全文获取类型
收费全文 | 88829篇 |
免费 | 8928篇 |
国内免费 | 6106篇 |
专业分类
电工技术 | 7429篇 |
技术理论 | 3篇 |
综合类 | 8972篇 |
化学工业 | 11728篇 |
金属工艺 | 6161篇 |
机械仪表 | 6528篇 |
建筑科学 | 6911篇 |
矿业工程 | 3071篇 |
能源动力 | 2537篇 |
轻工业 | 8586篇 |
水利工程 | 2734篇 |
石油天然气 | 3420篇 |
武器工业 | 1269篇 |
无线电 | 8705篇 |
一般工业技术 | 8098篇 |
冶金工业 | 3631篇 |
原子能技术 | 1449篇 |
自动化技术 | 12631篇 |
出版年
2024年 | 410篇 |
2023年 | 1146篇 |
2022年 | 2874篇 |
2021年 | 3754篇 |
2020年 | 2751篇 |
2019年 | 1979篇 |
2018年 | 2070篇 |
2017年 | 2520篇 |
2016年 | 2360篇 |
2015年 | 3741篇 |
2014年 | 4617篇 |
2013年 | 5702篇 |
2012年 | 7053篇 |
2011年 | 7429篇 |
2010年 | 7132篇 |
2009年 | 6928篇 |
2008年 | 6958篇 |
2007年 | 6884篇 |
2006年 | 6068篇 |
2005年 | 4966篇 |
2004年 | 3697篇 |
2003年 | 2598篇 |
2002年 | 2470篇 |
2001年 | 2341篇 |
2000年 | 1726篇 |
1999年 | 1012篇 |
1998年 | 510篇 |
1997年 | 439篇 |
1996年 | 359篇 |
1995年 | 267篇 |
1994年 | 239篇 |
1993年 | 180篇 |
1992年 | 135篇 |
1991年 | 123篇 |
1990年 | 83篇 |
1989年 | 84篇 |
1988年 | 55篇 |
1987年 | 37篇 |
1986年 | 34篇 |
1985年 | 20篇 |
1984年 | 17篇 |
1983年 | 14篇 |
1982年 | 7篇 |
1981年 | 12篇 |
1980年 | 26篇 |
1979年 | 13篇 |
1959年 | 10篇 |
1958年 | 2篇 |
1956年 | 2篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
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
23.
对"比较法"原理和应用情况进行了分析,说明其在房地产开发中能够科学地预测房地产的价格和收益,从而提高财务分析的科学性和权威性,为项目决策提供科学依据,以促进"比较法"在房地产开发中的应用。 相似文献
24.
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
25.
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
26.
27.
Wei Li Zhang Wei Pan Bin Luo Xi Hua Zou Meng Yao Wang 《Photonics Technology Letters, IEEE》2008,20(9):712-714
A theoretical construction of one-to-many (OTM) and many-to-one (MTO) chaos synchronization communications using semiconductor lasers is presented. One center laser provides strong injections (strong link) to other side lasers, and the side lasers also provide weak injections (weak link) to the center one. Simulation results show that the side lasers synchronize with the center laser through injection-locking. In addition, messages transmitted via the strong links or the weak links experience strong chaos pass filtering, enabling us to realize OTM and MTO communications. 相似文献
28.
29.
Yue Rong Yingbo Hua Swami A. Swindlehurst A.L. 《Signal Processing, IEEE Transactions on》2008,56(2):686-701
A space-time optimal power schedule for multiple distributed multiple-input multiple-output (MIMO) links without the knowledge of the instantaneous channel state information (CSI) at the transmitting nodes is proposed. A readily computable expression for the ergodic sum capacity of the MIMO links is derived. Based on this expression, which is a non-convex function of power allocation vectors, a projected gradient algorithm is developed to optimize the power allocation. For a symmetric set of MIMO links with independent identically distributed channels, it is observed that the space-time optimal power schedule reduces to a uniform isotropic power schedule when nominal interference is low, or to an orthogonal isotropic power schedule when nominal interference is high. Furthermore, the transition region between the latter two schedules is seen to be very sharp in terms of nominal interference-to-noise ratio (INR). For MIMO links with correlated channels, the corresponding space-time optimal power schedule is developed based on the knowledge of the channel correlation matrices. It is shown that the channel correlation has a great impact on the ergodic capacity and the optimality of different power scheduling approaches. 相似文献
30.
喷墨打印相纸及打印图像质量的分析 总被引:2,自引:1,他引:1
喷墨打印相纸随着数码相机的发展近几年在国内发展迅速。针对目前产品质量没有测量标准的现状,提出喷墨相纸的质量指标主要为4个,即白度、光泽度、油墨吸收性和防水性。给出了相应的测量方法。并指出相纸上油墨点的面积是衡量质量的第一重要指标,其次是点的圆度。另外对图像输出的质量介绍了一种科学的评价方法,即图像的逼真性分析。说明图像的打印墨点直径不应小于方形像素的对角线长,图像才能真实再现。 相似文献