全文获取类型
收费全文 | 15684篇 |
免费 | 445篇 |
国内免费 | 36篇 |
专业分类
电工技术 | 220篇 |
综合类 | 19篇 |
化学工业 | 2677篇 |
金属工艺 | 331篇 |
机械仪表 | 365篇 |
建筑科学 | 574篇 |
矿业工程 | 27篇 |
能源动力 | 333篇 |
轻工业 | 1775篇 |
水利工程 | 122篇 |
石油天然气 | 36篇 |
无线电 | 1637篇 |
一般工业技术 | 2422篇 |
冶金工业 | 3497篇 |
原子能技术 | 178篇 |
自动化技术 | 1952篇 |
出版年
2023年 | 62篇 |
2022年 | 156篇 |
2021年 | 271篇 |
2020年 | 175篇 |
2019年 | 230篇 |
2018年 | 274篇 |
2017年 | 253篇 |
2016年 | 323篇 |
2015年 | 195篇 |
2014年 | 339篇 |
2013年 | 749篇 |
2012年 | 589篇 |
2011年 | 722篇 |
2010年 | 581篇 |
2009年 | 549篇 |
2008年 | 650篇 |
2007年 | 623篇 |
2006年 | 510篇 |
2005年 | 500篇 |
2004年 | 412篇 |
2003年 | 381篇 |
2002年 | 360篇 |
2001年 | 350篇 |
2000年 | 338篇 |
1999年 | 362篇 |
1998年 | 1081篇 |
1997年 | 676篇 |
1996年 | 514篇 |
1995年 | 397篇 |
1994年 | 321篇 |
1993年 | 330篇 |
1992年 | 191篇 |
1991年 | 163篇 |
1990年 | 174篇 |
1989年 | 170篇 |
1988年 | 159篇 |
1987年 | 131篇 |
1986年 | 137篇 |
1985年 | 175篇 |
1984年 | 129篇 |
1983年 | 122篇 |
1982年 | 90篇 |
1981年 | 117篇 |
1980年 | 105篇 |
1979年 | 104篇 |
1978年 | 71篇 |
1977年 | 133篇 |
1976年 | 181篇 |
1975年 | 70篇 |
1973年 | 75篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Quality of Crude Fish Oil Extracted from Herring Byproducts of Varying States of Freshness 总被引:1,自引:0,他引:1
ABSTRACT: Herring byproducts were stored at 2 and 15 °C for up to 72 h. Over time, significant increases of total volatile bases (TVB), histamine, putrescine, cadaverine, and tyramine were detected. However, only tyramine and TVB levels were temperature-dependent. The level of total polyunsaturated fatty acids (PUFAs) was constant. Longer byproducts storage gave rise to an oil with higher levels of free fatty acids, eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and total PUFAs, while fluorescent compounds were lower. A higher storage temperature led to oil higher in α-tocopherol and EPA levels and lower in anisidine value. Surprisingly, the oil with the highest content of PUFAs was not produced from the freshest byproducts, and oil with low oxidation products can be extracted from stored byproducts. 相似文献
32.
Instructional texts rewritten by five expert teams: Revisions and retention improvements. 总被引:1,自引:0,他引:1
Britton Bruce K.; Van Dusen Lani; Gulg?z Sami; Glynn Shawn M. 《Canadian Metallurgical Quarterly》1989,81(2):226
700 undergraduates were tested in 3 experiments on original or rewritten versions of 52 instructional texts about Army job tasks, general science, philosophy, and history. Five experts had rewritten various sets of the texts and stated hypotheses about the efficacious features of their revisions. We tested their hypotheses and several others. Recall and recognition tests were given immediately and after a 24-hr delay. Results showed that revisions made by 3 of the 5 experts improved retention of text information. The kind and number of revisions and improvements varied across the text sets. Most expert hypotheses were not supported, and they made many revisions they were declaratively unaware of. Some of our hypotheses about the revision features were supported, but different features were effective for different sets of texts. It was concluded that some experts have effective knowledge about improving instructional text, but it exists primarily in procedural form. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
33.
34.
35.
36.
Static light scattering was used to investigate dilute dispersions of fine gamma -Fe/sub 2/O/sub 3/ magnetic particles. The particles were acicular and on average 0.39 mu m long and 0.056 mu m in diameter. They were dispersed in organic solvents at concentrations of approximately 10/sup -4/ vol%, corresponding to an average interparticle separation of 9 mu m. Computer programs using a coupled dipole algorithm to predict the scattering from the particles were written. Experimental results do not agree with computer calculations of the light scattering from single particles, but are consistent with scattering from thick ropelike agglomerates of particles. The size of these agglomerates was estimated after 10 s to be less than 100 particles, while the thickness of the ropes is at least 5 particles.<> 相似文献
37.
Christian P. Romero Jonathan I. Avila Edgardo Cisternas Guerau B. Cabrera Alejandro L. Cabrera Kristiaan Temst Margriet J. Van Bael 《Journal of Materials Science》2007,42(18):7667-7672
Hydrogen desorption curves were obtained from a sample composed of a square arrangement of Co dots with average diameter of
4.4 μm, separated by a distance of 11.6 μm. A macroscopic sample of Co dots grown on a 2.5 × 2.5 cm Si substrate was made
by standard lithographic techniques and used in these experiments. Thermal programmed desorption (TPD) was performed under
ultra-high vacuum conditions. Hydrogen TPD curves were obtained from a 1 × 1 cm Co dots samples displaying a maximum of intensity
at 425 K. Hydrogen TPD curve was also obtained from 1 cm× 1 cm samples of Co films and Co foils for comparison. The hydrogen
TPD curves have decreasing intensity from the Co foils to the Co dots and finally to the Co films. This indicates that there
are more sites for hydrogen adsorption on the Co dots than in the Co films. This is a surprising result because there is approximately
8.7 times less Co atoms exposed in the Co dots that in the Co film sample. A desorption energy of 27 kcal/mol was obtained
for the Co dots suggesting that hydrogen is adsorbed on an hcp hollow site of the Co dot crystalline structure. 相似文献
38.
D. M. Van Wie D. G. Drewry Jr. D. E. King C. M. Hudson 《Journal of Materials Science》2004,39(19):5915-5924
Hypersonic flight powered by airbreathing engines offers the potential for faster response time at long ranges, and reduced cost for access-to-space. In the present paper the operating environment of typical hypersonic vehicles are discussed, including results for the radiation equilibrium wall temperature of external vehicle surfaces and the flow properties through three sample engines spanning the range of hydrocarbon-fueled Mach 4-8 flight and hydrogen-fueled flight at speeds up to Mach 17. Flow conditions at several locations through the sample engines were calculated to provide indications of the required operating flow environment. Additional system consideration such a seals, joints, vehicle integration and in-service engineering are addressed. 相似文献
39.
B.J.W. Waarsing M. Nuttin H. Van Brussel B. Corteville 《IEEE transactions on systems, man and cybernetics. Part C, Applications and reviews》2005,35(1):53-65
This paper presents our approach to extend the niche of behavior-based robotics toward manipulation. We use results from neuroscience to derive some qualitative design rules for the mechanics of the manipulator, resulting in a next-generation manipulator, the "soft arm". By defining the basic behaviors of the manipulator as trajectory-producing behaviors (which is also biologically plausible), we have designed a first test case: writing on a board with a mobile manipulator. The soft arm has not yet been developed; therefore, we have emulated such a soft robot arm on an industrial robot. 相似文献
40.