全文获取类型
收费全文 | 73篇 |
免费 | 3篇 |
专业分类
76篇 |
出版年
2022年 | 1篇 |
2021年 | 2篇 |
2020年 | 1篇 |
2017年 | 3篇 |
2016年 | 4篇 |
2015年 | 3篇 |
2014年 | 3篇 |
2013年 | 1篇 |
2012年 | 2篇 |
2011年 | 2篇 |
2010年 | 4篇 |
2009年 | 2篇 |
2008年 | 4篇 |
2007年 | 2篇 |
2006年 | 4篇 |
2005年 | 5篇 |
2004年 | 4篇 |
2003年 | 2篇 |
2002年 | 2篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 3篇 |
1998年 | 5篇 |
1997年 | 1篇 |
1995年 | 3篇 |
1992年 | 1篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有76条查询结果,搜索用时 8 毫秒
31.
32.
N Lübcker J Dabrowski TA Zengeya PJ Oberholster G Hall S Woodborne 《African Journal of Aquatic Science》2016,41(4):399-411
The alien invasive silver carp Hypophthalmichthys molitrix established a self-sustaining feral population in an oligotrophic impoundment, Flag Boshielo Dam, in South Africa. The ability of this population to persist in a dam with low algal biomass (median annual suspended chlorophyll a = 0.08 µg l?1), and limited access to rivers considered large enough for successful spawning, has implications for their invasive potential in other systems. Stomach content and stable isotope analysis were used to assess the trophic ecology of H. molitrix, which was then compared with indigenous Mozambique tilapia Oreochromis mossambicus, on a seasonal basis during 2011. Hypophthalmichthys molitrix are generalist filter feeders, with a diet consisting primarily of sediment, vegetative detritus, dinoflagellates and diatoms. The dominance of sediments in their stomachs suggests occasional benthic scavenging. However, H. molitrix occupied a higher trophic level (TL = 2.8) than expected, suggesting that this population subsidised their diet with an unidentified dietary constituent, characterised by enriched nitrogen values. Although the stomach contents indicated dietary overlap between H. molitrix and O. mossambicus, stable isotopes revealed fine-scale resource partitioning, despite both species occupying the same trophic level. Nonetheless, the persistence of this feral H. molitrix population in an oligotrophic impoundment highlights their phenotypic plasticity. 相似文献
33.
Recently, a group of diplomonads has been found to use a genetic code in
which TAA and TAG encode glutamine rather than termination. To survey the
distribution of this characteristic in diplomonads, we sought to identify
TAA and TAG codons at positions where glutamine is expected in genes for
alpha-tubulin, elongation factor-1 alpha, and the gamma subunit of
eukaryotic translation initiation factor-2. These sequences show that the
variant genetic code is utilized by almost all diplomonads, with the genus
Giardia alone using the universal genetic code. Comparative phylogenetic
analysis reveals that the switch to this genetic code took place very early
in the evolution of diplomonads and was likely a single event. Termination
signals and downstream untranslated regions were also cloned from three
Hexamita genes. In all three of these genes, the predicted TGA termination
codon was found at the expected position. Interestingly, the untranslated
regions of these genes are high in AT. This is incongruent with the coding
regions, which are comparatively GC-rich.
相似文献
34.
Apoptosis is characterized by DNA strand breaks with a 3'-OH terminus, which are analyzed by terminal deoxy(d)-UTP nick end labeling (TUNEL). Proteinase K digestion is thought to be an essential step in the TUNEL procedure. The effects of decalcifying reagents on general staining and the TUNEL assay for cartilage sections are largely unknown. The effects of these reagents on retention and integrity of DNA in chondrocytes have not been described until now. We evaluated the effects of various decalcifying solutions, including 10% EDTA, 10% citric acid, 5% trichloroacetic acid, 5% acetic acid and a commercial hydrochloric acid-based reagent, on general cartilage staining and the TUNEL assay for cartilage. The effects of proteinase K on nucleus preservation were also examined. Decalcification with 10% EDTA gave the best result for general cartilage staining. Chondrocyte DNA was retained and intact after using this reagent. Decalcification with 10% EDTA is also the safest method of decalcification if the TUNEL assay is applied to cartilage. Proteinase K digestion may have adverse effects on nucleus preservation in cartilage. Awareness of these effects is important whenever the TUNEL assay is applied. 相似文献
35.
Surveys were distributed to New Zealand land users in 1998 and 2008 to acquire information about New Zealand frogs with the aim of compiling and mapping their distribution and inferred population trends without costly and time-consuming field surveys. The overall frog population trend was reported as declining, with possible causes reported as an increase in agriculture, an increase in the distribution of predatory fish and disease. The resultant maps could be used for four main purposes: 1) to identify regions where Litoria populations are known to occur, which can be eliminated when considering suitable regions for translocation of Leiopelma; 2) to identify growing or stable populations of Litoria species, which may assist future disease surveys, population monitoring and to identify sources of genetic material that may serve as an Ark for declining Australian populations; 3) to highlight populations that are in decline to enable effective targeting of detailed disease studies; and 4) to approximate the stability of amphibian populations in the absence of more accurate, but costly, scientific monitoring. 相似文献
36.
37.
PJ?Baker H?Johnston M?Abel HM?Charlton PJ?O'ShaughnessyEmail author 《Reproductive biology and endocrinology : RB&E》2003,1(1):4
During mammalian testis development distinct generations of fetal and adult Leydig cells arise. Luteinising hormone (LH) is
required for normal adult Leydig cell function and for the establishment of normal adult Leydig cell number but its role in
the process of adult Leydig cell differentiation has remained uncertain. In this study we have examined adult Leydig cell
differentiation in gonadotrophin-releasing hormone (GnRH)-null mice which are deficient in circulating gonadotrophins. Adult
Leydig cell differentiation was assessed by measuring expression of mRNA species encoding four specific markers of adult Leydig
cell differentiation in the mouse. Each of these markers (3β-hydroxysteroid dehydrogenase type VI (3βHSD VI), 17β-hydroxysteroid
dehydrogenase type III (17βHSD III), prostaglandin D (PGD)-synthetase and oestrogen sulphotransferase (EST)) is expressed
only in the adult Leydig cell lineage in the normal adult animal. Real-time PCR studies showed that all four markers are expressed
in adult GnRH-null mice. Localisation of 3βHSD VI and PGD-synthetase expression by in situ hybridisation confirmed that these genes are expressed in the interstitial tissue of the GnRH-null mouse. Treatment of animals
with human chorionic gonadotrophin increased expression of 3βHSD VI and 17βHSD III within 12 hours further indicating that
differentiated, but unstimulated cells already exist in the GnRH-null mouse. Thus, while previous studies have shown that
LH is required for adult Leydig cell proliferation and activity, results from the present study show that adult Leydig cell
differentiation will take place in animals deficient in LH. 相似文献
38.
39.
40.