全文获取类型
收费全文 | 297749篇 |
免费 | 36345篇 |
国内免费 | 14611篇 |
专业分类
电工技术 | 20155篇 |
技术理论 | 10篇 |
综合类 | 20166篇 |
化学工业 | 54258篇 |
金属工艺 | 16422篇 |
机械仪表 | 18704篇 |
建筑科学 | 23582篇 |
矿业工程 | 8900篇 |
能源动力 | 8526篇 |
轻工业 | 25456篇 |
水利工程 | 6080篇 |
石油天然气 | 15243篇 |
武器工业 | 2766篇 |
无线电 | 36471篇 |
一般工业技术 | 37471篇 |
冶金工业 | 11841篇 |
原子能技术 | 2875篇 |
自动化技术 | 39779篇 |
出版年
2024年 | 1269篇 |
2023年 | 4335篇 |
2022年 | 8413篇 |
2021年 | 11672篇 |
2020年 | 9956篇 |
2019年 | 9564篇 |
2018年 | 10259篇 |
2017年 | 11890篇 |
2016年 | 11318篇 |
2015年 | 14980篇 |
2014年 | 17663篇 |
2013年 | 21290篇 |
2012年 | 21566篇 |
2011年 | 22111篇 |
2010年 | 20602篇 |
2009年 | 19477篇 |
2008年 | 18702篇 |
2007年 | 17753篇 |
2006年 | 16813篇 |
2005年 | 13724篇 |
2004年 | 9680篇 |
2003年 | 8638篇 |
2002年 | 8242篇 |
2001年 | 7319篇 |
2000年 | 6438篇 |
1999年 | 5480篇 |
1998年 | 3639篇 |
1997年 | 2999篇 |
1996年 | 2874篇 |
1995年 | 2424篇 |
1994年 | 1978篇 |
1993年 | 1251篇 |
1992年 | 1051篇 |
1991年 | 742篇 |
1990年 | 599篇 |
1989年 | 507篇 |
1988年 | 366篇 |
1987年 | 246篇 |
1986年 | 215篇 |
1985年 | 108篇 |
1984年 | 91篇 |
1983年 | 70篇 |
1982年 | 71篇 |
1981年 | 70篇 |
1980年 | 67篇 |
1979年 | 41篇 |
1978年 | 11篇 |
1976年 | 10篇 |
1959年 | 12篇 |
1951年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
Jianxin Wei Mark R Pickering Michael R Frater John F Arnold John A Boman Wenjun Zeng 《IEEE transactions on image processing》2005,14(8):1033-1042
It is well known that tile-boundary artifacts occur in wavelet-based lossy image coding. However, until now, their cause has not been understood well. In this paper, we show that boundary artifacts are an inescapable consequence of the usual methods used to choose tile size and the type of symmetric extension employed in a wavelet-based image decomposition system. This paper presents a novel method for reducing these tile-boundary artifacts. The method employs odd tile sizes (2N + 1 samples) rather than the conventional even tile sizes (2N samples). It is shown that, for the same bit rate, an image compressed using an odd tile length low-pass first (OTLPF) convention has significantly less boundary artifacts than an image compressed using even tile sizes. The OTLPF convention can also be incorporated into the JPEG 2000 image compression algorithm using extensions defined in Part 2 of this standard. 相似文献
94.
95.
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
96.
Shi Wei Zhao Xuefeng Ma Conghui Management of the National Development Reform Commission 《中国通信》2008,(3)
After the new round of restructuring of Chinese telecom sector,it's pressing to formulate and implement asymmetric regulation policies so as to shape an effectively competitive market structure in a relatively short term.This paper reviewed the asymmetric regulation policies and practices carried out in foreign telecom market,and then according to the specific situations of Chinese telecom market,proposed the principles and corresponding policies for establishing an asymmetric regulation system fit for Chin... 相似文献
97.
Yun‐Seok Cho Bheong‐Uk Lee Kye‐Heon Oh 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(9):1211-1217
BACKGROUND: Environmental contamination by nitroaromatic compounds such as 2,4,6‐trinitrotoluene (TNT), hexahydro‐1,3,5‐trinitro‐1,3,5‐s‐triazine (RDX), atrazine, and/or simazine (TRAS) generated as waste from military and agricultural activities is a serious worldwide problem. Microbiological treatment of these compounds is an attractive method because many explosives and herbicides are biodegradable and the process can be made cost‐effective. We explored the feasibility of using cultures of Pseudomonas putida HK‐6 for simultaneous degradation of TRAS with the aim of microbial application in wastewater treatment in bench‐scale bioreactors. RESULTS: Experiments were conducted to study the effects of supplemental carbons, nitrogens, and Tween‐80 on the degradation of Ps. putida HK‐6 in media containing TRAS as target substrate(s). The most effective TRAS degradation was shown in the presence of molasses. Addition of nitrogen sources produced a delayed effect for the target substrate(s). Tween‐80 enhanced the degradation of target substrate(s). Simultaneous degradation of these compounds proceeded to completion within the given period. CONCLUSIONS: Ps. putida HK‐6 was capable of growth with TRAS, and the effects of supplements on TRAS degradation and simultaneous TRAS degradation were evaluated in bench‐scale bioreactors. The results of this study have practical applications in the processes of industrial waste stream treatment where the disposal of TRAS may be problematic. Copyright © 2008 Society of Chemical Industry 相似文献
98.
99.
随着人们对建筑安全的日益重视 ,对建筑抗震要求的提高 ,国内外有关规范都对箍筋末端的设置作了明确规定 ,要求做成 135度弯钩。而在工程实践中 ,由于施工上的技术困难 ,很多工程都只设置成 90度弯钩。笔者提出的箍筋末端 135度弯钩二次就位法在基本不增加 90度弯钩施工难度与费用的基础上实现了 135度弯钩的施工 ,其法是可行的 相似文献
100.
提出了基于压电技术的微操作系统的自动标定方法,采用混合式步进电机直接驱动的宏动平台,实现系统大行程宏动定位,安装在宏动平台上的压电陶瓷驱动的微动平台和精密光栅,实现亚微米级的分辨率和定位精度,通过以上两部分实现定位机构的全闭环反馈控制,采用显微视觉反馈获取微动台操作器在图像中的位置信息进行标定。实验结果表明:系统的动态和稳定性能良好,自动标定运算速度快,运行速度达到11 frame/s,实现了对系统的精确标定,标定精度达到0.1μm。 相似文献