全文获取类型
收费全文 | 12873篇 |
免费 | 734篇 |
国内免费 | 158篇 |
专业分类
电工技术 | 379篇 |
综合类 | 271篇 |
化学工业 | 2455篇 |
金属工艺 | 356篇 |
机械仪表 | 456篇 |
建筑科学 | 618篇 |
矿业工程 | 78篇 |
能源动力 | 437篇 |
轻工业 | 706篇 |
水利工程 | 73篇 |
石油天然气 | 277篇 |
武器工业 | 38篇 |
无线电 | 2210篇 |
一般工业技术 | 2259篇 |
冶金工业 | 1463篇 |
原子能技术 | 145篇 |
自动化技术 | 1544篇 |
出版年
2024年 | 21篇 |
2023年 | 153篇 |
2022年 | 221篇 |
2021年 | 293篇 |
2020年 | 233篇 |
2019年 | 192篇 |
2018年 | 285篇 |
2017年 | 303篇 |
2016年 | 273篇 |
2015年 | 304篇 |
2014年 | 459篇 |
2013年 | 789篇 |
2012年 | 651篇 |
2011年 | 737篇 |
2010年 | 581篇 |
2009年 | 663篇 |
2008年 | 662篇 |
2007年 | 620篇 |
2006年 | 585篇 |
2005年 | 517篇 |
2004年 | 439篇 |
2003年 | 424篇 |
2002年 | 374篇 |
2001年 | 347篇 |
2000年 | 337篇 |
1999年 | 330篇 |
1998年 | 592篇 |
1997年 | 410篇 |
1996年 | 311篇 |
1995年 | 214篇 |
1994年 | 199篇 |
1993年 | 208篇 |
1992年 | 131篇 |
1991年 | 104篇 |
1990年 | 92篇 |
1989年 | 74篇 |
1988年 | 65篇 |
1987年 | 76篇 |
1986年 | 74篇 |
1985年 | 44篇 |
1984年 | 38篇 |
1983年 | 23篇 |
1982年 | 18篇 |
1981年 | 48篇 |
1980年 | 30篇 |
1979年 | 23篇 |
1978年 | 26篇 |
1977年 | 44篇 |
1976年 | 45篇 |
1975年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
The design of a microstrip‐fed annular‐ring slot antenna (ARSA) with circular polarization (CP) radiation is initially studied. To obtain CP radiation with broad 3‐dB axial ratio (AR) bandwidth that can cover the WiMAX 2.3 GHz (2305–2320 MHz, 2345–2360 MHz) and WLAN 2.4 GHz (2400–2480 MHz) bands, a novel technique of extending an inverted L‐shaped slot from the bottom section of the annular‐ring is proposed. To suppress the harmonic modes induced by the CP ARSA, the technique of integrating a defected ground structure into the annular‐ring slot is further introduced. From the measured results, 10‐dB impedance bandwidth and 3‐dB AR bandwidth of 44.86 and 9.68% were achieved by the proposed harmonic suppressed CP ARSA. Furthermore, average gain and radiation efficiency of ~4.7 dBic and 71%, respectively, were also exhibited across the bands of interest. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:337–345, 2015. 相似文献
13.
Similarities and differences between male and female novice designers on color‐concept associations for warnings,action required,and signs and equipment status messages
下载免费PDF全文
![点击此处可从《Color research and application》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This research examined the male and female novice designers toward color associations for the concepts used for ‘warnings’, ‘action required’, and ‘signs and equipment status’ through a questionnaire‐based study. A total of 178 Hong Kong Chinese final year undergraduate design students (89 males and 89 females) participated in the study. The test used required the participants to indicate their choice of one of nine colors to associations with each of 38 concepts in a color‐concept table, so that any one color could be associated with any one of the concepts. For both male and female groups of novice designers, chi‐square tests revealed a strong color association for each concept tested in this study (P < .05). The results showed males and females agreed on some color‐concept association stereotypes which were therefore gender neutral. The male and female novice designers had the same color associations and similar levels of stereotype strengths for 21 concepts. The nine strongest and therefore most useful color‐concept association stereotypes for both male and female novice designers were: red‐danger, red‐fire, red‐hot, red‐stop, red‐emergency, red‐error, blue‐cold, blue‐male, and green‐exit. However, the male and female novice designers had different color association stereotypes for the standby (green vs. yellow), emergency exit (green vs. red), and toxic (purple vs. black) concepts, and the strengths of the 14 remaining associations for both groups were not at equivalent levels. Overall, it is anticipated that the findings of this study will act as a useful reference for novice designers and other design practitioners to optimize color coding in the design of ‘warnings’, ‘action required’, and ‘signs and equipment status’ messages. 相似文献
14.
15.
16.
17.
Xue‐Yong Liu Xiao‐Bin Ding Zhao‐Hui Zheng Yu‐Xing Peng Albert S
C Chan C
W Yip Xin‐Ping Long 《Polymer International》2003,52(2):235-240
Amphiphilic magnetic microspheres ranging in diameter from 5 to 100 µm were prepared by dispersion copolymerization of styrene and poly(ethylene oxide) vinylbenzyl (PEO‐VB) macromonomer (MPEO) in the presence of Fe3O4 magnetic fluid. The effects of various polymerization parameters on the average particle size were systematically investigated. The average particle size was found to increase with increasing styrene concentration and initiator concentration. It also increased with decreasing stabilizer concentration and molecular weight of MPEO. The content of the hydroxyl groups localized in the microspheres ranged from 0.01 to 0.2 mmol g?1. © 2003 Society of Chemical Industry 相似文献
18.
19.
Shi-Jin Ding Hang Hu Lim H.F. Kim S.J. Yu X.F. Chunxiang Zhu Li M.F. Byung Jin Cho Chan D.S.H. Rustagi S.C. Yu M.B. Chin A. Dim-Lee Kwong 《Electron Device Letters, IEEE》2003,24(12):730-732
For the first time, we successfully fabricated and demonstrated high performance metal-insulator-metal (MIM) capacitors with HfO/sub 2/-Al/sub 2/O/sub 3/ laminate dielectric using atomic layer deposition (ALD) technique. Our data indicates that the laminate MIM capacitor can provide high capacitance density of 12.8 fF//spl mu/m/sup 2/ from 10 kHz up to 20 GHz, very low leakage current of 3.2 /spl times/ 10/sup -8/ A/cm/sup 2/ at 3.3 V, small linear voltage coefficient of capacitance of 240 ppm/V together with quadratic one of 1830 ppm/V/sup 2/, temperature coefficient of capacitance of 182 ppm//spl deg/C, and high breakdown field of /spl sim/6 MV/cm as well as promising reliability. As a result, the HfO/sub 2/-Al/sub 2/O/sub 3/ laminate is a very promising candidate for next generation MIM capacitor for radio frequency and mixed signal integrated circuit applications. 相似文献
20.
中原油田岩石可钻性与声波时差关系研究 总被引:3,自引:0,他引:3
选取中原油田的大量岩心,采用常规岩石力学测试方法测定了岩石的可钻性、声波测试方法测定了岩石和岩屑声波时差,通过对测得的岩石可钻性级值和声波时差进行回归拟合,得出了中原油田岩石可钻性与声波时差的关系式。现场应用表明,该关系式较好地反映了中原油田地层岩石可钻性与声波时差的关系,可以在优选钻头时作为参考或直接应用。 相似文献