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   1487619篇
  免费   24389篇
  国内免费   6977篇
电工技术   34297篇
综合类   6352篇
化学工业   270219篇
金属工艺   63958篇
机械仪表   41847篇
建筑科学   45878篇
矿业工程   11425篇
能源动力   50238篇
轻工业   109103篇
水利工程   14999篇
石油天然气   37507篇
武器工业   140篇
无线电   196037篇
一般工业技术   280940篇
冶金工业   153613篇
原子能技术   33930篇
自动化技术   168502篇
  2021年   15580篇
  2020年   11853篇
  2019年   14622篇
  2018年   15488篇
  2017年   14853篇
  2016年   21300篇
  2015年   17379篇
  2014年   28695篇
  2013年   87805篇
  2012年   34923篇
  2011年   47032篇
  2010年   42131篇
  2009年   50752篇
  2008年   44027篇
  2007年   41202篇
  2006年   44111篇
  2005年   38829篇
  2004年   41057篇
  2003年   40961篇
  2002年   40093篇
  2001年   36765篇
  2000年   35352篇
  1999年   34102篇
  1998年   41781篇
  1997年   37339篇
  1996年   34121篇
  1995年   30088篇
  1994年   28283篇
  1993年   28142篇
  1992年   25993篇
  1991年   23047篇
  1990年   23383篇
  1989年   22520篇
  1988年   20919篇
  1987年   19231篇
  1986年   18624篇
  1985年   21984篇
  1984年   22197篇
  1983年   20163篇
  1982年   19186篇
  1981年   19275篇
  1980年   17917篇
  1979年   18450篇
  1978年   17657篇
  1977年   17369篇
  1976年   18053篇
  1975年   15935篇
  1974年   15439篇
  1973年   15528篇
  1972年   13001篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
901.
The Six Sigma approach is one of the more recent initiatives adopted by organisations who seek to make a paradigm shift in performance improvement (attacking at least one of the cost, quality, delivery measurements for improved competitiveness). Is there anything new about Six Sigma, does it offer improvements that other approaches cannot, or is it just a clever delivery of repackaged goods? The author investigates the above questions related to the Six Sigma approach  相似文献   
902.
Cables to moving parts on a linear actuator in production machines, such as pick-and-place machines, are a source of unreliability owing to the possible breaking of a cable. They further reduce the positioning precision of the actuator owing to additional forces. Slotted waveguide systems for rail vehicles based on 2.4 GHz transmission frequency are well known, but transmitters/receivers and waveguides are bulky. The paper reports on the reduction in size of the equipment, adapted to 5.8 GHz using a commercial off-the-shelf RadioLan communication module. Further, the efficient termination of the wave-guide and a new way to reduce standing-wave effects is also discussed.  相似文献   
903.
904.
The Kerendan carbonate platform (Oligocene Berai Limestone) covers a subsurface area measuring approximately 11 by 16 km in the westernmost Kutei Basin, Central Kalimantan. Aggradation of the Kerendan platform occurred during a major Oligocene transgression, and is contemporaneous with aggradation and backstepping of the Barito shelf margin which was located approximately 30 km to the south. The Kerendan platform is approximately 1,000 m thick, and comprises three aggrading seismic sequences identified by the downlap of basinal strata at the platform margin and downlap of transgressive strata within the platform. Carbonate deposition started in the Late Eocene, and ended when the upper limestone sequence drowned and was covered with shale in the Late Oligocene (approximately 28.6 Ma). Three depositional areas can be distinguished in seismic sections: (1) a platform interior (lagoon); (2) a slightly raised platform rim (1–2 km wide); and (3) a basinward‐dipping platform margin and slope. The margin of the platform is identified by inflections on the seismic profiles where the relatively flat platform top begins to slope basinward. Depositional models from outcrops combined with core from three Kerendan wells were used to extrapolate depositional facies onto the seismically‐defined platform. Platform‐interior (lagoon) facies consist largely of fossiliferous wackestones and packstones, and porosities are generally lower than 5%. The platform rim is characterized by interbedded bioclastic wackestones, packstones, grainstones and boundstones, with grainstones increasing toward the platform margin. Porosity preferentially occurs in packstones, grainstones and boundstones. The platform‐rim deposits have greater porosity (5–13%) than the platform interior because the platform run is more grainstone‐rich, and because acidic waters compacting out of basinal shales concentrated dissolution near the platform margin. Pore types include vuggy porosity, microporosity within grains, and intercrystalline porosity in dolomite in the upper part of the platform rim. Different pore types have resulted in variable but locally very high permeabilities (greater than 100 mD). Permeabilities decrease with depth as vuggy pores decrease, and microporosity becomes dominant.  相似文献   
905.
声波全波列测井中的反射纵波可以用来评价高角度裂缝和对井周附近地质结构进行成像。目前的研究主要侧重于直接从波形资料处理出发计算裂缝的位置和倾角 ,其可靠性和准确性无从评价和校验。文中采用模拟实验的方法记录了倾角为 6 0°~80°范围内的 8种倾角裂缝的反射脉冲纵波波形 ,自行推导了反演裂缝倾角的公式 ,结合波场分离技术对实验测量波形数据进行了处理 ,计算出的裂缝倾角与实际值具有良好的一致性。本文结果表明 ,利用至少 2个深度点的纵波反射波波形资料就可以准确地反演裂缝的倾角  相似文献   
906.
G. C. Bakos   《Applied Energy》2002,72(3-4):609-619
This paper deals with the technical feasibility and economic viability of a grid connected wind-energy conversion system (WECS) used to cover the energy demand of an average habitable dwelling. The various parts of the wind-energy system are described and the useful electrical energy production is determined using a simulation program based on the Monte Carlo method. An economic analysis of the WEC system is performed using a computerized assessment tool. Important financial indices are calculated and financial scenarios investigated.  相似文献   
907.
The performance of a home made MIS–p-Si solar cell was experimentally studied under various gamma irradiation doses (up to 500 Mrad). The effect of radiation dose on the IV and CV characteristics was investigated in this work. The obtained results showed that all the output parameters of the cells under investigation were degraded with gamma radiation exposure. In addition, the effects of fabrication conditions (metal thickness and adding of antireflection coating) on the cell output parameters were also investigated.  相似文献   
908.
909.
910.
简单介绍了碳氧比测井的原理及通常的数据处理方法。分析了由常规数据处理所得曲线仍然存在的问题及可能的成因 ,并给出了可行的修正办法。讨论了另一种可行的曲线异常数据的检测、剔除方法。实践表明 :文章讨论的两点建议都是可行的 ,并且在提高测量曲线质量的同时也提高了地层含油饱和度的解释精度。  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