全文获取类型
收费全文 | 1096篇 |
免费 | 14篇 |
专业分类
电工技术 | 15篇 |
综合类 | 1篇 |
化学工业 | 256篇 |
金属工艺 | 19篇 |
机械仪表 | 24篇 |
建筑科学 | 29篇 |
矿业工程 | 11篇 |
能源动力 | 15篇 |
轻工业 | 106篇 |
水利工程 | 2篇 |
石油天然气 | 3篇 |
无线电 | 36篇 |
一般工业技术 | 165篇 |
冶金工业 | 347篇 |
原子能技术 | 7篇 |
自动化技术 | 74篇 |
出版年
2021年 | 10篇 |
2019年 | 9篇 |
2018年 | 7篇 |
2017年 | 9篇 |
2016年 | 12篇 |
2015年 | 10篇 |
2014年 | 24篇 |
2013年 | 22篇 |
2012年 | 30篇 |
2011年 | 38篇 |
2010年 | 24篇 |
2009年 | 29篇 |
2008年 | 29篇 |
2007年 | 30篇 |
2006年 | 35篇 |
2005年 | 40篇 |
2004年 | 21篇 |
2003年 | 19篇 |
2002年 | 20篇 |
2001年 | 11篇 |
2000年 | 13篇 |
1999年 | 25篇 |
1998年 | 90篇 |
1997年 | 51篇 |
1996年 | 46篇 |
1995年 | 23篇 |
1994年 | 18篇 |
1993年 | 28篇 |
1992年 | 16篇 |
1991年 | 10篇 |
1990年 | 13篇 |
1989年 | 18篇 |
1988年 | 16篇 |
1986年 | 18篇 |
1985年 | 19篇 |
1984年 | 16篇 |
1983年 | 18篇 |
1982年 | 9篇 |
1981年 | 21篇 |
1980年 | 19篇 |
1979年 | 17篇 |
1978年 | 15篇 |
1977年 | 16篇 |
1976年 | 31篇 |
1975年 | 16篇 |
1974年 | 11篇 |
1973年 | 10篇 |
1971年 | 8篇 |
1970年 | 14篇 |
1969年 | 14篇 |
排序方式: 共有1110条查询结果,搜索用时 135 毫秒
1.
This paper investigates the mutual impact channels of Germany's major regional policy instrument (GRW) on regional economic development. Different from earlier studies which have predominately focused on a partial assessment of output effects, we explicitly endogenize the factor inputs of the underlying production function. This allows us to comprehensively assess the role of the GRW in driving per capita output, employment, human and physical capital intensities as well as the region's technological growth. The results from a spatial panel vector autoregressive model show that GRW funding has significant positive effects on regional output, the employment rate and human capital intensity. 相似文献
2.
Chemical oxygen demand (COD) assays are widely used for the estimation of the organic carbon content of water and wastewater. The procedure is subject to interference by free halogen ions, the oxidation of which creates artificially high COD values. As part of an investigation of the interferences involved in the COD determination of chemical industries wastewaters, we found that mercuric sulfate complexation, the standard procedure for neutralizing the halogen effects, is suitable for chlorides but is not applicable to bromides. This observation is true both in the presence or absence of chloride or ammonia. Care should therefore be exercised in the interpretation of COD data for bromide-containing samples. 相似文献
3.
4.
Supramolecular Chemistry in Molten Sulfur: Preorganization Effects Leading to Marked Enhancement of Carbon Nitride Photoelectrochemistry 下载免费PDF全文
Jingsan Xu Shaowen Cao Thomas Brenner Xiaofei Yang Jiaguo Yu Markus Antonietti Menny Shalom 《Advanced functional materials》2015,25(39):6265-6271
Here, a new method for enhancing the photoelectrochemical properties of carbon nitride thin films by in situ supramolecular‐driven preorganization of phenyl‐contained monomers in molten sulfur is reported. A detailed analysis of the chemical and photophysical properties suggests that the molten sulfur can texture the growth and induce more effective integration of phenyl groups into the carbon nitride electrodes, resulting in extended light absorption alongside with improved conductivity and better charge transfer. Furthermore, photophysical measurements indicate the formation of sub‐bands in the optical bandgap which is beneficial for exciton splitting. Moreover, the new bands can mediate hole transfer to the electrolyte, thus improving the photooxidation activity. The utilization of high temperature solvent as the polymerization medium opens new opportunities for the significant improvement of carbon nitride films toward an efficient photoactive material for various applications. 相似文献
5.
Farhani Mahdi Hils Gereon Spitzer Karl-Heinz 《Metallurgical and Materials Transactions B》2019,50(3):1193-1203
Metallurgical and Materials Transactions B - As a key part of investigating a new proposed Ti-alloy production process, Ti-Al alloys were produced by aluminothermic reduction experiments at... 相似文献
6.
Process optimization for efficient biomediated PHA production from animal-based waste streams 总被引:1,自引:1,他引:0
Michaela Titz Karl-Heinz Kettl Khurram Shahzad Martin Koller Hans Schnitzer Michael Narodoslawsky 《Clean Technologies and Environmental Policy》2012,14(3):495-503
Conventional polymers are made of crude oil components through chemical polymerization. The aim of the project ANIMPOL is to produce biopolymers by converting lipids into polyhydroxyalkanoates (PHA) in a novel process scheme to reduce dependence on crude oil and decrease greenhouse gas emissions. PHA constitutes a group of biobased and biodegradable polyesters that may substitute fossil-based polymers in a wide range of applications. Waste streams from slaughtering cattle are used as substrate material. Lipids from rendering are used in this process scheme for biodiesel production. Slaughtering waste streams may also be hydrolyzed to achieve higher lipid yield. Biodiesel then is separated into a high- and low-quality fraction. High-quality biodiesel meets requirements for sale as fuel and low quality is used for PHA production as carbon source. Selected offal material is used for acid hydrolysis and serves as a source of organic nitrogen as well as carbon source for PHA-free biomass with high production rate in fermentation process. Nitrogen is a limiting factor to control PHA production during the fermentation process. It is available for bacterial growth from hydrolyzed waste streams as well as added separately as NH4OH solution. Selected microbial strains are used to produce PHA from this substrate. The focus of the paper is about an overview of the whole process with the main focus on hydrolysis, to look for the possibility of using offal hydrolysis as an organic nitrogen substitute. The process design is optimized by minimizing waste streams and energy losses through cleaner production. Ecological evaluation of the process design will be done through footprint calculation according to Sustainable Process Index methodology. 相似文献
7.
8.
This paper presents a model of firm and market dynamics that is able to reproduce the empirically observed patterns on firm growth and its statistical characteristics. It goes beyond the existing firm models by reproducing all stylized facts established in the literature. Furthermore, the model is flexible in the sense that various parameter settings are identified that reproduce the stylized facts. We identify and discuss different ranges of the model’s parameters that allow for adapting the model to certain industries and life-cycle stages. 相似文献
9.
A growing body of work emphasizes the importance of regional factors for regional innovativeness. In this paper, about 70 variables approximating the social-economic characteristics of regions are aggregated to 12 regional factors. In four industry-specific set-ups their influence on firms?? innovativeness is tested. The study confirms that inter-industrial differences exist in the importance of these factors. In the empirical analyses a log-linear model is compared with a linear approach. While both are theoretically problematic it is shown that the log-linear model performs better in the empirical assessment. 相似文献
10.
R. Prasad S. Ter-AvetisyanD. Doria K.E. QuinnL. Romagnani P.S. Foster C.M. Brenner J.S. GreenP. Gallegos M.J.V. Streeter D.C. CarrollO. Tresca N.P. DoverC.A.J. Palmer J. SchreiberD. Neely Z. NajmudinP. McKenna M. ZepfM. Borghesi 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2011,653(1):113-115
We report on experimental investigations of proton acceleration from thin foil targets irradiated with ultra-short (∼50 fs), high contrast (∼1010) and ultra-intense (up to 1021 W/cm2) laser pulses. These measurements provided for the first time the opportunity to extend the scaling laws for the acceleration process in the ultra-short regime beyond the 1020 W/cm2 threshold. The scaling of accelerated proton energies was investigated by varying the thickness of Al targets (down to 50 nm) under 35° angle of laser incidence and with p-polarised light. 相似文献