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   1614篇
  免费   26篇
  国内免费   2篇
电工技术   11篇
综合类   1篇
化学工业   195篇
金属工艺   11篇
机械仪表   28篇
建筑科学   80篇
矿业工程   8篇
能源动力   33篇
轻工业   201篇
水利工程   16篇
石油天然气   3篇
无线电   126篇
一般工业技术   220篇
冶金工业   502篇
原子能技术   18篇
自动化技术   189篇
  2023年   6篇
  2022年   7篇
  2021年   18篇
  2020年   14篇
  2019年   20篇
  2018年   18篇
  2017年   23篇
  2016年   12篇
  2015年   17篇
  2014年   27篇
  2013年   80篇
  2012年   71篇
  2011年   54篇
  2010年   50篇
  2009年   49篇
  2008年   76篇
  2007年   68篇
  2006年   51篇
  2005年   56篇
  2004年   38篇
  2003年   45篇
  2002年   38篇
  2001年   39篇
  2000年   42篇
  1999年   35篇
  1998年   125篇
  1997年   77篇
  1996年   57篇
  1995年   40篇
  1994年   38篇
  1993年   34篇
  1992年   18篇
  1991年   27篇
  1990年   15篇
  1989年   15篇
  1988年   14篇
  1987年   16篇
  1986年   21篇
  1985年   25篇
  1984年   15篇
  1983年   10篇
  1982年   7篇
  1981年   8篇
  1980年   7篇
  1979年   10篇
  1978年   8篇
  1977年   13篇
  1976年   23篇
  1975年   7篇
  1974年   9篇
排序方式: 共有1642条查询结果,搜索用时 8 毫秒
11.
12.
28 isolates of canine parvovirus type-2 (CPV-2) were obtained from dogs with hemorrhagic gastroenteritis in Italy. The antigenic structure of CPV-2 isolates was characterized, using four discriminating monoclonal antibodies. In addition, four vaccinal strains were examined. Similar to reports from Australia and the United Kingdom, a much higher prevalence of CPV-2a (25/28 isolates) was observed than the other variant type, CPV-2b (3/28 isolates). DNA fragments (2.2 kbp) of representative strains of CPV-2, CPV-2a and CPV-2b were amplified by the polymerase chain reaction (PCR) and the products were digested by the restriction enzymes (RE) RsaI, HpaII, HindIII and PvuII. The RvaI enzyme allows the differentiation of CPV-2 from CPV-2a and CPV-2b.  相似文献   
13.
Thromboembolic events frequently complicate the clinical course of patients with inflammatory bowel disease (IBD). Hereditary thrombophilia may contribute to this tendency. Resistance to activated protein C is the most recently described thrombophilic state and may account for up to 40% of patients with thrombophilia. Thirty-seven patients with IBD were studied (mean age 44 years, range 18-82 years). Three patients had a history of thrombotic episodes. The 37 controls included 23 men and 17 women (mean age 48 years, range 16-89 years). Disease activity was assessed using the Harvey Bradshaw index for patients with Crohn's disease and the Truelove and Witts grading system for patients with ulcerative colitis. Levels of fibrinogen, antithrombin III (ATIII), protein C, protein S, activated protein C resistance (APCR), and the presence of a lupus anticoagulant (LA) were determined. Median ATIII levels in patients with IBD were significantly lower than controls (98% vs 106%, P = 0.007), while fibrinogen was elevated (4.2 vs 3.3 g/liter, P = 0.026) despite quiescent disease activity. LA was detected in 7/37 patients in the IBD group compared to 0/37 controls. (chi2 = 5.68, P = 0.017). No significant difference was observed in levels of inherited thrombophilic factors and in particular APCR between IBD patients and controls. In conclusion, the presence of inherited thrombophilic defects, in particular APCR, is uncommon in patients with IBD and does not merit routine screening.  相似文献   
14.
PURPOSE: This case report describes the clinical, scintigraphic, and pathologic findings in a patient with an unexpected finding of a cutaneous malignant melanoma. METHOD: Multiple imaging studies were done, as was a pathologic examination of a suspicious pigmented lesion on the patient's back. RESULT: A Tc-99m MDP bone scan showed diffuse uptake in the skeleton, lungs, kidneys, and stomach. CONCLUSION: Metastatic calcification, as shown by isotope scintigraphy, is an unusual manifestation of metastatic cancer from a primary cutaneous melanoma.  相似文献   
15.
Hemoptysis secondary to an aortobronchial fistula is rare and uniformly fatal when left untreated. The authors describe a case of massive hemoptysis caused by an aortopulmonary fistula in an infected Dacron graft used successfully to repair a coarctation of the aorta.  相似文献   
16.
In this article we overview the design and implementation of the second generation of Kansas Lava. Driven by the needs and experiences of implementing telemetry decoders and other circuits, we have made a number of improvements to both the external API and the internal representations used. We have retained our dual shallow/deep representation of signals in general, but now have a number of externally visible abstractions for combinatorial and sequential circuits, and enabled signals. We introduce these abstractions, as well as our abstractions for reading and writing memory. Internally, we found the need to represent unknown values inside our circuits, so we made aggressive use of associated type families to lift our values to allow unknowns, in a principled and regular way. We discuss this design decision, how it unfortunately complicates the internals of Kansas Lava, and how we mitigate this complexity. Finally, when connecting Kansas Lava to the real world, the standardized idiom of using named input and output ports is provided by Kansas Lava using a new monad, called Fabric. We present the design of this Fabric monad, and illustrate its use in a small but complete example.  相似文献   
17.
18.
19.
Abstract

Inter-play, an on-line index to plays in collections, anthologies and periodicals, provides easy access to the locations of printed plays by making citations for the location(s) of each play searchable by author and/or title. The process of converting the original card file play index into an electronic database available on the World Wide Web is described. The index has been designed to provide easy access to and broad coverage of available plays. New titles are added to the file on a regular basis, placing this Web publication squarely in the electronic journal arena.  相似文献   
20.
Abstract

In an earlier study of preservice elementary and middle school teachers’ beliefs about repeating decimals, Weller, Arnon, and Dubinsky (2009) reported on a comparison of the mathematical performance of 77 preservice teachers who completed an APOS-based instructional unit with 127 preservice teachers who completed traditional instruction. The purpose of the current study, based on 47 interviews conducted 4 months after the instruction, during which time there was no further instruction on this topic, is to determine the strength and stability (over time) of the students’ beliefs, to uncover thinking that did not arise in the earlier study, and to see whether the interviews yield similar comparative results. The interviews did uncover changes in student thinking. The students who received the APOS-based instruction developed stronger and more stable (over time) beliefs that a repeating decimal is a number; a repeating decimal has a fraction or integer to which it corresponds; a repeating decimal in general equals its corresponding fraction or integer; and, in particular, In addition, a number of indices and categories were developed that may prove useful in other studies consisting of the comparison of interview and questionnaire data involving a large number of interview subjects.  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