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   487108篇
  免费   7022篇
  国内免费   2055篇
电工技术   9304篇
综合类   1061篇
化学工业   70861篇
金属工艺   19331篇
机械仪表   14127篇
建筑科学   12512篇
矿业工程   1694篇
能源动力   12889篇
轻工业   43098篇
水利工程   4210篇
石油天然气   4471篇
武器工业   22篇
无线电   60173篇
一般工业技术   89475篇
冶金工业   102690篇
原子能技术   8304篇
自动化技术   41963篇
  2021年   3601篇
  2020年   2543篇
  2019年   3250篇
  2018年   5730篇
  2017年   5870篇
  2016年   6535篇
  2015年   4657篇
  2014年   7038篇
  2013年   21216篇
  2012年   12700篇
  2011年   17321篇
  2010年   12806篇
  2009年   14432篇
  2008年   15195篇
  2007年   15175篇
  2006年   13532篇
  2005年   14916篇
  2004年   13747篇
  2003年   13554篇
  2002年   11974篇
  2001年   12230篇
  2000年   10878篇
  1999年   11896篇
  1998年   32922篇
  1997年   22787篇
  1996年   17445篇
  1995年   12855篇
  1994年   11288篇
  1993年   11055篇
  1992年   7650篇
  1991年   7508篇
  1990年   7008篇
  1989年   6755篇
  1988年   6639篇
  1987年   5607篇
  1986年   5524篇
  1985年   6247篇
  1984年   5583篇
  1983年   5246篇
  1982年   4911篇
  1981年   4892篇
  1980年   4705篇
  1979年   4352篇
  1978年   4153篇
  1977年   5539篇
  1976年   8174篇
  1975年   3533篇
  1974年   3340篇
  1973年   3292篇
  1972年   2794篇
排序方式: 共有10000条查询结果,搜索用时 609 毫秒
21.

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   
22.
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   
23.
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   
24.
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   
25.
Wireless Personal Communications - In recent years, the emergence of Internet of things and cyber-physical system provide a proactive and efficacious solution to enable remote monitoring, machine...  相似文献   
26.
Multimedia Tools and Applications - In this paper, a hashing based watermarking technique for the protection and authentication of document image is proposed. Message Digest 5 (MD5) hashing is...  相似文献   
27.
Journal of Materials Science: Materials in Electronics - Nano Mn0.95M0.05S (M ≡ Cu, Mg) samples were produced using molten salt solid state reaction method. Rietveld analysis of X-ray...  相似文献   
28.
Deshmukh  P.  Sar  S. K.  Smječanin  N.  Nuhanović  M.  Lalwani  R. 《Radiochemistry》2022,64(4):532-542
Radiochemistry - Magnetically modified waste bark of the Aegle marmelos tree was prepared by using green synthesis method and was used in a batch system for U(VI) removal from aqueous solution. The...  相似文献   
29.
Kamar  M. S.  Shalan  A. S.  Youssef  W. M.  Hussein  A. E. M.  Khawassek  Y. M.  Taha  M. H. 《Radiochemistry》2022,64(2):244-256
Radiochemistry - Ferrugination, sericitization, desulfitization, chloritization, and kaolinitization of hydrothermal origin are the main wall rock alterations occurring within the NNW shear zones...  相似文献   
30.
This paper reports an investigation on the structure-properties correlation of trivalent metal oxide (Al2O3)-doped V2O5 ceramics synthesized by the melt-quench technique. XRD patterns confirmed a single orthorhombic V2O5 phase formation with increasing strain on the doping of Al2O3 in place of V2O5 in the samples estimated by Williamson-Hall analysis. FTIR and Raman investigations revealed a structural change as [VO5] polyhedra converts into [VO4] polyhedra on the doping of Al2O3 into V2O5. The optical band gap was found in a wide semiconductor range as confirmed by UV–visible spectroscopy analysis. The thermal and conductivity behavior of the prepared samples were studied using thermal gravimetric analysis (TGA) and impedance analyzer, respectively. All the prepared ceramics exhibit good DC conductivity (0.22–0.36 Sm-1) at 400 ?C. These materials can be considered for intermediate temperature solid oxide fuel cell (IT-SOFC)/battery applications due to their good conductivity and good thermal stability.  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