全文获取类型
收费全文 | 98598篇 |
免费 | 9872篇 |
国内免费 | 4881篇 |
专业分类
电工技术 | 7270篇 |
技术理论 | 10篇 |
综合类 | 7231篇 |
化学工业 | 15341篇 |
金属工艺 | 5966篇 |
机械仪表 | 6178篇 |
建筑科学 | 7916篇 |
矿业工程 | 3292篇 |
能源动力 | 2864篇 |
轻工业 | 5990篇 |
水利工程 | 2098篇 |
石油天然气 | 5731篇 |
武器工业 | 1016篇 |
无线电 | 11677篇 |
一般工业技术 | 11182篇 |
冶金工业 | 4194篇 |
原子能技术 | 1317篇 |
自动化技术 | 14078篇 |
出版年
2024年 | 296篇 |
2023年 | 1751篇 |
2022年 | 3213篇 |
2021年 | 4720篇 |
2020年 | 3619篇 |
2019年 | 2815篇 |
2018年 | 3296篇 |
2017年 | 3569篇 |
2016年 | 3200篇 |
2015年 | 4470篇 |
2014年 | 5487篇 |
2013年 | 6573篇 |
2012年 | 7238篇 |
2011年 | 7787篇 |
2010年 | 6635篇 |
2009年 | 6138篇 |
2008年 | 5938篇 |
2007年 | 5430篇 |
2006年 | 5363篇 |
2005年 | 4568篇 |
2004年 | 3077篇 |
2003年 | 2362篇 |
2002年 | 2167篇 |
2001年 | 1787篇 |
2000年 | 1852篇 |
1999年 | 1912篇 |
1998年 | 1463篇 |
1997年 | 1246篇 |
1996年 | 1228篇 |
1995年 | 948篇 |
1994年 | 785篇 |
1993年 | 581篇 |
1992年 | 463篇 |
1991年 | 308篇 |
1990年 | 246篇 |
1989年 | 205篇 |
1988年 | 182篇 |
1987年 | 107篇 |
1986年 | 79篇 |
1985年 | 50篇 |
1984年 | 29篇 |
1983年 | 27篇 |
1982年 | 44篇 |
1981年 | 22篇 |
1980年 | 19篇 |
1979年 | 9篇 |
1977年 | 9篇 |
1976年 | 11篇 |
1959年 | 9篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
As haze intensifies in China, controlling haze emission has become the country's top priority for environmental protection. Because haze moves across different regions, it is necessary to develop a data envelopment analysis (DEA) model underpinned by both competition and cooperation to evaluate the haze emission efficiency in different provinces. This study innovatively adopts the spatial econometrics to construct the co-opetition matrices of Chinese provinces, then builds the co-opetition DEA model to evaluate the haze emission efficiency of them, and finally uses the haze data of 2015 as an example to assess the applicability of the model. The results of the study include the following: First, compared with the traditional CCR (A. Charnes & W. W. Cooper & E. Rhodes) model, this study constructs the co-opetition DEA cross-efficiency model that integrates haze's feature of cross-border moving; thus, it is more in line with the reality of haze emission and movement. Second, compared with the efficiency value gained from the CCR model, the haze emission efficiency values for Tianjin and Guangdong, two decision-making units, register greater variance when using the DEA model. The reason might lie in that they have a different spatial transportation relationship with their surrounding provinces. Third, the haze emission efficiency of provinces, according to the evaluation based on the co-opetition DEA method, varies greatly: Those with high efficiency are mostly inland provinces with slow economic growth and adverse climatic conditions, whereas many of the provinces with low efficiency are located in the relatively prosperous East China. The specific co-opetition DEA model constructed in this study enriches the research on the DEA model, which can be applied to the emission efficiency evaluation of similar pollutants around the world and can contribute empirical support to the haze reducing efforts of the government with its empirical results. 相似文献
82.
生姜的根状茎为使用部分,其中包含姜油酮、姜油醇、姜油酚、蛋白质、粗脂肪、糖,并且钙、铁的含量也较为丰富,是人们日常生活当中不可或缺的调味品,还能够加工成为姜片、糖姜片和盐姜片等诸多食品,其在医药方面的应用也较为广泛,备受人们的推崇与喜爱。我国在生姜栽培方面的历史较为悠久,技术也较为成熟,每年生姜出口贸易都能为我国带来非常可观的经济效益。 相似文献
83.
Pyrochlore-type WO_3 powder was synthesized via hydrothermal method using aqueous sodium tungstate solution and oxalic acid as raw materials. The as-prepared powder was made into a soliquoid,from which films were made by dip coating process with indium-tin oxide(ITO).The obtained films were characterized by thermogravimetric and differential thermal analysis(TG-DTA), X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM), cyclic voltammetry(CV), chronoamperometry(CA) and ultravioletvisible(UV-Vis) absorption. Results show that the crystal of the pyrochlore-type WO_3 powder is perfect. When the calcination temperature rises from room temperature to500 ℃,the pyrochlore-type structure first becomes deformed, then it is destroyed and turns into amorphous phase,finally it will completely convert to WO_3 with a monoclinic structure. Electrochemical and optical tests demonstrate that the film calcined at 300 ℃ exhibits the best electrochromic performance and has a coloration efficiency of up to 68.5 cm~2 C~(-1) at 884 nm. 相似文献
84.
85.
Zhiyuan Jiang Peng Liu Qihui Chen Hung-Jue Sue Tim Bremner Lorenzo P. DiSano 《应用聚合物科学杂志》2020,137(33):48966
Interest in developing high-performance blends for niche applications has grown significantly in efforts to meet ever-increasing harsh environment demands. In this work, four model poly(aryl-ether-ketone)/polybenzimidazole (PAEK/PBI) blends were chosen to study the influence of premixing methods, processing, and matrix polymers, on their mechanical properties. Among the model poly(ether ether ketone) (PEEK) and PBI blends, mechanical properties are greatly enhanced by melt premixing. The molding process mainly affects the matrix crystallinity, which in turn greatly influences fracture toughness of the blend. Poly(ether ketone ketone) (PEKK) and PBI blend exhibits a slightly lower tensile strength and fracture toughness than PEEK/PBI due to the differences in inherent properties of PEEK and PEKK matrices and their interfacial interaction with PBI. The processing−structure–property relationship of PAEK/PBI blends is established to help guide optimal design of high-performance polymer blends for structural applications. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48966. 相似文献
86.
The support flux was first investigated as a separate influencing factor for its effect on performances of ceramic filtration membranes. Three pre-membranes were prepared by tape-casting and then transfer-coated to supports to form dual-layer ceramic membranes after sintering. Experiments demonstrated that membrane layers with almost the same properties were obtained despite the huge difference in support flux. When the support flux increases from 3.120 to 97.53 m3m?2h?1, the flux of these three membrane series have increased by 75%, 186% and 228%, respectively. Experimental rules can provide structural design and evaluation from the perspective of permeability. The limit membrane flux of a certain system was derived according to the resistance distribution law of internal membrane structure and the Darcy's theorem. On this basis, a method for designing support flux was proposed. Furthermore, we present a criterion to quickly and easily evaluate the match between the support and the top layer, which is the ratio of membrane resistance to total resistance. Finally, the filtration resistance of penetration caused by suction of membrane particles into the support was measured for the first time, taking the advantage of the transfer-coating method that inherently free of penetration. Our works are expected to deepen the understanding of the ceramic membrane structure and provided guidance for its rational design and optimization. 相似文献
87.
由于臭氧的强的氧化性能,使其成为一种强氧化剂和消毒剂;臭氧技术已经广泛用于废水处理行业,臭氧具有较好的的消毒杀菌、脱色、除臭味等作用,文章通过介绍臭氧的一些基本性质,臭氧消毒杀菌、氧化、脱色及除臭味的机理,臭氧的制取方式,现代臭氧技术的研究方向等,为废水处理中臭氧技术的应用提供参考。 相似文献
88.
89.
Peng Jiang Jiafeng Lu Kun Li Xiquan Chen Ruiqi Dan 《Fullerenes, Nanotubes and Carbon Nanostructures》2020,28(5):381-386
AbstractPreparation condition can affect the structure and the properties of nanofiber membrane. In order to explore suitable conditions to prepare the Fe3O4/PVDF nanofiber membrane with good hydrophobicity, the hydrophobicity of Fe3O4/PVDF nanofiber membranes obtained by electrospinning was investigated by changing preparation conditions like weight percentage of Fe3O4 nanoparticles, blending quality concentration of poly (vinylidene fluoride) (PVDF) and Fe3O4 nanoparticles, and positive voltage. And the variations of hydrophobicity of Fe3O4/PVDF nanofiber membranes modified by 1H, 1H, 2H, 2H-perfluorodecyl trimethoxysilane were studied. The results show that the hydrophobicity of Fe3O4/PVDF nanofiber membranes has changed under different preparation conditions. The contact angles of samples increased after a modification by 1H, 1H, 2H, 2H-perfluorodecyl trimethoxysilane, which indicates that the hydrophobicity of Fe3O4/PVDF nanofiber membranes has been enhanced. 相似文献
90.