全文获取类型
收费全文 | 14003篇 |
免费 | 1001篇 |
国内免费 | 116篇 |
专业分类
电工技术 | 208篇 |
综合类 | 66篇 |
化学工业 | 3635篇 |
金属工艺 | 359篇 |
机械仪表 | 498篇 |
建筑科学 | 528篇 |
矿业工程 | 21篇 |
能源动力 | 977篇 |
轻工业 | 1324篇 |
水利工程 | 192篇 |
石油天然气 | 228篇 |
武器工业 | 4篇 |
无线电 | 1436篇 |
一般工业技术 | 2635篇 |
冶金工业 | 500篇 |
原子能技术 | 103篇 |
自动化技术 | 2406篇 |
出版年
2024年 | 70篇 |
2023年 | 281篇 |
2022年 | 624篇 |
2021年 | 941篇 |
2020年 | 784篇 |
2019年 | 846篇 |
2018年 | 941篇 |
2017年 | 853篇 |
2016年 | 843篇 |
2015年 | 491篇 |
2014年 | 782篇 |
2013年 | 1410篇 |
2012年 | 913篇 |
2011年 | 965篇 |
2010年 | 678篇 |
2009年 | 609篇 |
2008年 | 427篇 |
2007年 | 367篇 |
2006年 | 309篇 |
2005年 | 199篇 |
2004年 | 183篇 |
2003年 | 155篇 |
2002年 | 125篇 |
2001年 | 98篇 |
2000年 | 90篇 |
1999年 | 83篇 |
1998年 | 143篇 |
1997年 | 117篇 |
1996年 | 100篇 |
1995年 | 72篇 |
1994年 | 53篇 |
1993年 | 60篇 |
1992年 | 46篇 |
1991年 | 38篇 |
1990年 | 41篇 |
1989年 | 32篇 |
1988年 | 25篇 |
1987年 | 24篇 |
1986年 | 37篇 |
1985年 | 27篇 |
1984年 | 29篇 |
1983年 | 26篇 |
1982年 | 21篇 |
1981年 | 21篇 |
1980年 | 19篇 |
1979年 | 17篇 |
1978年 | 18篇 |
1977年 | 18篇 |
1976年 | 24篇 |
1975年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
Norodin Fazli Seyed Mohammd Bagher Malaek Ali Abedian Hessamodin Teimouri 《Journal of Mechanical Science and Technology》2011,25(10):2495-2503
A set of recursive equations are introduced for optimum design of a wide range of hierarchical truss beams to satisfy a minimum required natural frequency. The design equations are based on a general analytical solution, which are derived based on a critical dimensional analysis. A practical example is examined in both 2D and 3D spaces, which promises substantial mass reduction, as much as 99%, when using high order hierarchical truss beams. The results are verified by numerical evaluation of three case studies. The approach looks also very promising to design nanostructures when it comes to the problems associated with vibration. 相似文献
993.
Gerardo F. Barbero Ali Liazid Marta Ferreiro-González Miguel Palma Carmelo G. Barroso 《International Journal of Food Properties》2016,19(5):984-992
A new chromatographic method for the separation of major capsaicinoids in peppers has been developed. Nordihydrocapsaicin, capsaicin, dihydrocapsaicin, homocapsaicin, and homodihydrocapsaicin have been separated by reversed-phase ultra-performance liquid chromatography. A gradient method has been developed using two solvents: 0.1% acetic acid in water and 0.1% acetic acid in methanol. The developed method allows the full separation of capsaicinoids in less than 3 min, with high reproducibility (relative standard deviation < 4.3%) and repeatability (relative standard deviation < 3.6%). Robustness regarding the total amount of methanol in the sample was determined. Comparison with previous reversed-phase high-performance liquid chromatography methods using both monolithic and conventional columns was also studied. Finally, the method was applied in the determination of major capsaicinoids in 16 hot pepper samples produced in Spain. 相似文献
994.
A new one-dimensional silver(I) coordination polymer, [Ag(μ-bpfb)(NO3)]n (1); bpfb = N,N′-bis(4-pyridylformamide)-1,4-benzene, has been synthesized and characterized by IR, 1H NMR and 13C NMR spectroscopy. The single crystal X-ray data show that the silver(I) 1D coordination polymer grows into a three-dimensional network by hydrogen bonding and π–π stacking interactions. Compound 1 with nanorod morphology was also prepared by sonochemical method. The cetyltrimethylammonium bromide (CTAB) as a cationic surfactant was used in reverse micelles technique to obtain spongy silver(I) bromide nanoparticles from compound 1. Also, different silver nanoparticles have been prepared via direct calcination at 673 K and thermal decomposition in oleic acid from compound 1. The nanostructures of [Ag(μ-bpfb)(NO3)]n (1), silver and silver(I) bromide were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray (EDAX) analysis. Thermal stability of compound 1 in both bulk and nano-sized form was studied by thermal gravimetric (TG) and differential thermal (DT) analyses. 相似文献
995.
996.
Momina Moetesum Fazle Hadi Muhammad Imran Abid Ali Minhas Athanasios V. Vasilakos 《Wireless Networks》2016,22(7):2189-2201
Provisioning buffer management mechanism is especially crucial in resource-constrained delay tolerant networks (DTNs) as maximum data delivery ratio with minimum overhead is expected in highly congested environments. However, most DTN protocols do not consider resource limitations (e.g., buffer, bandwidth) and hence, results in performance degradation. To strangle and mitigate the impact of frequent buffer overflows, this paper presents an adaptive and efficient buffer management scheme called size-aware drop (SAD) that strives to improve buffer utilization and avoid unnecessary message drops. To improve data delivery ratio, SAD exactly determines the requirement based on differential of newly arrived message(s) and available space. To vacate inevitable space from a congested buffer, SAD strives to avoid redundant message drops and deliberate to pick and discard most appropriate message(s) to minimize overhead. The performance of SAD is validated through extensive simulations in realistic environments (i.e., resource-constrained and congested) with different mobility models (i.e., Random Waypoint and disaster). Simulation results demonstrate the performance supremacy of SAD in terms of delivery probability and overhead ratio besides other metrics when compared to contemporary schemes based on Epidemic (DOA and DLA) and PRoPHET (SHLI and MOFO). 相似文献
997.
Hasan Ali Rayat Azimi Majid Zarei Amir Rafati Mohammad Noormohammadi 《Journal of Porous Materials》2016,23(2):357-363
A hard anodization (HA) technique is employed using different mixtures of phosphoric/oxalic acid for fast fabrication of alumina nanopore arrays in voltages higher than 200 V. The mixtures enable to avoid the breakdown of porous anodic alumina (PAA) in the high voltages. It is revealed for the first time that continuously tunable pore intervals (Dint) from 500 to 750 nm can be controlled by varying the concentrations of oxalic acid at anodization voltages (Uanod) from 230 to 360 V, far beyond the Uanod in the single electrolyte of phosphoric acid or oxalic acid. The ratios of interpore distance, pore diameter and barrier layer thickness to anodization voltage are in the range of conventional HA process for each acid mixture. In this approach, the PAA film growth rate is 26 µm/h, being 7 times larger than that in typical mild anodization. 相似文献
998.
Ali Keramat Ali Kargari Morteza Sohrabi† Hamed Mirshekar Hamidreza Sanaeepur 《化学工程与技术》2017,40(3):529-536
The kinetics of sucrose hydrolysis by invertase was studied in order to find a comprehensive model for the reaction pathway and mechanism. First, three common models of Michaelis‐Menten (MM), substrate inhibition (S2), and substrate clusters' inhibition (S3(I)) were investigated. The third model was found to better predict the initial sucrose concentration. Then, the S3(I) model was modified to cover the remaining pathway (S3(II)). Finally, a new comprehensive model (S3(III)) was evaluated, which in addition to what is considered in the two previously mentioned models (S3(I) and S3(II)) also involved the initial time lag. The model predictions showed an excellent agreement with the experimental data. The mean absolute error for the MM model is significantly reduced for the S3(III) model. 相似文献
999.
We have explored the electronic and optical properties of cubic (Al x Ga1?x )1?y Mn y As system using the FP-LAPW method. The unit cell has 64 atoms, so that one manganese (Mn) atom is placed in the position of gallium site, which corresponds to 3.125 % doping concentration with x = 12.5 %. Our calculations, using local density approximation + U (Hubbard parameter) scheme, predict that the ferromagnetic state for AlGaMnAs, with a magnetic moment of about 4.014 μB per Mn dopant is more favorable. Despite its electronic properties being strongly affected by inducing small amounts of Mn substitutional atoms in the cationic sublattice of AlGaAs, (Al x Ga1?x )1?y Mn y As possesses optical properties strictly less than those of Al x Ga1?x As, especially its optical conductivity at the peak 1.256 eV. The results indicate that AlGaMnAs may be a good candidate for optoelectronics when exploited in optical fiber networks, and it can still be of great interest because of its promising potential when used for spintronics. 相似文献
1000.
In this paper, five conventional LNG processes were investigated by energy and exergy analysis methods. On the basis of the energy analysis, three‐stage process of Linde AG and Stat oil (mixed fluid cascade [MFC]) has less energy consumption than the other ones (0.254 kWh/kg liquefied natural gas). Also, coefficient of performance of the cycles of this process is higher compared with the other ones. Exergy analysis results showed that the maximum exergy efficiency is related to the MFC process (51.82%). However, performance of the MFC process in terms of quality and quantity of energy consumption is considerable. But using three cycles in this process needs more components and consequently more fixed costs. In this study, sensitivity of coefficient of performance, specific energy consumption, and indexes of exergy analysis were also analyzed versus important operating variables for all cases. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献