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   7952篇
  免费   1187篇
  国内免费   448篇
化学   4079篇
晶体学   35篇
力学   791篇
综合类   188篇
数学   1948篇
物理学   2546篇
  2024年   10篇
  2023年   101篇
  2022年   284篇
  2021年   315篇
  2020年   388篇
  2019年   263篇
  2018年   240篇
  2017年   347篇
  2016年   413篇
  2015年   346篇
  2014年   482篇
  2013年   475篇
  2012年   500篇
  2011年   478篇
  2010年   391篇
  2009年   488篇
  2008年   446篇
  2007年   464篇
  2006年   443篇
  2005年   370篇
  2004年   334篇
  2003年   286篇
  2002年   238篇
  2001年   195篇
  2000年   198篇
  1999年   154篇
  1998年   159篇
  1997年   117篇
  1996年   97篇
  1995年   110篇
  1994年   83篇
  1993年   73篇
  1992年   61篇
  1991年   34篇
  1990年   31篇
  1989年   27篇
  1988年   14篇
  1987年   16篇
  1986年   16篇
  1985年   26篇
  1984年   17篇
  1983年   6篇
  1982年   9篇
  1981年   3篇
  1980年   6篇
  1979年   14篇
  1978年   5篇
  1977年   6篇
  1976年   5篇
  1971年   2篇
排序方式: 共有9587条查询结果,搜索用时 265 毫秒
991.
冯其波 《光子学报》1996,25(3):279-284
本文以基于 Buchadhl 象差系数得到的点列图为目标函数,只需追迹少许光线就可得到近似点列图,大大减少了计算量;同时采用了目标函数对结构参数偏导数解析求导原理并应用于光学自动设计,这样得到的解析偏导数不仅不存在原理误差,同时极大地减少了求得所需的时间;最后给出了使用 DFP-BFGS 优化方法设计一个双高斯物镜的实例.  相似文献   
992.
Summary We describe the simplest system which shows stochastic resonance. A linear(ized) theory for white and (almost) arbitrarily coloured noise is presented. The presented new system has new, unique properties which originate from itsnon-dynamical character; for example, the strength and phase shift of periodic response of the system is independent of the frequency. Experiments have been carried out with the following noise processes: (physical) white noise, (physical) Lorentzian noise and (physical) 1/f noise. With a small extension of the system, its linear-response regime can be significantly increased. As the system is similar to some simple models of neurones, the new results might have not only physical but also biological importance. Paper presented at the International Workshop “Fluctuations in Physics and Biology: Stochastic Resonance, Signal Processing and Related Phenomena”, Elba, 5–10 June 1994.  相似文献   
993.
机械结构的模糊优化设计   总被引:2,自引:0,他引:2  
本文阐述了机械结构模糊优化设计的必要性及方法,并以用于55千瓦风力发电机组的NGW92型行星齿轮传动为例,说明这一现代设计方法的实施及优良设计特性。  相似文献   
994.
光学设计的发展   总被引:1,自引:0,他引:1  
本文概述了光学设计所处的历史发展阶段,对智能化光学设计给出了定性的描述,指出了目前光学设计要解决的问题以及发展方向。  相似文献   
995.
Summary Strategies for computational association of molecular components entail a compromise between configurational exploration and accurate evaluation. Following the work of Meng et al. [Proteins, 17 (1993) 266], we investigate issues related to sampling and optimization in molecular docking within the context of the DOCK program. An extensive analysis of diverse sampling conditions for six receptor-ligand complexes has enabled us to evaluate the tractability and utility of on-the-fly force-field score minimization, as well as the method for configurational exploration. We find that the sampling scheme in DOCK is extremely robust in its ability to produce configurations near to those experimentally observed. Furthermore, despite the heavy resource demands of refinement, the incorporation of a rigid-body, grid-based simplex minimizer directly into the docking process results in a docking strategy that is more efficient at retrieving experimentally observed configurations than docking in the absence of optimization. We investigate the capacity for further performance enhancement by implementing a degeneracy checking protocol aimed at circumventing redundant optimizations of geometrically similar orientations. Finally, we present methods that assist in the selection of sampling levels appropriate to desired result quality and available computational resources.  相似文献   
996.
Summary Steric complementarity is a prerequisite for ligand-receptor recognition; this implies that drugs with a common receptor binding site should possess sterically similar binding surfaces. This principle is used as the basis for an automatic and unbiased method that superposes molecules. One molecule is rotated and translated to maximize the overlap between the two molecular surface volumes. A fast grid-based method is used to determine the extent of this overlap, and this is optimized using simulated annealing. Matches with high steric similarity scores are then sorted on the basis of both hydrogen-bond and electrostatic similarity between the matched molecules. Flexible molecules are treated as a set of rigid representative conformers. The algorithm has correctly predicted superpositions between a number of pairs of molecules, according to crystallographic data from ligands that have been co-crystallized at common enzyme binding sites.  相似文献   
997.
998.
We introduce and discuss a combination of methods and options that aim at the aerodynamical optimization of a flow around an arbitrary aircraft shape. The flow is governed by the Euler equations, discretized by a mixed element-volume method on a fixed unstructured tetrahedrization. The shape parametrization relies on the skin of the above mesh through a hierarchical representation. Descent-type and one-shot algorithms are devised and adapted to the solution of a few model problems.  相似文献   
999.
关于正交设计与均匀设计的比较(Ⅰ)   总被引:1,自引:0,他引:1  
本文通过对优化效率的比较,说明在主要方面正交设计要比均匀设计更好。  相似文献   
1000.
The selection of a monitoring network is formulated as a decision problem whose solutions would then be optimal. The theory is applied where the underlying field has a multivariate normal probability structure.  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