全文获取类型
收费全文 | 1404篇 |
免费 | 56篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 14篇 |
综合类 | 1篇 |
化学工业 | 376篇 |
金属工艺 | 51篇 |
机械仪表 | 29篇 |
建筑科学 | 65篇 |
矿业工程 | 1篇 |
能源动力 | 52篇 |
轻工业 | 170篇 |
水利工程 | 5篇 |
无线电 | 146篇 |
一般工业技术 | 282篇 |
冶金工业 | 57篇 |
原子能技术 | 12篇 |
自动化技术 | 201篇 |
出版年
2023年 | 8篇 |
2022年 | 24篇 |
2021年 | 53篇 |
2020年 | 25篇 |
2019年 | 26篇 |
2018年 | 26篇 |
2017年 | 22篇 |
2016年 | 32篇 |
2015年 | 27篇 |
2014年 | 52篇 |
2013年 | 109篇 |
2012年 | 81篇 |
2011年 | 132篇 |
2010年 | 98篇 |
2009年 | 83篇 |
2008年 | 83篇 |
2007年 | 63篇 |
2006年 | 66篇 |
2005年 | 49篇 |
2004年 | 38篇 |
2003年 | 41篇 |
2002年 | 37篇 |
2001年 | 20篇 |
2000年 | 19篇 |
1999年 | 23篇 |
1998年 | 14篇 |
1997年 | 31篇 |
1996年 | 16篇 |
1995年 | 22篇 |
1994年 | 15篇 |
1993年 | 12篇 |
1992年 | 9篇 |
1991年 | 13篇 |
1990年 | 4篇 |
1989年 | 10篇 |
1988年 | 4篇 |
1987年 | 12篇 |
1985年 | 10篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1973年 | 4篇 |
1972年 | 1篇 |
排序方式: 共有1462条查询结果,搜索用时 265 毫秒
911.
Numerical simulation of the interaction between two fire fronts in grassland and shrubland 总被引:1,自引:0,他引:1
The objective of this paper was to evaluate the potential for fully physical fire models to simulate the interactions between two converging fire fronts (a head fire and a back fire), in conditions similar to those encountered during suppression fire operations. The simulations were carried out using two fully physical models: FIRESTAR, in two dimensions, and Wildland Fire Dynamics Simulator, in three dimensions. Each modelling approach numerically solves a set of balance equations (mass, momentum, energy, etc.) governing the behaviour of the coupled system formed by the vegetation and the surrounding atmosphere. Two fuel profiles were tested: homogeneous grassland similar to landscapes in Australia and a shrubland representative of Mediterranean landscape (garrigue). Results from the two-dimensional and three-dimensional simulations were used to investigate how the two fire fronts interact together and mutually modify, or not, their own behaviour before merging. The results of these simulations showed that the merging of two fire fronts can result in a quick increase in fire-line intensity or in flame height. We concluded that physics-based simulations do reproduce reasonable and expected head- and back-fire interactions, but more work is needed to further understand the accuracy of such predictions. 相似文献
912.
Chanudet V Descloux S Harby A Sundt H Hansen BH Brakstad O Serça D Guerin F 《The Science of the total environment》2011,409(24):5382-5391
Gross CO2 and CH4 emissions (degassing and diffusion from the reservoir) and the carbon balance were assessed in 2009-2010 in two Southeast Asian sub-tropical reservoirs: the Nam Ngum and Nam Leuk Reservoirs (Lao PDR). These two reservoirs are within the same climatic area but differ mainly in age, size, residence time and initial biomass stock. The Nam Leuk Reservoir was impounded in 1999 after partial vegetation clearance and burning. However, GHG emissions are still significant 10 years after impoundment. CH4 diffusive flux ranged from 0.8 (January 2010) to 11.9 mmol m− 2 d− 1 (April 2009) and CO2 diffusive flux ranged from - 10.6 (October 2009) to 38.2 mmol m− 2 d− 1 (April 2009). These values are comparable to other tropical reservoirs. Moreover, degassing fluxes at the outlet of the powerhouse downstream of the turbines were very low. The tentative annual carbon balance calculation indicates that this reservoir was a carbon source with an annual carbon export (atmosphere + downstream river) of about 2.2 ± 1.0 GgC yr− 1.The Nam Ngum Reservoir was impounded in 1971 without any significant biomass removal. Diffusive and degassing CO2 and CH4 fluxes were lower than for other tropical reservoirs. Particularly, CO2 diffusive fluxes were always negative with values ranging from - 21.2 (April 2009) to - 2.7 mmol m−2 d−1 (January 2010). CH4 diffusive flux ranged from 0.1 (October 2009) to 0.6 mmol m−2 d−1 (April 2009) and no degassing downstream of the turbines was measured. As a consequence of these low values, the reservoir was a carbon sink with an estimated annual uptake of - 53 ± 35 GgC yr−1. 相似文献
913.
Effects of preharvest ultraviolet‐C irradiation on fruit phytochemical profiles and antioxidant capacity in three strawberry (Fragaria × ananassa Duch.) cultivars 下载免费PDF全文
914.
Mid-infrared Fourier transform fiber-optic reflection spectroscopy (mid-IR FORS) is a noninvasive and flexible spectroscopic technique. It is ideal in the art conservation field because of its portability for on-site and in situ analysis of art objects, analyses that require delicate handling, or analyses of objects that cannot be sampled. This paper studies the applicability of mid-IR FORS for the characterization of commercial artists' alkyd paints cast on different supports. As predicted, the quality of the spectra and intensity of characteristic peaks varied according to reflectivity, roughness, and materials used in the supports. The presence of organic binder was best identified by its carbonyl peak (the most intense) and CH(2) stretching peaks; however, this was not sufficient to distinguish between oil and alkyd binders. The differentiation and identification of alkyds and oils must rely on the unique fingerprint peaks. However, in some cases, the fingerprint peaks were difficult to interpret because of strong absorptions caused by inorganic paint fillers, often present in modern paint formulations, resulting in anomalous dispersion and reststrahlen distortions. 相似文献
915.
916.
Wang Y Canady TD Zhou Z Tang Y Price DN Bear DG Chi EY Schanze KS Whitten DG 《ACS applied materials & interfaces》2011,3(7):2209-2214
The antiviral activities of poly(phenylene ethynylene) (PPE)-based cationic conjugated polyelectrolytes (CPE) and oligo-phenylene ethynylenes (OPE) were investigated using two model viruses, the T4 and MS2 bacteriophages. Under UV/visible light irradiation, significant antiviral activity was observed for all of the CPEs and OPEs; without irradiation, most of these compounds exhibited high inactivation activity against the MS2 phage and moderate inactivation ability against the T4 phage. Transmission electron microscopy (TEM) and SDS polyacrylamide gel electrophoresis (SDS-PAGE) reveal that the CPEs and OPEs exert their antiviral activity by partial disassembly of the phage particle structure in the dark and photochemical damage of the phage capsid protein under UV/visible light irradiation. 相似文献
917.
918.
919.
The application of finite mixture regression models has recently gained an interest from highway safety researchers because of its considerable potential for addressing unobserved heterogeneity. Finite mixture models assume that the observations of a sample arise from two or more unobserved components with unknown proportions. Both fixed and varying weight parameter models have been shown to be useful for explaining the heterogeneity and the nature of the dispersion in crash data. Given the superior performance of the finite mixture model, this study, using observed and simulated data, investigated the relative performance of the finite mixture model and the traditional negative binomial (NB) model in terms of hotspot identification. For the observed data, rural multilane segment crash data for divided highways in California and Texas were used. The results showed that the difference measured by the percentage deviation in ranking orders was relatively small for this dataset. Nevertheless, the ranking results from the finite mixture model were considered more reliable than the NB model because of the better model specification. This finding was also supported by the simulation study which produced a high number of false positives and negatives when a mis-specified model was used for hotspot identification. Regarding an optimal threshold value for identifying hotspots, another simulation analysis indicated that there is a discrepancy between false discovery (increasing) and false negative rates (decreasing). Since the costs associated with false positives and false negatives are different, it is suggested that the selected optimal threshold value should be decided by considering the trade-offs between these two costs so that unnecessary expenses are minimized. 相似文献
920.
Alessandro Navarrini Anne Laure Fontana Doris Maier Patrice Serres Dominique Billon-Pierron 《Journal of Infrared, Millimeter and Terahertz Waves》2014,35(6-7):536-562
We present the design, construction and performance of backshort-tuned Single Side Band (SSB) and of fixed-tuned Double Side Band (DSB) Superconductor-Insulator-Superconductor (SIS) mixers covering the frequency range of 129-174 GHz (2 mm band). Receivers employing these SSB mixers have been continuously operated for astronomical observations on the six antennas of the IRAM Plateau de Bure Intereferometer (PdBI) since 2007 and on the IRAM 30 m Pico Veleta (PV) radio telescope since 2009. The DSB version of the mixer was employed in a prototype of a four-element focal plane array that was tested on the IRAM 30 m radio telescope. Both SSB and DSB mixers employ the same chip and are based on a wideband single ended probe transition from WR6 full-height waveguide to thin-film microstrip line and on a series array of two Nb/Al-AlOx/Nb junctions. The measured receiver noise for the four-element DSB mixer array pumped by a Gunn oscillator cascaded with a frequency doubler was in the range 25-35 K across the 135-168 GHz LO band. The PdBI and PV receivers equipped with the SSB mixers have measured noise temperatures in the range of 30 K to 60 K and an image sideband rejection below -10 dB over the 129-174 GHz RF band. The measurement results agree well with the predictions obtained through detailed simulations of the SIS receivers based on the standard theory of quantum mixing. 相似文献