全文获取类型
收费全文 | 177篇 |
免费 | 18篇 |
出版年
2021年 | 1篇 |
2019年 | 3篇 |
2018年 | 1篇 |
2017年 | 7篇 |
2016年 | 9篇 |
2015年 | 15篇 |
2014年 | 15篇 |
2013年 | 7篇 |
2012年 | 12篇 |
2011年 | 8篇 |
2010年 | 11篇 |
2009年 | 7篇 |
2008年 | 1篇 |
2007年 | 6篇 |
2006年 | 5篇 |
2005年 | 10篇 |
2004年 | 4篇 |
2003年 | 1篇 |
2002年 | 2篇 |
2001年 | 4篇 |
2000年 | 9篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 6篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1965年 | 1篇 |
1934年 | 1篇 |
排序方式: 共有195条查询结果,搜索用时 15 毫秒
1.
An Ustilago maydis ergosterol biosynthesis mutant (A14) which is partially blocked in sterol 14alpha-demethylase (P45014DM) activity is described. This mutant accumulated the abnormal 14alpha-methyl sterols, eburicol, 14alpha-methylfecosterol, and obtusifoliol, along with significant amounts of ergosterol. Although the A14 mutant grew nearly as well as the wild type, it was impaired in cell extension growth, which indicated a dysfunction in apical cell wall synthesis. The mutant was also found to be hypersensitive to the azole fungicides penconazole and tebuconazole. 相似文献
2.
3.
JA Kiernan 《Biotechnic & histochemistry》2013,88(5-6):203-210
Hexazonium pararosaniline is a valuable reagent that has been used in enzyme activity histochemistry for 50 years. It is an aqueous solution containing the tris-diazonium ion derived from pararosaniline, an aminotriarylmethane dye, and it contains an excess of nitrous acid that was not consumed in the diazotization reaction. Other investigators have found that immersion for 2 min in an acidic (pH 3.5) 0.0015 M hexazonium pararosaniline solution can protect cryostat sections of unfixed animal tissues from the deleterious effects of aqueous reagents such as buffered solutions used in immunohistochemistry, while preserving specific affinities for antibodies. In the present investigation hexazonium pararosaniline protected lymphoid tissue and striated muscle against the damaging effects of water or saline. The same protection was conferred on unfixed sections treated with dilute nitrous or hydrochloric acid in concentrations similar to those in hexazonium pararosaniline solutions. Model tissues (solutions, gels or films containing gelatin and/or bovine albumin) responded predictably to well known cross-linking (formaldehyde) or coagulant (mercuric chloride) fixatives. Hexazonium pararosaniline solutions prevented the dissolution of protein gels in water only after 9 or more days of contact, during which time considerable swelling occurred. It is concluded that there is no evidence for a “fixative” action of hexazonium pararosaniline. The protective effect on frozen sections of unfixed tissue is attributable probably to the low pH of the solution. 相似文献
4.
Water hyacinth Eichhornia crassipes is considered the most damaging aquatic weed in the world. However, few studies have quantified the impact of this weed economically and ecologically, and even fewer studies have quantified the benefits of its control. This paper focuses on water loss saving as the benefit derived from biological control of this plant between 1990 and 2013 at New Year’s Dam, Alicedale, Eastern Cape, South Africa. Estimates of water loss due to evapotranspiration from water hyacinth vary significantly; therefore, the study used three different rates, high, medium and low. A conservative raw agriculture value of R 0.26 per m3 was used to calculate the benefits derived by the water saved. The present benefit and cost values were determined using 10% and 5% discount rates. The benefit/cost ratio at the low evapotranspiration rate was less than one, implying that biological control was not economically viable but, at the higher evapotranspiration rates, the return justified the costs of biological control. However, at the marginal value product of water, the inclusion of the costs of damage to infrastructure, or the adverse effects of water hyacinth on biodiversity, would justify the use of biological control, even at the low transpiration rate. 相似文献
5.
The Tau/A152T mutation,a risk factor for frontotemporal‐spectrum disorders,leads to NR2B receptor‐mediated excitotoxicity 下载免费PDF全文
Astrid Sydow Frank JA Dennissen Zuzana Siskova Eckhard Mandelkow Eva‐Maria Mandelkow 《EMBO reports》2016,17(4):552-569
We report on a novel transgenic mouse model expressing human full‐length Tau with the Tau mutation A152T (hTauAT), a risk factor for FTD‐spectrum disorders including PSP and CBD. Brain neurons reveal pathological Tau conformation, hyperphosphorylation, mis‐sorting, aggregation, neuronal degeneration, and progressive loss, most prominently in area CA3 of the hippocampus. The mossy fiber pathway shows enhanced basal synaptic transmission without changes in short‐ or long‐term plasticity. In organotypic hippocampal slices, extracellular glutamate increases early above control levels, followed by a rise in neurotoxicity. These changes are normalized by inhibiting neurotransmitter release or by blocking voltage‐gated sodium channels. CA3 neurons show elevated intracellular calcium during rest and after activity induction which is sensitive to NR2B antagonizing drugs, demonstrating a pivotal role of extrasynaptic NMDA receptors. Slices show pronounced epileptiform activity and axonal sprouting of mossy fibers. Excitotoxic neuronal death is ameliorated by ceftriaxone, which stimulates astrocytic glutamate uptake via the transporter EAAT2/GLT1. In summary, hTauAT causes excitotoxicity mediated by NR2B‐containing NMDA receptors due to enhanced extracellular glutamate. 相似文献
6.
Ornament size and colour as alternative strategies for effective communication in gliding lizards 下载免费PDF全文
D. A. Klomp T. J. Ord I. Das A. Diesmos N. Ahmad D. Stuart‐Fox 《Journal of evolutionary biology》2016,29(9):1689-1700
Sexual ornamentation needs to be conspicuous to be effective in attracting potential mates and defending territories and indeed, a multitude of ways exists to achieve this. Two principal mechanisms for increasing conspicuousness are to increase the ornament's colour or brightness contrast against the background and to increase the size of the ornament. We assessed the relationship between the colour and size of the dewlap, a large extendible throat‐fan, across a range of species of gliding lizards (Agamidae; genus Draco) from Malaysia and the Philippines. We found a negative relationship across species between colour contrast against the background and dewlap size in males, but not in females, suggesting that males of different species use increasing colour contrast and dewlap size as alternative strategies for effective communication. Male dewlap size also increases with increasing sexual size dimorphism, and dewlap colour and brightness contrast increase with increasing sexual dichromatism in colour and brightness, respectively, suggesting that sexual selection may act on both dewlap size and colour. We further found evidence that relative predation intensity, as measured from predator attacks on models placed in the field, may play a role in the choice of strategy (high chromatic contrast or large dewlap area) a species employs. More broadly, these results highlight that each component in a signal (such as colour or size) may be influenced by different selection pressures and that by assessing components individually, we can gain a greater understanding of the evolution of signal diversity. 相似文献
7.
Hernandez-Trejo A B Estrada-Drouaillet JA López-Santillán C Rios-Velasco SE Varela-Fuentes R Rodríguez-Herrera E Osorio-Hernández 《Phyton》2019,88(1):47-54
The control of Spodoptera frugiperda is based
on synthetic insecticides, so some alternatives are the use of
entomopathogenic fungi (EF) and neem extract. The objective of
the study was to evaluate in vitro effectiveness of native EF and
neem extracts on S. frugiperda larvae. Six EF were identified by
DNA sequencing of ITS regions from three EF (Fusarium solani,
Metarrhizium robertsii, Nigrospora spherica and Penicillium
citrinum). They were evaluated in concentrations of 1 × 10⁸ spores/
mL. In addition, a second bioassay was carried out evaluating
only F. solani, M. robertsii and N. sphaerica and the addition
of vegetable oil. On the other hand, extraction of secondary
metabolites from neem seed (Azadirachta indica) was carried
out by performing, mass (g) and solvent volume (mL ethanol
and water) combinations, which were subjected to microwaves
and ultrasound. Subsequently, these extracts were evaluated
in concentrations of 3%, 4% and 5%. A survival analysis was
performed for each of the bioassays. With respect to the results
of the first bioassay, F. solani obtained a probability of survival of
0.476 on the seventh day, while in the second bioassay, M. robertsii
obtained 0.488 survival probability. This suggests that the expected
percentage of larvae that stay alive on the sixth day is 48.8%.
However, in the evaluation of the neem extract the combination
1:12/70% to 4% caused 84% mortality of larvae. The use of native
HE and neem extracts has potential for the control of S. frugiperda. 相似文献
8.
9.
Molecular characterization of 3-phosphoglycerate dehydrogenase deficiency--a neurometabolic disorder associated with reduced L-serine biosynthesis 下载免费PDF全文
Klomp LW de Koning TJ Malingré HE van Beurden EA Brink M Opdam FL Duran M Jaeken J Pineda M Van Maldergem L Poll-The BT van den Berg IE Berger R 《American journal of human genetics》2000,67(6):1389-1399
3-phosphoglycerate dehydrogenase (PHGDH) deficiency is a disorder of L-serine biosynthesis that is characterized by congenital microcephaly, psychomotor retardation, and seizures. To investigate the molecular basis for this disorder, the PHGDH mRNA sequence was characterized, and six patients from four families were analyzed for sequence variations. Five patients from three different families were homozygous for a single nucleotide substitution predicted to change valine at position 490 to methionine. The sixth patient was homozygous for a valine to methionine substitution at position 425; both mutations are located in the carboxyterminal part of PHGDH. In vitro expression of these mutant proteins resulted in significant reduction of PHGDH enzyme activities. RNA-blot analysis indicated abundant expression of PHGDH in adult and fetal brain tissue. Taken together with the severe neurological impairment in our patients, the data presented in this paper suggest an important role for PHGDH activity and L-serine biosynthesis in the metabolism, development, and function of the central nervous system. 相似文献
10.