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   1747篇
  免费   11篇
  国内免费   4篇
电工技术   9篇
综合类   1篇
化学工业   94篇
金属工艺   16篇
机械仪表   14篇
建筑科学   38篇
能源动力   5篇
轻工业   44篇
水利工程   8篇
石油天然气   1篇
无线电   29篇
一般工业技术   106篇
冶金工业   1356篇
原子能技术   7篇
自动化技术   34篇
  2020年   7篇
  2019年   7篇
  2017年   4篇
  2016年   8篇
  2015年   4篇
  2014年   9篇
  2013年   34篇
  2012年   23篇
  2011年   21篇
  2010年   16篇
  2009年   15篇
  2008年   18篇
  2007年   22篇
  2006年   13篇
  2005年   14篇
  2004年   16篇
  2003年   21篇
  2002年   12篇
  2001年   13篇
  2000年   8篇
  1999年   50篇
  1998年   372篇
  1997年   206篇
  1996年   160篇
  1995年   100篇
  1994年   79篇
  1993年   88篇
  1992年   13篇
  1991年   17篇
  1990年   23篇
  1989年   20篇
  1988年   32篇
  1987年   26篇
  1986年   18篇
  1985年   22篇
  1984年   6篇
  1983年   10篇
  1982年   12篇
  1981年   12篇
  1980年   13篇
  1979年   5篇
  1978年   5篇
  1977年   43篇
  1976年   86篇
  1975年   7篇
  1973年   6篇
  1972年   8篇
  1969年   5篇
  1967年   6篇
  1966年   4篇
排序方式: 共有1762条查询结果,搜索用时 0 毫秒
51.
52.
53.
The Personal Attributes Questionnaire (PAQ) is one of the pre-eminent measures of gender-specific personality characteristics. To evaluate the PAQ'S viability 20 yrs after its creation, the authors assessed the dimensionality and psychometric properties of the original PAQ and a French version using samples of 637 English-speaking and French-speaking university administrators. The structure of the English form of the PAQ was supported for both women and men when the data were submitted to confirmatory analyses. Support was not as convincing for the dimensionality of the French form of the PAQ, however. Some evidence for expected differences in mean Instrumentality and Expressivity scores was found between women and men. Findings support the continued use of the English PAQ as a measure of Instrumental and Expressive personality traits. Further study of the French PAQ is recommended. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
54.
55.
The effects of a book reading technique called interactive book reading on the language and literacy development of 4 yr olds from low-income families were evaluated. Teachers read books to children and reinforced the vocabulary in the books by presenting concrete objects that represented the words and by providing children with multiple opportunities to use the book-related words. The teachers also were trained to ask open-ended questions and to engage children in conversations about the book and activities. This provided children with opportunities to use language and learn vocabulary in a meaningful context. Children who were in the interactive book reading intervention group scored significantly better than children in the comparison group on Peabody Picture Vocabulary Test—III and other measures of receptive and expressive language. Book reading and related activities can promote the development of language and literacy skills in young children. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
56.
57.
The reinstatement of natural flow regimes is a rapidly emerging issue in river restoration worldwide. In northern Victoria, Australia, efforts are presently underway to restore a natural, intermittent flow regime to several streams which have received perennial diversions for both irrigation and stock and domestic water‐supplies for over 100 years. A pipeline to deliver water to landholders will significantly reduce transmission losses throughout the system allowing irrigation canals and diversion weirs to be decommissioned. The motivation for flow alteration in this system lies primarily in reducing inefficiencies in water delivery which, in turn, will be used to meet escalating demands on water resources. The ecological impact of the flow regime shift on these streams is likely to be substantial. This study utilized an existing artificial hydrological gradient (from perennial to intermittent) in two creek systems, to explore relationships between flow regime and a range of ecological variables. These data provide a benchmark against which to assess ecological changes once flow has been altered and form the basis for predicting changes that can assist future management decisions. Data collected from 10 sites across a strong hydrological gradient detected clear differences in geomorphology, water quality and biotic assemblages (macrophytes, macroinvertebrates and fish). By examining the relationship between flow regime and the distribution of biota we identify both the positive and negative outcomes of restoring naturally intermittent flow regimes within artificially perennial lowland streams. The reinstatement of intermittent flow regimes in artificially perennial streams will continue in many parts of the world as water delivery via these systems becomes increasingly uneconomical. While flow restoration may in principle be regarded as a positive step, these findings emphasize the need to consider fully the ecological consequences of restoring historical hydrological regimes to streams within the context of other human induced catchment disturbances. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   
58.
A study on zirconium nitride using TEM and nanoindentation was performed to assess the significant surface plasticity found to be introduced by sample polishing. Cross-sectional TEM results show strong evidence of plasticity via dislocations produced directly from surface grinding and polishing. These dislocations were found to glide on the slip system. Using nanoindentation to observe the effects of surface dislocation density, a critical shear stress was found that relates to dislocations nucleation and multiplication. Continued chemo-mechanical polishing increased the critical shear stress to approximately 1600 mN by reducing surface dislocations. It is postulated that vacancy clusters and oxide microcrystallites produced during surface processing provide dislocation nucleation and/or multiplication sites. Gentle chemo-mechanical polishing for several hours greatly reduced or eliminated preexisting dislocations such that the critical shear stress for nucleation approaches the theoretical limit (∼G/5).  相似文献   
59.
The present nationwide, multicenter clinical study was carried out in 26 departments of surgery to define the incidence and attendant mortality of intestinal infarction following abdominal aortic surgery, and to identify patients at risk of it. The data consist of 1752 patients who underwent abdominal aortic reconstruction during 1991-1993 as recorded in the Finnish national vascular registry (FINNVASC). Among the 1752 operations, 27 patients treated at 14 different hospitals had intestinal ischemia, and the complete patient records of all 27 cases were reanalyzed. The incidence of bowel infarction was 1.2%. Among patients operated on for a ruptured aneurysm it was 3.1%, whereas 1.0% of patients with nonruptured aneurysm and 0.6% of those operated on for aortoiliac occlusive disease developed intestinal infarction. In 14 patients (67%) the lesion affected the left colon. The overall 30-day mortality rate was 13% but reached 67% among those with intestinal infarction. We conclude that acute intestinal ischemia with bowel infarction is an infrequent but serious complication of abdominal aortic surgery. It is mainly related to surgery due to aneurysmal disease, and patients with occlusive aortoiliac disease present ischemic complications in the intestines less often. Hypotensive patients being treated for ruptured aneurysm are at greatest risk of intestinal ischemia.  相似文献   
60.
The DNA-dependent protein kinase (DNA-PK) consists of a heterodimer DNA-binding complex, Ku70 and Ku80, and a large catalytic subunit, DNA-PKcs. To examine the role of DNA-PKcs in lymphocyte development, radiation sensitivity, and tumorigenesis, we disrupted the mouse DNA-PKcs by homologous recombination. DNA-PKcs-null mice exhibit neither growth retardation nor a high frequency of T cell lymphoma development, but show severe immunodeficiency and radiation hypersensitivity. In contrast to the Ku70-/- and Ku80-/- phenotype, DNA-PKcs-null mice are blocked for V(D)J coding but not for signal-end joint formation. Furthermore, inactivation of DNA-PKcs leads to hyperplasia and dysplasia of the intestinal mucosa and production of aberrant crypt foci, suggesting a novel role of DNA-PKcs in tumor suppression.  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