全文获取类型
收费全文 | 853篇 |
免费 | 64篇 |
国内免费 | 4篇 |
专业分类
921篇 |
出版年
2023年 | 4篇 |
2022年 | 26篇 |
2021年 | 36篇 |
2020年 | 22篇 |
2019年 | 32篇 |
2018年 | 31篇 |
2017年 | 21篇 |
2016年 | 34篇 |
2015年 | 32篇 |
2014年 | 38篇 |
2013年 | 57篇 |
2012年 | 45篇 |
2011年 | 58篇 |
2010年 | 31篇 |
2009年 | 27篇 |
2008年 | 46篇 |
2007年 | 35篇 |
2006年 | 31篇 |
2005年 | 26篇 |
2004年 | 29篇 |
2003年 | 12篇 |
2002年 | 8篇 |
2001年 | 23篇 |
2000年 | 13篇 |
1999年 | 17篇 |
1998年 | 6篇 |
1997年 | 7篇 |
1996年 | 8篇 |
1995年 | 10篇 |
1993年 | 13篇 |
1992年 | 6篇 |
1991年 | 20篇 |
1990年 | 10篇 |
1989年 | 13篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1982年 | 4篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1976年 | 5篇 |
1973年 | 4篇 |
1972年 | 6篇 |
1971年 | 4篇 |
1966年 | 3篇 |
1954年 | 4篇 |
排序方式: 共有921条查询结果,搜索用时 11 毫秒
81.
Hantavirus infection induces the expression of RANTES and IP-10 without causing increased permeability in human lung microvascular endothelial cells 总被引:10,自引:0,他引:10 下载免费PDF全文
Sundstrom JB McMullan LK Spiropoulou CF Hooper WC Ansari AA Peters CJ Rollin PE 《Journal of virology》2001,75(13):6070-6085
Sin Nombre virus (SNV) and Hantaan virus (HTN) infect endothelial cells and are associated with different patterns of increased vascular permeability during human disease. It is thought that such patterns of increased vascular permeability are a consequence of endothelial activation and subsequent dysfunction mediated by differential immune responses to hantavirus infection. In this study, the ability of hantavirus to directly induce activation of human lung microvascular endothelial cells (HMVEC-Ls) was examined. No virus-specific modulation in the constitutive or cytokine-induced expression of cellular adhesion molecules (CD40, CD54, CD61, CD62E, CD62P, CD106, and major histocompatibility complex classes I and II) or in cytokines and chemokines (eotaxin, tumor necrosis factor alpha, interleukin 1beta [IL-1beta], IL-6, IL-8, MCP-1, MIP-1alpha, and MIP-1beta) was detected at either the protein or message level in hantavirus-infected HMVEC-Ls. Furthermore, no virus-specific enhancement of paracellular or transcellular permeability or changes in the organization and distribution of endothelial intercellular junctional proteins was observed. However, infection with either HTN or SNV resulted in detectable levels of the chemokines RANTES and IP-10 (the 10-kDa interferon-inducible protein) in HMVEC-Ls within 72 h and was associated with nuclear translocation of interferon regulatory factor 3 (IRF-3) and IRF-7. Gamma interferon (IFN-gamma)-induced expression of RANTES and IP-10 could also be detected in uninfected HMVEC-Ls and was associated with nuclear translocation of IRF-1 and IRF-3. Treatment of hantavirus-infected HMVEC-Ls with IFN-gamma for 24 h resulted in a synergistic enhancement in the expression of both RANTES and IP-10 and was associated with nuclear translocation of IRF-1, IRF-3, IRF-7, and NF-kappaB p65. These results reveal a possible mechanism by which hantavirus infection and a TH1 immune response can cooperate to synergistically enhance chemokine expression by HMVEC-Ls and trigger immune-mediated increases in vascular permeability. 相似文献
82.
Meiofauna of a sewage-polluted sandy beach, where sand alone constituted > 90%, was surveyed. Nematodes dominated the fauna
numerically at all stations, followed by harpacticoid copepods. Most of the animals were confined to the top 5 cm of the sediment.
A seasonal pattern was observed in the distribution of the fauna. There were significant spatial and temporal variations in
mean meiofauna density, attributed to organic discharge via sewage and prevailing environmental conditions in the study area. 相似文献
83.
The present study deals with the histochemical localization of glucose-6-phosphatase, malic dehydrogenase and aldolase in the microfilaria of Setaria cervi. Marked activity of glucose-6-phosphatase was observed in the cephalic cells, excretory and anal pores, G-cells and Innenk?rper. Malic dehydrogenase activity was noted throughout the body (including cuticle) of the microfilaria except for Innenk?rper. Intense aldolase activity was observed in the excretory pore and G-cells only. Muscle cells and anal pore were negative for this enzyme. 相似文献
84.
The paper presents multiplex panels of polymorphic microsatellites for two closely related cryptic species Pipistrellus pipistrellus and Pipistrellus pygmaeus. We tested the cross‐species amplification of 34 microsatellite loci, originally developed for five vespertilionid bat species. Ten and nine polymorphic loci in P. pipistrellus (mean number of alleles per locus = 10.5) and P. pygmaeus (8.1), respectively, in three multiplex polymerase chain reactions per species were amplified. All loci can be analysed in a single fragment analysis and can be used as markers to the study of evolution and the ecology of structured populations of socially living bats. 相似文献
85.
Ali MA Ismail R Choon TS Pandian S Hassan Ansari MZ 《Journal of enzyme inhibition and medicinal chemistry》2011,26(4):598-602
In this study, a series of novel 3-(substituted phenyl)-6,7-dimethoxy-3a,4-dihydro-3H-indeno[1,2-c]isoxazole analogues were synthesized and evaluated for antimycobacterial activity against Mycobacterium tuberculosis (MTB) H(37)Rv and isoniazid resistant M. tuberculosis (INHR-MTB). All the newly synthesized compounds were showing moderate to high inhibitory activities. The compound 6,7-dimethoxy-3-(4-chloro phenyl)-4H-indeno[1,2-c]isoxazole (4b) was found to be the most promising compound, active against MTB H(37)Rv and INHR-MTB with minimum inhibitory concentrations of 0.22 and 0.34 μM. 相似文献
86.
Dyscalculia, dyslexia, and specific language impairment (SLI) are relatively specific developmental learning disabilities in math, reading, and oral language, respectively, that occur in the context of average intellectual capacity and adequate environmental opportunities. Past research has been dominated by studies focused on single impairments despite the widespread recognition that overlapping and comorbid deficits are common. The present study took an epidemiological approach to study the learning profiles of a large school age sample in language, reading, and math. Both general learning profiles reflecting good or poor performance across measures and specific learning profiles involving either weak language, weak reading, weak math, or weak math and reading were observed. These latter four profiles characterized 70% of children with some evidence of a learning disability. Low scores in phonological short-term memory characterized clusters with a language-based weakness whereas low or variable phonological awareness was associated with the reading (but not language-based) weaknesses. The low math only group did not show these phonological deficits. These findings may suggest different etiologies for language-based deficits in language, reading, and math, reading-related impairments in reading and math, and isolated math disabilities. 相似文献
87.
Harshan HM Singh LP Arangasamy A Ansari MR Kumar S 《Animal reproduction science》2006,93(1-2):124-133
The study was conducted to assess the effect of heparin binding seminal plasma proteins (HBP) on freezability and in vitro fertilizing ability of buffalo cauda epididymal spermatozoa. Spermatozoal motility, viability and acrosomal integrity at prefreeze and post-thaw stages were studied. The in vitro fertilizing ability of spermatozoa was assessed by the application of two tests, i.e. bovine cervical mucus penetration test (BCMPT) and hypo-osmotic sperm swelling test (HOST). HBP isolated from buffalo seminal plasma and maintained in the laboratory were used for the study. Twelve pairs of epididymis from adult buffaloes slaughtered at the local abattoir were used for the study. The results indicated that HBP addition improved the progressive motility, BCMPT and HOST response at prefreeze level. HBP at a concentration of 40 microg/ml showed better results than HBP at a concentration of 80 microg/ml. However, subjecting the HBP treated spermatozoa to cryopreservation resulted in significant reduction of motility, viability, acrosomal integrity and response to BCMPT and HOST in the HBP treated groups when compared to those in control group. The deleterious effect of HBP was found to be concentration dependent with the higher concentration causing higher post-thaw damage. 相似文献
88.
The blood supply of the reverse temporalis muscle flap: anatomic study and clinical implications 总被引:3,自引:0,他引:3
Although the reverse temporalis muscle flap has been used clinically, the exact vascular connection between the superficial and deep temporal vessels has not been clearly defined. The purpose of this study was to investigate the vascular territory of the reverse temporalis muscle supplied by the superficial temporal vessels. Six cadaver heads were studied using a colored lead oxide injection through the superficial temporal artery. The specimens were examined macroscopically and radiographically. The reverse temporalis muscle flap was then applied to a clinical case presenting with traumatic anterior skull base defect communicating with the nasal cavity. The cadaver specimens demonstrated that the superficial temporal artery formed an average 1.3 +/- 0.2 cm in width of dense vascular zone, which was located within 1.8 cm below the superior temporal line. The dense vascular network further perfused the anterior and posterior deep temporal arteries and the muscular branch of the middle temporal artery to supply the temporalis muscle. The mean perfused area of the temporalis muscle was 83 percent, ranging from 79 to 89 percent, in five cadaver heads. One cadaver revealed only 55 percent of perfused area in the absence of the muscular branch of the middle temporal artery. The consistent area without perfusion was located in the distal third of the posterior portion of the reverse temporalis muscle. In clinical cases, the reverse temporalis muscle flap was used successfully to obliterate the anterior skull base defect without evidence of muscle flap necrosis. The exact blood supply to the distal third of the posterior portion of the reverse temporalis muscle flap needs to be investigated further in vivo. Particular attention was paid to the inclusion of the muscular branch of the middle temporal artery in this flap to augment the blood supply to the temporalis muscle. 相似文献
89.
Ahmad AS Zia S Sayeed I Ansari MA Ahmad M Salim S Yousuf S Islam F 《Biological trace element research》2005,103(1):59-68
The effect of 0.05, 0.1, and 0.2 mg sodium selenite/kg body weight ip on the activities of neurobehavioral, acetyl cholinesterase,
monoamine oxidase, and the content of dopamine and its metabolites in circadian rhythm centers of male Wistar rats was studied
after 7 d of treatment. The results show an appreciable increase in locomotion, stereo-events, distance traveled, and average
speed at the dose of 0.1 and 0.2 mg sodium selenite/kg. The data have shown hyperactivity of animals with various doses of
sodium selenite, and it was significant and dose-dependent after 3 d of treatment. The activity of acetylcholinesterase (AChE)
was inhibited dose dependently, and it was significant in preoptic area with 0.1 or 0.2 mg sodium selenite/kg. Conversely,
in the posterior hypothalamus its activity was significantly elevated with the dose of 0.2 mg sodium selenite/kg, but its
alteration in brain stem was not significant. Monoamine oxidase (MAO) activity was increased in preoptic area with the dose
of 0.1 mg sodium selenite/kg, but its alteration in posterior hypothalamus and brain stem was not significant. The content
of dopamine (DA), 3,4-dihydroxyphenyl acetic acid (DOPAC), and homovanilic acid (HVA) was elevated dose dependently and it
was significant with the doss of 0.1 and 0.2 mg sodium selenite/kg, but the content of DOPAC and HVA in posterior hypothalamus
was not significant with the dose of 0.1 mg sodium selenite/kg. 相似文献
90.
Patterns of linkage disequilibrium, homoplasy, and incompatibility are difficult to interpret because they depend on several factors, including the recombination process and the population structure. Here we introduce a novel model-based framework to infer recombination properties from such summary statistics in bacterial genomes. The underlying model is sequentially Markovian so that data can be simulated very efficiently, and we use approximate Bayesian computation techniques to infer parameters. As this does not require us to calculate the likelihood function, the model can be easily extended to investigate less probed aspects of recombination. In particular, we extend our model to account for the bias in the recombination process whereby closely related bacteria recombine more often with one another. We show that this model provides a good fit to a data set of Bacillus cereus genomes and estimate several recombination properties, including the rate of bias in recombination. All the methods described in this article are implemented in a software package that is freely available for download at http://code.google.com/p/clonalorigin/. 相似文献