全文获取类型
收费全文 | 74040篇 |
免费 | 7291篇 |
国内免费 | 4992篇 |
专业分类
电工技术 | 5481篇 |
技术理论 | 3篇 |
综合类 | 7666篇 |
化学工业 | 10248篇 |
金属工艺 | 5094篇 |
机械仪表 | 5264篇 |
建筑科学 | 5459篇 |
矿业工程 | 2591篇 |
能源动力 | 2004篇 |
轻工业 | 7539篇 |
水利工程 | 2156篇 |
石油天然气 | 3055篇 |
武器工业 | 1001篇 |
无线电 | 7448篇 |
一般工业技术 | 6586篇 |
冶金工业 | 2971篇 |
原子能技术 | 1164篇 |
自动化技术 | 10593篇 |
出版年
2024年 | 225篇 |
2023年 | 850篇 |
2022年 | 2325篇 |
2021年 | 3062篇 |
2020年 | 2271篇 |
2019年 | 1638篇 |
2018年 | 1826篇 |
2017年 | 1965篇 |
2016年 | 1891篇 |
2015年 | 3123篇 |
2014年 | 3920篇 |
2013年 | 4841篇 |
2012年 | 5892篇 |
2011年 | 6311篇 |
2010年 | 6010篇 |
2009年 | 5828篇 |
2008年 | 5912篇 |
2007年 | 5592篇 |
2006年 | 4990篇 |
2005年 | 4086篇 |
2004年 | 3019篇 |
2003年 | 2144篇 |
2002年 | 2061篇 |
2001年 | 1843篇 |
2000年 | 1352篇 |
1999年 | 882篇 |
1998年 | 469篇 |
1997年 | 408篇 |
1996年 | 337篇 |
1995年 | 250篇 |
1994年 | 222篇 |
1993年 | 167篇 |
1992年 | 125篇 |
1991年 | 112篇 |
1990年 | 69篇 |
1989年 | 82篇 |
1988年 | 49篇 |
1987年 | 29篇 |
1986年 | 24篇 |
1985年 | 18篇 |
1984年 | 7篇 |
1983年 | 17篇 |
1982年 | 4篇 |
1981年 | 9篇 |
1980年 | 18篇 |
1979年 | 10篇 |
1976年 | 2篇 |
1959年 | 25篇 |
1958年 | 2篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Xue‐Bing Zhao Lei Wang De‐Hua Liu 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(6):950-956
Previous work has shown that the enzymatic hydrolysis of sugarcane bagasse could be greatly enhanced by peracetic acid (PAA) pretreatment. There are several factors affecting the enzymatic digestibility of the biomass, including lignin and hemicelluloses content, cellulose crystallinity, acetyl group content, accessible surface area and so on. The objective of this work is to analyze the mechanism of the enhancement of enzymatic digestibility caused by PAA pretreatment. Delignification resulted in an increase of the surface area and reduction of the irreversible absorption of cellulase, which helped to increase the enzymatic digestibility. The Fourier transform infrared (FTIR) spectrum showed that the absorption peaks of aromatic skeletal vibrations were weakened or disappeared after PAA pretreatment. However, the infrared crystallization index (N.O'KI) was increased. X‐ray diffraction (XRD) analysis indicated that the crystallinity of PAA‐treated samples was increased owing to the partial removal of amorphous lignin and hemicelluloses and probable physical change of cellulose. The effect of acetyl group content on enzymatic digestibility is negligible compared with the degree of delignification and crystallinity. The results indicate that enhancement of enzymatic digestibility of sugarcane bagasse by PAA pretreatment is achieved mainly by delignification and an increase in the surface area and exposure of cellulose fibers. Copyright © 2008 Society of Chemical Industry 相似文献
92.
装备知识管理效用及实施策略分析 总被引:1,自引:1,他引:0
知识军事时代,知识逐渐成为战斗力提升的核心要素。武器装备的知识化管理,即装备知识管理,作为一种新的管理理念逐渐引起人们的重视,并将成为武器装备管理发展的新趋势。从探讨装备领域实施知识管理(knowledge management,KM)的重要性及目前装备工作中存在的现实问题出发,从提高装备决策质量、提升装备人才工作能力、防止装备知识流失、促进装备知识传递等方面分析了实施装备知识管理可能产生的效用。同时,还分析了装备知识管理实施的基本策略,以此为基础概括出了装备知识管理具有操作意义的实施步骤。 相似文献
93.
94.
95.
Local residence time,residence revolution,and residence volume distributions in twin‐screw extruders
Xian‐Ming Zhang Lian‐Fang Feng Sandrine Hoppe Guo‐Hua Hu 《Polymer Engineering and Science》2008,48(1):19-28
This work was aimed at studying the overall, partial, and local residence time distributions (RTD); overall, partial and local residence revolution distributions (RRD) and overall, partial and local residence volume distributions (RVD) in a co‐rotating twin screw extruder, on the one hand; and establishing the relationships among them, on the other hand. Emphasis was placed on the effects of the type and geometry of mixing elements (a gear block and various types of kneading elements differing in staggering angle) and process parameters on the RTD, RRD and RVD. The overall and partial RTD were directly measured in‐line during the extrusion process and the local ones were calculated by deconvolution based on a statistical theory. The local RTD allowed comparing the mixing performance of mixing elements. Also it was confirmed both experimentally and theoretically that specific throughput, defined as a ratio of throughput (Q) over screw speed (N), controlled all the above three types of residence distributions, be they local, partial or overall. The RRD and RVD do not provide more information on an extrusion process than the corresponding RTD. Rather they are different ways of representing the same phenomena. POLYM. ENG. SCI., 48:19–28, 2008. © 2007 Society of Plastics Engineers 相似文献
96.
试图构建企业以顾客为中心的营销策略过程的一般模型,并利用已有的研究成果对其构成要素进行了深入分析.在此基础上,对此模型所形成的企业营销策略循环进行分类分析,并以实例说明它们所代表的现实意义,从而为企业的决策提供帮助. 相似文献
97.
针对碳酸盐岩气藏部分气井生产效能低的状况,决定在长庆气田下古生界尝试开展加砂压裂重复改造试验,以期提高低产、低效气井的产量,延长气田稳产期。通过潜心研究、精细设计及现场质检监控,优选了4口老井进行加砂压裂重复改造现场试验。从试验结果来看,虽然只有1口井取得明显的改造效果,但4口井加砂压裂施工都是成功的,说明对碳酸盐岩气藏实施加砂压裂是可以实现的,但在选井思路和压裂工艺方面还有待探索和研究。 相似文献
98.
毛家河水电站库区岩溶发育特征及邻谷渗漏分析 总被引:1,自引:0,他引:1
毛家河水电站位于碳酸盐岩地区,库首距左岸邻谷可渡河14—23km、距右岸邻谷北盘江干流14.8km,水库两岸大型落水洞、溶洞及地下岩溶管道相对较为发育。为初步判断水库存在邻谷渗漏的可能性,对水库两岸可溶岩地层岩溶发育形态、特征及规律进行了勘察,并根据现场地质调查资料对3条可疑渗漏带进行了分析论证。 相似文献
99.
Transglutaminase (TGase) was separated from the culture broth of an isolated strain of Streptoverticillium mobaraense. The crude enzyme was prepared by centrifugation, ultrafiltration, precipitation by alcohol, centrifugation and freeze‐drying. The yield after these processes was 65–70%. Then the enzyme was purified to homogeneity by chromatography on CM‐cellulose and Sephadex G‐75 on which the yields were about 70% and 80%, respectively; the purified folds reached 2.5–4.7 and 1.08–2.06, respectively. The molecular weight of this TGase was 39,500–40,100 Da by gel filtration chromatography. Optimum enzyme activity was observed in the pH range of 5.0–7.0, and it was maintained stable at 20–40C. The optimal temperature and pH was 52C and 6.0, respectively. At 1 mM and 5 mM metal ion or inhibitors concentration, TGase activity was strongly inhibited by Zn2+ and NEM, and not affected obviously by Ba2+, Ca2+, Co2+, Cu2+, Fe2+, Fe3+, Mg2+, Mn2+, Na+ as well as PMSF and EDTA. The effects of these additions on this TGase were compared with those of other microbial TGases. 相似文献
100.