全文获取类型
收费全文 | 374529篇 |
免费 | 38527篇 |
国内免费 | 32411篇 |
专业分类
电工技术 | 24195篇 |
技术理论 | 10篇 |
综合类 | 24867篇 |
化学工业 | 101131篇 |
金属工艺 | 20866篇 |
机械仪表 | 17271篇 |
建筑科学 | 14806篇 |
矿业工程 | 6034篇 |
能源动力 | 11969篇 |
轻工业 | 39596篇 |
水利工程 | 3651篇 |
石油天然气 | 14101篇 |
武器工业 | 2699篇 |
无线电 | 43379篇 |
一般工业技术 | 40196篇 |
冶金工业 | 12206篇 |
原子能技术 | 5307篇 |
自动化技术 | 63183篇 |
出版年
2024年 | 1693篇 |
2023年 | 6329篇 |
2022年 | 11988篇 |
2021年 | 13713篇 |
2020年 | 12193篇 |
2019年 | 11162篇 |
2018年 | 10359篇 |
2017年 | 13311篇 |
2016年 | 14504篇 |
2015年 | 15537篇 |
2014年 | 18866篇 |
2013年 | 22781篇 |
2012年 | 26195篇 |
2011年 | 29444篇 |
2010年 | 22099篇 |
2009年 | 23378篇 |
2008年 | 23080篇 |
2007年 | 27082篇 |
2006年 | 25570篇 |
2005年 | 21018篇 |
2004年 | 16991篇 |
2003年 | 14469篇 |
2002年 | 11433篇 |
2001年 | 8930篇 |
2000年 | 7861篇 |
1999年 | 6570篇 |
1998年 | 5245篇 |
1997年 | 4091篇 |
1996年 | 3444篇 |
1995年 | 2848篇 |
1994年 | 2531篇 |
1993年 | 1905篇 |
1992年 | 1556篇 |
1991年 | 1241篇 |
1990年 | 1053篇 |
1989年 | 771篇 |
1988年 | 579篇 |
1987年 | 446篇 |
1986年 | 422篇 |
1985年 | 463篇 |
1984年 | 419篇 |
1983年 | 293篇 |
1982年 | 329篇 |
1981年 | 236篇 |
1980年 | 243篇 |
1979年 | 127篇 |
1978年 | 110篇 |
1977年 | 115篇 |
1976年 | 116篇 |
1975年 | 111篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
5.
6.
In this work, the longitudinal permeability of squarely packed dual-scale fiber preforms is studied theoretically. These fiber preforms are composed of aligned porous tows and the tows are tightly packed. The effective permeability is calculated as a parallel-like network of intra-tow permeability and inter-tow permeability, which are quantified by Darcy’s law and the inscribed radius between tows, respectively. The jump velocity at the interface between inter-tow fluids and porous tows is considered, as derived by substituting Beavers and Joseph’s correlation into Brinkman’s equation. We further examine the effects of intra-tow permeability on the effective permeability of the fibrous system with three interface conditions: (1) interface velocity = 0, (2) interface velocity = mean intra-tow velocity, and (3) interface velocity = jump velocity. The jump-velocity-based model is found to be closest to numerical data. The influence of the fiber volume fraction of tows on the effective permeability is also analyzed. 相似文献
7.
A hybrid sorbent material for removal of hydrogen sulfide from air was developed. The material is based on activated carbon and iron compounds obtained from waste iron(II) sulfate(VI) heptahydrate. The iron salt is deposited on the carbonaceous support and subjected to oxidation (Fe2+ to Fe3+) using atmospheric oxygen under alkaline conditions. An effect of H2O2 addition to the process on the composition of the resultant material was also examined. X-ray diffraction (XRD) analyses confirmed easy conversion of waste FeSO4·7H2O to iron oxides Fe3O4 and FeOOH. The activated carbon supporting iron oxides revealed a higher efficiency in H2S elimination from air compared to the commercial activated carbon, without any modification. 相似文献
8.
《Ceramics International》2020,46(3):3190-3202
In this study, nuclear shielding qualities of glass-ceramics with chemical composition Na2O3–BaO–PbO–Nb2O5–SiO2–Al2O3 containing different amount of BaO and PbO were investigated. The μρ values were simulated using GEANT4 toolkit at 0.015–20 MeV wide energy range and the obtained results were verified by theoretical WinXCOM results. The variables such as μρ, HVL, MFP, Zeff, Neff, EBF and EABF were computed to determine the gamma-ray shielding performances of studied glass ceramics. The results revealed that increase in PBO and BaO percentages in glass samples has caused to decrease the HVL, MFP, EBF and EABF values and increase μρ, Zeff values. It has been seen that N28 and S24 samples own superior protection ability against gamma radiation. In addition, the shielding capacity of these glass ceramics against charged and uncharged particles were predicted by determination of MSP and PR values for alpha, proton and ΣR values for neutrons. It has been concluded that PbO and BaO addition improve radiation shielding competences of glass ceramics. The data obtained from this study will be beneficial for designing glass ceramics shields for radiation protection enforcements. 相似文献
9.
Yasoub Eghbali Mahmoud Ferdosizade Naeiny 《International Journal of Communication Systems》2020,33(14)
In this paper, an off‐grid direction of arrival (DoA) estimation method is proposed for wideband signals. This method is based on the sparse representation (SR) of the array covariance matrix. Similar to the time domain DoA estimation methods, the correlation function of the sources was assumed to be the same and known. A new measurement vector is obtained using the lower‐left triangular elements of the covariance matrix. The DoAs are estimated by quantizing the entire range of continuous angle space into discrete grid points. However, the exact DoAs may be located between two grid points; therefore, this estimation has errors. The accuracy of DoA estimation is improved by the minimization of the difference between the new measurement vector and its estimated values. Simulation results revealed that the proposed method can enhance the DoA estimation accuracy of wideband signals. 相似文献
10.
Olatunde Adebayo Adeoti Sunday Olawale Koleoso 《Quality and Reliability Engineering International》2020,36(6):2170-2186
Several modifications and enhancements to control charts in increasing the performance of small and moderate process shifts have been introduced in the quality control charting techniques. In this paper, a new hybrid control chart for monitoring process location is proposed by combining two homogeneously weighted moving average (HWMA) control charts. The hybrid homogeneously weighted moving average (HHWMA) statistic is derived using two smoothing constants λ1 and λ2 . The average run length (ARL) and the standard deviation of the run length (SDRL) values of the HHWMA control chart are obtained and compared with some existing control charts for monitoring small and moderate shifts in the process location. The results of study show that the HHWMA control chart outperforms the existing control charts in many situations. The application of the HHWMA chart is demonstrated using a simulated data. 相似文献