全文获取类型
收费全文 | 630篇 |
免费 | 38篇 |
专业分类
668篇 |
出版年
2024年 | 2篇 |
2023年 | 10篇 |
2022年 | 19篇 |
2021年 | 22篇 |
2020年 | 20篇 |
2019年 | 13篇 |
2018年 | 20篇 |
2017年 | 21篇 |
2016年 | 30篇 |
2015年 | 42篇 |
2014年 | 46篇 |
2013年 | 38篇 |
2012年 | 54篇 |
2011年 | 48篇 |
2010年 | 27篇 |
2009年 | 24篇 |
2008年 | 31篇 |
2007年 | 33篇 |
2006年 | 28篇 |
2005年 | 27篇 |
2004年 | 21篇 |
2003年 | 15篇 |
2002年 | 16篇 |
2000年 | 3篇 |
1997年 | 3篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1971年 | 4篇 |
1970年 | 2篇 |
1969年 | 2篇 |
1968年 | 1篇 |
1967年 | 2篇 |
1966年 | 1篇 |
1965年 | 2篇 |
1964年 | 3篇 |
排序方式: 共有668条查询结果,搜索用时 15 毫秒
1.
Rats dehydrated for 8 days and subsequently rehydrated were given intracerebroventricularly (i.c.v.) methoxamine hydrochloride (MX) or dihydroergotamine methanosulphonate (DHE), each in a daily dose of 10 micrograms dissolved in 10 microliter of 0.9% sodium chloride. A single dose of MX injected to normally hydrated animals increased the release of hypothalamic and neurohypophysial vasopressin but did not affect significantly the oxytocic activity in the hypothalamus as well as in the neurohypophysis. Under conditions of dehydration MX did not influence the hypothalamic vasopressin content but it stimulated the neurohypophysial vasopressin depletion. On the contrary, MX distinctly inhibited the decrease of hypothalamic and neurohypophysial oxytocin content in dehydrated animals. In rehydrated animals MX restrained some what the renewal of hypothalamic vasopressin and oxytocin storage but intensified this process in the neurohypophysis. A single dose of DHE decreased the vasopressin content in the hypothalamus as well as the oxytocin content both in the hypothalamus and neurohypophysis. Under conditions of dehydration DHE stimulated the depletion of hypothalamic vasopressin and oxytocin. On the contrary, DHE strongly inhibited the depletion of oxytocin in the neurohypophysis of dehydrated rats. DHE restrained the renewal of hypothalamic vasopressin and oxytocin stores as well as intensified this process in the neurohypophysis of subsequently rehydrated rats. 相似文献
2.
Ana Luiza Menegatti Pavan Maria Eugênia Dela Rosa Guilherme Giacomini Fernando Antonio Bacchim Neto Seizo Yamashita Luiz Carlos Vulcano Sergio Barbosa Duarte José Ricardo de Arruda Miranda Diana Rodrigues de Pina 《PloS one》2016,11(4)
Digital radiographic imaging is increasing in veterinary practice. The use of radiation demands responsibility to maintain high image quality. Low doses are necessary because workers are requested to restrain the animal. Optimizing digital systems is necessary to avoid unnecessary exposure, causing the phenomenon known as dose creep. Homogeneous phantoms are widely used to optimize image quality and dose. We developed an automatic computational methodology to classify and quantify tissues (i.e., lung tissue, adipose tissue, muscle tissue, and bone) in canine chest computed tomography exams. The thickness of each tissue was converted to simulator materials (i.e., Lucite, aluminum, and air). Dogs were separated into groups of 20 animals each according to weight. Mean weights were 6.5 ± 2.0 kg, 15.0 ± 5.0 kg, 32.0 ± 5.5 kg, and 50.0 ± 12.0 kg, for the small, medium, large, and giant groups, respectively. The one-way analysis of variance revealed significant differences in all simulator material thicknesses (p < 0.05) quantified between groups. As a result, four phantoms were constructed for dorsoventral and lateral views. In conclusion, the present methodology allows the development of phantoms of the canine chest and possibly other body regions and/or animals. The proposed phantom is a practical tool that may be employed in future work to optimize veterinary X-ray procedures. 相似文献
3.
Colussi F Serpa V Delabona Pda S Manzine LR Voltatodio ML Alves R Mello BL Pereira N Farinas CS Golubev AM Santos MA Polikarpov I 《Journal of microbiology and biotechnology》2011,21(8):808-817
Because of its elevated cellulolytic activity, the filamentous fungus Trichoderma harzianum has a considerable potential in biomass hydrolysis applications. Trichoderma harzianum cellobiohydrolase I (ThCBHI), an exoglucanase, is an important enzyme in the process of cellulose degradation. Here, we report an easy single-step ion-exchange chromatographic method for purification of ThCBHI and its initial biophysical and biochemical characterization. The ThCBHI produced by induction with microcrystalline cellulose under submerged fermentation was purified on DEAE-Sephadex A-50 media and its identity was confirmed by mass spectrometry. The ThCBHI biochemical characterization showed that the protein has a molecular mass of 66 kDa and pI of 5.23. As confirmed by smallangle X-ray scattering (SAXS), both full-length ThCBHI and its catalytic core domain (CCD) obtained by digestion with papain are monomeric in solution. Secondary structure analysis of ThCBHI by circular dichroism revealed alpha- helices and beta-strands contents in the 28% and 38% range, respectively. The intrinsic fluorescence emission maximum of 337 nm was accounted for as different degrees of exposure of ThCBHI tryptophan residues to water. Moreover, ThCBHI displayed maximum activity at pH 5.0 and temperature of 50 degrees C with specific activities against Avicel and p-nitrophenyl-β-D-cellobioside of 1.25 U/mg and 1.53 U/mg, respectively. 相似文献
4.
Nasoethmoidal meningocele in a child presenting bilateral congenital cystic adenomatoid malformation: Evidence for a new entity or consequence of gestational exposures? 下载免费PDF全文
Ernani B. da Rosa Daniélle B. Silveira Laís G. Tsugami Nathan L. Bellé Izabelle O. Matos Luciano V. Targa Rosilene da S. Betat André C. da Cunha Rolando A.R. Villacis Sílvia R. Rogatto Luiza E. Dorfman Rafael F. M. Rosa Paulo R.G. Zen 《Birth defects research. Part A, Clinical and molecular teratology》2016,106(4):225-231
5.
Larry M. Palato Shannon Pilcher Alissa Oakes Arleen Lamba Jaris Torres Litza I. Ledesma Monjaraz Crystabel Munoz Edward Njoo Dillon J. Rinauro Kate Alexandra Menefee Angela Tun Betssy L. Jauregui Sarah Shapiro Olivia H. Nossiff Eileen Olivares Kevin Chang Viviane Nguyen Luiza A. Nogaj David A. Moffet 《Journal of peptide science》2019,25(8)
The aggregation of the 37‐amino acid polypeptide human islet amyloid polypeptide (hIAPP), as either insoluble amyloid or as small oligomers, appears to play a direct role in the death of human pancreatic β‐islet cells in type 2 diabetes. hIAPP is considered to be one of the most amyloidogenic proteins known. The quick aggregation of hIAPP leads to the formation of toxic species, such as oligomers and fibers, that damage mammalian cells (both human and rat pancreatic cells). Whether this toxicity is necessary for the progression of type 2 diabetes or merely a side effect of the disease remains unclear. If hIAPP aggregation into toxic amyloid is on‐path for developing type 2 diabetes in humans, islet amyloid polypeptide (IAPP) aggregation would likely need to play a similar role within other organisms known to develop the disease. In this work, we compared the aggregation potential and cellular toxicity of full‐length IAPP from several diabetic and nondiabetic organisms whose aggregation propensities had not yet been determined for full‐length IAPP. 相似文献
6.
Juliana A. Silva Ana Isabelle Pinheiro Maria Luiza Dourado Lilian Medina Adriano Queiroz Luiz Henrique Guimares Marcus Miranda Lessa Ednaldo L. Lago Paulo Roberto L. Machado Mary E. Wilson Edgar M. Carvalho Albert Schriefer 《PLoS neglected tropical diseases》2022,16(6)
BackgroundLeishmaniases are neglected tropical diseases that inflict great burden to poor areas of the globe. Intense research has aimed to identify parasite genetic signatures predictive of infection outcomes. Consistency of diagnostic tools based on these markers would greatly benefit from accurate understanding of Leishmania spp. population genetics. We explored two chromosomal loci to characterize a population of L. braziliensis causing human disease in Northeast Brazil.Methodology/Principal findingsTwo temporally distinct samples of L. braziliensis were obtained from patients attending the leishmaniasis clinic at the village of Corte de Pedra: (2008–2011) primary sample, N = 120; (1999–2001) validation sample, N = 35. Parasites were genotyped by Sanger’s sequencing of two 600 base pairs loci starting at nucleotide positions 3,074 and 425,451 of chromosomes 24 and 28, respectively. Genotypes based on haplotypes of biallelic positions in each locus were tested for several population genetic parameters as well as for geographic clustering within the region. Ample geographic overlap of genotypes at the two loci was observed as indicated by non-significant Cusick and Edward’s comparisons. No linkage disequilibrium was detected among combinations of haplotypes for both parasite samples. Homozygous and heterozygous genotypes displayed Hardy-Weinberg equilibrium (HWE) at both loci in the two samples when straight observed and expected counts were compared by Chi-square (p>0.5). However, Bayesian statistics using one million Monte-Carlo randomizations disclosed a less robust HWE for chromosome 24 genotypes, particularly in the primary sample (p = 0.04). Fixation indices (Fst) were consistently lower than 0.05 among individuals of the two samples at both tested loci, and no intra-populational structuralization could be detected using STRUCTURE software.Conclusions/SignificanceThese findings suggest that L. braziliensis can maintain stable populations in foci of human leishmaniasis and are capable of robust genetic recombination possibly due to events of sexual reproduction during the parasite’s lifecycle. 相似文献
7.
8.
Beatriz Pereira Moreno Gislaine Cristiane Mantovanelli Letycia Lopes Ricardo Adriano Antnio Silva Rubem Silvrio De Oliveira Emy Luiza Ishii‐Iwamoto Maria Helena Sarragiotto Debora Cristina Baldoqui 《化学与生物多样性》2020,17(3)
Studies of the phytotoxic effects between plants can be a crucial tool in the discovery of innovative compounds with herbicide potential. In this sense, we can highlight ruzigrass (Urochloa ruziziensis), which is traditionally used in the crop rotation system in order to reduce weed emergence. The aim of this work was to characterize the secondary metabolites of ruzigrass and to evaluate its phytotoxic effects. In total, eight compounds were isolated: friedelin, oleanolic acid, α‐amyrin, 1‐dehydrodiosgenone, sitosterol and stigmasterol glycosides, tricin and p‐coumaric acid. Phytotoxic effects of the crude methanolic extract and fractions of ruzigrass were assessed using germination rate, initial seedling growth, and biomass of Bidens pilosa, Euphorbia heterophylla and Ipomoea grandifolia. Chemometric analysis discriminated the weed species into three groups, and B. pilosa was the most affected by fractions of ruzigrass. The phytotoxic activities of 1‐dehydrodiosgenone, tricin, and p‐coumaric acid are also reported, and p‐coumaric acid and 1‐dehydrodiosgenone were active against B. pilosa. 相似文献
9.
Luiza Moraes Gabriel M. da Rosa Lucielen O. Santos Jorge A. V. Costa 《Biotechnology progress》2020,36(4):e2987
The present study was aimed to develop a membrane sparger (MS) integrated into a tubular photobioreactor to promote the increase of the carbon dioxide (CO2) fixation by Spirulina sp. LEB 18 cultures. The use of MS for the CO2 supply in Spirulina cultures resulted not only in the increase of DIC concentrations but also in the highest accumulated DIC concentration in the liquid medium (127.4 mg L−1 d−1). The highest values of biomass concentration (1.98 g L−1), biomass productivity (131.8 mg L−1 d−1), carbon in biomass (47.9% w w−1), CO2 fixation rate (231.6 mg L−1 d−1), and CO2 use efficiency (80.5% w w−1) by Spirulina were verified with MS, compared to the culture with conventional sparger for CO2 supply. Spirulina biomass in both culture conditions had high protein contents varying from 64.9 to 69% (w w−1). MS can be considered an innovative system for the supply of carbon for the microalgae cultivation and biomass production. Moreover, the use of membrane system might contribute to increased process efficiency with a reduced cost of biomass production. 相似文献