全文获取类型
收费全文 | 8236篇 |
免费 | 663篇 |
国内免费 | 876篇 |
专业分类
电工技术 | 309篇 |
综合类 | 491篇 |
化学工业 | 1178篇 |
金属工艺 | 242篇 |
机械仪表 | 556篇 |
建筑科学 | 229篇 |
矿业工程 | 80篇 |
能源动力 | 97篇 |
轻工业 | 440篇 |
水利工程 | 23篇 |
石油天然气 | 263篇 |
武器工业 | 145篇 |
无线电 | 2905篇 |
一般工业技术 | 875篇 |
冶金工业 | 98篇 |
原子能技术 | 954篇 |
自动化技术 | 890篇 |
出版年
2024年 | 13篇 |
2023年 | 84篇 |
2022年 | 130篇 |
2021年 | 137篇 |
2020年 | 180篇 |
2019年 | 120篇 |
2018年 | 147篇 |
2017年 | 216篇 |
2016年 | 273篇 |
2015年 | 301篇 |
2014年 | 431篇 |
2013年 | 517篇 |
2012年 | 555篇 |
2011年 | 660篇 |
2010年 | 447篇 |
2009年 | 519篇 |
2008年 | 500篇 |
2007年 | 615篇 |
2006年 | 532篇 |
2005年 | 482篇 |
2004年 | 413篇 |
2003年 | 401篇 |
2002年 | 296篇 |
2001年 | 232篇 |
2000年 | 232篇 |
1999年 | 200篇 |
1998年 | 164篇 |
1997年 | 195篇 |
1996年 | 159篇 |
1995年 | 142篇 |
1994年 | 114篇 |
1993年 | 92篇 |
1992年 | 77篇 |
1991年 | 56篇 |
1990年 | 37篇 |
1989年 | 16篇 |
1988年 | 21篇 |
1987年 | 17篇 |
1986年 | 20篇 |
1985年 | 9篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1966年 | 1篇 |
1959年 | 5篇 |
1957年 | 1篇 |
排序方式: 共有9775条查询结果,搜索用时 15 毫秒
71.
In sonic IR imaging, a major problem is exploring the heating characteristics of crack vicinity to guide the optimization of the test conditions. In this paper, the crack's heating characteristics of the metallic plate with an artificial fatigue crack has been studied. Experimental results showed that the during ultrasonic excitation the temperature rise of crack vicinity at the plate's excitation side is higher than that at its opposite side, whereas the total heating efficiency of the crack face appears to be stable. Through the profile mapping of the crack face, the frictional heating is mainly concentrated near the excitation side. Based on this phenomenon, we built a mathematical heat transfer model to calculate the temperature distribution of the crack vicinity and investigated the heating features of crack faces. Additionally, the mathematical model gives a quantitative relation between the depth of the heat source and the ratio of the temperature distribution of the crack vicinity at opposite side to that at the front side. This study aims to provide a quantitative evaluation method for locating the frictional heating areas in sonic IR imaging. 相似文献
72.
《Journal of Nuclear Science and Technology》2013,50(4):426-430
Laser isotope separation experiments of Gd and B by atomic and molecular methods, respectively, have been performed. Gadolinium-157 was selectively photoionized by means of three linearly polarized dye lasers, the excitation process of which is based on the polarization selection rules. The effect of magnetic field on isotopic selectivity was discussed. 10BCl3 was selectively photodissociated through IR multiphoton dissociation by the irradiation of TEA CO2 laser or free electron laser (FEL). Selectivity was improved by two-color laser irradiation. 相似文献
73.
《Ceramics International》2016,42(14):15209-15216
The effect of annealing temperature on photovoltaic and near-infrared (NIR) detector applications of PbS nanoparticles (NPs) and PbS/graphene nanocomposites was investigated. The products were synthesized by a simple co-precipitation method and graphene oxide (GO) sheets were used as graphene source. Several characterization techniques were used to show transfer of the GO into reduced graphene oxide (rGO) during the synthesis process. In addition, the effect of graphene concentrations on morphology, structure, photovoltaic, and detector parameters of the samples were studied. Transmission electron microscope (TEM) images showed that, the PbS NPs were agglomerated, while, the PbS/rGO nanocomposites were dispersed completely after annealing under H2/Ar gas atmosphere. UV–visible spectrometer showed an absorption peak for all samples in the near infrared red (NIR) region of the electromagnetic spectrum. The results indicated that, photocurrent intensity, responsivity of the samples to an NIR source, and solar-cell efficiency were affected by annealing of samples and graphene concentrations. 相似文献
74.
75.
We present the first active visible blind ultraviolet (UV) photodetector based on zinc oxide (ZnO) nanostructured AlGaN/GaN high electron mobility transistors (HEMTs). The ZnO nanorods (NRs) are selectively grown on the gate area by using hydrothermal method. It is shown that ZnO nanorod (NR)-gated UV detectors exhibit much superior performance in terms of response speed and recovery time to those of seed-layer-gated detectors. It is also found that the best response speed (~10 and~190 ms) and responsivity (~1.1×105 A/W) were observed from detectors of the shortest gate length of 2 µm among our NR-gated devices of three different gate dimensions, and this responsivity is about one order higher than the best performance of ZnO NR-based UV detectors reported to date. 相似文献
76.
A hybrid structure of single-crystal silicon (Si) and high-density polyethylene (HDPE) was developed as a new substrate for infrared lenses by using precision press molding. A thin HDPE film was used to laminate a silicon wafer and their interface was directly bonded by the silane cross-link. The HDPE film is easy to be hot-embossed to form three-dimensional surface microstructures and the silicon wafer provides a high stiffness for the hybrid substrate. The infrared (IR) optical properties of the hybrid substrate were examined by two kinds of measurements, transmittance and image sharpness. Interestingly, the transmittance measurement result shows that the IR transmittance of the hybrid substrate is higher than that of Si itself in some region of wavelength. The imaging test result shows that the hybrid substrate is capable to produce similar image quality as Si itself. These results strongly demonstrate that the developed Si–HDPE hybrid substrate is a promising alternative substrate material for IR lens. 相似文献
77.
Correlation of structural characterization and viscosity measurements with total unsaturation: An effective method for controlling ozonation in the preparation of ozonated grape seed and sunflower oils 下载免费PDF全文
78.
Regime shifts observed in Lake Kasumigaura,a large shallow lake in Japan: Analysis of a 40‐year limnological record 下载免费PDF全文
Lake Kasumigaura, which is composed of the two basins (Nishiura and Kitaura), is a large, shallow, hypereutrophic lake. Phytoplankton and water quality records from the past forty years were analysed to elucidate whether or not, when, and what type of certain regime shifts may have occurred, based on using inferential regime shift detectors. Characteristics of the phytoplankton and water quality changes were similar at 6 sampling sites in the two basins, with 20 water quality parameters being classified into four groups, based on cluster analysis. Shifts in dominant plankton groups (DPGs) and water quality occurring almost concomitantly, concentration on the period from 1987 to 1992 (Shift A) and from 1997 to 2001 (Shift B), with those observed for the two basins usually being similar with small differences. Two types of inferential regime shift detectors (sequential t‐test type; Rodionov's RSD and sequential F‐test type: package strucchange in R) yielded similar timings and significances of the shifts. Furthermore, changes in skewness and conditional heteroskedasticity (package early warnings in R) usually represented early warning signals before the shifts. Correlation analysis and ratios of dissolved inorganic nitrogen (DIN) vs. total phosphorus (TP) supported the hypothesis that phosphorus was the phytoplankton biomass limiting nutrient, except for one period for the Nishiura basin. Neither the nitrogen:phosphorus (N/P) ratio hypothesis and ammonia–nitrate (NH4‐N/NO3‐N) hypothesis satisfactorily explain the DPGs before and after Shift A (Microcystis spp. and Planktothrix spp., respectively), although it may be possible that these ratios triggered the DPG change in this shift. A considerable increase in silicon was observed for Shift B when the DPGs changed from cyanobacteria to diatoms. Further studies on the accurate types and triggers of the regime shifts are necessary to better understand the interactions between ecosystem and water quality for this and similar lakes elsewhere. 相似文献
79.
《Ceramics International》2020,46(10):16285-16290
Tailoring phase transition and microstructural evolution during sintering is crucial for the fabrication of ZnS ceramics transparent to infrared (IR) radiation. Herein, we have described the phase transition, microstructure, and related IR transmission of spark-plasma-sintered ZnS ceramics in terms of sintering temperature and pressure. The pore characteristics of spark-plasma-sintered ZnS ceramics were evaluated using Mie scattering theory. Changes in hexagonality and residual pore characteristics of the microstructure affected IR transmission of the sintered specimens. High temperature and pressure condition of SPS were found to increase excessive hexagonal phase (>20%), mainly contributing to a transmittance decay in the range 2–4 μm. 相似文献
80.
Irek I. Mukhamatdinov Sergey A. Sitnov Olga V. Slavkina Konstantin A. Bugaev Alexander V. Laikov 《Petroleum Science and Technology》2019,37(12):1410-1416
In this paper, we investigated the influence of steam treatment on structural group composition of resins and asphaltenes of heavy oil. The object of investigation was oil-saturated rocks from Riphean-Vendian complex. The extracted crude oil was determined as a high-viscous fluid. The resins and asphaltenes destructed in a small extent due to thermal treatment. The oil-soluble iron-based catalyst intensified the destructive processes. The content of sulfur compounds (-SO) in resins and asphaltenes drastically decreased due to reduction reaction of sulfoxide to sulfide and hydrogen sulfide. The results showed that catalytic aquathermolysis, even at low temperature ranges, promoted the cracking reaction of most macromolecular components and increased the content of light fractions of heavy oil. Consequently, it reduced its viscosity. 相似文献