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   17552篇
  免费   1595篇
  国内免费   449篇
电工技术   221篇
综合类   804篇
化学工业   4482篇
金属工艺   2300篇
机械仪表   746篇
建筑科学   1261篇
矿业工程   145篇
能源动力   344篇
轻工业   4604篇
水利工程   106篇
石油天然气   462篇
武器工业   76篇
无线电   542篇
一般工业技术   2126篇
冶金工业   988篇
原子能技术   105篇
自动化技术   284篇
  2024年   83篇
  2023年   266篇
  2022年   379篇
  2021年   636篇
  2020年   539篇
  2019年   543篇
  2018年   500篇
  2017年   585篇
  2016年   686篇
  2015年   580篇
  2014年   882篇
  2013年   1106篇
  2012年   1011篇
  2011年   1353篇
  2010年   911篇
  2009年   1022篇
  2008年   927篇
  2007年   957篇
  2006年   970篇
  2005年   784篇
  2004年   709篇
  2003年   701篇
  2002年   646篇
  2001年   475篇
  2000年   392篇
  1999年   300篇
  1998年   312篇
  1997年   250篇
  1996年   189篇
  1995年   166篇
  1994年   135篇
  1993年   105篇
  1992年   73篇
  1991年   70篇
  1990年   57篇
  1989年   41篇
  1988年   24篇
  1987年   29篇
  1986年   17篇
  1985年   29篇
  1984年   40篇
  1983年   17篇
  1982年   32篇
  1981年   6篇
  1980年   21篇
  1979年   8篇
  1978年   8篇
  1975年   9篇
  1974年   4篇
  1951年   5篇
排序方式: 共有10000条查询结果,搜索用时 49 毫秒
31.
石化企业是挥发性有机物(VOCs)的重点排放源,开展VOCs成分谱构建和溯源解析工作对石化企业进行有针对性的污染治理具有重要的意义。综述了石化企业VOCs排放特征的研究现状,重点介绍了石化企业VOCs源成分谱和溯源解析工作的研究进展和存在的问题,建议完善采样和分析方法,利用数学算法,构建基于生产工艺的源成分谱,优化解析模型,形成一套完善的溯源解析技术,从而为石化企业大气污染物溯源提供理论、技术支持,有效实现石化企业安全环保一体化监控。  相似文献   
32.
Lattice structure and rod-like shaped SbSI nanocrystals obtained by ball milling with rod thickness down to 70 nm, as estimated from X-ray diffraction (XRD) and electron microscopy, is similar to that of the bulk crystals. The dependence of the grain size on the milling duration is discussed in view of the chain-like crystalline structure of SbSI. Possible factors, responsible for the observed Raman line broadening, are discussed, scattering by surface phonons being considered the predominant one.  相似文献   
33.
Micro assembly injection moulding   总被引:1,自引:0,他引:1  
Injection moulding is established as one of the most common manufacturing processes of thermoplastics due to its high degree of automation and the short cycle times. Micro injection moulding is a rapidly growing technology that allows for the efficient production of very complex micro parts in high series. The “Market Analysis for Microsystems II 2002–2005” of the Nexus Task Force anticipates a yearly growth in the field of micro system technology of about 20% (Wechsung et al. 2002). This study identifies in addition to the continuous miniaturization the growing use of polymers in micro systems (Schneider et al. 2001). No other material group offers this wide range of material properties and permits to choose processing parameters and application properties according to necessities (Gächter 2000). While the production processes of micro technical components are mainly controllable, the assembly of these components to hybrid micro systems is a bottleneck to the industrial large scale production. The assembly itself represents a large fraction of the added product value and gains in importance with growing complexity and miniaturization of the systems.  相似文献   
34.
TbNiSiD1.78 has been studied by powder neutron diffraction below 100 K. The compound takes the hexagonal room temperature structure at 100 and 50 K (P63/mmc). At 2 K, below the antiferromagnetic ordering temperature of 10 K, there is a small orthorhombic distortion of the lattice. The refined unit-cell dimensions at 2 K (space group Pnma) are a=7.9505(2), b=4.02502(14), c=6.9823(2) Å. The magnetic moments of Tb are 8.71(6) μB, and are ordered antiferromagnetically along a.  相似文献   
35.
纸浆漂白废水中有机氯化物的排放与控制   总被引:7,自引:0,他引:7  
程言君 《中国造纸》1994,13(4):57-61
本文概述了纸浆漂白废水的特性,以及影响其有机氯化物发生量的因素。  相似文献   
36.
本文运用一典型的人工神经网络模型─“反向传播”模型,对高氧化态(Ⅱ─Ⅳ)三核金属簇合物的构型分布进行了分析,得到了较好的分类、预报结果为化合物结构分析提供了新的工具。  相似文献   
37.
论述了电磁铁铁芯 (硅钢片 )模具的设计要点及其线切割加工的技巧 ,提出了提高模具加工精度和使用寿命的有效措施。  相似文献   
38.
ABSTRACT: The traditional small-scale production of boucané, a cured smoked pork-belly product from Réunion, involves several unit operations that are performed in a single step. The aim of this study was to highligh the impact of 4 unit operations (salting, drying, cooking, and smoking) on stability, color, and flavor development in processed pork. These characateristics are the 3 main criteria of boucané's quality. Mass transfer, color, and volatile compounds were measured, analyzed, and compared in 4 products. Results indicated that a major quantity of volatile compounds detected in the processed meat were derived from the smoking process. Color variations were mainly explained by muscle pigment modification due to the cooking process, and by the input of volatile compounds of smoke.  相似文献   
39.
Recent developments in rubber-toughened structural acrylic adhesives now offer sheet steel fabricators the opportunity to replace conventional metal fastening techniques such as spot welding with lower cost, durable, more versatile structural adhesive bonding. These developments, in particular much improved ability to bond oily/waxy surfaces common to the motor car industry and improved retention of fracture toughness after exposure to paint stoving temperatures, are discussed in this paper.  相似文献   
40.
The mechanical fracture strength and toughness of short-fibre composites, injection moulded from compounds of poly(ethylene terephthalate) (PET) containing 10 and 30% (by weight) (w/o) glass, have been investigated and the dependence upon matrix hydrolytic stability determined. Mouldings have been characterised by several physical techniques to evaluate molecular weight, degradation rates, crystallinity and morphology, whilst time-dependent gravimetric data were derived to quantify sorption kinetics and allow comparisons with theoretical reaction rates to be made. During melt processing, PET is hydrolysed extremely rapidly by traces of moisture (<0.02w/o). yet the inherent strength of moulded composites declines significantly only below an apparently critical molecular weight. However, on long-term humid ageing in hot water, impact behaviour especially is rendered more complex by simultaneous crystallisation, molecular reorder and losses of interfacial bond strength.  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