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   2724篇
  免费   11篇
电工技术   5篇
化学工业   122篇
金属工艺   8篇
机械仪表   6篇
建筑科学   18篇
矿业工程   2篇
能源动力   13篇
轻工业   48篇
水利工程   8篇
石油天然气   5篇
无线电   89篇
一般工业技术   73篇
冶金工业   2260篇
原子能技术   4篇
自动化技术   74篇
  2021年   14篇
  2020年   11篇
  2019年   11篇
  2018年   11篇
  2014年   9篇
  2013年   28篇
  2012年   14篇
  2011年   26篇
  2010年   13篇
  2009年   14篇
  2008年   30篇
  2007年   24篇
  2006年   13篇
  2005年   19篇
  2004年   17篇
  2003年   18篇
  2002年   20篇
  2001年   19篇
  2000年   11篇
  1999年   76篇
  1998年   624篇
  1997年   356篇
  1996年   223篇
  1995年   121篇
  1994年   111篇
  1993年   138篇
  1992年   28篇
  1991年   34篇
  1990年   39篇
  1989年   49篇
  1988年   42篇
  1987年   51篇
  1986年   41篇
  1985年   31篇
  1984年   16篇
  1983年   13篇
  1982年   14篇
  1981年   19篇
  1980年   19篇
  1979年   8篇
  1978年   12篇
  1977年   60篇
  1976年   113篇
  1975年   16篇
  1974年   9篇
  1973年   11篇
  1972年   17篇
  1971年   11篇
  1964年   8篇
  1955年   7篇
排序方式: 共有2735条查询结果,搜索用时 15 毫秒
21.
22.
23.
24.
25.
This project reports the publication of a variety of existing curricular resources for emergency medicine on the global Internet in a format that allows hypertext links between related material, timely updates, and end-user feedback. Curricular elements were converted to Hypertext Markup Language with extensive links between related content. The completed document contains instructions for curriculum development, specific curricula for subspecialty areas within a residency, reading lists for subspecialty curricula, banks of images, and board-type questions with answers. Users are provided with a mechanism to provide immediate feedback to section editors with suggestions for changes, including new references. Access to all or part of the document can be controlled via passwords, but is potentially available to anyone with an Internet connection and a World Wide Web browser. The document may by viewed on the World Wide Web at: http:@www.brown.edu@Administration@emergency_Medicine@ curr.html.  相似文献   
26.
27.
28.
OBJECTIVE: The authors report the use of multiple implanted intraspinal port and catheter systems per test animal to study the in vivo functional characteristics and reliability of a new implantable spinal drug delivery port system. METHODS: Four ewes were each implanted with two epidural and one subarachnoid silicone elastomer catheters at the lumbar level. Each catheter was connected in series to one of three Therex filtered spinal delivery ports implanted subcutaneously in a similar grid pattern in each ewe to facilitate percutaneous identification. Saline (2 ml) was injected 3 times weekly in each port. The ease of injection and behavioral responses were recorded for 207-213 days of implantation until sacrifice/necropsy. RESULTS: All ports functioned reliably during the study. However, injection through two of the four subarachnoid catheters resulted in behavioral withdrawal responses intermittently. This behavioral pattern was much less common after epidural port injections. All four subarachnoid and four of eight epidural port and catheter systems were tested with local anesthetic just before sacrifice. Motor block was observed in three of four subarachnoid and three of four epidural port and catheter systems tested. Integrity of the other four epidural ports was tested by injection of methylene blue at sacrifice. This dye did not distribute in the epidural space in one of the latter four epidural ports (not local anesthetic tested) because of a concentric fibrotic reaction about the catheter. Similar fibrotic reactions surrounded the catheters that failed a functional test with local anesthetic. CONCLUSIONS: The implantable intraspinal port system tested functions reliably under repetitive percutaneous access. However, filtering such ports, though desirable to prevent entry of debris into the spinal canal, did not eliminate pericatheter chronic subarachnoid and epidural reaction. The number of test animals required to test 12 ports chronically was reduced by two-thirds without undue trauma to the individual test subject. Chronic percutaneous injection of an implanted subarachnoid system is feasible but may be associated with behavioral effects similar to that seen with chronic epidural systems. Fibrosis around chronic silicone catheters limited functional utility in one-fourth of the implanted test systems. Further study of the potential reactivity of chronic epidural and subarachnoid catheters is indicated.  相似文献   
29.
The inner filter effect is observed in luminescence whenever a second substance is present that has absorptions which overlap the luminescence. This results in a diminution of the luminescence at those wavelengths and is generally observed in solution. In the present communication we show that this effect can be observed when a solid rare earth complex is physically mixed with a solid luminescent organic matrix with which it does not interact. The resulting luminescence is reduced in emission intensity at those wavelengths corresponding to the absorptions of the rare earth ion. This is illustrated with a mixture of Na3[Ho(ODA)3] ·2NaClO4·6H2O and pyrene at 77 K, and it is shown that the absorption spectrum of the holmium complex can be extracted from the luminescence spectrum of pyrene. This absorption spectrum is in good agreement with that obtained by conventional spectroscopy with a single crystal.  相似文献   
30.
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