全文获取类型
收费全文 | 85864篇 |
免费 | 1186篇 |
国内免费 | 427篇 |
专业分类
电工技术 | 817篇 |
综合类 | 2326篇 |
化学工业 | 11905篇 |
金属工艺 | 4804篇 |
机械仪表 | 3110篇 |
建筑科学 | 2285篇 |
矿业工程 | 565篇 |
能源动力 | 1274篇 |
轻工业 | 3743篇 |
水利工程 | 1299篇 |
石油天然气 | 365篇 |
无线电 | 9450篇 |
一般工业技术 | 16643篇 |
冶金工业 | 2781篇 |
原子能技术 | 280篇 |
自动化技术 | 25830篇 |
出版年
2023年 | 51篇 |
2022年 | 81篇 |
2021年 | 164篇 |
2020年 | 154篇 |
2019年 | 183篇 |
2018年 | 14572篇 |
2017年 | 13494篇 |
2016年 | 10072篇 |
2015年 | 703篇 |
2014年 | 399篇 |
2013年 | 457篇 |
2012年 | 3311篇 |
2011年 | 9586篇 |
2010年 | 8384篇 |
2009年 | 5663篇 |
2008年 | 6840篇 |
2007年 | 7804篇 |
2006年 | 160篇 |
2005年 | 1242篇 |
2004年 | 1145篇 |
2003年 | 1191篇 |
2002年 | 558篇 |
2001年 | 109篇 |
2000年 | 188篇 |
1999年 | 68篇 |
1998年 | 71篇 |
1997年 | 39篇 |
1996年 | 55篇 |
1995年 | 20篇 |
1994年 | 17篇 |
1993年 | 18篇 |
1992年 | 11篇 |
1991年 | 27篇 |
1988年 | 9篇 |
1969年 | 25篇 |
1968年 | 43篇 |
1967年 | 33篇 |
1966年 | 42篇 |
1965年 | 45篇 |
1964年 | 11篇 |
1963年 | 28篇 |
1962年 | 22篇 |
1961年 | 18篇 |
1960年 | 30篇 |
1959年 | 35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 15 毫秒
11.
12.
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
13.
14.
15.
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
16.
17.
Cellulose dissolved in ionic liquid (1‐(carboxymethyl)pyridinium chloride)/water (60/40 w/w) mixture is regenerated in various non‐solvents, namely water, ethanol, methanol and acetone, to gain more insight into the contribution of non‐solvent medium to the morphology of regenerated cellulose. To this end, the initial and regenerated celluloses were characterized with respect to crystallinity, thermal stability, chemical structure and surface morphology using wide‐angle X‐ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy and scanning electron microscopy. According to the results, regardless of non‐solvent type, all regenerated samples have the same chemical structure and lower crystallinity in comparison to the initial cellulose, making them a promising candidate for efficient biofuel production based on enzymatic hydrolysis of cellulose. The reduction in crystallinity of regenerated samples is explained based on the potential of the non‐solvent to break the hydrogen bonds between cellulose chains and ionic liquid molecules as well as the affinity of water and non‐solvent which can be evaluated based on Hansen solubility parameter. The latter also determines the phase‐separation mechanism during the regeneration process, which in turn affects surface morphology of the regenerated cellulose. The pivotal effect of regenerated cellulose crystallinity on its thermal stability is also demonstrated. Regenerated cellulose with lower crystallinity is more susceptible to molecular rearrangement during heating and hence exhibits enhanced thermal stability. © 2019 Society of Chemical Industry 相似文献
18.
19.
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
20.
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