全文获取类型
收费全文 | 88285篇 |
免费 | 1175篇 |
国内免费 | 431篇 |
专业分类
电工技术 | 843篇 |
综合类 | 2325篇 |
化学工业 | 12329篇 |
金属工艺 | 4912篇 |
机械仪表 | 3132篇 |
建筑科学 | 2204篇 |
矿业工程 | 576篇 |
能源动力 | 1410篇 |
轻工业 | 3795篇 |
水利工程 | 1293篇 |
石油天然气 | 362篇 |
无线电 | 9857篇 |
一般工业技术 | 17357篇 |
冶金工业 | 3324篇 |
原子能技术 | 289篇 |
自动化技术 | 25883篇 |
出版年
2023年 | 75篇 |
2022年 | 104篇 |
2021年 | 181篇 |
2020年 | 157篇 |
2019年 | 132篇 |
2018年 | 14561篇 |
2017年 | 13494篇 |
2016年 | 10098篇 |
2015年 | 710篇 |
2014年 | 408篇 |
2013年 | 605篇 |
2012年 | 3341篇 |
2011年 | 9613篇 |
2010年 | 8449篇 |
2009年 | 5799篇 |
2008年 | 6930篇 |
2007年 | 7883篇 |
2006年 | 238篇 |
2005年 | 1313篇 |
2004年 | 1217篇 |
2003年 | 1260篇 |
2002年 | 619篇 |
2001年 | 162篇 |
2000年 | 241篇 |
1999年 | 126篇 |
1998年 | 197篇 |
1997年 | 135篇 |
1996年 | 164篇 |
1995年 | 91篇 |
1994年 | 94篇 |
1993年 | 88篇 |
1992年 | 70篇 |
1991年 | 91篇 |
1990年 | 68篇 |
1989年 | 47篇 |
1988年 | 55篇 |
1987年 | 45篇 |
1986年 | 43篇 |
1985年 | 47篇 |
1981年 | 35篇 |
1968年 | 45篇 |
1967年 | 35篇 |
1966年 | 50篇 |
1965年 | 45篇 |
1959年 | 35篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1956年 | 34篇 |
1955年 | 66篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
11.
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
12.
13.
14.
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
15.
16.
Karishma Tiwari Pulak Sarkar Solagna Modak Harwinder Singh Sumit Kumar Pramanik Santanu Karan Amitava Das 《Advanced materials (Deerfield Beach, Fla.)》2020,32(8):1905621
Separation membranes with higher molecular weight cut-offs are needed to separate ions and small molecules from a mixed feed. The molecular sieving phenomenon can be utilized to separate smaller species with well-defined dimensions from a mixture. Here, the formation of freestanding polyimine nanofilms with thicknesses down to ≈14 nm synthesized via self-assembly of pre-synthesized imine oligomers is reported. Nanofilms are fabricated at the water–xylene interface followed by reversible condensation of polymerization according to the Pieranski theory. Polyimine nanofilm composite membranes are made via transferring the freestanding nanofilm onto ultrafiltration supports. High water permeance of 49.5 L m-2 h−1 bar−1 is achieved with a complete rejection of brilliant blue-R (BBR; molecular weight = 825 g mol−1) and no more than 10% rejection of monovalent and divalent salts. However, for a mixed feed of BBR dye and monovalent salt, the salt rejection is increased to ≈18%. Membranes are also capable of separating small dyes (e.g., methyl orange; MO; molecular weight = 327 g mol−1) from a mixed feed of BBR and MO. Considering a thickness of ≈14 nm and its separation efficiency, the present membrane has significance in separation processes. 相似文献
17.
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
18.
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
19.
Recent increase in the number of digital photos in the content sharing and social networking websites has created an endless demand for techniques to analyze, navigate, and summarize these images. In this paper, we focus on image collection summarization. Earlier methods in image collection summarization consider representativeness and diversity criteria while recent ones also consider other criteria such as image quality, aesthetic or appeal. In this paper, we propose a multi-criteria context-sensitive approach for social image collection summarization. In the proposed method, two different sets of features are combined while each one looks at different criteria for image collection summarization: social attractiveness features and semantic features. The first feature set considers different aspects that make an image appealing such as image quality, aesthetic, and emotion to create attractiveness score for input images while the second one covers semantic content of images and assigns semantic score to them. We use social network infrastructure to identify attractiveness features and domain ontology for extracting ontology features. The final summarization is provided by integrating the attractiveness and semantic features of input images. The experimental results on a collection of human generated summaries on a set of Flickr images demonstrate the effectiveness of the proposed image collection summarization approach. 相似文献
20.
The physical mechanism of highly efficient photoluminescence (PL) emission from p-type silicon is described by a comparative study of the effectiveness of the etching parameters in an electrochemical anodization technique. Two series of porous silicon samples were prepared in a combination of anodization current and time, to maintain the total amount of anodic charge transfer constant. Photoluminescence studies show that irrespective of the amount of charge transfer, the samples prepared with comparatively higher current density show an efficient PL as well as stronger blueshift in the emission energy vis-à-vis the samples prepared for longer durations. An overall decrease in crystallite size, as estimated by Raman spectral analysis, was observed for both series of samples with the progress of charge transfer. Comparative analysis shows a marginal difference in crystallite size for both series of samples in the initial state of charge transfer, whereas major differences arise at higher values. This is explained with the formation of silicon suboxide on the porous surface at higher current density, leading to initiation of side wall reaction, and higher reduction rate in crystallite size as well as strong luminescence due to the carrier quantum confinement effect. 相似文献