全文获取类型
收费全文 | 233072篇 |
免费 | 25672篇 |
国内免费 | 16103篇 |
专业分类
电工技术 | 16601篇 |
技术理论 | 9篇 |
综合类 | 24427篇 |
化学工业 | 20303篇 |
金属工艺 | 8988篇 |
机械仪表 | 19872篇 |
建筑科学 | 24088篇 |
矿业工程 | 8161篇 |
能源动力 | 8682篇 |
轻工业 | 15666篇 |
水利工程 | 8547篇 |
石油天然气 | 10092篇 |
武器工业 | 3031篇 |
无线电 | 23751篇 |
一般工业技术 | 22118篇 |
冶金工业 | 8511篇 |
原子能技术 | 2977篇 |
自动化技术 | 49023篇 |
出版年
2024年 | 1075篇 |
2023年 | 3090篇 |
2022年 | 5906篇 |
2021年 | 6961篇 |
2020年 | 7203篇 |
2019年 | 5997篇 |
2018年 | 5843篇 |
2017年 | 7303篇 |
2016年 | 8582篇 |
2015年 | 9285篇 |
2014年 | 14675篇 |
2013年 | 14529篇 |
2012年 | 17561篇 |
2011年 | 19024篇 |
2010年 | 14302篇 |
2009年 | 14530篇 |
2008年 | 14321篇 |
2007年 | 16949篇 |
2006年 | 14578篇 |
2005年 | 12433篇 |
2004年 | 10438篇 |
2003年 | 8790篇 |
2002年 | 7030篇 |
2001年 | 5812篇 |
2000年 | 4881篇 |
1999年 | 3985篇 |
1998年 | 3359篇 |
1997年 | 2845篇 |
1996年 | 2347篇 |
1995年 | 1925篇 |
1994年 | 1691篇 |
1993年 | 1279篇 |
1992年 | 1158篇 |
1991年 | 858篇 |
1990年 | 729篇 |
1989年 | 605篇 |
1988年 | 504篇 |
1987年 | 334篇 |
1986年 | 310篇 |
1985年 | 269篇 |
1984年 | 286篇 |
1983年 | 277篇 |
1982年 | 224篇 |
1981年 | 114篇 |
1980年 | 110篇 |
1979年 | 71篇 |
1978年 | 54篇 |
1977年 | 48篇 |
1976年 | 45篇 |
1959年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
A theory is presented that explains how the visual system infers the lightness, opacity, and depth of surfaces from stereoscopic images. It is shown that the polarity and magnitude of image contrast play distinct roles in surface perception, which can be captured by 2 principles of perceptual inference. First, a contrast depth asymmetry principle articulates how the visual system computes the ordinal depth and lightness relationships from the polarity of local, binocularly matched image contrast. Second, a global transmittance anchoring principle expresses how variations in contrast magnitudes are used to infer the presence of transparent surfaces. It is argued that these principles provide a unified explanation of how the visual system computes the 3-D surface structure of opaque and transparent surfaces. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
62.
Novel lamellar mesostructured hydroxyapatites have firstly been synthesized by template-assisted technique. The mild and nontoxic surfactant, phosphoric acid monododecyl ester (MAP), is used to act as a structure-directing template. The structure of sample was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Scanning electron microscope and Transmission electron microscopy. The results indicate that the obtained sample is a well-organized lamellar mesostructured hydroxyapatite with a uniform layer spacing of 3.64 nm. 相似文献
63.
64.
65.
66.
Heat resistant coatings are required primarily for stacks, exhaust pipes, reactors, space crafts and similar equipments that are permanently or occasionally exposed to elevated temperatures. High-temperature coatings are generally based on silicone resin with ceramic and metallic pigments. In this study, iron oxide, cobalt oxide (thermo chromic compound) and aluminum oxide are used for the preparation of four new types of coloured pigments. The thermal resistant characteristics of these ceramic pigments were studied by differential thermal analysis, thermo gravimetric analysis and differential scanning calorimetric analysis. These ceramic pigments are found to be thermally stable up to 400 °C. 相似文献
67.
A new method of studying the corrosion inhibition mechanism of rare earth metal(REM) on LC4 Al alloy with the spilt cell technique was studied. The principle and experimental method of the spilt cell technique were analyzed. By measuring the change of net-electric current between the two electrodes caused by the change of the amount of oxygen in the solution and the addition of CeCl3, the influence of corrosive performance of CeCl3 on LC4 super-power aluminum alloy in the 0.1 mol·L−1 NaCl solution was investigated. Meanwhile, the conditional changes of pH values, CeCl3 solution, additire and time of performance were also studied. Finally, the features of electrode surface were revealed by using SEM and X-ray energy-dispersive spectrometry (EDS). By combining these with other electric chemical techniques, such as potential-time curve, polarization curve et al. 相似文献
68.
Uwe Kruger David Antory Juergen Hahn George W. Irwin Geoff McCullough 《Computers & Chemical Engineering》2005,29(11-12):2355
Although principal component analysis (PCA) is an important tool in standard multivariate data analysis, little interest has been devoted to assessing whether the underlying relationship within a given variable set can be described by a linear PCA model or whether nonlinear PCA must be utilized. This paper addresses this deficiency by introducing a nonlinearity measure for principal component models. The measure is based on the following two principles: (i) the range of recorded process operation is divided into smaller regions; and (ii) accuracy bounds are determined for the sum of the discarded eigenvalues. If this sum is within the accuracy bounds for each region, the process is assumed to be linear and vice versa. This procedure is automated through the use of cross-validation. Finally, the paper shows the utility of the new nonlinearity measure using two simulation studies and with data from an industrial melter process. 相似文献
69.
A feasibility analysis methodology adopted from reactive distillation is applied to membrane reactors. A model is formulated to depict the reactive liquid phase composition on the retentate side of a continuous type membrane reactor. The effects of both the chemical reaction kinetics and the membrane mass transfer kinetics on the feasible products are elucidated by means of retentate phase diagrams and bifurcation analysis. The proposed method can be applied to various membrane processes, independent of the specific structure of the membrane. Two quaternary reaction systems are considered to illustrate the methodology. In the first hypothetical system, it is shown how selective membranes can influence the sequence of effective volatilities which in turn affects the feasible products of the system. In the second example of practical importance, i.e. the heterogeneously catalysed synthesis of propyl acetate coupled with permeation through a porous polycarbonate membrane, the dusty gas model is applied to describe the component fluxes through the membrane. For the latter reaction system, the existence of reactive arheotrope is demonstrated. Arheotropes represent mass transfer controlled feasible products of membrane separation process. 相似文献
70.
在第一部分综合讨论的基础上对甘三酯立体专一分析方法作了初步探讨。以液体油(菜油)及固体脂(猪脂)为基质,系统地研究了这一分析方法,取得了经验并补充了一些具体验证方法。分析液体油的结果与文献数据相一致,分析猪脂的结果欠佳,还存在一些问题需待进一步研究。 相似文献