全文获取类型
收费全文 | 98326篇 |
免费 | 10325篇 |
国内免费 | 5145篇 |
专业分类
电工技术 | 7867篇 |
技术理论 | 9篇 |
综合类 | 7088篇 |
化学工业 | 15100篇 |
金属工艺 | 5852篇 |
机械仪表 | 6243篇 |
建筑科学 | 8005篇 |
矿业工程 | 3329篇 |
能源动力 | 2912篇 |
轻工业 | 6634篇 |
水利工程 | 2183篇 |
石油天然气 | 4985篇 |
武器工业 | 1065篇 |
无线电 | 11755篇 |
一般工业技术 | 11370篇 |
冶金工业 | 4144篇 |
原子能技术 | 1313篇 |
自动化技术 | 13942篇 |
出版年
2024年 | 542篇 |
2023年 | 1929篇 |
2022年 | 3984篇 |
2021年 | 5097篇 |
2020年 | 3871篇 |
2019年 | 2995篇 |
2018年 | 3425篇 |
2017年 | 3751篇 |
2016年 | 3329篇 |
2015年 | 4649篇 |
2014年 | 5660篇 |
2013年 | 6530篇 |
2012年 | 7233篇 |
2011年 | 7593篇 |
2010年 | 6485篇 |
2009年 | 6179篇 |
2008年 | 5992篇 |
2007年 | 5383篇 |
2006年 | 5227篇 |
2005年 | 4281篇 |
2004年 | 2859篇 |
2003年 | 2318篇 |
2002年 | 2136篇 |
2001年 | 1774篇 |
2000年 | 1738篇 |
1999年 | 1693篇 |
1998年 | 1317篇 |
1997年 | 1105篇 |
1996年 | 1044篇 |
1995年 | 826篇 |
1994年 | 649篇 |
1993年 | 488篇 |
1992年 | 433篇 |
1991年 | 259篇 |
1990年 | 230篇 |
1989年 | 194篇 |
1988年 | 158篇 |
1987年 | 96篇 |
1986年 | 62篇 |
1985年 | 64篇 |
1984年 | 32篇 |
1983年 | 33篇 |
1982年 | 35篇 |
1981年 | 17篇 |
1980年 | 21篇 |
1979年 | 13篇 |
1977年 | 10篇 |
1976年 | 12篇 |
1959年 | 9篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
本文叙述了我国管道业面临的市场机遇和受到天然气价格等因素的制约以及进口钢管的挑战。建议中国管道业应适当发展ERW610机组和UOE机组的高质量产品;在钢板上宜以X70级为主,设备潜力可向X80级为目标而努力。 相似文献
93.
Yoon Carolyn; Feinberg Fred; Hu Ping; Gutchess Angela Hall; Hedden Trey; Chen Hiu-Ying Mary; Jing Qicheng; Cui Yao; Park Denise C. 《Canadian Metallurgical Quarterly》2004,19(3):379
Understanding how aging influences cognition across different cultures has been hindered by a lack of standardized, cross-referenced verbal stimuli. This study introduces a database of such item-level stimuli for both younger and older adults, in China and the United States, and makes 3 distinct contributions. First, the authors specify which item categories generalize across age and/or cultural groups, rigorously quantifying differences among them. Second, they introduce novel, powerful methods to measure between-group differences in freely generated ranked data, the rank-ordered logit model and Hellinger Affinity. Finally, a broad archive of tested, cross-linguistic stimuli is now freely available to researchers: data, similarity measures, and all stimulus materials for 105 categories and 4 culture-by-age groups, comprising over 10,000 fully translated unique item responses. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
94.
Takuma Suzuki Hang-Ju Ko Agus Setiawan Jung-Jin Kim Koh Saitoh Masami Terauchi Takafumi Yao 《Materials Science in Semiconductor Processing》2003,6(5-6):519-521
We report the successful growth of Ga-polar GaN epilayers on O-polar ZnO templates pre-deposited on c-sapphire. Prior to GaN growth, NH3 is exposed onto the ZnO template. The polarity of the GaN layers is confirmed by etching of the surface and by conversion beam electron diffraction (CBED), while the O-polar ZnO is confirmed by CBED. It is suggested that the NH3 pre-exposure helps form a Zn3N2 layer, which possesses inversion symmetry and inverts the crystal from anion polar to cation polar. 相似文献
95.
中国3G业务的市场需求有两个方面:一是迅猛增长、规模庞大的用户群对移动语音业务的需求;二是较高收入用户群对移动数据业务的需求。3G运营商的目标市场包括大众用户对移动语音的需求、大众用户对移动数据业务的需求、企业用户对移动数据业务的需求以及批发型用户的需求等。本结合国内外移动运营商的数据业务开展状况,初步探讨了中国3G运营商的移动数据业务模式和3G业务的收入模式。 相似文献
96.
Lianshan Yan Yeh C. Yang G. Lin L. Chen Z. Shi Y.Q. Willner A.E. Yao X.S. 《Lightwave Technology, Journal of》2003,21(7):1676-1684
We demonstrate the first programmable group-delay module based on polarization switching. With a unique binary tuning mechanism, the device can generate any differential group delay value from -45 to +45 ps with a resolution of 1.40 ps, or any true-time-delay value from 0 to 45 ps with a resolution of 0.7 ps. The delay varying speeds for both applications are under 1 ms and can be as fast as 0.1 ms. We evaluate both the dynamic and static performances of the device while paying special attention to its dynamic figures of merit for polarization-mode dispersion emulation and compensation applications. Our experiment shows that the device exhibits a negligible transient-effect induced power penalty (<0.2 dB) in a 10-Gb/s nonreturn-to-zero system. 相似文献
97.
98.
Ultrastructure of sperm and eggs of the ocean pout (Macrozoarces americanus L.), an internally fertilizing marine teleost, was examined by scanning and transmission electron microscopy. The results showed that the sperm do not have an acrosome but have a very long mid-piece (one to two times the sperm head length) containing numerous well-developed elongated mitochondria. The sperm also have two tails (is biflagellate) each consisting of nine peripheral and one central pair (9 +/- 2) of microtubules. This long mid-piece and the biflagellate nature of the sperm appear to be associated with the long life-span of the sperm and with sperm dispersal in the ovary to fertilize the eggs internally. The ocean pout eggs are enveloped by a porous chorionic membrane similar to that found in other teleosts but have two micropyles, a condition likely related to a mechanism of egg fertilization which increases the egg fertility in the presence of low sperm numbers. Following insemination, some biochemically undefined excretions appeared on the surface of fertilized eggs and led to the acquisition of adherent capability of the eggs which formed a tightly associated egg mass in sea water. 相似文献
99.
Using a linear voltage ramp method, ultraslow dielectric relaxation processes of La-doped BaTiO3 boundary layer (BL) capacitors are measured at room temperature. For the electric polarization model of a double-layer dielectric, a procedure to calculate the electrical parameters of grain and grain boundary has been developed. Calculated results suggest that there is a shell on the surface of the grain. TEM images of the BL capacitor also show a lot of microregions with minor structural modifications. Relaxation times are estimated from the equivalent circuit and are in agreement with fitted results. 相似文献
100.