全文获取类型
收费全文 | 3592篇 |
免费 | 304篇 |
国内免费 | 5篇 |
专业分类
3901篇 |
出版年
2024年 | 4篇 |
2023年 | 21篇 |
2022年 | 60篇 |
2021年 | 97篇 |
2020年 | 48篇 |
2019年 | 66篇 |
2018年 | 88篇 |
2017年 | 70篇 |
2016年 | 133篇 |
2015年 | 191篇 |
2014年 | 215篇 |
2013年 | 276篇 |
2012年 | 294篇 |
2011年 | 285篇 |
2010年 | 185篇 |
2009年 | 159篇 |
2008年 | 192篇 |
2007年 | 203篇 |
2006年 | 195篇 |
2005年 | 203篇 |
2004年 | 190篇 |
2003年 | 175篇 |
2002年 | 160篇 |
2001年 | 33篇 |
2000年 | 19篇 |
1999年 | 29篇 |
1998年 | 53篇 |
1997年 | 33篇 |
1996年 | 21篇 |
1995年 | 22篇 |
1994年 | 14篇 |
1993年 | 18篇 |
1992年 | 13篇 |
1991年 | 10篇 |
1990年 | 10篇 |
1989年 | 9篇 |
1988年 | 9篇 |
1987年 | 11篇 |
1986年 | 5篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1977年 | 4篇 |
1974年 | 4篇 |
1964年 | 3篇 |
1962年 | 3篇 |
排序方式: 共有3901条查询结果,搜索用时 0 毫秒
41.
Capsule Using simulations in a geographical information system our results showed that systematic sampling with quadrats was the most accurate, precise and cost-effective method to survey Magellanic Penguin colonies.Aims To determine which sampling method gives better estimations of penguin abundance.Methods A virtual colony was generated deriving spatial parameters from a real survey and applying Kriging interpolation. Three sampling methods were then applied on this virtual colony: random sampling with quadrats; systematic sampling with quadrats; systematic sampling with fixed-width transects. The estimated abundance for each trial was compared to the abundance of the virtual colony to have a measure of accuracy and precision.Results Systematic sampling with quadrats estimated penguin abundance better than random or systematic sampling with transects since it achieved 100% accuracy and great precision after sampling only 2.1% of the virtual colony.Conclusion The use of a simulated colony allowed the comparison of several sampling methods traditionally used in Magellanic Penguin surveys. The results of this study are important in order to standardize sampling protocols for Magellanic Penguins and to have more comparable estimations to detect trends over time. Also, the methodological approach used here could be used to assess sampling methods for other colonial bird species. 相似文献
42.
43.
Abstract A Paddyfield Warbler was mist-netted at Van in eastern Anatolia on 8.5 1987. This is the second record for Turkey. 相似文献
44.
45.
46.
The presence of antibiotics in the environment and their subsequent impact on resistance development has raised concerns globally. Hospitals are a major source of antibiotics released into the environment. To reduce these residues, research to improve knowledge of the dynamics of antibiotic release from hospitals is essential. Therefore, we undertook a study to estimate seasonal and temporal variation in antibiotic release from two hospitals in India over a period of two years. For this, 6 sampling sessions of 24 hours each were conducted in the three prominent seasons of India, at all wastewater outlets of the two hospitals, using continuous and grab sampling methods. An in-house wastewater sampler was designed for continuous sampling. Eight antibiotics from four major antibiotic groups were selected for the study. To understand the temporal pattern of antibiotic release, each of the 24-hour sessions were divided in three sub-sampling sessions of 8 hours each. Solid phase extraction followed by liquid chromatography/tandem mass spectrometry (LC-MS/MS) was used to determine the antibiotic residues. Six of the eight antibiotics studied were detected in the wastewater samples. Both continuous and grab sampling methods indicated that the highest quantities of fluoroquinolones were released in winter followed by the rainy season and the summer. No temporal pattern in antibiotic release was detected. In general, in a common timeframe, continuous sampling showed less concentration of antibiotics in wastewater as compared to grab sampling. It is suggested that continuous sampling should be the method of choice as grab sampling gives erroneous results, it being indicative of the quantities of antibiotics present in wastewater only at the time of sampling. Based on our studies, calculations indicate that from hospitals in India, an estimated 89, 1 and 25 ng/L/day of fluroquinolones, metronidazole and sulfamethoxazole respectively, might be getting released into the environment per 100 hospital beds. 相似文献
47.
Mariana D. Carrillo-Del Valle Jorge A. De la Garza-García Efrén Díaz-Aparicio Arturo G. Valdivia-Flores Luis F. Cisneros-Guzmán Cecilia Rosario Ángel H. Manjarrez-Hernández Armando Navarro Juan Xicohtencatl-Cortes Pablo Maravilla Rigoberto Hernández-Castro 《European Journal of Wildlife Research》2016,62(4):415-421
48.
Virtual reconstruction of the Early Pleistocene mandible ATD6‐96 from Gran Dolina‐TD6‐2 (Sierra De Atapuerca,Spain) 下载免费PDF全文
49.
Sheila Ommeh Wei Zhang Ali Zohaib Jing Chen Huajun Zhang Ben Hu Xing-Yi Ge Xing-Lou Yang Moses Masika Vincent Obanda Yun Luo Shan Li Cecilia Waruhiu Bei Li Yan Zhu Desterio Ouma Vincent Odendo Lin-Fa Wang Danielle E. Anderson Jacqueline Lichoti Erick Mungube Francis Gakuya Peng Zhou Kisa-Juma Ngeiywa Bing Yan Bernard Agwanda Zheng-Li Shi 《中国病毒学》2019,34(1):115-115
50.