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   18783篇
  免费   493篇
  国内免费   17篇
电工技术   226篇
综合类   14篇
化学工业   2595篇
金属工艺   229篇
机械仪表   335篇
建筑科学   892篇
矿业工程   42篇
能源动力   452篇
轻工业   1943篇
水利工程   263篇
石油天然气   28篇
无线电   1709篇
一般工业技术   2377篇
冶金工业   5419篇
原子能技术   148篇
自动化技术   2621篇
  2023年   68篇
  2022年   152篇
  2021年   265篇
  2020年   136篇
  2019年   199篇
  2018年   266篇
  2017年   246篇
  2016年   271篇
  2015年   251篇
  2014年   389篇
  2013年   657篇
  2012年   677篇
  2011年   916篇
  2010年   634篇
  2009年   663篇
  2008年   697篇
  2007年   674篇
  2006年   566篇
  2005年   552篇
  2004年   505篇
  2003年   466篇
  2002年   427篇
  2001年   343篇
  2000年   319篇
  1999年   440篇
  1998年   1946篇
  1997年   1184篇
  1996年   799篇
  1995年   484篇
  1994年   466篇
  1993年   458篇
  1992年   201篇
  1991年   201篇
  1990年   193篇
  1989年   192篇
  1988年   196篇
  1987年   128篇
  1986年   130篇
  1985年   183篇
  1984年   139篇
  1983年   98篇
  1982年   106篇
  1981年   111篇
  1980年   86篇
  1979年   93篇
  1978年   79篇
  1977年   135篇
  1976年   148篇
  1975年   77篇
  1974年   71篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
181.
The present work analyses the total free energy of the material during the martensitic transformation. A general expression for the martensite fraction as a function of temperature is derived, assuming that the nonchemical free energyis proportional to th  相似文献   
182.
Thermodynamic analysis has greatly helped to compare and to improve the energy efficiency of all kinds of technological processes, and recently we have also attempted to analyse some important biochemical processes under intracellular conditions. This work has pointed to some key strategies on sustainable process operation, such as the exceptionally high thermodynamic efficiencies of chemical and solar energy conversion in living cells.From this it was expected that the sustainability strategies of specific biochemical processes and those of the ecosphere as a whole could be of guidance to current technological processes, especially now that there is a growing demand from government and industry to effectively deal with sustainability aspects in process analysis. Our focus on this issue has led to methodologies to quantify technological aspects of sustainability by making use of thermodynamic principles. Three indicators were constructed to express three technological aspects of process sustainability. First, an indicator for the sustainability of resource utilization considers the thermodynamic input and the availability the resources used in the process. Secondly, an efficiency indicator focuses on the conversion and loss of thermodynamic quantities in the process itself. Thirdly, an indicator for environmental compatibility takes into account the thermodynamic input required to prevent possible negative side effects of the process, such as global warming or water pollution. The three indicators are used to reflect on (un)sustainable characteristics of current technological processes compared to biochemical processes. Finally, we address the drawbacks of combining indicator values to express overall sustainability.  相似文献   
183.
Reaction-induced phase separation (RIPS) of miscible blends of poly(?-caprolactone) (PCL) and an epoxy resin based on poly(propylene oxide) (PPO) was used to prepare thermoplastic vulcanizates (TPVs) with fine rubber dispersions. Scanning electron microscopy (SEM) confirmed the formation of cross-linked rubber particles dispersed in the thermoplastic matrix at PCL contents ≥20 wt%. The morphology development during phase separation was studied by optical microscopy (OM) and time-resolved small-angle light scattering (SALS). It was shown that higher curing temperatures lead to a decrease in rubber particle size, but at the same time lead to an increase in the extent of particle connectivity. In some cases, gelation of the PPO-rich phase limits full structure development, which leads to extensive connectivity between the dispersed rubber particles and a strong deterioration in tensile properties.  相似文献   
184.
A system for the removal and control of dissolved oxygen (DO) from freshwater was designed and constructed with aquarium-type fish studies in mind. Degassed water was obtained using a partial vacuum of -14 psi, and DO regulated at an aquarium scale using electronically controlled aeration with timed partial water renewal. The degassing system was capable of producing water with approximately 1.7 mg L(-1) DO within 10 min of operation, and 0.55 mg L(-1) after 2h. The control system was capable of maintaining DO levels of ca 0.8 mg L(-1) over 48 h in the absence of aeration and further capable of precisely controlling DO levels as low as 1.16+/-0.002 mg L(-1) (mean+/-SEM) with aeration over a 48 h period.  相似文献   
185.
Workers in medium- or high-risk professions are often confronted with critical incidents at the workplace. The impact of these acute stressors may be serious and enduring. Many workers also experience chronic job stressors, such as work overload or role conflicts. This study examined the frequently neglected relationship of acute and chronic stressors with self-reported health symptoms, such as posttraumatic responses, fatigue, and burnout. This association was investigated in a sample of forensic doctors in the Netherlands (N = 84). It was found that the more traumatic events the respondents experienced, the more problems they reported in coping with the traumatic events. Chronic job stressors were associated with posttraumatic responses (intrusions and avoidances) and with burnout and fatigue. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
186.
187.
188.
Which signals are important in gaining attention in science? For a group of 1,371 scientific articles published in 17 demography journals in the years 1990-1992 we track their influence and discern which signals are important in receiving citations. Three types of signals are examined: the author's reputation (as producer of the idea), the journal (as the broker of the idea), and the state of uncitedness (as an indication of the assessment by the scientific community of an idea). The empirical analysis points out that, first, the reputation of journals plays an overriding role in gaining attention in science. Second, in contrast to common wisdom, the state of uncitedness does not affect the future probability of being cited. And third, the reputation of a journal may help to get late recognition (so-called sleeping beauties) as well as generate 'flash-in-the-pans': immediately noted articles but apparently not very influential in the long run.  相似文献   
189.
In 3 eye-tracking experiments, the authors investigated the use of morphological information during pronoun resolution. Experiments 1 and 2 showed that disruption occurred when a preferred assignment was inconsistent with gender information. Experiment 2 ensured that this difficulty was not due to the introduction of a new discourse entity. Experiment 3 showed that disruption also occurred when number information was inconsistent with the preferred assignment. The results indicate that the use of morphological information is delayed until after the computation of coreference relations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
190.
In a 2 × 2 factorial design the effects of (1) information presentation format and (2) contextual interference on training behavior, transfer performance and mental effort were studied for learning troubleshooting skills with a computer-based simulation. Participants studied information about the functioning of an alcohol distillery system (system principles) prior to practicing troubleshooting skills. Regarding the first factor, an expository (Exp) format, in which system principles, examples and a troubleshooting strategy were presented in a textual form, was compared to an inquisitory (Inq) format, in which participants had to predict the behavior of the system after they studied the system principles and in which demonstrations of the troubleshooting strategy were given. With regard to the second factor, a low contextual interference (LCI) condition in which participants practiced to diagnose types of system failures in a blocked schedule was compared to a high contextual interference (HCI) condition, in which different failure types were practiced in a random schedule. The main hypothesis is that the Inq and HCI conditions promote the development of cognitive schemata that enable learners to diagnose a malfunctioning system component by interpreting symptoms in terms of violations of system principles. Hence, they are expected to show higher transfer performance than participants in the traditional Exp and LCI conditions, who are believed to develop schemata containing associations between symptoms and malfunctioning components that are context-bound and less useful for diagnosing new failures. Contrary to the predictions, the traditional conditions (Exp and LCI) showed higher performance on a transfer test two weeks after training. Possible explanations for this result are discussed.  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