全文获取类型
收费全文 | 135篇 |
免费 | 13篇 |
专业分类
148篇 |
出版年
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 5篇 |
2015年 | 8篇 |
2014年 | 12篇 |
2013年 | 15篇 |
2012年 | 14篇 |
2011年 | 8篇 |
2010年 | 12篇 |
2009年 | 3篇 |
2008年 | 6篇 |
2007年 | 4篇 |
2006年 | 7篇 |
2005年 | 5篇 |
2003年 | 1篇 |
2002年 | 2篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1990年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1980年 | 2篇 |
1978年 | 1篇 |
排序方式: 共有148条查询结果,搜索用时 15 毫秒
21.
Sofia Bodare Gudasalamani Ravikanth Sascha A. Ismail Mohana Kumara Patel Ilaria Spanu Ramesh Vasudeva Ramanan Uma Shaanker Giovanni Giuseppe Vendramin Martin Lascoux Yoshiaki Tsuda 《Conservation Genetics》2017,18(1):1-15
Dysoxylum malabaricum (white cedar) is an economically important tree species, endemic to the Western Ghats, India, which is the world’s most densely populated biodiversity hotspot. In this study, we used variation at ten nuclear simple sequence repeat loci to investigate genetic diversity and fine scale spatial genetic structure (FSGS) in seedlings and adults of D. malabaricum from four forest patches in the northern part of the Western Ghats. When genetic variation was compared between seedlings and adults across locations, significant differences were detected in allelic richness, observed heterozygosity, fixation index (F IS), and relatedness (P < 0.05). Reduced genetic diversity and increased relatedness at the seedling stage might be due to fragmentation and disturbance. There was no FSGS at the adult stage and FSGS was limited to shorter distance classes at the seedling stage. However, there was clear spatial genetic structure at the landscape level (<50 km), regardless of age class, due to limited gene flow between forest patches. A comparison of the distributions of size classes in the four locations with published data from a more southern area, showed that large trees (diameter at breast height, DBH, >130 cm) are present in the southern sacred forests but not in the northern forest reserves. This pattern is likely due to stronger harvesting pressure in the north compared to the south, because in the north there are no cultural taboos regulating the extraction of natural resources. The implications for forest conservation in this biodiversity hotspot are discussed. 相似文献
22.
23.
Injectable nanocomposites of single-walled carbon nanotubes and biodegradable polymers for bone tissue engineering 总被引:1,自引:0,他引:1
We have investigated the dispersion of single-walled carbon nanotubes (SWNTs) and functionalized SWNTs (F-SWNTs) in the unsaturated, biodegradable polymer poly(propylene fumarate) (PPF) and examined the rheological properties of un-cross-linked nanocomposite formulations as well as the electrical and mechanical properties of cross-linked nanocomposites. F-SWNTs were produced from individual SWNTs by a diazonium-based method and dispersed better than unmodified SWNTs in both un-cross-linked and cross-linked PPF matrix. Cross-linked nanocomposites with F-SWNTs were superior to those with unmodified SWNTs in terms of their mechanical properties. Specifically, nanocomposites with 0.1 wt % F-SWNTs loading resulted in a 3-fold increase in both compressive modulus and flexural modulus and a 2-fold increase in both compressive offset yield strength and flexural strength when compared to pure PPF networks, whereas the use of 0.1 wt % SWNTs gained less than 37% mechanical reinforcement. These extraordinary mechanical enhancements considered together with Raman scattering and sol fraction measurements indicate strong SWNT-PPF interactions and increased cross-linking densities resulting in effective load transfer. With enhanced mechanical properties and capabilities of in situ injection and cross-linking, these SWNT/polymer nanocomposites hold significant implications for the fabrication of bone tissue engineering scaffolds. 相似文献
24.
A model of the steady-state electrochemical response of vascular smooth muscle cells to external stimuli is presented, which accounts for K, Na, and Ca fluxes. The results of the model are broadly in accordance with experimental data 1), at various transmural pressures; 2), with channel and pump blockade; and 3), under manipulation of external ionic concentrations. The model exhibits dual stable states which sometimes coexist, and abrupt transitions between these states may account for nongraded responses in arteries as external potassium or pressure is varied. The simulations suggest that changes in the intracellular sodium concentration ([Na]i) often accompany smooth muscle responses. For example, [Na]i values vary threefold over the range of pressures from 10 to 100 mmHg. 相似文献
25.
Kumar V Fahey PG Jong YJ Ramanan N O'Malley KL 《The Journal of biological chemistry》2012,287(8):5412-5425
26.
This study deals with an effective nucleic acids extraction method from various strains of Botryococcus braunii which possesses an extensive extracellular matrix. A method combining freeze/thaw and bead-beating with heterogeneous diameter of silica/zirconia beads was optimized to isolate DNA and RNA from microalgae, especially from B. braunii. Eukaryotic Microalgal Nucleic Acids Extraction (EMNE) method developed in this study showed at least 300 times higher DNA yield in all strains of B. braunii with high integrity and 50 times reduced working volume compared to commercially available DNA extraction kits. High quality RNA was also extracted using this method and more than two times the yield compared to existing methods. Real-time experiments confirmed the quality and quantity of the input DNA and RNA extracted using EMNE method. The method was also applied to other eukaryotic microalgae, such as diatoms, Chlamydomonas sp., Chlorella sp., and Scenedesmus sp. resulting in higher efficiencies. Cost-effectiveness analysis of DNA extraction by various methods revealed that EMNE method was superior to commercial kits and other reported methods by >15%. This method would immensely contribute to area of microalgal genomics. 相似文献
27.
28.
1-Thio-beta-D-galactofuranosides: synthesis and evaluation as beta-D- galactofuranosidase inhibitors
Marino C; Marino K; Miletti L; Manso Alves MJ; Colli W; de Lederkremer RM 《Glycobiology》1998,8(9):901-904
Beta-D-galactofuranosidase is a good chemotherapeutic target for the design
of inhibitors, since beta-D-galactofuranose is a constituent of important
parasite glycoconjugates but is not present in the host mammals. With this
aim, we have synthesized for the first time alkyl, benzyl and aryl
1-thio-beta-D-galactofuranosides by condensation of
penta-O-benzoyl-alpha,beta-D-galactofuranose with the corresponding thiols,
in the presence of SnCl4as catalyst. The complete chemical and
spectroscopical characterization of these compounds showed that the
reaction was stereoselective. Debenzoylation with sodium methoxide afforded
the beta-S-galactofuranosides in high yield. The thioglycosides were tested
as inhibitors of the beta-D- galactofuranosidase of Penicillium fellutanum,
using for the first time 4-nitrophenyl-beta-D-galactofuranoside as
chromogenic substrate. The 4- aminophenyl-1-thio-beta-D-galactofuranoside,
obtained by catalytic hydrogenation of the nitrophenyl derivative, was the
best inhibitor being then an adequate ligand for the preparation of an
affinity phase aimed at the isolation of beta-d-galactofuranosidases from
different sources. Also the inhibitory activity of d-galactono-1, 4-lactone
was shown.
相似文献
29.
Population genetics and phylogenetics of DNA sequence variation at multiple loci within the Drosophila melanogaster species complex 总被引:13,自引:1,他引:13
Two regions of the genome, a 1-kbp portion of the zeste locus and a 1.1-
kbp portion of the yolk protein 2 locus, were sequenced in six individuals
from each of four species: Drosophila melanogaster, D. simulans, D.
mauritiana, and D. sechellia. The species and strains were the same as
those of a previous study of a 1.9-kbp region of the period locus. No
evidence was found for recent balancing or directional selection or for the
accumulation of selected differences between species. Yolk protein 2 has a
high level of amino acid replacement variation and a low level of
synonymous variation, while zeste has the opposite pattern. This contrast
is consistent with information on gene function and patterns of codon bias.
Polymorphism levels are consistent with a ranking of effective population
sizes, from low to high, in the following order: D. sechellia, D.
melanogaster, D.mauritiana, and D. simulans. The apparent species
relationships are very similar to those suggested by the period locus
study. In particular, D. simulans appears to be a large population that is
still segregating variation that arose before the separation of D.
mauritiana and D. sechellia. It is estimated that the separation of
ancestral D. melanogaster from the other species occurred 2.5-3.4 Mya. The
separations of D. sechellia and D. mauritiana from ancestral D. simulans
appear to have occurred 0.58- 0.86 Mya, with D. mauritiana having diverged
from ancestral D. simulans 0.1 Myr more recently than D. sechellia.
相似文献
30.
Mariana A Antunes Soraia C Abreu Fernanda F Cruz Ana Clara Teixeira Miquéias Lopes-Pacheco Elga Bandeira Priscilla C Olsen Bruno L Diaz Christina M Takyia Isalira PRG Freitas Nazareth N Rocha Vera L Capelozzi Débora G Xisto Daniel J Weiss Marcelo M Morales Patricia RM Rocco 《Respiratory research》2014,15(1)
We sought to assess whether the effects of mesenchymal stromal cells (MSC) on lung inflammation and remodeling in experimental emphysema would differ according to MSC source and administration route. Emphysema was induced in C57BL/6 mice by intratracheal (IT) administration of porcine pancreatic elastase (0.1 UI) weekly for 1 month. After the last elastase instillation, saline or MSCs (1×105), isolated from either mouse bone marrow (BM), adipose tissue (AD) or lung tissue (L), were administered intravenously (IV) or IT. After 1 week, mice were euthanized. Regardless of administration route, MSCs from each source yielded: 1) decreased mean linear intercept, neutrophil infiltration, and cell apoptosis; 2) increased elastic fiber content; 3) reduced alveolar epithelial and endothelial cell damage; and 4) decreased keratinocyte-derived chemokine (KC, a mouse analog of interleukin-8) and transforming growth factor-β levels in lung tissue. In contrast with IV, IT MSC administration further reduced alveolar hyperinflation (BM-MSC) and collagen fiber content (BM-MSC and L-MSC). Intravenous administration of BM- and AD-MSCs reduced the number of M1 macrophages and pulmonary hypertension on echocardiography, while increasing vascular endothelial growth factor. Only BM-MSCs (IV > IT) increased the number of M2 macrophages. In conclusion, different MSC sources and administration routes variably reduced elastase-induced lung damage, but IV administration of BM-MSCs resulted in better cardiovascular function and change of the macrophage phenotype from M1 to M2. 相似文献