全文获取类型
收费全文 | 253篇 |
免费 | 32篇 |
国内免费 | 1篇 |
出版年
2021年 | 5篇 |
2020年 | 2篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2017年 | 15篇 |
2016年 | 12篇 |
2015年 | 11篇 |
2014年 | 7篇 |
2013年 | 8篇 |
2012年 | 14篇 |
2011年 | 16篇 |
2010年 | 11篇 |
2009年 | 12篇 |
2008年 | 14篇 |
2007年 | 15篇 |
2006年 | 10篇 |
2005年 | 11篇 |
2004年 | 10篇 |
2003年 | 10篇 |
2002年 | 6篇 |
2001年 | 9篇 |
2000年 | 5篇 |
1999年 | 2篇 |
1998年 | 11篇 |
1997年 | 7篇 |
1996年 | 5篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 6篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1986年 | 2篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1972年 | 1篇 |
1969年 | 2篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1959年 | 1篇 |
1933年 | 1篇 |
1931年 | 1篇 |
1924年 | 1篇 |
1920年 | 1篇 |
1918年 | 1篇 |
1917年 | 1篇 |
排序方式: 共有286条查询结果,搜索用时 31 毫秒
261.
The conservation and restoration of degraded landscapes continues to be a major activity with the demand for seed increasing to meet growing global targets. Seed collected from natural plant populations is often irregular and unpredictable, limiting the diversity of species that can be conserved through restoration programs and the area that can be restored. Seed production areas (SPAs; seed orchards, seed increase) are one option for improving seed supply and quality to meet the demand from conservation and restoration programs. We evaluated genetic diversity, inbreeding and mating system parameters in adults and seed from remnants and SPAs of Acacia montana and Dodonaea viscosa subsp. cuneata, two key restoration species in south-eastern Australia. Overall, we found no significant differences in genetic diversity between remnants and SPAs of both species or between adult and seed cohorts. In contrast, we found significant inbreeding in many remnants and their seed crops suggesting that some inbred seed were used to establish these SPAs. We also found significant inbreeding in some SPAs and their seed crops and that SPAs were often biased towards one to two source remnants. Additional germplasm is now required to broaden the representativeness of remnants in the SPAs and the genetic base of seed being produced for restoration programs. 相似文献
262.
263.
264.
265.
Molecular evolution of the period gene in Drosophila athabasca 总被引:1,自引:0,他引:1
We measured nucleotide variability within and between the three semispecies
of the Drosophila athabasca complex, at the period (per) gene by using a
polymerase chain reaction-based four-cutter restriction- enzyme analysis.
The levels of polymorphism varied considerably between the three
semispecies. Our results for per, combined with previous data for X-linked
allozymes, suggest that the X chromosome in the western- northern
semispecies is less variable than expected under an equilibrium-neutral
model. Both the pattern of divergence between the semispecies and a
cladistic clustering of per haplotypes support the previously hypothesized
grouping of eastern A and eastern B as the two most recently diverged
semispecies. A 21-bp in-frame segment in the region of per which shares
sequence similarity with the neuronal development gene single minded is
deleted in all eastern A and eastern B flies examined but is present in all
of the western-northern flies and all other published per sequences.
Despite these hints that there may be significant differences at the per
gene between the semispecies, especially the western-northern group versus
the two eastern groups, there is no compelling evidence that per is
involved in the mating song differences between the semispecies.
相似文献
266.
Parity as a determinant of birth weight in the rhesus monkey 总被引:1,自引:0,他引:1
267.
Kinetic constants were determined for the interaction of the HIV-2 aspartic proteinase with a synthetic substrate and a number of inhibitors at several pH values. Acetyl-pepstatin was more effective towards HIV-2 proteinase than the renin inhibitor, H-261; this effect is exactly the opposite from that observed previously for the proteinase from the HIV-1 AIDS virus. 相似文献
268.
269.
270.
Ichthyological Research - Specimens of Squalus cubensis (n = 137; 38.5–67.3 cm total length–TL) and Squalus cf. quasimodo (n = 183; 41.1–93.2 cm TL) were opportunistically... 相似文献