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   639篇
  免费   70篇
  国内免费   22篇
化学   156篇
晶体学   10篇
力学   80篇
综合类   17篇
数学   207篇
物理学   261篇
  2024年   3篇
  2023年   7篇
  2022年   13篇
  2021年   17篇
  2020年   19篇
  2019年   17篇
  2018年   18篇
  2017年   20篇
  2016年   23篇
  2015年   16篇
  2014年   28篇
  2013年   48篇
  2012年   25篇
  2011年   37篇
  2010年   23篇
  2009年   42篇
  2008年   44篇
  2007年   49篇
  2006年   40篇
  2005年   30篇
  2004年   23篇
  2003年   16篇
  2002年   13篇
  2001年   26篇
  2000年   12篇
  1999年   16篇
  1998年   15篇
  1997年   14篇
  1996年   5篇
  1995年   4篇
  1994年   11篇
  1993年   5篇
  1992年   10篇
  1991年   9篇
  1990年   2篇
  1989年   5篇
  1988年   4篇
  1987年   3篇
  1986年   3篇
  1985年   3篇
  1984年   4篇
  1983年   1篇
  1982年   3篇
  1981年   1篇
  1980年   1篇
  1976年   3篇
排序方式: 共有731条查询结果,搜索用时 15 毫秒
31.
以陆生植物美人蕉(Canna generalis)、紫背万年青(Rhoeo discolor)为对象,研究了其不同的种植方式对净化富营养化水体中磷的影响.结果表明,美人蕉、紫背万年青的双倍生物量组对水体中TP、DTP和DIP的去除率与它们的单倍生物量组呈显著性差异,植物对水体中P的去除效果随着植物生物量的适度增加而提高.两种陆生植物的复合种植体系对TP、DTP和DTP的去除率和单一种植体系差别不明显,说明美人蕉、紫背万年青的不同种植体系对水体中TP、DTP和DIP去除率的影响不大.从美人蕉、紫背万年青去除水体中TP、DTP和DIP的动态过程拟合模型可以看出各植物处理组对水体中不同形态P有良好的去除效应.  相似文献   
32.
Computer Simulation of a 3-D Sensing System with Structured Illumination   总被引:1,自引:0,他引:1  
A computer simulation system of three-dimensional sensing with structured illumination is presented. It includes the generation of deformed fringe patterns from 3-D shapes and the reconstruction of 3-D shapes, conversely. Some experimental results of the deformed fringe pattern and the reconstructed object shapes are presented. We have also discussed the effect of some major system parameters on the measurement results and considered how to correct these parameters according to the measurement result of the standard plane. Using this simulation system, the major system parameters: environmental conditions, measurement accuracy and algorithm evaluation of the 3-D shape measurement system based on PMP, FTP, SPM, etc., can be researched. © 1997 Elsevier Science Ltd. All rights reserved.  相似文献   
33.
We use Monte Carlo simulation to calculate the distributions of particles under adsorption force near planar and cylindrical surfaces,respectively.Both hard sphere interaction and repulsive Yukawa (screened coulomb) interaction are employed in our simulations.We study the influence of the inter-particle potentials.The difference between the MC simulation results and the analytical results of ideal gas model shows that the interaction between particles plays an important role in the density distribution under external fields.Moreover,the 2-dimensional constructions of particles close to the surface are studied and show relations of the interaction between particles.These results may indicate us how to improve the methods of building nanoparticle coatings and nano-scale patterns.  相似文献   
34.
Selective fabrication of superhydrophilic (S-philic) region on a superhydrophobic (S-phobic) surface requires complex technology and high cost, which has limited applications of extreme wettability patterns. In this paper, a twice-chemical-etching approach without special modification is used to prepare the extreme wettability patterns. Superhydrophobicity and superhydrophilicity can be successfully achieved after twice chemical etching for 20 seconds. The obtained patterns can maintain their extreme wettability for at least 30 days. Functional platforms with single-S-philic and multi-S-philic regions are fabricated to manipulate water and various organic liquids with water-film protection in an air environment.  相似文献   
35.
A modified derivative sign binary method is proposed to extract fringe skeletons from interferometric fringe patterns. A fringe direction map ranging from 0° to 360° is obtained with an unambiguous relationship between the grayscale and fringe tangent direction. Using this approach, the derivative sign binary map is detected without a fringe direction jump. The dark (light) fringe intensity minimum (maximum) can be extracted automatically to define fringe skeletons. In addition, two different anisotropic one-dimensional filters are described that can be used for further improving the fringe quality. Examples are provided for a holographic interferogram and a Moiré fringe pattern to illustrate applications and benefits of the approach.  相似文献   
36.
In this paper we explore the relation between information patterns and Nash Equilibria in extensive games. By information we mean what players know about moves made by others, as well as by chance. For the most part we confine ourselves to pure strategies. But in Section 2 behavioral strategies are also examined. It turns out that they can be modeled as pure strategies of an appropriately enlarged game. Our results, applied to the enlarged game, can then be reinterpreted in terms of the behavioral strategies of the original game.  相似文献   
37.
The use of non-contact laser techniques for the generation of ultrasound has extended the limits of the application of traditional ultrasonic techniques. This paper focusses on the use of one such non-contact laser technique, known as ‘optical fibre array’, to generate shear and surface waves. The shear wave experimental directivity pattern results are presented and compared with the theoretical results of a single source and an array source. The experimental directivity results for the surface wave are also presented, and compared with the theoretical results. The data show that the array enhances signal generation in the forward direction for both shear and surface waves. The array gain is also discussed. The receiver for the directivity measurements was a contact piezoelectric transducer.  相似文献   
38.
An anisotropic triangular Ising model in which the first- and second-order parameters and the field parameters are functionally related is solved exactly by representing the distribution of the atom patterns in terms of a suitably constructed Markov process. The probabilities of patterns, defined as the probabilities generated by this process, are a mathematically tractable alternative to the classical representation of these probabilities in terms of the partition function. The interaction and field parameters of this Ising model, its magnetization, free energy, and its nearest neighbor correlation functions, are expressed in terms of the parameters of this Markov process. Special cases are worked out in detail and numerical examples are given.  相似文献   
39.
在高极化多自旋液体样品中,同时存在着分子间偶极(D)耦合和分子内标量(J)耦合,它们的共同作用产生了一些原来观测不到的分子间多量子相干信号。而且,信号的裂分模式与只存在J耦合的多自旋体系中观测到的多量子相干信号的裂分模式不同。本文从理论和实验上研究了这些禁阻的共振峰及其独特的裂分模式。为了比较验证,我们以I2S3+X自旋体系为例,结合使用选择和非选择性的射频脉冲序列来获得分子间双量子相干信号的五种裂分模式。进而归纳出对IpSq+Xk (p, q, k = 1, 2, 3,…)自旋体系普适的裂分模式规则。并指出,它们中如(1:0:-1)的裂分模式会放大J耦合裂分,使得J耦合常数的测量更精确,特别在J耦合常数很小或不均匀场中的J耦合常数的测量中具有诱人的应用前景。结果表明理论预测,计算机模拟和实验观测结果三者吻合的很好。  相似文献   
40.
We prove the existence of four solutions for the p-Laplacian equation
  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