全文获取类型
收费全文 | 20671篇 |
免费 | 2365篇 |
国内免费 | 1273篇 |
专业分类
电工技术 | 1612篇 |
技术理论 | 1篇 |
综合类 | 1565篇 |
化学工业 | 3088篇 |
金属工艺 | 1122篇 |
机械仪表 | 1377篇 |
建筑科学 | 1609篇 |
矿业工程 | 641篇 |
能源动力 | 661篇 |
轻工业 | 1335篇 |
水利工程 | 598篇 |
石油天然气 | 910篇 |
武器工业 | 166篇 |
无线电 | 2638篇 |
一般工业技术 | 2362篇 |
冶金工业 | 785篇 |
原子能技术 | 418篇 |
自动化技术 | 3421篇 |
出版年
2024年 | 105篇 |
2023年 | 323篇 |
2022年 | 604篇 |
2021年 | 921篇 |
2020年 | 668篇 |
2019年 | 648篇 |
2018年 | 584篇 |
2017年 | 684篇 |
2016年 | 673篇 |
2015年 | 822篇 |
2014年 | 1116篇 |
2013年 | 1230篇 |
2012年 | 1355篇 |
2011年 | 1559篇 |
2010年 | 1437篇 |
2009年 | 1357篇 |
2008年 | 1249篇 |
2007年 | 1197篇 |
2006年 | 1225篇 |
2005年 | 907篇 |
2004年 | 777篇 |
2003年 | 796篇 |
2002年 | 937篇 |
2001年 | 736篇 |
2000年 | 497篇 |
1999年 | 452篇 |
1998年 | 284篇 |
1997年 | 211篇 |
1996年 | 180篇 |
1995年 | 143篇 |
1994年 | 123篇 |
1993年 | 99篇 |
1992年 | 82篇 |
1991年 | 69篇 |
1990年 | 64篇 |
1989年 | 45篇 |
1988年 | 45篇 |
1987年 | 16篇 |
1986年 | 18篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1959年 | 4篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
981.
Preparation of high toughness and high transparency polylactide blends resin based on multiarmed polycaprolactone‐block‐poly(l‐lactide) 下载免费PDF全文
Xinchao Bian Bao Zhang Bin Sun Zhiqiang Sun Sheng Xiang Gao Li Xuesi Chen 《Polymer Engineering and Science》2016,56(10):1125-1137
Modification of poly(l ‐lactide) (PLLA) via blending with two or more polymers is one of the effective approaches used to overcome the brittleness of PLLA, which often requires the addition of a compatibilizer and generate opaque materials. To solve this problem, multiarmed polycaprolactone‐block‐PLLA (PCL‐b‐PLLA) was synthesized by consecutive ring‐opening polymerization of ε‐caprolactone and l ‐lactide using multihydroxyl alcohols as initiator. The structure and composition was confirmed by proton nuclear magnetic resonance and gel permeation chromatography. PLLA/multiarmed PCL‐b‐PLLA blends with various blend ratios were prepared via melt mixing. The presence of multiarmed PCL‐b‐PLLA (30%) in the PLLA matrix exhibited more than 80 times improvement in the elongation at break, as compared to unmodified PLLA. The addition of multiarmed PCL‐b‐PLLA in the PLLA contributed to the enhancement of the storage modulus in the low frequency, which was related to the entanglement of the PLLA and multiarmed PCL‐b‐PLLA. The blend interface had no obvious phase separation, and showed good adhesion between dispersed block copolymer phases within the continuous PLLA phase. The compatibilization mechanism and toughing mechanism were proposed. The resulting PLLA blends also showed good transparency. The current research opened a new route available to prepare transparent PLA‐based resin with enhanced properties. POLYM. ENG. SCI., 56:1125–1137, 2016. © 2016 Society of Plastics Engineers 相似文献
982.
983.
Weirui Zhao Sheng Hu Jun Huang Piyu Ke Shanjing Yao Yinlin Lei Lehe Mei Jinbo Wang 《中国化学工程学报》2016,24(7):909-913
The activity of whole-cell biocatalysts is strongly compromised by the cell envelope, which is a permeability barrier against the diffusion of substrates and products. Although common chemical or physical permeabilization methods used in cultured cells enhance cell permeability, these methods inevitably add several extra processing steps after cell cultivation, as well as impede large scale processing. To increase membrane permeability and cellbound glutamate decarboxylase(GAD) activity of recombinant Escherichia coli(BL21(DE3)-p ET28a-gad B) cells without the need for an additional permeabilization step, we investigated the permeabilizing effects of adding cell wall synthesis inhibitors or surfactants to the culture media. Ampicillin was the most effective at improving cell-bound GAD activity of the BL21(DE3)-p ET28a-gad B, although it decreased the cell biomass yield. The best permeabilization effect was observed using an ampicillin concentration of 5 μg·ml-1. Using this concentration,the cell biomass did decrease by 40.58%, but the cell-bound GAD activity of BL21(DE3)-p ET28a-gad B and total cell-bound GAD activity per milliliter of culture was enhanced by 6.24- and 3.64-fold, respectively. Treatment of BL21(DE3)-p ET28a-gad B cells with 5 μg·ml-1ampicillin resulted in structural changes to the cell envelope,but did not substantially affect GAD expression. By entrapping the ampicillin-treated cells in an open pore gelation matrix, which is a polymer derived from polyvinyl alcohol(PVA), alginate, and boric acid, the transformation rate of γ-aminobutyric acid(GABA) at the 10 th cycle produced by immobilized and permeabilized cells remained 46% of the first cycle. GAD activity of the immobilized, permeabilized cells remained over 90% after30 days of storage at 4 °C. 相似文献
984.
985.
986.
987.
988.
大分子键合处理氢氧化铝的表面性质及其与常用聚合物的界面特性 总被引:3,自引:1,他引:3
本文研究了经大分子以键合方式包覆处理的氢氧化铝粉末的表面性质以及其与常用聚合物的界面特性。结果表明:(1)与末处理过的氢氧化铝相比,非极性液体与处理过的氢氧化铝压片的接触角变化较小,而极性液体与它的接触角一般明显增大。(2)改性后的氢氧化铝的表面张力均明显下降,其中表面张力有极性分量大幅度下降而色散分量稍有提高。与常见聚合物的界面张力以及它的极性分量和色散分量均降而色散分量稍有提高。与常见聚合物的 相似文献
989.
本文在分析了常用模板匹配字符识别方法的问题之后,以车牌字符中常用的字母、数字为例,提出了一种新的基于数字字母特征的编码方法,解决了模板匹配法中的字符图像与模板尺寸不符等问题,提高了识别率。 相似文献
990.