全文获取类型
收费全文 | 110332篇 |
免费 | 8740篇 |
国内免费 | 6603篇 |
专业分类
电工技术 | 3609篇 |
技术理论 | 2篇 |
综合类 | 6606篇 |
化学工业 | 26576篇 |
金属工艺 | 11090篇 |
机械仪表 | 5459篇 |
建筑科学 | 3640篇 |
矿业工程 | 2549篇 |
能源动力 | 3191篇 |
轻工业 | 6459篇 |
水利工程 | 1227篇 |
石油天然气 | 3374篇 |
武器工业 | 805篇 |
无线电 | 12575篇 |
一般工业技术 | 16470篇 |
冶金工业 | 4115篇 |
原子能技术 | 1625篇 |
自动化技术 | 16303篇 |
出版年
2024年 | 363篇 |
2023年 | 1744篇 |
2022年 | 3055篇 |
2021年 | 3607篇 |
2020年 | 3008篇 |
2019年 | 2722篇 |
2018年 | 2495篇 |
2017年 | 3165篇 |
2016年 | 3638篇 |
2015年 | 3888篇 |
2014年 | 5722篇 |
2013年 | 6006篇 |
2012年 | 6722篇 |
2011年 | 9533篇 |
2010年 | 7218篇 |
2009年 | 7989篇 |
2008年 | 6964篇 |
2007年 | 7782篇 |
2006年 | 6875篇 |
2005年 | 5904篇 |
2004年 | 4793篇 |
2003年 | 4467篇 |
2002年 | 3695篇 |
2001年 | 2461篇 |
2000年 | 2255篇 |
1999年 | 1847篇 |
1998年 | 1431篇 |
1997年 | 1170篇 |
1996年 | 985篇 |
1995年 | 750篇 |
1994年 | 705篇 |
1993年 | 558篇 |
1992年 | 460篇 |
1991年 | 362篇 |
1990年 | 279篇 |
1989年 | 226篇 |
1988年 | 141篇 |
1987年 | 121篇 |
1986年 | 126篇 |
1985年 | 80篇 |
1984年 | 57篇 |
1983年 | 47篇 |
1982年 | 54篇 |
1981年 | 31篇 |
1980年 | 46篇 |
1979年 | 34篇 |
1978年 | 11篇 |
1977年 | 21篇 |
1976年 | 17篇 |
1974年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Catalytic Hydrocracking of a Bitumen‐Derived Asphaltene over NiMo/γ‐Al2O3 at Various Temperatures
下载免费PDF全文
![点击此处可从《化学工程与技术》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Hydrocracking of a bitumen‐derived asphaltene over NiMo/γ‐Al2O3 was investigated in a microbatch reactor at varying temperatures. The molar kinetics of asphaltene cracking reaction was examined by fitting the experimental data. Below a defined temperature, the molar reaction showed the first‐order kinetic feature while at higher temperatures secondary reactions such as coke formation became significant, causing deviation of the reaction behavior from the proposed first‐order kinetic model. Selectivity analysis proved that dominant products varied from gases to liquids to gases with increasing temperature, shifting the dominant reaction from C–S bonds cleavage to C–C bonds cleavage. 相似文献
102.
Elucidation of colour development and microstructural characteristics of Allium sativum fumigated with acetic acid
下载免费PDF全文
![点击此处可从《International Journal of Food Science & Technology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Li Li Dan Wang Xihong Li Yu Wang Xiaofeng Ju 《International Journal of Food Science & Technology》2015,50(5):1083-1088
It has been well known that the greening of Allium sativum cloves could be formed after immersed in acetic acid solution. Nonetheless, no investigation was reported on colour development of A. sativum in response to acetic acid vapour until now. In this study, the brief exposure of A. sativum to acetic acid vapour (200–400 ppm) was combined with controlled atmosphere (5%, 20% and 80% CO2) packaging storage to break cell membrane and green garlic. The garlic bulbs were fumigated with acetic acid before controlled CO2 atmosphere packaging for 25 days at 4 °C. Fumigation with 200 ppm acetic acid followed by high CO2 atmosphere packaging (80% CO2) facilitated the garlic greening. It was also verified that γ‐glutamyl transpeptidase was involved in garlic greening in present study, and the compromise of glacial acetic acid vapour fumigation and CO2 gas atmosphere in package stored at low temperature could result in garlic greening as well. 相似文献
103.
A fluorene-centered perylene monoimide dimer, PMI-F-PMI with a partly non-coplanar configuration has been developed as a potential non-fullerene acceptor for organic solar cells (OSCs). The optimum power conversion efficiency (PCE) of the OSC based on PMI-F-PMI as acceptor and poly (3-hexyl thiophene) (P3HT) as donor is up to 2.30% after annealing at 150 °C. The PCE of 2.30% is the highest value for the OSCs based on P3HT donor and non-fullerene acceptor lies in that PMI-F-PMI’s lowest unoccupied molecular orbital (LUMO) level around −3.50 eV matches well with the donor P3HT to produce higher open-circuit voltage (Voc) of 0.98 V. Meanwhile, PMI-F-PMI makes remarkable contribution to devices’ light absorption as the maximum EQE (30%) of the devices is at 512 nm, same to the maximum absorption wavelength of PMI-F-PMI. The other favorable characteristics of PMI-F-PMI in bulk heterojunction (BHJ) active layers is proved through the photo current density measures, the relatively balanced electron–hole transport, and the smooth morphology with root mean square (RMS) value of 1.86 nm. For these advantages, PMI-F-PMI overwhelms its sister PMI-F and parent PMI as an acceptor in BHJ solar cells. 相似文献
104.
This paper presents an experimental study of low velocity impact response of carbon/epoxy asymmetrically tapered laminates. The tests are realised at energy between 10 and 30 J on two types of layup with multiple terminated plies. The type and localisation of damage are analysed using C-scan and micrographs. Then, the data is compared with the response of corresponding respective plain laminate. The effects of some tapering parameters (taper angle, drop-off disposition and configuration) on the impact damage mechanisms are also investigated. Very similar impact damage phenomena are found between tapered and plain laminates. The presence of material discontinuity due to the resin pocket affects less the damage mechanism than the structural difference between the thick and the thin sections. 相似文献
105.
Adem Sreedhar I. Neelakanta Reddy Qui Thanh Hoai Ta Gitae Namgung Eunbin Cho Jin-Seo Noh 《Ceramics International》2019,45(6):6985-6993
In this paper, novel morphology correlation between silver nanowires (AgNWs) and cobalt (Co)-doped ZnO (Co-ZnO) flake-like thin films (nanowire/flake-like) has been proposed for enhanced photoelectrochemical (PEC) water splitting activity. Here in, high-quality AgNWs/Co-ZnO heterostructures enabled superior visible light water splitting activity compared to the pure ZnO and AgNWs/ZnO. To address the strategic effect of AgNWs coupling and transition metal (Co-2?at%) doping into the ZnO host lattice, we have carried out the X-ray diffraction, field emission scanning microscopy, X-ray photoelectron spectroscopy, UV–Vis transmittance, water contact angle and PEC analyses. In this way, PEC water splitting activity was mainly examined by linear sweep voltammetry (I-V), amperometric I-t and photoconversion efficiency (η) studies. The experimental results provide clear evidence of morphology correlation between AgNWs and Co-ZnO flake-like structures for strong visible light absorption. Specifically, AgNWs/Co-ZnO composites exhibited significant enhancement in the photocurrent density (7.0?×?10?4 A/cm2) than AgNWs/ZnO (3.2?×?10?4 A/cm2) and pure ZnO (1.5?×?10?6 A/cm2). As a result, detailed AgNWs/Co-ZnO geometry has great potential for photoconversion efficiency (0.73%). In a word, the merits of controllable AgNWs/Co-ZnO heterostructure are proposed to improve the visible light harvesting and charge carrier generation for energy conversion devices. 相似文献
106.
The main aim of this work is dual computer analysis of probabilistic coefficients for the homogenized tensor of the polymer filled with the rubber particles having randomized Poisson ratios of both constituents. The major issue is to verify an influence of a randomness in rubber Poisson ratio close to the compressibility limit on the uncertainty of the effective tensor probabilistic characteristics. Probabilistic analysis presented here is carried out using mainly the stochastic perturbation technique provided by the common application of the traditional FEM commercial code ABAQUS and the symbolic computations package MAPLE. This FEM-based technique employs polynomial response function of the optimum order recovered from the weighted least squares method and following a set of deterministic solutions obtained for various values of the randomized input parameter. Optimization procedure is released entirely into a symbolic environment, where maximization of the correlation factor together with minimization of the fitting variance and approximation error are applied. Homogenization technique consists in equating of deformation energies for the real composite and the artificial one characterized by the effective elasticity tensor with uncertainty. 相似文献
107.
介绍了一种基于高性能浮点DSP芯片TMS320C32、CPLD芯片XC95288和A/D采样芯片AD976组成的多路采集系统的工作原理以及设计方法。通过对第一路施加特殊的电压量,在CCS开发环境下读取采样缓冲区的值,并利用Matlab对采样数据进行了全波傅氏变换。此外,该系统已在继电保护中得到广泛应用,实践表明,该系统能较好地解决多路模拟量的采集,并确保了采样数据的安全可靠性。 相似文献
108.
109.
110.
The lead-free piezoelectric ceramics (Na.47Bi.47Ba.06)1-xCaxTiO3 (x?=?0, 0.01, 0.02, 0.03, 0.05, and 0.08, abbreviated as BNBTC/0, BNBTC/1, BNBTC/2, BNBTC/3, BNBTC/5, and BNBTC/8, respectively) were obtained using the solid-state reaction method. The structure, electric conductivity, and dielectric, ferroelectric, and piezoelectric properties of the Ca2+-doped (Na.47Bi.47Ba.06)TiO3 ceramics were thoroughly investigated. The ceramics sintered at 1200?°C exhibit dense microstructures, having relative densities higher than 96%. The X-ray diffraction results demonstrate that all ceramics have a pure perovskite structure. The mean grain sizes of the ceramics are related to the Ca2+ quantity. A small quantity of Ca2+ ions (x?≤?0.03) improves the piezoelectric and ferroelectric properties of the samples. The dielectric behavior of the samples is sensitive to the Ca2+ content and electric poling. The results demonstrate that the electrical properties of the (Na.47Bi.47Ba.06)TiO3 lead-free ceramics can be well tuned by varying the Ca2+ quantity. 相似文献