首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   275篇
  免费   6篇
  2024年   1篇
  2023年   1篇
  2022年   1篇
  2021年   2篇
  2020年   1篇
  2019年   3篇
  2017年   2篇
  2016年   6篇
  2015年   2篇
  2014年   11篇
  2013年   9篇
  2012年   28篇
  2011年   36篇
  2010年   19篇
  2009年   8篇
  2008年   24篇
  2007年   31篇
  2006年   26篇
  2005年   25篇
  2004年   10篇
  2003年   16篇
  2002年   5篇
  2001年   2篇
  2000年   2篇
  1999年   1篇
  1995年   2篇
  1993年   1篇
  1991年   1篇
  1989年   2篇
  1985年   1篇
  1982年   1篇
  1974年   1篇
排序方式: 共有281条查询结果,搜索用时 46 毫秒
131.
The primary aims of this study were to examine Croatian truck drivers' sexual contact with sex workers, estimate the frequency of condom use, and assess knowledge of HIV/AIDS within this population. The research was conducted from June 14 to September 16, 2005 at customs offices and accompanying parking lots in four Croatian cities. The sample consists of 69 truck drivers. Information about sexual behavior and condom use were gathered by using a semi-structured interview. Knowledge of HIV/AIDS, measured with a self-administered questionnaire, was found to be low. Six respondents (8.7%) had correctly answered all 13 questions. By contrast, 73% of drivers considered themselves well informed about HIV/AIDS, indicating that most drivers overestimate their knowledge. The majority of respondents (n=62) assumed that most of their colleagues engage in sexual contact with sex workers while on the road, although only one third of respondents reported that they personally have paid for sex. All of the respondents who reported engaging in sexual contact with sex workers stated that they always use condoms. Fear of being infected with a sexually transmitted infection was reported as the main reason for condom use.  相似文献   
132.
The aim of the study was to identify motor structures in elite female volleyball players aged 14-17, and to assess the effect of these motor structures on their technical and situation efficiency. For this purpose, a battery of 12 motor tests as predictor variables, and a set of six technical elements and evaluation of performance quality as criterion variables were applied in a sample of 147 female volleyballers aged 14-15 and a sample of 50 female volleyballers aged 16-17. Analysis of variance between subgroups within the groups of volleyballers aged 14-15 and those aged 16-17 showed the results on all motor tests to improve with the increase in situation performance, which was especially pronounced in the tests assessing explosive strength and agility. The same held true for the results on all tests assessing volleyball techniques, spike and block in particular. In both samples, factor analysis of motor tests isolated two factors underlain by the generation and regulation of strength, and the mechanism of speed regulation. Canonical correlation analysis between the motor regulatory mechanisms and technical elements revealed determination of the mechanisms of strength and technical efficiency in both samples. Regression correlation analysis showed the mechanisms of strength regulation and speed to be good predictors of game performance in female volleyballers aged 14-15 and 16-17, whereby the mechanism of strength regulation had greater effect on the game performance than the mechanism of speed regulation. Regression correlation analysis also revealed the set of 6 techniques evaluated to be a good predictor of situation efficiency in both groups of female volleyballers aged 14-15 and 16-17. The block and spike techniques were found to be the best predictors of game performance quality in the former, and the techniques of spike and block in the latter. Based on the results obtained, a possible model of selection for supreme score achievement in female volleyball is described.  相似文献   
133.
The RecBCD enzyme of Escherichia coli consists of three subunits RecB, RecC and RecD. RecBCD enzyme activities are regulated by its interaction with recombination hotspot Chi. Biochemical and genetic evidence suggest that interaction with Chi affects RecD subunit, and that RecD polypeptide overproduction antagonizes this interaction, suggesting that intact RecD replaces a Chi-modified one. We used bacteria with fragmented chromosomes due to double-strand breaks inflicted by UV and gamma-irradiation to explore in which way increased concentrations of RecBCD's individual subunits affect DNA metabolism. We confirmed that RecD overproduction alters RecBCD-dependent DNA repair and degradation in E. coli. Also, we found that RecB and RecC overproduction did not affect these processes. To determine the basis for the effects of RecD polypeptide overproduction, we monitored activities of RecBCD enzyme on gamma-damaged chromosomal DNA and, in parallel, on lambda and T4 2 phage DNA duplexes provided at intervals. We found that gamma-irradiated wild-type bacteria became transient, and RecD overproducers permanent recB(-)/C(-) phenocopies for processing phage DNA that is provided in parallel. Since this inability of irradiated bacteria to process extrachromosomal DNA substrates coincided in both cases with ongoing degradation of chromosomal DNA, which lasted much longer in RecD overproducers, we were led to conclude that the RecB(-)/C(-) phenotype is acquired as a consequence of RecBCD enzyme titration on damaged chromosomal DNA. This conclusion was corroborated by our observation that no inhibition of RecBCD activity occurs in gamma-irradiated RecBCD overproducers. Together, these results strongly indicate that RecD overproduction prevents dissociation of RecBCD enzyme from DNA substrate and thus increases its processivity.  相似文献   
134.
135.
A class of linearly perturbed discrete-time single species scramble competition models, like the Ricker map, is considered. Perturbations can be of both recruitment and harvesting types. Stability (bistability) is considered for models, where parameters of the map do not depend on time. For models with recruitment, the result is in accordance with Levin and May conjecture [S.A. Levin, R.M. May, A note on difference delay equations, Theor. Pop. Biol. 9 (1976) 178]: the local stability of the positive equilibrium implies its global stability. For intrinsic growth rate r-->infinity the way to chaos is broken down to get extinction of population for the depletion case and to establish a stable two-cycle period for models with immigration. The latter behaviour is also studied for models with random discrete constant perturbations of recruitment type. Extinction, persistence and existence of periodic solutions are studied for the perturbed Ricker model with time-dependent parameters.  相似文献   
136.
Rolling leukocytes deform and show a large area of contact with endothelium under physiological flow conditions. We studied the effect of cytoplasmic viscosity on leukocyte rolling using our three-dimensional numerical algorithm that treats leukocyte as a compound droplet in which the core phase (nucleus) and the shell phase (cytoplasm) are viscoelastic fluids. The algorithm includes the mechanical properties of the cell cortex by cortical tension and considers leukocyte microvilli that deform viscoelastically and form viscous tethers at supercritical force. Stochastic binding kinetics describes binding of adhesion molecules. The leukocyte cytoplasmic viscosity plays a critical role in leukocyte rolling on an adhesive substrate. High-viscosity cells are characterized by high mean rolling velocities, increased temporal fluctuations in the instantaneous velocity, and a high probability for detachment from the substrate. A decrease in the rolling velocity, drag, and torque with the formation of a large, flat contact area in low-viscosity cells leads to a dramatic decrease in the bond force and stable rolling. Using values of viscosity consistent with step aspiration studies of human neutrophils (5-30 Pa·s), our computational model predicts the velocities and shape changes of rolling leukocytes as observed in vitro and in vivo.  相似文献   
137.
The aim of this study is to show what part of our County has the most population with age-related macular degeneration (ARMD) and how some types frequently appear in same parts. The County includes 3 different geographic areas: Gorski Kotar, Coast and Islands. ARMD is the leading cause of visual impairment and blindness in developed countries. There are two categories of ARMD: atrophic or "dry" ARMD and exudative or"wet" ARMD. Our epidemiological study group includes 60 patients (33 females, 27 males) with both types of ARMD and they mostly spent their life times in our County. Patients were examined and treated in our Clinic during 2008 and 2009. We also examined which contribution factor (age, genetics, UV-exposure, diet, iris and macular pigment) is more common and found a links with occupation, residence and habits. Our study shows that ARMD in our County is most frequent in interval of 61-80 years. Incidence of ARMD is mild increased in female (55%). Significant incidence of ARMD is connected with patients who work outdoor more than 5 hours daily (70 %). There were no significant difference between patients in different areas[-Gorski Kotar and Coast (p = 0.9260), Gorshi Kotar and Islands (p = 0.8382) and Coast and Islands (p = 0.8546) connected with occupations. Regions Coast and Islands had more cases of ARMD than Gorski Kotar, but in Gorski Kotar patients had greater percent of "wet" type. Difference is statistically significant between areas Gorski Kotar and Islands (chi2 = 4.675, p = 0.0306). Also, there were statistically significant difference in nutrition between Gorski Kotar and Islands (chi2 = 4.17, p = 0.0411). Incidence of ARMD is related with less iris and macular pigment--47 patients (77%). There was an increased risk for exudative type in Trs?e and Cabar in Gorski Kotar  相似文献   
138.
Mental disorders frequently begin in childhood or adolescence. Psychotropic medications have various indications for the treatment of mental dis­orders in this age group and are used not infrequently off‐label. However, the adverse effects of these medications require special attention during developmentally sensitive periods of life. For this meta‐review, we systematically searched network meta‐analyses and meta‐analyses of randomized controlled trials (RCTs), individual RCTs, and cohort studies reporting on 78 a priori selected adverse events across 19 categories of 80 psychotropic medications – including antidepressants, antipsychotics, anti‐attention‐deficit/hyperactivity disorder (ADHD) medications and mood stabilizers – in children and adolescents with mental disorders. We included data from nine network meta‐analyses, 39 meta‐analyses, 90 individual RCTs, and eight cohort studies, including 337,686 children and adolescents. Data on ≥20% of the 78 adverse events were available for six antidepressants (sertraline, escitalopram, paroxetine, fluoxetine, venlafaxine and vilazodone), eight antipsychotics (risperidone, quetiapine, aripiprazole, lurasidone, paliperidone, ziprasidone, olanzapine and asenapine), three anti‐ADHD medications (methylphenidate, atomoxetine and guanfacine), and two mood stabilizers (valproate and lithium). Among these medications with data on ≥20% of the 78 adverse events, a safer profile emerged for escitalopram and fluoxetine among antidepressants, lurasidone for antipsychotics, methylphenidate among anti‐ADHD medications, and lithium among mood stabilizers. The available literature raised most concerns about the safety of venlafaxine, olanzapine, atomoxetine, guanfacine and valproate. Nausea/vomiting and discontinuation due to adverse event were most frequently associated with antidepressants; sedation, extrapyramidal side effects, and weight gain with antipsychotics; anorexia and insomnia with anti‐ADHD medications; sedation and weight gain with mood stabilizers. The results of this comprehensive and updated quantitative systematic meta‐review of top‐tier evidence regarding the safety of antidepressants, antipsychotics, anti‐ADHD medications and mood stabilizers in children and adolescents can inform clinical practice, research and treatment guidelines.  相似文献   
139.
We previously demonstrated safe and reliable gene transfer to the dorsal root ganglion (DRG) using a direct microinjection procedure to deliver recombinant adeno-associated virus (AAV) vector. In this study, we proceed to compare the in vivo transduction patterns of self-complementary (sc) AAV6 and AAV8 in the peripheral sensory pathway. A single, direct microinjection of either AAV6 or AAV8 expressing EGFP, at the adjusted titer of 2×109 viral particle per DRG, into the lumbar (L) 4 and L5 DRGs of adult rats resulted in efficient EGFP expression (48±20% for AAV6 and 25±4% for AAV8, mean ± SD) selectively in sensory neurons and their axonal projections 3 weeks after injection, which remained stable for up to 3 months. AAV6 efficiently transfers EGFP to all neuronal size groups without differential neurotropism, while AAV8 predominantly targets large-sized neurons. Neurons transduced with AAV6 penetrate into the spinal dorsal horn (DH) and terminate predominantly in superficial DH laminae, as well as in the dorsal columns and deeper laminae III-V. Only few AAV8-transduced afferents were evident in the superficial laminae, and spinal EGFP was mostly present in the deeper dorsal horn (lamina III-V) and dorsal columns, with substantial projections to the ventral horn. AAV6-mediated EGFP-positive nerve fibers were widely observed in the medial plantar skin of ipsilateral hindpaws. No apparent inflammation, tissue damage, or major pain behaviors were observed for either AAV serotype. Taken together, both AAV6 and AAV8 are efficient and safe vectors for transgene delivery to primary sensory neurons, but they exhibit distinct functional features. Intraganglionic delivery of AAV6 is more uniform and efficient compared to AAV8 in gene transfer to peripheral sensory neurons and their axonal processes.  相似文献   
140.
Reaction of the potassium salts of (EtO)2P(O)CH2C6H4-4-(NHC(S)NHP(S)(OiPr)2) (HLI), (CH2NHC(S)NHP(S)(OiPr)2)2 (H2LII) or cyclam(C(S)NHP(S)(OiPr)2)4 (H4LIII) with [Cu(PPh3)3I] or a mixture of CuI and Ph2P(CH2)1-3PPh2 or Ph2P(C5H4FeC5H4)PPh2 in aqueous EtOH/CH2Cl2 leads to [Cu(PPh3)LI] (1), [Cu2(Ph2PCH2PPh2)2LII] (2), [Cu{Ph2P(CH2)2PPh2}LI] (3), [Cu{Ph2P(CH2)3PPh2}LI] (4), [Cu{Ph2P(C5H4FeC5H4)PPh2}LI] (5), [Cu2(PPh3)2LII] (6), [Cu2(Ph2PCH2PPh2)LII] (7), [Cu2{Ph2P(CH2)2PPh2}2LII] (8), [Cu2{Ph2P(CH2)3PPh2}2LII] (9), [Cu2{Ph2P(C5H4FeC5H4)PPh2}2LII] (10), [Cu8(Ph2PCH2PPh2)8LIIII4] (11), [Cu4{Ph2P(CH2)2PPh2}4LIII] (12), [Cu4{Ph2P(CH2)3PPh2}4LIII] (13) or [Cu4{Ph2P(C5H4FeC5H4)PPh2}4LIII] (14) complexes. The structures of these compounds were investigated by IR, 1H, 31P{1H} NMR spectroscopy; their compositions were examined by microanalysis. The luminescent properties of the complexes 1-14 in the solid state are reported.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号