全文获取类型
收费全文 | 25280篇 |
免费 | 2541篇 |
国内免费 | 1228篇 |
专业分类
电工技术 | 1425篇 |
技术理论 | 5篇 |
综合类 | 1847篇 |
化学工业 | 4367篇 |
金属工艺 | 1459篇 |
机械仪表 | 1477篇 |
建筑科学 | 1950篇 |
矿业工程 | 733篇 |
能源动力 | 622篇 |
轻工业 | 2775篇 |
水利工程 | 411篇 |
石油天然气 | 1334篇 |
武器工业 | 172篇 |
无线电 | 3048篇 |
一般工业技术 | 2867篇 |
冶金工业 | 1101篇 |
原子能技术 | 228篇 |
自动化技术 | 3228篇 |
出版年
2024年 | 168篇 |
2023年 | 526篇 |
2022年 | 942篇 |
2021年 | 1245篇 |
2020年 | 910篇 |
2019年 | 823篇 |
2018年 | 899篇 |
2017年 | 912篇 |
2016年 | 830篇 |
2015年 | 1106篇 |
2014年 | 1364篇 |
2013年 | 1527篇 |
2012年 | 1700篇 |
2011年 | 1607篇 |
2010年 | 1462篇 |
2009年 | 1395篇 |
2008年 | 1326篇 |
2007年 | 1230篇 |
2006年 | 1203篇 |
2005年 | 967篇 |
2004年 | 738篇 |
2003年 | 925篇 |
2002年 | 1164篇 |
2001年 | 949篇 |
2000年 | 666篇 |
1999年 | 585篇 |
1998年 | 344篇 |
1997年 | 305篇 |
1996年 | 283篇 |
1995年 | 226篇 |
1994年 | 176篇 |
1993年 | 137篇 |
1992年 | 96篇 |
1991年 | 79篇 |
1990年 | 72篇 |
1989年 | 43篇 |
1988年 | 35篇 |
1987年 | 16篇 |
1986年 | 20篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 11篇 |
1959年 | 2篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
王家沟流域属暖温带大陆性季风气候,冬季严寒少雪,春季干燥多风,夏季酷热多雨,秋季温凉适中,雨热同季,当地常见暴雨历时大多在2h以下,这种短历时、大强度的暴雨最易引起水土流失。分析了流域治理前后径流泥沙的来源情况,为同类型小流域综合治理提供科学依据。 相似文献
52.
53.
54.
J. Chen J. B. Xu K. Xue J. An N. Ke W. Cao H. B. Xia J. Shi D. C. Tian 《Microelectronics Reliability》2005,45(1):137-142
Transition-metal compound TiC60 thin films were grown by co-deposition from two separated sources of fullerene C60 powder and titanium. Study of structural properties of the films, by Raman spectroscopy, atomic force microscopy, and scanning tunneling spectroscopy reveals that the films have a deformed C60 structure with certain amount of sp3 bonds and a rough surface with a large number of nanoclusters. z–V tunnelling spectroscopic measurements suggest that several charge transport mechanisms are involved in as the tip penetrates into the thin film. Conventional field electron emission (FEE) measurements show a high emission current density of 10 mA/cm2 and a low turn-on field less than 8 V/μm, with the field enhancement factors being 659 and 1947 for low-field region and high-field region, respectively. By exploiting STM tunneling spectroscopy, local FEE on nanometer scale has also been characterized in comparison with the conventional FEE. The respective field enhancement factors are estimated to be 99–355 for a gap varying from 36 to 6 nm. The enhanced FEE of TiC60 thin films can be ascribed to structural variation of C60 in the films and the electrical conducting paths formed by titanium nanocrystallites embedded in C60 matrix. 相似文献
55.
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
56.
57.
58.
A new torque estimator for switched reluctance motor (SRM) drives based on 2-D rotary regression analysis is presented in this paper. The proposed torque estimator is composed of a bicubic regressive polynomial as a function of rotor position and input current. The regressive coefficients can be computed offline or online from the torque characteristics acquired either experimentally or from numerical computation. Furthermore, a torque estimation method by taking mutual coupling into consideration is proposed. It can be seen that the estimated and experimentally obtained self-coupling and mutual-coupling torque characteristics are in good agreement with each other. In addition, the dynamic torque waveforms with and without the mutual coupling, estimated by the proposed estimator, are found to be virtually the same as those obtained from the bicubic spline interpolation for SRM drives with single-pulse voltage, hysteresis current chopping, as well as with voltage pulse width modulation control. The success of all the case studies being reported is a good validation of the usefulness and accuracy of the proposed real-time torque estimator that, as described in this paper, can be used to quickly estimate the instantaneous output torque of SRM drives. 相似文献
59.
文章提出了针对“整合分级的RBAC访问控制”系统的改进模型。新模型充分发挥了基于角色和分级两套访问控制逻辑的优点,并通过引入XACML,有效地实现了策略管理和访问判决的标准化、统一化,在角色定义的基础上实现了两种逻辑的无缝整合。 相似文献
60.