全文获取类型
收费全文 | 33006篇 |
免费 | 2147篇 |
国内免费 | 27篇 |
专业分类
电工技术 | 226篇 |
综合类 | 17篇 |
化学工业 | 6642篇 |
金属工艺 | 621篇 |
机械仪表 | 697篇 |
建筑科学 | 927篇 |
矿业工程 | 70篇 |
能源动力 | 569篇 |
轻工业 | 5563篇 |
水利工程 | 312篇 |
石油天然气 | 116篇 |
武器工业 | 5篇 |
无线电 | 1224篇 |
一般工业技术 | 5608篇 |
冶金工业 | 8035篇 |
原子能技术 | 116篇 |
自动化技术 | 4432篇 |
出版年
2024年 | 59篇 |
2023年 | 289篇 |
2022年 | 315篇 |
2021年 | 788篇 |
2020年 | 667篇 |
2019年 | 751篇 |
2018年 | 1363篇 |
2017年 | 1311篇 |
2016年 | 1361篇 |
2015年 | 1045篇 |
2014年 | 1232篇 |
2013年 | 2592篇 |
2012年 | 1928篇 |
2011年 | 1753篇 |
2010年 | 1452篇 |
2009年 | 1291篇 |
2008年 | 1279篇 |
2007年 | 1215篇 |
2006年 | 794篇 |
2005年 | 682篇 |
2004年 | 645篇 |
2003年 | 570篇 |
2002年 | 556篇 |
2001年 | 412篇 |
2000年 | 383篇 |
1999年 | 437篇 |
1998年 | 2373篇 |
1997年 | 1614篇 |
1996年 | 1027篇 |
1995年 | 620篇 |
1994年 | 468篇 |
1993年 | 555篇 |
1992年 | 207篇 |
1991年 | 208篇 |
1990年 | 153篇 |
1989年 | 154篇 |
1988年 | 160篇 |
1987年 | 138篇 |
1986年 | 118篇 |
1985年 | 141篇 |
1984年 | 126篇 |
1983年 | 98篇 |
1982年 | 130篇 |
1981年 | 145篇 |
1980年 | 154篇 |
1979年 | 78篇 |
1978年 | 80篇 |
1977年 | 277篇 |
1976年 | 621篇 |
1973年 | 63篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
91.
M A M Maqueda Sergio A Martinez D Narváez Miriam G Rodriguez Ricardo Aguilar Victor M Herrero 《Water science and technology》2006,53(11):135-142
The Mexican petrochemical industry, Morelos S.A. de C.V., is one of the biggest and more important petroleum industries in Mexico and Latin America. It has an activated sludge system to treat its wastewater flow, which is approximately 7,000 m3/d. The wastewater contains volatile organic carbon substances classified as toxics. The old surface aeration system was changed for fine bubble diffusers; however, one major drawback of the new aeration system is that the temperature in the bioreactor has increased due to the compression of the air, which at the compressor exit reaches 85 degrees C. This effect results in the temperature in the bioreactor attaining 32 degrees C during the fall, whereas in the spring and summer, the bioreactor temperature reaches higher values than 40 degrees C. The high temperatures reduce the microorganism activity and cause a higher volatilisation rate of volatile compounds, among other effects, which affect the performance of the biological treatment. This work was performed to obtain a better modelling of the wastewater treatment from the petrochemical industry. The model describes the effect of the temperature on the performance of the biological treatment. The model was obtained from tests that were carried out in laboratory reactors with 14 L capacity, which were operated at different temperatures (from 30 to 45 degrees C), with the same wastewater and conditions as the actual system. 相似文献
92.
93.
There are some foods that contain mutagenic or carcinogenic agents, some of which occur naturally and others that may be formed during preparation or cooking. Several foods such as legumes, also contain natural antimutagens and/or anticarcinogens. Lupine is one such legume that contains high amounts of protein (40%) and oils (14%). About 90 species of lupine have been reported throughout Mexico. However, the use of this crop as a source of food has been limited by the presence of antinutritional agents such as phenolic compounds (PC), carbohydrates (CH) and quinolizidinic alkaloids (Qas). It has also been suggested that consuming these compounds can affect human health and may even reduce the risk of disease. The objective of this work was to determine the effect of PC, CH and Qas, isolated and quantified from Lupinus campestris on the mutagenicity of 1-nitropyrene (1-NP) as a model mutagen and we used the Salmonella typhimurium tester strain YG1024 by the Kado microsuspension method. The results indicate that L. campestris seeds have 11 mg (+)catechin equivalent g(-1) seed coat; 120.3 mg g(-1) seeds and 2.13 mg g(-1) seeds of PC, CH and Qas, respectively. 1-NP mutagenicity was inhibited by 86% for PC, 76% for CH and 75% for Qas at concentrations of 200, 512 and 13.6 microg/tube, respectively. 相似文献
94.
Nina Georgieva Kostova Elka Kraleva Alla A. Spojakina Erika Godocikova Peter Balaz 《Journal of Materials Science》2007,42(10):3321-3325
The Al-MCM-41 has been used as support to prepare Mo-containing catalysts. The 12- molybdophosphoric heteropoly acid (HPMo)
is used as initial compound. The catalysts are synthesized by two different methods: incipient impregnation with aqueous solution
of the acid and mechanochemical synthesis. The samples were tested in the reaction of the thiophene hydrodesulfurization after
activation with mixture H2 + H2S. The effect of the preparation method of the catalysts on their physicochemical and catalytic properties has been studied.
A partial destruction of the loaded compound is observed in mechanochemically treated sample whereas the aggregates are formed
from the particles of different size in the impregnated sample. The specific surface area of the sample prepared by mechanical–chemical
treatment decreases 2–3 times, while the total pore volume is about four times lower. The HDS activity is higher on the impregnated
sample than on the mechanochemically treated one. 相似文献
95.
Igor Studart Medeiros Erika R. M. Andreeta Antonio C. Hernandes 《Journal of Materials Science》2007,42(11):3874-3877
96.
A. Hernández O. Arés C. Hart D. Domínguez H. Pastoriza A. Butera 《Journal of Low Temperature Physics》2004,135(1-2):119-122
The response of mesoscopic superconductors to an ac magnetic field is investigated both experimentally and with numerical simulations. We study small square samples with dimensions of the order of the penetration depth. We obtain the ac susceptibitity χ=χ′+iχ″ at microwave frequencies as a function of the dc magnetic field H dc. We find that the dissipation, given by x″, has a non monotonous behavior in mesoscopic samples. In the numerical simulations we obtain that the dissipation increases before the penetration of vortices and then it decreases abruptly after vortices have entered, the sample. This is verified experimentally, where we find that χ″ has strong oscillations as a function of H dc in small squares of Pb. 相似文献
97.
98.
99.
Per Johan Råsmark Čestmír Koňák Petr Štěpánek Christer Elvingson 《Polymer Bulletin》2005,54(4-5):335-342
Summary Dynamic light scattering was used to investigate the dynamics of sodium poly(styrene sulfonate) and fully neutralized poly(acrylic acid) gels as a function of the degree of swelling and weight ratio of cross-linking agent. It was shown that the collective diffusion coefficient increases with increasing degree of swelling and that the diffusion coefficient shows stronger concentration dependence than predicted by scaling arguments. For gel samples measured at the swelling equilibrium, the diffusion coefficient increases with increasing gel concentration for both gel systems. 相似文献
100.
Summary Electropolymerization of o-(CH3O)2C6H4 (Veratrole) in dry acetonitrile/tetrabutylammonium tetrafluoroborate at platinum electrode, yields a green polymeric conducting solid. As the pressure is increased, the material becomes more conductive, but sharp changes towards lower conductivity occur at 4.2 and 6.2 metric tons pressure, probably due to phase transitions. The photoconductivity shows an exponential increase as temperature is increased, but it shows reversible changes at 200 K, 225 K and 250 K during slow warming, also attributable to phase transitions. Photoconductivity of Polyveratrole increases with the radiation frequency, being higher under blue light than under red of infrared radiation and there is a linear increase of photoconductivity with radiation density. Conductivity transients show that the conductivity increases exponentially with time to the saturation point within few minutes, and it also decreases exponentially when the light is turned off and the circuit is open. This behaviour can be explained by formation and encounter of electron and hole as current carriers. A preliminary study indicates a piezoelectric effect for the material. absorption spectroscopy allowed the measurements of the material band gap. 相似文献