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11.
The main objective of this paper is to decompose the productivity growth of Egyptian cotton production. We employ the stochastic frontier approach and decompose the changes in total factor productivity (CTFP) growth into four components: technical progress (TP), changes in scale component (CSC), changes in allocative efficiency (CAE), and changes in technical efficiency (CTE). Considering a situation of scarce statistical information, we propose four alternative empirical models, with the purpose of looking for convergence in the results. The results provide evidence that in this production system total productivity does not increase, which is mainly due to the negative average contributions of CAE and TP. Policy implications are offered in light of the results. 相似文献
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Gelareh Valadi Javad Eshaghi Rad Yahia Khodakarami Mostafa Nemati Peykani Karen A. Harper 《Journal of Plant Ecology》2022,15(2):413
伊朗稀疏橡木林片段对草本植物物种多样性和土壤特性的边缘影响
温带和热带森林中的森林边缘现象已经得到了很好的研究,但在稀疏的橡木林片段中的相关研究却较为缺乏。本文研究了稀疏橡木林片段对植物物种多样性和土壤特性的边缘影响。本研究沿着伊朗克尔曼沙赫省3个小型(<10 ha)和3个大型(>10 ha)橡木林片段的3个横断面收集了从边缘到内部的相 关数据,测量了0(森林边缘)、25、50、100和150 m处的草本植物(高度<0.5 m)和土壤特性。使用香农指数量化了物种多样性,使用稀疏标准化方法比较了两个大小不同片段中的物种丰富度,并应用了非度量多维测度排序研究了物种组成的变化。通过随机化测试估算了边缘影响的距离,并利用Tukey HSD事后检验法的广义线性混合模型评估了距边缘距离和片段大小对多样性和土壤特性的影响。研究结果表明,大小片段边缘具有较高的物种丰富度、多样性和均匀度,而大片段边缘的土壤氮和有机碳含量则较内部更低(边缘50 m范围内的变化最大)。大小片段的物种组成、土壤有机碳和氮总量都存在显 著差异。本研究关于这些稀疏森林对草本植物和土壤特性产生显著边缘影响的发现,对于边缘研究,尤其是边缘和草本植物的相关研究具有重大贡献。 相似文献
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Clearance of a productive lentivirus infection in calves experimentally inoculated with caprine arthritis-encephalitis virus
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Morin T Guiguen F Bouzar BA Villet S Greenland T Grezel D Gounel F Gallay K Garnier C Durand J Alogninouwa T Mselli-Lakhal L Mornex JF Chebloune Y 《Journal of virology》2003,77(11):6430-6437
Lentiviruses have long been considered host-specific pathogens, but several recent observations demonstrated their capacity to conquer new hosts from different species, genera, and families. From these cross-species infections emerged new animal and human infectious diseases. The successful colonization and adaptation of a lentivirus to a nonnatural host depends on unspecific and specific host barriers. Some of those barriers exert a relative control of viral replication (i.e., cytotoxic T-lymphocyte response, viral inhibitory factors), but none of them was found able to totally clear the infection once the retrovirus is fully adapted in its host. In this study we examined the evolution of the host-lentivirus interactions occurring in an experimental animal model of cross-species infection in order to analyze the efficiency of those barriers in preventing the establishment of a persistent infection. Five newborn calves were inoculated with caprine arthritis-encephalitis virus (CAEV), and the evolution of infection was studied for more than 12 months. All the animals seroconverted in the first 0.75 to 1 month following the inoculation and remained seropositive for the remaining time of the experiment. Viral infection was productive during 4 months with isolation of replication competent virus from the blood cells and organs of the early euthanized animals. After 4 months of infection, neither replication-competent virus nor virus genome could be detected in blood cells or in the classical target organs, even after an experimental immunosuppression. No evidence of in vitro restriction of CAEV replication was observed in cells from tissues explanted from organs of these calves. These data provide the demonstration of a natural clearance of lentivirus infection following experimental inoculation of a nonnatural host, enabling perspectives of development of new potential vaccine strategies to fight against lentivirus infections. 相似文献
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Lamara A Fieni F Mselli-Lakhal L Chatagnon G Bruyas JF Tainturier D Battut I Fornazero C Chebloune Y 《Theriogenology》2002,58(6):1153-1163
The aim of this study was to investigate whether cells of early goat embryos isolated from in vivo-fertilized goats interact with the caprine arthritis-encephalitis virus (CAEV) in vitro and whether the embryonic zona pellucida (ZP) protects early embryo cells from CAEV infection. ZP-free and ZP-intact 8-16 cell embryos were inoculated for 2 h with CAEVat the 10(4) tissue culture infectious dose 50 (TCID50)/ml. Infected embryos were incubated for 72 h over feeder monolayer containing caprine oviduct epithelial cells (COECs) and CAEV indicator goat synovial membrane (GSM) cells. Noninoculated ZP-free and ZP-intact embryos were submitted to similar treatments and used as controls. Six days postinoculation, infectious virus assay of the wash fluids of inoculated early goat embryos showed typical CAEV-induced cytopathic effects (CPE) on indicator GSM monolayers, with fluids of the first two washes only. The mixed cell monolayer (COEC + GSM) used as feeder cells for CAEV inoculated ZP-free embryos showed CPE. In contrast, none of the feeder monolayers, used for culture of CAEV inoculated ZP-intact embryos or the noninoculated controls, developed any CPE. CAEV exposure apparently did not interfere with development of ZP-free embryos in vitro during the 72 h study period when compared with untreated controls (34.6 and 36% blastocysts, respectively, P > 0.05). From these results one can conclude that the transmission of infectious molecularly cloned CAEV-pBSCA (plasmid binding site CAEV) by embryonic cells from in vivo-produced embryos at the 8-16 cell stages is possible with ZP-free embryos. The absence of interactions between ZP-intact embryos and CAEV in vitro suggests that the ZP is an efficient protective embryo barrier. 相似文献
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Purification of a 130-kDa T cell glycoprotein that binds human interleukin 4 with high affinity 总被引:3,自引:0,他引:3
J P Galizzi B Castle O Djossou N Harada H Cabrillat S A Yahia R Barrett M Howard J Banchereau 《The Journal of biological chemistry》1990,265(1):439-444
The interleukin 4 (IL-4) receptor was purified from the gibbon T cell line MLA 144. These cells were found to express high numbers of human IL-4-binding proteins (5000-6000 sites/cell) with an affinity constant (Kd) similar to that measured in human cell lines (Kd = 40-70 pM). Affinity cross-linking of 125I-IL-4 to human cell lines and MLA 144 cells demonstrated the labeling of three proteins of approximately 130, 75, and 65 kDa. Human IL-4-binding sites were solubilized from MLA 144 cells using Triton X-100 and then purified by carboxymethyl chromatography, which removed 50% of the protein without loss of IL-4-binding activity. Then sequential affinity purification over wheat germ agglutinin and a single IL-4 Affi-Gel 10 column resulted in a final 8000-fold purification of the IL-4 receptor. When analyzed on a silver-stained sodium dodecyl sulfate-polyacrylamide gel, the purified receptor migrated as a single molecular species of 130 +/- 5 kDa. Identification of the 130-kDa protein as the IL-4 receptor was demonstrated by cross-linking experiments and specific binding of 125I-IL-4 to nitrocellulose membranes after electrophoretic transfer of the purified receptor on sodium dodecyl sulfate-polyacrylamide gel. 相似文献
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Dicko A Diallo AI Tembine I Dicko Y Dara N Sidibe Y Santara G Diawara H Conaré T Djimde A Chandramohan D Cousens S Milligan PJ Diallo DA Doumbo OK Greenwood B 《PLoS medicine》2011,8(2):e1000407