全文获取类型
收费全文 | 113410篇 |
免费 | 10025篇 |
国内免费 | 14872篇 |
专业分类
化学 | 75768篇 |
晶体学 | 2525篇 |
力学 | 4375篇 |
综合类 | 978篇 |
数学 | 21158篇 |
物理学 | 33503篇 |
出版年
2024年 | 159篇 |
2023年 | 1547篇 |
2022年 | 1691篇 |
2021年 | 2965篇 |
2020年 | 3317篇 |
2019年 | 3243篇 |
2018年 | 2808篇 |
2017年 | 3223篇 |
2016年 | 3626篇 |
2015年 | 3308篇 |
2014年 | 4651篇 |
2013年 | 9045篇 |
2012年 | 6069篇 |
2011年 | 6635篇 |
2010年 | 5630篇 |
2009年 | 7317篇 |
2008年 | 7532篇 |
2007年 | 7922篇 |
2006年 | 6977篇 |
2005年 | 5773篇 |
2004年 | 5236篇 |
2003年 | 5031篇 |
2002年 | 5141篇 |
2001年 | 3851篇 |
2000年 | 3625篇 |
1999年 | 3078篇 |
1998年 | 2833篇 |
1997年 | 1973篇 |
1996年 | 1807篇 |
1995年 | 1696篇 |
1994年 | 1643篇 |
1993年 | 1245篇 |
1992年 | 1253篇 |
1991年 | 885篇 |
1990年 | 735篇 |
1989年 | 619篇 |
1988年 | 542篇 |
1987年 | 452篇 |
1986年 | 391篇 |
1985年 | 400篇 |
1984年 | 376篇 |
1983年 | 198篇 |
1982年 | 314篇 |
1981年 | 315篇 |
1980年 | 226篇 |
1979年 | 257篇 |
1978年 | 186篇 |
1977年 | 165篇 |
1976年 | 110篇 |
1973年 | 90篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
111.
112.
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
113.
设计性、研究性实验对学生创新能力的培养 总被引:6,自引:0,他引:6
根据设计性、研究性实验的特点,从几个方面、不同的角度,阐述了设计性、研究性实验对学生创新能力培养的作用与意义。 相似文献
114.
根据Pegg-Barnett位相定义, 计算了一种新的奇偶非线性相干态的位相概率分布函数, 利用数值计算方法研究了它们的位相统计性质. 数值计算结果表明:新的奇偶非线性相干态的位相特性与通常奇偶相干态的位相特性截然不同. 相似文献
115.
Based on the vectorial Rayleigh–Sommerfeld diffraction integrals, analytical expressions for the transversal and axial field distribution of plane waves propagating through a thin lens followed by a small circular aperture are derived and used to study the focusing and diffraction properties of plane waves. Some special cases of our general result are discussed, and illustrative numerical calculation results are given. It is found that the vectorial nonparaxial approach should be applied if the aperture dimension is comparable with the wavelength or the focusing is strong. 相似文献
116.
Shougo Higashi 《Surface science》2006,600(3):591-597
We have studied the individual adsorption of Mn and Bi, and their coadsorption on Cu(0 0 1) by low-energy electron diffraction (LEED). For Mn, we have determined the c(2 × 2) structure formed at 300 K, whose structure had been determined by several methods. We reconfirmed by a tensor LEED analysis that it is a substitutional structure and that a previously reported large corrugation (0.30 Å) between substitutional Mn and remaining surface Cu atoms coincides perfectly with the present value. In the individual adsorption of Bi, we have found a c(4 × 2) structure, which is formed by cooling below ∼250 K a surface prepared by Bi deposition of ∼0.25 ML coverage at 300 K where streaky half-order LEED spots appear. The c(4 × 2) structure has been determined by the tensor LEED analysis at 130 K and it is a substitutional structure. In the coadsorption, we found a c(6 × 4) structure, which has been determined by the tensor LEED analysis. It is very similar to the previously determined structure of the c(6 × 4) formed by coadsorption of Mg and Bi, and embedded MnBi4 clusters are arranged in the top Cu layer instead of MgBi4. Large lateral displacements of Bi atoms in the c(6 × 4)-(Mn + Bi) suggest that the Mn atoms undergo the size-enhancement caused by their large magnetic moment. 相似文献
117.
In this paper, the influence functions and limiting distributions of the canonical correlations and coefficients based on affine equivariant scatter matrices are developed for elliptically symmetric distributions. General formulas for limiting variances and covariances of the canonical correlations and canonical vectors based on scatter matrices are obtained. Also the use of the so-called shape matrices in canonical analysis is investigated. The scatter and shape matrices based on the affine equivariant Sign Covariance Matrix as well as the Tyler's shape matrix serve as examples. Their finite sample and limiting efficiencies are compared to those of the Minimum Covariance Determinant estimators and S-estimator through theoretical and simulation studies. The theory is illustrated by an example. 相似文献
118.
Maria Kordaki Athanasia Balomenou 《International Journal of Computers for Mathematical Learning》2006,11(1):99-135
This study focuses on the constructions in terms of area and perimeter in equivalent triangles developed by students aged 12–15 years-old, using the tools provided by Cabri-Geometry II [Labore (1990). Cabri-Geometry (software), Université de Grenoble]. Twenty-five students participated in a learning experiment where they were asked to construct: (a) pairs of equivalent triangles “in as many ways as possible” and to study their area and their perimeter using any of the tools provided and (b) “any possible sequence of modifications of an original triangle into other equivalent ones”. As regards the concept of area and in contrast to a paper and pencil environment, Cabri provided students with different and potential opportunities in terms of: (a) means of construction, (b) control, (c) variety of representations and (d) linking representations, by exploiting its capability for continuous modifications. By exploiting these opportunities in the context of the given open tasks, students were helped by the tools provided to develop a broader view of the concept of area than the typical view they would construct in a typical paper and pencil environment. 相似文献
119.
We consider normal ≡ Gaussian seemingly unrelated regressions (SUR) with incomplete data (ID). Imposing a natural minimal set of conditional independence constraints, we find a restricted SUR/ID model whose likelihood function and parameter space factor into the product of the likelihood functions and the parameter spaces of standard complete data multivariate analysis of variance models. Hence, the restricted model has a unimodal likelihood and permits explicit likelihood inference. In the development of our methodology, we review and extend existing results for complete data SUR models and the multivariate ID problem. 相似文献
120.
The moduli space of torus sextics with the configuration of singularities {A2+A5+2E6} has two connected components. We compute the fundamental groups π1(CP2−C) for sextics C in both components and study their differences. 相似文献