全文获取类型
收费全文 | 168篇 |
免费 | 8篇 |
出版年
2015年 | 3篇 |
2014年 | 5篇 |
2013年 | 5篇 |
2012年 | 9篇 |
2011年 | 5篇 |
2010年 | 15篇 |
2009年 | 6篇 |
2008年 | 9篇 |
2007年 | 7篇 |
2006年 | 5篇 |
2005年 | 3篇 |
2004年 | 2篇 |
2003年 | 3篇 |
2002年 | 2篇 |
2001年 | 4篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1995年 | 2篇 |
1993年 | 2篇 |
1988年 | 3篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1980年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 6篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1965年 | 2篇 |
1960年 | 1篇 |
1959年 | 2篇 |
1958年 | 2篇 |
1957年 | 2篇 |
1956年 | 3篇 |
1955年 | 1篇 |
1954年 | 4篇 |
1953年 | 1篇 |
1952年 | 2篇 |
1951年 | 4篇 |
1950年 | 6篇 |
1949年 | 2篇 |
1948年 | 1篇 |
1946年 | 1篇 |
1944年 | 1篇 |
1927年 | 1篇 |
排序方式: 共有176条查询结果,搜索用时 562 毫秒
71.
J. P. Dudley G. C. Criag † D. ST. C. Gibson G. Haynes J. Klimowicz 《African Journal of Ecology》2001,39(2):187-194
African bush elephants inhabiting the undeveloped Kalahari Sands region of Hwange National Park, Zimbabwe are subject to episodic mortality during droughts. We monitored the drought‐related mortality of elephants in Hwange National Park over the course of an extended drought between 1993 and 1995. The drought‐related mortality of elephants was higher during 1994 than 1995, despite significantly higher rainfall in 1994 than 1995. We found significant differences in the age‐specific mortality of elephants during 1994 and 1995. The cumulative mortality profile from this study differed significantly from previous die‐offs at this site, with a higher mortality among adult age classes than that reported from earlier studies in Hwange National Park. The effective duration of the rainy season, not total annual precipitation, appears to be the best predictor for the potential severity of drought mortality among elephants in the Kalahari Sands habitats of Hwange National Park. 相似文献
72.
Background
The polarization of somite-derived sclerotomes into anterior and posterior halves underlies vertebral morphogenesis and spinal nerve segmentation. To characterize the full extent of molecular differences that underlie this polarity, we have undertaken a systematic comparison of gene expression between the two sclerotome halves in the mouse embryo. 相似文献73.
74.
75.
76.
The genus Pseudostegania Butler is revised. In addition to the two species known, four species are described as new: P. lijiangensis sp. nov. from Yunnan Province, P. qinlingensis sp. nov. from Gansu and Shaanxi Provinces, P. zhoui sp. nov. from Sichuan Province (China) and P. burmaensis sp. nov. from Burma (Myanmar); two species are newly combined with Pseudostegania: P. distinctaria (Leech, 1897), comb. nov. and P. yargongaria (Oberthür, 1916), comb. nov. All the known species are redescribed and lectotypes are designated for P. defectata (Christoph, 1881), P. distinctaria and P. yargongaria. The generic characters, based on all species, are summarized. The tribal placement of Pseudostegania is discussed. Illustrations of moths and genitalia are presented. 相似文献
77.
DAVID STÅHLBERG MIKAEL HEDRÉN 《Biological journal of the Linnean Society. Linnean Society of London》2010,101(3):503-525
Taxonomic complexity may be associated with migration history and polyploidy. We used plastid and nuclear DNA markers to investigate the evolutionary history of the systematically challenging Dactylorhiza maculata polyploid complex. A total of 1833 individuals from 298 populations from throughout Europe were analysed. We found that gene flow was limited between the two major taxa, diploid ssp. fuchsii (including ssp. saccifera) and tetraploid ssp. maculata. A minimum of three autotetraploid lineages were discerned: (1) southern/western ssp. maculata; (2) northern/eastern ssp. maculata; and (3) Central European ssp. fuchsii. The two ssp. maculata lineages, which probably pre‐date the last glaciation, form a contact zone with high genetic diversity in central Scandinavia. Intermediate plastid haplotypes in the contact zone hint at recombination. Central Europe may have been a source area for the postglacial migration for the southern/western lineage of ssp. maculata, as well as for ssp. fuchsii. The northern/eastern lineage of ssp. maculata may have survived the LGM in central Russia west of the Urals. The tetraploid lineage of ssp. fuchsii is indistinguishable from diploid ssp. fuchsii, and is probably of postglacial origin. The Mediterranean region and the Caucasus have not contributed to the northward migration of either ssp. fuchsii or ssp. maculata. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 503–525. 相似文献
78.
LAURE GAUFICHON CÉLINE MASCLAUX‐DAUBRESSE GUILLAUME TCHERKEZ MICHÈLE REISDORF‐CREN YUKIKO SAKAKIBARA TOSHIHARU HASE GILLES CLÉMENT JEAN‐CHRISTOPHE AVICE OLIVIER GRANDJEAN ANNE MARMAGNE STÉPHANIE BOUTET‐MERCEY MARIANNE AZZOPARDI FABIENNE SOULAY AKIRA SUZUKI 《Plant, cell & environment》2013,36(2):328-342
We investigated the function of ASN2, one of the three genes encoding asparagine synthetase (EC 6.3.5.4), which is the most highly expressed in vegetative leaves of Arabidopsis thaliana. Expression of ASN2 and parallel higher asparagine content in darkness suggest that leaf metabolism involves ASN2 for asparagine synthesis. In asn2‐1 knockout and asn2‐2 knockdown lines, ASN2 disruption caused a defective growth phenotype and ammonium accumulation. The asn2 mutant leaves displayed a depleted asparagine and an accumulation of alanine, GABA, pyruvate and fumarate, indicating an alanine formation from pyruvate through the GABA shunt to consume excess ammonium in the absence of asparagine synthesis. By contrast, asparagine did not contribute to photorespiratory nitrogen recycle as photosynthetic net CO2 assimilation was not significantly different between lines under both 21 and 2% O2. ASN2 was found in phloem companion cells by in situ hybridization and immunolocalization. Moreover, lack of asparagine in asn2 phloem sap and lowered 15N flux to sinks, accompanied by the delayed yellowing (senescence) of asn2 leaves, in the absence of asparagine support a specific role of asparagine in phloem loading and nitrogen reallocation. We conclude that ASN2 is essential for nitrogen assimilation, distribution and remobilization (via the phloem) within the plant. 相似文献
79.
A cytological basis for a map of the nucleolar chromosome in man 总被引:1,自引:0,他引:1
80.
International bacteriological code of nomenclature 总被引:1,自引:0,他引:1