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   21731篇
  免费   909篇
  国内免费   318篇
电工技术   475篇
综合类   543篇
化学工业   4001篇
金属工艺   546篇
机械仪表   744篇
建筑科学   876篇
矿业工程   181篇
能源动力   625篇
轻工业   2170篇
水利工程   252篇
石油天然气   178篇
武器工业   27篇
无线电   2440篇
一般工业技术   2962篇
冶金工业   3762篇
原子能技术   175篇
自动化技术   3001篇
  2023年   116篇
  2022年   381篇
  2021年   515篇
  2020年   288篇
  2019年   368篇
  2018年   418篇
  2017年   405篇
  2016年   435篇
  2015年   374篇
  2014年   584篇
  2013年   1085篇
  2012年   837篇
  2011年   1050篇
  2010年   796篇
  2009年   863篇
  2008年   837篇
  2007年   863篇
  2006年   739篇
  2005年   627篇
  2004年   700篇
  2003年   918篇
  2002年   1210篇
  2001年   1024篇
  2000年   595篇
  1999年   539篇
  1998年   1345篇
  1997年   869篇
  1996年   645篇
  1995年   430篇
  1994年   325篇
  1993年   358篇
  1992年   197篇
  1991年   156篇
  1990年   149篇
  1989年   138篇
  1988年   134篇
  1987年   115篇
  1986年   116篇
  1985年   155篇
  1984年   92篇
  1983年   99篇
  1982年   85篇
  1981年   106篇
  1980年   107篇
  1979年   64篇
  1978年   53篇
  1977年   104篇
  1976年   193篇
  1975年   56篇
  1973年   53篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
71.
72.
为了更好地指导现场钻井液施工,利用微机建立有关数据库和相应的设计软件,根据地质、工程的要求和井下情况进行钻井液设计,其特点是资料全面、程序运行可靠且操作简便,设计符合现场情况,施工顺利。在千12区块,用微机设计的109口井与人工设计的75口井相比,钻井速度提高,井下复杂情况减少,提高了经济效益。  相似文献   
73.
Applicability of different temperature oscillation calorimetry algorithms, previously proposed in the literature, for the evaluation of the heat transfer coefficient during the course of the reaction, is analysed by referring to the experimental data from a methyl methacrylate polymerisation reactor.Results are coincident in the nominal case (no errors on data), while differences appear in the elaboration of real data. The effect of uncertainty in the experimental data has been simulated in terms of error on the amplitude and on the phase of reactor and jacket temperature profiles.This approach allows to indicate algorithms having the best robustness properties and to give an explanation of phase errors in terms of a lumped parameter which accounts for different phenomena, not included in the basic hypotheses of the method. Based on this observation, a procedure to eliminate this source of errors from experimental data is proposed for the more general algorithm presented to handle oscillating temperature profiles generated by different techniques.  相似文献   
74.
Plasma-polymerized hexamethyldisiloxane (HMDS) films have been prepared as both planar and channel wave guides. The optical attenuation results measured in both the planar and channel HMDS wave guides were found to be similar, thus demonstrating that the inherent solvent resistance and chemical inertness of the plasma polymerized films allows the use of common photoresist techniques, including application of the photoresist, photomasking, and subsequent etching. This may be contrasted with wave guides made from conventional polymers, where careful consideration must be given to photoresist/polymer compatibility, because the photoresist solvents may adversely affect the underlying polymer and lead to degradation of the material during processing. © 1995 John Wiley & Sons, Inc.  相似文献   
75.
Adhesions have been suggested as a possible cause of chronic abdominal pain, but the reports of their etiological role conflict. Lysis of adhesions has been proposed as the therapeutic modality of choice, although the reports of success are controversial. The aim our prospective study was to determine whether laparoscopic adhesiolysis ameliorates chronic abdominal pain in patients with abdominal adhesions. Forty-one patients with chronic abdominal pain lasting for more than 6 months, but with no abnormal findings other than adhesions found at laparoscopy, underwent laparoscopic adhesiolysis. 37 patients (90.2%) were available for follow-up after a median time interval of 18 months (range: 12-41 months). Twenty-two patients (59.4%) were free from abdominal pain and 9 (24.3%) patients reported significant amelioration of their pain. Six (16.2%) patients had no amelioration. In conclusion the laparoscopy is an effective tool for the evaluation of patients with chronic abdominal pain, and laparoscopic adhesiolysis cures of ameliorates chronic abdominal pain in more than 80% of patients.  相似文献   
76.
The principal neutralizing domain, IGPGRAF sequence, from the V3-loop of HIV-1 was inserted in two positions on the surface of the protein that makes up the capside shell of the insect Flock House Virus. The hybrid proteins were expressed in insect cells via recombinant baculoviruses. Three different hybrids were used as immunogens: two with a single copy of the insert in different positions of the carrier protein and a third with two copies of the insert at the same positions as before. All hybrid proteins induced strong and broad specific immune response in guinea pigs against different V3-loop sequences. However, only one of the hybrid proteins was able to induce a strong neutralizing response against MN and IIIB HIV-1 isolates. Our results demonstrate that a very short peptide sequence of HIV-1 can constitute a valuable immunogen able to induce a neutralizing response if presented to the immune system in the context of the FHV capsomer structure.  相似文献   
77.
78.
79.
As the antibiotic arsenal expands with the development of new oral agents, selecting appropriate therapy is becoming more difficult. What are the therapeutic indications for the newer antimicrobials, and what advantages do they have over traditional agents? Drs Gleckman and De La Rosa discuss current issues related to antibiotic treatment and offer specific recommendations for the best use of the newer agents.  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