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   30328篇
  免费   1429篇
  国内免费   216篇
电工技术   547篇
综合类   358篇
化学工业   4982篇
金属工艺   841篇
机械仪表   739篇
建筑科学   850篇
矿业工程   190篇
能源动力   490篇
轻工业   4100篇
水利工程   223篇
石油天然气   163篇
武器工业   17篇
无线电   1669篇
一般工业技术   5435篇
冶金工业   7566篇
原子能技术   182篇
自动化技术   3621篇
  2023年   310篇
  2022年   262篇
  2021年   622篇
  2020年   519篇
  2019年   440篇
  2018年   912篇
  2017年   817篇
  2016年   922篇
  2015年   811篇
  2014年   958篇
  2013年   1781篇
  2012年   1357篇
  2011年   1346篇
  2010年   1147篇
  2009年   1102篇
  2008年   1247篇
  2007年   1198篇
  2006年   866篇
  2005年   690篇
  2004年   547篇
  2003年   601篇
  2002年   621篇
  2001年   509篇
  2000年   387篇
  1999年   491篇
  1998年   2362篇
  1997年   1416篇
  1996年   983篇
  1995年   603篇
  1994年   492篇
  1993年   435篇
  1992年   178篇
  1991年   186篇
  1990年   156篇
  1989年   166篇
  1988年   153篇
  1987年   163篇
  1986年   146篇
  1985年   227篇
  1984年   189篇
  1983年   169篇
  1982年   129篇
  1981年   179篇
  1980年   177篇
  1979年   125篇
  1978年   106篇
  1977年   226篇
  1976年   489篇
  1974年   88篇
  1973年   113篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
In this study, the effects of the phosphonic acid based sequestering agent EDTMPA used in the textile dye baths on colour and organic matter removal by ozone oxidation was experimentally investigated. Procion Navy HEXL dyestuff that has been commonly used for the reactive dyeing of cellulose fibers was selected as the model component. The organic matter oxidation by ozone was determined to obey the pseudo-first order kinetics as they are treated singly or in combination. COD removal rates obtained from pseudo-first order reaction kinetics showed that oxidation of Navy HEXL alone (0.0947 L/min) was faster than that of EDTMPA (0.0171 L/min) and EDTMPA with dye (0.0155 L/min) at pH 3.0. It was also found that reaction rates of single EDTMPA removal and EDTMPA and dye mixture removal increased as the reaction pH was increased from 3.0 to 10.5.  相似文献   
12.
1前言及历史背景 为避免钢水造成燃烧或破碎引起对人体的可能伤害,必须对连铸平台的平面布置进行分析.  相似文献   
13.
Due to clearly distinguishable damage symptoms, it is differentiated between the surface and sub‐surface failure mode of rolling bearings. Material states red out by X‐ray diffraction (XRD) residual stress measurements point to a variety of loading conditions especially at raceway surfaces that are associated with several competing failure mechanisms. The corresponding lifetime reduction can range from the lower fatigue strength region to material ratcheting in extreme cases. Relevant position of the microstructural changes and nature of the failure mechanisms are characterized. The time alteration of the XRD material parameters measured at or near the surface and at the depth of the maximum equivalent stress correlates, in a different manner, with the statistical parameter of the 10 % bearing life. Both failure modes are illustrated by concrete examples. Contaminated lubricant and boundary lubrication, which represent practically important surface‐induced failures, are discussed in more detail. Gray staining, i.e. shallow pitting, often occurs without distinct indication of global material aging by means of XRD characteristics. Here, scanning electron microscopy observations and electron microprobe analyses point to corrosion fatigue as acting surface failure mechanism. The interaction between material and lubricant under complex loading regimes particularly of mixed friction and corrosion opens further failure research areas in the field of tribology.  相似文献   
14.
15.
SiGe-HBTs have the potential for outstanding analog and digital or mixed-signal high frequency circuits widely based on standard Si technology. Here we review on MBE grown transistors and circuits. Processes and results of a research-like SiGe HBT and two possible production relevant HBT versions are presented. The high frequency results with fmax and fT up to 120 GHz and a minimum noise figure of 0.9 dB at 10 GHz demonstrate the advantage of using MBE samples with steep and high base doping and high germanium contents. A comparison to the concept of reported low doped, low germanium and triangular profiled SiGe base layers, realized by UHV-CVD, is given. In addition, some circuit demonstrators of SiGe-ICs will be presented.  相似文献   
16.
17.
18.
Among various pharmacological agents used to reduce bleeding after open-heart operations, high-dose aprotinin therapy seems most promising. However, its long-term effects are still obscure; there is almost always possibility of bypass graft occlusions produced by the hypercoagulable state induced by aprotinin in coronary bypass operations. Topical application of aprotinin into the pericardial cavity could prevent the adverse effects. Fifty patients were prospectively studied to evaluate the effects of topical aprotinin. One million KIU of aprotinin was poured into the pericardial cavity before closure of the sternotomy in group 1 (n = 25). Patients in group 2 (n = 25) served as controls. Total postoperative bleeding was significantly reduced in group 1 when compared with that of group 2 (722.7 +/- 230.8 versus 1,282.6 +/- 225.7 mL; p < 0.01). The use of banked donor blood products was significantly less in group 1 than in group 2 (0.33 +/- 0.67 versus 1.36 +/- 0.86 units; p < 0.01). These results show that topical use of aprotinin reduces post-operative blood loss and need for transfusion. It seems promising and warrants further studies to be done.  相似文献   
19.
20.
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