全文获取类型
收费全文 | 726篇 |
免费 | 18篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 12篇 |
综合类 | 6篇 |
化学工业 | 148篇 |
金属工艺 | 14篇 |
机械仪表 | 5篇 |
建筑科学 | 79篇 |
矿业工程 | 7篇 |
能源动力 | 40篇 |
轻工业 | 68篇 |
水利工程 | 8篇 |
石油天然气 | 1篇 |
无线电 | 59篇 |
一般工业技术 | 100篇 |
冶金工业 | 69篇 |
原子能技术 | 2篇 |
自动化技术 | 127篇 |
出版年
2023年 | 3篇 |
2022年 | 14篇 |
2021年 | 14篇 |
2020年 | 5篇 |
2019年 | 8篇 |
2018年 | 14篇 |
2017年 | 14篇 |
2016年 | 21篇 |
2015年 | 19篇 |
2014年 | 18篇 |
2013年 | 37篇 |
2012年 | 27篇 |
2011年 | 43篇 |
2010年 | 24篇 |
2009年 | 27篇 |
2008年 | 39篇 |
2007年 | 38篇 |
2006年 | 37篇 |
2005年 | 32篇 |
2004年 | 18篇 |
2003年 | 21篇 |
2002年 | 21篇 |
2001年 | 21篇 |
2000年 | 16篇 |
1999年 | 20篇 |
1998年 | 19篇 |
1997年 | 11篇 |
1996年 | 8篇 |
1995年 | 8篇 |
1994年 | 8篇 |
1993年 | 13篇 |
1992年 | 8篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 9篇 |
1988年 | 8篇 |
1987年 | 5篇 |
1986年 | 9篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 4篇 |
排序方式: 共有745条查询结果,搜索用时 15 毫秒
1.
Process-based models have been extensively applied to assess the impact of landuse change on water quantity and quality at landscape scales. However, the routine application of those models suffers from large computational efforts, lack of transparency and the requirement of many input parameters. Data-based models such as Feed-Forward Multilayer Perceptrons (MLP) and Classification and Regression Trees (CART) may be used as effective models, i.e. simple approximations of complex process-based models. These data-based approaches can subsequently be applied for scenario analysis and as a transparent management tool provided climatic boundary conditions and the basic model assumptions of the process-based models do not change dramatically. In this study, we apply MLP, CART and Multiple Linear Regression (LR) to model the spatially distributed and spatially aggregated percolation in soils using weather, groundwater and soil data. The percolation data is obtained via numerical experiments with Hydrus1D. Thus, the complex process-based model is approximated using simpler data-based approaches. The MLP model explains most of the percolation variance in time and space without using any soil information. This reflects the effective dimensionality of the process-based model and suggests that percolation in the study area may be modelled much simpler than using Hydrus1D. The CART model shows that soil properties play a negligible role for percolation under wet climatic conditions. However, they become more important if the conditions turn drier. The LR method does not yield satisfactory predictions for the spatially distributed percolation however the spatially aggregated percolation is well approximated. This may indicate that the soils behave simpler (i.e. more linear) when percolation dynamics are upscaled. 相似文献
2.
Suggests that it is difficult to get an exact account of gambling behavior in Norway. It appears that gambling behavior in Norway has increased 50% during the observed 5-yr period. Little is known about the prevalence of problematic gambling. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
3.
The distribution of the sum of a finite number of identically distributed random variables is in many cases easily determined given that the variables are independent. The moments of any order of the sum can always be expressed by the moments of the single term without computational problems. However, in the case of dependency between the terms even calculation of a few of the first moments of the sum presents serious computational problems.By use of computerized symbol manipulations it is practicable to obtain exact moments of partial sums of stationary sequences of mutually dependent lognormal variables or polynomials of standard Gaussian variables. The dependency structure is induced by specifying the autocorrelation structure of the sequence of standard Gaussian variables. Particularly useful polynomials are the Winterstein approximations that distributionally fit with non-Gaussian variables up to the moments of the fourth order [Winterstein, S. R. Nonlinear vibration models for extremes and fatigue. J. Engng Mech. ASCE 114 (1988) 1772–1790]1. A method to obtain the Winterstein approximation to a partial sum of a sequence of Winterstein approximations is explained and results are given for different autocorrelation functions of the generic Gaussian sequence.The primary purpose of the investigation is to provide a tool for judging the validity of the central limit theorem argument in specific applicational situations occurring in stochastic mechanics, that is, to judge the speed of convergence of the distribution of a sum (or an integral) of mutually dependent random variables to the Gaussian distribution. The paper is closely related to the work in Ditlevsen et al. [Ditlevsen, O., Mohr, G. & Hoffmeyer, P. Integration of non-Gaussian fields. Prob. Engng Mech 11 (1996) 15–23]2. 相似文献
4.
5.
Anna-Lena Larsson Jos Solis Gunnar A. Niklasson 《Solar Energy Materials & Solar Cells》2007,91(13):1248-1252
Thin films of amorphous and polycrystalline tungsten oxide were produced by reactive dc magnetron sputtering and nanocrystalline films were deposited by advanced gas evaporation. The films were submitted to electrochemical intercalation of Li ions before infrared reflectance measurements were carried out. For crystalline films, the reflectance in the wavelength region 10–30 μm increases upon intercalation, indicating an increasing free-electron contribution. On the other hand, all the films display an increased absorption at wavelengths less than 10 μm when intercalated. The thermal emittance could be varied from about 0.5 to 0.7–0.75 by intercalation in films with thicknesses in excess of 1 μm. Both absorption and interference contribute to the emittance contrast. 相似文献
6.
A numerical method has been developed for the performance prediction of spiral wound modules with constant and tapered permeate spacers, It takes into account the pressure drop in the brine and permeate channels and makes use of a three parameter model for the mass transfer through the membrane. For a given application and operating conditions, optimum geometrical characteristics of modules can be found. Tapering the permeate spacer the specific permeation rate can be increased by 10-30%, the wider the membrane the higher the value. 相似文献
7.
Xylose fermentation by Pichia stipitis was examined using a two-stage batch process. The cells were first grown aerobically on D-xylose (5 g/L), whereafter additional xylose (10 g/L) was added and fermented during anaerobic conditions (T=30°C). The optimum pH value for a fermentation with constant pH was found to be 4.5 (maximum specific ethanol production rate 0.21 g/(g h). Forced square wave cycling of the pH between 4 and 5, and 3.5 and 5.5 (cycle time 30 min) during the fermentation stage resulted in a fermentation rate lower than the maximum rate, but with unchanged ethanol yields. 相似文献
8.
Microsomes of developing soya bean cotyledons transfer oleate from oleoyl-CoA to phosphatidylcholine (PC) by two different
mechanisms: one in which oleate transfer is accompanied by the release of free CoA and another which results in the exchange
of oleate from oleoyl-CoA for unsaturated 18-carbon fatty acids of PC. The acyl exchange can be demonstrated only when bovine
serum albumin is present in the incubation medium. ATP-dependent acyl-CoA synthetase is not involved in the exchange process,
which apparently does not require any cofactors. In light of this exchange process, the oleate desaturase system was reinvestigated
in order to determine what the actual substrate for this system is. Upon incubation of microsomes with high concentrations
of [14C] oleoyl-CoA, bovine serum albumin and NADH, it could be conclusively demonstrated that most oleic acid is desaturated while
part of the PC molecule. The amounts of [14C] linoleoyl-CoA formed could be explained entirely by the acyl exchange. The physiological significance of the acyl exchange
system is discussed. A new method for separation of acyl-CoA from other lipids and free CoA using reversed phase column chromatography
also is described. 相似文献
9.
Automation of deburring and cleaning of castings is desirable for many reasons. The major reasons are dangerous working conditions, difficulties in finding workers for cleaning sections, and improved profitability. A suitable robot cell capable of using different tools, such as cup grinders, disc grinders and rotary files, is the solution. This robot should be completed with sensors in order to keep the quality of the cleaned surface at an acceptable level. Although using sensors simplifies both the programming and quality control there are still other problems that need to be solved. These involve selection of machining data, e.g. feeding rate and grinding force in a force controlled operation based on parameters such as tool type, disc grinder and geometry. In order to decrease the programming time, a process model for disc grinders has been developed. This article investigates this process model and pays attention to problems such as wavy or burned surfaces and the effect of a robot's repetition accuracy in the results obtained. Many aspects treated in this article are quite general, and can be applied in other types of grinding operations. 相似文献
10.
Maktuba Mohid Julian F. Miller Simon L. Harding Gunnar Tufte Mark K. Massey Michael C. Petty 《Soft Computing - A Fusion of Foundations, Methodologies and Applications》2016,20(8):3007-3022
Evolution-in-materio uses evolutionary algorithms to exploit properties of materials to solve computational problems without requiring a detailed understanding of such properties. We show that using a purpose-built hardware platform called Mecobo, it is possible to solve computational problems by evolving voltages and signals applied to an electrode array covered with a carbon nanotube–polymer composite. We demonstrate for the first time that this methodology can be applied to function optimization and also to the tone discriminator problem (TDP). For function optimization, we evaluate the approach on a suite of optimization benchmarks and obtain results that in some cases come very close to the global optimum or are comparable with those obtained using well-known software-based evolutionary approach. We also obtain good results in comparison with prior work on the tone discriminator problem. In the case of the TDP we also investigated the relative merits of different mixtures of materials and organizations of electrode array. 相似文献