全文获取类型
收费全文 | 85719篇 |
免费 | 10460篇 |
国内免费 | 5172篇 |
专业分类
电工技术 | 5376篇 |
技术理论 | 9篇 |
综合类 | 5635篇 |
化学工业 | 26555篇 |
金属工艺 | 8246篇 |
机械仪表 | 2931篇 |
建筑科学 | 3180篇 |
矿业工程 | 1689篇 |
能源动力 | 4176篇 |
轻工业 | 4582篇 |
水利工程 | 581篇 |
石油天然气 | 3924篇 |
武器工业 | 576篇 |
无线电 | 8982篇 |
一般工业技术 | 15565篇 |
冶金工业 | 5568篇 |
原子能技术 | 951篇 |
自动化技术 | 2825篇 |
出版年
2024年 | 469篇 |
2023年 | 1963篇 |
2022年 | 2727篇 |
2021年 | 3060篇 |
2020年 | 3308篇 |
2019年 | 3138篇 |
2018年 | 2861篇 |
2017年 | 3365篇 |
2016年 | 3403篇 |
2015年 | 3274篇 |
2014年 | 4675篇 |
2013年 | 5092篇 |
2012年 | 5863篇 |
2011年 | 6165篇 |
2010年 | 4417篇 |
2009年 | 4859篇 |
2008年 | 4158篇 |
2007年 | 5205篇 |
2006年 | 4983篇 |
2005年 | 4099篇 |
2004年 | 3490篇 |
2003年 | 3394篇 |
2002年 | 2780篇 |
2001年 | 2348篇 |
2000年 | 2139篇 |
1999年 | 1637篇 |
1998年 | 1469篇 |
1997年 | 1200篇 |
1996年 | 996篇 |
1995年 | 893篇 |
1994年 | 795篇 |
1993年 | 554篇 |
1992年 | 541篇 |
1991年 | 421篇 |
1990年 | 397篇 |
1989年 | 326篇 |
1988年 | 169篇 |
1987年 | 116篇 |
1986年 | 94篇 |
1985年 | 106篇 |
1984年 | 97篇 |
1983年 | 79篇 |
1982年 | 63篇 |
1981年 | 32篇 |
1980年 | 39篇 |
1979年 | 10篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1959年 | 9篇 |
1951年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
通过制备不同晶相结构〔单斜相(m-ZrO_2)、四方相(t-ZrO_2)和无定型(a-ZrO_2)〕ZrO_2载体,再通过沉积沉淀法制得Cu/m-ZrO_2、Cu/t-ZrO_2和Cu/a-ZrO_2催化剂,分别用于催化二乙醇胺脱氢合成亚氨基二乙酸反应。采用XRD、氮气物理吸附脱附、XPS、H_2-TPR、CO_2-TPD对催化剂的结构进行了表征。结果表明,Cu/m-ZrO_2催化剂界面更加有利于Cu~+/Cu~0稳定存在,具有更多的碱性位点,且抗氧化性较好。在二乙醇胺脱氢反应中,Cu/m-ZrO_2催化剂性能最好,反应时间为2.5 h,亚氨基二乙酸收率为97.64%。 相似文献
2.
3.
《Displays》2015
Modern liquid crystal displays (LCDs) require novel technologies, such as new alignment methods to eliminate alignment layers, fast response and long operation time. To this end, we report an overview of recent efforts in LCD technologies devoted to realize more display modes having no alignment layer, faster switching time and low battery consumption. In particular, we overview recent advances on the liquid crystals (LCs) alignment for display applications, which includes superfine nanostructures, polymeric microchannels and polymer stabilized LCs. Furthermore, we analyze the main optical and electro-optical properties of new generation LCDs displays addressing a particular attention to LCs blue phase hosting gold nanoparticles. Moreover, we focus on the progress of electrofluidic displays, which demonstrates characteristics that are similar to LCDs, with attention on various pixel designs, operation principles and possible future trends of the technology. 相似文献
4.
《Food Control》2015
In this work a multicommuted flow system employing copper–4,4′- dipyridyl coordination compound as the solid-phase reagent for the spectrophotometric determination of reducing sugar was developed. The coordination compound was synthesized through a reaction of the 4,4′-dipyridyl and copper (II) nitrate, under hydrothermal conditions. The complex was characterized by infrared spectroscopy (FTIR), power X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and thermogravimetric analysis (TGA). Based on the characterization, a multicommuted spectrophotometric procedure for the determination of reducing sugar using copper (II) complex as solid reagent is proposed. The proposed method was based on the redox reaction between a monosaccharide, such as fructose and glucose (reducing sugar) and Cu(II). This reaction, mediated in an alkaline medium, produces a yellow compound that can be determined by absorption electronic spectroscopy (λABS = 420 nm). Under optimum experimental conditions, a linear response ranging from 1.0 to 20.0 g L−1 (R = 0.9978 and n = 5), a detection (3σ criterion) and quantification (10σ criterion) limit estimated at 0.23 and 0.75 g L−1, respectively, a standard deviation relative of 4.7% (n = 7), for a reference solution of 10.0 g L−1 reducing sugar, and a sampling rate of 75 determinations per hour were achieved. The proposed system was applied to the determination of reducing sugars in coconut water and juices. The analysis of ten samples and the application of the t-test to the results found, and those obtained using reference procedures (AOAC), provided no significant differences at a 95% confidence level. This system enabled the analysis of reducing sugar with ease and simplicity, providing a significant economy of the solid reagent (600 μg per determination) and reducing effluent generation. 相似文献
5.
Eight datasets of 1-h black carbon (BC) concentrations measured in Warsaw agglomeration (Poland), at urban background and sub-urban sites, and in Racibórz, a small town in Upper Silesia district (regional background site) were analyzed to evaluate BC levels, daily profiles and statistical distributions of concentrations in Central-Eastern European region. The observed mean levels ranged from 1483 ng m−3 in suburban site during summer to 3358 ng m−3 in regional background site in winter. Observed diurnal patterns were bimodal in the locations dominated by traffic emissions, but unimodal, with elevated evening peak in individually heated residential area. Three theoretical frequency distributions were applied to fit analyzed datasets separately. The lognormal distribution was the most appropriate to represent the middle-range values, while the high concentrations were satisfactorily predicted by the type I two-parameter exponential distribution which was used to estimate the return periods of extreme concentrations for winter months. 相似文献
6.
To improve the electrochemical properties of rare-earth–Mg–Ni-based hydrogen storage alloys, the effects of stoichiometry and Cu-substitution on the phase structure and thermodynamic properties of the ... 相似文献
7.
The conversion of lignocellulosic biomass (LCB) to microbial oils is attracting a growing amount of attention. However, the growth of the oleaginous yeast Rhodotorula glutinis on LCB hydrolysate (mainly rice straw) only will lead to a low lipid mass fraction, in the range of 10–20%. This study shows that the addition of crude glycerol to the LCB hydrolysate medium can efficiently raise the lipid mass fraction to the range of 30–40%. Crude glycerol is a by-product in the biodiesel production process. The use of renewable LCB hydrolysate and crude glycerol would greatly reduce the substrate cost for microbial oil production using R. glutinis. In addition, the results of experiments show that a low-cost airlift bioreactor is a more suitable fermentation process for the growth of R. glutinis than the use of a conventional agitation tank. When using mixed carbon sources of LCB hydrolysate with 30 kg m−3 of reducing sugars and 30 kg m−3 of crude glycerol, a maximal cell mass of 21.4 kg m−3 and lipid mass fraction of 58.5 ± 6.2 were achieved in an internal loop airlift bioreactor, and this process may have the potential to be applied in scale-up production. 相似文献
8.
2.4GHz动态CMOS分频器的设计 总被引:1,自引:0,他引:1
对现阶段的主流高速CMOS分频器进行分析和比较,在此基础上设计一种采用TSPC(truesingle phase clock)和E-TSPC(extended TSPC)技术的前置双模分频器电路.该分频器大大提高了工作频率,采用0.6μm CMOS工艺参数进行仿真的结果表明,在5V电源电压下,最高频率达到3GHz,功耗仅为8mW. 相似文献
9.
10.
Navab SinghAuthor Vitae Moitreyee Mukherjee-RoyAuthor VitaeSohan Singh MehtaAuthor Vitae 《Microelectronics Journal》2003,34(4):237-245
The patterning of contact holes by selecting out-of-focus image plane (defocus) using attenuated phase shift masks (APSM) has been studied. Defocus is found to enhance the image modulation at low partial coherence for contact holes with negative local average of mask function. Semi-dense holes up to 130 nm in 8% APSM have been printed by 0.5 μm defocus at a partial coherence of 0.31 using KrF scanner with highest numerical aperture of 0.68. However, these holes were closed with in-focus imaging. Defocus is also found to be beneficial for patterning the pitches that have extensive side lobes with in-focus imaging. 相似文献