全文获取类型
收费全文 | 18464篇 |
免费 | 3527篇 |
国内免费 | 2241篇 |
专业分类
化学 | 13752篇 |
晶体学 | 156篇 |
力学 | 1038篇 |
综合类 | 165篇 |
数学 | 1900篇 |
物理学 | 7221篇 |
出版年
2024年 | 45篇 |
2023年 | 449篇 |
2022年 | 452篇 |
2021年 | 689篇 |
2020年 | 877篇 |
2019年 | 859篇 |
2018年 | 696篇 |
2017年 | 612篇 |
2016年 | 958篇 |
2015年 | 894篇 |
2014年 | 1063篇 |
2013年 | 1413篇 |
2012年 | 1793篇 |
2011年 | 1761篇 |
2010年 | 1224篇 |
2009年 | 1115篇 |
2008年 | 1265篇 |
2007年 | 1137篇 |
2006年 | 964篇 |
2005年 | 802篇 |
2004年 | 602篇 |
2003年 | 540篇 |
2002年 | 530篇 |
2001年 | 457篇 |
2000年 | 352篇 |
1999年 | 432篇 |
1998年 | 333篇 |
1997年 | 270篇 |
1996年 | 279篇 |
1995年 | 228篇 |
1994年 | 198篇 |
1993年 | 180篇 |
1992年 | 150篇 |
1991年 | 120篇 |
1990年 | 123篇 |
1989年 | 88篇 |
1988年 | 68篇 |
1987年 | 61篇 |
1986年 | 41篇 |
1985年 | 35篇 |
1984年 | 20篇 |
1983年 | 17篇 |
1982年 | 16篇 |
1981年 | 10篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1959年 | 2篇 |
1957年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 390 毫秒
71.
Improving Construction for Connected Dominating Set with Steiner Tree in Wireless Sensor Networks 总被引:2,自引:0,他引:2
Manki Min Hongwei Du Xiaohua Jia Christina Xiao Huang Scott C.-H. Huang Weili Wu 《Journal of Global Optimization》2006,35(1):111-119
The connected dominating set plays an important role in ad hoc wireless networking. Many constructions for approximating the minimum connected dominating set have been proposed in the
literature. In this paper, we propose a new one with Steiner tree, which produces approximation solution within a factor of
6.8 from optimal. This approximation algorithm can also be implemented distributedly. 相似文献
72.
Baoqiang Li Dechang Jia Yu Zhou Qiaoling Hu Wei Cai 《Journal of magnetism and magnetic materials》2006
Chitosan/magnetite nanocomposite was synthesized induced by magnetic field via in situ hybridization in ambient condition. Results of XRD patterns and TEM micrographs indicated that magnetite particles with 10–20 nm were dispersed in chitosan homogeneously. An interesting result is that magnetite nanoparticles were assembled to form chain-like structures under the influence of the external magnetic field, which mimics the magnetite chains inside of magnetotatic bacteria. The saturated magnetization (Ms) of nano-magnetite in chitosan was 50.54 emu/g, which is as high as 54% of bulk magnetite. The remanence (Mr) and coercivity (Hc) were 4 emu/g and14.8 Oe, respectively, which indicated that magnetite nanoparticles were superparamagnetic. The key of route is that a pre-precipitated chitosan hydrogel membrane, used as chemical reactor, which controlled the precipitation of chitosan precipitation and in situ transformation of magnetite from the precursor simultaneously in the magnetic field environment. 相似文献
73.
Banach空间二阶周期边值问题解的存在性 总被引:2,自引:0,他引:2
利用一些比较结果,讨论了Banach空间中二阶周期边值问题解的存在性,获得了若干解的存在性与唯一性结果。 相似文献
74.
2002年理综考试共30题,物理试题有10题,其中客观题6题,主观题4题,共120分.内容很贴近课本,没有出现前两年较为热门的"信息题",考试更加注重对学生的学习基础、学习能力的考查.试题灵活而不落俗套,新颖而不离基础,强调能力而不偏离教材,考查素质而不脱离实际. 相似文献
75.
76.
77.
Huimin Xie Biao Li Robert Geer Bai Xu James Castracane 《Optics and Lasers in Engineering》2003,40(3):163-177
A focused ion beam (FIB) Moiré method is proposed to measure the in-plane deformation of object in a micrometer scale. The FIB Moiré is generated by the interference between a prepared specimen grating and FIB raster scan lines. The principle of the FIB Moiré is described. The sensitivity and accuracy of deformation measurement are discussed in detail. Several specimen gratings with 0.14 and 0.20 μm spacing are used to generate FIB Moiré patterns. The FIB Moiré method is successfully used to measure the residual deformation in a micro-electro-mechanical system structure after removing the SiO2 sacrificial layer with a 5000 lines/mm grating. The results demonstrate the feasibility of this method. 相似文献
78.
The problem of generating a matrix A with specified eigen‐pair, where A is a symmetric and anti‐persymmetric matrix, is presented. An existence theorem is given and proved. A general expression of such a matrix is provided. We denote the set of such matrices by ??????En. The optimal approximation problem associated with ??????En is discussed, that is: to find the nearest matrix to a given matrix A* by A∈??????En. The existence and uniqueness of the optimal approximation problem is proved and the expression is provided for this nearest matrix. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
79.
A facile, rapid and regioselective method for the 1-O-deacylation of peracylated glycopyranoses is described which occurs under mild conditions by absorption onto alumina using microwave irradiation. 相似文献
80.
微孔激光器作为应用于近场光信息存储系统中的一种新型光源,它的出射光斑的近场特性对于近场光存储是十分重要的。针对纳米孔径运用角谱进行Fox-Li数值迭代,得到不同孔径微孔激光器的基模光强分布,然后运用二维非线性时域有限差分法分析微孔激光器出射端即微孔金属膜的近场光学性质,模拟计算了不同孔径和厚度的微孔金属膜的光强近场分布,从应用于近场光存储的角度,给出反映其近场光学特性的相关数据。发现由于TM模式下金属存在局域表面等离子增强效应,使得其出射强度比TE模式高一个数量级,从而更适于作为实际中近场光存储系统和原理试验的光学头。 相似文献