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   5556篇
  免费   229篇
  国内免费   7篇
电工技术   149篇
综合类   13篇
化学工业   1409篇
金属工艺   117篇
机械仪表   104篇
建筑科学   431篇
矿业工程   10篇
能源动力   122篇
轻工业   751篇
水利工程   35篇
石油天然气   13篇
无线电   303篇
一般工业技术   925篇
冶金工业   637篇
原子能技术   58篇
自动化技术   715篇
  2021年   69篇
  2020年   55篇
  2019年   58篇
  2018年   66篇
  2017年   85篇
  2016年   115篇
  2015年   138篇
  2014年   150篇
  2013年   249篇
  2012年   227篇
  2011年   243篇
  2010年   210篇
  2009年   224篇
  2008年   221篇
  2007年   259篇
  2006年   205篇
  2005年   206篇
  2004年   183篇
  2003年   128篇
  2002年   138篇
  2001年   112篇
  2000年   100篇
  1999年   78篇
  1998年   88篇
  1997年   85篇
  1996年   82篇
  1995年   75篇
  1994年   55篇
  1993年   78篇
  1992年   80篇
  1991年   53篇
  1990年   62篇
  1989年   61篇
  1988年   40篇
  1987年   71篇
  1986年   58篇
  1985年   72篇
  1984年   65篇
  1983年   61篇
  1982年   63篇
  1981年   68篇
  1980年   67篇
  1979年   68篇
  1978年   51篇
  1977年   54篇
  1976年   57篇
  1975年   56篇
  1974年   67篇
  1973年   49篇
  1970年   41篇
排序方式: 共有5792条查询结果,搜索用时 234 毫秒
991.
The role of enzymes in modern detergency   总被引:1,自引:0,他引:1  
Enzymes have effectively assisted the development and improvement of modern household and industrial detergents. The major classes of detergent enzymes—proteases, lipases, amylases, and cellulases—each provide specific benefits for application in laundry and automatic dishwashing. Historically, proteases were first to be used extensively in laundry detergents. In addition to raising the level of cleaning, they have also provided environmental benefits by reducing energy consumption through shorter washing times, lower washing temperatures, and reduced water consumption. Today proteases are joined by lipases and amylases in improving detergent efficacy especially for household laundering at lower temperatures and, in industrial cleaning operations, at lower pH levels. Cellulases contribute to overall fabric care by rejuvenating or maintaining the new appearance of washed garments. Enzymes are produced by fermentation technologies that utilize renewable resources.  相似文献   
992.
A systematic structure‐selectivity study was carried out for the enantioselective hydrogenation of activated ketones with chirally modified Pt/Al2O3 catalysts. For this, 18 modifiers containing an extended aromatic system able to form a strong adsorption complex with the Pt surface, and a suitable chiral group with an amino function capable to interact with the keto group of the substrate ( HCd, Qd, HCn, Qn , and semi‐synthetic derivatives, as well as synthetic analogues) were prepared and tested on 8 different activated ketones in AcOH and toluene under standard conditions. It was found that relatively small structural changes of the substrate and/or modifier structures strongly affected the enantioselectivity, and that no “best” modifier exists for all substrates. The highest ees for all substrates were obtained with quinuclidine‐derived modifiers in combination with naphthalene or quinoline rings, either in AcOH (substrates 1 – 5 and 8 , all carrying an sp3 carbon next to the keto group) or toluene ( 6 and 7 , with an sp2 carbon next to the ketone). The presence and nature of the substituent R' at the quinuclidine significantly affected the ee (positive and negative effects). Certain combinations of an aromatic system and an amino function were preferred: For the quinuclidine moiety, quinoline and to a somewhat lesser extent naphthalene were a better match, while for the pyrrolidinylmethyl group anthracene was better suited. Methylation of the OH group often had a positive effect for hydrogenations in AcOH but not in toluene. With the exception of 8 , higher ees were obtained for the Cd / Qn series [leading to (R)‐products] than for the Cn / Qd series [leading to (S)‐products]. In several cases, opposite structure‐selectivity trends were detected when comparing reactions in toluene and AcOH, indicating a significant influence of the solvent.  相似文献   
993.
Recommendations of the DGGT Committee “Geotechnics of Landfill Structures”. The Committee “Geotechnics of Landfill Structures”, formerly “Geotechnics of Landfills and Contaminated Land”, published up to now 75 recommendations. The series is continued by the revised recommendations E2‐1 “Principles of geotechnical design for landfills” and E1‐3 “Site investigation with geophysical methods”, as well as by a draft version of a new recommendation E5‐10 “Tasks and required qualification of an independent inspector for mineral components in lining systems”. Other subjects and revised recommendations are reported.  相似文献   
994.
995.
996.
Requirements for inverted roofs with separating layer – notes on the application of EN ISO 6946. This paper explains the application of the EN ISO 6946 standard for different regions in Europe in terms of heat losses through inverted roofs. For determining the heat transfer coefficient of inverted roofs, the October 2003 version of this standard takes into account additional heat loss due to precipitation. This enables additional roof heat losses originating from the flow of warmed precipitation below the thermal insulation to be calculated. The heat loss depends on the quantity of precipitation and on the proportion of water that drains directly between the roof sealing layer and the thermal insulation. The paper explains the application of the standard for different regions in Europe. Supplementary climatic data and boundary conditions for different regions are provided. In addition, the requirements for the separating layer in inverted roofs with separating layer are described. Using the technique described, heat losses due to precipitation can be reduced to such an extent that they are negligible for the purpose of the calculation.  相似文献   
997.
Verification of Crack Limitation for Circular Cross Section The verification of the crack limitation for circular cross sections such as bored piles is often neglected. In some cases for instance for predominantly bending members the crack limitation is the fundamental proof. Thus all necessary principals for the crack limitation of circular cross sections were provided. The analytical approaches are proved by experiments. There is a good conformance between the theoretical approach provided and the tests.  相似文献   
998.
999.
国际放射防护委员会(ICRP)提出了“防护量”这一概念。最常用的防护量,即有效剂量E,用于设定照射限值,并在实用辐射防护中使用,以实现最优化原则。然而,有效剂量不是一个可测量的量,基于此国际辐射单位与测量委员会(ICRU)为外照射的剂量测定提出了一个可测量的量,即实用量,用于估计有效剂量。目前使用的实用量定义于20世纪80年代,当时核工业是职业辐射防护的主要关注点。当前,在其他辐射领域,特别是高能辐射,实用量的不足之处变得很明显:可能高估或低估有效剂量。因此,ICRU和ICRP在全面研究的基础上,为外照射的剂量测定提出了新的实用量,以克服上述缺点。实用量的新定义与防护量(包括有效剂量)的定义更具相关性,特别是使用了相同的仿真体模。当前提出的实用量通过缩小防护量与实用量之间的定义差异简化了辐射防护量体系,并从整体上改进了对有效剂量的估计。本文讨论了提出的新实用量对实际剂量测定的影响。  相似文献   
1000.
Opus is a new programming language designed to assist in coordinating the execution of multiple, independent program modules. With the help of Opus, coarse grained task parallelism between data parallel modules can be expressed in a clean and structured way. In this paper we address the problems of how to build a compilation and runtime support system that can efficiently implement the Opus constructs. Our design considers the often‐conflicting goals of efficiency and modular construction through software re‐use. In particular, we present the system requirements for an efficient Opus implementation, the Opus runtime system, and describe how they work together to provide the underlying services that the Opus compiler needs for a broad class of machines. Copyright © 2000 John Wiley & Sons, Ltd.  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