全文获取类型
收费全文 | 8576篇 |
免费 | 1479篇 |
国内免费 | 1002篇 |
专业分类
电工技术 | 374篇 |
技术理论 | 1篇 |
综合类 | 333篇 |
化学工业 | 1114篇 |
金属工艺 | 330篇 |
机械仪表 | 179篇 |
建筑科学 | 141篇 |
矿业工程 | 52篇 |
能源动力 | 371篇 |
轻工业 | 127篇 |
水利工程 | 39篇 |
石油天然气 | 80篇 |
武器工业 | 44篇 |
无线电 | 2085篇 |
一般工业技术 | 1374篇 |
冶金工业 | 145篇 |
原子能技术 | 79篇 |
自动化技术 | 4189篇 |
出版年
2024年 | 8篇 |
2023年 | 38篇 |
2022年 | 89篇 |
2021年 | 78篇 |
2020年 | 83篇 |
2019年 | 56篇 |
2018年 | 33篇 |
2017年 | 38篇 |
2016年 | 59篇 |
2015年 | 71篇 |
2014年 | 149篇 |
2013年 | 311篇 |
2012年 | 370篇 |
2011年 | 388篇 |
2010年 | 422篇 |
2009年 | 607篇 |
2008年 | 1097篇 |
2007年 | 1995篇 |
2006年 | 1779篇 |
2005年 | 909篇 |
2004年 | 424篇 |
2003年 | 322篇 |
2002年 | 305篇 |
2001年 | 202篇 |
2000年 | 232篇 |
1999年 | 158篇 |
1998年 | 164篇 |
1997年 | 135篇 |
1996年 | 125篇 |
1995年 | 90篇 |
1994年 | 66篇 |
1993年 | 108篇 |
1992年 | 107篇 |
1991年 | 16篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1988年 | 8篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1979年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
This work presents a distributed time‐slot assignment algorithm which adopts TDMA as Medium Access Control, specially suited to support applications with strict delay, jitter, and throughput requirements characterized by convergecast traffic pattern in sensor networks. (e.g. wireless video surveillance sensor networks). The proposed algorithm has three characteristics: (1) every node is guaranteed a path to the base station for its data delivery. In the path, sufficient resource is reserved and weighted fairness can be achieved. (2) It uses cascading time‐slot assignment and jitter minimization algorithm in each node to minimize jitter and end‐to‐end delay. (3) Nodes are only active during their scheduled slots and sleep otherwise. This offers energy saving by reducing idle listening and avoiding overhearing. The performance of the proposed algorithm is evaluated over simulations and analyzed theoretically in comparison with existing slot assignment algorithm. The results show that our algorithm provides lower end‐to‐end delay, jitter, and higher throughput. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
92.
The difference in the melting points of polyamide 66 (PA66) fiber and polyamide 6 (PA6) film permits the preparation of all-polyamide
(all-PA) composites by film-packing. Good interface performance and integrated consolidation structure in this all-PA composite
are contributed to the similar chemical composition between PA66 fiber and PA6 matrix. In this paper, the non-isothermal crystallization
kinetics and melting behaviors of PA6 matrix in all-PA composite are studied by differential scanning calorimetry (DSC), in
which the modified Avrami equation, Ozawa model, and Mo equation combining Avrami and Ozawa equation are employed. It is found
that the Mo equation exhibits great advantages in treating the non-isothermal crystallization kinetics for both neat PA6 and
PA6 matrix in all-PA composite. The crystal morphologies of single PA66 fiber–PA6 composite by polarizing microscope (POM)
clearly show a transcrystallinity layer of PA6 around PA66 fiber that proves a remarkable nucleation effect of PA66 fiber
surface on the crystallization of PA6 matrix. 相似文献
93.
Z. W. Du B. L. Shao A. S. Liu G. H. Wu J. F. Qian Z. Y. Zhang Z. Gao 《Journal of Materials Science》2011,46(8):2733-2740
The structure of near-stoichiometric Ni51Fe24Ga25 Heusler alloy synthesized by a melt-spinning technique has been studied using transmission electron microscopy. The main
phase possessed a local, well-defined L21 high-atomic order structure, and some fcc structural γ phase and lamellar twin structures were also present. At room temperature,
a rich variety of micro-modulated domains in the parent phase was observed. The domain structures were aligned along the 〈110〉,
〈100〉, 〈211〉, and ~14° off 〈110〉 directions, resulting in a complex tweed contrast. These are possibly the precursors of martensitic
transformation (MT). Below the MT temperature, Ms, the cubic parent phase transformed into modulated martensitic variants,
which were composed of lamellar structures with predominantly 10 and 14 M modulated structures along the 〈110〉 directions. 相似文献
94.
Shanmu Dong Xiao Chen Lin Gu Haibo Wang Pengxian Han Li Wang Liquan Chen 《Materials Research Bulletin》2011,46(6):835-839
TiN/VN core-shell composites are prepared by a two-step strategy involving coating of commercial TiN nanoparticles with V2O5·nH2O sols followed by ammonia reduction. The highest specific capacitance of 170 F g−1 is obtained when scanned at 2 mV s−1 and a promising rate capacity performance is maintained at higher voltage sweep rates. These results indicate that these composites with good electronic conductivity can deliver a favorable capacity performance. 相似文献
95.
Cr doped ZnO (Zn1 ? xCrxO) thin films with different Cr concentrations (0.4, 1.5, and 8.9 at.%) were deposited on Si substrates using RF magnetron sputtering. Film crystal structure was characterized using X-ray diffraction, and vibrating sample magnetometer measurements were used to investigate their magnetic properties. Unstable ZnO structure is present at low Cr concentrations, while secondary phases appear at higher Cr concentrations. 8.9 at.% Zn1 ? xCrxO film exhibits room temperature ferromagnetism and high 325 K Curie temperature, even after 300 °C annealing for 1 h. This result is promising and demonstrates Cr doped ZnO film's potential use in practical applications. 相似文献
96.
Dense nanocrystalline BaTiO3 ceramics are successfully prepared by the high pressure assisted sintering. Microstructures are observed by scanning electronic
microscopes. The grain sizes are estimated to be about 30 and 150 nm. In comparison, BaTiO3 ceramics with the grain size of 600 nm and 1.5 μm are fabricated by conventional pressure-less sintering. The thermal properties
of BaTiO3 ceramics with different grain sizes are investigated by differential scanning calorimetry and thermal expansion. The results
suggest that the enthalpy values for the tetragonal-cubic transition decreased and the thermal expansion values increased
with decreasing grain size. Furthermore, the Curie temperature shifts to lower temperature with decreasing grain size. 相似文献
97.
98.
采用尼龙无纺布(PNF)作为结构化增韧层,利用树脂传递模塑(RTM)工艺制备了PNF层间增韧改性的碳纤维增强环氧树脂基复合材料(U3160-PNF/3266),研究了U3160-PNF/3266复合材料的吸湿特性及湿热老化对其耐热性能的影响。结果表明:增韧前后复合材料具有相似的吸湿动力学特性,但在吸湿初期,U3160-PNF/3266复合材料具有更大的吸湿速率,达到饱和吸湿后,U3160-PNF/3266复合材料的饱和吸湿率约为0.96%,略大于非增韧复合材料U3160/3266的0.87%。随着湿热老化时间的增加,两种复合材料的玻璃化转变温度均逐渐降低,并随着吸湿率的饱和而趋于平稳,达到饱和吸湿后,U3160-PNF/3266和U3160/3266复合材料的玻璃化转变温度分别下降了约15%和14%。 相似文献
99.
100.
The present study validated the capability of the AM2.1, a model developed at NOAA's Geophysical Fluid Dynamics Laboratory (GFDL), in reproducing the fundamental features of the East Asian Subtropical Westerly Jet Stream (EASWJ). The main behaviors of the EASWJ are also investigated through the reanalysis of observational NCEP/NCAR data. The mean state of the EASWJ, including its intensity, location, structure, and seasonal evolution is generally well-portrayed in the model. Compared with the observation, the model tends to reproduce a weaker jet center. And, during summer, the simulated jet center is northward-situated. Results also demonstrate the model captures the variability of EASWJ during summer well. The results of the empirical orthogonal function (EOF) applied on the zonal wind at 200hPa (U200) over East Asia for both the observation and simulation indicate an inter-decadal shift around the late 1970s. The correlation coefficient between the corresponding principle components is as great as 0.42 with significance at the 99% confidence level. 相似文献