全文获取类型
收费全文 | 5319篇 |
免费 | 328篇 |
国内免费 | 22篇 |
专业分类
电工技术 | 85篇 |
综合类 | 9篇 |
化学工业 | 1124篇 |
金属工艺 | 116篇 |
机械仪表 | 129篇 |
建筑科学 | 188篇 |
矿业工程 | 8篇 |
能源动力 | 184篇 |
轻工业 | 336篇 |
水利工程 | 32篇 |
石油天然气 | 23篇 |
无线电 | 989篇 |
一般工业技术 | 1019篇 |
冶金工业 | 459篇 |
原子能技术 | 29篇 |
自动化技术 | 939篇 |
出版年
2024年 | 9篇 |
2023年 | 97篇 |
2022年 | 186篇 |
2021年 | 284篇 |
2020年 | 222篇 |
2019年 | 185篇 |
2018年 | 233篇 |
2017年 | 195篇 |
2016年 | 282篇 |
2015年 | 174篇 |
2014年 | 235篇 |
2013年 | 359篇 |
2012年 | 280篇 |
2011年 | 317篇 |
2010年 | 229篇 |
2009年 | 224篇 |
2008年 | 220篇 |
2007年 | 192篇 |
2006年 | 146篇 |
2005年 | 132篇 |
2004年 | 106篇 |
2003年 | 90篇 |
2002年 | 83篇 |
2001年 | 87篇 |
2000年 | 55篇 |
1999年 | 64篇 |
1998年 | 210篇 |
1997年 | 99篇 |
1996年 | 89篇 |
1995年 | 80篇 |
1994年 | 49篇 |
1993年 | 74篇 |
1992年 | 39篇 |
1991年 | 41篇 |
1990年 | 25篇 |
1989年 | 36篇 |
1988年 | 22篇 |
1987年 | 22篇 |
1986年 | 22篇 |
1985年 | 21篇 |
1984年 | 25篇 |
1983年 | 15篇 |
1982年 | 13篇 |
1981年 | 14篇 |
1980年 | 13篇 |
1979年 | 11篇 |
1978年 | 14篇 |
1977年 | 12篇 |
1975年 | 7篇 |
1973年 | 8篇 |
排序方式: 共有5669条查询结果,搜索用时 15 毫秒
921.
Hem Raj Khatri Hai Nguyen James K. Dunaway Jianglong Zhu 《Frontiers of Chemical Science and Engineering》2015,9(3):359
Reductive iodonio-Claisen rearrangement (RICR) involving λ3-iodanes and allyl or substituted-allyl silanes in fluoroalcohols, such as 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) and 2,2,2-trifluoroethanol (TFE), was studied for the synthesis of complex ortho-allyl or substituted-allyl iodoarenes. In comparison to the previously reported condition involving boron trifluoride diethyl etherate, the RICR mediated by fluoroalcohols was found to proceed more effectively. The resulting complex ortho-allyl iodoarenes are useful synthetic intermediates and can be readily converted to various heterocyclic compounds. 相似文献
922.
923.
Optical fiber sensors based on the total light transmittance are widely used to measure the volume fraction of particles in suspensions. However, the sensor response depends not only on the volume fraction but also on the particle size. The particle size effect is studied for a sensor configuration consisting of two linear arrays of fibers on each of two blocks: the emitting and receiving blocks. These two linear arrays are arranged with three adjacent fibers (one fiber on the first array, two fibers on the second array) forming a perfect triangle. The almost superimposition of the calculated sensor response versus the extinction factor for different particle sizes allows for the application of single- curve models. Two single-curve models that describe the sensor response for all particle sizes ranging from 36 to 200 microm are proposed. The models are validated by Monte Carlo simulation for different particle sizes and are valid within a detectable volume fraction. The single-curve models proposed provide an easier approach to creating a database for sensor calibration for suspended sediment concentration measurements. 相似文献
924.
Objectives
To examine the phenomenon of non‐smokers spontaneously taking action to seek help for smokers; to provide profiles of non‐smoking helpers by language and ethnic groups.Setting
A large, statewide tobacco quitline (California Smokers'' Helpline) in operation since 1992 in California, providing free cessation services in English, Spanish, Mandarin, Cantonese, Korean, and Vietnamese.Subjects
Callers between August 1992 and September 2005 who identified themselves as either white, black, Hispanic, American Indian, or Asian (n = 349 110). A subset of these were “proxies”: callers seeking help for someone else. For more detailed analysis, n = 2143 non‐smoking proxies calling from October 2004 through September 2005.Main outcome measures
Proportions of proxies among all callers in each of seven language/ethnic groups; demographics of proxies; and proxies'' relationships to smokers on whose behalf they called.Results
Over 22 000 non‐smoking proxies called. Proportions differed dramatically across language/ethnic groups, from mean (±95% confidence interval) 2.7 (0.3)% among English‐speaking American Indians through 9.3 (0.3)% among English‐speaking Hispanics to 35.3 (0.7)% among Asian‐speaking Asians. Beyond the differences in proportion, however, remarkable similarities emerged across all groups. Proxies were primarily women (79.2 (1.7)%), living in the same household as the smokers (65.0 (2.1)%), and having either explicit or implicit understandings with the smokers that calling on their behalf was acceptable (90.0 (1.3)%).Conclusions
The willingness of non‐smokers to seek help for smokers holds promise for tobacco cessation and may help address ethnic and language disparities. Non‐smoking women in smokers'' households may be the first group to target. 相似文献925.
926.
Design of pedestrian friendly vehicle bumper 总被引:2,自引:0,他引:2
Tso-Liang Teng Van-Luc Ngo Trong-Hai Nguyen 《Journal of Mechanical Science and Technology》2010,24(10):2067-2073
Car-pedestrian accidents take thousands of lives worldwide annually. Therefore, pedestrian protection is an important issue
in traffic safety. How to consider a pedestrian friendliness vehicle and then propose pedestrian protection methods are urgent
works for minimizing pedestrian injury. For designing a pedestrian friendly vehicle bumper, this study adopts the European
Enhanced Vehicle-safety Committee/ Working Group 17 (EEVC/WG17) regulations of legform impactor to bumper tests. Analyzing
the pedestrian friendliness of a vehicle bumper by using LS-DYNA is described in detail. Simulation results were analyzed
to identify the reasons for the unfriendliness. Furthermore, the analysis of the influence of bumper structure on pedestrian
leg was performed and then some guideline was suggested. The analyzed models and results obtained could help evaluate pedestrian
friendliness of a vehicle and guide the future development of pedestrian friendly vehicle technologies. 相似文献
927.
We demonstrate writing and probing of light-induced waveguides in photorefractive bulk LiNbO3 crystal using an endlessly single-mode photonic crystal fiber. The optical waveguides are written at visible wavelengths by slightly raising the ferroelectric crystal temperature to benefit from the pyroelectric-driven photorefractive effect and the guiding properties are investigated at telecom wavelengths using the same photonic crystal fiber. End butt coupling with this photonic crystal fiber enables writing and probing of optical waveguides due to the self-alignment properties of spatial solitons. 相似文献
928.
Zhizhao Che Teck Neng Wong Nam-Trung Nguyen 《International Journal of Heat and Mass Transfer》2012,55(7-8):1947-1956
Plug flow can significantly enhance heat transfer in microchannels as compared to single phase flow. Using an analytical model of flow field, heat transfer in plug flow is investigated. The constant-surface-temperature boundary condition is considered. Three stages of the heat transfer in plugs are identified: (i) development of thermal boundary layer; (ii) advection of heated/fresh fluid in the plug; and (iii) thermally fully developed flow. Due to the transport of heated fluid and fresh fluid within the plug by the recirculating flow, oscillations of the Nusselt number at high Peclet numbers are observed and explained. The effects of the Peclet number and the plug length on the heat transfer process are evaluated. The results show that short plugs are preferable to long plugs since short plugs result in high Nusselt numbers and high heat transfer indices. 相似文献
929.
Xianming Shi Tuan Anh Nguyen Zhiyong Suo Jianlin Wu Jing Gong Recep Avci 《Surface & coatings technology》2012
Nano-silica particles were deposited on acid-etched hydrophilic aluminum (Al) substrates by immersion in well-dispersed nano-silica aqueous suspension and tetramethylamonium hydroxide, followed by a heat treatment. The surface was then further treated by a reaction with fluorosilane. The hydrophobicity, surface morphology, and mechanical properties of the coated Al substrates were investigated, along with their electrochemical properties over time of exposure to two NaCl solutions (0.3% and 3% by weight). All the coated Al surfaces exhibited a water contact angle of 155–158°, i.e., superhydrophobicity. The use of nano-silica suspension significantly enhanced the hydrophobicity of the coated Al. Artificial neural networks were used to provide quantitative understanding in how the microstructure of the treated Al surface contributed to its superhydrophobicity and electrochemical properties. When Ra, total (nano-roughness + micro-roughness) exceeds 450 nm, WCA is greater than 154°, independent of the nano/micro-roughness ratio (RRNM). FESEM and AFM images of these surfaces suggest that a rough two-length-scale hierarchical structure coupled with the low surface energy of fluorosilane topcoat led to the superhydrophobicity of the formed coatings. The coating prepared with the 0.2% nano-silica suspension (vs. other concentrations) featured the highest Young's modulus and the best corrosion protection to the Al substrate in both NaCl solutions. 相似文献
930.
Dong Nguyen Thanh Mandeep Singh Pavel Ulbrich František Štěpánek Nina Strnadová 《Materials Research Bulletin》2012,47(1):42-50
We present a novel way of enhancing the utility of low cost readily available laterite by impregnating it with the α-MnO2 nanorods, thus making a composite material suitable for the removal of As(V) from aqueous media. The composites were synthesized by two methods: (i) ball-milling of a physical blend of laterite with pre-synthesized MnO2; and (ii) in situ formation of MnO2 in the presence of laterite. The BET surface area of composites prepared by both methods was markedly higher compared to un-modified laterite, and the presence of MnO2 in the composite was also confirmed by XRD analysis and TEM microscopy. The adsorption capacity for As(V) was found to be highly pH dependent and the adsorption kinetics followed a pseudo second-order kinetic model. The Langmuir adsorption isotherm was found to be the best model to describe the adsorption equilibrium of As(V) onto un-modified laterite as well both ball-milled and in situ formed composite. The adsorption capacities at room temperature and pH 7.0 were found to be 1.50 mg g?1, 8.93 mg g?1 and 9.70 mg g?1, for un-modified laterite, ball-milled and in situ formed composite, respectively. 相似文献