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   1537627篇
  免费   34607篇
  国内免费   11591篇
电工技术   39229篇
技术理论   6篇
综合类   13277篇
化学工业   272978篇
金属工艺   67676篇
机械仪表   46154篇
建筑科学   50361篇
矿业工程   13360篇
能源动力   51946篇
轻工业   116171篇
水利工程   16734篇
石油天然气   40060篇
武器工业   934篇
无线电   203747篇
一般工业技术   286997篇
冶金工业   150305篇
原子能技术   34731篇
自动化技术   179159篇
  2021年   18704篇
  2020年   14476篇
  2019年   16489篇
  2018年   17486篇
  2017年   17087篇
  2016年   23172篇
  2015年   20626篇
  2014年   32935篇
  2013年   92638篇
  2012年   40595篇
  2011年   53029篇
  2010年   47505篇
  2009年   55506篇
  2008年   48919篇
  2007年   45487篇
  2006年   48303篇
  2005年   42007篇
  2004年   43233篇
  2003年   42823篇
  2002年   41979篇
  2001年   38470篇
  2000年   36405篇
  1999年   34950篇
  1998年   40447篇
  1997年   36588篇
  1996年   33746篇
  1995年   29889篇
  1994年   28135篇
  1993年   27945篇
  1992年   26191篇
  1991年   23173篇
  1990年   23126篇
  1989年   21938篇
  1988年   20493篇
  1987年   18883篇
  1986年   18343篇
  1985年   21636篇
  1984年   21942篇
  1983年   19891篇
  1982年   18906篇
  1981年   18951篇
  1980年   17585篇
  1979年   18216篇
  1978年   17454篇
  1977年   16934篇
  1976年   17476篇
  1975年   15736篇
  1974年   15337篇
  1973年   15393篇
  1972年   12914篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
Glass and Ceramics - An analysis of the specific mechanisms of the influence of the state of the grain structure on the thermoelectric properties (electrical resistivity and total thermal...  相似文献   
112.

ResearchGate has emerged as a popular professional network for scientists and researchers in a very short span. Similar to Google Scholar, the ResearchGate indexing uses an automatic crawling algorithm that extracts bibliographic data, citations, and other information about scholarly articles from various sources. However, it has been observed that the two platforms often show different publication and citation data for the same institutions, journals, and authors. While several previous studies analysed different aspects of ResearchGate and Google Scholar, the quantum of differences in publications, citations, and metrics between the two and the probable reasons for the same are not explored much. This article, therefore, attempts to bridge this research gap by analysing and measuring the differences in publications, citations, and different metrics of the two platforms for a large data set of highly cited authors. The results indicate that there are significantly high differences in publications and citations for the same authors captured by the two platforms, with Google Scholar having higher counts for a vast majority of the cases. The different metrics computed by the two platforms also differ in their values, showing different degrees of correlation. The coverage policy, indexing errors, author attribution mechanism, and strategy to deal with predatory publishing are found to be the main probable reasons for the differences in the two platforms.

  相似文献   
113.
An ecofriendly and biodegradable porous structure was prepared from drying aqueous foams based on nano fibrillated cellulose (NFC), extracted from softwood pulp by subcritical water/CO2 treatment (SC-NFC). The primary aim of this work was to use the modified SC-NFC as stabilizer for a water-based Pickering emulsion which upon drying, yielded porous cellulosic materials, a good dye adsorbent. In order to exploit the carboxymethylated SC-NFC (CMSC-NFC, with a degree of substitution of 0.35 and a charge density of 649 μeqv/g) as a stabilizer for water-based Pickering emulsion in subsequent step, an optimized quantity of octyl amine (30 mg/g of SC-NFC) was added to make them partially hydrophobic. A series of dry foam structures were prepared by varying the concentrations of treated CMSC-NFCs and 4 wt% was found to be the optimum concentration to yield foam with high porosity (99%) and low density (0.038 g/cc) along with high compression strength (0.24 MPa), superior to the conventionally extracted NFC. The foams were applied to capture as high as 98% of methylene blue dyes, making them a potential green candidate for treating industrial effluent. In addition, the dye adsorption kinetics and isotherms were found to be well suited with second order kinetics and Langmuir isotherm models.  相似文献   
114.
Refractories and Industrial Ceramics - Technology for producing alumina-periclase-carbon refractories of the brands APUK-D and APU-D is developed and implemented. Use of complex antioxidant and...  相似文献   
115.
116.
Equilibrium swelling and rheological tests were adopted to systematically investigate the effects of softener type and dosage on the crosslink densities. The results turned out that the chemical crosslink density could be distinguished from the physical crosslink density by comparing the results of equilibrium swelling and rheological tests. The liquid butadiene (LB) as a softener leads to the greatest reduction in crosslink density, followed by polyethylene wax (PW) and paraffinic oil (PO). The tensile strength decreases with increasing PO content while shows peak values with increase of LB and PW contents. The dependencies of chemical crosslink density on the aging time under 150°C are quite different for the three softeners, which can be expected from the double crosslinking networks consisting of small softener and large main crosslinking networks. Further investigation has been performed to correlate the tensile strength with chemical crosslink density of ethylene propylene diene monomer elastomer vulcanizates. Three different linear relationships can be obtained for the softeners independent of the aging time. It can now be expected from this study that the role of some new softeners in rubber compounds is not only confined to plasticization but also forms crosslinking networks in the peroxide-cured rubbers.  相似文献   
117.
Laser ablation of high-temperature ceramic coatings results in thermal residual stresses due to which the coatings fail by cracking and debonding. Hence, the measurement of such residual stresses during laser ablation process holds utmost importance from the view of performance of coatings in extreme conditions. The present research aims at investigating the effect of laser parameters such as laser pulse energy, scanning speed and line spacing on thermal residual stresses induced in tantalum carbide-coated graphite substrates. Residual stresses were measured using micro-Raman spectroscopy and correlated with Raman peak shifts. Transient thermal analysis was performed using COMSOL Multiphysics to model the single ablated track and residual stresses were reported at low, moderate and high pulse energy regimes. The results showed that the initial laser conditions caused higher tensile residual stresses. Moderate pulse energy regime comprised higher compressive residual stresses due to off centre overlapping of the laser pulses. Higher pulse energy (250 μJ), higher scanning speed (1000 mm/s) and moderate line spacing (20 μm) caused accumulation of tensile residual stresses during the final stage of laser ablation. The deviation of experimental residual stresses from COMSOL numerical model was attributed to unaccounted additional stresses induced during thermal spraying process and deformation potentials in the numerical model.  相似文献   
118.
Fibre Chemistry - An analysis of the aramid fiber market including the range of industrial textile materials containing chemical fibers for specialized protective clothing of metallurgical workers,...  相似文献   
119.
马永强  孙伟  边静  张健立  刘志 《电视技术》2021,45(11):103-105
针对数字图像水印技术,通过对闭运算得到的图像再进行开运算,使实验得到的图像区域较为完整,采用4×4的正方形结构元素,使得图像区域有更多的白色像素被置为黑色,对图像进行取反操作,能够对图像区域的非连通区域进行填充.希望能够利用精确的图像分割算法,实现对复杂版面的文档图像的有效切割,在一定程度上对图像数字水印的推广起到促进作用.  相似文献   
120.
Sheng  Mingming  Yang  Rongkun  Gong  Hongyu  Zhang  Yujun  Lin  Xiao  Jing  Jie 《Journal of Materials Science》2022,57(10):5805-5824
Journal of Materials Science - With the extensive use of high-power electronic appliances, polymer-based thermal insulation composites with excellent thermal properties are utilized in the field of...  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