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   2249篇
  免费   162篇
  国内免费   34篇
耳鼻咽喉   15篇
儿科学   99篇
妇产科学   99篇
基础医学   269篇
口腔科学   101篇
临床医学   209篇
内科学   523篇
皮肤病学   57篇
神经病学   112篇
特种医学   281篇
外科学   187篇
综合类   56篇
预防医学   169篇
眼科学   34篇
药学   104篇
中国医学   2篇
肿瘤学   128篇
  2023年   11篇
  2022年   22篇
  2021年   41篇
  2020年   26篇
  2019年   38篇
  2018年   51篇
  2017年   41篇
  2016年   38篇
  2015年   52篇
  2014年   65篇
  2013年   64篇
  2012年   88篇
  2011年   103篇
  2010年   75篇
  2009年   60篇
  2008年   76篇
  2007年   88篇
  2006年   89篇
  2005年   72篇
  2004年   68篇
  2003年   59篇
  2002年   65篇
  2001年   55篇
  2000年   67篇
  1999年   51篇
  1998年   76篇
  1997年   85篇
  1996年   87篇
  1995年   53篇
  1994年   48篇
  1993年   48篇
  1992年   48篇
  1991年   32篇
  1990年   42篇
  1989年   64篇
  1988年   57篇
  1987年   47篇
  1986年   45篇
  1985年   43篇
  1984年   15篇
  1983年   23篇
  1982年   13篇
  1981年   19篇
  1980年   19篇
  1979年   10篇
  1978年   9篇
  1977年   13篇
  1976年   12篇
  1975年   9篇
  1971年   10篇
排序方式: 共有2445条查询结果,搜索用时 15 毫秒
21.
Objectives: To assess: (i) the size of placental transfusion following a 30 s delay in cord clamping following vaginal and Caesarean births; and (ii) the feasibility of delaying cord clamping in the labour ward and particularly in the operating theatre.
Methods: Fourty-six infants born at 26–33 weeks gestation were randomized to having the umbilical cord clamped either immediately or 30 s after birth. The venous haematocrit was measured at 1 and at 4 h of age.
Results: There were trends towards higher mean haematocrits in the infants following delayed clamping, but these were not significant either at 1 h (55±7.7 vs 52.9±7) or at 4 h of age (55±7 vs 52.5±7). The trends were more marked in the infants born by Caesarean section, and in those born at 26–29 weeks gestation.
Conclusions: A 30 s delay in cord clamping is feasible at both vaginal and Caesarean births, but does not lead to the predicted difference in infant haematocrit. Although physiological studies suggest that a placental transfusion of 15–20 mL/kg occurs within 30 s of delivery, these data suggest that future trials should either delay cord clamping for more than 30 s, or should alter the position of the infant in relation to the uterus in order to facilitate the transfusion. Delayed cord clamping is feasible at Caesarean section.  相似文献   
22.
Objective: To evaluate the incidence and severity of apnoea and bradycardia in hospitalized preterm infants following immunization at 2 months of age, and identify risk factors.
Methodology: A prospective study of 98 preterm infants, of gestational age 24–31 weeks, immunized at approximately 2 months post natal age with diphtheria-tetanus-whole cell pertussis vaccine (DTPw) in the neonatal intensive care unit (NICU) at King George V Hospital Sydney. Half the infants also received Haemophilus influenzae type b conjugate vaccine (Hib) simultaneously. All infants were monitored for apnoea and bradycardia in the 24 h periods pre- and post immunization.
Results: Only one infant had apnoea and/or bradycardia pre-immunization compared with 17 post immunization. For 12 infants these events were brief, self-limiting and not associated with desaturations (oxygen saturation <90%). However, for five infants (30%) these events were associated with oxygen desaturation and two of these infants required supplemental oxygen. The group that had apnoea and/or bradycardia and the group that did not were not significantly different in terms of gestational age, birth weight and other variables. Infants who received Hib together with DTPw were less likely to have apnoea and/or bradycardia than those given DTPw alone.
Conclusion: When considering immunization for preterm infants, the benefits of early immunization must be balanced against the risk of apnoea and bradycardia. We recommend that the cardio-respiratory function of hospitalized infants born at less than 31 weeks gestation be monitored for 48 h post immunization.  相似文献   
23.
OBJECTIVE: Because the survival rate has increased for extremely low birth weight neonates, many have raised the concern that the rate of developmental disability among survivors will also increase. To address this concern, we analyzed changes over time in survival and major neurosensory impairment in a sample of extremely low birth weight infants born between July 1, 1979, and June 30, 1994. METHODS: The study sample included 513 infants with birth weights of 501 to 800 g who were cared for in either of the two neonatal intensive care units that serve a 17-county region in northwest North Carolina and who were born to mothers residing in that region. At 1 year of age (corrected for gestation), survivors were examined by a pediatrician and were tested using the Bayley Scales of Infant Development. Major neurosensory impairment was defined as cerebral palsy, a Bayley Mental Developmental Index <68, or blindness. A total of 209/216 (97%) of survivors were examined at 1 year of age. Epoch of birth was defined as follows: epoch 1, July 1, 1979 to June 30, 1984; epoch 2, July 1, 1984 to June 30, 1989; and epoch 3, July 1, 1989 to June 30, 1994. RESULTS: Survival rates for epochs 1, 2, and 3 were, respectively, 24/120 (20%), 63/175 (36%), and 129/218 (59%). In contrast, the proportions with a major neurosensory impairment did not increase over time; rates for successive epochs were 6/24 (25%), 17/61 (28%), and 26/124 (21%). Rates of cerebral palsy were 3/24 (13%), 12/61 (20%), and 9/124 (7%); rates of delayed mental development were 4/24 (17%), 12/61 (20%), and 17/124 (14%); and rates of blindness were 2/24 (8%), 0/62, and 5/124 (4%), respectively. CONCLUSIONS: This analysis suggests that the increasing survival of extremely low birth weight neonates since the late 1970s has not resulted in an increased rate of major developmental problems identifiable at 1 year of age.  相似文献   
24.
This study was designed to compare the growth of Pakistani schoolchildren in the UK with the 1990 UK growth standards. Measurements of height, weight, and sitting height were performed on 785 Pakistani schoolchildren aged 5-14 years with the mean values for each age and sex being plotted on the UK growth standards. The results were expressed as SD scores relative to the 1990 reference data. The mean height for the boys was only 0.2 SD scores below the mean for the new growth standards with the mean height for the girls being 0.4 SD scores below the mean. The mean values for weight and body mass index were 0.3 and 0.5 SD scores less than the mean for boys and girls respectively. This study demonstrates that the growth of Pakistani schoolchildren in the UK is comparable to the 1990 UK growth standards with only minor differences. It is not safe to assume that short stature or low body weight in a Pakistani child is due to his or her ethnic background.  相似文献   
25.
OBJECTIVE: The ketogenic diet is a high-fat, low-protein, low-carbohydrate diet developed in the 1920s for the treatment of children with difficult to control seizures. Despite advances in both the pharmacotherapy and the surgery of epilepsy, many children continue to have difficult-to-control seizures. This prospective study sought to determine the ketogenic diet's effectiveness and tolerability in children refractory to today's medications. METHODS: One hundred fifty consecutive children, ages 1 to 16 years, virtually all of whom continued to have more than two seizures per week despite adequate therapy with at least two anticonvulsant medications, were prospectively enrolled in this study, treated with the ketogenic diet, and followed for a minimum of 1 year. Seizure frequency was tabulated from patients' daily seizure calendars and seizure reduction calculated as percentage of baseline frequency. Adverse events and reasons for diet discontinuation were recorded. RESULTS: The children (mean age, 5.3 years), averaged 410 seizures per month before the diet, despite an exposure to a mean of 6.2 antiepileptic medications. Three months after diet initiation, 83% of those starting remained on the diet and 34% had >90% decrease in seizures. At 6 months, 71% still remained on the diet and 32% had a >90% decrease in seizures. At 1 year, 55% remained on the diet and 27% had a >90% decrease in seizure frequency. Most of those discontinuing the diet did so because it was either insufficiently effective or too restrictive. Seven percent stopped because of intercurrent illness. CONCLUSIONS: The ketogenic diet should be considered as alternative therapy for children with difficult-to-control seizures. It is more effective than many of the new anticonvulsant medications and is well tolerated by children and families when it is effective.  相似文献   
26.
Type I NOS (nNOS) catalytic activity represents the activity of full-size protein and truncated protein variants originated from many different spliced mRNA variants. Splice mRNA variants are thought to be important in determining the differential organ and subcellular expression of Type I NOS. The present study was directed to increase our understanding of the developmental regulation of Type I NOS in fetal brain. In four discrete areas of the fetal brain, we measured steady-state mRNA levels and catalytic activity and protein mass in the soluble and particulate fractions. Under general anesthesia, we collected sensory-motor cortex, striatum, hippocampus and cerebellum from sheep fetuses at 105, 115, 125 and 135 days gestation (32 fetuses). NOS protein in the soluble and particulate fractions was characterized using Western blot (molecular weight) and arginine to citrulline conversion (enzymatic activity). At the mRNA level, steady state levels were determined using probes directed against exon 2 and exon 21/22 by ribonuclease protection assay (RPA). Our data show that NOS catalytic activity is regulated in a region, subcellular and temporal manner. NOS activity was higher in the soluble fraction in all brain regions and significantly higher levels were found in the soluble fraction of striatum and particulate fraction of hippocampus (P<0.05 by ANOVA). Western blot analysis revealed three distinct molecular weight bands for Type I NOS (155, 144 and 136 kDa). The bands were present in all brain regions and in both cellular compartments with the 155 kDa band being the most abundant molecular form. Truncated protein variants accounted for 25% and 15% of total Type I NOS protein in the soluble fraction and particulate fraction respectively. RPA analysis showed a differential regulation of mRNA variants with exon 2 frame deletions in striatum and hippocampus. A coordinated increase with advancing gestational age of catalytic activity, the full-length protein, the protein variants and steady state mRNA levels was observed in cortex and striatum as demonstrated by higher levels at 125 and 135 days gestation (P<0.05 by ANOVA). NOS enzymatic activity was Ca(2+) and calmodulin dependent. However, in the particulate fraction 20% of the NOS activity was resistant to calmodulin inhibition. In summary, fetal brain Type I NOS mRNA variants are differentially regulated according to brain regions. Our data suggests that exon 2 deleted mRNA variants have low translation efficiency as indicated by the lack of parallel expression of truncated Type I NOS protein variants.  相似文献   
27.
28.
A prophylactic hepatitis C virus (HCV) vaccine that elicits neutralizing antibodies could be key to HCV eradication. However, the genetic and antigenic properties of HCV envelope (E1E2) proteins capable of inducing anti-HCV broadly neutralizing antibodies (bNAbs) in humans have not been defined. Here, we investigated the development of bNAbs in longitudinal plasma of HCV-infected persons with persistent infection or spontaneous clearance of multiple reinfections. By measuring plasma antibody neutralization of a heterologous virus panel, we found that the breadth and potency of the antibody response increased upon exposure to multiple genetically distinct infections and with longer duration of viremia. Greater genetic divergence between infecting strains was not associated with enhanced neutralizing breadth. Rather, repeated exposure to antigenically related, antibody-sensitive E1E2s was associated with potent bNAb induction. These data reveal that a prime-boost vaccine strategy with genetically distinct, antibody-sensitive viruses is a promising approach to inducing potent bNAbs in humans.  相似文献   
29.
The amino acid L-arginine is crucial for nitric oxide (NO) synthesis, an important molecule regulating vascular tone. Considering that vascular dysfunction precedes cardiovascular disease, supplementation with precursors of NO synthesis (e.g., L-arginine) is warranted. However, supplementation of L-citrulline is recommended instead of L-arginine since most L-arginine is catabolized during its course to the endothelium. Given that L-citrulline, found mainly in watermelon, can be converted to L-arginine, watermelon supplementation seems to be effective in increasing plasma L-arginine and improving vascular function. Nonetheless, there are divergent findings when investigating the effect of watermelon supplementation on vascular function, which may be explained by the L-citrulline dose in watermelon products. In some instances, offering a sufficient amount of L-citrulline can be impaired by the greater volume (>700 mL) of watermelon needed to reach a proper dose of L-citrulline. Thus, food technology can be applied to reduce the watermelon volume and make supplementation more convenient. Therefore, this narrative review aims to discuss the current evidence showing the effects of watermelon ingestion on vascular health parameters, exploring the critical relevance of food technology for acceptable L-citrulline content in these products. Watermelon-derived L-citrulline appears as a supplementation that can improve vascular function, including arterial stiffness and blood pressure. Applying food technologies to concentrate bioactive compounds in a reduced volume is warranted so that its ingestion can be more convenient, improving the adherence of those who want to ingest watermelon products daily.  相似文献   
30.
Adolescents exposed to food and beverage advertisements (FBAs) typically low in nutrient density can be influenced in their food choices, eating behaviors, and health. This study examines the association between perceptions and trust of FBAs (key predictor) and the outcome of daily consumption of ultra-processed foods (UPFs) in parent-adolescent dyads, with risk of food insecurity as a potential moderator. Cross-sectional data from the Family, Life, Activity, Sun, Health and Eating (FLASHE) study was used to test actor and partner effects using structural equation modeling. The final model was adjusted for parent sex and education level, and effects were compared between dyads at risk of food insecurity (n = 605) and dyads not at risk (n = 1008). In the unadjusted model, actor effects (parent: b = 0.23, p = 0.001; adolescent b = 0.12, p = 0.001) and parent-partner effects were found (b = 0.08, p = 0.004). The final comparative model produced similar results for dyads not at risk of food insecurity (parent actor: b = 0.27, p = 0.001; parent partner: b = 0.10, p = 0.01; adolescent actor: b = 0.11, p = 0.003). For dyads at risk of food insecurity, only actor effects were significant (parent: b = 0.22, p = 0.001; adolescent: b = 0.11, p = 0.013). These findings suggest that parents’ favorability towards FBAs influence parent-adolescent unhealthy food consumption, and that this association is different when accounting for risk of food insecurity.  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