全文获取类型
收费全文 | 851篇 |
免费 | 78篇 |
出版年
2023年 | 9篇 |
2022年 | 11篇 |
2021年 | 27篇 |
2020年 | 13篇 |
2019年 | 16篇 |
2018年 | 24篇 |
2017年 | 22篇 |
2016年 | 36篇 |
2015年 | 48篇 |
2014年 | 41篇 |
2013年 | 51篇 |
2012年 | 63篇 |
2011年 | 55篇 |
2010年 | 56篇 |
2009年 | 42篇 |
2008年 | 43篇 |
2007年 | 46篇 |
2006年 | 36篇 |
2005年 | 28篇 |
2004年 | 32篇 |
2003年 | 39篇 |
2002年 | 25篇 |
2001年 | 12篇 |
2000年 | 11篇 |
1999年 | 13篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1996年 | 5篇 |
1995年 | 7篇 |
1994年 | 2篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1976年 | 4篇 |
1975年 | 15篇 |
1974年 | 8篇 |
1973年 | 4篇 |
1971年 | 2篇 |
1967年 | 4篇 |
1966年 | 3篇 |
排序方式: 共有929条查询结果,搜索用时 130 毫秒
61.
Michael P. Lerario Gino Gialdini Daniel M. Lapidus Mesha M. Shaw Babak B. Navi Alexander E. Merkler Gregory Y. H. Lip Jeff S. Healey Hooman Kamel 《PloS one》2015,10(12)
Background
We aimed to estimate the risk of ischemic stroke after intracranial hemorrhage in patients with atrial fibrillation.Materials and Methods
Using discharge data from all nonfederal acute care hospitals and emergency departments in California, Florida, and New York from 2005 to 2012, we identified patients at the time of a first-recorded encounter with a diagnosis of atrial fibrillation. Ischemic stroke and intracranial hemorrhage were identified using validated diagnosis codes. Kaplan-Meier survival statistics and Cox proportional hazard analyses were used to evaluate cumulative rates of ischemic stroke and the relationship between incident intracranial hemorrhage and subsequent stroke.Results
Among 2,084,735 patients with atrial fibrillation, 50,468 (2.4%) developed intracranial hemorrhage and 89,594 (4.3%) developed ischemic stroke during a mean follow-up period of 3.2 years. The 1-year cumulative rate of stroke was 8.1% (95% CI, 7.5–8.7%) after intracerebral hemorrhage, 3.9% (95% CI, 3.5–4.3%) after subdural hemorrhage, and 2.0% (95% CI, 2.0–2.1%) in those without intracranial hemorrhage. After adjustment for the CHA2DS2-VASc score, stroke risk was elevated after both intracerebral hemorrhage (hazard ratio [HR], 2.8; 95% CI, 2.6–2.9) and subdural hemorrhage (HR, 1.6; 95% CI, 1.5–1.7). Cumulative 1-year rates of stroke ranged from 0.9% in those with subdural hemorrhage and a CHA2DS2-VASc score of 0, to 33.3% in those with intracerebral hemorrhage and a CHA2DS2-VASc score of 9.Conclusions
In a large, heterogeneous cohort, patients with atrial fibrillation faced a substantially heightened risk of ischemic stroke after intracranial hemorrhage. The risk was most marked in those with intracerebral hemorrhage and high CHA2DS2-VASc scores. 相似文献62.
Suzan M. Doornwaard Tom F. M. ter Bogt Ellen Reitz Regina J. J. M. van den Eijnden 《PloS one》2015,10(6)
Research on the role of sex-related Internet use in adolescents’ sexual development has often isolated the Internet and online behaviors from other, offline influencing factors in adolescents’ lives, such as processes in the peer domain. The aim of this study was to test an integrative model explaining how receptive (i.e., use of sexually explicit Internet material [SEIM]) and interactive (i.e., use of social networking sites [SNS]) sex-related online behaviors interrelate with perceived peer norms in predicting adolescents’ experience with sexual behavior. Structural equation modeling on longitudinal data from 1,132 Dutch adolescents (Mage T1 = 13.95; range 11-17; 52.7% boys) demonstrated concurrent, direct, and indirect effects between sex-related online behaviors, perceived peer norms, and experience with sexual behavior. SEIM use (among boys) and SNS use (among boys and girls) predicted increases in adolescents’ perceptions of peer approval of sexual behavior and/or in their estimates of the numbers of sexually active peers. These perceptions, in turn, predicted increases in adolescents’ level of experience with sexual behavior at the end of the study. Boys’ SNS use also directly predicted increased levels of experience with sexual behavior. These findings highlight the need for multisystemic research and intervention development to promote adolescents’ sexual health. 相似文献
63.
Kalthoum Tizaoui Wajih Kaabachi Marwa Ouled Salah Amira Ben Amor Agnès Hamzaoui Kamel Hamzaoui 《Cellular immunology》2014
Recent genetic surveys have identified vitamin D receptor (VDR) as a susceptibility gene for several autoimmune diseases. This study was designed to investigate the association of VDR gene polymorphisms with Behçet’s disease (BD) and Rheumatoid arthritis (RA). A case–control study including 151 BD, 106 RA patients and an appropriate number of healthy control subjects were performed using polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) techniques. Association between TaqI polymorphism and BD was marginal under codominant and recessive models (P = 0.078 and P = 0.058, respectively). After stratification, we found evidence for a significant association between TaqI polymorphism and BD in the elderly subjects (P = 0.037). The minor ApaI a allele tended to confer an increased risk for BD susceptibility (P = 0.087). BD patients with VDR homozygous AA or aa genotypes were at increased risk for development of erythema nodosum (EN) skin manifestation (P = 0.038). No significant association was observed for VDR ApaI and TaqI polymorphisms with RA risk (P > 0.05). TaqI and ApaI polymorphisms might be modestly implicated in BD pathogenesis. They could be considered as potential biomarkers in BD rather than susceptibility genes. However, TaqI and ApaI seemed not to be implicated in RA pathogenesis. 相似文献
64.
Mohamad Rida Nesreen Ghaddar Kamel Ghali Jamal Hoballah 《International journal of biometeorology》2014,58(9):1825-1843
A bioheat model for the elderly was developed focusing on blood flow circulatory changes that influence their thermal response in warm and cold environments to predict skin and core temperatures for different segments of the body especially the fingers. The young adult model of Karaki et al. (Int J Therm Sci 67:41–51, 2013) was modified by incorporation of the physiological thermoregulatory and vasomotor changes based on literature observations of physiological changes in the elderly compared to young adults such as lower metabolism and vasoconstriction diminished ability, skin blood flow and its minimum and maximum values, the sweating values, skin fat thickness, as well as the change in threshold parameter related to core or skin temperatures which triggers thermoregulatory action for sweating, maximum dilatation, and maximum constriction. The developed model was validated with published experimental data for elderly exposure to transient and steady hot and cold environments. Predicted finger skin temperature, mean skin temperature, and core temperature were in agreement with published experimental data at a maximum error less than 0.5 °C in the mean skin temperature. The elderly bioheat model showed an increase in finger skin temperature and a decrease in core temperature in cold exposure while it showed a decrease in finger skin temperature and an increase in core temperature in hot exposure. 相似文献
65.
Mohamad Rida Wafaa Karaki Nesreen Ghaddar Kamel Ghali Jamal Hoballah 《International journal of biometeorology》2014,58(9):1905-1918
The purpose of this work was to integrate a new mathematical model with a bioheat model, based on physiology and first principles, to predict thermoregulatory arterio-venous anastomoses (AVA) and cold-induced vasodilation (CIVD) reaction to local cooling. The transient energy balance equations of body segments constrained by thermoregulatory controls were solved numerically to predict segmental core and skin temperatures, and arterial blood flow for given metabolic rate and environmental conditions. Two similar AVA–CIVD mechanisms were incorporated. The first was activated during drop in local skin temperature (<32 °C). The second mechanism was activated at a minimum finger skin temperature, T CIVD, min, where the AVA flow is dilated and constricted once the skin temperature reached a maximum value. The value of T CIVD,min was determined empirically from values reported in literature for hand immersions in cold fluid. When compared with published data, the model predicted accurately the onset time of CIVD at 25 min and T CIVD,min at 10 °C for hand exposure to still air at 0 °C. Good agreement was also obtained between predicted finger skin temperature and experimentally published values for repeated immersion in cold water at environmental conditions of 30, 25, and 20 °C. The CIVD thermal response was found related to core body temperature, finger skin temperature, and initial finger sensible heat loss rate upon exposure to cold fluid. The model captured central and local stimulations of the CIVD and accommodated observed variability reported in literature of onset time of CIVD reaction and T CIVD,min. 相似文献
66.
Development and organization of polarity-specific segregation of primary vestibular afferent fibers in mice 总被引:1,自引:0,他引:1
A striking feature of vestibular hair cells is the polarized arrangement of their stereocilia as the basis for their directional
sensitivity. In mammals, each of the vestibular end organs is characterized by a distinct distribution of these polarized
cells. We utilized the technique of post-fixation transganglionic neuronal tracing with fluorescent lipid soluble dyes in
embryonic and postnatal mice to investigate whether these polarity characteristics correlate with the pattern of connections
between the endorgans and their central targets; the vestibular nuclei and cerebellum. We found that the cerebellar and brainstem
projections develop independently from each other and have a non-overlapping distribution of neurons and afferents from E11.5
on. In addition, we show that the vestibular fibers projecting to the cerebellum originate preferentially from the lateral
half of the utricular macula and the medial half of the saccular macula. In contrast, the brainstem vestibular afferents originate
primarily from the medial half of the utricular macula and the lateral half of the saccular macula. This indicates that the
line of hair cell polarity reversal within the striola region segregates almost mutually exclusive central projections. A
possible interpretation of this feature is that this macular organization provides an inhibitory side-loop through the cerebellum
to produce synergistic tuning effects in the vestibular nuclei. The canal cristae project to the brainstem vestibular nuclei
and cerebellum, but the projection to the vestibulocerebellum originates preferentially from the superior half of each of
the cristae. The reason for this pattern is not clear, but it may compensate for unequal activation of crista hair cells or
may be an evolutionary atavism reflecting a different polarity organization in ancestral vertebrate ears. 相似文献
67.
Paul J. Geutjes Suzan T.M. Nillesen Gerwen Lammers Willeke F. Daamen Toin H. van Kuppevelt 《Protein expression and purification》2010,69(1):76-82
Large-scale production of recombinant rat vascular endothelial growth factor (rrVEGF-164) is desirable for angiogenic studies. In this study, biologically active recombinant rat vascular endothelial growth factor (rrVEGF-164) was cloned and expressed in the yeast Pichia pastoris, and large-scale production was performed by fermentation. cDNA encoding VEGF-164 was prepared from embryonic rat tissue RNA, and a recombinant pPIC9HV/rVEGF-164 plasmid, containing an AOX1 promoter, was constructed. The methylotrophic P. pastoris was used as the eukaryotic expression system. After transformation, rrVEGF-164 was produced by fermentation (~124 mg/L) and purified by heparin affinity chromatography. SDS–PAGE indicated that rrVEGF-164 was produced as a disulphide-bridged dimer of 48 kDa which was purified to near homogeneity by heparin affinity chromatography in a large quantity. A bioassay indicated a three- to fivefold increase in endothelial cell proliferation after 3 days, due to the addition of the produced rrVEGF-164. The produced rrVEGF-164 showed a higher biological activity than a commercially available, mouse cell line-based, growth factor. In conclusion, using the P. pastoris expression system we were able to produce biologically active rat VEGF-164 in high quantities and this may provide a powerful tool for basic and applied life sciences. 相似文献
68.
Eighty‐two isolates of Rhizoctonia solani were recorded from roots of naturally‐infected seedlings of the Egyptian cotton (Gossypium barbadense L.). Anastomosis groups (AGs) of the isolates were determined by using 13 different AGs testers. Three (3.7%) of the isolates were identified as R. solani AG7, while the remaining isolates were belonging to the AG 2‐1, AG4 and AG5. The identification of the three isolates was based on the frequency of the C2 reaction with the AG7 tester isolate. No fusion was observed between AG7 and isolates representing the other 13 AGs. Colonies of AG7 isolates grown on potato dextrose agar (PDA), malt yeast agar (MYA) and melt peptone agar (MPA) were brown to dark brown with aerial mycelium and sclerotia. The isolates had pitted sclerotial clusters and brownish exudates after 21 days of culturing on PDA, but without clear zonation. Pathogenicity test under greenhouse conditions revealed that AG7 caused the common symptoms of damping–off, which included seed rot, lesions on the hypocotyls and root rot. 相似文献
69.
Mohamed Ben Sghaier Jihed Boubaker Aicha Neffati Ilef Limem Ines Skandrani Wissem Bhouri Ines Bouhlel Soumaya Kilani Leila Chekir‐Ghedira Kamel Ghedira 《化学与生物多样性》2010,7(7):1754-1763
The mutagenic and antimutagenic effects of the essential oil extracted from the aerial parts of Teucrium ramosissimum were evaluated by the bacterial reverse mutation assay in Salmonella typhimurium TA98, TA100, and TA1535, with and without exogenous metabolic activation (S9 fraction). The T. ramosissimum essential oil showed no mutagenic effect. In contrast, our results established that it possessed antimutagenic effects against sodium azide (SA), aflatoxin B1 (AFB1), benzo[a]pyrene (B[a]P), and 4‐nitro‐o‐phenylenediamine (NOPD). The antioxidant capacity of the tested essential oil was evaluated using enzymatic, i.e., the xanthine/xanthine oxidase (X/XOD) assay, and nonenzymatic systems, i.e., the nitro‐blue tetrazolium (NBT)/riboflavin and the DPPH assays. A moderate free radical‐scavenging activity was observed towards DPPH. and O$\rm{{_{2}^{{^\cdot} -}}}$ . In contrast, T. ramosissimum essential oil showed no effect for all the tested concentrations in the X/XOD assay. 相似文献
70.
Elizabeth A. Archie Tammy Henry Jesus E. Maldonado Cynthia J. Moss Joyce H. Poole Virginia R. Pearson Suzan Murray Susan C. Alberts Robert C. Fleischer 《Immunogenetics》2010,62(2):85-100
Genes of the vertebrate major histocompatibility complex (MHC) are crucial to defense against infectious disease, provide
an important measure of functional genetic diversity, and have been implicated in mate choice and kin recognition. As a result,
MHC loci have been characterized for a number of vertebrate species, especially mammals; however, elephants are a notable
exception. Our study is the first to characterize patterns of genetic diversity and natural selection in the elephant MHC.
We did so using DNA sequences from a single, expressed DQA locus in elephants. We characterized six alleles in 30 African
elephants (Loxodonta africana) and four alleles in three Asian elephants (Elephas maximus). In addition, for two of the African alleles and three of the Asian alleles, we characterized complete coding sequences
(exons 1–5) and nearly complete non-coding sequences (introns 2–4) for the class II DQA loci. Compared to DQA in other wild
mammals, we found moderate polymorphism and allelic diversity and similar patterns of selection; patterns of non-synonymous
and synonymous substitutions were consistent with balancing selection acting on the peptides involved in antigen binding in
the second exon. In addition, balancing selection has led to strong trans-species allelism that has maintained multiple allelic
lineages across both genera of extant elephants for at least 6 million years. We discuss our results in the context of MHC
diversity in other mammals and patterns of evolution in elephants. 相似文献