全文获取类型
收费全文 | 676篇 |
免费 | 12篇 |
国内免费 | 15篇 |
专业分类
系统科学 | 18篇 |
丛书文集 | 9篇 |
理论与方法论 | 8篇 |
现状及发展 | 163篇 |
研究方法 | 28篇 |
综合类 | 452篇 |
自然研究 | 25篇 |
出版年
2021年 | 4篇 |
2020年 | 8篇 |
2019年 | 5篇 |
2018年 | 14篇 |
2017年 | 9篇 |
2016年 | 20篇 |
2015年 | 22篇 |
2014年 | 21篇 |
2013年 | 42篇 |
2012年 | 103篇 |
2011年 | 55篇 |
2010年 | 11篇 |
2009年 | 35篇 |
2008年 | 21篇 |
2007年 | 10篇 |
2006年 | 16篇 |
2005年 | 13篇 |
2004年 | 41篇 |
2003年 | 18篇 |
2002年 | 30篇 |
2001年 | 41篇 |
2000年 | 17篇 |
1999年 | 10篇 |
1998年 | 19篇 |
1997年 | 22篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 6篇 |
1978年 | 9篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1970年 | 2篇 |
1969年 | 3篇 |
1968年 | 6篇 |
1967年 | 3篇 |
1966年 | 5篇 |
1963年 | 2篇 |
排序方式: 共有703条查询结果,搜索用时 62 毫秒
141.
We propose a new framework for building composite leading indicators for the Spanish economy using monthly targeted predictors and small‐scale dynamic factor models. Our leading indicator index, based on the low‐frequency components of four monthly economic variables, is able to predict the onset of the Spanish recessions as well as the gross domestic product (GDP) growth cycles and classical industrial production cycles, both historically and in real time. Also, our leading indicator provides substantial aid in forecasting annual and quarterly GDP growth rates. Using only real data available at the beginning of each forecast period, our indicator one‐step‐ahead forecasts shows substantial improvements over other alternatives. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
142.
143.
Aurea Anguera de Sojo Juan Ares Juan A. Lara David Lizcano María A. Martínez Juan Pazos 《Foundations of Science》2013,18(3):545-557
In the centenary year of Turing’s birth, a lot of good things are sure to be written about him. But it is hard to find something new to write about Turing. This is the biggest merit of this article: it shows how von Neumann’s architecture of the modern computer is a serendipitous consequence of the universal Turing machine, built to solve a logical problem. 相似文献
144.
本文以矩形孔为例,给出了物体平面相对系统光轴倾斜时夫琅和费衍射场的理论计算。 相似文献
145.
本文论述毕奥-萨伐尔定律求出的磁场是运动电荷的推迟效应可以忽略下的磁场的近似 相似文献
146.
基于随机模糊样本的统计学习理论基础 总被引:1,自引:0,他引:1
首先介绍了随机模糊理论的基本内容,进而证明了基于随机模糊样本的统计学习理论的关键定理,且讨论了学习过程一致收敛速度的界,为系统建立不确定样本的统计学习理论并构建相应的支持向量机奠定了理论基础. 相似文献
147.
148.
149.
Adriano Cavalleri Mariana F. Lindner Milton de S. Mendonça Jr 《Journal of Natural History》2016,50(21-22):1389-1410
The tribe Haplothripini includes a large diversity of Thysanoptera–Phlaeothripinae, comprising more than 550 species in about 35 genera. They are characterised by having a maxillary bridge in the head, prosternal basantra well developed and fore wings with a median constriction. Members of this group are present in all geographical regions, but are particularly poorly studied in Central and South America. In this study, we describe a new genus and species, Myrciathrips variabilis gen. et. sp. nov., and a new Haplothrips species; and propose two new combinations: Karnyothrips grassoi (De Santis), and Mirothrips vespicola (De Santis). A key to the nine Haplothripini genera now recognised from Central and South America is provided, together with an updated key to Haplothrips and Mirothrips species. A total of 45 species of Haplothripini are now recognised from Central and South America, and a list of these and their distributions is given. The genera Karnyothrips, Haplothrips and Leptothrips are the most commonly encountered, and some exotic species such as Androthrips ramachandrai and Dolichothrips indicus are now widespread in the Americas. 相似文献
150.
Marina Vianna Braga Paloma Martins Mendonça Rodrigo Rocha Barbosa Gary James Blomquist Shênia Patricia Corrêa Novo Juliana da Matta Furniel Dutra 《Journal of Natural History》2016,50(21-22):1381-1388
Insect puparia were found adhered to the ribs and other tissues in the abdominal cavity of a natural male mummy found in Itacambira (State of Minas Gerais, Brazil) dating to the Colonial Period. They were collected for identification by scanning electron microscopy, and for comparison of several morphological features with those described in the literature. The puparia were found open and dorsoventrally flattened, making it difficult to visualize the dorsal projections. The tegument is covered by tapered spines and contains rows of small tubercles on the dorsal and lateral regions of the puparium. The posterior spiracle consists of four parallel openings arranged in pairs. These results are indicative that the specimens belong to the species Megaselia scalaris (Loew, 1866) (Diptera: Phoridae). Additionally, cuticular hydrocarbons of the puparia were analysed by gas chromatography coupled to mass spectrometry and compared with the profile of M. scalaris reared in the laboratory. 相似文献