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   6429篇
  免费   1138篇
  国内免费   397篇
化学   2005篇
晶体学   35篇
力学   504篇
综合类   236篇
数学   2137篇
物理学   3047篇
  2024年   21篇
  2023年   110篇
  2022年   365篇
  2021年   348篇
  2020年   222篇
  2019年   169篇
  2018年   137篇
  2017年   266篇
  2016年   323篇
  2015年   252篇
  2014年   435篇
  2013年   529篇
  2012年   430篇
  2011年   393篇
  2010年   366篇
  2009年   407篇
  2008年   383篇
  2007年   403篇
  2006年   330篇
  2005年   249篇
  2004年   211篇
  2003年   224篇
  2002年   211篇
  2001年   164篇
  2000年   173篇
  1999年   139篇
  1998年   120篇
  1997年   103篇
  1996年   99篇
  1995年   53篇
  1994年   65篇
  1993年   62篇
  1992年   30篇
  1991年   27篇
  1990年   28篇
  1989年   15篇
  1988年   14篇
  1987年   9篇
  1986年   19篇
  1985年   16篇
  1984年   13篇
  1982年   6篇
  1981年   7篇
  1980年   1篇
  1979年   4篇
  1977年   5篇
  1975年   1篇
  1972年   1篇
  1967年   1篇
  1959年   4篇
排序方式: 共有7964条查询结果,搜索用时 750 毫秒
241.
杜景林  郑若钦  谢立 《物理学报》2015,64(1):18901-018901
旨在研究无线传感器与执行器网络(WSANs)中节点失效情况下恢复执行器(actor)节点服务的算法. 首先说明了WSANs中的实时覆盖模型, 证明WSANs覆盖恢复问题是NP难问题, 给出了近似求解方案. 在此基础上, 提出了一种基于六边形蜂巢结构的移动容错算法HMFR用于恢复失效actor节点, HMFR 算法在限制网络初始部署的条件下拥有很好的性能. 通过实验与现有的恢复算法进行比较, 发现HMFR算法在actor覆盖sensor节点数和移动距离方面有更好的性能.  相似文献   
242.
李娜  杨晓丽 《物理学报》2015,64(22):220503-220503
以电耦合的Terman-Wang小世界神经元网络系统为研究对象, 研究了空间关联白噪声影响下神经元网络系统的同步动力学. 首先将动力学平均场近似理论扩展到受空间关联白噪声影响下的小世界网络系统中, 将描述网络系统动力学演化的2N维随机微分方程简化为11个确定性的矩微分方程. 其次, 基于动力学平均场近似理论所推导的矩方程, 讨论了空间关联噪声、网络结构参数对神经元网络系统同步动力学的关键影响, 发现较大的噪声空间关联系数、耦合强度及节点平均度均对神经元网络系统同步放电具有积极作用. 进一步地, 利用计算机仿真数值模拟原神经元网络系统的同步动力学, 并与基于动力学平均场近似理论所得到的结果进行比较, 发现二者具有较好的一致性.  相似文献   
243.
陈娜  权东晓  裴昌幸  杨宏 《中国物理 B》2015,24(2):20304-020304
To realize practical wide-area quantum communication,a satellite-to-ground network with partially entangled states is developed in this paper.For efficiency and security reasons,the existing method of quantum communication in distributed wireless quantum networks with partially entangled states cannot be applied directly to the proposed quantum network.Based on this point,an efficient and secure quantum communication scheme with partially entangled states is presented.In our scheme,the source node performs teleportation only after an end-to-end entangled state has been established by entanglement swapping with partially entangled states.Thus,the security of quantum communication is guaranteed.The destination node recovers the transmitted quantum bit with the help of an auxiliary quantum bit and specially defined unitary matrices.Detailed calculations and simulation analyses show that the probability of successfully transferring a quantum bit in the presented scheme is high.In addition,the auxiliary quantum bit provides a heralded mechanism for successful communication.Based on the critical components that are presented in this article an efficient,secure,and practical wide-area quantum communication can be achieved.  相似文献   
244.
王正斌  吴昭质  高超 《中国物理 B》2015,24(2):28503-028503
The nonlinear properties of lattice network-based(LNB) composite right-/left-handed transmission lines(CRLH TLs)with nonlinear capacitors are experimentally investigated.Harmonic generation,subharmonic generation,and parametric excitation are clearly observed in an unbalanced LNB CRLH TL separately.While the balanced design of the novel nonlinear TL shows that the subharmonic generation and parametric processes can be suppressed,and almost the same power level of the higher harmonics can be achieved over a wide bandwidth range,which are difficult to find in conventional CRLH TLs.  相似文献   
245.
Silica particles functionalized with quaternary ammonium groups were prepared by interpenetrating polyethylenimine (PEI) into silica particles and crosslinking with diiodopentane, followed by octyliodide alkylation and methyliodide quaternarization (S‐QA‐PEI). The synthesized S‐QA‐PEI particles were identified with a slight particle size increase of 2–3 µm. Different ratios of PEI:silica particles were prepared and analyzed. While silica particles are negatively charged, ?16.7 ± 5.11 mV, the prepared S‐QA‐PEI particles are positively charged, +50–60 mV. These particles were embedded in poly(ethylene vinyl acetate) and poly(ethylene methacrylic acid) coatings which exhibited strong antibacterial activity. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
246.
The partitioning constants and Gibbs free energies of transfer of poly(oxyethylene) n‐alkyl ethers between dodecane and the protic ionic liquids (ILs) ethylammonium nitrate (EAN) and propylammonium nitrate (PAN) are determined. EAN and PAN have a sponge‐like nanostructure that consists of interpenetrating charged and apolar domains. This study reveals that the ILs solvate the hydrophobic and hydrophilic parts of the amphiphiles differently. The ethoxy groups are dissolved in the polar region of both ILs by means of hydrogen bonds. The environment is remarkably water‐like and, as in water, the solubility of the ethoxy groups in EAN decreases on warming, which underscores the critical role of the IL hydrogen‐bond network for solubility. In contrast, amphiphile alkyl chains are not preferentially solvated by the charged or uncharged regions of the ILs. Rather, they experience an average IL composition and, as a result, partitioning from dodecane into the IL increases as the cation alkyl chain is lengthened from ethyl to propyl, because the IL apolar volume fraction increases. Together, these results show that surfactant dissolution in ILs is related to structural compatibility between the head or tail group and the IL nanostructure. Thus, these partitioning studies reveal parameters for the effective molecular design of surfactants in ILs.  相似文献   
247.
A new Gd coordination polymer based on 2-(pyridin-4-yl)-I H-imidazole-4,5-dicarboxylate (H3PIDC) has been synthesized under hydrothermal conditions, formulated as {[Gd3(HPIDC)3(PIDC)(H2O)4].3H2O}n (1). The compound crystallizes in the monoclinic system, space group C2/c with a=20.951(7), b = 9.515(3), c = 27.483(10) A,β= 106.176(6)°, Z = 4, V= 5262(3) A3, C40 H45 Gd3 N12 O30, Dc = 2.071 g/cm3, Mr=1645.63, λ (MoKa)=0.71073A, μ=3.846mm-1, F(000)=3204, the final R=0.0390 and wR= 0.1332. Complex 1 is a two-dimensional MOF built up from T-shaped 3-connected HPIDC2 , PIDC3 and 4-connected metal nodes. Dielectric constant of complex 1 was measured at different frequencies with temperature variation.  相似文献   
248.
This study is focused on multiscale characterization and constitutive parameters identification of selectively laser sintered PA12 specimens. The process parameters and change in crystallinity due to 3D printing were identified via differential scanning calorimetry (DSC). Tension, compression, shear, flexural and fracture tests performed on samples fabricated, both in 0° and 90° directions reveal that the tensile toughness of samples printed in 0° orientation, outperform samples printed in 90° orientation by an average of 24%. Cryogenically fractured samples were analyzed via SEM and micro-computed tomography to analyze 2D/3D defects and correlate the microstructure with macroscopic properties. The constitutive parameters for a strain-rate and temperature-dependent Three Network (TN) material model were identified using the measured mechanical properties. Furthermore, mechanical response of micro-architected Kelvin lattice structure was analyzed by Finite Element Method employing the TN constitutive model and the predictions were corroborated with measurements.  相似文献   
249.
In this work, we present the modeling of the peak deceleration (PD) using data of the experimental drop test. Specimens with different thicknesses and areas tested in the drop test device which has adaptable height and weight. In the empirical modeling of the PD, the thickness, area, drop mass and drop height considered as separable functions. An analytical model and Neural Network (NN) was used as the empirical models. Further, the stress on the material was calculated using differential equations and the Finite Element Method (FEM). The Obtained PD from the experimental test, analytical and NN models was converted to the stress on the material using a derived differential equation. Finally, the best model for analyzing the PD and Stress on the material was presented.  相似文献   
250.
综述了可拉伸超韧水凝胶的设计原理及其在组织工程和柔性电子器件领域的应用. 通过将网络结构层次、 化学结构、 增韧机制与宏观力学性能相结合, 重点讨论了单网络水凝胶、 双网络水凝胶、 纳米复合水凝胶及其它水凝胶等可拉伸超韧水凝胶的研究进展, 并总结和展望了新思路和新方向.  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