全文获取类型
收费全文 | 97485篇 |
免费 | 11065篇 |
国内免费 | 7056篇 |
专业分类
电工技术 | 8348篇 |
技术理论 | 2篇 |
综合类 | 9747篇 |
化学工业 | 13512篇 |
金属工艺 | 6168篇 |
机械仪表 | 6907篇 |
建筑科学 | 7947篇 |
矿业工程 | 3244篇 |
能源动力 | 2519篇 |
轻工业 | 10199篇 |
水利工程 | 2883篇 |
石油天然气 | 3369篇 |
武器工业 | 1208篇 |
无线电 | 10616篇 |
一般工业技术 | 9267篇 |
冶金工业 | 3469篇 |
原子能技术 | 1610篇 |
自动化技术 | 14591篇 |
出版年
2024年 | 332篇 |
2023年 | 1731篇 |
2022年 | 3667篇 |
2021年 | 4864篇 |
2020年 | 3661篇 |
2019年 | 2677篇 |
2018年 | 2997篇 |
2017年 | 3394篇 |
2016年 | 2897篇 |
2015年 | 4391篇 |
2014年 | 5753篇 |
2013年 | 6781篇 |
2012年 | 8083篇 |
2011年 | 8372篇 |
2010年 | 7943篇 |
2009年 | 7334篇 |
2008年 | 7277篇 |
2007年 | 7115篇 |
2006年 | 6147篇 |
2005年 | 4852篇 |
2004年 | 3482篇 |
2003年 | 2492篇 |
2002年 | 2307篇 |
2001年 | 1988篇 |
2000年 | 1621篇 |
1999年 | 964篇 |
1998年 | 441篇 |
1997年 | 410篇 |
1996年 | 347篇 |
1995年 | 277篇 |
1994年 | 206篇 |
1993年 | 173篇 |
1992年 | 130篇 |
1991年 | 98篇 |
1990年 | 68篇 |
1989年 | 73篇 |
1988年 | 50篇 |
1987年 | 30篇 |
1986年 | 30篇 |
1985年 | 18篇 |
1984年 | 17篇 |
1983年 | 5篇 |
1982年 | 13篇 |
1981年 | 16篇 |
1980年 | 31篇 |
1979年 | 15篇 |
1977年 | 2篇 |
1966年 | 1篇 |
1959年 | 15篇 |
1951年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
52.
Scientometrics - Due to the development of academic, more and more attentions are paid to citation recommendation. To solve the citation recommendation problem, researchers begin to focus on the... 相似文献
53.
54.
就经典分水岭图像分割算法中存在的过分割问题,提出一种结合位图切割和区域合并的彩色图像分割算法。对原始彩色图像通过空域梯度算子求其梯度图像,并利用位图切割重建梯度图像;对新梯度图像进行分水岭预分割;对预分割图像基于异质性最小原则进行区域合并,并获得最终分割结果。相比于现有的同类方法,该算法引入位图切割,抑制噪声对分割结果的影响,在边缘模糊处分割准确,得到符合人类视觉的较小分割区域数目,同时在运行效率上提高。 相似文献
55.
Jie Gao Zhikai Li Mei Dong Weibin Fan Jianguo Wang 《Frontiers of Chemical Science and Engineering》2020,14(5):847
Coal-based ethanol production by hydration of ethylene is limited by the low equilibrium ethylene conversion at elevated temperature. To improve ethylene conversion, coupling hydration of ethylene with a potential ethanol consumption reaction was analyzed thermodynamically. Five reactions have been attempted and compared: (1) dehydration of ethanol to ethyl ether ( ), (2) dehydrogenation of ethanol to acetaldehyde ( ), (3) esterification of acetic acid with ethanol ( ), (4) dehydrogenation of ethanol to ethyl acetate ( ), and (5) oxidative dehydrogenation of ethanol to ethyl acetate ( ). The equilibrium constants and equilibrium distributions of the coupled reactions were calculated and the effects of feed composition, temperature and pressure upon the ethylene equilibrium conversion were examined. The results show that dehydrogenation of ethanol to acetaldehyde has little effect on ethylene conversion, whereas for dehydrogenation of ethanol to acetaldehyde and ethyl acetate, ethylene conversion can be improved from 8% to 12.8% and 18.5%, respectively, under conditions of H2O/C2H4 = 2, 10 atm and 300°C. The esterification of acetic acid with ethanol can greatly enhance the ethylene conversion to 22.5%; in particular, ethylene can be actually completely converted to ethyl acetate by coupling oxidative dehydrogenation of ethanol. 相似文献
56.
采用酸处理方法对CoPd/TiO2催化剂进行改性,并将酸改性催化剂用于温和条件下CH4-CO2梯阶转化直接合成C2含氧化合物(乙酸和乙醇)的反应。在150~300℃考察了浸酸方式和不同种类酸处理对催化剂活性和选择性的影响。采用X射线衍射(XRD)、X射线光电子能谱(XPS)、NH3程序升温脱附(NH3-TPD)和N2吸附对催化剂进行了表征。结果表明,酸改性明显提高了CoPd/TiO2上C2含氧化合物的生成速率和选择性。浸酸方式对催化剂性能和结构有显著影响,先用酸浸渍载体然后再浸渍活性金属所得催化剂具有更高的活性。在H3PO4、HNO3和HCl中,H3PO4浸渍的催化剂活性最佳,在150℃时C2含氧化合物(乙酸和乙醇)的生成速率为3365 μg/(g·h),选择性达到91%。 相似文献
57.
The aim of this study is to investigate the synergistic effects of modified TiO2/multifunctionalized graphene oxide nanosheets at different ratios on the interface compatibility between starch and poly(lactic acid) (PLA). To this end, silanylated nano-TiO2 (MTiO2, 1 and 2%) and alkylated maleic anhydride grafted graphene oxide (f-GO, 0.1, 0.2, and 0.4%) at different combinations are blended with the PLA-starch composites using solution blending technique. Then, the synergistic effects of MTiO2 and f-GO on PLA/starch matrix are investigated in terms of the morphology, crystallinity, structural characterization, thermal stability, dynamic mechanical, and antiaging properties, and the related mechanisms. The Raman and Fourier transform infrared spectroscopy spectra verify the successful synthesis of the two modified nanofillers (f-GO and MTiO2) and the formation of strong hydrogen bond within the PLA-starch nanocomposites. Due to the strong interfacial interaction and the synergistic effect from the combination of 1% MTiO2 and 0.2% f-GO, obvious improvement was observed in PLA-starch versus other nanocomposites in terms of morphology, thermal stability, surface hydrophobicity, storage modulus, ultraviolet-shielding capacity, and aging-resistance. Furthermore, differential scanning calorimeter (DSC), isothermal crystallization kinetic, and X-ray diffraction analysis demonstrate that f-GO and the M-TiO2 significantly synergize in enhancing the crystallization rate and crystallinity of PLA/starch matrix. These results provide novel insights for constructing high-performance nanocomposites and facilitate their applications in food packaging. 相似文献
58.
Shensong Wang Zheng Wu Jie Chen Jiangping Ma Jingshi Ying Shouchen Cui Shigang Yu Yongming Hu Jinhe Zhao Yanmin Jia 《Ceramics International》2019,45(9):11703-11708
In this work, the hydrothermally-synthesized sodium niobate nanowires were used to decompose Rhodamine B dye solution through the piezo-catalytic effect. With the sodium niobate catalyst, a high piezo-catalytic degradation ratio of ~80% was achieved under the excitation of vibration for the Rhodamine B dye solution (~5?mg/l). These active species in the catalytic process, hydroxyl radicals and superoxide radicals with the strong oxidation ability, were also observed, which confirmed the key role of piezoelectric effect for piezo-catalysis. The piezo-catalysis of sodium niobate nanowires provides a high-efficiency and reusable tool in application in depredating the dye wastewater. 相似文献
59.
60.
Baizhan Li Chenqiu Du Hong Liu Wei Yu Jie Zheng Meilan Tan Zhenxing Jin Wenjie Li Jing Wu Lu Chen Runming Yao 《Indoor air》2019,29(2):308-319
The extensive research interests in environmental temperature can be linked to human productivity / performance as well as comfort and health; while the mechanisms of physiological indices responding to temperature variations remain incompletely understood. This study adopted a physiological sensory nerve conduction velocity (SCV) as a temperature‐sensitive biomarker to explore the thermoregulatory mechanisms of human responding to annual temperatures. The measurements of subjects’ SCV (over 600 samples) were conducted in a naturally ventilated environment over all four seasons. The results showed a positive correlation between SCV and annual temperatures and a Boltzmann model was adopted to depict the S‐shaped trend of SCV with operative temperatures from 5°C to 40°C. The SCV increased linearly with operative temperatures from 14.28°C to 20.5°C and responded sensitively for 10.19°C‐24.59°C, while tended to be stable beyond that. The subjects’ thermal sensations were linearly related to SCV, elaborating the relation between human physiological regulations and subjective thermal perception variations. The findings reveal the body SCV regulatory characteristics in different operative temperature intervals, thereby giving a deeper insight into human autonomic thermoregulation and benefiting for built environment designs, meantime minimizing the temperature‐invoked risks to human health and well‐being. 相似文献