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   528469篇
  免费   19779篇
  国内免费   9091篇
电工技术   16183篇
技术理论   14篇
综合类   13371篇
化学工业   82371篇
金属工艺   22738篇
机械仪表   21836篇
建筑科学   25054篇
矿业工程   5991篇
能源动力   13946篇
轻工业   44369篇
水利工程   6466篇
石油天然气   13146篇
武器工业   1350篇
无线电   66051篇
一般工业技术   85994篇
冶金工业   59202篇
原子能技术   5677篇
自动化技术   73580篇
  2023年   3757篇
  2022年   6821篇
  2021年   9682篇
  2020年   7085篇
  2019年   6623篇
  2018年   21049篇
  2017年   20942篇
  2016年   17512篇
  2015年   9895篇
  2014年   13254篇
  2013年   24054篇
  2012年   21595篇
  2011年   31779篇
  2010年   26387篇
  2009年   24594篇
  2008年   25679篇
  2007年   26189篇
  2006年   18960篇
  2005年   17950篇
  2004年   14536篇
  2003年   13721篇
  2002年   12163篇
  2001年   11650篇
  2000年   11215篇
  1999年   12345篇
  1998年   21462篇
  1997年   15559篇
  1996年   12410篇
  1995年   9746篇
  1994年   8393篇
  1993年   7683篇
  1992年   5627篇
  1991年   5000篇
  1990年   4511篇
  1989年   4200篇
  1988年   3919篇
  1987年   3061篇
  1986年   2859篇
  1985年   3456篇
  1984年   2992篇
  1983年   2738篇
  1982年   2488篇
  1981年   2516篇
  1980年   2314篇
  1979年   2133篇
  1978年   1931篇
  1977年   2225篇
  1976年   2782篇
  1975年   1616篇
  1973年   1584篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
This being a design-build project, the challenge faced during preparations of the Employer’s requirements for design and construction of the Istanbul Strait immersed tunnel was to give the contractor as much freedom as possible and yet specify enough so that the Employer obtained the required facility. When completed, this will be a world-class facility. This paper discusses on a strategic level many of the aspects to be presented by the author in two papers in later sessions of the day. Unusual features of this crossing include the deepest ever immersed tunnel crossing, extra waterproofing requirements, strong currents with bi-directional flow, close proximity of the North Anatolian Fault which is predicted to have a major seismic event during the life of the tunnel, and the method of connecting the adjacent bored tunnels to the immersed tunnel. Safety during tunnel construction and operation has been paramount, and resulted in changes to contract packaging and extra requirements. Other challenges discussed include fish migration, control of an international waterway, environmental issues and ensuring the stability of the soft soils during a seismic event.  相似文献   
992.
993.
董公馆是一个6层楼的公寓,依山而建,业主将他交到设计师手里,让他在这基础上活活变出一个精美的“公馆”。  相似文献   
994.
In the XML file of the original article, H. Redl’s affiliation is incorrect. It is listed correctly in both the paper and PDF versions of the article, and can be found below: The online version of the original article can be found at  相似文献   
995.
Arranga  E.C. Coyle  F.P. 《Computer》1997,30(3):126-128
The authors list the perceptions they have uncovered and counter them with the reality of Cobol. Some of the perceptions are: Cobol is a mainframe language-it has been available on PCs since their inception; Cobol stopped evolving in the 1970s, stopped growing in popularity in the 1980s, and stopped being used to develop client-server and Web-based applications in the 1990s; and Cobol is not an object-oriented language, when, in fact, it has objects galore  相似文献   
996.
Industrial wastes consigned to disposal sites frequently contain substantial amounts of heavy metals. We have successfully applied proton induced X-ray emission analysis (PIXE) in the conduct of heavy metal (Hg, Cd, Cr, As) toxicity studies using precision cut rabbit renal cortical slices. The large beam diameter (4000 μm) of the proton macroprobe at The University of Arizona Ion Beam Analysis facility allowed an overall concentration of the metal(s) of interest in the samples to be determined, but lacked the ability to resolve point concentrations in the tissue. The ability to locate these areas has now been made available to us with the addition of a rastering microprobe (μ-PIXE) to the facility. Studies now being conducted in our laboratory using this micro-technique include analysis of renal tissue taken from rabbits injected intraperitoneally with HgCl2, K2Cr2O7, and NaAsO2. The small beam size (3 μm) and the ability to raster this beam over areas of up to 125 μm × 125 μm has allowed regional mapping of endogenous and non-endogenous metal concentrations and revealed trends in heavy metal deposition in in vivo treated renal tissue, significantly increasing the amount of information obtained from these animal studies using PIXE alone. The combination of small beam size, high resolution, and multi-element detection makes μ-PIXE a powerful tool for investigating the impact of non-endogenous metals on the kidney.  相似文献   
997.
This letter presents for the first time, the experimentally determined majority carrier mobilities in the accumulation layer of a MOSFET for both p-type and n-type channel doping for a wide range of doping concentrations. The measured carrier mobility is observed to follow a universal behavior at high transverse fields, similar to that observed for minority carriers in MOS inversion layers. At the higher doping levels, the effective mobility for majority carriers at low to moderate transverse fields is found to be very close to the bulk mobility. This is believed to be due to carrier screening of the ionized impurity scattering which dominates at the higher doping concentrations  相似文献   
998.
This paper presents the computer-aided design (CAD) and performance analysis of a novel direct-driven wheel brushless DC motor drive for electric vehicles (EVs). The proposed motor is a permanent magnet square-wave motor, whose rotor with rare earth magnets forms the exterior of the motor, which can be fitted with a wheel tire to realize the direct drive for each wheel of an EV. The interior stator with its windings is rigidly mounted onto the suspension and frame structure of the vehicle. In order to achieve the direct drive without any mechanical transmission for EVs, the wheel motor has been designed as a low-speed high-torque motor. The design and optimization of the motor geometry was achieved with the aid of finite-element electromagnetic field analysis. Simulation studies on the transient performance of the motor drive were also carried out. This involved the creation of the motor transient model and formulation of a motor control strategy to ensure the wheel motor drive runs efficiently in the entire permitted speed and load range. The application of CAD techniques in the design of this very unconventional drive is described in this paper  相似文献   
999.
We present a scattering center extraction algorithm to parameterize the backscattered data from complex targets collected over large angular apertures. This parameterization is based on a scattering center model of the target, but includes an aspect-dependent amplitude function for each scattering center. A two-dimensional (2-D) adaptive Gaussian representation (AGR) algorithm is used to extract the position and the amplitude function associated with each scattering center. The algorithm is tested with data generated by the Xpatch radar simulation code as well as chamber measurement data. The results show that a very good compression ratio can be achieved, resulting in a compact scattering center model of the target. Once such model is available, we can easily reconstruct range profiles and ISAR images at any aspect on the same plane with good accuracy  相似文献   
1000.
A decay of fresh-cut celery (Apium graveolens) segments stored at < 5°C in sealed film bags began with a water soaking of the cut surfaces. Slimy moisture accumulated inside the bags. The segments water soaked completely, softened, discolored and sometimes disintegrated. Total aerobic bacterial populations isolated from decayed segments ranged from log10 7.0–7.7 CFU/g tissue weight. The predominant bacteria, identified by fatty acid analysis as Pseudomonas fluorescens and P. marginalis, caused water soaking, soft rot, and discoloration in freshly inoculated celery tissues stored at 5 or 25°C. Leuconostoc mesenteroides was also isolated and may have been responsible for slime production.  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