首页 | 官方网站   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   307421篇
  免费   18844篇
  国内免费   1803篇
工业技术   328068篇
  2021年   3006篇
  2020年   3365篇
  2019年   5514篇
  2018年   6700篇
  2017年   6977篇
  2016年   7754篇
  2015年   6815篇
  2014年   8646篇
  2013年   17005篇
  2012年   11003篇
  2011年   13054篇
  2010年   11169篇
  2009年   11566篇
  2008年   11910篇
  2007年   11711篇
  2006年   10276篇
  2005年   8913篇
  2004年   8171篇
  2003年   7674篇
  2002年   7568篇
  2001年   7459篇
  2000年   7049篇
  1999年   6490篇
  1998年   13845篇
  1997年   10203篇
  1996年   7678篇
  1995年   5750篇
  1994年   5257篇
  1993年   5165篇
  1992年   4021篇
  1991年   3829篇
  1990年   3876篇
  1989年   3834篇
  1988年   3585篇
  1987年   3068篇
  1986年   3102篇
  1985年   3467篇
  1984年   3360篇
  1983年   3104篇
  1982年   2741篇
  1981年   2959篇
  1980年   2689篇
  1979年   2860篇
  1978年   2760篇
  1977年   2906篇
  1976年   3814篇
  1975年   2453篇
  1974年   2295篇
  1973年   2318篇
  1972年   1983篇
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
91.
92.
93.
94.
High Temperature - The temperature dependences of the viscosity of liquid Fe90B x Si(10 − x) alloys are studied in the mode of heating and subsequent cooling. The temperature dependences of...  相似文献   
95.
Russian Engineering Research - Formulas are derived for the most important parameters of channel extrusion.  相似文献   
96.
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   
97.
98.
Cystoseira hakodatensis is an unutilised brown algae belonging to family Sargassaceae. A crude methanol extract from the algae showed inhibitory effects on the growths of Bacillus cereus and Bacillus licheniformis. To isolate the major antimicrobial agent, a sequential active‐guided isolation procedure was applied: liquid–liquid extraction, column chromatography and bio‐autography. A marked antimicrobial agent (active α) was isolated in hydrophobic fraction and was determined to phenolics without carbohydrates and proteins by phytochemical test. Regarding the antimicrobial potential, the isolated active α showed better inhibitory effects against B. cereus and B. licheniformis at 2 and 4 times of lower concentrations (62.5 and 31.3 μg mL?1) in comparison with epigallocatechin gallate. These results showed that C. hakodatensis is a potential source of antimicrobial agent capable of preventing the growth of the two bacteria.  相似文献   
99.
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   
100.
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-23

京公网安备 11010802026262号