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   864篇
  免费   31篇
  国内免费   2篇
电工技术   18篇
综合类   1篇
化学工业   314篇
金属工艺   32篇
机械仪表   24篇
建筑科学   20篇
能源动力   22篇
轻工业   63篇
水利工程   4篇
石油天然气   1篇
无线电   28篇
一般工业技术   207篇
冶金工业   69篇
原子能技术   36篇
自动化技术   58篇
  2023年   9篇
  2022年   23篇
  2021年   18篇
  2020年   10篇
  2019年   22篇
  2018年   20篇
  2017年   19篇
  2016年   20篇
  2015年   12篇
  2014年   28篇
  2013年   54篇
  2012年   52篇
  2011年   56篇
  2010年   42篇
  2009年   42篇
  2008年   48篇
  2007年   47篇
  2006年   32篇
  2005年   33篇
  2004年   33篇
  2003年   26篇
  2002年   22篇
  2001年   16篇
  2000年   16篇
  1999年   19篇
  1998年   34篇
  1997年   20篇
  1996年   19篇
  1995年   10篇
  1994年   12篇
  1993年   13篇
  1992年   8篇
  1991年   7篇
  1990年   5篇
  1989年   6篇
  1988年   3篇
  1987年   8篇
  1986年   7篇
  1985年   3篇
  1981年   3篇
  1980年   1篇
  1978年   1篇
  1977年   3篇
  1976年   3篇
  1974年   1篇
  1973年   4篇
  1972年   1篇
  1971年   2篇
  1970年   1篇
  1969年   1篇
排序方式: 共有897条查询结果,搜索用时 15 毫秒
101.
Many biological systems use extensive networks for the transport of resources and information. Ants are no exception. How do biological systems achieve efficient transportation networks in the absence of centralized control and without global knowledge of the environment? Here, we address this question by studying the formation and properties of inter-nest transportation networks in the Argentine ant (Linepithema humile). We find that the formation of inter-nest networks depends on the number of ants involved in the construction process. When the number of ants is sufficient and networks do form, they tend to have short total length but a low level of robustness. These networks are topologically similar to either minimum spanning trees or Steiner networks. The process of network formation involves an initial construction of multiple links followed by a pruning process that reduces the number of trails. Our study thus illuminates the conditions under and the process by which minimal biological transport networks can be constructed.  相似文献   
102.
103.
A detailed procedure of full-electromagnetic Vlasov simulation technique is presented. Our new unsplitting conservative scheme exactly satisfies the continuity equation for charge. The implicit Finite Difference Time Domain method is also adopted for computation of electromagnetic fields, which is not restricted by the CFL condition for light. The Geospace Environment Modeling magnetic reconnection challenge problem is adopted as a benchmark test. The characteristics of the present Vlasov code are studied by varying the resolution in configuration space.  相似文献   
104.
Fluoroaluminate glasses containing various concentrations of Eu2+ were prepared under a reducing atmosphere for the present study, and the wavelength dependence of the Faraday rotation angle was examined. The magnitude of the Verdet constant (Vc) increased as the concentration of Eu2+ increased. In addition, the Verdet constant of glasses containing 5 cat.% Eu2+ was larger than that of fluoroaluminate glasses containing the same concentration of Tb3+ in the wavelength region from 400 to 600 nm. The effective transition wavelength, λt, for glasses containing Eu2+ as well as those containing Tb3+ was evaluated based on the Van Vleck and Hebb theory. Factors dominating the Verdet constant of those glasses are discussed in this report.  相似文献   
105.
Si3N4/carbon fiber composites have been produced with and without seeding by an extrusion and sintering process. In both cases the carbon fibers were aligned along the direction of extrusion, but the Si3N4 grains were only aligned in the seeded material. The mechanical properties of the specimens showed anisotropy with respect to the grain alignment, with both strength and toughness being highest in the direction parallel to the extruding direction. In this direction the seeded specimen, where both the Si3N4 grains and the carbon fibers were aligned, showed both higher fracture toughness and higher fracture strength than the nonseeded specimen where only the fibers were aligned.  相似文献   
106.
The right atrial posterior septum, including the coronary sinus (CS) ostium, is an important landmark in radiofrequency catheter ablation therapy for supraventricular tachycardia or atrial flutter. The anatomical findings around the CS ostium would be useful to determine a target site or line during catheter ablation. The aim of the study was to test the ability of the imaging catheter to identify structures in the posterior septal area of the right atrium and to evaluate the feasibility of guidance for catheter placement in the CS using a cardioscope that we recently developed. In 12 anesthetized dogs, the cardioscope, consisting of a deflectable 7 Fr fiberoptic endoscope with an inflatable and transparent balloon, was introduced into the right atrium via the femoral vein. The cardioscope was manipulated to observe the right atrial posterior septum. A deflectable electrode catheter was inserted via the jugular vein and positioned in the CS under cardioscopic guidance. In 10 of 12 dogs, the right atrial posterior septum, including the CS ostium, and the tendon of Todaro could be anatomically identified by cardioscopy. It was possible to position an electrode catheter in the CS in all 10 dogs under direct vision without fluoroscopy. But the CS ostium could not be detected in the remaining two dogs, although the cardioscope was placed at as many sites as possible. No complication occurred. The balloon-tipped cardioscope appears to be useful in observing the right atrialposterior septum and in guiding an electrode catheter into the CS.  相似文献   
107.
The interlayers of montmorillonite clay were pillared with silica-titania sol particles by ion exchange in aqueous solutions. The water in the pillared clay was substituted with ethanol which was in turn extracted with CO2 under supercritical conditions. This drying procedure avoids the formation of liquid-vapour interfaces which give rise to shrinkage of the swelled pillared structure. Highly porous structures with well developed card-house structures resulted. The pore structure was investigated and compared with that of samples prepared by conventional air-drying procedures.  相似文献   
108.
A computer-driven, swept-frequency measurement technique is developed on the basis of resonance birefringence acoustoelasticity to evaluate the stresses in thin plates. The resonance frequency depends on the thickness and the elastic wave velocity; they change with stress because of the Poisson effect and the acoustoelastic effect. The resonance frequency is obtained from the spectral response curve in the electric impedance of the piezoelectric transducer. The frequency displacement induced by acoustically coupling the transducer can be minimized by employing the resonance peak closest to the transducer fundamental frequency. To illustrate the method, the residual stress is measured in butt-welded aluminum alloy plates and is compared with the results of conventional methods.  相似文献   
109.
110.
A 1.5-GHz four-stage microstrip bandpass filter was designed with the miniaturized hairpin resonator structure to reduce the configuration in size. The filter was fabricated using high-T c superconducting films on a 12 × 12 mm2 LaAlO3 substrate. The passband insertion loss of the filter was measured to be -0.4 dB at 77 K, while it was estimated by a planar electromagnetic simulator to around -19 dB when gold films are used instead of the superconducting films.  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