全文获取类型
收费全文 | 69263篇 |
免费 | 6508篇 |
国内免费 | 3659篇 |
专业分类
电工技术 | 4669篇 |
技术理论 | 10篇 |
综合类 | 4818篇 |
化学工业 | 11218篇 |
金属工艺 | 4130篇 |
机械仪表 | 4533篇 |
建筑科学 | 5461篇 |
矿业工程 | 2275篇 |
能源动力 | 2096篇 |
轻工业 | 4198篇 |
水利工程 | 1198篇 |
石油天然气 | 4648篇 |
武器工业 | 713篇 |
无线电 | 7777篇 |
一般工业技术 | 8166篇 |
冶金工业 | 3287篇 |
原子能技术 | 716篇 |
自动化技术 | 9517篇 |
出版年
2024年 | 370篇 |
2023年 | 1370篇 |
2022年 | 2251篇 |
2021年 | 3177篇 |
2020年 | 2385篇 |
2019年 | 1937篇 |
2018年 | 2174篇 |
2017年 | 2409篇 |
2016年 | 2135篇 |
2015年 | 2841篇 |
2014年 | 3457篇 |
2013年 | 4302篇 |
2012年 | 4486篇 |
2011年 | 4901篇 |
2010年 | 4204篇 |
2009年 | 3978篇 |
2008年 | 4048篇 |
2007年 | 3806篇 |
2006年 | 3718篇 |
2005年 | 3197篇 |
2004年 | 2138篇 |
2003年 | 1969篇 |
2002年 | 1952篇 |
2001年 | 1746篇 |
2000年 | 1632篇 |
1999年 | 1714篇 |
1998年 | 1266篇 |
1997年 | 1101篇 |
1996年 | 971篇 |
1995年 | 873篇 |
1994年 | 707篇 |
1993年 | 536篇 |
1992年 | 417篇 |
1991年 | 299篇 |
1990年 | 260篇 |
1989年 | 168篇 |
1988年 | 154篇 |
1987年 | 96篇 |
1986年 | 79篇 |
1985年 | 38篇 |
1984年 | 33篇 |
1983年 | 35篇 |
1982年 | 32篇 |
1981年 | 18篇 |
1980年 | 15篇 |
1979年 | 9篇 |
1977年 | 3篇 |
1976年 | 8篇 |
1973年 | 4篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
双检合并技术在海底电缆地震资料处理中被广泛应用,可衰减电缆鬼波的影响。传统方式以水、陆检记录的波场记录相同为假设,电缆鬼波压制效果差,合并效果并不理想。在分析交叉鬼波化双检合并技术基本原理的基础上,综合利用水检资料与陆检鬼波褶积的结果和陆检资料与水检鬼波褶积的结果求取刻度算子,同时在地震资料处理中利用陆检资料标定水检资料,从而优化了交叉鬼波化双检合并技术。实际资料处理结果表明,改进后的技术可有效衰减电缆鬼波,分离出上行波场,大幅度拓宽地震资料频带,提高地震资料分辨率,从而提供更丰富的构造细节信息。 相似文献
23.
Weikang Dong Ruishi Qi Tiansheng Liu Yi Li Ning Li Ze Hua Zirui Gao Shuyuan Zhang Kaihui Liu Jiandong Guo Peng Gao 《Advanced materials (Deerfield Beach, Fla.)》2020,32(46):2002014
Hyperbolic phonon polaritons (HPhPs) in orthorhombic-phase molybdenum trioxide (α-MoO3) show in-plane hyperbolicity, great wavelength compression, and ultralong lifetime, therefore holding great potential in nanophotonic applications. However, its polaritonic response in the far-infrared (FIR) range remains unexplored due to challenges in experimental characterization. Here, monochromated electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM) is used to probe HPhPs in α-MoO3 in both mid-infrared (MIR) and FIR frequencies and correlate their behaviors with microstructures and orientations. It is found that low structural symmetry leads to various phonon modes and multiple Reststrahlen bands (RBs) over a broad spectral range (over 70 meV) and in different directions (55–63 meV and 119–125 meV along the b-axis, 68–106 meV along the c-axis, and 101–121 meV along the a-axis). These HPhPs can be selectively excited by controlling the direction of swift electrons. These findings provide new opportunities in nanophotonic and optoelectronic applications, such as directed light propagation, hyperlenses, and heat transfer. 相似文献
24.
25.
26.
Minli Yu Ke Wang Harrie Vredenburg 《International Journal of Hydrogen Energy》2021,46(41):21261-21273
The primary aim of this study is to provide insights into different low-carbon hydrogen production methods. Low-carbon hydrogen includes green hydrogen (hydrogen from renewable electricity), blue hydrogen (hydrogen from fossil fuels with CO2 emissions reduced by the use of Carbon Capture Use and Storage) and aqua hydrogen (hydrogen from fossil fuels via the new technology). Green hydrogen is an expensive strategy compared to fossil-based hydrogen. Blue hydrogen has some attractive features, but the CCUS technology is high cost and blue hydrogen is not inherently carbon free. Therefore, engineering scientists have been focusing on developing other low-cost and low-carbon hydrogen technology. A new economical technology to extract hydrogen from oil sands (natural bitumen) and oil fields with very low cost and without carbon emissions has been developed and commercialized in Western Canada. Aqua hydrogen is a term we have coined for production of hydrogen from this new hydrogen production technology. Aqua is a color halfway between green and blue and thus represents a form of hydrogen production that does not emit CO2, like green hydrogen, yet is produced from fossil fuel energy, like blue hydrogen. Unlike CCUS, blue hydrogen, which is clearly compensatory with respect to carbon emissions as it captures, uses and stores produced CO2, the new production method is transformative in that it does not emit CO2 in the first place. In order to promote the development of the low-carbon hydrogen economy, the current challenges, future directions and policy recommendations of low-carbon hydrogen production methods including green hydrogen, blue hydrogen, and aqua hydrogen are investigated in the paper. 相似文献
27.
28.
For rechargeable wireless sensor networks, limited energy storage capacity, dynamic energy supply, low and dynamic duty cycles cause that it is unpractical to maintain a fixed routing path for packets delivery permanently from a source to destination in a distributed scenario. Therefore, before data delivery, a sensor has to update its waking schedule continuously and share them to its neighbors, which lead to high energy expenditure for reestablishing path links frequently and low efficiency of energy utilization for collecting packets. In this work, we propose the maximum data generation rate routing protocol based on data flow controlling technology. For a sensor, it does not share its waking schedule to its neighbors and cache any waking schedules of other sensors. Hence, the energy consumption for time synchronization, location information and waking schedule shared will be reduced significantly. The saving energy can be used for improving data collection rate. Simulation shows our scheme is efficient to improve packets generation rate in rechargeable wireless sensor networks. 相似文献
29.
Replacement of precious single metal catalysts with cost-effective, highly-dispersed composite catalysts for catalytic hydrothermal conversion of residue holds tremendous promise for the residue upgrading technologies. Organic metals were added to the feed as the oil-soluble precursors, and transformed into the catalytic active phases in this work. Physical properties and structures of the composite catalysts had been investigated by X-ray fluorescence spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscope and transmission electron microscopy. The composite catalysts were found to be highly efficient in the catalytic hydrothermal conversion of both model compound and residue. Increased metal dispersion and synergistic effects of two metals played indispensable roles in such catalytic system. Results showed that under the test conditions in the article, the catalyst had the best catalytic performance when the mass ratio of molybdenum to iron was 1.5. 相似文献
30.
In this paper, we first re-examine the previous protocol of controlled quantum secure direct communication of Zhang et al.’s scheme, which was found insecure under two kinds of attacks, fake entangled particles attack and disentanglement attack. Then, by changing the party of the preparation of cluster states and using unitary operations, we present an improved protocol which can avoid these two kinds of attacks. Moreover, the protocol is proposed using the three-qubit partially entangled set of states. It is more efficient by only using three particles rather than four or even more to transmit one bit secret information. Given our using state is much easier to prepare for multiqubit states and our protocol needs less measurement resource, it makes this protocol more convenient from an applied point of view. 相似文献