全文获取类型
收费全文 | 1567篇 |
免费 | 106篇 |
出版年
2022年 | 11篇 |
2021年 | 15篇 |
2020年 | 9篇 |
2019年 | 9篇 |
2018年 | 17篇 |
2017年 | 17篇 |
2016年 | 23篇 |
2015年 | 53篇 |
2014年 | 64篇 |
2013年 | 65篇 |
2012年 | 89篇 |
2011年 | 89篇 |
2010年 | 74篇 |
2009年 | 47篇 |
2008年 | 62篇 |
2007年 | 82篇 |
2006年 | 62篇 |
2005年 | 70篇 |
2004年 | 49篇 |
2003年 | 72篇 |
2002年 | 73篇 |
2001年 | 16篇 |
1999年 | 12篇 |
1998年 | 19篇 |
1997年 | 14篇 |
1996年 | 11篇 |
1995年 | 9篇 |
1988年 | 9篇 |
1986年 | 13篇 |
1985年 | 9篇 |
1984年 | 18篇 |
1983年 | 18篇 |
1982年 | 19篇 |
1980年 | 15篇 |
1979年 | 12篇 |
1978年 | 14篇 |
1977年 | 10篇 |
1976年 | 11篇 |
1974年 | 11篇 |
1973年 | 10篇 |
1972年 | 10篇 |
1971年 | 10篇 |
1970年 | 18篇 |
1968年 | 17篇 |
1967年 | 10篇 |
1954年 | 8篇 |
1941年 | 8篇 |
1937年 | 13篇 |
1934年 | 9篇 |
1930年 | 9篇 |
排序方式: 共有1673条查询结果,搜索用时 15 毫秒
51.
María Lorena Falcone Ferreyra Eduardo Rodriguez María Isabel Casas Guillermo Labadie Erich Grotewold Paula Casati 《The Journal of biological chemistry》2013,288(44):31678-31688
Flavonoids accumulate in plant vacuoles usually as O-glycosylated derivatives, but several species can also synthesize flavonoid C-glycosides. Recently, we demonstrated that a flavanone 2-hydroxylase (ZmF2H1, CYP93G5) converts flavanones to the corresponding 2-hydroxy derivatives, which are expected to serve as substrates for C-glycosylation. Here, we isolated a cDNA encoding a UDP-dependent glycosyltransferase (UGT708A6), and its activity was characterized by in vitro and in vivo bioconversion assays. In vitro assays using 2-hydroxyflavanones as substrates and in vivo activity assays in yeast co-expressing ZmF2H1 and UGT708A6 show the formation of the flavones C-glycosides. UGT708A6 can also O-glycosylate flavanones in bioconversion assays in Escherichia coli as well as by in vitro assays with the purified recombinant protein. Thus, UGT708A6 is a bifunctional glycosyltransferase that can produce both C- and O-glycosidated flavonoids, a property not previously described for any other glycosyltransferase. 相似文献
52.
Erich Y.T. Nakasu Simoni C. Dias Carmen S.S. Pires David A. Andow Debora Pires Paula Pedro Henrique B. Togni Tainã R. Macedo Edison R. Sujii Maria F.G. de Sá Eliana M.G. Fontes 《Entomologia Experimentalis et Applicata》2013,148(2):105-115
Insect predators are exposed to the Cry1Ac toxin in Bt cotton fields through several pathways. In this study, we investigated the effects of activated Cry1Ac added to a diet on Cycloneda sanguinea (L.) (Coleoptera: Coccinellidae), which is one of the main predators of non‐target pests in Brazilian cotton. Direct bitrophic exposure of C. sanguinea to Cry1Ac was done by feeding beetles with Aphis gossypii (Glover) (Hemiptera: Aphidae) sprayed with 500 μg per ml Cry1Ac solution. Larval and pupal survival, development time, aphid consumption, and adult longevity were recorded daily. Couples within the same experimental treatment were paired and numbers of eggs laid and hatched per female were recorded daily. Net replacement rate was calculated for each female. During development, a C. sanguinea larva consumed on average 1.8 μg of activated Cry1Ac. No significant differences due to Cry1Ac were observed for any of the response variables, except aphid consumption. Larvae receiving Cry1Ac consumed more aphids than larvae receiving distilled water alone. Additional statistical analyses were conducted to evaluate independence of responses, and for the independent responses, a simple meta‐analysis was conducted to test the null hypothesis that all responses were zero. Nearly all of the response variables were statistically independent. Two pairs of responses were not independent, but the associated multivariate tests were not significant. The meta‐analysis suggested that all effects were not different from random variation around zero and no cumulative effects could be detected. Our results indicated that bitrophic exposure to activated Cry1Ac is likely to have little or no adverse ecological effect on C. sanguinea. 相似文献
53.
The lamellarity of liposomes is an important parameter to be controlled in liposomal delivery–release applications. A practical estimate of the degree of liposome lamellarity can be obtained by measuring the relative external surface area of the liposomes using a chemical assay. All such assays are based on a signal change caused by exposed marker lipids on reaction with a specific externally added reagent. However, a quantitative determination is often distorted by background reactions and contributions of internal lipid labeling. In the so-called TNBS assay, the marker lipid is phosphatidylethanolamine (PE) and the externally added reagent is TNBS (2,4,6-trinotrobenzene sulfonate). Mechanistic aspects of the TNBS assay were considered for improving the assay. Internal lipid labeling via PE flip-flop and/or TNBS permeation was minimal not only in cholesterol-containing liposomes but also in cholesterol-free liposomes if in the latter case membrane fluidity was decreased by slightly increasing the PE content. Compared with earlier versions of the TNBS assay, the amount of marker lipid and the time for analysis could be reduced considerably. The elaborated protocol was also applied to liposomes prepared from lipidic egg yolk isolates, offering a simple and inexpensive method for the development and in-process control of new liposome formation technologies. 相似文献
54.
Eleanor S. Drummond Jill Muhling Ralph N. Martins Linda K. Wijaya Erich M. Ehlert Alan R. Harvey 《PloS one》2013,8(3)
Accumulation of beta amyloid (Aβ) in the brain is a primary feature of Alzheimer’s disease (AD) but the exact molecular mechanisms by which Aβ exerts its toxic actions are not yet entirely clear. We documented pathological changes 3 and 6 months after localised injection of recombinant, bi-cistronic adeno-associated viral vectors (rAAV2) expressing human Aβ40-GFP, Aβ42-GFP, C100-GFP or C100V717F-GFP into the hippocampus and cerebellum of 8 week old male mice. Injection of all rAAV2 vectors resulted in wide-spread transduction within the hippocampus and cerebellum, as shown by expression of transgene mRNA and GFP protein. Despite the lack of accumulation of Aβ protein after injection with AAV vectors, injection of rAAV2-Aβ42-GFP and rAAV2- C100V717F-GFP into the hippocampus resulted in significantly increased microgliosis and altered permeability of the blood brain barrier, the latter revealed by high levels of immunoglobulin G (IgG) around the injection site and the presence of IgG positive cells. In comparison, injection of rAAV2-Aβ40-GFP and rAAV2-C100-GFP into the hippocampus resulted in substantially less neuropathology. Injection of rAAV2 vectors into the cerebellum resulted in similar types of pathological changes, but to a lesser degree. The use of viral vectors to express different types of Aβ and C100 is a powerful technique with which to examine the direct in vivo consequences of Aβ expression in different regions of the mature nervous system and will allow experimentation and analysis of pathological AD-like changes in a broader range of species other than mouse. 相似文献
55.
Aline Bertin Marine Chanson Jo?l Delaveau Frédéric Mercerand Erich M?stl Ludovic Calandreau Cécile Arnould Christine Leterrier Anne Collin 《PloS one》2013,8(2)
Background
Environmental challenges might affect the maternal organism and indirectly affect the later ontogeny of the progeny. We investigated the cross-generation impact of a moderate heat challenge in chickens. We hypothesized that a warm temperature–within the thermotolerance range- would affect the hormonal environment provided to embryos by mothers, and in turn, affect the morphology and behavioral phenotype of offspring.Methodology/Principal Findings
Laying hens were raised under a standard thermal condition at 21°C (controls) or 30°C (experimental) for 5 consecutive weeks. A significant increase was observed in the internal temperature of hens exposed to the warm treatment; however plasma corticosterone levels remained unaffected. The laying rate was not affected, but experimental hens laid lighter eggs than the controls during the treatment. As expected, the maternal thermal environment affected yolk hormone contents. Eggs laid by the experimental hens showed significantly higher concentrations of yolk progesterone, testosterone, and estradiol. All chicks were raised under standard thermal conditions. The quality of hatchlings, growth, feeding behavior and emotional reactivity of chicks were analyzed. Offspring of experimental hens (C30 chicks) were lighter but obtained better morphological quality scores at hatching than the controls (C21 chicks). C30 chicks expressed lesser distress calls when exposed to a novel food. Unlike C21 chicks, C30 chicks expressed no preference for energetic food.Conclusion/Significance
Our findings suggest that moderate heat challenge triggers maternal effects and modulate the developmental trajectory of offspring in a way that may be adaptive. This suggests that the impact of heat challenges on captive or wild populations might have a cross-generation effect. 相似文献56.
Oliver G. Bosch Michael Wagner Frank Jessen Kai-Uwe Kühn Alexius Joe Erich Seifritz Wolfgang Maier Hans-Jürgen Biersack Boris B. Quednow 《PloS one》2013,8(4)
Introduction
3,4-Methylenedioxymethamphetamine (MDMA, “ecstasy”) is a recreational club drug with supposed neurotoxic effects selectively on the serotonin system. MDMA users consistently exhibit memory dysfunction but there is an ongoing debate if these deficits are induced mainly by alterations in the prefrontal or mediotemporal cortex, especially the hippocampus. Thus, we investigated the relation of verbal memory deficits with alterations of regional cerebral brain glucose metabolism (rMRGlu) in recreational MDMA users.Methods
Brain glucose metabolism in rest was assessed using 2-deoxy-2-(18F)fluoro-D-glucose positron emission tomography (18FDG PET) in 19 male recreational users of MDMA and 19 male drug-naïve controls. 18FDG PET data were correlated with memory performance assessed with a German version of the Rey Auditory Verbal Learning Test.Results
As previously shown, MDMA users showed significant impairment in verbal declarative memory performance. PET scans revealed significantly decreased rMRGlu in the bilateral dorsolateral prefrontal and inferior parietal cortex, bilateral thalamus, right hippocampus, right precuneus, right cerebellum, and pons (at the level of raphe nuclei) of MDMA users. Among MDMA users, learning and recall were positively correlated with rMRGlu predominantly in bilateral frontal and parietal brain regions, while recognition was additionally related to rMRGlu in the right mediotemporal and bihemispheric lateral temporal cortex. Moreover, cumulative lifetime dose of MDMA was negatively correlated with rMRGlu in the left dorsolateral and bilateral orbital and medial PFC, left inferior parietal and right lateral temporal cortex.Conclusions
Verbal learning and recall deficits of recreational MDMA users are correlated with glucose hypometabolism in prefrontal and parietal cortex, while word recognition was additionally correlated with mediotemporal hypometabolism. We conclude that memory deficits of MDMA users arise from combined fronto-parieto-mediotemporal dysfunction. 相似文献57.
58.
59.
Simon Nimpf Gregory Charles Nordmann Daniel Kagerbauer Erich Pascal Malkemper Lukas Landler Artemis Papadaki-Anastasopoulou Lyubov Ushakova Andrea Wenninger-Weinzierl Maria Novatchkova Peter Vincent Thomas Lendl Martin Colombini Matthew J. Mason David Anthony Keays 《Current biology : CB》2019,29(23):4052-4059.e4
60.
Glycosylation is the most frequent PTM and contributes significantly to the function of proteins depending on the type of glycosylation. Especially glycan structures like the glycosaminoglycans are considered to constitute themselves the major function of the glycoconjugate which is therefore termed proteoglycan. Here we review recent views on and novel tools for analysing the proteoglycanome, which are directly related to the type of glycanation under investigation. We define the major function of the proteoglycanome to be its interaction with various proteins in many different (patho-)physiological conditions. This is exemplified by the differential glycosaminoglycan-interactome of healthy versus arthritic patient sera. 相似文献