全文获取类型
收费全文 | 58676篇 |
免费 | 5883篇 |
国内免费 | 11052篇 |
专业分类
化学 | 47055篇 |
晶体学 | 1886篇 |
力学 | 1324篇 |
综合类 | 575篇 |
数学 | 9645篇 |
物理学 | 15126篇 |
出版年
2024年 | 180篇 |
2023年 | 1002篇 |
2022年 | 1895篇 |
2021年 | 1921篇 |
2020年 | 1968篇 |
2019年 | 1819篇 |
2018年 | 1537篇 |
2017年 | 1975篇 |
2016年 | 2115篇 |
2015年 | 1776篇 |
2014年 | 2488篇 |
2013年 | 5249篇 |
2012年 | 3641篇 |
2011年 | 3853篇 |
2010年 | 3365篇 |
2009年 | 4010篇 |
2008年 | 3888篇 |
2007年 | 3990篇 |
2006年 | 3772篇 |
2005年 | 3317篇 |
2004年 | 3130篇 |
2003年 | 2621篇 |
2002年 | 2263篇 |
2001年 | 1892篇 |
2000年 | 1737篇 |
1999年 | 1464篇 |
1998年 | 1222篇 |
1997年 | 1062篇 |
1996年 | 931篇 |
1995年 | 905篇 |
1994年 | 788篇 |
1993年 | 631篇 |
1992年 | 600篇 |
1991年 | 463篇 |
1990年 | 319篇 |
1989年 | 277篇 |
1988年 | 231篇 |
1987年 | 174篇 |
1986年 | 139篇 |
1985年 | 162篇 |
1984年 | 143篇 |
1983年 | 53篇 |
1982年 | 99篇 |
1981年 | 109篇 |
1980年 | 84篇 |
1979年 | 89篇 |
1978年 | 55篇 |
1977年 | 65篇 |
1976年 | 41篇 |
1973年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
The theory of tree-growing (RECPAM approach) is developed for outcome variables which are distributed as the canonical exponential family. The general RECPAM approach (consisting of three steps: recursive partition, pruning and amalgamation), is reviewed. This is seen as constructing a partition with maximal information content about a parameter to be predicted, followed by simplification by the elimination of ‘negligible’ information. The measure of information is defined for an exponential family outcome as a deviance difference, and appropriate modifications of pruning and amalgamation rules are discussed. It is further shown how the proposed approach makes it possible to develop tree-growing for situations usually treated by generalized linear models (GLIM). In particular, Poisson and logistic regression can be tree-structured. Moreover, censored survival data can be treated, as in GLIM, by observing a formal equivalence of the likelihood under random censoring and an appropriate Poisson model. Three examples are given of application to Poisson, binary and censored survival data. 相似文献
12.
采用密度泛函方法(B3P86)对 Fe_2分子结构进行了优化.计算结果中未观察到自旋污染,基态波函数与高态波函数并未混杂,结果表明,Fe_2中有8个未配对电子,这些电子空间分布不同和自旋平行产生的自旋极化效应,使 Fe_2能量最低.计算结果表明,Fe_2分子的基态是~9∑_g~ ,并非~7Δ_u,进而表明 Fe_2的自旋平行效应比电子自旋配对效应要强.计算得到该分子基态的二阶、三阶和四阶力常数分别为1.4115×10~(-2)aJ/nm~2、-37.1751×10~3aJ/nm~3和 98.7596×10~4aJ/nm~4;光谱数据ω_eχ_e、B_e、α_e分别为0.3522、0.0345、 0.4963×10~(-4)cm~(-1);离解能为3.5522eV,平衡键长为0.2137nm,振动频率为292.914cm~(-1);并得到了 Murrel-Sorbie 函数. 相似文献
13.
We employ a first-principles plane wave method with the
relativistic analytic pseudopotential of Hartwigsen, Goedecker and Hutter
(HGH) scheme in the frame of DFT to calculate
the equilibrium lattice parameters and the thermodynamic properties of
AlB2 compound with hcp structure. The obtained lattice parameters are in
good agreement with the available experimental data and those calculated by
others. Through the quasi-harmonic Debye model, obtained successfully are
the dependences of the
normalized lattice parameters a/a0 and c/c0 on pressure P, the normalized
primitive cell volume V/V0 on pressure P, the variation of the thermal
expansion α with pressure P and temperature T, as well as the Debye
temperature \ThetaD and the heat capacity CV on pressure P and
temperature T. 相似文献
14.
《Electroanalysis》2006,18(6):595-604
The following two numerical models have been applied to zinc cations electroreduction in 1 M NaClO4 water solution: a classical EE model describing the concentration of involved species in solution (semi infinitive diffusion region), an extended EE model describing both: the concentration of involved species in solution and the concentration of metallic zinc inside mercury drop (in limited area of diffusion). In the latter model the inner part of mercury drop and surrounding solution were treated as dynamic interrelated system. Both models were applied to experimental cyclic voltammetric CV data in 1 M NaClO4, the results compared and discussed. The concentration profiles of all species including metallic zinc inside mercury drop were performed. The presented integrated model is essential for theoretical and analytical aspects of the electrochemistry of mercury soluble metal cations and amalgams. 相似文献
15.
使用SAC/SAC-CI方法,利用D95(d),6-311g**以及cc-PVTZ等基组,对B2分子的基态(X3Σg-)和第一激发态(A3Σu-)的平衡结构和谐振频率进行了优化计算.通过对3个基组的计算结果的比较,得出了D95(d)基组为3个基组中的最优基组的结论;使用D95(d)基组,利用SAC的GSUM(Group Sum of Operators)方法对基态(X3Σg-),SAC-CI的GSUM方法对激发态(A3Σu-)进行单点能扫描计算,用正规方程组拟合Murrell-Sorbie函数,得到了相应电子态的完整势能函数;从得到的势能函数计算了与基态(X3Σg-)和第一激发态(A3Σu-)相对应的光谱常数(Be,αe,ωe和ωeχe),结果与实验数据吻合. 相似文献
16.
Eva Lesanska 《Applications of Mathematics》2002,47(5):411-426
The problem is to determine nonsensitiveness regions for threshold ellipsoids within a regular mixed linear model. 相似文献
17.
LIU Jixue ZHANG Sanguo & CHEN Xiru Department of Statistics Finance University of Science Technology of China Hefei China Department of Mathematics Graduate School of Chinese Academy of Sciences Beijing China 《中国科学A辑(英文版)》2006,49(6):752-769
This paper studies the linear EV model when replicate observations are made only on independent variables. We construct the estimates of regression coefficients and prove the consistency and asymptotic normality under some proper conditions. Results obtained reveal the difference between the case where the independent and dependent variables are observed repeatedly and simultaneously and the case studied in this article. 相似文献
18.
GAO Jing ZHOU Xiaohua CHEN Xun Chongqing University Chemical Engineering Department Chongqing China 《Chinese Journal of Reactive Polymers》2006,(2)
1. INTRODUCTION In the process of coking plant, about 30%~35% sulfur is transformed to H2S and some other sulfide, which form impurity in coal gas together with NH3 and HCN. Only 0.1% H2S containing in air can lead to die, so it is very important to carry on desulphurization and decyanation with coal gas [1~3]. Currently desulphurization and decyanation craft technique have Dry Oxidation Technology, Wet Oxidation Technology and Liquid Absorption Technology [2] three main kinds. The… 相似文献
19.
20.
The breakthrough and stoichiometric SO2 adsorption efficiencies of a biomass supported Na2CO3 system (80 wt %Na2CO3/straw) have reached 48.9% and 80.6% respectively at a desulfurization temperature of 80℃. 相似文献