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   12713篇
  免费   1036篇
  国内免费   397篇
电工技术   659篇
综合类   479篇
化学工业   2086篇
金属工艺   492篇
机械仪表   550篇
建筑科学   696篇
矿业工程   149篇
能源动力   383篇
轻工业   1241篇
水利工程   206篇
石油天然气   266篇
武器工业   75篇
无线电   1746篇
一般工业技术   1667篇
冶金工业   1504篇
原子能技术   153篇
自动化技术   1794篇
  2024年   62篇
  2023年   215篇
  2022年   433篇
  2021年   635篇
  2020年   460篇
  2019年   400篇
  2018年   445篇
  2017年   418篇
  2016年   437篇
  2015年   486篇
  2014年   619篇
  2013年   754篇
  2012年   782篇
  2011年   882篇
  2010年   651篇
  2009年   595篇
  2008年   611篇
  2007年   539篇
  2006年   437篇
  2005年   357篇
  2004年   307篇
  2003年   263篇
  2002年   291篇
  2001年   224篇
  2000年   188篇
  1999年   207篇
  1998年   510篇
  1997年   325篇
  1996年   259篇
  1995年   143篇
  1994年   152篇
  1993年   132篇
  1992年   82篇
  1991年   86篇
  1990年   66篇
  1989年   76篇
  1988年   48篇
  1987年   43篇
  1986年   43篇
  1985年   47篇
  1984年   38篇
  1983年   41篇
  1982年   39篇
  1981年   31篇
  1980年   30篇
  1979年   24篇
  1977年   43篇
  1976年   63篇
  1975年   17篇
  1973年   16篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Changes in the contents of waxes and fatty alcohols during deodorization/physical refining of bleached olive oil were studied. Experiments were carried out with 1.85% acidity oil, which was physically refined in a discontinuous deodorizer of 250-kg maximum capacity using nitrogen as stripping gas instead of steam. The variables studied were load and temperature of oil in the deodorizer as well as N2 flow. Analyses of waxes and alcohols were carried out at different operation times. The maximum content of wax was always observed when the oil reached the deodorization temperature. The variation in the wax content depended on temperature and N2 flow. Wax decomposition started and continued during the operating time, and a progressive decrease, which was pronounced between 3 and 4 h, was observed. Small changes in waxes were observed between 4 and 5 h. Total content of fatty alcohols diminished throughout the operating time, and changes did not depend on the variables studied.  相似文献   
72.
Oligomerization of glycine (gly) and diglycine (gly2) on montmorillonite was performed as cyclic, drying-wetting process at temperatures below 100°C, under varying reaction conditions. The influence of substrate/clay ratio, temperature and pH was found to be different for amino acid (AA) dimerization, cyclic anhydride (CA) formation and peptide chain elongation. High temperatures and neutral pH favour CA formation over diglycine production. An AA/catalyst ratio of 0.2 mmol/g leads to optimal yields. This supports the assumption that amino acid dimerization and CA formation take place at the edges of clay particles. Peptide chain elongation, starting from gly2, produces higher yields at higher temperatures and neutral pH.  相似文献   
73.
This paper reports experimental and numerical results of an investigation of five identical cogeneration systems using PEM (Polymer Exchange Membrane) fuel cells and running on natural gas. The natural gas is reformed locally to produce hydrogen. The accuracy of numerical results is validated by comparison with experimental data and the system performances are analysed in terms of electrical, thermal and total efficiencies. It appears that the energetic performances are low, particularly at low current. Simple solutions for enhancing the system electrical performances by modifying control laws are proposed.  相似文献   
74.
An abdominal wall hernia is a protrusion of the intestine through an opening or area of weakness in the abdominal wall. Correct pre-operative identification of abdominal wall hernia meshes could help surgeons adjust the surgical plan to meet the expected difficulty and morbidity of operating through or removing the previous mesh. First, we present herein for the first time the application of image analysis for automated identification of hernia meshes. Second, we discuss the novel development of a new entropy-based image texture feature using geostatistics and indicator kriging. Third, we seek to enhance the hernia mesh identification by combining the new texture feature with the gray-level co-occurrence matrix feature of the image. The two features can characterize complementary information of anatomic details of the abdominal hernia wall and its mesh on computed tomography. Experimental results have demonstrated the effectiveness of the proposed study. The new computational tool has potential for personalized mesh identification which can assist surgeons in the diagnosis and repair of complex abdominal wall hernias.  相似文献   
75.
Spectroscopic techniques are used to confirm the chemistry of solutions of [Pd(NH3)2Cl2] in aqueous NH4Cl at various pH. In addition, potential sweep and step methods at rotating and stationary disc electrodes (both vitreous carbon and freshly plated palladium) are used to investigate palladium deposition from a standard electroplating bath, [Pd(NH3)2Cl2] in NH4Cl/NH3 (pH 8.9). The relative importance of oxygen reduction, hydrogen absorption and hydrogen evolution as competing cathode reactions under various conditions is defined and the advantage of strong convection for high rate plating is demonstrated.  相似文献   
76.
Reactive mixing in a wavy torus reactor (WTR) has been examined experimentally. Its performances are compared to these of two other reactors: a plane torus reactor (PTR) and a baffled stirred tank reactor (BSTR). hydrodynamics of mixing has been studied using a plug flow model with axial dispersion for the WTR and PTR. The effect of axial dispersion on the kinetic of a chemical reaction was then analysed for the WTR, PTR and BSTR. Mixing times were slightly longer for the WTR due to a weaker axial dispersion. We also noticed an improvement of the convertion rate for low dissipated power.  相似文献   
77.
Molecular dynamics (MD) simulations of-Al2O3, using a pairwise additive interaction potential of Pauling's type with four different radii for aluminum atoms, were analysed in order to determine the influence of the radius on the modification of coordination numbers of A1 relative to the ideal structure, at two different temperatures of 300 and 1500 K. It is found that the best choice is the radius of penta-coordinated aluminum, reproducing structural and vibrational properties of the compound in excellent agreement with experimentally observed properties.  相似文献   
78.
Random Forests receive much attention from researchers because of their excellent performance. As Breiman suggested, the performance of Random Forests depends on the strength of the weak learners in the forests and the diversity among them. However, in the literature, many researchers only considered pre-processing of the data or post-processing of the Random Forests models. In this paper, we propose a new method to increase the diversity of each tree in the forests and thereby improve the overall accuracy. During the training process of each individual tree in the forest, different rotation spaces are concatenated into a higher space at the root node. Then the best split is exhaustively searched within this higher space. The location where the best split lies decides which rotation method to be used for all subsequent nodes. The performance of the proposed method here is evaluated on 42 benchmark data sets from various research fields and compared with the standard Random Forests. The results show that the proposed method improves the performance of the Random Forests in most cases.  相似文献   
79.
SRAM-based pipelined architectures for high-speed IP lookup using Field Programmable Gate Arrays (FPGAs) has recently attracted a great deal of attention from researchers. Due to the limited amount of on-chip memory and the number of I/O pins of FPGAs, compact data structures providing high memory efficiency are in great demand.  相似文献   
80.
刘瑛  张宁  张乐 《河南化工》2006,23(7):45-47
分析了南阳石蜡精细化工厂的基础油用阿伦尼乌斯公式计算的粘度数值与实测粘度数值的关系,对其系数进行校正,成功得出了精确度较高的润滑油调和数学模型,并经现场应用,证明可用于生产中.  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