全文获取类型
收费全文 | 12681篇 |
免费 | 993篇 |
国内免费 | 372篇 |
专业分类
电工技术 | 292篇 |
综合类 | 1283篇 |
化学工业 | 2003篇 |
金属工艺 | 398篇 |
机械仪表 | 961篇 |
建筑科学 | 2492篇 |
矿业工程 | 262篇 |
能源动力 | 333篇 |
轻工业 | 835篇 |
水利工程 | 279篇 |
石油天然气 | 206篇 |
武器工业 | 53篇 |
无线电 | 565篇 |
一般工业技术 | 1483篇 |
冶金工业 | 304篇 |
原子能技术 | 202篇 |
自动化技术 | 2095篇 |
出版年
2024年 | 32篇 |
2023年 | 127篇 |
2022年 | 146篇 |
2021年 | 300篇 |
2020年 | 300篇 |
2019年 | 237篇 |
2018年 | 285篇 |
2017年 | 298篇 |
2016年 | 384篇 |
2015年 | 424篇 |
2014年 | 722篇 |
2013年 | 723篇 |
2012年 | 664篇 |
2011年 | 828篇 |
2010年 | 756篇 |
2009年 | 814篇 |
2008年 | 760篇 |
2007年 | 912篇 |
2006年 | 756篇 |
2005年 | 648篇 |
2004年 | 586篇 |
2003年 | 531篇 |
2002年 | 443篇 |
2001年 | 318篇 |
2000年 | 320篇 |
1999年 | 280篇 |
1998年 | 233篇 |
1997年 | 200篇 |
1996年 | 186篇 |
1995年 | 130篇 |
1994年 | 92篇 |
1993年 | 90篇 |
1992年 | 102篇 |
1991年 | 65篇 |
1990年 | 61篇 |
1989年 | 41篇 |
1988年 | 47篇 |
1987年 | 31篇 |
1986年 | 36篇 |
1985年 | 42篇 |
1984年 | 26篇 |
1983年 | 16篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1977年 | 4篇 |
1965年 | 6篇 |
1963年 | 3篇 |
1956年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
R. T. DeHoff 《Journal of microscopy》1985,138(2):143-151
Elements of surfaces that bound a phase (β) in a two phase mixture (α+β) may be classified as: (a) convex (++) if both principal curvatures are positive; (b) concave (? ?) if both are negative; and (c) saddle (+ ?) if one is positive and the other negative. This classification excludes the limiting cases for which one or both of the principal curvatures is zero. The traces of these surfaces that form the boundaries of the β areas on a representative two dimensional section may also be: (a) convex (+) if the local curvature is positive; or (b) concave (?) if it is negative. Line intercepts may be tabulated separately for intersections with convex (+) and concave (?) segments of boundary. This paper presents a derivation of fundamental stereological formulae that relate these counting measurements to three-dimensional geometric properties of the structure they sample. 相似文献
22.
冲切成槽法施工薄壁砼防渗墙,是一种新型防渗墙施工方法,它是利用特制的扁钻头对风化基岩或卵石层进行冲切成槽的施工方法,在工艺上有着较强的优越性. 相似文献
23.
林梦雷 《吉林化工学院学报》2003,20(2):83-84
给出曲面的第Φr 形式在广义Ⅱ 等距下的公式的概念.借助混变张量,得到曲面的第Φr 形式在广义Ⅱ 等距下的公式. 相似文献
24.
Myers Mark G.; MacPherson Laura; McCarthy Denis M.; Brown Sandra A. 《Canadian Metallurgical Quarterly》2003,15(2):163
The goal of the present studies was to construct and validate a short form of the 50-item Smoking Consequences Questionnaire (SCQ; T. H. Brandon & T. B. Baker, 1991), a measure of smoking outcome expectancies. In Study 1, a 21-item short form (S-SCQ) was derived from a sample of 107 young adults previously treated for substance abuse. In Study 2, the measure was cross-validated on 125 adolescents in treatment for substance abuse. Confirmatory factor analyses revealed good model fit and factorial invariance for the 4 S-SCQ subscales across both samples. Validation analyses on each sample found that subscale scores generally correlated significantly with smoking-related variables. The present studies provide initial evidence for the utility of the S-SCQ when used with young adults and adolescents. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
25.
Adaptive generation of surfaces in volume data 总被引:1,自引:1,他引:0
A widespread approach to generating polygonal approximations of iso-surfaces or contour surfaces in volume data is the socalled marching-cubes algorithm. This algorithm, however, has the disadvantage that the number of polygonal chains generated is considerable. The splitting-box algorithm presented here reduces the number of polygonal chains by adapting their size to the shape of the surface. The resulting polygonal chains offer a wide spectrum for representing the contour surface. An exact representation is achieved by a new type of generic patches calculated from the polygonal chains. Approximations of different quality may be obtained by combining the algorithm generating the patches with simple triangulations. 相似文献
26.
It is shown that steady-state kinetic data do not allow the discrimination between the redox and associated mechanisms of the partial oxidation reactions. A discrimination between these mechanisms was performed using transient experiments. The obtained rate expressions are in agreement with experimental kinetic data for catalytic partial oxidation of o-xylene.
An influence of the conjugate oxidation of a catalyst surface on dynamics and kinetics of the heterogeneous catalytic oxidative reactions is considered. Computing simulation of methane oxidative coupling of methane reaction at lowered temperature and elevated pressure has been performed. It showed that the reaction order with respect to oxygen exceeding unity is consistent with the chain branching mechanism of the reaction in the presence of TiSi2 and TiB2 and showed the important role of the branching chain cycles in the low-temperature OCM reaction at elevated pressure. 相似文献
27.
Titipong Issariyakul Mangesh G. KulkarniAjay K. Dalai Narendra N. Bakhshi 《Fuel Processing Technology》2007
Transesterification of waste fryer grease (WFG) containing 5–6 wt.% free fatty acid (FFA) was carried out with methanol, ethanol, and mixtures of methanol/ethanol maintaining the oil to alcohol molar ratio of 1:6, and initially with KOH as a catalyst. Mixtures of methanol and ethanol were used for transesterification in order to use the better solvent property of ethanol and rapid equilibrium using methanol. Formation of soap by reaction of FFA present in WFG with KOH instigated difficulty in the separation of glycerol from biodiesel ester. To untangle this problem, two-stage (acid and alkali catalyzed) method was used for biodiesel synthesis. More than 90% ester was obtained when two-stage method was used compared to ∼ 50% ester in single stage alkaline catalyst. In the case of mixed alcohol, a relatively smaller amount of ethyl esters was formed along with methyl esters. Acid value, viscosity, and cetane number of all the esters prepared from WFG were within the range of the ASTM standard. Esters obtained from WFG showed good performance as a lubricity additive. 相似文献
28.
简述土壤源热泵基本工作原理、埋管形式、优势及实用性,工程实例介绍北京九华山庄二期土壤热泵系统的设计、施工、调试情况,阐述了选择复合式系统的理由。 相似文献
29.
某跨线桥施工支架方案设计 总被引:1,自引:0,他引:1
结合某大桥的概况,根据梁体施工工艺要求、现场实地勘察情况确定跨线施工方案,支架采用布架灵活、搭拆方便、承载力大的WDJ碗扣式多功能钢支架,部分预应力现浇连续箱梁采用支墩加纵梁预留门洞的支架现浇,取得良好效果。 相似文献
30.