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   252961篇
  免费   2803篇
  国内免费   875篇
电工技术   4822篇
综合类   194篇
化学工业   36126篇
金属工艺   9525篇
机械仪表   7549篇
建筑科学   6076篇
矿业工程   880篇
能源动力   7225篇
轻工业   21132篇
水利工程   2205篇
石油天然气   3230篇
武器工业   15篇
无线电   34279篇
一般工业技术   49990篇
冶金工业   48544篇
原子能技术   5079篇
自动化技术   19768篇
  2021年   2174篇
  2020年   1560篇
  2019年   1915篇
  2018年   3274篇
  2017年   3314篇
  2016年   3404篇
  2015年   2217篇
  2014年   3956篇
  2013年   11498篇
  2012年   6235篇
  2011年   8576篇
  2010年   6911篇
  2009年   7886篇
  2008年   8402篇
  2007年   8302篇
  2006年   7372篇
  2005年   6506篇
  2004年   6284篇
  2003年   6559篇
  2002年   6036篇
  2001年   6516篇
  2000年   5976篇
  1999年   6392篇
  1998年   16482篇
  1997年   11416篇
  1996年   8793篇
  1995年   6607篇
  1994年   5903篇
  1993年   5842篇
  1992年   4132篇
  1991年   4025篇
  1990年   3858篇
  1989年   3650篇
  1988年   3560篇
  1987年   3021篇
  1986年   2945篇
  1985年   3206篇
  1984年   2926篇
  1983年   2830篇
  1982年   2638篇
  1981年   2543篇
  1980年   2462篇
  1979年   2305篇
  1978年   2107篇
  1977年   2604篇
  1976年   3563篇
  1975年   1768篇
  1974年   1729篇
  1973年   1665篇
  1972年   1465篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
Die Regelung über die Erlangung der Parteistellung übergangener Nachbarn durch Geltendmachung von Einwendungen bis l?ngstens drei Monate nach dem angezeigten Baubeginn ist wegen der Anknüpfung an einen untauglichen Zeitpunkt verfassungswidrig.  相似文献   
152.
Long-term human space exploration will require contingencies for emergency medical procedures including some capability to perform surgery. The ability to perform minimally invasive surgery (MIS) would be an important capability. The use of small incisions reduces surgical risk, but also eliminates the ability of the surgeon to view and touch the surgical environment directly. Robotic surgery, or telerobotic surgery, may provide emergency surgical care in remote or harsh environments such as space flight, or extremely forward environments such as battlefields. However, because current surgical robots are large and require extensive support personnel, their implementation has remained limited in forward environments, and they would be difficult, or impossible, to use in space flight or on battlefields. This paper presents experimental analysis of miniature fixed-base and mobile in vivo robots to support MIS surgery in remote and harsh environments. The objective is to develop wireless imaging and task-assisting robots that can be placed inside the abdominal cavity during surgery. Such robots will provide surgical task assistance and enable an on-site or remote surgeon to view the surgical environment from multiple angles. This approach is applicable to long-duration space flight, battlefield situations, and for traditional medical centers and other remote surgical locations.  相似文献   
153.
The results of the effect of ultrasonic treatment of ZnSe crystals on the structure of the energy spectrum of electronic states of centers with deep levels forming photoelectric and luminescent properties of this compound are presented. It is for the first time proved experimentally that the climb of edge dislocations under the effect of ultrasound leads to regrouping and generation of defects forming deep levels, which manifest themselves in phenomena of photosensitivity and radiative recombination.  相似文献   
154.
A wafer level packaging technique has been developed with an inherent advantage of good solder joint co-planarity suitable for wafer level testing. A suitable weak metallization scheme has also been established for the detachment process. During the fabrication process, the compliancy of the solder joint is enhanced through stretching to achieve a small shape factor. Thermal cycling reliability of these hourglass-shaped, stretch solder interconnections has been found to be considerably better than that of the conventional spherical-shaped solder bumps.  相似文献   
155.
This paper is a tutorial on GrÖbner bases and a survey on the applications of GrÖbner bases in the broad field of signals and systems. A reasonably detailed review is given of several fundamental theoretical issues that occur in the use of GrÖbner bases in multidimensional signals and systems applications. These topics include the primeness of multivariate polynomial matrices, multivariate unimodular polynomial matrix completion, and prime factorization of multivariate polynomial matrices. A brief review is also presented on the wide-ranging applications of GrÖbner bases in multidimensional as well as one-dimensional circuits, networks, control, coding, signals, and systems and other related areas like robotics and applied mechanics. The impact and scope of GrÖbner bases in signals and systems are highlighted with respect to what has already been accomplished as a stepping stone to expanding future research.   相似文献   
156.
The following letter presents a study regarding GaN-based light-emitting diodes (LEDs) with p-type AlGaN electron blocking layers (EBLs) of different thicknesses. The study revealed that the LEDs could endure higher electrostatic discharge (ESD) levels as the thickness of the AlGaN EBL increased. The observed improvement in the ESD endurance ability could be attributed to the fact that the thickened p-AlGaN EBL may partly fill the dislocation-related pits that occur on the surface of the InGaN-GaN multiple-quantum well (MQW) and that are due to the strain and the low-temperature-growth process. If these dislocation-related pits are not partly suppressed, they will eventually result in numerous surface pits associated with threading dislocations that intersect the InGaN-GaN (MQW), thereby reducing the ESD endurance ability. The results of the experiment show that the ESD endurance voltages could increase from 1500 to 6000 V when the thickness of the p-AlGaN EBL in the GaN LEDs is increased from 32.5 to 130 nm, while the forward voltages and light output powers remained almost the same.  相似文献   
157.
158.
159.
Theoretical and experimetal methods have been developed to characterize the effect of mechanical loading on the mesoscopic and macroscopic mechanical state of polycrystalline materials. Ferritic and austenitic single-phase materials were first analyzed, then phase interaction was studied in a multiductile phase material (austeno-ferritic duplex steel) and a natural reinforced composite (pearlitic steel). The theoretical method is based on the self-consistent approach in which elastic and plastic characteristics of the phases have been applied through the micromechanical behavior of single-crystal-using slip systems and microscopic hardening. The effects of a crystallographic texture and phase interaction during loading and after unloading were studied. The elastic and plastic anisotropy of the grains having the same crystallographic orientation were assessed by diffraction strain analysis. The simulation was compared with the experiments performed using the X-ray diffraction technique. In the considered duplex and pearlitic steels, it was observed that the ferrite stress state is much lower than the austenite and cementite ones. The results of diffraction strain distribution have showed the pertinence of the models and give valuable information, for example, for the yield stress and the hardening parameters of each phase in a two-phase material.  相似文献   
160.
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