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   1536076篇
  免费   24934篇
  国内免费   6996篇
电工技术   34342篇
综合类   6495篇
化学工业   273223篇
金属工艺   64275篇
机械仪表   42951篇
建筑科学   47782篇
矿业工程   11405篇
能源动力   50474篇
轻工业   118853篇
水利工程   15555篇
石油天然气   37308篇
武器工业   137篇
无线电   196978篇
一般工业技术   289584篇
冶金工业   172110篇
原子能技术   33854篇
自动化技术   172680篇
  2021年   15821篇
  2020年   12029篇
  2019年   14824篇
  2018年   15100篇
  2017年   14279篇
  2016年   21387篇
  2015年   17584篇
  2014年   29025篇
  2013年   88376篇
  2012年   36702篇
  2011年   49180篇
  2010年   42653篇
  2009年   50788篇
  2008年   45899篇
  2007年   43093篇
  2006年   46028篇
  2005年   40212篇
  2004年   42701篇
  2003年   42497篇
  2002年   41550篇
  2001年   38476篇
  2000年   36767篇
  1999年   35769篇
  1998年   47421篇
  1997年   40883篇
  1996年   36556篇
  1995年   31637篇
  1994年   29689篇
  1993年   29242篇
  1992年   26590篇
  1991年   23682篇
  1990年   23929篇
  1989年   22989篇
  1988年   21499篇
  1987年   19757篇
  1986年   19238篇
  1985年   22608篇
  1984年   22725篇
  1983年   20608篇
  1982年   19450篇
  1981年   19524篇
  1980年   18121篇
  1979年   18772篇
  1978年   17948篇
  1977年   18040篇
  1976年   19627篇
  1975年   16130篇
  1974年   15663篇
  1973年   15732篇
  1972年   13224篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
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   
992.
We present uniaxial tensile test results for 30–50 nm thick freestanding aluminum films. Young’s modulus and ductility were found to decrease monotonically with grain size. Reverse Hall–Petch behavior was observed with no appreciable room temperature creep. Non-linear elasticity with small irreversible deformation was observed for 50 nm thick specimens.  相似文献   
993.
本文分析了目前制约我国城市可持续发展的最主要因素是低效率的土地利用方式 ,若使地上、地面、地下空间协调发展 ,合理科学的规划好地下空间 ,珍惜地下空间资源 ,健全地下空间法律法规 ,统一地下空间管理机构 ,则可高效率的利用土地。  相似文献   
994.
Following up on recent studies of the Zn-rich corners of the Zn-Fe-Ni and Zn-Fe-Si ternary systems, a 450 °C isothermal section of the Zn-Fe-Ni-Si quaternary phase diagram with the Zn composition being fixed at 93 at.% was determined experimentally using optical microscopy, scanning electron microscopy (SEM) coupled with energy dispersive x-ray spectroscopy (EDS), and x-ray diffractometry (XRD). FeSi was found to be in equilibrium with almost all phases in the section, including the T, ζ, Ni-δ, NiSi2, and FeSi2 phases, as well as the liquid phase (L). Silicon solubilities in the T, ζ, and Ni-δ phases were rather limited. However, the solubilities of Fe and Zn in the NiSi2 phase, at 4.5 at.% and 7.2 at.%, respectively, were appreciable. The existence of the (L+NiSi2+Ni-δ) three-phase equilibrium state apparently prevents other Ni-Si compounds from entering equilibrium with the liquid at 450 °C. No true quaternary compound was found in the study.  相似文献   
995.
996.
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   
997.
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   
998.
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   
999.
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   
1000.
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