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   21293篇
  免费   513篇
  国内免费   21篇
电工技术   273篇
综合类   26篇
化学工业   3045篇
金属工艺   278篇
机械仪表   387篇
建筑科学   992篇
矿业工程   47篇
能源动力   504篇
轻工业   2238篇
水利工程   287篇
石油天然气   29篇
无线电   1874篇
一般工业技术   2760篇
冶金工业   6054篇
原子能技术   159篇
自动化技术   2874篇
  2023年   76篇
  2022年   178篇
  2021年   303篇
  2020年   159篇
  2019年   232篇
  2018年   299篇
  2017年   280篇
  2016年   322篇
  2015年   287篇
  2014年   452篇
  2013年   739篇
  2012年   764篇
  2011年   1039篇
  2010年   727篇
  2009年   761篇
  2008年   786篇
  2007年   782篇
  2006年   632篇
  2005年   617篇
  2004年   565篇
  2003年   532篇
  2002年   479篇
  2001年   384篇
  2000年   351篇
  1999年   487篇
  1998年   2138篇
  1997年   1303篇
  1996年   885篇
  1995年   540篇
  1994年   533篇
  1993年   512篇
  1992年   232篇
  1991年   220篇
  1990年   227篇
  1989年   218篇
  1988年   226篇
  1987年   147篇
  1986年   148篇
  1985年   206篇
  1984年   160篇
  1983年   113篇
  1982年   120篇
  1981年   133篇
  1980年   101篇
  1979年   111篇
  1978年   92篇
  1977年   157篇
  1976年   178篇
  1975年   88篇
  1974年   78篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
The authors report results of a study into the role of components of first-language (L1; Dutch) and second-language (L2; English) reading comprehension. Differences in the contributions of components of L1 and L2 reading comprehension are analyzed, in particular processing speed in L1 and L2. Findings indicate that regression weights of the L1 and L2 components are different. Although correlations between most processing speed components and reading comprehension are substantial, there are no unique contributions to the explanation of either L1 or L2 reading comprehension when linguistic and metacognitive knowledge are accounted for. In addition, L1 reading comprehension is shown to have a large contribution to L2 reading comprehension, supporting theories of L1-L2 transfer of reading skills. Results are discussed from a developmental perspective. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
142.
143.
A PIN diode controlled variable attenuator using a 0-dB branch-line coupler   总被引:3,自引:0,他引:3  
We describe a simple PIN diode controlled variable attenuator that employs a 0-dB branch line directional coupler. The response of the attenuator was measured between 1.3 GHz and 2.6 GHz. At the center frequency, the attenuation monotonically varied from 0.7 dB to 23 dB with the control voltage, and the distributed branch-line coupler structure resulted in low input reflection. Our attenuator is easier to design, smaller in area than a double hybrid coupled attenuator, and has comparable or better reflection and attenuation performance characteristics.  相似文献   
144.
145.
A procedure is described by which the length of a tendon at the onset of loading is determined objectively. The procedure includes the fitting of third-order polynomial functions on the load-elongation data. The onset of loading is detected by an increasing fit of the polynomial by selective data reduction of the initial part of the load-elongation curve. The procedure results in an objective and reproducible definition of the zero strain level of a tendon.  相似文献   
146.
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   
147.
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   
148.
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   
149.
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   
150.
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