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   345473篇
  免费   18173篇
  国内免费   708篇
电工技术   6954篇
综合类   556篇
化学工业   62042篇
金属工艺   10582篇
机械仪表   9471篇
建筑科学   9441篇
矿业工程   865篇
能源动力   9353篇
轻工业   37429篇
水利工程   2789篇
石油天然气   3701篇
武器工业   9篇
无线电   46347篇
一般工业技术   69224篇
冶金工业   58786篇
原子能技术   5473篇
自动化技术   31332篇
  2021年   2519篇
  2020年   3029篇
  2019年   5214篇
  2018年   6549篇
  2017年   6725篇
  2016年   7232篇
  2015年   6303篇
  2014年   8089篇
  2013年   19068篇
  2012年   9948篇
  2011年   12339篇
  2010年   10439篇
  2009年   11525篇
  2008年   11584篇
  2007年   11342篇
  2006年   10075篇
  2005年   9184篇
  2004年   9023篇
  2003年   8730篇
  2002年   8526篇
  2001年   8591篇
  2000年   8216篇
  1999年   8050篇
  1998年   18057篇
  1997年   13107篇
  1996年   10273篇
  1995年   8001篇
  1994年   7340篇
  1993年   7029篇
  1992年   5349篇
  1991年   5122篇
  1990年   5015篇
  1989年   4797篇
  1988年   4656篇
  1987年   3864篇
  1986年   3997篇
  1985年   4710篇
  1984年   4245篇
  1983年   3993篇
  1982年   3572篇
  1981年   3742篇
  1980年   3437篇
  1979年   3384篇
  1978年   3207篇
  1977年   3815篇
  1976年   4893篇
  1975年   2753篇
  1974年   2649篇
  1973年   2647篇
  1972年   2214篇
排序方式: 共有10000条查询结果,搜索用时 32 毫秒
61.
Evaluation of kinetic distribution and behaviors of nanoparticles in vivo provides crucial clues into their roles in living organisms. Extracellular vesicles are evolutionary conserved nanoparticles, known to play important biological functions in intercellular, inter‐species, and inter‐kingdom communication. In this study, the first kinetic analysis of the biodistribution of outer membrane vesicles (OMVs)—bacterial extracellular vesicles—with immune‐modulatory functions is performed. OMVs, injected intraperitoneally, spread to the whole mouse body and accumulate in the liver, lung, spleen, and kidney within 3 h of administration. As an early systemic inflammation response, increased levels of TNF‐α and IL‐6 are observed in serum and bronchoalveolar lavage fluid. In addition, the number of leukocytes and platelets in the blood is decreased. OMVs and cytokine concentrations, as well as body temperature are gradually decreased 6 h after OMV injection, in concomitance with the formation of eye exudates, and of an increase in ICAM‐1 levels in the lung. Following OMV elimination, most of the inflammatory signs are reverted, 12 h post‐injection. However, leukocytes in bronchoalveolar lavage fluid are increased as a late reaction. Taken together, these results suggest that OMVs are effective mediators of long distance communication in vivo.  相似文献   
62.
Cases of isolated hepatic tuberculosis (TB) are rare. The diagnosis is often delayed or missed because of nonspecific symptoms and laboratory findings. Besides, the disease is extremely rare even in a country where TB is an alarming public health problem. This report demonstrates the difficulty in correctly diagnosing local hepatic TB. We report the case of a 62‐year‐old male patient with end‐stage renal disease treated with hemodialysis, who developed 2 months of abdominal distension and general anorexia, with hyperechoic hepatic lesions on ultrasound. Computed tomography suspected multiple liver tumors. The liver biopsy finally led to the diagnosis of TB of the liver without other involvements. We conclude that isolated hepatic TB is one of the rare forms of extrapulmonary TB in dialysis patients. A greater awareness of this rare clinical entity may prevent needless surgical interventions.  相似文献   
63.
64.
65.
66.
Litvyak  V. M.  Cherbunin  R. V.  Kalevich  V. K.  Kavokin  K. V. 《Semiconductors》2020,54(12):1728-1729
Semiconductors - We found bulk n-GaAs layers grown by liquid phase epitaxy to be irregularly stressed. Deformation created by this stress causes a small but detectable quadrupole splitting of...  相似文献   
67.
Wireless Personal Communications - A relatively new area of research and development is Swarm Robotics. It is a part of the swarm intelligence field. In the proposed paper, we shall use swarm...  相似文献   
68.
Atom scattering is becoming recognized as a sensitive probe of the electron–phonon interaction parameter λ at metal and metal-overlayer surfaces. Here, the theory is developed, linking λ to the thermal attenuation of atom scattering spectra (in particular, the Debye–Waller factor), to conducting materials of different dimensions, from quasi-1D systems such as W(110):H(1 × 1) and Bi(114), to quasi-2D layered chalcogenides, and high-dimensional surfaces such as quasicrystalline 2ML-Ba(0001)/Cu(001) and d-AlNiCo(00001). Values of λ obtained using He atoms compare favorably with known values for the bulk materials. The corresponding analysis indicates in addition, the number of layers contributing to the electron–phonon interaction, which is measured in an atom surface collision.  相似文献   
69.
Journal of Communications Technology and Electronics - This paper implements mathematically rigorous extended trial function algorithm to address cubic–quartic optical solitons in...  相似文献   
70.
Unreliable mobility values, and particularly greatly overestimated values and severely distorted temperature dependences, have recently hampered the development of the organic transistor field. Given that organic field‐effect transistors (OFETs) have been routinely used to evaluate mobility, precise parameter extraction using the electrical properties of OFETs is thus of primary importance. This review examines the origins of the various mobilities that must be determined for OFET applications, the relevant extraction methods, and the data selection limitations, which help in avoiding conceptual errors during mobility extraction. For increased precision, the review also discusses device fabrication considerations, calibration of both the specific gate‐dielectric capacitance and the threshold voltage, the contact effects, and the bias and temperature dependences, which must actually be handled with great care but have mostly been overlooked to date. This review serves as a systematic overview of the OFET mobility extraction process to ensure high precision and will also aid in improving future research.  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