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   3466篇
  免费   46篇
  国内免费   15篇
电工技术   133篇
综合类   3篇
化学工业   766篇
金属工艺   116篇
机械仪表   89篇
建筑科学   59篇
能源动力   177篇
轻工业   207篇
水利工程   12篇
石油天然气   6篇
无线电   379篇
一般工业技术   577篇
冶金工业   673篇
原子能技术   95篇
自动化技术   235篇
  2023年   22篇
  2022年   38篇
  2021年   64篇
  2020年   30篇
  2019年   46篇
  2018年   41篇
  2017年   42篇
  2016年   52篇
  2015年   48篇
  2014年   66篇
  2013年   185篇
  2012年   120篇
  2011年   178篇
  2010年   143篇
  2009年   132篇
  2008年   143篇
  2007年   138篇
  2006年   118篇
  2005年   85篇
  2004年   95篇
  2003年   122篇
  2002年   84篇
  2001年   68篇
  2000年   55篇
  1999年   88篇
  1998年   315篇
  1997年   179篇
  1996年   112篇
  1995年   70篇
  1994年   88篇
  1993年   75篇
  1992年   44篇
  1991年   35篇
  1990年   47篇
  1989年   35篇
  1988年   24篇
  1987年   26篇
  1986年   27篇
  1985年   32篇
  1984年   24篇
  1983年   30篇
  1982年   16篇
  1981年   16篇
  1980年   26篇
  1979年   13篇
  1978年   13篇
  1977年   12篇
  1976年   21篇
  1975年   10篇
  1974年   10篇
排序方式: 共有3527条查询结果,搜索用时 0 毫秒
21.
An FM-CW radar system was applied to detect a human body buried in a very wet snowpack. This radar uses the L-band microwave frequency with a maximum output power of 100 mW, and utilizes digital signal processing techniques. Field experiments were carried out to detect and map a human body embedded at a depth of 125 cm in a natural snowpack. The radar is shown to have a potential ability to detect avalanche victims, indicating that it may become a tool for snow rescuer operations  相似文献   
22.
The conventional loading criterion in the theory of plasticity becomes ambiguous when it is applied to materials that exhibit straining softening. For instance, it can not differentiate the softening behavior from the unloading process. On the other hand, the loading criterion proposed recently by Qu and Yin is free from such problems, and is more suitable for a general elasto-plastic analysis by finite element method. In the first part of this paper the proposed loading criterion is first reviewed and discussed to highlight the difficulties associated with the inequality conditions used in the conventional as well as the proposed loading criteria. This paper then proceeds to discuss the proposed criterion and reveals its implications. Although the proposed inequality conditions are not generally known in the field, it is found that they are essential and significant in the theory of plasticity.  相似文献   
23.
In a 63-year-old male patient with gastric cancer having multiple liver metastases, the metastatic lesions responded well to postoperative staggered intraarterial infusion therapy with MTX and 5-FU. The intraarterial infusion therapy was administered once a week. A total of 5 courses of this therapy produced marked regression of liver metastases and remarkable necrosis. The effect was thus rated as PR. The patient is healthy and has been successfully rehabilitated. His dose is oral 5-FU (200 mg x 2).  相似文献   
24.
A patient with subacute bacterial endocarditis and a peripheral mycotic aneurysm is presented. We used a combined multi-slice surface anatomy scanning (SAS) and contrast-enhanced MR angiography image to determine the exact location of the small lesion by applying a skin marker on the scalp and visualizing the relationship of the marker to the brain surface structures and to the lesion. This technique was useful for the removal of a small peripheral aneurysm using only a limited craniotomy.  相似文献   
25.
In the first half of the paper, various types of processing pertaining to a polygon, using the 4×4 determinant theories are explained along with a new containment test algorithm of a point in a polygon. In the latter half of the paper, a general-purpose geometric processor, the POLYGON ENGINE, is presented which can deal with various types of interference problems, such as Boolean operations in solid modelling, hidden line and surface eliminations, ray tracing and so on. It is, a successor of the TRIANGLE PROCESSOR and is also based upon the 4×4 determinant theories [4–6]. While the TRIANGLE PROCESSOR processes a triangulated polygon on a triangle-by-triangle basis, the POLYGON ENGINE can treat a polygon without triangulation. The latter is expected to be more functional, more efficient and easier to use.  相似文献   
26.
27.
The bipolar/FET characteristics of the 2DEG-HBT are analyzed extensively by a two-dimensional numerical simulator based on a drift-diffusion model. For bipolar operations at high collector current densities, it is confirmed that the cutoff frequency fT is determined mainly by the collector transit time of holes and by the charging time of the extrinsic base-collector capacitance C bcEXT. The charging times of the emitter and base regions and the base transit time are shown to be negligible. A high cutoff frequency FT (88 GHz) and current gain hFE (760) are obtained for an emitter size of 1×10 μm2, and undoped collector thickness of 150 nm, and a collector current density Jc of 105 A/cm2. The FET operation of the same 2DEG-HBT structure shows a threshold voltage Vth of 0.74 V, the transconductance Gmmax of 80 mS/mm, and maximum cutoff frequency FTmax of 15 GHz. The dependence of the device performance on material parameters is analyzed extensively from a device design point of view  相似文献   
28.
The wide scattering in tool life of natural mono-crystalline diamond tools is considered to depend on intrinsic crystalline defects due to nitrogen impurities in raw diamond. In this paper, the correlation was investigated between the amounts and types of the impurity evaluated by infrared absorption (IRA) and the crater wear and chipping resistances. As a result, diamonds including less total amount of impurity show larger wear resistance and that with larger amount of B2-aggregates show larger chipping resistance. This suggests that the inspection by IRA can be a useful method for screening of raw diamond for highly durable cutting tools.  相似文献   
29.
Radiation damages due to 8 MeV electron irradiation in electrical properties of CuInSe2 thin films have been investigated. The n-type CuInSe2 films in which the carrier concentration was about 3×1016 cm−3, were epitaxially grown on a GaAs(0 0 1) substrate by RF diode sputtering. No significant change in the electrical properties was observed under the electron fluence <3×1016 e cm−2. As the electron fluence exceeded 1017 e cm−2, both the carrier concentration and Hall mobility slightly decreased. The carrier removal rate was estimated to be about 0.8 cm−1, which is slightly lower than that of III–V compound materials.  相似文献   
30.
Watching and tracking an object while seeing a much wider view is one of advantages of the eye system. We proposed and developed a tracking camera system that mimics the eyes by using double-lens modules. In the system, a wide view is captured through the wide-lens module, while the target in it is tracked and magnified through the telescopic lens module. Electronic circuits for tracking control are implemented onto the reconfigurable VLSI or FPGA in order to embed the parallelism in the tracking algorithm into the hardware. A successfully developed FPGA-based prototype performs high-speed tracking at the video-rate. This work was present in part at the 12th International Symposium on Artificial Life and Robotics, Oita, Japan, January 25–27, 2007  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