全文获取类型
收费全文 | 1915篇 |
免费 | 203篇 |
国内免费 | 3篇 |
专业分类
2121篇 |
出版年
2023年 | 19篇 |
2022年 | 37篇 |
2021年 | 63篇 |
2020年 | 22篇 |
2019年 | 32篇 |
2018年 | 45篇 |
2017年 | 32篇 |
2016年 | 55篇 |
2015年 | 94篇 |
2014年 | 128篇 |
2013年 | 139篇 |
2012年 | 162篇 |
2011年 | 150篇 |
2010年 | 104篇 |
2009年 | 91篇 |
2008年 | 122篇 |
2007年 | 106篇 |
2006年 | 106篇 |
2005年 | 72篇 |
2004年 | 79篇 |
2003年 | 82篇 |
2002年 | 68篇 |
2001年 | 19篇 |
2000年 | 10篇 |
1999年 | 18篇 |
1998年 | 20篇 |
1997年 | 11篇 |
1996年 | 13篇 |
1994年 | 13篇 |
1993年 | 8篇 |
1992年 | 11篇 |
1991年 | 13篇 |
1990年 | 7篇 |
1989年 | 8篇 |
1987年 | 7篇 |
1986年 | 9篇 |
1985年 | 5篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 8篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1976年 | 5篇 |
1975年 | 9篇 |
1974年 | 6篇 |
1973年 | 6篇 |
1972年 | 5篇 |
1971年 | 6篇 |
1969年 | 5篇 |
排序方式: 共有2121条查询结果,搜索用时 15 毫秒
21.
蛋鸡J亚群禽白血病的分子生物学诊断 总被引:21,自引:0,他引:21
根据J亚群白血病病毒(ALV-J)原型株HPRS-103的序列设计了一对针对外源性ALV-J引物H5和H7,从发生ML病死鸡的肿瘤、骨髓、肝脏、脾脏和输卵管组织中提取DNA作为模板,经PCR扩增得到长度为545bp的片段,对其序列进行测定后,与ALV-J原型株HPRS-103的序列进行了比较,发现其核苷酸同源性为97.4%,所编码氨基酸的同源性为96.1%。该片段含有ALV-J gp85编码基因的部分序列和ALV-J pol基因的部分序列,从分子水平上证实了蛋鸡发生J亚群禽白血病,进一步证明了此前根据病理学观察、免疫组化及免疫荧光诊断的结果。这是首次从分子水平上证明蛋用型鸡发生J亚群禽白血病。 相似文献
22.
Norton PA Comunale MA Krakover J Rodemich L Pirog N D'Amelio A Philip R Mehta AS Block TM 《Journal of cellular biochemistry》2008,104(1):136-149
The association between elevated circulating levels of GP73 (and fucosylated GP73 in particular) and hepatocellular carcinoma suggests that a thorough analysis of the extent of GP73 glycosylation is warranted. Detailed analysis of the glycosylation patterns of such low abundance proteins are hampered by technical difficulties. Using conventional lectin affinity chromatography, we have established that three quarters of the GP73 secreted from a cell line derived from HCC is fucosylated. Using mass spectrometry, we have established that at least two of three potential sites of N-linked glycosylation are occupied on most molecules of GP73 secreted from cultured hepatoma cells. Furthermore, the oligosaccharides added to recombinant GP73 resemble those present in the bulk of secreted protein, mostly bi-antennary with core fucose, with a smaller fraction of tri- and tetra-antennary structures. The frequency of fucosylation observed on the recombinant protein agrees well with the pattern of lectin binding of the endogenous secreted protein. Finally, we have developed a method to interrogate the glycans added to either the near full length protein or at a particular sequon, providing proof of concept that a small peptide embedded in a heterologous context can preserve both fucosylation and a high level of branching of oligosaccharides added. 相似文献
23.
Emily M. Duncan Annette C. Broderick Wayne J. Fuller Tamara S. Galloway Matthew H. Godfrey Mark Hamann Colin J. Limpus Penelope K. Lindeque Andrew G. Mayes Lucy C. M. Omeyer David Santillo Robin T. E. Snape Brendan J. Godley 《Global Change Biology》2019,25(2):744-752
Despite concerns regarding the environmental impacts of microplastics, knowledge of the incidence and levels of synthetic particles in large marine vertebrates is lacking. Here, we utilize an optimized enzymatic digestion methodology, previously developed for zooplankton, to explore whether synthetic particles could be isolated from marine turtle ingesta. We report the presence of synthetic particles in every turtle subjected to investigation (n = 102) which included individuals from all seven species of marine turtle, sampled from three ocean basins (Atlantic [ATL]: n = 30, four species; Mediterranean (MED): n = 56, two species; Pacific (PAC): n = 16, five species). Most particles (n = 811) were fibres (ATL: 77.1% MED: 85.3% PAC: 64.8%) with blue and black being the dominant colours. In lesser quantities were fragments (ATL: 22.9%: MED: 14.7% PAC: 20.2%) and microbeads (4.8%; PAC only; to our knowledge the first isolation of microbeads from marine megavertebrates). Fourier transform infrared spectroscopy (FT‐IR) of a subsample of particles (n = 169) showed a range of synthetic materials such as elastomers (MED: 61.2%; PAC: 3.4%), thermoplastics (ATL: 36.8%: MED: 20.7% PAC: 27.7%) and synthetic regenerated cellulosic fibres (SRCF; ATL: 63.2%: MED: 5.8% PAC: 68.9%). Synthetic particles being isolated from species occupying different trophic levels suggest the possibility of multiple ingestion pathways. These include exposure from polluted seawater and sediments and/or additional trophic transfer from contaminated prey/forage items. We assess the likelihood that microplastic ingestion presents a significant conservation problem at current levels compared to other anthropogenic threats. 相似文献
24.
Development and Validation of a Real-Time PCR Method To Quantify Rumen Protozoa and Examination of Variability between Entodinium Populations in Sheep Offered a Hay-Based Diet 总被引:2,自引:0,他引:2 下载免费PDF全文
Lucy C. Skillman Andrew F. Toovey Andrew J. Williams Andr-Denis G. Wright 《Applied microbiology》2006,72(1):200-206
PCR and real-time PCR primers for the 18S rRNA gene of rumen protozoa (Entodinium and Dasytricha spp.) were designed, and their specificities were tested against a range of rumen microbes and protozoal groups. External standards were prepared from DNA extracts of a rumen matrix containing known numbers and species of protozoa. The efficiency of PCR () was calculated following amplification of serial dilutions of each standard and was used to calculate the numbers of protozoa in each sample collected; serial dilutions of DNA were used similarly to calculate PCR efficiency. Species of Entodinium, the most prevalent of the rumen protozoa, were enumerated in rumen samples collected from 100 1-year-old merino wethers by microscopy and real-time PCR. Both the counts developed by the real-time PCR method and microscopic counts were accurate and repeatable, with a strong correlation between them (R2 = 0.8), particularly when the PCR efficiency was close to optimal (i.e., two copies per cycle). The advantages and disadvantages of each procedure are discussed. Entodinium represented on average 98% of the total protozoa, and populations within the same sheep were relatively stable, but greater variation occurred between different sheep (100 and 106 entodinia per gram of rumen contents). With this inherent variability, it was estimated that, to detect a statistically significant (P = 0.05) 20% change in Entodinium populations, 52 sheep per treatment group would be required. 相似文献
25.
Vector-borne diseases are of global importance to human and animal health. Empirical trials of effective methods to control
vectors and their pathogens can be difficult for practical, financial and ethical reasons. Here, therefore, we use a mathematical
model to predict the effectiveness of a vector-borne disease control method. As a case study, we use the tick-louping ill
virus system, where sheep are treated with acaricide in an attempt to control ticks and disease in red grouse , an economically
important game bird. We ran the model under different scenarios of sheep flock sizes, alternative host (deer) densities, acaricide
efficacies and tick burdens. The model predicted that, with very low deer densities, using sheep as tick mops can reduce the
tick population and virus prevalence. However, treatment is ineffective above a certain threshold deer density, dependent
on the comparative tick burden on sheep and deer. The model also predicted that high efficacy levels of acaricide must be
maintained for effective tick control. This study suggests that benignly managing one host species to protect another host
species from a vector and pathogen can be effective under certain conditions. It also highlights the importance of understanding
the ecological complexity of a system, in order to target control methods only under certain circumstances for maximum effectiveness. 相似文献
26.
Martin Gael Oyono Sebastien Kenmoe Ngu Njei Abanda Guy Roussel Takuissu Jean Thierry Ebogo-Belobo Raoul Kenfack-Momo Cyprien Kengne-Nde Donatien Serge Mbaga Serges Tchatchouang Josiane Kenfack-Zanguim Robertine Lontuo Fogang Elisabeth Zeukoo Menkem Juliette Laure Ndzie Ondigui Ginette Irma Kame-Ngasse Jeannette Nina Magoudjou-Pekam Arnol Bowo-Ngandji Seraphine Nkie Esemu Lucy Ndip 《PLoS neglected tropical diseases》2022,16(7)
Yellow fever (YF) has re-emerged in the last two decades causing several outbreaks in endemic countries and spreading to new receptive regions. This changing epidemiology of YF creates new challenges for global public health efforts. Yellow fever is caused by the yellow fever virus (YFV) that circulates between humans, the mosquito vector, and non-human primates (NHP). In this systematic review and meta-analysis, we review and analyse data on the case fatality rate (CFR) and prevalence of YFV in humans, and on the prevalence of YFV in arthropods, and NHP in sub-Saharan Africa (SSA). We performed a comprehensive literature search in PubMed, Web of Science, African Journal Online, and African Index Medicus databases. We included studies reporting data on the CFR and/or prevalence of YFV. Extracted data was verified and analysed using the random effect meta-analysis. We conducted subgroup, sensitivity analysis, and publication bias analyses using the random effect meta-analysis while I2 statistic was employed to determine heterogeneity. This review was registered with PROSPERO under the identification CRD42021242444. The final meta-analysis included 55 studies. The overall case fatality rate due to YFV was 31.1% (18.3–45.4) in humans and pooled prevalence of YFV infection was 9.4% (6.9–12.2) in humans. Only five studies in West and East Africa detected the YFV in mosquito species of the genus Aedes and in Anopheles funestus. In NHP, YFV antibodies were found only in members of the Cercopithecidae family. Our analysis provides evidence on the ongoing circulation of the YFV in humans, Aedes mosquitoes and NHP in SSA. These observations highlight the ongoing transmission of the YFV and its potential to cause large outbreaks in SSA. As such, strategies such as those proposed by the WHO’s Eliminate Yellow Fever Epidemics (EYE) initiative are urgently needed to control and prevent yellow fever outbreaks in SSA. 相似文献
27.
28.
29.
Yang X Harkins LK Zubanova O Harrington A Kovalenko D Nadeau RJ Chen PY Toher JL Lindner V Liaw L Friesel R 《Developmental biology》2008,321(1):64-76
The FGF signaling pathway plays essential roles in endochondral ossification by regulating osteoblast proliferation and differentiation, chondrocyte proliferation, hypertrophy, and apoptosis. FGF signaling is controlled by the complementary action of both positive and negative regulators of the signal transduction pathway. The Spry proteins are crucial regulators of receptor tyrosine kinase-mediated MAPK signaling activity. Sprys are expressed in close proximity to FGF signaling centers and regulate FGFR-ERK-mediated organogenesis. During endochondral ossification, Spry genes are expressed in prehypertrophic and hypertrophic chondrocytes. Using a conditional transgenic approach in chondrocytes in vivo, the forced expression of Spry1 resulted in neonatal lethality with accompanying skeletal abnormalities resembling thanatophoric dysplasia II, including increased apoptosis and decreased chondrocyte proliferation in the presumptive reserve and proliferating zones. In vitro chondrocyte cultures recapitulated the inhibitory effect of Spry1 on chondrocyte proliferation. In addition, overexpression of Spry1 resulted in sustained ERK activation and increased expression of p21 and STAT1. Immunoprecipitation experiments revealed that Spry1 expression in chondrocyte cultures resulted in decreased FGFR2 ubiquitination and increased FGFR2 stability. These results suggest that constitutive expression of Spry1 in chondrocytes results in attenuated FGFR2 degradation, sustained ERK activation, and up-regulation of p21Cip and STAT1 causing dysregulated chondrocyte proliferation and terminal differentiation. 相似文献
30.
Lauren E. Hartley‐Tassell Lucy K. Shewell Christopher J. Day Jennifer C. Wilson Randeep Sandhu Julian M. Ketley Victoria Korolik 《Molecular microbiology》2010,75(3):710-730
Campylobacter jejuni is a highly motile bacterium that responds via chemotaxis to environmental stimuli to migrate towards favourable conditions. Previous in silico analysis of the C. jejuni strain NCTC11168 genome sequence identified 10 open reading frames, tlp1‐10, that encode putative chemosensory receptors. We describe the characterization of the role and specificity of the Tlp1 chemoreceptor (Cj1506c). In vitro and in vivo models were used to determine if Tlp1 had a role in host colonization. The tlp1‐ isogenic mutant was more adherent in cell culture, however, showed reduced colonization ability in chickens. Specific interactions between the purified sensory domain of Tlp1 and l ‐aspartate were identified using an amino acid array and saturation transfer difference nuclear magnetic resonance spectroscopy. Chemotaxis assays showed differences between migration of wild‐type C. jejuni cells and that of a tlp1‐ isogenic mutant, specifically towards aspartate. Furthermore, using yeast two‐hybrid and three‐hybrid systems for analysis of protein–protein interactions, the cytoplasmic signalling domain of Tlp1 was found to preferentially interact with CheV, rather than the CheW homologue of the chemotaxis signalling pathway; this interaction was confirmed using immune precipitation assays. This is the first identification of an aspartate receptor in bacteria other than Escherichia coli and Salmonella enterica serovar Typhimurium. 相似文献