全文获取类型
收费全文 | 147篇 |
免费 | 10篇 |
国内免费 | 2篇 |
出版年
2023年 | 1篇 |
2021年 | 3篇 |
2018年 | 3篇 |
2017年 | 5篇 |
2016年 | 4篇 |
2015年 | 7篇 |
2014年 | 7篇 |
2013年 | 6篇 |
2012年 | 8篇 |
2011年 | 10篇 |
2010年 | 5篇 |
2009年 | 11篇 |
2008年 | 12篇 |
2007年 | 11篇 |
2006年 | 7篇 |
2005年 | 6篇 |
2004年 | 7篇 |
2003年 | 6篇 |
2002年 | 9篇 |
2001年 | 2篇 |
2000年 | 6篇 |
1999年 | 4篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 6篇 |
1995年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1987年 | 1篇 |
1981年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
排序方式: 共有159条查询结果,搜索用时 234 毫秒
31.
竹叶眼子菜(Potamogeton malaianus)、微齿眼子菜(Potamogeton maackianus)、苦草(Vallisneria spiralis)、穗花狐尾藻(Myriophyllum spicatum)、黑藻(Hydrilla verticillata)是长江中下游湖泊主要的沉水植物。在栽培条件下,它们的无性繁殖速率(单位时间内新增个体数)大小顺序为黑藻>微齿眼子菜>竹叶眼子菜>苦草>穗花狐尾藻。同时采用抛掷实验的方法观察研究了这5种沉水植物及其无性繁殖体的存活和生根情况;完整植株存活率为黑藻>穗花狐尾藻>微齿眼子菜>竹叶眼子菜>苦草,无性繁殖体部分存活率为黑藻>苦草>穗花狐尾藻>微齿眼子菜>竹叶眼子菜。生根能力和其存活时间长短相关,而且生根能力与存活率大小基本一致。在实验中,只有穗花狐尾藻的断枝存活率和生根能力存在差异,故无性繁殖体生根能力为黑藻>苦草>微齿眼子菜>竹叶眼子菜>穗花狐尾藻。 相似文献
32.
本文用脑室灌注和Fura2测定细胞内游离钙技术观察了地塞米松(dexamethasone,DEX)对家兔乙二醇双(2氨基乙醚)四乙酸性发热效应和下丘脑细胞内游离钙浓度([Ca2+]i)的影响,借此深入探讨地塞米松解热作用的中枢机制。结果发现:脑室灌注乙二醇双(2氨基乙醚)四乙酸(06nmol)引起家兔结肠温度明显升高,静脉注射地塞米松(5mg/kg)显著抑制家兔乙二醇双(2氨基乙醚)四乙酸性发热,地塞米松(60~120μmol/L)并不影响下丘脑细胞内[Ca2+]i,而事先脑室灌注抑制基因转录的放线菌素D(3nmol)则完全取消了地塞米松对乙二醇双(2氨基乙醚)四乙酸性发热的解热作用。这些结果提示:地塞米松显著抑制家兔乙二醇双(2氨基乙醚)四乙酸性发热,其机制与地塞米松激活脑内某些基因的表达有关,而与下丘脑神经细胞跨膜钙离子流无关。 相似文献
33.
34.
Phosphatidylinositol 3‐kinase inhibition potentiates glucocorticoid response in B‐cell acute lymphoblastic leukemia 下载免费PDF全文
Cecilia Evangelisti Alessandra Cappellini Mariana Oliveira Rita Fragoso João T. Barata Alice Bertaina Franco Locatelli Carolina Simioni Luca M. Neri Francesca Chiarini Annalisa Lonetti Francesca Buontempo Ester Orsini Andrea Pession Lucia Manzoli Alberto Maria Martelli Camilla Evangelisti 《Journal of cellular physiology》2018,233(3):1796-1811
35.
36.
37.
Intraspecific nuclear DNA variation in Drosophila 总被引:18,自引:6,他引:12
We have summarized and analyzed all available nuclear DNA sequence
polymorphism studies for three species of Drosophila, D. melanogaster (24
loci), D. simulans (12 loci), and D. pseudoobscura (5 loci). Our major
findings are: (1) The average nucleotide heterozygosity ranges from about
0.4% to 2% depending upon species and function of the region, i.e., coding
or noncoding. (2) Compared to D. simulans and D. pseudoobscura (which are
about equally variable), D. melanogaster displays a low degree of DNA
polymorphism. (3) Noncoding introns and 3' and 5' flanking DNA shows less
polymorphism than silent sites within coding DNA. (4) X-linked genes are
less variable than autosomal genes. (5) Transition (Ts) and transversion
(Tv) polymorphisms are about equally frequent in non-coding DNA and at
fourfold degenerate sites in coding DNA while Ts polymorphisms outnumber Tv
polymorphisms by about 2:1 in total coding DNA. The increased Ts
polymorphism in coding regions is likely due to the structure of the
genetic code: silent changes are more often Ts's than are replacement
substitutions. (6) The proportion of replacement polymorphisms is
significantly higher in D. melanogaster than in D. simulans. (7) The level
of variation in coding DNA and the adjacent noncoding DNA is significantly
correlated indicating regional effects, most notably recombination. (8)
Surprisingly, the level of polymorphism at silent coding sites in D.
melanogaster is positively correlated with degree of codon usage bias. (9)
Three proposed tests of the neutral theory of DNA polymorphisms have been
performed on the data: Tajima's test, the HKA test, and the
McDonald-Kreitman test. About half of the loci fail to conform to the
expectations of neutral theory by one of the tests. We conclude that many
variables are affecting levels of DNA polymorphism in Drosophila, from
properties of nucleotides to population history and, perhaps, mating
structure. No simple, all encompassing explanation satisfactorily accounts
for the data.
相似文献
38.
Caccone A; Moriyama EN; Gleason JM; Nigro L; Powell JR 《Molecular biology and evolution》1996,13(9):1224-1232
Drosophila melanogaster belongs to a closely related group of eight species
collectively known as the melanogaster subgroup; all are native to
sub-Saharan Africa and islands off the east coast of Africa. The
phylogenetic relationships of most species in this subgroup have been well
documented; however, the three most closely related species, D. simulans,
D. sechellia, and D. mauritiana, have remained problematic from a
phylogenetic standpoint as no data set has unambiguously resolved them. We
present new DNA sequence data on the nullo and Serendipity-alpha genes and
combine them with all available nuclear DNA sequence data; the total data
encompass 12 genes and the ITS of rDNA. A methodological problem arose
because nine of the genes had information on intraspecific polymorphisms in
at least one species. We explored the effect of inclusion/exclusion of
polymorphic sites and found that it had very little effect on phylogenetic
inferences, due largely to the fact that 82% of polymorphisms are
autapomorphies (unique to one species). We have also reanalyzed our
previous DNA-DNA hybridization data with a bootstrap procedure. The
combined sequence data set and the DNA-DNA hybridization data strongly
support the sister status of the two island species, D. sechellia and D.
mauritiana. This at least partially resolves what had been a paradox of
parallel evolution in these two species.
相似文献
39.
S Erić S Ke T Barata T Solmajer J Antić Stanković Z Juranić V Savić M Zloh 《Bioorganic & medicinal chemistry》2012,20(17):5220-5228
A set of 16 previously synthesized aryl-aminopyridine and aryl-aminoquinoline derivatives have been evaluated for cytotoxic activity against three cancer cell lines (human cervical cancer-HeLa; human chronic myeloid leukemia-K562; human melanoma-Fem-x) and two types of normal peripheral blood mononuclear cells, with and without phytohemaglutinin (PBMC-PHA; PBMC+PHA). Twelve of the studied compounds showed moderate cytotoxicity, with selectivity against K562 but not the remaining two cancer cell lines. Four compounds were not active in cytotoxicity assays, presumably due to high predicted lipophilicity and low solubility. To rationalize the observed cytotoxic effects, structure-based virtual screening was carried out against a pool of potential targets constructed using the inverse docking program Tarfisdock and bibliographical references. The putative targets were identified on the basis of the best correlation between docking scores and in vitro cytotoxicity. It is proposed that the mechanism of action of the studied aminopyridines involves the disruption of signaling pathways and cancer cell cycle through the inhibition of cyclin-dependent kinases and several tyrosine kinases, namely Bcr-Abl kinase and KIT receptor kinase. The obtained results can guide further structural modifications of the studied compounds aimed at developing selective agents targeting proteins involved in cancer cell survival and proliferation. 相似文献
40.
This survey reports the occurrence, diversity and similarity of marine fungi associated with five categories of drift substrates (Arundo donax, Phragmites australis, Spartina maritima, "other stems" and driftwood) collected on four sandy beaches of the western coast of Portugal. "Other stems" and driftwood are composite samples with a variety of identified and unidentified pieces of non-woody and woody substrates respectively. Fifty-six taxa were identified, including 38 Ascomycota and 18 anamorphic fungi. Twenty-six taxa were generalists; however several cases of "substrate recurrence" were identified. The very frequent fungi differed among the categories of studied substrates, with the exception of Corollospora maritima, very frequent on four categories. Except for S. maritima, P. australis and driftwood, cases of multiple fungal colonization were rare. S. maritima was the single substrate with five different marine fungi on one sample, as well as with the highest number of very frequent fungi, highest percentage of colonization and average number of fungi per sample. Driftwood presented the highest value of fungal richness (37 taxa) and A. donax the lowest (22 taxa). ANOSIM analysis of similarity showed that all substrates supported different fungal communities with the exception of the pair P. australis/"other stems". The effect of sample size on estimated fungal richness was tested, and the results let us conclude that, although most of the sporadic fungi (<1% occurrence) will be detected only in a very large number of samples, 60 samples of A. donax and "other stems" and 70 samples of all the other substrates may suffice to assess their respective representative marine mycota. 相似文献