全文获取类型
收费全文 | 471498篇 |
免费 | 7409篇 |
国内免费 | 2610篇 |
专业分类
电工技术 | 9020篇 |
技术理论 | 5篇 |
综合类 | 1345篇 |
化学工业 | 72856篇 |
金属工艺 | 17703篇 |
机械仪表 | 13776篇 |
建筑科学 | 12349篇 |
矿业工程 | 2152篇 |
能源动力 | 11821篇 |
轻工业 | 48455篇 |
水利工程 | 4635篇 |
石油天然气 | 7660篇 |
武器工业 | 248篇 |
无线电 | 55488篇 |
一般工业技术 | 87041篇 |
冶金工业 | 87475篇 |
原子能技术 | 8272篇 |
自动化技术 | 41216篇 |
出版年
2021年 | 3907篇 |
2020年 | 2803篇 |
2019年 | 3455篇 |
2018年 | 5458篇 |
2017年 | 5439篇 |
2016年 | 6005篇 |
2015年 | 4602篇 |
2014年 | 7491篇 |
2013年 | 21454篇 |
2012年 | 13076篇 |
2011年 | 18057篇 |
2010年 | 14189篇 |
2009年 | 15613篇 |
2008年 | 16741篇 |
2007年 | 16869篇 |
2006年 | 15204篇 |
2005年 | 13514篇 |
2004年 | 12541篇 |
2003年 | 12109篇 |
2002年 | 11671篇 |
2001年 | 12064篇 |
2000年 | 11096篇 |
1999年 | 11537篇 |
1998年 | 26739篇 |
1997年 | 19177篇 |
1996年 | 14620篇 |
1995年 | 11091篇 |
1994年 | 9962篇 |
1993年 | 9703篇 |
1992年 | 7238篇 |
1991年 | 6877篇 |
1990年 | 6813篇 |
1989年 | 6556篇 |
1988年 | 6285篇 |
1987年 | 5220篇 |
1986年 | 5145篇 |
1985年 | 6097篇 |
1984年 | 5703篇 |
1983年 | 5254篇 |
1982年 | 4703篇 |
1981年 | 4960篇 |
1980年 | 4529篇 |
1979年 | 4608篇 |
1978年 | 4362篇 |
1977年 | 4758篇 |
1976年 | 6115篇 |
1975年 | 3804篇 |
1974年 | 3593篇 |
1973年 | 3673篇 |
1972年 | 3006篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
993.
The Uniform Covering by Probabilistic Rejection (UCPR) algorithm was used, in conjunction with the Soil and Water Assessment Tool (SWAT) model, to identify P loads from point source and nonpoint source polluters in the upper Etowah River basin (UERB) in Georgia. The key findings of the research are as follows. The mean absolute error was preferred over the root mean square error as a search criterion for the UCPR algorithm when water quality observations are scarce. The undocumented P load from point sources in the UERB was consistently estimated as about 43 kg/d by the proposed method; but the method was not able to identify the broiler litter application rate to the poultry/beef operation pastures. Point sources (both documented and undocumented), poultry/beef operation pastures, and forests are the three major contributors of P. During 1992-1996, on average they accounted for 36.4, 31.7, and 17.2% of P load from the UERB, respectively. 相似文献
994.
Eva M. Valero Juan L. Nieves Sérgio M. C. Nascimento Kinjiro Amano David H. Foster 《Color research and application》2007,32(5):352-360
Many spectral‐recovery methods using RGB digital cameras assume the underlying smoothness of illuminant and reflectance spectra, and apply low‐dimensional linear models. The aim of the present work was to test whether a direct‐mapping method could be used instead of a linear‐models approach to recover spectral radiances and reflectances from natural scenes with an RGB digital camera and colored filters. In computer simulations, a conventional RGB digital camera with up to three colored filters was used to image scenes drawn from a hyperspectral image database. Three measures were used to evaluate recovery with the direct‐mapping method: goodness‐of‐fit, root‐mean‐square error, and a color‐difference metric. It was found that with two and three filters both spectral radiances and reflectances could be recovered sufficiently accurately for many practical applications. With little increase in computational complexity, an RGB camera and a few colored filters can provide significantly better recovery of natural scenes than an RGB camera alone. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 352–360, 2007 相似文献
995.
The design of vehicles transporting hazardous materials has important public safety and economic implications. Conventional wisdom among industry and government has held that a thicker tank on railroad tank cars and trucks reduces risk. However, a thicker tank increases vehicle weight and thus leads to an increase in the number of shipments required to transport the same amount of product and consequently greater exposure to accidents. In this research we develop a model that analyzes the tradeoff between increased damage resistance and greater exposure to accidents in which the objective function is minimization of the probability of release. The model accounts for the reduction in tank car release probability as a function of tank thickness, and the increased exposure to accidents that occurs due to the increased number of shipments needed for the heavier car. Three variables affecting this optimal thickness are considered in this paper: the volumetric capacity of the tank, the probability of release from other, non-tank sources, and the weight capacity of the car. Sensitivity analyses using the model indicate that for any particular configuration of tank car there is an optimal thickness. This optimal thickness is affected by several factors and there is no single optimum for all tank cars. 相似文献
996.
Blair J.D. Correale A. Jr. Cranford H.C. Dombrowski D.A. Erdelyi C.K. Hoffman C.R. Lamphere J.L. Lang K.W. Lee J.K. Mullen J.M. Norman V.R. Oakland S.F. 《Solid-State Circuits, IEEE Journal of》1989,24(6):1647-1655
The authors describe a 9.02×9.02-mm chip built in 1-μm CMOS with two levels of metal and an additional mask level for fabricating capacitors. It contains both analog and digital circuits and has provisions for self-test. The function includes the transmitter, receiver, protocol handler, an microprocessor, as well as interfaces for RAM/ROM storage, IBM PC bus, IBM PS/2 bus, IBM 3174 bus, and Motorola 68000 bus. The physical design terrains are formed by 24K circuits of standard cell gates, a 10K-circuit equivalent hand-honed custom microprocessor, and an analog macro. The chip operates from a single 5-V supply, and the power consumption is 0.8 W nominal at 16 Mb/s. The chip can also be operated at 4 Mb/s 相似文献
997.
The digital multistep method generates uniform pseudorandom numbers by transforming sequences of integers obtained by multistep recursions. The statistical independence properties of these pseudorandom numbers depend on the characteristic polynomial of the recursion. We describe a method of calculating characteristic polynomials that are optimal with respect to statistical independence of pairs of successive pseudorandom numbers. Tables of such optimal characteristic polynomials for degrees ≤64 are included. 相似文献
998.
The effects of adding sodium hydroxide (NaOH), separately or in combinastion with various inorganic phosphates, on meat emulsion characteristics were studied. In comparing the addition of either NaPP or NaOH, 0.075% NaOH resulted in a higher raw emulsion pH and greater solubilized protein than 0.30% NaPP, but NaPP resulted in a more stable emulsion. The combination of 0.075% NaOH and 0.30% NaPP resulted in a soluble protein level less than when the ingredients were added individually and only slightly higher than if neither were present. The addition of NaOH (at 1 part NaOH to 4 parts phosphate) decreased cooked yields. With NaAPP and NaPP, NaOH reduced yields below that of the control. 相似文献
999.
General formulae are derived for the reflection of insolation from finite plane surfaces unto tilted sensors. These results are reduced to various special cases which are compared to known results when possible. Both circular and rectangular geometries are considered. 相似文献