全文获取类型
收费全文 | 1462篇 |
免费 | 14篇 |
学科分类
工业技术 | 1476篇 |
出版年
2019年 | 7篇 |
2018年 | 4篇 |
2017年 | 6篇 |
2016年 | 10篇 |
2015年 | 8篇 |
2014年 | 22篇 |
2013年 | 15篇 |
2012年 | 16篇 |
2011年 | 18篇 |
2010年 | 12篇 |
2009年 | 21篇 |
2008年 | 19篇 |
2007年 | 13篇 |
2006年 | 15篇 |
2005年 | 26篇 |
2004年 | 13篇 |
2003年 | 9篇 |
2002年 | 11篇 |
2001年 | 7篇 |
2000年 | 9篇 |
1999年 | 39篇 |
1998年 | 334篇 |
1997年 | 175篇 |
1996年 | 149篇 |
1995年 | 71篇 |
1994年 | 46篇 |
1993年 | 68篇 |
1992年 | 16篇 |
1991年 | 19篇 |
1990年 | 21篇 |
1989年 | 20篇 |
1988年 | 9篇 |
1987年 | 12篇 |
1986年 | 16篇 |
1985年 | 17篇 |
1984年 | 8篇 |
1983年 | 9篇 |
1982年 | 4篇 |
1981年 | 15篇 |
1980年 | 13篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 26篇 |
1976年 | 59篇 |
1975年 | 8篇 |
1971年 | 6篇 |
1970年 | 4篇 |
1969年 | 4篇 |
1968年 | 3篇 |
1967年 | 3篇 |
排序方式: 共有1476条查询结果,搜索用时 15 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.
6.
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
7.
8.
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
9.
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
10.
Harken AD Randers-Pehrson G Johnson GW Brenner DJ 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2011,269(18):1992-1996
A soft X-ray microbeam using proton-induced X-ray emission (PIXE) of characteristic titanium (Kα 4.5 keV) as the X-ray source has been developed at the Radiological Research Accelerator Facility (RARAF) at Columbia University. The proton beam is focused to a 120 μm × 50 μm spot on the titanium target using an electrostatic quadrupole quadruplet previously used for the charged particle microbeam studies at RARAF. The proton induced X-rays from this spot project a 50 μm round X-ray generation spot into the vertical direction. The X-rays are focused to a spot size of 5 μm in diameter using a Fresnel zone plate. The X-rays have an attenuation length of (1/e length of ∼145 μm) allowing more consistent dose delivery across the depth of a single cell layer and penetration into tissue samples than previous ultrasoft X-ray systems. The irradiation end station is based on our previous design to allow quick comparison to charged particle experiments and for mixed irradiation experiments. 相似文献