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   1566篇
  免费   59篇
  国内免费   5篇
电工技术   24篇
综合类   13篇
化学工业   519篇
金属工艺   52篇
机械仪表   24篇
建筑科学   59篇
矿业工程   11篇
能源动力   52篇
轻工业   139篇
水利工程   12篇
石油天然气   14篇
无线电   80篇
一般工业技术   282篇
冶金工业   87篇
原子能技术   26篇
自动化技术   236篇
  2023年   14篇
  2022年   28篇
  2021年   45篇
  2020年   37篇
  2019年   37篇
  2018年   40篇
  2017年   48篇
  2016年   40篇
  2015年   43篇
  2014年   60篇
  2013年   88篇
  2012年   78篇
  2011年   92篇
  2010年   84篇
  2009年   75篇
  2008年   68篇
  2007年   56篇
  2006年   37篇
  2005年   44篇
  2004年   41篇
  2003年   41篇
  2002年   26篇
  2001年   19篇
  2000年   35篇
  1999年   47篇
  1998年   49篇
  1997年   42篇
  1996年   18篇
  1995年   10篇
  1994年   9篇
  1993年   24篇
  1992年   8篇
  1990年   5篇
  1989年   5篇
  1988年   5篇
  1987年   5篇
  1986年   10篇
  1984年   12篇
  1983年   13篇
  1982年   18篇
  1981年   19篇
  1980年   14篇
  1979年   13篇
  1978年   8篇
  1977年   18篇
  1976年   18篇
  1975年   12篇
  1974年   12篇
  1973年   15篇
  1971年   5篇
排序方式: 共有1630条查询结果,搜索用时 15 毫秒
1.
2.
ABSTRACT

Nine sowing densities of linseed were compared in a two-year experiment. Self-regulation of the density of a linseed stand resulted in a differentiated branching of the plants. The number of capsules on a linseed shoot, as well as seeds in the capsule, and the number of seeds from the shoot were highly varied from year to year, and there is even a stronger differentiation in the weight of 1000 seeds. Linear relationships were noted between the mass of seeds from the linseed plant and the number of capsules. The yield of linseed was affected by both factors. An increasing sowing rate reduced the seed yield from the shoot and the plant. At lower seeding rates, the lateral shoots contributed in the seeds yield of the plant to a higher degree compared to the main ones.  相似文献   
3.
4.
5.
In [Turek (1996). Int. J. Numer. Meth. Fluids 22, 987–1011], we had performed numerical comparisons for different time stepping schemes for the incompressible Navier–Stokes equations. In this paper, we present the numerical analysis in the context of the Navier–Stokes equations for a modified time-stepping θ-scheme which has been recently proposed by Glowinski [Glowinski (2003). In: Ciarlet, P. G., and Lions, J. L. (eds.), Handbook of Numerical Analysis, Vol. IX, North-Holland, Amsterdam, pp. 3–1176]. Like the well-known classical Fractional-Step-θ-scheme which had been introduced by Glowinski [Glowinski (1985). In Murman, E. M. and Abarbanel, S. S. (eds.), Progress and Supercomputing in Computational Fluid Dynamics, Birkh?user, Boston MA; Bristeau et al. (1987). Comput. Phys. Rep. 6, 73–187], too, and which is still one of the most popular time stepping schemes, with or without operator splitting techniques, this new scheme consists of 3 substeps with nonequidistant substepping to build one macro time step. However, in contrast to the Fractional-Step-θ-scheme, the second substep can be formulated as an extrapolation step for previously computed data only, and the two remaining substeps look like a Backward Euler step so that no expensive operator evaluations for the right hand side vector with older solutions, as for instance in the Crank–Nicolson scheme, have to be performed. This modified scheme is implicit, strongly A-stable and second order accurate, too, which promises some advantageous behavior, particularly in implicit CFD simulations for the nonstationary Navier–Stokes equations. Representative numerical results, based on the software package FEATFLOW [Turek (2000). FEATFLOW Finite element software for the incompressible Navier–Stokes equations: User Manual, Release 1.2, University of Dortmund] are obtained for typical flow problems with benchmark character which provide a fair rating of the solution schemes, particularly in long time simulations.Dedicated to David Gottlieb on the occasion of his 60th anniversary  相似文献   
6.
The present paper outlines the views of the Government of Aragon on the National Hydrological Plan of Spain. It concludes that the transfer of water from the Ebro River will accentuate the differences among some regions of Spain in terms of their development potentials. It will unquestionably constrain the future development of regions that are already disadvantaged, such as Aragon. Alternatives are proposed where the regions in need of water can obtain it, but without adversely affecting the economic, social and environmental sustainability of the region and the people of Aragon.  相似文献   
7.
SecA is a dynamic protein that undergoes ATP-dependent membrane cycling to drive protein translocation across the Escherichia coli inner membrane. To understand more about this process, azide-resistant (azi) and signal sequence suppressor (prlD) alleles of secA were studied. We found that azide resistance is cold sensitive because of a direct effect on protein export, suggesting that SecA-membrane interaction is regulated by an endothermic step that is azide inhibitable. secG function is required for expression of azide-resistant and signal sequence suppressor activities of azi and prlD alleles, and in turn, these alleles suppress cold-sensitive and export-defective phenotypes of a secG null mutant. These remarkable genetic observations support biochemical data indicating that SecG promotes SecA membrane cycling and that this process is dependent on an endothermic change in SecA conformation.  相似文献   
8.
The paper gives a bibliographical review of the finite element methods (FEMs) applied for the analysis of pressure vessel structures/components and piping from the theoretical as well as practical points of view. The range of applications of FEMs in this area is wide and cannot be presented in a single paper; therefore the aim of this review is to give the reader an encyclopaedic view of the differnt possibilities that exist today for the finite element analysis in the fields of pressure vessels and piping. The bibliography at the end of the paper contains approximately 1900 references to papers, conference proceedings and theses/dissertations on the subject that were published in 1976–1996. These are classified in the following categories: linear and non-linear, static and dynamic, stress and deflection analysis; stability problems; thermal problems; fracture mechanics problems; contact problems; fluid-structure interaction problems; manufacturing of pipes and tubes; welded pipes and pressure vessel components; development of special finite elements for pressure vessels and pipes; finite element software; and other topics. Also finite element software, general purpose and special purpose codes, used for the analysis of pressure vessels and pipes are briefly discussed and presented.  相似文献   
9.
Linear oligosiloxanes functionalized with bulky side chain tris(trimethylsilyl)hexyl (TTSH) substituents were transformed into cross-linked materials by UV 193 nm excimer pulsed laser ablation. The process occurred without any catalyst, by reactions of radicals formed in UV laser induced photolysis of side tris(trimethylsilyl)hexyl groups. Chemical changes were monitored by FTIR, LC/UV, GC/MS and solubility tests.  相似文献   
10.
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