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   206627篇
  免费   16263篇
  国内免费   7892篇
电工技术   11396篇
技术理论   14篇
综合类   11355篇
化学工业   35933篇
金属工艺   10600篇
机械仪表   12131篇
建筑科学   16704篇
矿业工程   4970篇
能源动力   5895篇
轻工业   12789篇
水利工程   3258篇
石油天然气   11189篇
武器工业   1349篇
无线电   25560篇
一般工业技术   26857篇
冶金工业   11017篇
原子能技术   2130篇
自动化技术   27635篇
  2024年   899篇
  2023年   3289篇
  2022年   5906篇
  2021年   7985篇
  2020年   5872篇
  2019年   5077篇
  2018年   5477篇
  2017年   6265篇
  2016年   5754篇
  2015年   7382篇
  2014年   9609篇
  2013年   12375篇
  2012年   12347篇
  2011年   13996篇
  2010年   11729篇
  2009年   11560篇
  2008年   10957篇
  2007年   10540篇
  2006年   10947篇
  2005年   9703篇
  2004年   6613篇
  2003年   5820篇
  2002年   5293篇
  2001年   4745篇
  2000年   4904篇
  1999年   5659篇
  1998年   5301篇
  1997年   4363篇
  1996年   3967篇
  1995年   3318篇
  1994年   2771篇
  1993年   2188篇
  1992年   1702篇
  1991年   1282篇
  1990年   1018篇
  1989年   878篇
  1988年   682篇
  1987年   496篇
  1986年   396篇
  1985年   334篇
  1984年   213篇
  1983年   198篇
  1982年   163篇
  1981年   145篇
  1980年   133篇
  1979年   98篇
  1978年   63篇
  1977年   63篇
  1976年   77篇
  1975年   38篇
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
991.
油气源对比结果表明,准噶尔盆地吉木萨尔凹陷东斜坡原油分为两类,第Ⅰ类原油为低成熟一成熟油,来源于吉木萨尔凹陷二叠系平地泉组烃源岩;第Ⅱ类原油为高成熟油,来源于该区二叠系石炭系烃源岩。来自吉木萨尔凹陷二叠系平地泉组烃源岩的梧桐沟组的第Ⅰ类原油,根据生物降解程度可分为,未遭受生物降解的原油,遭受轻微生物降解的原油和遭受中等生物降解的原油。吉木萨尔凹陷东斜坡梧桐沟组原油至少存在两期油气成藏。  相似文献   
992.
The electron spin resonance (ESR) spectra of end‐group spin labelled poly(ethylene oxide) (SLPEO) using 2,2,6,6‐tetramethyl‐piperdine‐1‐oxyl nitroxide and its blends with poly(styrene‐co‐4‐vinylphenol) (STVPhs) of different hydroxyl contents were recorded over a wide temperature range. For a blend of SLPEO and pure polystyrene (PS), the ESR spectrum was composed of a single motion component, indicating that PS was immiscible with PEO. For blends composed of SLPEO and different‐hydroxyl‐content STVPhs, two spectral components with different motion rates were observed over a certain temperature range. The difference between the motion rates should be attributed to micro‐heterogeneity in the blends, with the faster rate corresponding to a nitroxide radical motion trapped in the PEO‐rich domain and the slower rate corresponding to a nitroxide radical motion trapped in the STVPh‐rich domain. Variations in the values of a number of the ESR parameters (Ta, Td and T50G) and the apparent activation energy (Ea) with hydroxyl content in the blends indicated that the miscibility of the blends increased with increasing hydrogen‐bonding density due to specific interactions between the hydroxyl groups in STVPh and the ether oxygens in PEO. Copyright © 2004 Society of Chemical Industry  相似文献   
993.
陈会民 《中国电梯》2006,17(17):8-10
创新是唯一的方向 今天,中国已经成为全球电梯最大的制造基地和产品市场,但是随着市场竞争的加剧,使原有的单纯依靠低制造成本的发展模式已经越来越不能适应企业发展的需要。创新已经成为电梯企业越来越重要的必然选择。创新无所不包,管理、文化、技术、产品……电梯企业应该以什么作为突破口?  相似文献   
994.
A simple, low-cost, low-temperature, and shape-controllable approach has been demonstrated to fabricate polymer microlens arrays (MLAs). By using microcontact printing of the self-assembled monolayers and then spin coating, the microlenses were able to organize themselves on the patterned glass substrate. High-quality MLAs made of NOA65 prepolymer with lens-diameters of 50, 75, and 100 mum have been fabricated by this method. Lens shapes can be controlled by changing the spin rates of the prepolymer coating. Optical measurements have revealed an excellent light-collecting capability from the fabricated MLAs. It is anticipated that the technique will be ideally suited to low-cost and high-volume production  相似文献   
995.
论述了银山型钢有限公司炼钢厂2#板坯连铸机自投产以来其振动台存在的问题,根据实际情况分析论证并进行改造实施,实施后效果明显。  相似文献   
996.
This paper presents the use of molecular dynamics (MD) simulation in the investigation of the surface topography of early-stage film growth on a GMR (giant-magnetoresistance) corrugated structure. The size of the simulated system is limited in order to reduce the computational workload. The numerical model adopts the Morse potential and the Verlet-leapfrog time evolution scheme [R.W. Hockney, 1970; D. Potter, 1972 (Chapter 5). [1]] to describe the atomic interactions which take place between the atoms. The impact energy transferred from the incident atoms to the substrate is modeled by rescaling the atoms within the upper substrate layers. It is found that the important properties of the film-substrate system may be obtained after the deposition of just several atomic layers. The influence of the impact velocity upon the coating parameters is investigated by varying the incident energy of the deposited atoms. The current results indicate that the surface coverage is poor, when atoms are deposited at low incident energies upon a low temperature substrate. At a higher incident energy, the deposited film tends to exhibit a quasi-layer-by-layer growth mechanism, which results in an improved surface coverage. Finally, it is demonstrated that a distinct quasi-fluid behavior is evident on the substrate when the atoms are deposited at high incident energies.  相似文献   
997.
内复合换热管与复合管板焊接工艺试验研究   总被引:1,自引:1,他引:0  
介绍复合管与复合管板的管头设计及其焊接试验,结果表明,如果管内壁不锈钢复合层的厚度达到或大于0.5mm,则管头的焊接质量能满足要求,否则管头焊缝容易开裂。内、外双面复合管和复合管板的管头焊接工艺,与仅有内壁单层不锈钢复合层的复合管和复合管板的管头焊接工艺相同。  相似文献   
998.
999.
The paper describes some geotechnical properties of the soft soils in Guangzhou College City, China, which are difficult to both sample and test. Laboratory and in situ tests were carried out to assess the physical and mechanical indices of the soils. The data were statistically analyzed and linear regression undertaken such that equations could be developed by which the geotechnical properties of the soft soils can be predicted. The statistical validity of the degree of correlation confirmed that using these equations, the mechanical indices can be estimated from physical indices determined by routine testing.   相似文献   
1000.
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