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   35266篇
  免费   1669篇
  国内免费   332篇
电工技术   690篇
综合类   566篇
化学工业   6387篇
金属工艺   1006篇
机械仪表   990篇
建筑科学   1448篇
矿业工程   245篇
能源动力   1148篇
轻工业   4648篇
水利工程   359篇
石油天然气   304篇
武器工业   28篇
无线电   2937篇
一般工业技术   4962篇
冶金工业   6583篇
原子能技术   332篇
自动化技术   4634篇
  2024年   79篇
  2023年   277篇
  2022年   766篇
  2021年   1111篇
  2020年   771篇
  2019年   785篇
  2018年   914篇
  2017年   1001篇
  2016年   976篇
  2015年   829篇
  2014年   1236篇
  2013年   1898篇
  2012年   1718篇
  2011年   2086篇
  2010年   1539篇
  2009年   1611篇
  2008年   1461篇
  2007年   1300篇
  2006年   1100篇
  2005年   1075篇
  2004年   1071篇
  2003年   987篇
  2002年   965篇
  2001年   839篇
  2000年   646篇
  1999年   625篇
  1998年   2121篇
  1997年   1379篇
  1996年   988篇
  1995年   668篇
  1994年   514篇
  1993年   567篇
  1992年   249篇
  1991年   303篇
  1990年   249篇
  1989年   206篇
  1988年   226篇
  1987年   171篇
  1986年   168篇
  1985年   187篇
  1984年   134篇
  1983年   99篇
  1982年   121篇
  1981年   133篇
  1980年   123篇
  1979年   96篇
  1978年   82篇
  1977年   147篇
  1976年   232篇
  1975年   89篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Spatial soliton-induced guiding by cross-phase modulation   总被引:1,自引:0,他引:1  
The authors show that spatial solitons are able to induce the stable guiding of a weak probe beam in a homogeneous Kerr-type nonlinear media through cross-phase modulation (XPM). The modes of the induced waveguide are derived from the propagation equation of the probe. Experiments have been performed in Kerr liquid CS2, with beams of picosecond duration at infrared and visible wavelengths. Stable guiding of a green probe induced by an IR soliton beam has been demonstrated in several different experimental situations. Induced antiguiding and beam splitting are also reported for pump and probe of perpendicular polarizations. All results are in excellent agreement with numerical simulations of the propagation  相似文献   
22.
Generator rotor angle measurement is useful in identification of electric machine parameters in the d and q axes and as an indicator of stability of the operating condition. Rotor angle measurements with the appropriate bandwidth are also very useful in observation of rotor torsional oscillations both for monitoring and protection against undamped torsional modes, and for use in control schemes designed to damp torsional oscillations. A method of measurement of synchronous machine rotor angle from an analysis of the phase angle of zero sequence harmonic components of terminal voltage is presented  相似文献   
23.
The humidity response characteristics of La doped BaTiO3 with different sintered densities and room temperature electrical conductivities were investigated using complex impedance measurement. The samples with low density and high resistivity showed the large and nearly linear sensitivity to the change of humidity. The impedance spectra of samples, when exposed to high humidity, can exhibit microstructure-related features, even though they do not give rise to a noticeable characteristic change when exposed to low humidity. The observed impedance patterns were dependent upon the density, and hence the oxidation kinetics of BaTiO3.  相似文献   
24.
Ischemia‐reperfusion injury of the bone occurs due to traumatic and non‐traumatic alterations affecting blood supply to the bone. It is likely to occur also upon insertion of an implant. Ischemia‐reperfusion injury of the bone has been studied by interruption of blood supply in situ, in limb replantation/transplantation models, in revascularized bone grafts and non‐vascularized bone fragments, as well as in isolated cultured cells. All cells of the bone are affected, including osteoblasts, osteocytes, osteoclasts, chondrocytes, and bone marrow cells. Critical ischemia times for induction of bone cell death, either in the ischemic period or following reperfusion, are in the range of 3 to 7 h. These critical ischemia times are significantly increased by decreasing the temperature from 37 °C to 0–4 °C. Anoxia is the most likely trigger of cell injury in the ischemic phase. In the reperfusion phase, reactive oxygen species are decisively involved in the injurious process. In general, however, the available information on the mechanism of ischemia‐reperfusion injury of the bone is relatively sparse. On the other hand, there are clear similarities to the mechanisms of ischemia‐reperfusion injury known from other organs, and there is a clear potential for protection against ischemia‐reperfusion injury of the bone.  相似文献   
25.
The aim of this article is to illustrate a framework for flood risk mapping at pan-European scale produced by the Weather-Driven Natural Hazards (WDNH) action of the EC-JRC-IES. Early results are presented in the form of flood risk index maps. We assess several flood risk factors that contribute to the occurrence of flood disasters. Among the causal factors of a flood disaster one is triggering a natural event in the form of extreme precipitation and consequently extreme river discharge and extreme flood water levels. The threatening natural event represents the hazard component in our assessment. Furthermore exposure and vulnerability are anthropogenic factors that contribute also to flood risk. In the proposed approach, flood risk is considered on the light of exposure, vulnerability and hazard. We use a methodology with a marked territorial approach for the assessment of the flood risk. Hence, based on mathematical calculations, risk is the product of hazard, exposure and vulnerability. Improvements on datasets availability and spatial scale are foreseen in the next phases of this study. This study is also a contribution to the discussion about the need for communication tools between the natural hazard scientific community and the political and decision making players in this field.  相似文献   
26.
An analysis is made of longitudinal effects in semiconductor lasers with low facet reflectivities. For this purpose, a self-consistent model is used based on the beam propagation method, which takes into account both the lateral and longitudinal dimension. The calculations show that longitudinal effects have a significant influence on the output fields in the laser.  相似文献   
27.
Adjuvant-induced arthritis is an animal model of chronic inflammatory disease widely used in anti-inflammatory and immunosuppressive drugs testing. When the development and the inhibition of the induced arthritis are measured by the injected paw oedema, it is difficult to delineate the immunological contribution from the persistent non-specific primary section. To study the influence of volume and composition of the injected adjuvant upon the primary non-specific inflammation, we devised a 3X4 factorial experiment on a strain of inbred rats with a low susceptibility to adjuvant-induced arthritis. The injection of mineral oil alone produces a persistent oedema. The injection of mycobacteriae in suspension in saline induces a rapid inflammatory response followed by a fast decrease of the oedema. When complete adjuvant is used, there is always a very strong interaction between the effects of the two components of the adjuvant, i.e. the measured oedemas are much greater than the calculated values, For a given injected volume, the inflammation is maximum when the concentration of mycobacteriae is 2.5 mg/ml. All the rats injected with complete adjuvant present a transient oedema of the non-injected hind paw. This oedema is very small and proportional to the amount of mycobacteria injected.  相似文献   
28.
为使北京谱仪端盖族射计数器更好地工作在自猝灭流光SQS模式下,提高其能量分辨以及线性等指标,用Ar,CO2,Lsobutane三元工作气体对探测器的工作性能进行了仔细研究,找出了一适合于主雇地数器的工作气体,此外,还研究了异丁的纯度对探测器性能的影响。  相似文献   
29.
Computer-aided engineering tools are routinely used to simulate forging and heat-treatment operations and to perform thermal and stress analyses. This review gives a few examples of the current uses of process modeling tools and outlines some developing capabilities and near-term applications.  相似文献   
30.
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