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   22841篇
  免费   1718篇
  国内免费   32篇
耳鼻咽喉   172篇
儿科学   766篇
妇产科学   615篇
基础医学   3002篇
口腔科学   239篇
临床医学   2961篇
内科学   4210篇
皮肤病学   278篇
神经病学   2248篇
特种医学   436篇
外科学   2266篇
综合类   384篇
一般理论   81篇
预防医学   3451篇
眼科学   247篇
药学   1307篇
中国医学   17篇
肿瘤学   1911篇
  2024年   42篇
  2023年   301篇
  2022年   470篇
  2021年   983篇
  2020年   608篇
  2019年   932篇
  2018年   941篇
  2017年   702篇
  2016年   750篇
  2015年   769篇
  2014年   998篇
  2013年   1368篇
  2012年   2097篇
  2011年   2039篇
  2010年   1064篇
  2009年   854篇
  2008年   1495篇
  2007年   1419篇
  2006年   1411篇
  2005年   1282篇
  2004年   1105篇
  2003年   913篇
  2002年   801篇
  2001年   108篇
  2000年   103篇
  1999年   125篇
  1998年   172篇
  1997年   98篇
  1996年   72篇
  1995年   60篇
  1994年   41篇
  1993年   49篇
  1992年   31篇
  1991年   25篇
  1990年   31篇
  1989年   18篇
  1988年   18篇
  1987年   17篇
  1986年   17篇
  1985年   29篇
  1984年   29篇
  1983年   23篇
  1982年   29篇
  1981年   38篇
  1980年   17篇
  1979年   10篇
  1978年   14篇
  1977年   10篇
  1975年   8篇
  1928年   5篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
STUDY OBJECTIVE: Bacterial vaginosis (BV) is a common infection and has been associated with adverse health outcomes, including preterm birth, pelvic inflammatory disease (PID), and acquisition of HIV. There are limited data on recurrent BV in adolescents. A relationship between the frequency of BV recurrence and specific risk factors might shed light on the pathophysiology of BV and lead to targeted interventions. METHODS: Design: Record-based historical clinic study. Setting: Adolescent visits to two sexually transmitted disease (STD) clinics between 1990 and 2002. Participants: 254 girls who had >/= 2 episodes of BV and at least 3 clinical visits, matched on clinic attendance frequency to 254 girls with only 1 documented BV episode and 254 girls with no history of BV. MAIN OUTCOME MEASURE: Risk factor differences between groups. ANALYSIS: Multinomial logistic regression with robust estimator of the standard errors, accounting for repeated measures. RESULTS: 5,977 adolescent girls visited the clinics. 1509 (25%) had at least one episode of BV; of those, 303 (19.9%) had 2 or more BV episodes. Girls with a history of 1 BV episode and girls with a history of 2 or more BV episodes were more likely to be infected with Trichomonas vaginalis [OR 1.77, 95% CI: 1.17-2.67, OR 1.56, 95% CI: 1.05-2.34] and be diagnosed with PID [OR 1.50, 95% CI: 1.02-2.22, OR 2.05, 95% CI: 1.41-2.98] compared to girls with no BV history, respectively. Girls with a history of BV were also more likely to report active oral sex and lack of contraceptive use. CONCLUSION: Adolescent girls who attend STD clinics have a high prevalence of BV. Although the association between BV and PID is not clearly causal, when one condition is diagnosed, evaluation and counseling for the other may reduce recurrence and sequelae.  相似文献   
83.
1. A substance extracted from group A hemolytic streptococcus is described, which induces active immunity in mice, and in rabbits gives rise to precipitins and to protective antibodies passively transferable to mice. 2. The active immunity in mice is principally type-specific, but some degree of non-type-specific immunity is also developed. The passively transferable protective antibodies are type-specific with only a slight suggestion of non-type specificity. In the precipitin test, the rabbit immune sera give both type-specific and non-type-specific reactions which have not been fully analyzed serologically. 3. Substances contained in the extract absorb the protective antibodies from the serum of rabbits immunized with whole hemolytic streptococci. 4. The most satisfactory method of extraction so far developed is fully described. Chemical tests on the material are consistent with the presence of protein and nucleic acid. 5. The type-specific M substance, prepared as previously described, was compared in some of its antigenic properties with the above mentioned substance. It was found capable of inducing active immunity in mice and of absorbing protective antibody from anti-bacterial immune serum in a manner qualitatively similar to that obtained with the preparations made by the newer methods.  相似文献   
84.
Factors associated with 5-year risk of hip fracture in postmenopausal women   总被引:6,自引:0,他引:6  
Context  The 329 000 hip fractures that annually occur in the United States are associated with high morbidity, mortality, and cost. Identification of those at high risk is a step toward prevention. Objective  To develop an algorithm to predict the 5-year risk of hip fracture in postmenopausal women. Design, Setting, and Participants  A total of 93 676 women who participated in the observational component of the Women's Health Initiative (WHI), a multiethnic longitudinal study, were used to develop a predictive algorithm based on commonly available clinical features. Selected factors that predicted hip fracture were then validated by 68 132 women who participated in the clinical trial. The model was tested in a subset of 10 750 women who had undergone dual-energy x-ray absorptiometry (DXA) scans for bone mass density assessment. Main Outcome Measure  The prediction of centrally adjudicated hip fracture, measured by the area under the receiver operator characteristic (ROC) curves. Results  During a mean (SD) follow-up of 7.6 (1.7) years, 1132 hip fractures were identified among women participating in the observational study (annualized rate, 0.16%), whereas during a mean follow-up of 8.0 (1.7) years, 791 hip fractures occurred among women participating in the clinical trial (annualized rate, 0.14%). Eleven factors predicted hip fracture within 5 years: age, self-reported health, weight, height, race/ethnicity, self-reported physical activity, history of fracture after age 54 years, parental hip fracture, current smoking, current corticosteroid use, and treated diabetes. Receiver operating characteristic curves showed that the algorithm had an area under the curve of 80% (95% confidence interval [CI], 0.77%-0.82%) when tested in the cohort of different women who were in the clinical trial. A simplified point score was developed for the probability of hip fracture. Receiver operating characteristic curves comparing DXA-scan prediction based on a 10% subset of the cohort and the algorithm among those who participated the clinical trial were similar, with an area under the curve of 79% (95% CI, 73%-85%) vs 71% (95% CI, 66%-76%). Conclusion  This algorithm, based on 11 clinical factors, may be useful to predict the 5-year risk of hip fracture among postmenopausal women of various ethnic backgrounds. Further studies are needed to assess the clinical implication of the algorithm in general and specifically to identify treatment benefits.   相似文献   
85.
Maternal and Child Health Journal - Objectives Vital to implementation of the World Health Organization (WHO) Safe Childbirth Checklist (SCC), designed to improve delivery of 28 essential birth...  相似文献   
86.
Covert Human Intelligence Sources (CHIS) provide unique access to criminals and organised crime groups, and their collection of intelligence is vital to understanding England and Wales’ threat picture. Rapport is essential to the establishment and maintenance of effective professional relationships between source handlers and their CHIS. Thus, rapport-based interviewing is a fundamental factor to maximising intelligence yield. The present research gained unprecedented access to 105 real-life audio recorded telephone interactions between England and Wales police source handlers and CHIS. This research quantified both the rapport component behaviours (e.g., attention, positivity, and coordination) displayed by the source handler and the intelligence yielded from the CHIS, in order to investigate the frequencies of these rapport components and their relationship to intelligence yield. Overall rapport, attention and coordination significantly correlated with intelligence yield, while positivity did not. Attention was the most frequently used component of rapport, followed by positivity, and then coordination.Key words: Covert Human Intelligence Source, human intelligence, HUMINT, intelligence, interviewing, rapport, source handler  相似文献   
87.
Childhood maladaptive aggression is associated with disrupted functional connectivity within amygdala-prefrontal circuitry. In this study, neural correlates of childhood aggression were probed using the intrinsic connectivity distribution, a voxel-wise metric of global resting-state brain connectivity. This sample included 38 children with aggressive behavior (26 boys, 12 girls) ages 8–16 years and 21 healthy controls (14 boys, 6 girls) matched for age and IQ. Functional MRI data were acquired during resting state, and differential patterns of intrinsic functional connectivity were tested in a priori regions of interest implicated in the pathophysiology of aggressive behavior. Next, correlational analyses tested for associations between functional connectivity and severity of aggression measured by the Reactive-Proactive Aggression Questionnaire in children with aggression. Children with aggressive behavior showed increased global connectivity in the bilateral amygdala relative to controls. Greater severity of aggressive behavior was associated with decreasing global connectivity in the dorsal anterior cingulate and ventromedial prefrontal cortex. Follow-up seed analysis revealed that aggression was also positively correlated with left amygdala connectivity with the dorsal anterior cingulate, ventromedial and dorsolateral prefrontal cortical regions. These results highlight the potential role of connectivity of the amygdala and medial prefrontal and anterior cingulate cortices in modulating the severity of aggressive behavior in treatment-seeking children.  相似文献   
88.
Snakebite is a neglected tropical disease that causes high rates of global mortality and morbidity. Although snakebite can cause a variety of pathologies in victims, haemotoxic effects are particularly common and are typically characterised by haemorrhage and/or venom-induced consumption coagulopathy. Despite polyclonal antibody-based antivenoms being the mainstay life-saving therapy for snakebite, they are associated with limited cross-snake species efficacy, as there is often extensive toxin variation between snake venoms, including those used as immunogens for antivenom production. This restricts the therapeutic utility of any antivenom to certain geographical regions. In this study, we explored the feasibility of using recombinantly expressed toxins as immunogens to stimulate focused, pathology-specific, antibodies in order to broadly counteract specific toxins associated with snakebite envenoming. Three snake venom serine proteases (SVSP) toxins, sourced from geographically diverse and medically important viper snake venoms, were successfully expressed in HEK293F mammalian cells and used for murine immunisation. Analyses of the resulting antibody responses revealed that ancrod and RVV-V stimulated the strongest immune responses, and that experimental antivenoms directed against these recombinant SVSP toxins, and a mixture of the three different immunogens, extensively recognised and exhibited immunological binding towards a variety of native snake venoms. While the experimental antivenoms showed some reduction in abnormal clotting parameters stimulated by the toxin immunogens and crude venom, specifically reducing the depletion of fibrinogen levels and prolongation of prothrombin times, fibrinogen degradation experiments revealed that they broadly protected against venom- and toxin-induced fibrinogenolytic functional activities. Overall, our findings further strengthen the case for the use of recombinant venom toxins as supplemental immunogens to stimulate focused and desirable antibody responses capable of neutralising venom-induced pathological effects, and therefore potentially circumventing some of the limitations associated with current snakebite therapies.  相似文献   
89.
90.
From 2010 to 2013, genotype I avian influenza A(H9N2) viruses of the G1-lineage were isolated from several poultry species in Egypt. In 2014, novel reassortant H9N2 viruses were detected in pigeons designated as genotype II. To monitor the subsequent genetic evolution of Egyptian A(H9N2) viruses, we characterized the full genomes of 173 viruses isolated through active surveillance from 2017 to 2022. In addition, we compared the virological characteristics and pathogenicity of representative viruses. Phylogenetic analysis of the HA indicated that all studied sequences from 2017–2021 were grouped into G1-like H9N2 viruses previously detected in Egypt. Phylogenetic analysis indicated that the Egyptian A(H9N2) viruses had undergone further reassortment, inheriting four genes (PB2, PB1, PA, NS) from genotype II, with their remaining segments deriving from genotype I viruses (these viruses designated as genotype III). Studying the virological features of the two most dominant genotypes (I and III) of Egyptian H9N2 viruses in vitro and in vivo indicated that both replicated well in mammalian cells, but did not show any clinical signs in chickens, ducks, and mice. Monitoring avian influenza viruses through surveillance programs and understanding the genetic and antigenic characteristics of circulating H9N2 viruses are essential for risk assessment and influenza pandemic preparedness.  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