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   433篇
  免费   41篇
  国内免费   50篇
化学   128篇
晶体学   1篇
力学   25篇
综合类   2篇
数学   244篇
物理学   124篇
  2023年   11篇
  2022年   16篇
  2021年   15篇
  2020年   16篇
  2019年   10篇
  2018年   16篇
  2017年   21篇
  2016年   11篇
  2015年   24篇
  2014年   17篇
  2013年   28篇
  2012年   37篇
  2011年   34篇
  2010年   29篇
  2009年   38篇
  2008年   45篇
  2007年   41篇
  2006年   30篇
  2005年   28篇
  2004年   9篇
  2003年   10篇
  2002年   8篇
  2001年   11篇
  2000年   4篇
  1999年   10篇
  1998年   2篇
  1995年   1篇
  1992年   1篇
  1991年   1篇
排序方式: 共有524条查询结果,搜索用时 15 毫秒
81.
In this paper the optical parameters at infrared frequencies of metallic thin films were obtained experimentally using a variable angle spectroscopic ellipsometer and used to simulate numerically the frequency response of antennas and antenna-coupled detectors at infrared frequencies (5–15 μm). The simulation results agree with previously published data and practical guidelines are presented for the design and fabrication of dipole and bowtie antennas at infrared frequencies.  相似文献   
82.
It is important to calculate the Hausdorff dimension and the Hausdorff mesure respect to this dimension for some fractal sets. By using the usual method of Mass Distribution, we can only calculate the Hausdorff dimension. In this paper, we will construct an integral formula by using lower inverse s-density and then use it to calculate the Hausdorff measures for some fractional dimensional sets.  相似文献   
83.
新颖的双通道输出高功率掺铒光纤宽带光源   总被引:1,自引:3,他引:1  
王秀琳  黄文财 《光子学报》2007,36(1):124-127
在分析L波段放大自发辐射(ASE)谱产生原理的基础上,设计出一种新颖的双级结构掺铒光纤ASE宽带光源,该光源可在两个端口分别输出高功率的C波段和L波段的ASE谱.设计将C波段ASE谱注入到掺铒光纤中作为L波段ASE谱的二次抽运源,使得L波段ASE谱功率得到了有效提高.优化光源结构参量后从两个端口分别获得了12.97 dBm和12.81 dBm的C波段和L波段ASE宽带谱.将两个输出端口组合得到了功率为15.9 dBm,泵浦转换效率达到21.6%的C+L波段超宽带ASE光源.  相似文献   
84.
Isotope dilution analysis method coupled with flow injection and inductively coupled plasma mass spectrometry (ID-FI-ICP-MS), enabled trace lead concentration in seawater to be determined and the high salt concentration in the matrix, such as Na+, Ca2+ and Mg2+, to be removed on-line. The operational parameters of the FI system including pH for the chelating reaction, concentration of 8-hydroxyquinoline-5-sulfonic acid (8-HQS), sample loading time and injection speed, washing time and speed, eluting acid concentration and eluting speed, and instrumental parameters for ICP-MS were optimized and selected. Accurate results could be achieved because the isotope ratios required can be precisely measured in the range of the eluting peak by means of ID-FI-ICP-MS. The 3σ detection limit was 0.204 ng ml−1. The trace lead concentration of seawater in south Xiamen, China was 0.988 ± 0.039 ng ml−1. The recoveries of spiked Pb standard in seawater and standard reference water (GBW 08607) were 97.9 and 101.0%, respectively, with a relative standard deviation of 0.98%. This method can be used to determine trace lead concentration in high salt matrix samples, and is especially useful when the eluting peaks do not have a Gaussian-distribution.  相似文献   
85.
水杨酸甲酯清除羟基自由基活性的研究   总被引:1,自引:0,他引:1  
马建华 《化学通报》2006,69(3):228-230
利用脉冲辐解技术研究了水杨酸甲酯清除羟基自由基反应的瞬态吸收谱,测定了水杨酸甲酯与羟基自由基反应的表观速率常数。辅以常规检测方法,测定了水杨酸甲酯对羟基自由基的清除率。结果表明,水杨酸甲酯能快速有效清除羟基自由基。探讨了水杨酸甲酯清除羟基自由基的反应机制。  相似文献   
86.
研究了不经分离、一次性制备氨基化联吡啶钌掺杂的双层二氧化硅纳米小球的方法。实验证明该纳米小球尺寸均匀,光稳定性、水溶性好,分散稳定。通过简单的偶联反应后,它能有效的和蛋白质结合,结合后的蛋白能保持其生物活性。以此纳米荧光小球为标记物,应用于蛋白质微阵列的定量检测,结果发现其效果明显优于相同条件下以异硫氰酸荧光素(FITC)为标记物的定量结果,检出限可以达到3.5 mg/L。  相似文献   
87.
该文证明了广义α-stable过程局部时增量的H  相似文献   
88.
Let G be a simple graph with adjacency matrix A(G) and (G,x) the permanental polynomial of G. Let G × H denotes the Cartesian product of graphs G and H. Inspired by Kleins idea to compute the permanent of some matrices (Mol. Phy. 31 (3) (1976) 811–823), in this paper in terms of some orientation of graphs we study the permanental polynomial of a type of graphs. Here are some of our main results.1.If G is a bipartite graph containing no subgraph which is an even subdivision of K 2,3, then G has an orientation G e such that (G,x) = det (xI-A(G e )), where A(G e ) denotes the skew adjacency matrix of G e.2.Let G be a 2-connected outerplanar bipartite graph with n vertices. Then there exists a 2-connected outerplanar bipartite graph with 2n+2 vertices such that (G,x) is a factor of .3.Let T be an arbitrary tree with n vertices. Then , where 1 , 2 , ..., n are the eigenvalues of T.  相似文献   
89.
Quinones including menadione are ubiquitous in nature. They play important roles in aerobic respira- tion and photosynthesis[1,2]. In addition, exogenous quinones are used as antibiotics and anticancer drugs. Their function is closely related to their red…  相似文献   
90.
This paper deals with the existence of solutions to the elliptic equation -△uμu/|x|2=λu |u|2*-2u f(x, u) in Ω, u = 0 on ( a)Ω, where Ω is a bounded domain in RN(N≥3),0∈Ω,2*=2N/N-2,λ>0,λ(a)σμ, σμ is the spectrum of the operator -△- μI/|x|2with zero Dirichlet boundary condition, 0 <μ<-μ,-μ=(N-2)2/4,f(x,u) is an asymmetric lower order perturbation of |u|2*-1 at infinity. Using the dual variational methods, the existence of nontrivial solutions is proved.  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