全文获取类型
收费全文 | 273001篇 |
免费 | 2488篇 |
国内免费 | 692篇 |
专业分类
电工技术 | 5817篇 |
综合类 | 209篇 |
化学工业 | 36207篇 |
金属工艺 | 14027篇 |
机械仪表 | 11269篇 |
建筑科学 | 5358篇 |
矿业工程 | 1488篇 |
能源动力 | 5363篇 |
轻工业 | 15649篇 |
水利工程 | 2797篇 |
石油天然气 | 4201篇 |
武器工业 | 7篇 |
无线电 | 34358篇 |
一般工业技术 | 57117篇 |
冶金工业 | 51217篇 |
原子能技术 | 4622篇 |
自动化技术 | 26475篇 |
出版年
2021年 | 1315篇 |
2020年 | 1006篇 |
2019年 | 1352篇 |
2018年 | 10717篇 |
2017年 | 11269篇 |
2016年 | 6987篇 |
2015年 | 2078篇 |
2014年 | 2784篇 |
2013年 | 8144篇 |
2012年 | 7136篇 |
2011年 | 14532篇 |
2010年 | 13040篇 |
2009年 | 12615篇 |
2008年 | 12830篇 |
2007年 | 14846篇 |
2006年 | 5756篇 |
2005年 | 8970篇 |
2004年 | 7280篇 |
2003年 | 6760篇 |
2002年 | 5567篇 |
2001年 | 5404篇 |
2000年 | 5074篇 |
1999年 | 5482篇 |
1998年 | 15652篇 |
1997年 | 10345篇 |
1996年 | 7971篇 |
1995年 | 5819篇 |
1994年 | 5063篇 |
1993年 | 5059篇 |
1992年 | 3413篇 |
1991年 | 3299篇 |
1990年 | 3230篇 |
1989年 | 3049篇 |
1988年 | 2798篇 |
1987年 | 2244篇 |
1986年 | 2315篇 |
1985年 | 2615篇 |
1984年 | 2321篇 |
1983年 | 2071篇 |
1982年 | 1907篇 |
1981年 | 2051篇 |
1980年 | 1793篇 |
1979年 | 1665篇 |
1978年 | 1658篇 |
1977年 | 2021篇 |
1976年 | 2702篇 |
1975年 | 1423篇 |
1974年 | 1374篇 |
1973年 | 1320篇 |
1972年 | 1125篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
S. A. Abramov A. A. Bogolyubskaya V. A. Rostovtsev V. F. Edneral 《Programming and Computer Software》2007,33(2):55-59
An annual report on meetings of the scientific research seminar on computer algebra is presented. 相似文献
992.
A compound concentrator guide has been investigated that provides uniform energy distribution over the receiver. The values of the focal parameters of the parabolas that form the quasi-parabolic guide curve have been determined. The parametric equations of the curve along which the parabolas foci travel have been set up. Arrangement variants of the guide curve branches have been considered, and the compound concentrators have been assessed. 相似文献
993.
Waters in the Great Lakes basin contain more than 400 contaminant chemicals that potentially affect fishery resources, commerce, and human inhabitants. We determined in the laboratory the effects of selected contaminants on the toxicity of the widely used lampricides TFM (3-trifluoromethyl-4-nitrophenol) and Bayer 73 (2′,5-dichloro-4′-nitrosalicylanilide) to three species of fish—rainbow trout (Salmo gairdneri), white sucker (Catostomus commersoni), and fathead minnow (Pimephales promelas). The fish were exposed to paired mixtures of lampricides and selected contaminants in standardized, acute static toxicity tests to determine the resulting type of response—less than additive, additive, or greater than additive (synergistic). As expected, the toxicities of combinations of lampricides with organic pesticides, metal, industrial or municipal pollutants, and tannic acid were mostly additive. However, the toxicity of a combination of TFM, Delnav, and malathion was synergistic, and extremely small quantities of each chemical became lethal when mixed. The concentration that produced 50% mortality was 1.64 mg/L for TFM alone but only 0.041 mg/L for TFM with the pesticides. Toxicities of the pesticides in the combination also increased commensurately. The triple combination of chemicals produced extraordinary synergism and effectively demonstrated the hazards that may result if certain chemical combinations occur in the aquatic environment. However, synergism is not the only kind of toxic action that produces hazards to aquatic organisms. All three types of toxic action are of concern because toxic units produced by contaminant chemicals add to the toxic units of applied management chemicals. Since the toxicity of the majority of chemical combinations is simply additive, this cumulative toxic action contributes more total units to aquatic environments than the extreme actions of less than additive and synergism. The toxicity of the lampricide TFM, as well as other management chemicals, is reinforced by the presence of any contaminant that contributes additional units of toxicity. Therefore, all types of cumulative toxic action should be of concern to people and agencies involved with protecting the environment. 相似文献
994.
995.
A Graphene Field-Effect Device 总被引:2,自引:0,他引:2
In this letter, a top-gated field-effect device (FED) manufactured from monolayer graphene is investigated. Except for graphene deposition, a conventional top-down CMOS-compatible process flow is applied. Carrier mobilities in graphene pseudo-MOS structures are compared to those obtained from the top-gated Graphene-FEDs. The extracted values exceed the universal mobility of silicon and silicon-on-insulator MOSFETs 相似文献
996.
Opasjumruskit K. Thanthipwan T. Sathusen O. Sirinamarattana P. Gadmanee P. Pootarapan E. Wongkomet N. Thanachayanont A. Thamsirianunt M. 《Pervasive Computing, IEEE》2006,5(1):54-61
Emerging RFID technology lets us embed sensors into a very small chip, creating a wireless sensing device. So, we set out to develop such a single-chip versatile temperature sensor. We also wanted to be able to transfer our design to an implantable temperature sensor for an animal healthcare application with minimal structural modification. We discuss the implementation of temperature sensor. The fully integrated complementary metal-oxide semiconductor (CMOS) batteryless device measures temperature and performs calibration to compensate for the sensor's inherent imperfections. An RF link using passive RFID's backscattering technique wirelessly transmits the data to a reading device while extracting power from the same "airwave," letting the device operate anywhere and last almost forever. The entire microchip, including the temperature sensor, consumes less than a few microamperes over a half a second, so the scanning device can capture data from longer read distances. 相似文献
997.
S. Kar T. Searles E. Lee G. B. Viswanathan H. L. Fraser J. Tiley R. Banerjee 《Metallurgical and Materials Transactions A》2006,37(3):559-566
The development of a set of computational tools that permit microstructurally based predictions for the tensile properties
of commercially important titanium alloys, such as Ti-6Al-4V, is a valuable step toward the accelerated maturation of materials.
This paper will discuss the development of neural network models based on a Bayesian framework to predict the yield and ultimate
tensile strengths of Ti-6Al-4V at room temperature. The development of such rules-based model requires the population of extensive
databases, which in the present case are microstructurally based. The steps involved in database development include producing
controlled variations of the microstructure using novel approaches to heat treatments, the use of standardized stereology
protocols to characterize and quantify microstructural features rapidly, and mechanical testing of the heat-treated specimens.
These databases have been used to train and test neural network models for prediction of tensile properties. In addition,
these models have been used to identify the influence of individual microstructural features on the tensile properties, consequently
guiding the efforts toward development of more robust mechanistically based models. Based on the neural network model, it
is possible to investigate the influence of individual microstructural features on the tensile properties, and in certain
cases these dependencies can point toward unrecognized phenomena. For example, the apparently unexpected trend of increase
in tensile strength with increasing prior β-grain size has led to the determination of the pronounced role of the basketweave microstructure in strengthening these alloys,
especially in case of larger prior β grains.
This article is based on a presentation made in the symposium “Computational Aspects of Mechanical Properties of Materials,”
which occurred at the 2005 TMS Annual Meeting, February 13–17, 2005, in San Francisco, CA, under the auspices of the MPMD-Computational
Materials Science & Engineering (Jt. ASM-MSCTS) Committee. 相似文献
998.
The effect of the growth dynamics of heterotrophs on the composition and properties of peat lipids was demonstrated. Microbiological processes resulted in a considerable change in the amounts of water-soluble polysaccharide and polyphenol fractions. The lipid content remained practically unchanged under various model experiment conditions. In this case, an increase in the concentration of alkanes and the antioxidant activity of lipids was observed. The accumulation of antioxidants and an increase in the amount of chrysenes in lipids support the role of a microbiological factor in the origin of hydrocarbons. 相似文献
999.
An unconventional method of determining the color of clay and ceramic materials in air-dry and calcined states in equal-color coordinates of the color space using the color characteristics (saturation, hue, yellow hue, lightness, color coordinate) is employed to classify clays from the Gzhel’ deposit. The method is recommended for adjusting the color range of ceramic articles. 相似文献
1000.