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   1135篇
  免费   63篇
  国内免费   1篇
化学   855篇
晶体学   12篇
力学   36篇
数学   78篇
物理学   218篇
  2023年   7篇
  2022年   16篇
  2021年   23篇
  2020年   34篇
  2019年   25篇
  2018年   29篇
  2017年   29篇
  2016年   57篇
  2015年   42篇
  2014年   55篇
  2013年   85篇
  2012年   100篇
  2011年   75篇
  2010年   44篇
  2009年   44篇
  2008年   89篇
  2007年   50篇
  2006年   47篇
  2005年   44篇
  2004年   39篇
  2003年   28篇
  2002年   34篇
  2001年   8篇
  2000年   7篇
  1998年   4篇
  1997年   6篇
  1996年   11篇
  1994年   3篇
  1991年   7篇
  1990年   3篇
  1986年   7篇
  1985年   10篇
  1984年   10篇
  1983年   5篇
  1982年   3篇
  1981年   8篇
  1980年   4篇
  1979年   5篇
  1978年   10篇
  1977年   4篇
  1975年   3篇
  1969年   6篇
  1968年   6篇
  1964年   4篇
  1963年   6篇
  1962年   6篇
  1961年   12篇
  1958年   7篇
  1957年   3篇
  1955年   5篇
排序方式: 共有1199条查询结果,搜索用时 31 毫秒
81.
82.
Shelyubskii wavelength scan technique to measure glass homogeneity is described. The Raman-Shelyubskii theory, which is based upon interference optics and which, hitherto, was believed to be the underlying mechanism, is discarded. A computer simulation of light scattering based on geometric optics principles fits the observed transmission vs wavelength curves very well.  相似文献   
83.
Applied Biochemistry and Biotechnology - Extracellular proteins produced by yeast have been observed to stratify in the extracellular fluid of a batch bioreactor, thus creating a vertical...  相似文献   
84.
We present a switched control law for stabilizing an underactuated underwater vehicle (UUV) moving in a horizontal plane in a neutrally buoyant condition. The control law consists of a sequential series of control actions, each of which achieves a certain objective, finally resulting in the system being moved to the origin. Finite-time controllers are employed at each stage to achieve the desired objective. Simulation results are presented to validate the control law.  相似文献   
85.
This paper deals with a new solution technique for approximately solving certain variational problems in elasticity by using discrete optimization techniques that were originally used in information theory. This allows us to easily and approximately solve large deformation buckling problems for slender cantilever beams (including post-buckling behavior) as well as problems where the strain energy function is non-convex.The core idea is to quantize or discretize the variables describing the possible configurations of the body. This, when combined with the fact that the variational problem has an inherent Markov structure allows us to use computationally efficient search techniques based on dynamic programming (equivalent to finding the shortest path in a weighted directed graph) to find optimal solutions within the quantized state space. The results can be used in two ways: (1) directly as a fast approximate solution to the variational problem (2) As a means for finding very good (nearly minimum energy) initial configurations for application of conventional minimization techniques, which might otherwise fail because of a poor starting configurations which are far from the global minimum. We demonstrate both these uses in the paper.  相似文献   
86.
87.
    
A kinetic study of the tumor-associated galactopyranosyl-(1→3)-2-acetamido-2-deoxy-α-d-galactopyranoside (T-antigen) with lectin peanut agglutinin is described. The disaccharide antigen was synthesized by chemical methods and was functionalized suitably for immobilization onto a carboxy-methylated sensor chip. The ligand immobilized surface was allowed interaction with the lectin peanut agglutinin, which acted as the analyte and the interaction was studied by the surface plasmon resonance method. The ligand—lectin interaction was characterized by the kinetic on-off rates and a bivalent analyte binding model was found to describe the observed kinetic constants. It was identified that the antigen-lectin interaction had a faster association rate constant (k a1) and a slower dissociation rate constant (k d1) in the initial binding step. The subsequent binding step showed much reduced kinetic rates. The antigen-lectin interaction was compared with the kinetic rates of the interaction of a galactopyranosyl-(1→4)-β-d-galactopyranoside derivative and a mannopyranoside derivative with the lectin.  相似文献   
88.
Over the past three decades there has been nearly exponential growth in drying R&D on a global scale. Although thermal drying had always been the workhorse of almost all major industrial sectors, the need for and opportunities in basic as well as industrial research became clear only after the energy crisis of the early 1970s. Although the price of oil did drop subsequently the awareness of the significance of improving the drying operation to save energy, improve product quality as well as reduce environmental effect remained and indeed has flourished over recent years. New drying technologies, better operational strategies and control of industrial dryers, as well as improved and more reliable scale-up methodologies have contributed to better cost-effectiveness and better quality dried products. Yet there is no universally or even widely applicable drying theory on the horizon. Most mathematical models of drying remain product-equipment specific for a variety of reasons. In this paper, we examine the role of innovation in drying in various industrial sectors, e.g. paper, wood, foods, agriculture, waste management, etc. Progress made over the past three decades and the challenges ahead are outlined. Some areas in need of further research are identified. Examples of intensification of innovation in dryer designs via mathematical modeling are discussed. Finally, the need for closer interaction between academia and industry is stressed as the key to successful drying R&D in the coming decade.  相似文献   
89.
Palladium catalyzed intramolecular aminoacetoxylation of d-ribose derived alkenyl tosylsulfonamide to deliver l-deoxyallonojirimycin in an overall yield of 19%. The preliminary screening of l-deoxyallonojirimycin against carbohydrate processing enzymes showed moderate inhibitory activity against α-glucosidase (yeast) and α-mannosidases.  相似文献   
90.
Habenaria edgeworthii Hook. f. ex Collett is an important terrestrial orchid used in different Ayurvedic formulations. In the present study, variations among morphological, phytochemical and molecular markers were assessed. A significant difference was observed among populations using morphological traits. Inter-simple sequence repeat (ISSR) data revealed lower genetic diversity at population level (He = 0.207) as compared to species level (He = 0.334). Analysis of molecular variance (AMOVA) indicates 74 % variation among populations and 26 % within population. Tuber extracts showed significantly (p < 0.05) higher total phenolics and flavonoids among the populations. Antioxidant activity determined by 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging and ferric reducing antioxidant power (FRAP) assays exhibited considerable antioxidant potential. Furthermore, the associations between molecular and morphological and phytochemical attributes were studied using multiple regression analysis (MRA). Several ISSR fragments were associated with some morphological and phytochemical traits. These ISSR fragments can be useful for breeding programme of the species when no other genetic information, such as linkage maps and quantitative trait loci, is available.  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