全文获取类型
收费全文 | 156258篇 |
免费 | 8309篇 |
国内免费 | 4043篇 |
专业分类
电工技术 | 5489篇 |
技术理论 | 9篇 |
综合类 | 7155篇 |
化学工业 | 23485篇 |
金属工艺 | 8947篇 |
机械仪表 | 7642篇 |
建筑科学 | 7557篇 |
矿业工程 | 2625篇 |
能源动力 | 3357篇 |
轻工业 | 8256篇 |
水利工程 | 2780篇 |
石油天然气 | 4218篇 |
武器工业 | 852篇 |
无线电 | 18154篇 |
一般工业技术 | 24961篇 |
冶金工业 | 6449篇 |
原子能技术 | 1284篇 |
自动化技术 | 35390篇 |
出版年
2024年 | 309篇 |
2023年 | 1222篇 |
2022年 | 2341篇 |
2021年 | 3356篇 |
2020年 | 2522篇 |
2019年 | 2126篇 |
2018年 | 16466篇 |
2017年 | 15638篇 |
2016年 | 12041篇 |
2015年 | 3864篇 |
2014年 | 4159篇 |
2013年 | 5003篇 |
2012年 | 8165篇 |
2011年 | 14435篇 |
2010年 | 12736篇 |
2009年 | 9786篇 |
2008年 | 10829篇 |
2007年 | 11655篇 |
2006年 | 4080篇 |
2005年 | 4446篇 |
2004年 | 3479篇 |
2003年 | 3228篇 |
2002年 | 2656篇 |
2001年 | 2023篇 |
2000年 | 1823篇 |
1999年 | 1681篇 |
1998年 | 1438篇 |
1997年 | 1202篇 |
1996年 | 1032篇 |
1995年 | 826篇 |
1994年 | 635篇 |
1993年 | 525篇 |
1992年 | 426篇 |
1991年 | 348篇 |
1990年 | 233篇 |
1989年 | 213篇 |
1988年 | 191篇 |
1987年 | 105篇 |
1986年 | 118篇 |
1985年 | 90篇 |
1984年 | 49篇 |
1982年 | 49篇 |
1981年 | 51篇 |
1968年 | 52篇 |
1967年 | 42篇 |
1966年 | 52篇 |
1965年 | 55篇 |
1959年 | 42篇 |
1955年 | 65篇 |
1954年 | 69篇 |
排序方式: 共有10000条查询结果,搜索用时 515 毫秒
81.
82.
Li Jinghang Zhao Zhigang Zhang Shaohui Su Cheng 《Journal of Mechanical Science and Technology》2021,35(10):4727-4735
Journal of Mechanical Science and Technology - A multi-robot collaborative towing system fixed on floating base for high load marine work was established in this paper, and its dynamics and... 相似文献
83.
Ziqian Wang Yalan Chen Yating He Weidong Jiang Yan Long Guangyin Fan 《International Journal of Hydrogen Energy》2021,46(21):11587-11596
Developing high-efficiency and low-cost catalysts for hydrogen evolution from hydrolysis of ammonia borane (AB) is significant and critical for the exploitation and utilization of hydrogen energy. Herein, the in-situ fabrication of well-dispersed and small bimetallic RuNi alloy nanoparticles (NPs) with tuned compositions and concomitant hydrolysis of AB are successfully achieved by using graphitic carbon nitride (g-C3N4) as a NP support without additional stabilizing ligands. The optimized Ru1Ni7.5/g-C3N4 catalyst exhibits an excellent catalytic activity with a high turnover frequency of 901 min?1 and an activation energy of 28.46 kJ mol?1 without any base additives, overtaking the activities of many previously reported catalysts for AB hydrolysis. The kinetic studies indicate that the AB hydrolysis over Ru1Ni7.5/g-C3N4 is first-order and zero-order reactions with respect to the catalyst and AB concentrations, respectively. Ru1Ni7.5/g-C3N4 has a good recyclability with 46% of the initial catalytic activity retained even after five runs. The high performance of Ru1Ni7.5/g-C3N4 should be assigned to the small-sized alloy NPs with abundant accessible active sites and the synergistic effect between the composition-tuned Ru–Ni bimetals. This work highlights a potentially powerful and simple strategy for preparing highly active bimetallic alloy catalysts for AB hydrolysis to generate hydrogen. 相似文献
84.
85.
Gert Schubring 《NTM》2003,11(2):90-99
Enno Heeren Dirksen (1788–1850) was one of several mathematicians originating from Eastern Frisia at the end of the eighteenth
century to acquire prominence in neohumanist reformed Prussia. While striving—like so many of his contemporaries—for more
rigour in the foundations of calculus, his work is significant due to his unusual emphasis on the semiotic aspects of the
basic concepts. As a clear-sighted propagator of Cauchy's conceptual innovations in Germany, his achievements in improving
sign expressions of such concepts enabled him to clarify hitherto not differentiated multiple limit processes—although less
successfully in constructive concept formation itself.
The contribution is based on the analysis of Dirksen's published texts and on the numerous texts which remained drafts for
his projected voluminousOrganon der gesamten Analysis.
Menso Folkerts zum 60. Geburtstag gewidmet 相似文献
Menso Folkerts zum 60. Geburtstag gewidmet 相似文献
86.
Yang Aiying Wang Ziyu Zhang Zhaoyi Chen Zhangyuan Wu Deming 《电子科学学刊(英文版)》2003,20(6):461-466
A 10Gbit/s recirculating system is configured with Chirped Fiber Bragg Grating (CFBG) for the dispersion compensation. For the first time, the transmission distance in the loop reaches 1000km with bit error rate of 10-9. The effect of the group delay ripple of the fiber grating is also investigated in the recirculating systems, and it is shown that the transmission distance is limited to 4 cycles (4×167.1km ) in the loop with the power penalty fluctuation below 1.0dB. Thus the group delay ripple should be reduced to allow for the wavelength drift of±5GHz. At the end of this letter, the principles are given for designing long haul recirculating systems with dispersion compensation CFBG. 相似文献
87.
Popular biorthogonal wavelet filters via a lifting scheme and its application in image compression 总被引:2,自引:0,他引:2
Cheng L. Liang D.L. Zhang Z.H. 《Vision, Image and Signal Processing, IEE Proceedings -》2003,150(4):227-232
A technique using a lifting scheme is presented for constructing compactly supported wavelets whose coefficients are composed of free variables locating in an interval. An efficient approach-based wavelet for image compression is developed by selecting the coefficients of the 9-7 wavelet filter and associated lifting scheme. Furthermore, the rationalised coefficients wavelet filter that can be implemented with simple integer arithmetic is achieved and its characteristic is close to the well known original irrational coefficients 9-7 wavelet filters developed by A. Cohen et al. (Commun. Pure Appl. Maths., vol.45, no.1, p.485-560, 1992). To reduce the computational cost of image coding applications further, an acceleration technique is proposed for the lifting steps. Software and hardware simulations show that the new method has very low complexity, and simultaneously preserves the high quality of the compressed image. 相似文献
88.
Yu Zhao Zhigang Xu Zongshi Li Weihong Qiao Lubai Cheng 《Petroleum Science and Technology》2006,24(7):821-827
Heavy alkyl benzene sulfonates (HABS) were synthesized, and their interfacial tensions were measured and compared with those of petroleum sulfonates ORS-41. Effects of their coupling with lignosulfonate were also studied. The results showed that HABS exhibited good interfacial activities and the system of HABS blending with LS displayed better interfacial activities than ORS-41 and therefore reduced the prime cost. Their best proportions of synergism were from 3:1 to 4:1. HABS might be a more promising alkali-surfactant-polymer (ASP) flooding agent. 相似文献
89.
湘中海相浅层湘冷1井酸压工艺研究及应用 总被引:2,自引:0,他引:2
湘冷1井具有气层埋藏浅(400m-500m)、纵向上裂隙发育的特点,属低孔、低渗的含泥质灰岩致密储层。大量室内实验和研究采用“前置液酸压+闭合酸化”工艺技术,并优选了相应降阻酸和闭合酸配方。通过酸压实现了该井工业油气流的突破,取得了明显的增产效果,为新区海相浅层气的开发探索出了一套成熟的改造增产措施。 相似文献
90.
在取得土料场土料物理力学性质参数的情况下,遵循碾压试验基本原理、方法及参数组合,进行了现场碾压试验,通过试验成果的分析,得出了大坝碾压试验结论,为大坝土方填筑提供了技术依据。 相似文献