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   29858篇
  免费   1162篇
  国内免费   111篇
电工技术   392篇
综合类   230篇
化学工业   5524篇
金属工艺   649篇
机械仪表   648篇
建筑科学   999篇
矿业工程   93篇
能源动力   970篇
轻工业   4165篇
水利工程   252篇
石油天然气   159篇
武器工业   6篇
无线电   2321篇
一般工业技术   4296篇
冶金工业   6328篇
原子能技术   247篇
自动化技术   3852篇
  2024年   55篇
  2023年   165篇
  2022年   551篇
  2021年   859篇
  2020年   570篇
  2019年   658篇
  2018年   762篇
  2017年   821篇
  2016年   771篇
  2015年   591篇
  2014年   904篇
  2013年   1528篇
  2012年   1339篇
  2011年   1671篇
  2010年   1240篇
  2009年   1268篇
  2008年   1171篇
  2007年   1024篇
  2006年   808篇
  2005年   867篇
  2004年   926篇
  2003年   831篇
  2002年   810篇
  2001年   709篇
  2000年   560篇
  1999年   543篇
  1998年   2062篇
  1997年   1347篇
  1996年   941篇
  1995年   614篇
  1994年   480篇
  1993年   551篇
  1992年   223篇
  1991年   285篇
  1990年   231篇
  1989年   192篇
  1988年   206篇
  1987年   159篇
  1986年   164篇
  1985年   182篇
  1984年   129篇
  1983年   90篇
  1982年   118篇
  1981年   120篇
  1980年   115篇
  1979年   91篇
  1978年   75篇
  1977年   139篇
  1976年   232篇
  1975年   84篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
BACKGROUND: We assessed the utility of scintigraphy with indium 111-labeled polyclonal human IgG scintigraphy in patients with fever of unknown origin that fulfilled the criteria of temperature of 38.3 degrees C or more for at least 3 weeks and no diagnosis during 1 week of hospital admission. We compared the utility of this technique with results of scintigraphic techniques reported in the literature. METHODS: Data for all patients seen at our university hospital in whom 111In-IgG scanning was performed were analyzed and checked for the criteria for fever of unknown origin. The literature on the utility of scintigraphic techniques in patients with fever of unknown origin was reviewed. RESULTS: We studied 24 patients with fever of unknown origin. In 13 patients, focal 111In-IgG accumulation was observed. In nine (38%) of those, the positive 111In-IgG scintigram led to the final diagnosis; in the other four patients (17%), the scintigraphic findings were not helpful. In the 11 patients with negative 111In-IgG scans, extensive diagnostic workup produced no infection as the final diagnosis in nine patients (38%), one had an abscess in a renal cyst that was detected several months later, and in the other the cause of fever was an infected intravenous line. The overall sensitivity and specificity of 111In-IgG scintigraphy were 81% and 69%, respectively. The positive predictive value was 69% and the negative predictive value was 82%. CONCLUSIONS: Our results show that 111In-IgG scintigraphy significantly contributed to the diagnostic process in patients with fever of unknown origin. A positive scan increased the likelihood of finding the cause of the fever, and a negative scan ruled out an inflammatory component with a high degree of certainty. These data compare favorably with data in the literature concerning other radiopharmaceuticals; a larger prospective evaluation of this technique is indicated.  相似文献   
103.
104.
105.
The seroprevalence of HIV-1 and HIV-2 among pregnant women in Maputo, the capital of Mozambique, was compared between the years 1982/83, 1988 and 1990. None of the 432 serum samples collected in 1982/83 was positive for HIV antibodies whereas in 1988 the HIV-1 and HIV-2 seroprevalence was 0.4% (2/500) and 0.6% (3/500), respectively, and in 1990 0.6% (12/2014) and 0.2% (4/2014), respectively. These results indicate that HIV infection has been introduced recently in Maputo and is spreading at a slow rate among women.  相似文献   
106.
107.
A method for identifying a set of candidate words that matches well with a given utterance is discussed. The method uses precomputed groups of acoustically similar words. Given a vocabulary, for each word a short list of words that are acoustically similar to it is computed. These groups are constructed using training utterances recorded by several speakers and used in an isolated utterance recognition system to construct candidate word lists during recognition. Experiments show that the correct word appears on the short list of candidate words constructed during recognition using this scheme over 98% of the time  相似文献   
108.
109.
110.
Aqueous extracts of the coralline red algaeBossiella orbigniana have been shown to catalyze the enzymatic oxidation of arachidonic acid to a previously unreported ω6 eicosapentaenoic acid product. This unique fatty acid contains a conjugated tetraene with absorption maxima at 293, 306, and 321 nm, and was identified by spectral methods as 5(Z),8(Z),10(E),12(E),14(Z)-eicosapentaenoic acid. The compound was given the trivial name bosseopentaenoic acid. Under experimental conditions, production of bosseopentaenoic acid was linear up to 2 hr and dioxygen was consumed. Bosseopentaenoic acid, along with several other conjugated tetraenes, was also present in the algae endogenously as revealed by a comparison of the ultraviolet (UV) spectra and the high-performance liquid chromatographic (HPLC) pattern of the purified product and the organic extract ofBossiella.  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