全文获取类型
收费全文 | 102603篇 |
免费 | 9186篇 |
国内免费 | 26篇 |
出版年
2023年 | 452篇 |
2022年 | 636篇 |
2021年 | 1339篇 |
2020年 | 929篇 |
2019年 | 1090篇 |
2018年 | 1854篇 |
2017年 | 1743篇 |
2016年 | 2418篇 |
2015年 | 3259篇 |
2014年 | 3662篇 |
2013年 | 4885篇 |
2012年 | 7050篇 |
2011年 | 7256篇 |
2010年 | 4175篇 |
2009年 | 3381篇 |
2008年 | 6015篇 |
2007年 | 6145篇 |
2006年 | 5812篇 |
2005年 | 5358篇 |
2004年 | 5181篇 |
2003年 | 4803篇 |
2002年 | 4753篇 |
2001年 | 2381篇 |
2000年 | 2479篇 |
1999年 | 1739篇 |
1998年 | 1282篇 |
1997年 | 929篇 |
1996年 | 915篇 |
1995年 | 832篇 |
1994年 | 872篇 |
1993年 | 832篇 |
1992年 | 1022篇 |
1991年 | 823篇 |
1990年 | 794篇 |
1989年 | 763篇 |
1988年 | 706篇 |
1987年 | 676篇 |
1986年 | 629篇 |
1985年 | 705篇 |
1984年 | 807篇 |
1983年 | 732篇 |
1982年 | 732篇 |
1981年 | 679篇 |
1980年 | 667篇 |
1979年 | 586篇 |
1978年 | 575篇 |
1977年 | 507篇 |
1976年 | 499篇 |
1975年 | 494篇 |
1974年 | 456篇 |
排序方式: 共有10000条查询结果,搜索用时 368 毫秒
11.
Thomas J Hughes 《BMJ (Clinical research ed.)》1980,281(6239):562-563
12.
13.
14.
In a section of the Liassic southwest of the village of Préjano (Prov. Logroño) Sinemurian Dasyclad algae were found for the first time in the “Bankkalk-Series” of the “Carniolas-Formation” which is not dated up to that time. Six species,Dissocladella lucasi (Cros & Lemoine),Dissocladella iberica nov. sp.,Dissocladella ebroensis nov. sp.,Sestrosphaera liasina Pia,Gyroporella retica (Zanin) andMacroporella nov. sp. aff. sturi Bystricky are described. 相似文献
15.
16.
17.
18.
Georg Söderbom 《Ethnos》2013,78(1-2):95-100
Current debates over the concept of culture are examined, especially with regard to the relationship of culture to bounded collectivities, human nature, and individuality; present‐day views are seen against the background of back‐and‐forth swings in the history of anthropological thought. Recent theorizing about cultural acquisition is also considered. 相似文献
19.
20.
Thomas A. Worthington Shannon K. Brewer Nicole Farless Timothy B. Grabowski Mark S. Gregory 《PloS one》2014,9(5)
Habitat fragmentation and flow regulation are significant factors related to the decline and extinction of freshwater biota. Pelagic-broadcast spawning cyprinids require moving water and some length of unfragmented stream to complete their life cycle. However, it is unknown how discharge and habitat features interact at multiple spatial scales to alter the transport of semi-buoyant fish eggs. Our objective was to assess the relationship between downstream drift of semi-buoyant egg surrogates (gellan beads) and discharge and habitat complexity. We quantified transport time of a known quantity of beads using 2–3 sampling devices at each of seven locations on the North Canadian and Canadian rivers. Transport time was assessed based on median capture time (time at which 50% of beads were captured) and sampling period (time period when 2.5% and 97.5% of beads were captured). Habitat complexity was assessed by calculating width∶depth ratios at each site, and several habitat metrics determined using analyses of aerial photographs. Median time of egg capture was negatively correlated to site discharge. The temporal extent of the sampling period at each site was negatively correlated to both site discharge and habitat-patch dispersion. Our results highlight the role of discharge in driving transport times, but also indicate that higher dispersion of habitat patches relates to increased retention of beads within the river. These results could be used to target restoration activities or prioritize water use to create and maintain habitat complexity within large, fragmented river systems. 相似文献