全文获取类型
收费全文 | 152165篇 |
免费 | 8823篇 |
国内免费 | 4248篇 |
专业分类
电工技术 | 6652篇 |
技术理论 | 8篇 |
综合类 | 7565篇 |
化学工业 | 21517篇 |
金属工艺 | 9019篇 |
机械仪表 | 7495篇 |
建筑科学 | 7888篇 |
矿业工程 | 3000篇 |
能源动力 | 3202篇 |
轻工业 | 7932篇 |
水利工程 | 2941篇 |
石油天然气 | 3988篇 |
武器工业 | 836篇 |
无线电 | 17321篇 |
一般工业技术 | 23744篇 |
冶金工业 | 5479篇 |
原子能技术 | 1229篇 |
自动化技术 | 35420篇 |
出版年
2024年 | 338篇 |
2023年 | 1328篇 |
2022年 | 2827篇 |
2021年 | 3800篇 |
2020年 | 2810篇 |
2019年 | 2136篇 |
2018年 | 16652篇 |
2017年 | 15814篇 |
2016年 | 12230篇 |
2015年 | 4045篇 |
2014年 | 4325篇 |
2013年 | 5057篇 |
2012年 | 8611篇 |
2011年 | 15088篇 |
2010年 | 13123篇 |
2009年 | 10074篇 |
2008年 | 11156篇 |
2007年 | 11722篇 |
2006年 | 3915篇 |
2005年 | 4320篇 |
2004年 | 3207篇 |
2003年 | 2691篇 |
2002年 | 1926篇 |
2001年 | 1205篇 |
2000年 | 1250篇 |
1999年 | 1010篇 |
1998年 | 776篇 |
1997年 | 631篇 |
1996年 | 655篇 |
1995年 | 427篇 |
1994年 | 364篇 |
1993年 | 264篇 |
1992年 | 230篇 |
1991年 | 150篇 |
1990年 | 107篇 |
1989年 | 83篇 |
1988年 | 87篇 |
1987年 | 43篇 |
1986年 | 32篇 |
1968年 | 43篇 |
1967年 | 33篇 |
1966年 | 42篇 |
1965年 | 45篇 |
1960年 | 30篇 |
1959年 | 45篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1956年 | 34篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
51.
In this paper, we consider the classical finite mixture model, which is an effective tool for modeling lifetime distributions for random samples from heterogeneous populations. We discuss new results on stochastic comparison for two finite mixtures when each of them is drawn from one of the following semiparametric families, i.e., proportional hazards, accelerated lifetime and proportional reversed hazards. 相似文献
52.
53.
54.
Variations of Incomplete Open Cubes is the major project by the twentieth-century conceptual artist Sol LeWitt. In this paper we interpret the enumerative component of the project as embeddings of graphs. This formulation permits use of an algorithm to check the completeness of the list of the structures produced by the artist. Our conclusion is that the artist found the correct number of structures (that is, 122), but that his list contains a mistake in the presentation of a pair of incomplete cubes, a discovery that appears not to have been noted before. 相似文献
55.
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
56.
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
57.
58.
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
59.
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
60.
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