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   22221篇
  免费   819篇
  国内免费   320篇
电工技术   469篇
综合类   543篇
化学工业   3769篇
金属工艺   519篇
机械仪表   732篇
建筑科学   857篇
矿业工程   180篇
能源动力   565篇
轻工业   2078篇
水利工程   247篇
石油天然气   178篇
武器工业   27篇
无线电   2377篇
一般工业技术   2793篇
冶金工业   5038篇
原子能技术   168篇
自动化技术   2820篇
  2023年   110篇
  2022年   340篇
  2021年   467篇
  2020年   270篇
  2019年   332篇
  2018年   383篇
  2017年   359篇
  2016年   397篇
  2015年   350篇
  2014年   526篇
  2013年   1021篇
  2012年   795篇
  2011年   973篇
  2010年   751篇
  2009年   811篇
  2008年   797篇
  2007年   824篇
  2006年   715篇
  2005年   610篇
  2004年   685篇
  2003年   900篇
  2002年   1190篇
  2001年   1017篇
  2000年   592篇
  1999年   569篇
  1998年   1715篇
  1997年   1080篇
  1996年   798篇
  1995年   503篇
  1994年   391篇
  1993年   414篇
  1992年   211篇
  1991年   177篇
  1990年   166篇
  1989年   143篇
  1988年   145篇
  1987年   132篇
  1986年   128篇
  1985年   165篇
  1984年   88篇
  1983年   94篇
  1982年   95篇
  1981年   116篇
  1980年   111篇
  1979年   62篇
  1978年   53篇
  1977年   150篇
  1976年   297篇
  1975年   52篇
  1973年   52篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
51.
52.
53.
Results from this laboratory have shown that bone metabolism is directly related to extracellular pH and that high concentrations of tobramycin released from impregnated polymethylmethacryrate (PMMA) beads has pH-dependent toxic effects on bone. In the present study, beneficial effects of calcium hydroxide-impregnated PMMA were investigated regarding tobramycin toxicity and bone metabolism in chick embryo tibiae in vitro. Also using Ca(OH)2 as a pH regulator, the antibiotic efficacy of tobramycin-impregnated PMMA was evaluated with respect to inhibition of Staphylococcus aureus growth. When Ca(OH)2 was added to PMMA beads containing tobramycin, the beads released hydroxyl and calcium ions into the culture medium and released more antibiotic than beads containing only tobramycin. Bone metabolism (glycolysis, total protein synthesis, and collagen synthesis) was enhanced by Ca(OH)2-impregnated beads with or without tobramycin. Additionally, bacterial growth was inhibited more strongly when S. aureus was incubated with tobramycin- and Ca(OH)2-impregnated PMMA disks than with disks containing only tobramycin. This study demonstrates the feasibility of adding Ca(OH)2 to tobramycin-impregnated PMMA beads as a regulator of local pH and a promoter of bone metabolism for protection of bone when high concentrations of tobramycin are used to treat osteomyelitis. It also suggests that lower concentrations of antibiotic may be effective if Ca(OH)2 and tobramycin are administered simultaneously.  相似文献   
54.
55.
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   
56.
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   
57.
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   
58.
59.
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   
60.
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