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   2801篇
  免费   73篇
  国内免费   7篇
电工技术   28篇
综合类   2篇
化学工业   521篇
金属工艺   38篇
机械仪表   65篇
建筑科学   197篇
矿业工程   7篇
能源动力   92篇
轻工业   228篇
水利工程   23篇
石油天然气   17篇
无线电   210篇
一般工业技术   463篇
冶金工业   639篇
原子能技术   18篇
自动化技术   333篇
  2023年   15篇
  2022年   21篇
  2021年   34篇
  2020年   25篇
  2019年   30篇
  2018年   39篇
  2017年   40篇
  2016年   55篇
  2015年   35篇
  2014年   60篇
  2013年   174篇
  2012年   106篇
  2011年   152篇
  2010年   103篇
  2009年   89篇
  2008年   127篇
  2007年   121篇
  2006年   89篇
  2005年   94篇
  2004年   81篇
  2003年   81篇
  2002年   64篇
  2001年   52篇
  2000年   64篇
  1999年   63篇
  1998年   136篇
  1997年   80篇
  1996年   69篇
  1995年   54篇
  1994年   49篇
  1993年   51篇
  1992年   32篇
  1991年   23篇
  1990年   31篇
  1989年   35篇
  1988年   33篇
  1987年   29篇
  1986年   32篇
  1985年   44篇
  1984年   32篇
  1983年   26篇
  1982年   26篇
  1981年   37篇
  1980年   20篇
  1978年   19篇
  1977年   22篇
  1976年   21篇
  1975年   29篇
  1974年   16篇
  1973年   19篇
排序方式: 共有2881条查询结果,搜索用时 15 毫秒
1.
2.
3.
The socioemotional functioning of schizophrenic and schizotypic individuals is marked by withdrawal, poor organization, and limited emotional displays. Such behavioral tendencies and lack of social enjoyment in schizotypy could be linked to the relative situational demands or role ambiguity inherent in specific social activities. To determine whether high-schizotypy individuals prefer more clearly role-defined social activities (e.g., visiting relatives) to more ambiguous, novel situations (e.g., going alone to a party), the authors gathered reports from 52 high-schizotypy and 60 low-schizotypy individuals on their enjoyment and frequency of engaging in social situations varying in relative situational demand. Parallel reports were obtained from knowledgeable others. Group × Situational Demand interactions revealed the hypothesized pattern of reduced frequency and enjoyment ratings for ambiguous or novel situations by the high-schizotypy participants in both self and others' reports. Groups were more comparable in their reported frequency and enjoyment of less ambiguous situations. Results suggest the importance of situational demands in the socioemotional experience and behavioral withdrawal in schizotypy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
4.
5.
A new method of implementing efficient FIR filters is presented. It involves approximation of an equiripple FIR by a rounding operation and application of the derived impulse response by a simple recursive equation. The technique is extremely efficient for lowpass, highpass, bandpass, and bandstop filters with sharp transitions and low edge frequencies  相似文献   
6.
7.
The MSMIE protocol [SBC89] allows processors in a distributed system to communicate via shared memory. It was designed to meet the reliability and efficiency needs of applications such as nuclear safety systems. We present a formal model of the MSMIE protocol expressed in the notation CCS. Desirable properties of the protocol are expressed in the modal mu-calculus, an expressive modal logic. We show that the protocol lacks an important liveness property. In actual operation, additional operating constraints are checked to avoid potential problems. We present a modified protocol and show that it possesses the liveness property even without checking operating constraints. We also show how parts of the analysis were automated with the Concurrency Workbench.  相似文献   
8.
Although the full mechanisms are not yet elucidated, research into the mechanism of toxicity of aluminum (Al) on bone formation and remodeling and on hematopoietic tissue is ongoing. In contrast little information exists on the interactive effects of systemic Al and the kidney. In bone, both clinically and experimentally, high doses of Al inhibit remodeling, slowing both osteoblast and osteoclast activities and producing osteomalacia and adynamic bone disease. In contrast, while very low levels of Al are mitogenic in bones of experimental animals, the effect of low levels of Al in humans is unknown. Aluminum has been shown to have its mitogenic action at the osteoblast, but whether the effect on resorption is viz osteoblast-directed changes in osteoclast activity has not yet been determined. Parathyroid hormone (PTH) levels are disrupted by Al in humans and animals. Whether altered PTH levels play a major or even a minor role in Al-dependent osteotoxicity requires clarification. In hematopoietic tissue, Al causes a microcytic anemia, not reversible by iron. Friend leukemia cells treated with Al have been reported to accumulate excess iron, without incorporating it into ferritin or heme. It is not yet known which steps in iron metabolism are disrupted by Al, if they involve a single mechanism of action, or even if this disruption in iron metabolism accounts for the anemia seen in Al toxicosis. In kidney, research is needed to evaluate Al nephrotoxicity; there are almost no studies in this area. Furthermore, research is needed to evaluate mechanisms of renal Al excretion, presently shown by one study to occur at the distal tubule. Such studies might well throw light on whether Al plays a role in aggravating renal insufficiency, or whether the role of the kidney in Al toxicosis is limited to the causative effect of renal compromise on Al accumulation. In summary, while a number of mechanisms have been proposed for the toxic action of Al, no single mechanism emerges to explain these diverse effects of systemic Al. Recommendations for future research are presented and summarized in Table 1.  相似文献   
9.
Packaging engineers need to be able to accurately determine the forces present in the shipping environment in order to protect packaged goods. The purpose of this study was to determine the vertical vibration levels measured in three separate truck-trailer suspension systems; conventional leaf-spring, conventional air-ride and damaged air-ride. The main conclusion reached in this study is that the air-ride suspension when maintained gives lower power density (PD) levels on all road surfaces studied. A damaged air-ride suspension and leaf-spring suspension are very similar in response frequencies, although the damaged air-ride produces higher vibration levels at lower frequencies.  相似文献   
10.
This paper describes an approach, conceptual framework, and software architecture for dynamic reconfiguration of the order picking system. The research and development project was sponsored by the Material Handling Research Center (MHRC), a National Science Foundation sponsored Cooperative Industry/University Research Center. The storage configuration is assumed to be an in-the-aisle order picking system in which stockkeeping units (SKUs) can occupy variable capacity storage locations and stock-splitting is allowed among zones (clusters). The product mix may include multiple product families with different life cycles, correlated demand within families and commonality of demand across families.  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