全文获取类型
收费全文 | 5791篇 |
免费 | 695篇 |
国内免费 | 3篇 |
专业分类
6489篇 |
出版年
2021年 | 50篇 |
2018年 | 53篇 |
2016年 | 92篇 |
2015年 | 121篇 |
2014年 | 139篇 |
2013年 | 189篇 |
2012年 | 246篇 |
2011年 | 189篇 |
2010年 | 143篇 |
2009年 | 140篇 |
2008年 | 205篇 |
2007年 | 204篇 |
2006年 | 214篇 |
2005年 | 192篇 |
2004年 | 187篇 |
2003年 | 181篇 |
2002年 | 186篇 |
2001年 | 198篇 |
2000年 | 194篇 |
1999年 | 165篇 |
1998年 | 81篇 |
1997年 | 106篇 |
1996年 | 101篇 |
1995年 | 86篇 |
1994年 | 89篇 |
1993年 | 88篇 |
1992年 | 118篇 |
1991年 | 113篇 |
1990年 | 144篇 |
1989年 | 123篇 |
1988年 | 104篇 |
1987年 | 114篇 |
1986年 | 97篇 |
1985年 | 124篇 |
1984年 | 90篇 |
1983年 | 72篇 |
1982年 | 80篇 |
1981年 | 69篇 |
1980年 | 76篇 |
1979年 | 85篇 |
1978年 | 72篇 |
1977年 | 64篇 |
1976年 | 76篇 |
1975年 | 70篇 |
1974年 | 73篇 |
1973年 | 73篇 |
1972年 | 75篇 |
1971年 | 62篇 |
1969年 | 47篇 |
1968年 | 51篇 |
排序方式: 共有6489条查询结果,搜索用时 15 毫秒
991.
992.
993.
The haplotype data reported in this paper have been submitted to (MGD) and have been assigned the accession numbers: MGD-CREX-235 (back-cross data); MGD-CREX-236 (intercross data). 相似文献
994.
995.
996.
997.
The field of mesenchymal stromal cell (MSC) biology and clinical cellular therapy has grown exponentially over the last few decades. With discovery of multiple tissue specific sources of stromal cells, invariably being termed MSCs, and their increasing clinical application, there is a need to further delineate the true definition of a mesenchymal stromal cell and to recognise the inherit differences between cell sources; both their potential and limitations.In this review, we discuss the importance of considering every stromal cell source as an independent entity and the need to critically evaluate and appreciate the true phenotype of these cells and their safety when considering their use in novel cell therapies. 相似文献
998.
999.
Testate amoeba records indicate regional 20th‐century lowering of water tables in ombrotrophic peatlands in central‐northern Alberta,Canada 下载免费PDF全文
Simon van Bellen Gabriel Magnan Lauren Davies Duane Froese Gillian Mullan‐Boudreau Claudio Zaccone Michelle Garneau William Shotyk 《Global Change Biology》2018,24(7):2758-2774
Testate amoebae are abundant in the surface layers of northern peatlands. Analysis of their fossilized shell (test) assemblages allows for reconstructions of local water‐table depths (WTD). We have reconstructed WTD dynamics for five peat cores from peatlands ranging in distance from the Athabasca bituminous sands (ABS) region in western Canada. Amoeba assemblages were combined with plant macrofossil records, acid‐insoluble ash (AIA) fluxes and instrumental climate data to identify drivers for environmental change. Two functional traits of testate amoebae, mixotrophy and the tendency to integrate xenogenic mineral matter in test construction, were quantified to infer possible effects of AIA flux on testate amoeba presence. Age–depth models showed the cores each covered at least the last ~315 years, with some spanning the last millennium. Testate amoeba assemblages were likely affected by permafrost development in two of the peatlands, yet the most important shift in assemblages was detected after 1960 CE. This shift represents a significant apparent lowering of water tables in four out of five cores, with a mean drop of ~15 cm. Over the last 50 years, assemblages shifted towards more xerophilous taxa, a trend which was best explained by increasing Sphagnum s. Acutifolia and, to a lesser extent, mean summer temperature. This trend was most evident in the two cores from the sites located farthest away from the ABS region. AIA flux variations did not show a clear effect on mineral‐agglutinating taxa, nor on S. s. Acutifolia presence. We therefore suggest the drying trend was forced by the establishment of S. s. Acutifolia, driven by enhanced productivity following regional warming. Such recent apparent drying of peatlands, which may only be reconstructed by appropriate indicators combined with high chronological control, may affect vulnerability to future burning and promote emissions of CO2. 相似文献
1000.