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   24740篇
  免费   1047篇
  国内免费   33篇
电工技术   350篇
综合类   38篇
化学工业   5618篇
金属工艺   383篇
机械仪表   481篇
建筑科学   1316篇
矿业工程   100篇
能源动力   622篇
轻工业   1906篇
水利工程   232篇
石油天然气   71篇
无线电   1840篇
一般工业技术   4522篇
冶金工业   4590篇
原子能技术   204篇
自动化技术   3547篇
  2023年   200篇
  2022年   286篇
  2021年   568篇
  2020年   343篇
  2019年   436篇
  2018年   543篇
  2017年   467篇
  2016年   637篇
  2015年   562篇
  2014年   753篇
  2013年   1426篇
  2012年   1170篇
  2011年   1521篇
  2010年   1087篇
  2009年   1023篇
  2008年   1154篇
  2007年   1091篇
  2006年   947篇
  2005年   766篇
  2004年   748篇
  2003年   662篇
  2002年   566篇
  2001年   432篇
  2000年   376篇
  1999年   405篇
  1998年   786篇
  1997年   562篇
  1996年   450篇
  1995年   417篇
  1994年   382篇
  1993年   367篇
  1992年   271篇
  1991年   196篇
  1990年   272篇
  1989年   261篇
  1988年   217篇
  1987年   226篇
  1986年   227篇
  1985年   265篇
  1984年   224篇
  1983年   224篇
  1982年   207篇
  1981年   195篇
  1980年   168篇
  1979年   193篇
  1978年   167篇
  1977年   186篇
  1976年   234篇
  1975年   160篇
  1974年   123篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
描述汽车显示器架构中的外部和内部接口及整合选型方案.  相似文献   
72.
You may not know it, but some of your employees are installing vulnerable software — and you are silently accepting it, you may even encourage them to do so…  相似文献   
73.
This paper presents data relating to the performance of sprinklers and detectors in real office fire situations. For sprinklers, these data are additional to that associated with the standardized testing used to determine the design delivery density and pressure requirements for various occupancy situations, and provide a useful insight into the effect of sprinklers on developing fires with various office situations. The data given in this paper include the times for activation of various types of sprinkler heads (normal and fast response), the efficacy of the systems as far as extinguishment is concerned, estimates of the maximum size of the fires prior to commencement of extinguishment and associated air temperatures at various locations within the office enclosures. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   
74.
The cellulose solvent dimethyl sulfoxide (DMSO)/tetrabutylammonium fluoride trihydrate (TBAF) was successfully applied as reaction medium for the synthesis of allyl cellulose by conversion of the polymer with allyl chloride in the presence of solid NaOH. Samples with degree of substitution from 0.50 to 2.98 were accessible by varying the molar ratio anhydroglucose unit:allyl chloride:NaOH and reaction time. DMSO/TBAF was found to be an efficient reaction medium for the preparation of highly functionalized samples from spruce sulfite pulp with degree of polymerization of about 500 even in a scale of 50 g. The allyl cellulose samples were characterized by means of FTIR- and NMR spectroscopy. Size exclusion chromatography revealed negligible polymer degradation during synthesis and purification of the samples.  相似文献   
75.
76.
For decades, it is believed that astringency is due to the polyphenol-induced complexation of proline-rich salivary proteins in the oral cavity. In order to compare for the first time the human sensory threshold concentrations and the salivary protein binding activity of a series of astringent stimuli, human saliva protein was incubated for 5 min at 37 °C in the presence of astringent food-derived compounds and, after micro-centrifugation, the amount of the target molecules in the supernatant was quantitatively determined by HPLC-UV/Vis. Significant protein binding was observed for (−)-epigallocatechin-3-gallate, (−)-gallocatechin-3-gallate, (+)-gallocatechin, and (−)-catechin-3-gallate, all of which containing at least one galloyl moiety in the molecule and exhibiting rather high sensory thresholds of more than 200 μmol/L. In comparison, (+)-catechin and procyanidin B2, both lacking in any galloyl function, showed only comparatively low binding activity and, most interestingly, quercetin-3-O-α-l-rhamnopyranosyl-(1 → 6)-β-d-glucopyranoside and 3-carboxymethyl-indole-1-N-β-d-glucopyranoside did not show any protein binding at all, although the later N- and O-glycosides exhibited extraordinarily low sensory threshold concentrations of less than 0.001 and 0.0003 μmol/L, respectively. The data give some first evidence that the quantity of the non-bound, “free” astringent stimulus in the saliva liquid might be more closely related to the sensory perception of astringency than the amount complexed or precipitated by proteins. It is therefore questionable as to whether oral perception of astringency is related to the complexation and/or precipitation of salivary proteins.  相似文献   
77.
This study describes a laboratory method for the estimation of emission from preservative-treated wood in the different situations where emissions could enter the environment for use classes 3 (not in contact with ground) and 4 and 5 (in contact with the ground, fresh water or sea water) according to OECD Guidelines. Samples of scotch pine sapwood (Pinus sylvestris L.) were treated with CCA (1% and 2%), ACQ-1900 (3% and 7%), ACQ-2200 (2%), Tanalith E 3491 (2% and 2.8%), and Wolmanit CX-8 (2%).  相似文献   
78.
79.
80.
Introducing new technology in a healthcare setting is a complex undertaking. In an environment in which accuracy, security, and reliability are critical elements, careful planning is the primary factor in ensuring a successful implementation.  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