首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4066篇
  免费   799篇
  国内免费   692篇
化学   2592篇
晶体学   93篇
力学   421篇
综合类   50篇
数学   764篇
物理学   1637篇
  2024年   19篇
  2023年   56篇
  2022年   147篇
  2021年   140篇
  2020年   227篇
  2019年   154篇
  2018年   160篇
  2017年   167篇
  2016年   210篇
  2015年   196篇
  2014年   214篇
  2013年   384篇
  2012年   239篇
  2011年   249篇
  2010年   215篇
  2009年   271篇
  2008年   254篇
  2007年   298篇
  2006年   235篇
  2005年   238篇
  2004年   204篇
  2003年   218篇
  2002年   179篇
  2001年   152篇
  2000年   109篇
  1999年   92篇
  1998年   102篇
  1997年   87篇
  1996年   73篇
  1995年   40篇
  1994年   42篇
  1993年   27篇
  1992年   27篇
  1991年   31篇
  1990年   12篇
  1989年   14篇
  1988年   9篇
  1987年   10篇
  1986年   8篇
  1985年   11篇
  1984年   11篇
  1983年   1篇
  1982年   7篇
  1981年   1篇
  1980年   4篇
  1979年   5篇
  1978年   2篇
  1977年   3篇
  1973年   1篇
  1957年   2篇
排序方式: 共有5557条查询结果,搜索用时 15 毫秒
31.
32.
康社峰 《应用光学》1996,17(1):15-17
介绍双色红外制导信息处理系统的基本原理,包括双色红外玫瑰线扫描制导原理,双色信号处理硬件原理,目标识别及方位角计算技术。  相似文献   
33.
To address the problem of a poor security image encryption algorithm based on a single chaotic map, this paper proposes a cascade modulation chaotic system (CMCS) that can generate multiple chaotic maps. On this basis, a multi-image encryption algorithm with block-scrambling-diffusion is proposed using CMCS. The algorithm makes full use of the features of CMCS to achieve the effect of one encryption at a time for images. Firstly, the key-value associated with the plaintexts is generated using a secure hash algorithm-512 (SHA-512) operation and random sequence, and the three images are fully confused by the double scrambling mechanism. Secondly, the scrambled image is converted into a bit-level matrix, and the pixel values are evenly distributed using the bit-group diffusion. Finally, the non-sequence diffusion of hexadecimal addition and subtraction rules is used to improve the security of the encryption algorithm. Experimental results demonstrate that the encryption algorithm proposed in this paper has a good encryption effect and can resist various attacks.  相似文献   
34.
A generalised form of a local contact condition for the charge profile in a primitive model planar double layer [Bhuiyan, Outhwaite, and Henderson, Mol. Phys. 107, 343 (2009)] at low electrode charge is examined for completely asymmetric, binary electrolytes. The cation and anion sizes are taken to be different from each other with the valencies being 2+:1? or 1+:2?, while the electrode surface charge density is varied from being negative through zero to being positive. Monte Carlo simulation data obtained for such double layer systems at varying ionic radius ratios and electrolyte concentrations suggest the generalised contact relation to be valid at low charge on the electrode.  相似文献   
35.
葛萌  王勇 《强激光与粒子束》2013,25(03):675-679
根据微波网络理论,将单耦合口输出回路的冷测模拟物理模型进行扩展,使其适用于双耦合口回路。并在此模型的基础上提出了计算双间隙双耦合口输出回路间隙阻抗频率特性的冷测模拟方法。运用该方法,结合软件仿真,计算分析了某S波段双间隙双耦合口输出腔,分别得到该回路工作在2模式下的阻抗实部与虚部的频率特性,并对计算结果的合理性作了论证。最后通过将计算结果与采用场分析法及散射参数方法得到的结果进行比较和分析,进一步验证该冷测模拟方法的可靠性。  相似文献   
36.
We prove that the quantum double of the quasi-Hopf algebra of dimension attached in [P. Etingof, S. Gelaki, On radically graded finite-dimensional quasi-Hopf algebras, Mosc. Math. J. 5 (2) (2005) 371–378] to a simple complex Lie algebra and a primitive root of unity q of order n2 is equivalent to Lusztig's small quantum group (under some conditions on n). We also give a conceptual construction of using the notion of de-equivariantization of tensor categories.  相似文献   
37.
Bulk Bi2NiMnO6 has been shown to be ferromagnetic and ferroelectric. Here, we report a systematic study of the influence of the deposition conditions on the growth of (Bi0.9La0.1)2NiMnO6 thin films onto (0 0 1) SrTiO3 substrates by pulsed laser deposition. Oxygen pressure and substrate temperature have been varied from 0.3 to 0.6 mbar and 600 to 660 °C, respectively. Whereas it is found that single-phase and epitaxial films can be obtained in a relatively broad oxygen pressure range, the temperature window, centred on 620 °C, is extremely narrow. Films of low roughness, about 1 unit cell, have been obtained. It is found that the magnetisation of the films, which are ferromagnetic with Curie temperatures about 100 K, is lower than the expected theoretical value, which might be attributed to an incomplete Ni-O-Mn long-range ordering.  相似文献   
38.
We classify the algebraic surfaces with Eisenbud‐Harris general fibration of genus 4 over a rational curve or an elliptic curve whose slope attains the lower bound. The classification of our surfaces is strongly related to the result of the classification for certain relative quadric hypersurfaces in 3‐dimensional projective space bundles over a rational curve and an elliptic curve. We further prove some results about the canonical maps, the quadric hulls of the canonical images and the deformation for these surfaces.  相似文献   
39.
在中高能质子诱发散裂反应相关核工程设计中,可靠的蒙特卡罗模拟程序结合核反应理论模型具有较好的理论指导意义。本工作中,利用GEANT4耦合INCL4和ABLA理论模型以及FLUKA耦合PEANUT模型模拟计算了几百MeV至几个GeV质子轰击Be,Al,Fe,W,U等靶后30°,60°,120°,150°出射角产生的散裂中子双微分截面,并与现有实验数据进行了比较。结果发现,FLUKA和GEANT4模拟计算较好地再现了Al,Fe,W,U等靶实验测量数据。然而,模拟结果明显低估了Be靶出射中子能量小于10 MeV能区的实验数据。For the design of nuclear engineering related with medium-high energy proton induced spallation reaction,the reliable Monte Carlo simulation codes coupled with nuclear reaction models have a good theoretical guidance.In this work,the production spallation neutron double differential cross sections at 30°,60°,120°,150°emission angle for Be,Al,Fe,W,U target materials at incident proton energies between several hundred MeV and GeV are theoretically calculated by using the GEANT4 coupled INCL4 and ABLA,and the FLUKA coupled PEANUT.The calculated results were compared with the available experimental data.It is found that the GEANT4 and FLUKA calculations well reproduced the experimental measurement of Al,Fe,W,U target materials.However,calculations obviously underestimated the emission neutrons of Be target for lower than 10 MeV energy range.  相似文献   
40.
A new dicarboxylic acid modified Mg‐Al LDH (DLDH) containing imide groups was prepared and its effects on the thermal and mechanical properties of the new synthesized aliphatic‐aromatic poly (amide‐imide) (PAI) were investigated via preparation of PAI/nanocomposite films by solution casting method. The results of X‐ray diffraction (XRD), field emission‐scanning electron microscopy (FE‐SEM) and transmission electron microscopy (TEM) showed a uniform dispersion for LDH layers into the PAI matrix. For comparison, the effects of polyacrylic acid‐co‐poly‐2‐acrylamido‐ 2‐methylpropanesulfonic acid (PAMPS‐co‐PAA) modified Mg‐Al LDH (ALDH) on the PAI properties were also studied. The thermogravimetric analysis (TGA) results exhibited that the temperature at 5 mass% loss (T5) increased from 277 °C to 310 °C for nanocomposite containing 2 mass% of DLDH, while T5 for nanocomposite containing 2 mass% of ALDH increased to 320 °C, along with the more enhancement of char residue compared to the neat PAI. According to the tensile test results, with 5 mass% DLDH loading in the PAI matrix, the tensile strength increased from 51.6 to 70.8 MPa along with an increase in Young's modulus. Also the Young's modulus of PAI nanocomposite containing 5 mass% ALDH reduced from 1.95 to 0.81 GPa.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号