全文获取类型
收费全文 | 274309篇 |
免费 | 12327篇 |
国内免费 | 2012篇 |
专业分类
化学 | 175437篇 |
晶体学 | 3794篇 |
力学 | 9811篇 |
综合类 | 4篇 |
数学 | 27837篇 |
物理学 | 71765篇 |
出版年
2020年 | 2889篇 |
2019年 | 4181篇 |
2018年 | 3151篇 |
2017年 | 2560篇 |
2016年 | 6655篇 |
2015年 | 6102篇 |
2014年 | 6728篇 |
2013年 | 14201篇 |
2012年 | 11041篇 |
2011年 | 11799篇 |
2010年 | 8864篇 |
2009年 | 8394篇 |
2008年 | 10953篇 |
2007年 | 10549篇 |
2006年 | 9745篇 |
2005年 | 9410篇 |
2004年 | 8443篇 |
2003年 | 7365篇 |
2002年 | 7648篇 |
2001年 | 7886篇 |
2000年 | 6285篇 |
1999年 | 4343篇 |
1998年 | 3159篇 |
1997年 | 3169篇 |
1996年 | 3222篇 |
1995年 | 2855篇 |
1994年 | 2769篇 |
1993年 | 2670篇 |
1992年 | 3181篇 |
1991年 | 3001篇 |
1990年 | 2938篇 |
1989年 | 2963篇 |
1988年 | 2842篇 |
1987年 | 2865篇 |
1986年 | 2629篇 |
1985年 | 3664篇 |
1984年 | 3653篇 |
1983年 | 2983篇 |
1982年 | 3249篇 |
1981年 | 3173篇 |
1980年 | 3058篇 |
1979年 | 3183篇 |
1978年 | 3412篇 |
1977年 | 3186篇 |
1976年 | 3179篇 |
1975年 | 3009篇 |
1974年 | 2964篇 |
1973年 | 2956篇 |
1968年 | 2023篇 |
1967年 | 2211篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
An optical system for the parallel evaluation of in- and out-of-plane dynamical deformations will be described. A double pulse laser with pulse separation in the microsecond range is used for the investigations. Two separate interferograms of an object under test, in its undeformed and deformed state, are recorded in a few microseconds. The object is illuminated from two different directions and imaged onto a CCD sensor. This produces two sensitivity vectors. The reference beams have different directions in order to produce two directional spatial carriers. The Fourier method is used for quantitative evaluation, and the measurements along different sensitivity vectors are separated in the Fourier domain. The phases of the two interferograms are obtained from the complex amplitudes and the two dimensional deformation is calculated from the phases. Experimental results are presented. 相似文献
993.
X. H. Sun 《Acta Mathematica Hungarica》1994,65(3):229-236
994.
The length-distribution of stereoregular sequences in low-density polyethylene (LDPE) is determined by a computer-aided analysis of cp-melting curves within the framework of thermodynamics of eutectoid copolymers. Small-angle x-ray scattering patterns are then described by using the structure data derived. One of the results is that fluctuations of the mean electron-density are increasingly reduced with an increasing degree of crystallinity.Dedicated to Prof. Dr. W. Pechhold on the occasion of his 60th birthday 相似文献
995.
Different amounts of Li3PO4 were mixed to a fixed ratio of LiI:Li2WO4, ground and pelletised before subjected to sintering at 70°C for 7 days. XRD shows that the product formed after sintering
process is most likely Li6P4W8O32 due to peaks present at 10.6°, 22.4°, 24.0°, 24.4, 26.2°, 32.4° and 34.0°. Conductivity studies show that the sample with
25 wt.% Li3PO4 exhibits the highest room temperature conductivity of 3.42×10−3 Scm−1. Conductivity is expected to occur through channel-like structures which could have formed due to corner or edge sharing
of polyhedra. FTIR studies have shown the existence of WO4 tetrahedra and WO6 octahedral at 850 cm−1 and 952 cm−1, and phosphate tetrahedral at 564 cm−1, 700 cm−1, 890 cm−1 and 1030 cm−1. 相似文献
996.
Zi‐Cai Li Tzon‐Tzer Lu Hung‐Tsai Huang Alexander H.‐D. Cheng 《Numerical Methods for Partial Differential Equations》2007,23(1):93-144
In this article we survey the Trefftz method (TM), the collocation method (CM), and the collocation Trefftz method (CTM). We also review the coupling techniques for the interzonal conditions, which include the indirect Trefftz method, the original Trefftz method, the penalty plus hybrid Trefftz method, and the direct Trefftz method. Other boundary methods are also briefly described. Key issues in these algorithms, including the error analysis, are addressed. New numerical results are reported. Comparisons among TMs and other numerical methods are made. It is concluded that the CTM is the simplest algorithm and provides the most accurate solution with the best numerical stability. © 2006 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2007 相似文献
997.
W. Brüggemann K. Fischer H. Jahnke 《Journal of Mathematical Modelling and Algorithms》2003,2(2):153-169
In Part I of this study, we suggest to identify an operations research (OR) problem with the equivalence class of models describing the problem and enhance the standard computer-science theory of computational complexity to be applicable to this situation of an often model-based OR context. The Discrete Lot-sizing and Scheduling Problem (DLSP) is analysed here in detail to demonstrate the difficulties which can arise if these aspects are neglected and to illustrate the new theoretical concept. In addition, a new minimal model is introduced for the DLSP which makes this problem eventually amenable to a rigorous analysis of its computational complexity. 相似文献
998.
Francisco‐Javier Sayas 《Numerical Methods for Partial Differential Equations》2003,19(5):555-570
This article presents and analyzes a simple method for the exterior Laplace equation through the coupling of finite and boundary element methods. The main novelty is the use of a smooth parametric artificial boundary where boundary elements fit without effort together with a straight approximate triangulation in the bounded area, with the coupling done only in nodes. A numerically integrated version of the algorithm is also analyzed. Finally, an isoparametric variant with higher order is proposed. © 2003 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 19: 555–570, 2003 相似文献
999.
1000.