全文获取类型
收费全文 | 968篇 |
免费 | 58篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 12篇 |
2021年 | 14篇 |
2020年 | 9篇 |
2019年 | 13篇 |
2018年 | 17篇 |
2017年 | 6篇 |
2016年 | 26篇 |
2015年 | 42篇 |
2014年 | 54篇 |
2013年 | 82篇 |
2012年 | 83篇 |
2011年 | 69篇 |
2010年 | 50篇 |
2009年 | 43篇 |
2008年 | 64篇 |
2007年 | 62篇 |
2006年 | 66篇 |
2005年 | 55篇 |
2004年 | 77篇 |
2003年 | 51篇 |
2002年 | 45篇 |
2001年 | 8篇 |
2000年 | 9篇 |
1999年 | 4篇 |
1998年 | 8篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1964年 | 1篇 |
排序方式: 共有1026条查询结果,搜索用时 46 毫秒
91.
In vitro micropropagation by direct organogenesis and somatic embryogenesis via callus was developed for Crambe tataria (Brassicaceae). C. tataria is an endemic species of the Pontic-Pannonic region, but it is also present in Italy, where it is localized in Friuli on
a characteristic grassland formation, called “magredi”. C. tataria is regarded as an endangered species. Leaf and root explants were subjected to plant regulator treatments, which invoked
different morphogenic responses. Leaf explants produced more callus than root explants and a higher amount of callus was obtained
with 1 mg l−1 2,4-D in combination with 2 mg l−1 Kin. Somatic embryogenesis was obtained in calli maintained in a delayed subculture regime on media containing BAP in combination
with NAA. Root explants cultured with BAP combined with NAA developed adventitious rosette shoots. Shoots rooted on half-strength
MS media, and the number of roots per plantlet and their length were heavily dependent on sucrose content. The in vitro regenerated
plantlets were acclimatized ex vitro and a mean of 50% of the plantlets survived and showed a true-to-type growth habit. This
study describes the development of two in vitro micropropagation protocols, via direct organogenesis and via embryogenesis
from callus, that are the basis for the application of in vitro tools for the establishment of basal collections with representative
genetic diversity and for the long-term storage of plant genetic material. 相似文献
92.
93.
Proteomics of the bacterial cross-talk by quorum sensing 总被引:1,自引:0,他引:1
94.
Annamaria Leccese Raffaella Viti Susanna Bartolini 《Central European Journal of Biology》2011,6(2):199-204
Two solvent extraction procedures were used to investigate the extraction efficiency in terms of total antioxidant capacity
and total phenols in apricot fruit. Samples were either sequentially extracted with aqueous ethanol (ethanol/water 80% v/v)
and tetrahydrofuran or directly extracted with tetrahydrofuran. Each extract was analyzed for total antioxidant capacity by
the Trolox Equivalent Antioxidant Capacity (TEAC) assay and total phenols by the Folin-Ciocalteu assay. The results showed
that using sequential solvent extraction, the majority (85%) of the total antioxidant capacity and total phenols was due to
hydrophilic compounds. In tetrahydrofuran direct extractions, the total antioxidant capacity and total phenols were higher
than values obtained with aqueous ethanol and the sum of results obtained from sequential extracts for either total antioxidant
capacity or total phenols was similar to the tetrahydrofuran-extract antioxidant values. A linear correlation between total
antioxidant capacity and total phenols was found and was independent of the solvent extraction method. In conclusion, the
choice of solvent is related to the antioxidant potential of fruit and depends on the food hydrophilic/lipophilic composition. 相似文献
95.
Lichtner M Mastroianni CM Rossi R Russo G Belvisi V Marocco R Mascia C Del Borgo C Mengoni F Sauzullo I d'Ettorre G D'Agostino C Massetti AP Vullo V 《PloS one》2011,6(5):e19872
Background
Dysregulation of host immune responses plays a critical role in the pathogenesis of severe 2009 pandemic H1N1 infection. Whether H1N1 virus could escape innate immune defense in vivo remains to be investigated. The aim of this study was to evaluate the pattern of innate immune response during human 2009 H1N1 infection. We performed the enumeration of circulating myeloid dendritic cells (mDC) and plasmacytoid DC (pDC) in blood from patients with H1N1 pneumonia shortly after the onset of symptoms and during follow-up at different intervals of time. The analysis of CD4 and CD8 count, CD38 T-cell activation marker and serum cytokine/chemokine plasma levels was also done.Methodology/Principal Findings
Blood samples were collected from 13 hospitalized patients with confirmed H1N1-related pneumonia at time of admission and at weeks 1, 4, and 16 of follow-up. 13 healthy donors were enrolled as controls. In the acute phase of the disease, H1N1-infected patients exhibited a significant depletion in both circulating pDC and mDC in conjunction with a decrease of CD4 and CD8 T cell count. In addition, we found plasmatic hyperproduction of IP-10 and RANTES, whereas increase in T-cell immune activation was found at all time points. When we assessed the changes in DC count over time, we observed a progressive normalization of mDC number. On the contrary, H1N1-infected patients did not achieve a complete recovery of pDC count as values remained lower than healthy controls even after 16 weeks of follow-up.Conclusions
H1N1 disease is associated with a profound depletion of DC subsets. The persistence of pDC deficit for several weeks after disease recovery could be due to H1N1 virus itself or to a preexisting impairment of innate immunity. 相似文献96.
Manfredini R Boari B Smolensky MH Salmi R la Cecilia O Maria Malagoni A Haus E Manfredini F 《Chronobiology international》2005,22(3):417-453
Stroke is the culmination of a heterogeneous group of cerebrovascular diseases that is manifested as ischemia or hemorrhage of one or more blood vessels of the brain. The occurrence of many acute cardiovascular events—such as myocardial infarction, sudden cardiac death, pulmonary embolism, critical limb ischemia, and aortic aneurysm rupture—exhibits prominent 24 h patterning, with a major morning peak and secondary early evening peak. The incidence of stroke exhibits the same 24 h pattern. Although ischemic and hemorrhagic strokes are different entities and are characterized by different pathophysiological mechanisms, they share an identical double-peak 24 h pattern. A constellation of endogenous circadian rhythms and exogenous cyclic factors are involved. The staging of the circadian rhythms in vascular tone, coagulative balance, and blood pressure plus temporal patterns in posture, physical activity, emotional stress, and medication effects play central and/or triggering roles. Features of the circadian rhythm of blood pressure, in terms of their chronic and acute effects on cerebral vessels, and of coagulation are especially important. Clinical medicine has been most concerned with the prevention of stroke in the morning, when population-based studies show it is of greatest risk during the 24 h; however, improved protection of at-risk patients against stroke in the early evening, the second most vulnerable time of cerebrovascular accidents, has received relatively little attention thus far. 相似文献
97.
Salmona M Capobianco R Colombo L De Luigi A Rossi G Mangieri M Giaccone G Quaglio E Chiesa R Donati MB Tagliavini F Forloni G 《Journal of virology》2005,79(17):11225-11230
To investigate whether plasminogen may feature in scrapie infection, we inoculated plasminogen-deficient (Plg(-/-)), heterozygous plasminogen-deficient (Plg(+/-)), and wild-type (Plg(+/+)) mice by the intracerebral or intraperitoneal (i.p.) route with the RML scrapie strain and monitored the onset of neurological signs of disease, survival time, brain, and accumulation of scrapie disease-associated forms of the prion protein (PrP(Sc)). Only after i.p. inoculation, a slight, although significant, difference in survival (P < 0.05) between Plg(-/-) and Plg(+/+) mice was observed. Neuropathological examination and Western blot analysis were carried out when the first signs of disease appeared in Plg(+/+) animals (175 days after i.p. inoculation) and when mice reached the terminal stage of illness. At the onset of symptoms, PrP(Sc) accumulation was higher in the brain and spleen of Plg(+/+) and Plg(+/-) mice than in those of Plg(-/-) mice, and these differences were paralleled by differences in the severity of spongiform changes and astrogliosis in the cerebral cortex and subcortical gray structures. Immunohistochemical analysis of the spleens before inoculation did not show any impairment of the immune system affecting follicular dendritic or lymphoid cells in Plg(-/-) mice. Once the disease progressed and mice began to die of infection, differences were no longer apparent in either brains or spleens. In conclusion, our data indicate that plasminogen has no major effect on the survival of scrapie agent-infected mice. 相似文献
98.
Miozzi L Balestrini R Bolchi A Novero M Ottonello S Bonfante P 《The New phytologist》2005,167(1):229-238
TbSP1 is a secreted and surface-associated phospholipase A(2) previously found to be up-regulated in C- or N-deprived free-living mycelia from the ectomycorrhizal ascomycete Tuber borchii. As nutrient limitation is considered an important environmental factor favouring the transition to symbiotic status, TbSP1 was suggested to be involved in the formation of mycorrhizas. An in vitro symbiosis system between Cistus incanus and T. borchii was set up: TbSP1 mRNA levels in free-living mycelia and in mycorrhizas sampled in different districts of the plant-fungus interaction were examined. In the same samples, TbSP1 protein expression was analysed by immunoelectron microscopy. A substantially enhanced TbSP1 mRNA expression, compared with nutrient-limited but free-living mycelia, was detected in the presence of the plant and reached maximal levels in fully developed mycorrhizas. A similar expression trend was revealed by immunolocalization experiments. We have shown that TbSP1 appears to respond to two partially overlapping yet distinct stimuli: nutrient starvation and mycorrhiza formation. 相似文献
99.
100.
MicroPET imaging of MCF-7 tumors in mice via unr mRNA-targeted peptide nucleic acids 总被引:7,自引:0,他引:7
As more becomes known about the expression profiles of normal and cancerous cells, it should become possible to design antisense-based imaging agents for the early detection of cancer noninvasively. In this report, we rationally designed and synthesized three antisense and one sense hybrid PNA (peptide nucleic acid) to the unr mRNA that is highly overexpressed in a breast cancer cell line (MCF-7). The conjugates had a four-lysine tail at the carboxy terminus for cell permeation and a DOTA (1,4,7,10-tetraazacyclododecane-N,N',N',N'-tetraacetic acid) chelating moiety at the amino terminal end for chelating (64)Cu for biodistribution and microPET imaging studies. Biodistribution of two (64)Cu-labeled conjugates with antisense and sense sequences (PNA50 and PNA50S) showed high uptake and long retention in kidney and low uptake and efficient clearance in blood and muscle in normal balb/c mice when administered intravenously or intraperitoneally. Intraperitoneal administration, however, gave a much slower release rate. MCF-7 tumors (100-320 mg) in CB-17 SCID mice were imaged with all four (64)Cu-labeled PNA conjugates by microPET, but the image contrast varied with different time points and different conjugates. Of the conjugates studied, (64)Cu-DOTA-Y-PNA50-K4 showed the best tumor image quality at all time points with a tumor/muscle ratio of 6.6 +/- 1.1 at 24 h postinjection, which is among the highest reported for radiolabeled oligonucleotides. Our work further strengthens the potential of antigene and antisense PNAs to be utilized as specific molecular probes for early detection of cancer and ultimately for patient specific radiotherapy. 相似文献