全文获取类型
收费全文 | 1918篇 |
免费 | 83篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 18篇 |
综合类 | 1篇 |
化学工业 | 336篇 |
金属工艺 | 112篇 |
机械仪表 | 42篇 |
建筑科学 | 38篇 |
矿业工程 | 2篇 |
能源动力 | 106篇 |
轻工业 | 111篇 |
水利工程 | 5篇 |
石油天然气 | 3篇 |
无线电 | 205篇 |
一般工业技术 | 497篇 |
冶金工业 | 145篇 |
原子能技术 | 22篇 |
自动化技术 | 363篇 |
出版年
2024年 | 7篇 |
2023年 | 33篇 |
2022年 | 64篇 |
2021年 | 58篇 |
2020年 | 52篇 |
2019年 | 69篇 |
2018年 | 88篇 |
2017年 | 78篇 |
2016年 | 87篇 |
2015年 | 59篇 |
2014年 | 71篇 |
2013年 | 145篇 |
2012年 | 109篇 |
2011年 | 121篇 |
2010年 | 92篇 |
2009年 | 97篇 |
2008年 | 95篇 |
2007年 | 84篇 |
2006年 | 61篇 |
2005年 | 55篇 |
2004年 | 48篇 |
2003年 | 36篇 |
2002年 | 35篇 |
2001年 | 26篇 |
2000年 | 21篇 |
1999年 | 21篇 |
1998年 | 19篇 |
1997年 | 28篇 |
1996年 | 18篇 |
1995年 | 21篇 |
1994年 | 22篇 |
1993年 | 19篇 |
1992年 | 17篇 |
1991年 | 17篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1988年 | 19篇 |
1987年 | 9篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1984年 | 16篇 |
1983年 | 6篇 |
1982年 | 16篇 |
1981年 | 6篇 |
1979年 | 4篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1973年 | 6篇 |
1972年 | 2篇 |
1971年 | 4篇 |
排序方式: 共有2006条查询结果,搜索用时 15 毫秒
991.
In this work, direct laser interference patterning of hydrogen-free tetrahedral amorphous carbon (ta-C) thin films using an ultraviolet (UV) nanosecond pulsed laser is investigated. Using this method, line-like arrays with submicrometer resolution were fabricated. In particular, a 180 nm grating period was successfully produced. In addition, it was found that depending on the laser energy density, the tetrahedral carbon film either graphitizes or crystallizes locally at the interference maxima positions. Furthermore, the crystallization is accompanied with a delamination of the film and even the formation of carbon fiber-like structures. The electrical properties of graphitized and delaminated ta-C were measured. 相似文献
992.
Dr. Evangelos C. Tatsis Dr. Eva Eylert Dr. Ravi Kumar Maddula Dr. Elena Ostrozhenkova Dr. Aleš Svatoš Prof. Dr. Wolfgang Eisenreich Dr. Bernd Schneider 《Chembiochem : a European journal of chemical biology》2014,15(11):1645-1650
Nudicaulins are unique alkaloids responsible for the yellow color of the petals of some papaveraceaous plants. To elucidate the unknown biosynthetic origin of the skeleton, a 13CO2‐pulse/chase experiment was performed with growing Papaver nudicaule plants. 13C NMR analysis revealed more than 20 multiple 13C‐enriched isotopologues in nudicaulins from the petals of 13CO2‐labeled plants. The complex labeling pattern was compared with the isotopologue composition of a kaempferol derivative that was isolated from petals of the same 13CO2‐labeled plants. The deconvolution of the labeling profiles indicated that the nudicaulin scaffold is assembled from products or intermediates of indole metabolism, the phenylpropanoid pathway, and the polyketide biosynthesis. Naringenin‐type compounds and tryptophan/tryptamine are potential substrates for the condensation reaction finally generating the aglycone skeleton of nudicaulins. 相似文献
993.
Chromium substituted polycrystalline Yttrium Iron Garnets (Y3Fe5–xCrxO12 with x = 0 to 0.5) were prepared in single‐phase form with lattice constant in the range of 12.3775 Å to 12.3560 Å. All samples exhibit ferrimagnetic transition with transition temperature (Tc) in the range of 547 K for x = 0 to 494 K for x = 0.5. The saturation magnetization value at room temperature is found to increase with Cr concentration that is, from 24.8 to 26.6 emu/g and this is attributed to the preferential occupation of Cr3+ ions at octahedral site of Fe3+ ions. The frequency dependence of impedance data shows the relaxation and thermal activation of charge carriers across grains and grain boundaries. The complex impedance spectra were modeled by considering equivalent circuits having contributions from the resistance and constant phase element due to grains and grain boundaries and capacitance across grain boundaries. The dielectric constant is found to increase from 20 to 52 as the Cr concentration is increased and it is attributed to hopping of charge carriers across Fe2+–Fe3+ centers. The Arrhenius plots of relaxation time of charge carriers and conductivity show an anomaly in the vicinity of ferrimagnetic transition temperature and it highlights the presence of magneto‐electric coupling. 相似文献
994.
In this paper, we numerically investigate the heat transfer in a continuously moving convective‐radiative fin with variable thermal conductivity by using Haar wavelets. Heat is dissipated to the environment simultaneously through convection and radiation. The effect of various significant parameters—in particular the thermal conductivity parameter a, convection‐sink temperature θa, radiation‐sink temperature θs, convection‐radiation parameter Nc, radiation‐conduction parameter Nr, and Peclet number Pe—on the temperature profile of the fin are discussed and interpreted physically through illustrative graphs. Computational results obtained by the present method are in good agreement with the standard numerical solutions. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21038 相似文献
995.
Transient surface heat flux prediction, from temperature signals using one‐dimensional heat conduction modeling, is the major objective of present investigation. The techniques reported in the literature based on spline ?tting (linear and cubic) and least square polynomial ?tting of temperature data are evaluated for prediction of surface heat flux through various analytical modeling. In addition, a Laplace‐based technique is also incorporated here to predict surface heat flux where the least square polynomial ?tting technique is used to discretize the temperature data. The temperature time histories obtained from an in‐house built, one‐dimensional ?nite volume computation solver, and experiments (i.e., shock tunnel testing and flight data) are considered for the performance assessment of these methods. Heat flux recovery from all the methods for smooth temperature signals is seen to be in good agreement with a reasonable accuracy of ±5%. However, it has been noticed that the spline based ?tting techniques supersede the polynomial‐based ?tting techniques for prediction of heat flux from discontinuous or noisy temperature signals. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21050 相似文献
996.
Ranga Rao Ambati Deepika Gogisetty Ravishankar Gokare Aswathanarayana Sarada Ravi Panduranga Narasimharao Bikkina Lei Bo 《Critical reviews in food science and nutrition》2019,59(12):1880-1902
Microalgae are rich source of various bioactive molecules such as carotenoids, lipids, fatty acids, hydrocarbons, proteins, carbohydrates, amino acids, etc. and in recent Years carotenoids from algae gained commercial recognition in the global market for food and cosmeceutical applications. However, the production of carotenoids from algae is not yet fully cost effective to compete with synthetic ones. In this context the present review examines the technologies/methods in relation to mass production of algae, cell harvesting for extraction of carotenoids, optimizing extraction methods etc. Research studies from different microalgal species such as Spirulina platensis, Haematococcus pluvialis, Dunaliella salina, Chlorella sps., Nannochloropsis sps., Scenedesmus sps., Chlorococcum sps., Botryococcus braunii and Diatoms in relation to carotenoid content, chemical structure, extraction and processing of carotenoids are discussed. Further these carotenoid pigments, are useful in various health applications and their use in food, feed, nutraceutical, pharmaceutical and cosmeceutical industries was briefly touched upon. The commercial value of algal carotenoids has also been discussed in this review. Possible recommendations for future research studies are proposed. 相似文献
997.
Ravi K. Laxman Arthur K. Hochberg David A. Roberts Raymond N. Vrtis Saul Ovalle 《Advanced functional materials》1996,6(2):93-99
Deposition processes and film properties of plasma-enhanced chemical vapour deposition (PECVD) films derived from fluoroalkylsilanes are described. The fluorinated silicon dioxide (FSG) films have lower dielectric constants (3.3–3.7) than non-fluorinated silicon dioxide films (>4). With similar dielectric strengths, the reduced capacitance obtained with FSG films makes them useful as intermetal dielectrics (IMDs). The films are characterised using Fourier transform infrared spectroscopy, Auger electron spectroscopy, ellipsometry and capacitance-voltage measurements. Characterisation of the changes in FSG upon exposure to ambient conditions and a method for stabilising the films are presented 相似文献
998.
Bhatt Ravi Rai Anuj Chanda Sukalpa Krishnan Narayanan C. 《International Journal on Document Analysis and Recognition》2023,26(1):51-63
International Journal on Document Analysis and Recognition (IJDAR) - Annotating words in a historical document image archive for word image recognition purpose demands time and skilled human... 相似文献
999.
M. Ravi Tasher Ali Sheikh Yaka Bulo 《International Journal of Communication Systems》2023,36(9):e5470
The user far from the base station (BS) can decode the signal via direct transmission or a relay network, but it cannot achieve higher throughput because of its high error probability. The MIMO-NOMA-Relay networks are replaced by MIMO-NOMA-RIS to achieve higher throughput in the proposal. The MIMO-NOMA-RIS sends a superimposed signal to the receiver using a multiple RIS beam scanning algorithm. They can improve the strength of the signal as well as improve the throughput and reduce the probability of error. As more reflecting surface area increases, the strength of the beam-forming signal also increases, which means that the user could receive more signal strength than the direct transmission, amplify and forward (A&F) relay network. In multi-user case, use the max–min power control algorithm (MMPCA) to allocate optimum power to a weaker channel strength user and achieve an optimum result. Method 1 used a single user with RIS to find the system equations. In both single-user and multi-user scenarios, we use MIMO-NOMA-RIS. Our proposed method's complexity is low because of its simplicity. In our proposed method, the MMPCA is used for optimum power allocation, and the resulting non-convex function is converted into a convex one by using successive convex approximations. The result section shows that the RIS achieved the highest throughput and the lowest probability of error. 相似文献
1000.
Ramesh Shunmugiah Veluchamy Rose Mary Shameena Beegum Puthiya P. Ravi Pandiselvam Sugatha Padmanabhan Neenu Sathyan Sandip Shil Vittal Niral Manikantan Musuvadi Ramarathinam Ankanahalli Narayanashetty Lokesha Kodathalu Seetharamaiah Shivashankara Kukkehalli Balachandra Hebbar 《Journal of the science of food and agriculture》2023,103(1):370-379