C18-ol) , elaidic (C18-el ) and stearolic (C18-st). The order of measured CAgC values is: C18-ol>C18-el>C18>C18-st, whereas the order of decreasing magnitude of the observed hydrolytic rate constants of the monomeric species (km) is: C18>C18-el>C18-ol> C18-st. These rather unanticipated results are discussed. 相似文献
99.
Lubomír Kubáček 《Mathematica Slovaca》2007,57(6):571-588
The multivariate model, where not only parameters of the mean value of the observation matrix, but also some other parameters
occur in constraints, is considered in the paper. Some basic inference is presented under the condition that the covariance
matrix is either unknown, or partially unknown, or known.
Supported by the grant of the Council of Czech Republic MSM 6 198 959 214. 相似文献
100.
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