全文获取类型
收费全文 | 217220篇 |
免费 | 15982篇 |
国内免费 | 7938篇 |
专业分类
电工技术 | 11362篇 |
技术理论 | 14篇 |
综合类 | 11581篇 |
化学工业 | 36002篇 |
金属工艺 | 13020篇 |
机械仪表 | 13116篇 |
建筑科学 | 13431篇 |
矿业工程 | 5617篇 |
能源动力 | 5241篇 |
轻工业 | 12831篇 |
水利工程 | 3963篇 |
石油天然气 | 13124篇 |
武器工业 | 1436篇 |
无线电 | 22922篇 |
一般工业技术 | 32647篇 |
冶金工业 | 13959篇 |
原子能技术 | 5426篇 |
自动化技术 | 25448篇 |
出版年
2024年 | 936篇 |
2023年 | 3117篇 |
2022年 | 6078篇 |
2021年 | 8311篇 |
2020年 | 6207篇 |
2019年 | 5314篇 |
2018年 | 6636篇 |
2017年 | 7227篇 |
2016年 | 6621篇 |
2015年 | 7595篇 |
2014年 | 9827篇 |
2013年 | 11833篇 |
2012年 | 12662篇 |
2011年 | 13653篇 |
2010年 | 11722篇 |
2009年 | 11234篇 |
2008年 | 11085篇 |
2007年 | 10470篇 |
2006年 | 10051篇 |
2005年 | 8606篇 |
2004年 | 6252篇 |
2003年 | 6010篇 |
2002年 | 5968篇 |
2001年 | 5297篇 |
2000年 | 4904篇 |
1999年 | 4733篇 |
1998年 | 3756篇 |
1997年 | 3181篇 |
1996年 | 2953篇 |
1995年 | 2588篇 |
1994年 | 2154篇 |
1993年 | 1697篇 |
1992年 | 1569篇 |
1991年 | 1364篇 |
1990年 | 1324篇 |
1989年 | 1201篇 |
1988年 | 1069篇 |
1987年 | 948篇 |
1986年 | 855篇 |
1985年 | 777篇 |
1984年 | 754篇 |
1981年 | 698篇 |
1979年 | 743篇 |
1978年 | 784篇 |
1977年 | 749篇 |
1976年 | 769篇 |
1975年 | 717篇 |
1974年 | 721篇 |
1973年 | 726篇 |
1972年 | 706篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
Hao Li Pengcheng Zhang Shengquan Yu Hongyu Yang Bin Tang Fuhai Li Shuren Zhang 《Ceramics International》2019,45(9):11639-11647
Mg2(Ti1-xSnx)O4 (x?=?0–1) ceramics were prepared through conventional solid-state method. This paper focused on the dependence of microwave dielectric properties on crystal structural characteristics via crystal structure refinement, Raman spectra study and complex chemical bond theory. XRD spectrums delineated the phase information of a spinel structure, and structural characteristic of these compositions were achieved with the help of Rietveld refinements. Raman spectrums were used to depict the correlations between vibrational phonon modes and dielectric properties. The variation of permittivity is ascribed to the Mg2(Ti1-xSnx)O4 average bond covalency. The relationship among the B-site octahedral bond energy, tetrahedral bond energy and temperature coefficient are discussed by defining on the change rate of bond energy and the contribution rate of octahedral bond energy. The quality factor is affected by systematic total lattice energy, and the research of XPS patterns illustrated that oxygen vacancies can be effectively restrained in rich oxygen sintering process. Obviously, the microwave dielectric properties of Mg2(Ti1-xSnx)O4 compounds were obtained (= 12.18, ?=?170,130?GHz, ?=??53.1?ppm/°C, x?=?0.2). 相似文献
53.
54.
Understanding semantic word shifts in scientific domains is essential for facilitating interdisciplinary communication. Using a data set of published papers in the field of information retrieval (IR), this paper studies the semantic shifts of words in IR based on mining per-word topic distribution over time. We propose that semantic word shifts not only occur over time, but also over topics. The shifts are examined from two perspectives, the topic-level and the context-level. According to the over-time word-topic distribution, stable words and unstable words are recognized. The diverging and converging trends in the unstable type reveal characteristics of the topic evolution process. The context-level shifts are further detected by similarities between word vectors. Our work associates semantic word shifts with the evolving of topics, which facilitates a better understanding of semantic word shifts from both topics and contexts. 相似文献
55.
Research funding has been seen as one of the most important resource in the reward system of science. And usage of publications denotes an interesting perspective of user behavior in scientific communication. This study aims to address the relationship between funding and Usage Count, which is a new metrics item established on the platform of Web of Science. Full records of 300,010 articles published in 2013 were downloaded in October 2015, and divided into six disciplines, including information science library science, education educational research, economics, computer science, materials science, and chemistry. Seven indicators were proposed to measure the impact, including Funding rate, Citation per paper, Usage rate, Usage per paper, Citation difference, Usage difference, and Conversion rate. It concluded funding has impact on usage and citation, and funded papers attract more usage, but varying in different disciplines. Usage Count can be used in the extension of citation metrics but with limits. This study originally engages with usage metrics and detected that there is positive correlation between usage and funding. 相似文献
56.
57.
L. S. Belevskii N. V. Koptseva I. V. Belevskaya Yu. Yu. Efimova 《Russian Metallurgy (Metally)》2015,2015(9):753-758
The microstructure and properties of the functional coatings formed by impact friction processing of product surfaces with a flexible tool are studied. It is established that the processing produces a hard nanostructured surface layer with fragments up to 0.13 µm in size, as it is achieved by severe plastic deformation. 相似文献
58.
Golovin V. A. Pechnikov N. V. Shchelkov V. A. Tsivadze A. Yu. 《Protection of Metals and Physical Chemistry of Surfaces》2018,54(6):1221-1232
Protection of Metals and Physical Chemistry of Surfaces - The possibility is shown of creating a chart of local corrosion damage in the walls of heat-exchange tubes on the basis of the data of... 相似文献
59.
Hai Huang Haichao An Haibo Ma Shenyan Chen 《International journal for numerical methods in engineering》2019,117(3):291-315
This work presents an engineering method for optimizing structures made of bars, beams, plates, or a combination of those components. Corresponding problems involve both continuous (size) and discrete (topology) variables. Using a branched multipoint approximate function, which involves such mixed variables, a series of sequential approximate problems are constructed to make the primal problem explicit. To solve the approximate problems, genetic algorithm (GA) is utilized to optimize discrete variables, and when calculating individual fitness values in GA, a second-level approximate problem only involving retained continuous variables is built to optimize continuous variables. The solution to the second-level approximate problem can be easily obtained with dual methods. Structural analyses are only needed before improving the branched approximate functions in the iteration cycles. The method aims at optimal design of discrete structures consisting of bars, beams, plates, or other components. Numerical examples are given to illustrate its effectiveness, including frame topology optimization, layout optimization of stiffeners modeled with beams or shells, concurrent layout optimization of beam and shell components, and an application in a microsatellite structure. Optimization results show that the number of structural analyses is dramatically decreased when compared with pure GA while even comparable to pure sizing optimization. 相似文献
60.
This study assessed the collection efficiency (CE) of two popularly used sampling devices (BioSampler and Coriolis sampler) for fungal aerosols. Phosphate‐buffered saline (PBS) supplemented with or without surfactant (Tween‐20, Tween‐80, or Triton X‐100) and antifoam agent was prepared and used as collection liquids. The agar impactor (BioStage) was simultaneously operated with liquid‐based samplers to collect fungi from seven sites located at a university building, public library, and animal farming. Fungal concentrations determined by liquid samplers were divided by those by BioStage, and the ratio values represented CE. Results indicate that the CE of BioSampler was superior to that of Coriolis (P = 0.0001) and the PBS containing surfactant collected fungi better than that without surfactant (P < 0.0001), whereas antifoam agent showed no influence (P = 0.8). Moreover, fungal concentrations determined by BioSampler with surfactant‐added PBS were statistically indifferent from those by BioStage (P > 0.05) with a Spearman correlation coefficient of 0.81‐0.83 (P < 0.01). In addition to sampler and collection liquid, sampling location was also identified as a significant CE factor (P = 0.006), implying potential influences by fungal genera in the studied fields. Overall, BioSampler with surfactant‐supplemented PBS (eg, Triton X‐100) is recommended considering the great CE and compatibility with a variety of analytical assays. 相似文献