全文获取类型
收费全文 | 153843篇 |
免费 | 11417篇 |
国内免费 | 5951篇 |
专业分类
电工技术 | 6607篇 |
技术理论 | 2篇 |
综合类 | 9091篇 |
化学工业 | 26926篇 |
金属工艺 | 7650篇 |
机械仪表 | 9598篇 |
建筑科学 | 8341篇 |
矿业工程 | 2384篇 |
能源动力 | 4942篇 |
轻工业 | 13220篇 |
水利工程 | 2445篇 |
石油天然气 | 4024篇 |
武器工业 | 809篇 |
无线电 | 20515篇 |
一般工业技术 | 22016篇 |
冶金工业 | 9406篇 |
原子能技术 | 2084篇 |
自动化技术 | 21151篇 |
出版年
2024年 | 408篇 |
2023年 | 1714篇 |
2022年 | 3184篇 |
2021年 | 4652篇 |
2020年 | 3584篇 |
2019年 | 3383篇 |
2018年 | 3891篇 |
2017年 | 4206篇 |
2016年 | 4461篇 |
2015年 | 4942篇 |
2014年 | 6928篇 |
2013年 | 9229篇 |
2012年 | 10208篇 |
2011年 | 11333篇 |
2010年 | 9838篇 |
2009年 | 9873篇 |
2008年 | 9619篇 |
2007年 | 8825篇 |
2006年 | 8349篇 |
2005年 | 6992篇 |
2004年 | 5969篇 |
2003年 | 5525篇 |
2002年 | 5954篇 |
2001年 | 5152篇 |
2000年 | 3713篇 |
1999年 | 2911篇 |
1998年 | 3217篇 |
1997年 | 2345篇 |
1996年 | 1914篇 |
1995年 | 1485篇 |
1994年 | 1196篇 |
1993年 | 999篇 |
1992年 | 766篇 |
1991年 | 646篇 |
1990年 | 562篇 |
1989年 | 486篇 |
1988年 | 393篇 |
1987年 | 324篇 |
1986年 | 224篇 |
1985年 | 273篇 |
1984年 | 219篇 |
1983年 | 148篇 |
1982年 | 110篇 |
1981年 | 117篇 |
1980年 | 111篇 |
1979年 | 104篇 |
1978年 | 75篇 |
1977年 | 109篇 |
1976年 | 161篇 |
1975年 | 70篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
Won Tae KimCheolho Bai Young I. Cho 《International Journal of Heat and Mass Transfer》2002,45(3):597-607
The present study introduces a new experimental method to visualize the fouling process of CaCO3. A mini-channel heat exchanger system with a microscopic imaging technique was developed for real-time visualization of the fouling process. The present study discussed how scale started initially, how scale formed thick layers, and how a small crystal grew into a large one, touching the adjacent one. Detail microscopic images of scale crystals and corresponding fouling resistances were obtained over the entire fouling process. The microscopic observation indicated that the fouling process could be divided into three stages: an induction period, a period of uniform generation of nuclei, and a period of uniform growth of scale. Sudden appearance of numerous small nuclei indicated the end of the induction period, a key event before the rapid increase in the fouling resistance. The present experimental method using microscopic images of the wet fouling process provides a valuable insight on the fouling mechanism. 相似文献
62.
Kim DeFronzo Haselhoff 《Journal of Urban Affairs》2002,24(4):425-443
I argue that the motivation for the San Fernando Valley secession movement can be explained as a desire for local control based on democratic ideals, but I emphasize that the movement is also motivated in part by the tangible benefits that accompany such autonomy. After a brief look at possible economic and racial motivations behind the secession movement, I look for a political divide between the city and the Valley, based on literature that has found political divisions between urban and suburban areas. Evidence of a political divide is mixed, but does indicate that the Valley lacks representation in comparison to the rest of the city. Valley residents may also fear increasing minority political power, which could erode the dominance of Valley whites at the polls. There is also evidence that those who favor secession are most dissatisfied with representation and most concerned with getting their fair share of services from the city, indicating a strong desire for more local control. Images of a smaller, more democratic government, and a more engaged local civic community are prime motivations in the Valley’s quest for autonomy, though the possibility of reduced taxes, land use control, and increased political power do offer secessionists clear substantive benefits in addition to more democratic goals. 相似文献
63.
64.
Hyun-Goo Kim Wha-Nam Myung K. Sumiyama K. Suzuki 《Journal of Alloys and Compounds》2002,340(1-2):270-274
We report upon the chemical leaching and magnetic properties of nanoscale crystalline Al0.6(Co25Cu75)0.4 alloy powders produced by rod milling. X-Ray diffractometry (XRD), transmission electron microscopy, differential scanning calorimetry, vibrating sample magnetometry, and superconducting quantum interference device magnetometry were used to characterize the as-milled and leached specimens. After 400 h of milling, only the b.c.c. phase of the intermetallic compound γ-Al3.892Cu6.10808 was detected by XRD. After annealing the leached specimen at 600 °C for 1 h, the nanoscale crystalline phase was transformed into the f.c.c. Cu phase, and this was accompanied by a change in the magnetic properties. The peaks of the magnetization shifted towards lower temperature with increasing external field. The temperature behavior at Tf (45 K) for direct current (d.c.) magnetic susceptibility measurements was quite different for field cooling and zero-field cooling. After cooling the leached specimen from 800 °C, magnetization increased gradually. 相似文献
66.
Liang Y.C. Wenjiang Zeng Pick Hong Ong Zhaoxia Gao Jun Cai Balasubramanian N. 《Electron Device Letters, IEEE》2002,23(12):700-703
In this letter, a concise process technology is proposed for the first time to enable the fabrication of good quality three-dimensional (3-D) suspended radio frequency (RF) micro-inductors on bulk silicon, without utilizing the lithography process on sidewall and trench-bottom patterning. Samples were fabricated to demonstrate the applicability of the proposed process technology. 相似文献
67.
在概括了自蔓延高温合成陶瓷内衬钢管的制备原理基础上,从降低陶瓷层孔隙率,减少陶瓷层裂纹和提高陶瓷层结合强度等方面,论述了提高自蔓延高温合成陶瓷内衬钢管性能的措施,对自蔓延高温合成陶瓷内衬钢管的应用现状及展望进行了评述。 相似文献
68.
69.
In this paper, a localized MEI method (L-MEI) is developed and combined with the domain decomposition method (DDM) for the simulation of scattering by a concave cylinder. In the L-MEI, the whole domain is decomposed into many subdomains. Different from the conventional MEI method, the MEI coefficients of the L-MEI method in each subdomain are only dependent on the localized metrons that are defined in the subdomain. The localization of metrons has the following advantages: (1) speeding up the calculation of MEI coefficients and saving memory, (2) making the MEI method available for concave structures, and (3) obtaining a band sparse matrix directly without any modification 相似文献
70.
基于数字信号处理器的直流电机控制系统 总被引:4,自引:0,他引:4
介绍了定点数字信号处理器(DSP)TMS320F240的一般性能及其在永磁无刷直流电机控制上的应用,给出了硬件设计方案、软件策略及输出结果。 相似文献