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   471600篇
  免费   6353篇
  国内免费   1239篇
电工技术   8847篇
综合类   692篇
化学工业   70157篇
金属工艺   17146篇
机械仪表   13713篇
建筑科学   11912篇
矿业工程   2076篇
能源动力   12636篇
轻工业   43906篇
水利工程   4481篇
石油天然气   7166篇
武器工业   15篇
无线电   57454篇
一般工业技术   90828篇
冶金工业   88417篇
原子能技术   9589篇
自动化技术   40157篇
  2021年   3597篇
  2019年   3426篇
  2018年   5714篇
  2017年   5616篇
  2016年   5881篇
  2015年   4054篇
  2014年   6973篇
  2013年   21595篇
  2012年   11407篇
  2011年   15846篇
  2010年   12538篇
  2009年   14376篇
  2008年   14836篇
  2007年   14825篇
  2006年   13011篇
  2005年   12076篇
  2004年   11762篇
  2003年   11427篇
  2002年   10950篇
  2001年   11227篇
  2000年   10809篇
  1999年   11315篇
  1998年   26985篇
  1997年   19454篇
  1996年   15298篇
  1995年   11622篇
  1994年   10645篇
  1993年   10248篇
  1992年   7820篇
  1991年   7480篇
  1990年   7219篇
  1989年   7154篇
  1988年   6940篇
  1987年   5853篇
  1986年   5898篇
  1985年   6930篇
  1984年   6359篇
  1983年   5963篇
  1982年   5309篇
  1981年   5567篇
  1980年   5120篇
  1979年   5123篇
  1978年   4973篇
  1977年   5816篇
  1976年   7601篇
  1975年   4291篇
  1974年   4145篇
  1973年   4172篇
  1972年   3424篇
  1971年   3087篇
排序方式: 共有10000条查询结果,搜索用时 566 毫秒
81.
82.
Potential mGAT4 inhibitors derived from the lead substance (S)-SNAP-5114 have been synthesized and characterized for their inhibitory potency. Variations from the parent compound included the substitution of one of its aromatic 4-methoxy and 4-methoxyphenyl groups, respectively, with a more polar moiety, including a carboxylic acid, alcohol, nitrile, carboxamide, sulfonamide, aldehyde or ketone function, or amino acid partial structures. Furthermore, it was investigated how the substitution of more than one of the aromatic 4-methoxy groups affects the potency and selectivity of the resulting compounds. Among the synthesized test substances (S)-1-{2-[(4-formylphenyl)bis(4-methoxyphenyl)-methoxy]ethyl}piperidine-3-carboxylic acid, that features a carbaldehyde function in place of one of the aromatic 4-methoxy moieties of (S)-SNAP-5114, was found to have a pIC50 value of 5.89±0.07, hence constituting a slightly more potent mGAT4 inhibitor than the parent substance while showing comparable subtype selectivity.  相似文献   
83.
JOM - Alpha-radiation damage in metals is a concern for long-term radioactive storage and systems that produce nuclear energy. Accurate prediction of irradiated material properties and failure...  相似文献   
84.
85.
86.
87.
88.
89.
The work reported involved the fabrication of an electrospun tubular conduit of a gelatin and polycaprolactone (PCL) blend as an adventitia‐equivalent construct. Gelatin was included as the matrix for increased biocompatibility with the addition of PCL for durability. This is contrary to most of the literature available for biomaterials based on blends of gelatin and PCL where PCL is the major matrix. The work includes the assiduous selection of key electrospinning parameters to obtain smooth bead‐free fibres with a narrow distribution of pore size and fibre diameter. Few reports elucidate the optimization of all electrospinning parameters to fabricate tubular conduits with a focus on obtaining homogeneous pores and fibres. This stepwise investigation would be unique for the fabrication of gelatin–PCL electrospun tubular constructs. The fabricated microfibrous gelatin–PCL constructs had pores of size ca 50–100 μm reportedly conducive for cell infiltration. The measured value of surface roughness of 57.99 ± 17.4 nm is reported to be favourable for protein adhesion and cell adhesion. The elastic modulus was observed to be similar to that of the tunica adventitia of the native artery. Preliminary in vitro and in vivo biocompatibility tests suggest safe applicability as a biomaterial. Minimal cytotoxicity was observed using MTT assay. Subcutaneous implantation of the scaffold demonstrated acute inflammation which decreased by day 15. The findings of this study could enable the fabrication of smooth bead‐free microfibrous gelatin–PCL tubular construct as viable biomaterial which can be included in a bilayer or a trilayer scaffold for vascular tissue engineering. © 2019 Society of Chemical Industry  相似文献   
90.
Intended learning outcomes (ILOs) indicate what learners will be able to achieve after they are taught. Traditionally, ILOs are expressed as plain text or unstructured documents. What if all ILOs of a specific course of study can be conceptualized through a structured diagrammatic technique? It was hypothesized that learners can benefit from this conceptualization in learning, especially in self‐regulated learning. The aim of this study was to investigate whether the ILOs represented in unstructured or structured formats can facilitate learners to identify learning paths. The results revealed that the mean ratings of all learning paths were statistically significantly higher with structured ILOs.  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