全文获取类型
收费全文 | 3179篇 |
免费 | 44篇 |
国内免费 | 75篇 |
专业分类
电工技术 | 35篇 |
综合类 | 63篇 |
化学工业 | 74篇 |
金属工艺 | 226篇 |
机械仪表 | 83篇 |
建筑科学 | 55篇 |
能源动力 | 15篇 |
轻工业 | 465篇 |
水利工程 | 21篇 |
武器工业 | 1篇 |
无线电 | 56篇 |
一般工业技术 | 172篇 |
冶金工业 | 1838篇 |
原子能技术 | 26篇 |
自动化技术 | 168篇 |
出版年
2022年 | 8篇 |
2021年 | 14篇 |
2020年 | 11篇 |
2019年 | 17篇 |
2018年 | 12篇 |
2017年 | 6篇 |
2016年 | 11篇 |
2015年 | 12篇 |
2014年 | 55篇 |
2013年 | 239篇 |
2012年 | 79篇 |
2011年 | 114篇 |
2010年 | 71篇 |
2009年 | 90篇 |
2008年 | 42篇 |
2007年 | 39篇 |
2006年 | 56篇 |
2005年 | 26篇 |
2004年 | 44篇 |
2003年 | 27篇 |
2002年 | 15篇 |
2001年 | 12篇 |
2000年 | 11篇 |
1999年 | 53篇 |
1998年 | 561篇 |
1997年 | 342篇 |
1996年 | 214篇 |
1995年 | 121篇 |
1994年 | 98篇 |
1993年 | 116篇 |
1992年 | 33篇 |
1991年 | 55篇 |
1990年 | 47篇 |
1989年 | 44篇 |
1988年 | 52篇 |
1987年 | 43篇 |
1986年 | 49篇 |
1985年 | 29篇 |
1984年 | 9篇 |
1983年 | 20篇 |
1982年 | 22篇 |
1981年 | 24篇 |
1980年 | 38篇 |
1979年 | 20篇 |
1978年 | 19篇 |
1977年 | 63篇 |
1976年 | 140篇 |
1975年 | 16篇 |
1974年 | 9篇 |
1957年 | 7篇 |
排序方式: 共有3298条查询结果,搜索用时 0 毫秒
11.
理论上研究了吸收层材料的光学常数,该常数满足从紫外线到近红外波长范围的四层结构的光子-热转换的高效率。通过使用有效介质近似(EMA)模型,复合材料(金属陶瓷)的光学性能与模拟材料的光学性能非常吻合。此外,提出了使用Ti-MgF2金属陶瓷作为吸收层的具有高光子-热转换效率的四层膜结构,其在300~1 600 nm的波长范围内具有约95.1%的高吸收率。研究结果为实现高效率的光热转换器件提供了新途径,显示了优良的应用前景。 相似文献
12.
This paper describes the design and implementation of a 3 KHz band HF data broadcast communication system, using a quantized frequency modulation, adaptive lattice equalizer together with forward error correcting code (FEC) to obtain a high link reliability and low error rate. A frequency diversity approach is also used in the selection of the timely best carrier frequency, and a microcomputer is implemented into the system for automatic best carrier acquisition, data transmission and clock synchronization, with minimum operator's attention. Extensive field experiments were conducted and experimental results indicate that the system can achieve, for daytime operation, a link reliability of 87–98%, with a probability of error between 10?4 to 10?5, depending upon data rate (50, 75bps) and FECs used. For night time operation, the link reliability reduces to from 65–93% with a probability of error down in the order of 10?3. 相似文献
13.
14.
15.
A simple and accurate model of a permanent magnet synchronous motor (PMSM) with a light load is presented in this paper. The light-load condition is always needed in integrated circuit manufacturing machines in order to achieve a fast, accurate and minimum overshoot response. The model proposed here can help a designer to specify the controller's specifications and also to verify the hardware of motor drives. The differential equations of the PMSM are handled by the macromodels in PSPICETM. Moreover, it is revealed that the PMSM system is operating in a 4-state mode rather than a 2-state mode. Experimental results are provided to verify the simulation results of this model. The heavy load condition is also simulated. 相似文献
16.
After the remarkable increase of Internet users and broadband Internet subscribers at the end of the 20th century, the size of Korean Internet and e-commerce market steadily increased but the growth rate has been either stagnant or decreased. Trends of Korean Internet and e-commerce market are summarized in this paper the trends on Internet usage are introduced. Trends of online games, blogs and wireless Internet are introduced. The trends of Korean Internet market may have implications for China and Japan. 相似文献
17.
18.
Polyphenoloxidase (PPO) was isolated from two varieties of grapes grown in the northeastern United States and its characteristics were studied. The temperature and pH optima for both enzymes were 25°C and 5.5, respectively. The thermal inactivation of PPO followed first-order kinetics; with the Niagara enzyme being more heat stable than Ravat PPO. The substrate specificity of the grape PPO clearly showed high affinity toward the o-diphenolic compounds, with a high affinity toward caffeic acid. Inhibition studies indicated that L-cysteine and sodium diethyldithiocarbamate were the most potent. 相似文献
19.
A Microscopical Study of the Structure of Meat Emulsions and Its Relationship to Thermal Stability 总被引:1,自引:0,他引:1
Meat emulsions were examined by light microscopy to determine the relationships between structure and emulsion stability. Beef-meat based emulsions were prepared either by varying chopping temperature or by adding soy plastic fats of different hardness. Formation of fat channels was observed in uncooked emulsions prepared either at a chopping temperature of 26°C or with soft plastic fat of 0.25cm?1 hardness index. Such fat channel formations caused discontinuity of protein matrix, leading to fat separation during cooking and weakening of textural strength of products. Changes in fat globule size and distribution as affected by melting properties or hardness of fats were clearly reflected by changes in emulsion stability. Results suggest that emulsion stability is determined largely by the physical properties of protein matrix and fat incorporated. Stable emulsions were obtained with fats of appropriate melting properties and hardness and relatively cohesive protein matrix under given comminution conditions which allowed uniform fat distribution. 相似文献
20.
Characterization of functionally gradient epoxy/carbon fibre composite prepared under centrifugal force 总被引:2,自引:0,他引:2
Centrifugal force was employed in order to induce a spatial gradient of fibre distribution in the epoxy/carbon fibre system.
The gradient structure of the epoxy/carbon fibre composite can be controlled by varying the rotation time and the material
parameters, such as fibre length, fibre content and matrix viscosity. The spatial gradient distribution of carbon fibres in
an epoxy matrix was achieved by the combined mechanism of packing and settling. The mechanical properties of the functionally
gradient epoxy/carbon fibre composite were also investigated. At the same content of carbon fibre, the flexural strength of
the functionally gradient composite was higher than that of conventional isotropic composite.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献