全文获取类型
收费全文 | 1635篇 |
免费 | 73篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 19篇 |
综合类 | 2篇 |
化学工业 | 393篇 |
金属工艺 | 29篇 |
机械仪表 | 36篇 |
建筑科学 | 80篇 |
矿业工程 | 9篇 |
能源动力 | 43篇 |
轻工业 | 158篇 |
水利工程 | 14篇 |
石油天然气 | 6篇 |
无线电 | 150篇 |
一般工业技术 | 303篇 |
冶金工业 | 245篇 |
原子能技术 | 14篇 |
自动化技术 | 213篇 |
出版年
2023年 | 15篇 |
2022年 | 30篇 |
2021年 | 42篇 |
2020年 | 31篇 |
2019年 | 30篇 |
2018年 | 36篇 |
2017年 | 40篇 |
2016年 | 42篇 |
2015年 | 43篇 |
2014年 | 52篇 |
2013年 | 111篇 |
2012年 | 65篇 |
2011年 | 96篇 |
2010年 | 65篇 |
2009年 | 67篇 |
2008年 | 66篇 |
2007年 | 77篇 |
2006年 | 59篇 |
2005年 | 50篇 |
2004年 | 30篇 |
2003年 | 37篇 |
2002年 | 38篇 |
2001年 | 28篇 |
2000年 | 18篇 |
1999年 | 31篇 |
1998年 | 64篇 |
1997年 | 49篇 |
1996年 | 31篇 |
1995年 | 23篇 |
1994年 | 23篇 |
1993年 | 20篇 |
1992年 | 25篇 |
1991年 | 18篇 |
1990年 | 16篇 |
1989年 | 12篇 |
1988年 | 13篇 |
1987年 | 16篇 |
1986年 | 12篇 |
1985年 | 19篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 13篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1977年 | 17篇 |
1976年 | 27篇 |
1975年 | 10篇 |
1973年 | 7篇 |
1972年 | 8篇 |
1969年 | 8篇 |
排序方式: 共有1714条查询结果,搜索用时 15 毫秒
61.
Data Mining and Knowledge Discovery - We present an approach for the prediction of user authorship and feedback behavior with shared content. We consider that users use models of other users and... 相似文献
62.
Fernanda P. Disconzi Wellington Balmant Jose Viriato Coelho Vargas Pedro H.R. Peixoto Dhyogo M. Taher Andre B. Mariano 《国际能源研究杂志》2019,43(8):3421-3435
The aim of the present work was to develop a transient mathematical model focused on microalgae biomass drying, considering two phases: solid (wet biomass) and gas (drying air). Mass and thermal energy balances were written for each phase producing a system of ordinary differential equations (ODE). The solution of the ODE set delivers the temperature and air humidity ratio and biomass profiles with respect to time. The numerical results were directly compared with temperature experimental measurements—for both phases—and with the biomass humidity content. Data from experiment 1 were used to carry out the mathematical model adjustment, whereas data from experiment 2 were used for the experimental validation of the model. The model was adjusted by proposing a new correlation for the mass transfer coefficient and by calibrating the heat transfer coefficient. The transient numerical results were in good quantitative and qualitative agreement with the experimental results, ie, within the experimental error bars. Then the experimentally validated mathematical model was utilized to optimize the following parameters: (i) the electric heater power ( ) and the dry air mass flow rate ( ) and (ii) the convection oven length to width ratio (L/W). The goal was to minimize system energy consumption (objective function). The optimization procedure was subject to the following physical constraints: (i) fixed convection oven total volume and (ii) fixed biomass and drying air contact surface area. For the oven original geometry, = 3.0 kW and = 9 g s?1 were numerically found for minimum energy consumption, so that 36.9% and 43.5% energy consumption decreases were obtained, respectively, in comparison with the measurements of experiment 1. Next, the numerical geometric optimization found (L/W)opt = 9, with and , which was capable to reach a 51.6% energy consumption reduction in comparison with the original system tested in experiment 1. The novelty of this work consists of the development and experimental validation of a physically based microalgae biomass drying mathematical model, ie, instead of using empirical correlations to predict the drying time and temperature profiles and then minimize system energy consumption. Therefore, the results show that it is reasonable to state that the model could be used to design, control, and optimize drying systems with configurations similar to the one analyzed in this study. 相似文献
63.
<正>当一座建筑呈现在室内设计师的眼前时,它往往已经粉刷了墙体,隐藏了所有管线,你已经无法认识它最本原的面貌,设计师无非是在此基础上不断地叠加更多的装饰,让它越来越华丽,遮盖一切最初的痕迹,抹去所有最原始的结构。有没有一位设计师的工作是主动剥去建筑的外衣,让它更加暴露更加原始?总部位于巴西的MNMA Studio就用这样的逆向思维为时尚品牌Haight设计了一个80 m~2零售店, 相似文献
64.
Xu Chen Andre Sutrisno Lingyang Zhu Leslie J. Struble 《Journal of the American Ceramic Society》2017,100(5):2285-2295
The nanostructural evolution during formation of geopolymers and its correlation with setting have not been well understood. In this study, penetration resistance and ultrasonic wave reflection tests were conducted to measure setting, and solid‐state 27Al NMR and liquid‐state 29Si NMR were used to examine nanostructural changes in a metakaolin geopolymer as a function of time. Aluminum was released rapidly during the first 10 hour after mixing and immediately condensed with silicate species in solution to form larger sized aluminosilicate oligomers, which then condensed to form large structural units. Our evidence suggests these units form near metakaolin particle surface. Smaller sized silicate ions in the sol phase then attach to these units to form a gel with a more interconnected network structure. The initial stage of this attaching process was seen to be associated with set, which in this mixture occurred at 15 hour. 相似文献
65.
The mechanical and adhesion behavior of cationically polymerized, partially crystalline epoxy networks is presented. For this, a reactive and a nonreactive poly(?-caprolactone) (PCL) were used as the crystalline component for the formation of copolymers and polymer alloys, respectively. The trade-off between toughness on the one hand and glass transition temperature and mechanical strength on the other can be reduced by the presence of nanostructures in combination with small crystalline domains (1 μm), as in the case of epoxy/PCL-based polymer alloys. This structure–property relationship reveals that a certain degree of crystallinity leads to enhanced toughness in cationically polymerized epoxy networks. 相似文献
66.
Andre Matthew Loyd Roger W. Nightingale Yin Song Jason F. Luck Hattie Cutcliffe Barry S. Myers Cameron ‘Dale’ Bass 《Accident; analysis and prevention》2014
Given the high incidence of TBI, head injury has been studied extensively using both cadavers and anthropomorphic test devices (ATDs). However, few studies have benchmarked the response of ATD heads against human data. Hence, the objective of this study is to investigate the response of adult and ATD heads in impact, and to compare adult Hybrid III head responses to the adult head responses. 相似文献
67.
Highly Crystalline Films of PCPDTBT with Branched Side Chains by Solvent Vapor Crystallization: Influence on Opto‐Electronic Properties
下载免费PDF全文
![点击此处可从《Advanced materials (Deerfield Beach, Fla.)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
68.
Taking path dependence seriously: an historical institutionalist research agenda in planning history
Andre Sorensen 《Planning Perspectives》2013,28(1):17-38
This paper outlines an historical institutionalist (HI) research agenda for planning history. HI approaches to the understanding of institutions, path dependence, positive feedback effects in public policy, and patterned processes of institutional change offer a robust theoretical framework and a valuable set of conceptual and analytic tools for the analysis of continuity and change in public policy. Yet, to date, there has been no systematic effort to incorporate historical institutionalism into planning history research. The body of the paper proposes planning history relevant definitions of institutions, path dependence, critical junctures, and incremental change processes, outlines recent HI literature applying and extending these concepts, and frames a number of research questions for planning history that these approaches suggest. A concluding section explores the potential application and leverage of HI approaches to the study of planning history and international comparative planning studies and outlines a research agenda. 相似文献
69.
Screening,Molecular Cloning,and Biochemical Characterization of an Alcohol Dehydrogenase from Pichia pastoris Useful for the Kinetic Resolution of a Racemic β‐Hydroxy‐β‐trifluoromethyl Ketone
下载免费PDF全文
![点击此处可从《Chembiochem : a European journal of chemical biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dalia Bulut Dr. Nongnaphat Duangdee Prof. Dr. Harald Gröger Prof. Dr. Albrecht Berkessel Prof. Dr. Werner Hummel 《Chembiochem : a European journal of chemical biology》2016,17(14):1349-1358
The stereoselective synthesis of chiral 1,3‐diols with the aid of biocatalysts is an attractive tool in organic chemistry. Besides the reduction of diketones, an alternative approach consists of the stereoselective reduction of β‐hydroxy ketones (aldols). Thus, we screened for an alcohol dehydrogenase (ADH) that would selectively reduce a β‐hydroxy‐β‐trifluoromethyl ketone. One potential starting material for this process is readily available by aldol addition of acetone to 2,2,2‐trifluoroacetophenone. Over 200 strains were screened, and only a few yeast strains showed stereoselective reduction activities. The enzyme responsible for the reduction of the β‐hydroxy‐β‐trifluoromethyl ketone was identified after purification and subsequent MALDI‐TOF mass spectrometric analysis. As a result, a new NADP+‐dependent ADH from Pichia pastoris (PPADH) was identified and confirmed to be capable of stereospecific and diastereoselective reduction of the β‐hydroxy‐β‐trifluoromethyl ketone to its corresponding 1,3‐diol. The gene encoding PPADH was cloned and heterologously expressed in Escherichia coli BL21(DE3). To determine the influence of an N‐ or C‐terminal His‐tag fusion, three different recombinant plasmids were constructed. Interestingly, the variant with the N‐terminal His‐tag showed the highest activity; consequently, this variant was purified and characterized. Kinetic parameters and the dependency of activity on pH and temperature were determined. PPADH shows a substrate preference for the reduction of linear and branched aliphatic aldehydes. Surprisingly, the enzyme shows no comparable activity towards ketones other than the β‐hydroxy‐β‐trifluoromethyl ketone. 相似文献
70.