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   1104篇
  免费   28篇
  国内免费   9篇
电工技术   10篇
综合类   1篇
化学工业   168篇
金属工艺   13篇
机械仪表   19篇
建筑科学   99篇
矿业工程   29篇
能源动力   45篇
轻工业   68篇
水利工程   5篇
石油天然气   8篇
无线电   140篇
一般工业技术   137篇
冶金工业   108篇
原子能技术   6篇
自动化技术   285篇
  2022年   8篇
  2021年   13篇
  2020年   6篇
  2019年   12篇
  2018年   18篇
  2017年   17篇
  2016年   14篇
  2015年   19篇
  2014年   19篇
  2013年   99篇
  2012年   45篇
  2011年   42篇
  2010年   28篇
  2009年   40篇
  2008年   41篇
  2007年   58篇
  2006年   61篇
  2005年   65篇
  2004年   60篇
  2003年   55篇
  2002年   36篇
  2001年   34篇
  2000年   33篇
  1999年   34篇
  1998年   28篇
  1997年   28篇
  1996年   29篇
  1995年   22篇
  1994年   20篇
  1993年   8篇
  1992年   7篇
  1991年   12篇
  1990年   7篇
  1989年   8篇
  1988年   6篇
  1987年   8篇
  1986年   7篇
  1985年   14篇
  1984年   12篇
  1983年   8篇
  1982年   7篇
  1981年   5篇
  1980年   5篇
  1979年   9篇
  1978年   4篇
  1977年   6篇
  1974年   4篇
  1973年   3篇
  1968年   3篇
  1963年   3篇
排序方式: 共有1141条查询结果,搜索用时 15 毫秒
1.
Alewives (Alosa pseudoharengus), the major prey fish for Lake Ontario, contain thiaminase. They are associated with development of a thiamine deficiency in salmonines which greatly increases the potential for developing an early mortality syndrome (EMS). To assess the possible effects of thiamine deficiency on salmonine reproduction we measured egg thiamine concentrations for five species of Lake Ontario salmonines. From this we estimated the proportion of families susceptible to EMS based on whether they were below the ED20, the egg thiamine concentration associated with 20% mortality due to EMS. The ED20s were 1.52, 2.63, and 2.99 nmol/g egg for Chinook salmon (Oncorhynchus tshawytscha), lake trout (Salvelinus namaycush), and coho salmon (Oncorhynchus kisutch), respectively. Based on the proportion of fish having egg thiamine concentrations falling below the ED20, the risk of developing EMS in Lake Ontario was highest for lake trout, followed by coho (O. kisutch), and Chinook salmon, with the least risk for rainbow trout (O. mykiss). For lake trout from western Lake Ontario, mean egg thiamine concentration showed significant annual variability during 1994 to 2003, when the proportion of lake trout at risk of developing EMS based on ED20 ranged between 77 and 100%. Variation in the annual mean egg thiamine concentration for western Lake Ontario lake trout was positively related (p < 0.001, r2 = 0.94) with indices of annual adult alewife biomass. While suggesting the possible involvement of density-dependent changes in alewives, the changes are small relative to egg thiamine concentrations when alewife are not part of the diet and are of insufficient magnitude to allow for natural reproduction by lake trout.  相似文献   
2.
An improved code density test for flash A/D converters is proposed, revealing some dynamic phenomena (e.g., missing codes) hidden by the conventional approach. Formulas are reported for obtaining, from code density, effective noise estimates fully consistent with those provided by waveform analysis. Finally, it is shown that the variance of noise estimates obtained by time-domain analysis may be unacceptably large if the observation window is not properly chosen  相似文献   
3.
4.
5.
This paper describes a database model based on the original rough sets theory. Its rough relations permit the representation of a rough set of tuples not definable in terms of the elementary classes, except through use of lower and upper approximations. The rough relational database model also incorporates indiscernibility in the representation and in all the operators of the rough relational algebra. This indiscernibility is based strictly on equivalence classes which must be defined for every attribute domain. There are several obvious applications for which the rough relational database model can more accurately model an enterprise than does the standard relational model. These include systems involving ambiguous, imprecise, or uncertain data. Retrieval over mismatched domains caused by the merging of one or more applications can be facilitated by the use of indiscernibility, and naive system users can achieve greater recall with the rough relational database. In addition, applications inherently “rough” could be more easily implemented and maintained in the rough relational database.  相似文献   
6.
In order to evaluate the efficacy of a TSH suppressive dose of levothyroxine to reduce the volume of a single thyroid nodule we studied 55 euthyroid patient: 45 (group A) were suppressed with LT4 (mean 1.7 +/- 0.9 micrograms/Kg/day) for 21.3 +/- 5.3 months, and 10 patients (group B) served as controls. All the nodules were "cold" at scintiscanning, solid at ultrasonography and benign by fine-needle aspiration cytology. As responders were assumed the nodules shrinked at the end of treatment of 50% in volume. Thyroid function values (TSH, T4, FT4, T3, FT3, thyroid peroxidase and thyroglobulin antibodies), clinical and ultrasonographic findings were evaluated initially and at the end of the study. A significant nodular volume decrease occurred in 8 treated patients (17.8%) while 37 (82.2%) amongst the group suppressed and all controls showed no change (A vs B = NS). In two untreated patients new nodules were noted; no new nodules were discovered in the treated group (A vs B p < 005). No side effects occurred in any treated patient, even if at the end of treatment a significant T4 and FT4 (p < 0.01) increase was observed. No one onset parameter can predict the response to the therapy. These results suggest that only a small group of patients affected by a single thyroid nodule seems to respond to a TSH suppressive therapy.  相似文献   
7.
就性能而非市场份额来说,Opera一直是MicrosoftInternet Explorer的强有力的替代产品在过去两周,我一直在使用Opera 7.1作为我的主要浏览器。我想说它给我的印象深刻。就性能而非市场份额来说,Opera(www.opera.com) 一直是Microsoft InternetExplorer的强有力的替代产品。我感觉Opera比IE要快,并且它还有一个很棒的下载管理器,在一个单独的屏幕上保留着下载文件。再加上一个弹出式阻截器和带有标签的界面,可以将你打开的页面限定在Opera主窗口内。多元搜索窗口把你的搜索请求发送到Google 和AlltheWeb,然后在并列的窗口显示结果。对O…  相似文献   
8.
Bill Howard 《个人电脑》2003,9(2):121-121
现在名牌笔记本电脑也卖到1000美元以下了,你也该想想你的下一台PC是否应该是笔记本  相似文献   
9.
It starts in a small way. An Internet-originated electronic mail message received by various technical ratings and Combat Information Center (CIC) officers on a ship deployed in a very high threat area of the Persian Gulf relays news of a natural disaster involving their families that supposedly occurred during a cookout:  相似文献   
10.
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