全文获取类型
收费全文 | 47981篇 |
免费 | 6929篇 |
国内免费 | 3489篇 |
专业分类
电工技术 | 10394篇 |
技术理论 | 1篇 |
综合类 | 5080篇 |
化学工业 | 5971篇 |
金属工艺 | 1427篇 |
机械仪表 | 2412篇 |
建筑科学 | 3836篇 |
矿业工程 | 1512篇 |
能源动力 | 2014篇 |
轻工业 | 1676篇 |
水利工程 | 1740篇 |
石油天然气 | 2932篇 |
武器工业 | 512篇 |
无线电 | 5263篇 |
一般工业技术 | 4381篇 |
冶金工业 | 1855篇 |
原子能技术 | 1017篇 |
自动化技术 | 6376篇 |
出版年
2024年 | 113篇 |
2023年 | 722篇 |
2022年 | 1416篇 |
2021年 | 1752篇 |
2020年 | 1969篇 |
2019年 | 1687篇 |
2018年 | 1629篇 |
2017年 | 1992篇 |
2016年 | 2047篇 |
2015年 | 2181篇 |
2014年 | 3115篇 |
2013年 | 3438篇 |
2012年 | 3583篇 |
2011年 | 3753篇 |
2010年 | 2695篇 |
2009年 | 2870篇 |
2008年 | 2740篇 |
2007年 | 3078篇 |
2006年 | 2868篇 |
2005年 | 2298篇 |
2004年 | 2042篇 |
2003年 | 1757篇 |
2002年 | 1443篇 |
2001年 | 1157篇 |
2000年 | 979篇 |
1999年 | 851篇 |
1998年 | 693篇 |
1997年 | 534篇 |
1996年 | 480篇 |
1995年 | 448篇 |
1994年 | 450篇 |
1993年 | 317篇 |
1992年 | 235篇 |
1991年 | 227篇 |
1990年 | 180篇 |
1989年 | 150篇 |
1988年 | 110篇 |
1987年 | 85篇 |
1986年 | 59篇 |
1985年 | 58篇 |
1984年 | 37篇 |
1983年 | 29篇 |
1982年 | 37篇 |
1981年 | 19篇 |
1980年 | 19篇 |
1979年 | 10篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1959年 | 8篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
Kumari Asha Neeraj Kumar Biswas Sakshi Saxena Vibha Rani Satsangi Rohit Shrivastav Rama Kant Sahab Dass 《International Journal of Hydrogen Energy》2021,46(40):20858-20870
The present study attempts quantitative determination of changes in the morphological surface features viz. fractal dimension, lower and upper cut off length scale through Power Spectral Density analysis prior to and after irradiation of 100 KeV Ar+ ion beam at incidence angles of 0°, 40° and 60° on ZnO thin films. All the unirradiated and irradiated samples are subjected to photoelectrochemical characterization and a correlation between photoelectrochemical performance and morphological parameters is established. Sample irradiated at 40° angle at the fluence of 5 × 1016 ions/cm2 is found to possess maximum fractal dimension of 2.72, lower and upper cut off length scale of 3.16 nm and 63.00 nm respectively. This sample exhibits maximum photocurrent density of 3.19 mA/cm2 and applied bias photon-to-current efficiency of 1.12% at 1.23 V/RHE. Hydrogen gas collected for duration of 1 h for the same sample was ~4.83 mLcm?2. 相似文献
32.
Effective distribution coefficients of 9 impurities in 1,2-diphenylethane have been calculated by directional crystallization under different ambient frozen temperature. The effect of varied zone size, temperature difference between the melt and ambient frozen environment, number of zone on purity of 1,2-diphenylethane have been also investigated during the process of zone refining. The results indicate that the product purity in the intermediate purified region with varied zone size is higher 0.04%-0.2% than that with constant zone size. The product purity increases with temperature difference between the melt and ambient frozen environment. The appropriate temperature difference is adopted 50℃. The product purity in the intermediate region of sample bar with 2 molten zones is higher 0.05%-0.43% than that with 1 molten zone. In addition, the change of enthalpy and entropy between impurities and 1,2-diphenylethane have been determined. 相似文献
33.
《Ceramics International》2022,48(8):10480-10485
Advanced nano-porous super thermal insulation materials are widely used in spacecraft, soler-thermal shielding, heat exchangers, photocatalytic carriers due to their low thermal conductivity. In this work, adopting dry preparation technology, nano-Al2O3, nano-SiO2, SiC and glass fibers as raw materials, novel nanometer alumina-silica insulation board (NAIB) were prepared. The preparation process was simple, safe, and reliable. In addition, the NAIB exhibited a high porosity (91.3–92.3%), small pore size (39.83–44.15 nm), low bulk density (0.22–0.26 g/cm3), better volumetric stability, and low thermal conductivity (0.031–0.050 W/(m·K) (200–800 °C)), respectively. The as-prepared NAIB could render them suitable for application as high-temperature thermal insulation materials. 相似文献
34.
配电网停电会造成电力系统供配电可靠性以及服务质量下降,研究基于地理信息系统(GIS)单线图的配网停电单模拟操作应用。利用网格长度作为基本单位建立坐标系,以选取起始点与终止点为基础,通过四参数法将GIS坐标映射至图纸网格内,实现配网内设备初步布局,将杆塔、站房和整体均匀分布作为优化目标,设置多目标优化目标函数实现GIS单线图最终优化。选取某电力公司配网作为单模拟操作应用对象,模拟结果表明,单模拟操作配网停电后,该配网各负荷点年故障率、次平均停电时间以及年停电时间均有所减少,可有效提升配网的供配电可靠性。 相似文献
35.
36.
《Ceramics International》2022,48(3):3869-3874
Lead-based relaxor ferroelectric crystals, such as Pb(Mg1/3Nb2/3)O3-PbTiO3, are promising for functional applications due to their outstanding ferroelectric properties. Revealing ferroelectric domain structure and phase distribution at the nanoscale are important to understand the basic theory of ferroelectricity and promote their practical applications. In this study, the ferroelectric domain structure and atomic-scale phase distribution in a Pb(Mg1/3Nb2/3)O3 - 35 at.% PbTiO3 single crystal in the region of morphotropic phase boundary are systematically investigated by a combination of optical microscopy, scanning electron microscopy, and aberration-corrected transmission electron microscopy. It is found that 90° and 180° coarse domains are formed simultaneously in the ferroelectric single crystal. Moreover, there are tweed-like nano-domains formed inside each coarse single domain. Through careful investigations of distribution of stress and tetragonality, it is revealed that the tweed-like nano-domains are composed of nano-sized rhombohedral (R), monoclinic (M), and tetragonal (T) phases. The nano-scale T, M, R phases have the best, moderate, and lowest ferroelectricity, respectively. 相似文献
37.
Ya-Nan Yang Yin-Ning Zhou Bo Ouyang Yi-Yang Wu Xi-Bao Zhang Zheng-Hong Luo 《American Institute of Chemical Engineers》2022,68(5):e17645
The computational fluid dynamics (CFD) and kinetic-based moment methods coupled approach is adopted to simulate the bulk copolymerization of styrene–acrylonitrile (SAN) in a stirred tank reactor. Numerical simulations are carried out to investigate the impacts of impeller speed, monomer ratio, initiator ratio, and initial reaction temperature on the copolymerization process and product properties. Particularly, the Chaos theory is selected as a criterion for evaluating the occurrence of the thermal runaway. The Flory's and Stockmayer's distributions are employed to calculate chain length distribution and copolymer composition distribution of copolymer. The simulation results highlight that the appearance of thermal runaway can be postponed by properly increasing the rotation speed, decreasing the initiator loadings, initial acrylonitrile contents and initial reactor temperature. Furthermore, significant differences exist in the product properties that predicted by the ideal and non-ideal models, which demonstrates that the temperature heterogeneity plays a crucial role in SAN copolymerization. This study could offer references for the safe operation and design of polymerization processes. 相似文献
38.
In [1] a procedure for bias-free estimation of the autocorrelation function is introduced for equidistantly sampled data with randomly occurring samples being invalid. The method incorporates sample-and-hold interpolation of the missing data points. The occurring dynamic error of the primary estimate of the correlation function is treated by a deconvolution procedure with two parameters and with , which are the on-diagonal and the aside-diagonal parameters of a specific correction matrix (at all lag times except zero). The parameters and were obtained as a function of the probability α of a sample to be valid by numerical simulation. However, explicit expressions for the parameters and can be derived, which might improve the usability of the deconvolution procedure in [1]. 相似文献
39.
《等离子体科学和技术》2019,21(11):115403-44
In this paper, a honeycomb structure jet array with seven jet units was adopted to generate plasmas. Both the average discharge power and the emission intensity of the main excited species increase with increasing applied voltage. There are three stages of discharge evolution at different applied voltages: initial discharge, uniform discharge and strong coupling discharge.The spatial distribution of the emission intensity of the excited species can be divided into three categories: growth class, weakening class and variation class. The gas temperature along the whole plasma plume at different applied voltages is maintained at around 320K and can be widely used in heat-labile applications. 相似文献
40.
The ordered weighted averaging (OWA) operators play a crucial role in aggregating multiple criteria evaluations into an overall assessment supporting the decision makers’ choice. One key point steps is to determine the associated weights. In this paper, we first briefly review some main methods for determining the weights by using distribution functions. Then we propose a new approach for determining OWA weights by using the regular increasing monotone quantifier. Motivated by the idea of normal distribution-based method to determine the OWA weights, we develop a method based on elliptical distributions for determining the OWA weights, and some of its desirable properties have been investigated. 相似文献