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   361084篇
  免费   28841篇
  国内免费   15688篇
电工技术   20916篇
技术理论   45篇
综合类   25370篇
化学工业   60549篇
金属工艺   20866篇
机械仪表   22645篇
建筑科学   27702篇
矿业工程   11675篇
能源动力   9875篇
轻工业   24207篇
水利工程   6766篇
石油天然气   23417篇
武器工业   2795篇
无线电   39623篇
一般工业技术   40164篇
冶金工业   19071篇
原子能技术   3649篇
自动化技术   46278篇
  2024年   1463篇
  2023年   5584篇
  2022年   9952篇
  2021年   13860篇
  2020年   10446篇
  2019年   8580篇
  2018年   9903篇
  2017年   11124篇
  2016年   10215篇
  2015年   13948篇
  2014年   17593篇
  2013年   21244篇
  2012年   22932篇
  2011年   25464篇
  2010年   22452篇
  2009年   21305篇
  2008年   20894篇
  2007年   19919篇
  2006年   20273篇
  2005年   17840篇
  2004年   12117篇
  2003年   10838篇
  2002年   10011篇
  2001年   8920篇
  2000年   8838篇
  1999年   9483篇
  1998年   7418篇
  1997年   6280篇
  1996年   5922篇
  1995年   4857篇
  1994年   3981篇
  1993年   2680篇
  1992年   2116篇
  1991年   1622篇
  1990年   1268篇
  1989年   1040篇
  1988年   883篇
  1987年   563篇
  1986年   442篇
  1985年   282篇
  1984年   234篇
  1983年   187篇
  1982年   139篇
  1981年   92篇
  1980年   110篇
  1979年   52篇
  1978年   29篇
  1977年   41篇
  1976年   62篇
  1974年   15篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
A self-nanoemulsifying drug delivery system (SNEDDS) was developed to enhance the absorption of heparin after oral administration, in which heparin was compounded with phospholipids to achieve better fat solubility in the form of heparin-phospholipid (HEP-Pc) complex. HEP-Pc complex was prepared using the solvent evaporation method, which increased the solubility of heparin in n-octanol. The successful preparation of HEP-Pc complex was confirmed by differential scanning calorimetry (DSC), Fourier-transform infrared (FT-IR) spectroscopy, NMR, and SEM. A heparin lipid microemulsion (HEP-LM) was prepared by high-pressure homogenization and characterized. HEP-LM can enhance the absorption of heparin after oral administration, significantly prolong activated partial thromboplastin time (APTT) and thrombin time (TT) in mice, and reduce fibrinogen (FIB) content. All these outcomes indicate that HEP-LM has great potential as an oral heparin formulation.  相似文献   
72.
在液化天然气(LNG)接收站工程设计建设过程中,火炬系统的设计是保证LNG接收站安全生产的必要条件。以国内某LNG接收站为例,分析了LNG蒸发气(BOG)产生的因素和机理,及6种工况组合下火炬排放量的计算方法。结果表明:在工况1条件下与实际生产情况吻合良好,其对应的火炬气排放量约为142.7 t/h。在此基础上确定了:BOG支管管径为DN600,BOG总管的管径为DN900;被分离液滴的直径不大于600μm;火炬分液罐尺寸为?2.5 m×8.0 m;电加热器的功率为195 kW;火炬形式为封闭式地面火炬。研究结果可为今后LNG接收站项目火炬系统的处理能力及设备配置提供理论指导。  相似文献   
73.
Refining ceramic microstructures to the nanometric range to minimize light scattering provides an interesting methodology for developing novel optical ceramic materials. In this work, we reported the fabrication and properties of a new nanocomposite optical ceramic of Gd2O3-MgO. The citric acid sol-gel combustion method was adopted to fabricate Gd2O3-MgO nanocomposites with fine-grain sizes, dense microstructures and homogeneous phase domains. Nanopowders with low agglomeration and improved sinterability can be obtained by elaborating Φ values. Further refining of the microstructure of the nanocomposites was achieved by elaborating the hot-pressing conditions. The sample sintered at 65 MPa and 1300 °C showed a quite high hardness value of 14.3 ± 0.2 GPa, a high transmittance of 80.3 %–84.7 % over the 3?6 μm wavelength range, due mainly to its extremely fine-grain size of Gd2O3 and MgO (93 and 78 nm, respectively) and high density.  相似文献   
74.
75.
76.
本文对吉林油田低注入井五参数测井过程中遇到的一些问题进行分析,并相应提出一系列行之有效的解决方法。  相似文献   
77.
Feature-based methods have been developed in the past decades for the registration of optical satellite images. However, it is still a challenging problem to handle well the registration between medium and high spatial resolution images due to the large difference of the spatial structural features and local details for the same objects. In this study, an automated co-registration technique is proposed that integrates an improved SIFT (I-SIFT) and a novel matching strategy called spatial consistency constraints (SCC) to cope with the large difference in spatial resolutions between the image pair. Three constraints on angle, distance, and ratio are introduced to re the initial matching features obtained by I-SIFT. Three groups of experiments were conducted to validate the effectiveness of the proposed method. The experiments used high resolution multispectral and panoramic SPOT 5/6 images and Landsat 5/8 orthorectification images. Experimental results show that the registration error lies in about 1 pixel of high-resolution images and demonstrate that the proposed I-SIFT-SCC approach is suitable for fine registration of optical satellite images from medium spatial resolution to high spatial resolution with resolution ratio up to 6.  相似文献   
78.
针对和成矿业井下原矿含泥量和含水量较大,且矿泥中存在绿泥石、高岭土等黏土类矿物,造成供矿系统粘堵严重,系统台时量仅为设计水平一半的问题,对原矿进行了洗矿工艺研究。通过洗矿工艺,将原矿中的矿块和矿泥分离,实现矿块和矿泥按粒度分选,彻底解决了供矿系统粘堵严重的问题,稳定了磨选系统给矿量。  相似文献   
79.
Amino acid modified polyaspartic acids were evaluated as calcium-scale inhibitors. Feasibility of scale inhibition experiments was analyzed by molecular dynamics simulation and Gaussian optimization, and the scale inhibition mechanism was theoretically analyzed. Scale inhibition performance was studied by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, static scale inhibition experiments, and electrochemical performance testing, which provided an experimental basis for the molecular dynamics simulation. The experimental results showed that Arg-SA-PASP has better scale inhibition and corrosion inhibition performance than His-SA-PASP. The scale inhibition effect increased with increasing concentration. Electrochemical tests indicated that Arg-SA-PASP is an excellent scale and corrosion inhibitor.  相似文献   
80.
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