全文获取类型
收费全文 | 4724篇 |
免费 | 207篇 |
出版年
2020年 | 74篇 |
2019年 | 100篇 |
2018年 | 133篇 |
2017年 | 137篇 |
2016年 | 167篇 |
2015年 | 111篇 |
2014年 | 110篇 |
2013年 | 1429篇 |
2012年 | 143篇 |
2011年 | 174篇 |
2010年 | 161篇 |
2009年 | 137篇 |
2008年 | 110篇 |
2007年 | 112篇 |
2006年 | 111篇 |
2005年 | 72篇 |
2004年 | 57篇 |
2003年 | 68篇 |
2002年 | 66篇 |
2001年 | 75篇 |
2000年 | 69篇 |
1999年 | 77篇 |
1998年 | 55篇 |
1997年 | 42篇 |
1996年 | 32篇 |
1995年 | 49篇 |
1994年 | 34篇 |
1993年 | 43篇 |
1992年 | 28篇 |
1991年 | 36篇 |
1990年 | 42篇 |
1989年 | 39篇 |
1988年 | 28篇 |
1987年 | 40篇 |
1986年 | 41篇 |
1985年 | 49篇 |
1984年 | 52篇 |
1983年 | 48篇 |
1982年 | 39篇 |
1981年 | 46篇 |
1980年 | 42篇 |
1979年 | 39篇 |
1978年 | 37篇 |
1977年 | 36篇 |
1976年 | 27篇 |
1975年 | 27篇 |
1974年 | 28篇 |
1973年 | 30篇 |
1972年 | 29篇 |
1970年 | 27篇 |
排序方式: 共有4931条查询结果,搜索用时 515 毫秒
141.
142.
143.
144.
145.
146.
147.
148.
Empirical aspects of the movement of strontium through the food chain suggest that the level of bone strontium can be used as an indicator of the percentage of meat in human diet. In general, skeletal remains from agricultural peoples are expected to have high bone strontium levels relative to hunter-gatherers from the same geographical region because plants contain relatively higher amounts of strontium when compared with animal products. The results of the study described in this paper, however, indicate that the inclusion of molluscs as a component of the diet may produce the opposite of the expected strontium values. Burials from an Archaic (c. 2500 BC) hunting-gathering population excavated from Luo25, an archaeological site in northern Alabama, USA, exhibit a mean bone strontium level (
atomic absorption;
neutron activation) that is higher than the mean level from an agricultural Mississippian (c. AD 1400) population (
atomic absorption;
neutron activation) that was buried at the same site. The samples were analysed by two techniques (atomic absorption spectrometry and neutron activation analysis) and the results compared favourably; therefore, the results can be accepted as valid rather than being due to technique error. We propose that the ingestion of molluscs, whose meat is known to contain large amounts of strontium, has produced this reversal from expected results. 相似文献
149.
John S. Ambler 《政策研究杂志》1981,10(1):136-149
The more highly politicized nature of French, as compared to British universities can be explained only partially in terms of such cultural and Political differences as the greater strength of the revolutionary tradition in France and the more conservative tenor of French governments in the l960's and 1970's. Political tensions in French higher education are also in Dart the result of policy choices, notably the greater speed of expansion of enrollments in France as compared to Britain and the form of French university elections, which strengthened politicized unions. 相似文献
150.