全文获取类型
收费全文 | 189篇 |
免费 | 2篇 |
国内免费 | 2篇 |
专业分类
系统科学 | 3篇 |
现状及发展 | 21篇 |
研究方法 | 31篇 |
综合类 | 107篇 |
自然研究 | 31篇 |
出版年
2018年 | 4篇 |
2017年 | 4篇 |
2016年 | 2篇 |
2014年 | 1篇 |
2013年 | 1篇 |
2012年 | 10篇 |
2011年 | 44篇 |
2010年 | 1篇 |
2009年 | 1篇 |
2008年 | 16篇 |
2007年 | 12篇 |
2006年 | 11篇 |
2005年 | 16篇 |
2004年 | 16篇 |
2003年 | 16篇 |
2002年 | 16篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1997年 | 1篇 |
1995年 | 1篇 |
1992年 | 3篇 |
1988年 | 1篇 |
1982年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1973年 | 1篇 |
1959年 | 1篇 |
1958年 | 1篇 |
1956年 | 2篇 |
1955年 | 2篇 |
1954年 | 2篇 |
1948年 | 1篇 |
排序方式: 共有193条查询结果,搜索用时 296 毫秒
61.
Variation in gene expression within and among natural populations 总被引:21,自引:0,他引:21
62.
63.
Host-induced epidemic spread of the cholera bacterium 总被引:33,自引:0,他引:33
Merrell DS Butler SM Qadri F Dolganov NA Alam A Cohen MB Calderwood SB Schoolnik GK Camilli A 《Nature》2002,417(6889):642-645
64.
Males of Cavernocypris subterranea were found for the first time in an Idaho spring. The bisexual form is described on soft body parts and valves. The genus Cavernocypris now includes 2 bisexual and 1 parthenogenteic species. 相似文献
65.
Scott A. Mensing Robert G. Elston Jr. Gary L. Raines Robin J. Tausch Cheryl L. Nowak 《西北部美国博物学家》2011,60(2)
Fossil packrat ( Neotoma ) middens provide an important source of paleoecologic data in the arid West. This study describes and tests a predictive GIS model that uses the eights-of-evidence method for determining areas with a high probability of containing fossil middens in central Nevada. Model variables included geology, elevation, and aspect. Geology was found to be the most important variable tested. We produced a map of 4 probability classes validated by field-checking 21 randomly selected 1-km 2 sites throughout the study area. Our high-probability category reduced the search area to only 3.5% of the total study area. Fossil middens were found on 8 of 21 sites (38%). Geologic types that contained middens were granite, limestone, and volcanic tuff. A 2nd run of the model with the new midden localities added to the training set helped narrow the total search area even further. This analysis demonstrates that the weights-of-evidence method provides an effective tool both for guiding research design and for helping locate midden sites within specific localities. With only a limited training dataset and a simple set of mapped criteria, a model can be constructed that is both predictive and testable. We intend to continue development of the model to improve our ability to predict the location of Pleistocene-age middens and to locate middens on low-probability sites. This method, designed for mineral exploration, has wide potential application within the natural sciences. 相似文献
66.
Fifty-seven fish of three genera were taken from the Colorado River in west central Colorado and examined for external parasites. No external parasites were found on Ictalurus. Seven percent of the Hybognathus and 100 percent of the Catastomus were infected with a Hirudinean of the species Helobdella stagnalis. 相似文献
67.
We determined the distribution and estimated population number of Preston White River springfish ( Crenichthys baileyi albivallis ) in summer 1998 and winter 1999. The total population was < 5000 fish persisting in only 4 of 6 spring systems from which it had been previously captured. To improve its status, we recommend conservation measures. 相似文献
68.
69.
70.