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   122000篇
  免费   9853篇
  国内免费   4700篇
电工技术   6932篇
技术理论   2篇
综合类   6069篇
化学工业   20559篇
金属工艺   6923篇
机械仪表   8317篇
建筑科学   6510篇
矿业工程   2243篇
能源动力   4429篇
轻工业   8761篇
水利工程   2155篇
石油天然气   3553篇
武器工业   1017篇
无线电   16354篇
一般工业技术   17869篇
冶金工业   7263篇
原子能技术   1575篇
自动化技术   16022篇
  2024年   313篇
  2023年   1419篇
  2022年   2709篇
  2021年   4173篇
  2020年   3080篇
  2019年   2741篇
  2018年   3205篇
  2017年   3587篇
  2016年   3840篇
  2015年   4268篇
  2014年   5911篇
  2013年   7433篇
  2012年   8883篇
  2011年   9775篇
  2010年   8470篇
  2009年   8344篇
  2008年   8090篇
  2007年   7192篇
  2006年   6626篇
  2005年   5492篇
  2004年   4509篇
  2003年   4230篇
  2002年   4211篇
  2001年   3650篇
  2000年   2544篇
  1999年   2024篇
  1998年   2159篇
  1997年   1505篇
  1996年   1231篇
  1995年   887篇
  1994年   711篇
  1993年   577篇
  1992年   416篇
  1991年   366篇
  1990年   346篇
  1989年   312篇
  1988年   242篇
  1987年   204篇
  1986年   146篇
  1985年   121篇
  1984年   101篇
  1983年   75篇
  1982年   48篇
  1981年   49篇
  1980年   38篇
  1979年   36篇
  1978年   32篇
  1977年   41篇
  1976年   64篇
  1975年   23篇
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
71.
首先揭示出民族风格是与时代风格对立统一、相互依存的一个概念。因而特定的时代需要具有时代精神的民族风格──创新民族风格。在探索此风格的过程中.我们首先要学习日本的战略,然后在学习的基础上实现超越。  相似文献   
72.
Interfacial reactions in the squeeze-cast SAE 329 Al alloy reinforced with SAFFIL and carbon fibers were investigated using scanning and transmission electron microscopy and secondary ion mass spectroscopy. The SiO2 layer added as a binder for the preform of SAFFIL fiber appeared to prevent excessive reaction between the fiber and the molten Al alloy during casting. In the as-cast composite, the reaction between the SiO2 layer and the Al alloy is considered to produce MgO crystals in the vicinity of SAFFIL fiber. With subsequent heat treatment of the composite to the T6 condition, small crystals of MgO and MgAl2O4 were found to form at the surface of SAFFIL fiber as a result of interfacial reaction between the SiO2 layer and the Al alloy. Even at the T6 condition, significant reactions between the Al alloy and SAFFIL fiber itself were not observed, indicating the effective role of the binder layer in suppressing the degradation of SAFFIL fiber by reaction with the Al alloy.  相似文献   
73.
Flexible manufacturing systems (FMSs) are able to process a wide variety of operations, but the specific mix of operations that can be performed at any point in time depends upon the combination of tools loaded onto the machines. The machines have tool magazines with finite capacities. We consider the problem of assigning operations and their associated tools to machines (or groups of machines) to maximize the throughput for a specified steady-state mix of orders. Since this objective is difficult to deal with directly, we use an intermediate objective of meeting workload targets for each machine group as closely as possible. A certain form of this intermediate objective has been shown to correlate highly with the original objective.

Since it is computationally intractable to find optimal solutions for problems with more than 20 operations, fast heuristic algorithms are developed. These algorithms are adapted from multi-dimensional bin-packing algorithms. Computational results are reported.  相似文献   
74.
75.
76.
The Technical Specifications (TSs) for a nuclear power plant is an important licensing document which defines various operational requirements or conditions. In light of the recent trends to move towards risk-based regulation, many researchers analyzed the risk impacts associated with the TS requirements, using the plant models, such as event trees or fault trees, that were developed as part of probabilistic safety assessments. This paper presents the insights gained from a review of these risk-based analyses of TSs, focussing on surveillance requirements and AOT (allowed outage time) requirements.  相似文献   
77.
The incidence of stress fractures is increasing among competitive and recreational athletes as well as among children and the elderly. By understanding the continuum of bone's response to stress and maintaining an appropriate index of suspicion, the health care provider can diagnose these injuries appropriately. An accurate history and examination is essential and will differentiate stress fractures from other stress reactions. The more common stress fractures are discussed.  相似文献   
78.
PURPOSE: Normal retina is firmly attached to the retinal pigment epithelium, but the force of this adhesion drops precipitously within the first 2-3 min after enucleation. The purpose was to study metabolic factors that might be relevant to this postmortem failure of adhesion. METHODS: Dutch rabbit retina was manually peeled from the retinal pigment epithelium on strips of enucleated eyecup within a 37 degrees C bath. Retinal adhesiveness was measured by observing the amount of retinal pigment epithelium that remained adherent to the retina. RESULTS: Autologous whole blood in place of salt solution retarded the decrease in adhesiveness. A solution of hemoglobin alone was similarly effective, whereas methemoglobin solution failed to help the persistence of retinal adhesion. Bubbling oxygen into the salt solution and circulating it to avoid oxygen depletion at the tissue boundary also proved effective at sustaining retinal adhesiveness. Eyes made ischemic in vivo for 5 min or longer, by elevating intraocular pressure, showed virtually no retinal adhesion when enucleated immediately thereafter. However, eyes made ischemic for 10 min, but allowed to regain circulation for 5 min before enucleation, showed a return of retinal adhesiveness to 80% of normal. CONCLUSIONS: Oxidative metabolism is critical to the maintenance of retinal adhesiveness, and the effects of oxygen deprivation on adhesion are reversible within a certain time period.  相似文献   
79.
80.
Al,Ga取代Bi:DyIG薄膜的磁和磁光特性的研究   总被引:1,自引:0,他引:1  
本文报道用热分解法在玻璃衬底上制备了Al和Ga取代的Bi:DYIG薄膜,对其磁和磁光特性做了详细研究.Al和Ga取代的薄膜均可获得好的矩形比和高的矫顽力.对于Bi1.2Dy1.8Fe5-xMXO12(M=A1,GZ)薄膜,A1和G2的最佳替代成份分别为1.0和G.7;最佳晶化温度分别为700o℃和675℃.在波长510nm附近,法拉第旋转角可达8°/um左右.光学吸收和品质因子的研究结果表明,Al和Ga取代能够影响光学吸收和品质因子,其中Ga取代对光学吸收和品质因子的影响较大.  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