全文获取类型
收费全文 | 73198篇 |
免费 | 6603篇 |
国内免费 | 3223篇 |
专业分类
电工技术 | 4165篇 |
技术理论 | 5篇 |
综合类 | 4850篇 |
化学工业 | 12465篇 |
金属工艺 | 4143篇 |
机械仪表 | 4349篇 |
建筑科学 | 5498篇 |
矿业工程 | 2159篇 |
能源动力 | 1955篇 |
轻工业 | 4489篇 |
水利工程 | 1290篇 |
石油天然气 | 5004篇 |
武器工业 | 601篇 |
无线电 | 8794篇 |
一般工业技术 | 8711篇 |
冶金工业 | 3315篇 |
原子能技术 | 816篇 |
自动化技术 | 10415篇 |
出版年
2024年 | 395篇 |
2023年 | 1365篇 |
2022年 | 2449篇 |
2021年 | 3380篇 |
2020年 | 2532篇 |
2019年 | 1995篇 |
2018年 | 2366篇 |
2017年 | 2528篇 |
2016年 | 2109篇 |
2015年 | 2889篇 |
2014年 | 3720篇 |
2013年 | 4365篇 |
2012年 | 4758篇 |
2011年 | 5197篇 |
2010年 | 4534篇 |
2009年 | 3944篇 |
2008年 | 3999篇 |
2007年 | 3666篇 |
2006年 | 3778篇 |
2005年 | 3339篇 |
2004年 | 2221篇 |
2003年 | 1883篇 |
2002年 | 1780篇 |
2001年 | 1540篇 |
2000年 | 1652篇 |
1999年 | 1964篇 |
1998年 | 1530篇 |
1997年 | 1288篇 |
1996年 | 1243篇 |
1995年 | 1020篇 |
1994年 | 841篇 |
1993年 | 601篇 |
1992年 | 497篇 |
1991年 | 366篇 |
1990年 | 273篇 |
1989年 | 224篇 |
1988年 | 195篇 |
1987年 | 118篇 |
1986年 | 97篇 |
1985年 | 61篇 |
1984年 | 49篇 |
1983年 | 46篇 |
1982年 | 51篇 |
1981年 | 36篇 |
1980年 | 34篇 |
1979年 | 14篇 |
1978年 | 13篇 |
1977年 | 17篇 |
1976年 | 10篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
樊琳 《石油化工安全环保技术》2020,(2):1-3,I0001
分包商安全能力不足以及总包商安全管理薄弱,已成为导致工程建设项目事故多发的重要原因。将分包商的安全管理有效纳入到总承包商的安全管理体系内,做好分包商的安全管理,对提高总承包商的安全绩效、确保施工安全,具有极其重要的现实意义。从总承包商和分包商两个角度,研究分析分包安全管理中存在的问题及原因,得出分包安全管理各种问题的根源主要是经济利益,管理源头在总承包单位,站在总承包商的视角提出加强分包商安全管理的建议。 相似文献
32.
ABSTRACT Contact tracing is widely considered as an effective procedure in the fight against epidemic diseases. However, one of the challenges for technology based contact tracing is the high number of false positives, questioning its trust-worthiness and efficiency amongst the wider population for mass adoption. To this end, this paper proposes a novel, yet practical smartphone-based contact tracing approach, employing WiFi and acoustic sound for relative distance estimate, in addition to the air pressure and the magnetic field for ambient environment matching. We present a model combining six smartphone sensors, prioritising some of them when certain conditions are met. We empirically verified our approach in various realistic environments to demonstrate an achievement of up to 95% fewer false positives, and 62% more accurate than Bluetooth-only system. To the best of our knowledge, this paper was one of the first work to propose a combination of smartphone sensors for contact tracing. 相似文献
33.
Yu-Jiao Liu Xiao-Yang Fan Dr. Dong-Dong Zhang Yin-Zheng Xia Dr. Yan-Jun Hu Feng-Lei Jiang Prof. Fu-Ling Zhou Prof. Yi Liu 《ChemMedChem》2020,15(6):552-558
Based on the potential therapeutic value in targeting mitochondria and the fluorophore tracing ability, a fluorescent mitochondria-targeted organic arsenical PDT-PAO-F16 was fabricated, which not only visualized the cellular distribution, but also exerted anti-cancer activity in vitro and in vivo via targeting pyruvate dehydrogenase complex (PDHC) and respiratory chain complexes in mitochondria. In details, PDT-PAO-F16 mainly accumulated into mitochondria within hours and suppressed the activity of PDHC resulting in the inhibition of ATP synthesis and thermogenesis disorder. Moreover, the suppression of respiratory chain complex I and IV accelerated the mitochondrial dysfunction leading to caspase family-dependent apoptosis. In vivo, the acute promyelocytic leukemia was greatly alleviated in the PDT-PAO-F16 treated group in APL mice model. Our results demonstrated the organic arsenical precursor with fluorescence imaging and target-anticancer efficacy is a promising anticancer drug. 相似文献
34.
Meifang Luo Chaozhong Guo Xinyi Luo Zhaoxu Li Yuan Qin Weizhong Zhang 《International Journal of Hydrogen Energy》2021,46(2):2117-2127
It is of great urgency to design inexpensive and high-performance oxygen reduction reaction (ORR) electrocatalysts derived from biowastes as substitutes for Pt-based materials in electrochemical energy-conversion devices. Here we propose a strategy to synthesize three-dimensional (3D) porous nitrogen-doped network carbons to catalyze the ORR from two-step pyrolysis engineering of biowaste scale combined with the use of a ZnCl2 activator and a FeCl2 promotor. Electrochemical tests show that the synthesized network carbons have exhibited comparable ORR catalytic activity with a half-wave potential (~0.85 V vs. RHE) and outstanding cyclical stability in comparison to the Pt/C catalyst. Beyond that, a high electron transfer number (~3.8) and a low peroxide yield (<7.6%) can be obtained, indicating a four-electron reaction pathway. The maximum power density is ~68 mW cm?2, but continuous discharge curves (at a constant potential of ~1.30 V) for 12 h are not obviously declined in Zn-air battery tests using synthesized network carbons as the cathodic catalyst. The formation of 3D porous structures with high BET surface area can effectively expose the surface catalytic sites and promote mass transportation to boost the ORR activity. This work may open a new idea to prepare porous carbon-based catalysts for some important reactions in new energy devices. 相似文献
35.
Baofeng Hou Hong He Ruixiu Jia Meilong Fu Yanbin Cao Shaoqun He Liwen Luo Youqing Huang 《应用聚合物科学杂志》2019,136(10):47161
The synthesis and performance of a novel temperature-tolerant foamed resin for enhanced oil recovery were investigated using various methods, including infrared, NMR, scanning electron microscopy (SEM), and displacement experiments. Polycondensation of furfuryl alcohol prepolymers was confirmed by the infrared and NMR results. The poor temperature tolerance of furfuryl alcohol prepolymers after gelation at high temperatures is mainly due to the fracture of furan rings. The addition of ester additives is an effective method of increasing the temperature tolerance of the prepared foamed resins and can effectively reduce the weight-loss rate of the polycondensation products. The SEM results show that the skeleton structure of the foamed resin remains intact after high-temperature treatment. Thus, the novel plugging agent system has excellent thermal stability and still has a high strength (>0.8 MPa) after high-temperature aging treatment for 40 days, giving the prepared foamed resin a good plugging performance (plugging rate > 91%) at 250 °C. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47161. 相似文献
36.
基于目前中国改进型三环路压水堆(CPR1000)部分机组存在因中间量程电流饱和导致无法在48%额定功率(Pn)完成定值标定及核电厂大修经济性考虑,采用MCNP程序及核设计软件包SCIENCE,研究分析中间量程保护定值标定的新方法。分析结果表明,中间量程保护定值标定调整至30%Pn功率平台实施,采用改进方法标定的保护定值更接近于设计值。 相似文献
37.
Initialization speed is one of the most important factors in network real time kinematic (NRTK) performance. Owing to the low correlation among the error s 相似文献
38.
39.
40.
Xiaohu Ren Xilou Pu Hongfeng Yin Yun Tang Hudie Yuan Huiqing Fan 《Ceramics International》2021,47(9):12122-12129
Hexagonal barium ferries is a promising and efficient microwave (MW) absorbing material, but the low dielectric loss and poor conductivity have limited their extensive applications. In this work, a simple tactic of coating conductive polymer PANI on hexaferrite BaCo2Fe16O27 is presented, wherein the dielectric properties are customized, and more significantly, the electromagnetic loss is greatly enhanced. As displayed from structural characterizations, PANI were coated equably on the surface of hexaferrite grains by an in-situ polymerization process. The outcomes exhibit the as-prepared PANI@hexaferrite composite has remarkable electromagnetic wave absorption capacity. When the thickness is 6.0 mm, the minimal RL of ?40.4 dB was achieved at 2.9 GHz. The effective absorption bandwidth (RL < ?20 dB) of 0.65 GHz, 0.53 GHz, 0.65 GHz, 0.52 GHz, 0.46 GHz and 0.39 GHz was achieved separately when the thickness ranges from 4 to 9 mm. The highly efficient MW absorbing performance of PANI@hexaferrite composite were the consequence of multiple loss mechanisms and perfect impedance matching. It is demonstrated that the PANI@hexaferrite composite with excellent MW absorption performance is expected to be potential MW absorbers for extensive applications. 相似文献