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   8391篇
  免费   432篇
  国内免费   106篇
耳鼻咽喉   109篇
儿科学   355篇
妇产科学   813篇
基础医学   813篇
口腔科学   102篇
临床医学   695篇
内科学   1269篇
皮肤病学   60篇
神经病学   520篇
特种医学   249篇
外科学   657篇
综合类   1064篇
预防医学   1198篇
眼科学   154篇
药学   534篇
  2篇
中国医学   69篇
肿瘤学   266篇
  2023年   132篇
  2022年   317篇
  2021年   449篇
  2020年   338篇
  2019年   281篇
  2018年   266篇
  2017年   301篇
  2016年   328篇
  2015年   321篇
  2014年   712篇
  2013年   698篇
  2012年   484篇
  2011年   593篇
  2010年   422篇
  2009年   404篇
  2008年   367篇
  2007年   371篇
  2006年   310篇
  2005年   261篇
  2004年   203篇
  2003年   141篇
  2002年   117篇
  2001年   101篇
  2000年   84篇
  1999年   77篇
  1998年   82篇
  1997年   62篇
  1996年   57篇
  1995年   60篇
  1994年   49篇
  1993年   48篇
  1992年   46篇
  1991年   29篇
  1990年   34篇
  1989年   30篇
  1988年   16篇
  1987年   23篇
  1986年   30篇
  1985年   40篇
  1984年   31篇
  1983年   20篇
  1982年   29篇
  1981年   18篇
  1980年   24篇
  1979年   21篇
  1978年   13篇
  1977年   19篇
  1975年   11篇
  1974年   11篇
  1972年   11篇
排序方式: 共有8929条查询结果,搜索用时 15 毫秒
21.
Summary: The effect of gestational age on neonatal ictal and interictal durations has not been investigated. Sixty-eight neonates with 644 electrographic seizures were identified retrospectively. Thirty-five full-term (FT) neonates were compared with 33 preterm (PT) neonates. Eighteen older preterm infants (OPT) [>31 weeks estimated gestational age (EGA)] were also compared with 15 young preterm infants (YPT) of ≤31 weeks EGA. Ictal/ interictal durations were calculated for the total cohort with and without status epilepticus (SE). Statistical analyses were two-tailed t tests, chi-square calculations, and one-way analysis of variance (ANOVA) with Duncan's multiple-range test. Eleven of 35 (33%) FT had SE as compared with 3 of 33 (9%) PT (chi-square = 7.8, p < 0.05). The mean ictal duration was 14.2 min for FT infants as compared with 3.1 min for PT infants (p < 0.01); only borderline differences were noted after those with SE were excluded. Interictal durations were longer for OPT than YPT (p < 0.05). By ANOVA and Duncan's multiple-range tests, group differences included longer mean ictal durations for FT infants as compared with OPT infants (p = 0.06, ANOVA; p < 0.05, Duncan's), and longer mean interictal durations for FT infants versus OPT and OPT versus YPT (p = 0.02, ANOVA; p < 0.05, Duncan's). More developed neuronal networks result in longer ictal durations in FT than in PT neonates, including FT infants with SE. Inhibitory networks responsible for longer interictal periods are more dominant in OPT infants than in YPT infants, reflecting maturational changes that suppress seizure activity during the latter part of the third trimester before the infant reaches an FT corrected age.  相似文献   
22.
Reference data files support the evaluation of myocardial perfusion single-photon emission tomography (SPET). The aim of this study was to create a large reference data base for technetium-99m sestamibi SPET, age and gender matched to the general patient population. One hundred and twenty-eight healthy volunteers (76 males and 52 females) with a likelihood of coronary artery disease of less than 5% underwent rest and maximal exercise99mTc-sestamibi SPET with a 2-day protocol and 180° elliptical rotation. The normalized activity values of99mTc-sestamibi in the inferior wall differed significantly between men and women. Age variations were found for men in the anterior wall. Normalized activity values in all four walls were strikingly similar during rest and stress. Our results suggest that the use of reference files in99mTc-sestamibi SPET requires a gender- and, for males, possibly an age-matched reference population. Different reference files at rest and during stress might not be necessary.  相似文献   
23.
目的探讨MR扩散张量成像(DTI)观察豆状核年龄相关性变化的价值与意义。方法69名健康志愿者纳入本研究。入组对象按年龄分为3组:≤30岁(I)组,22例;31~50岁(Ⅱ)组,24例;〉50岁(Ⅲ)组,23例。利用DTI分别测量受试者大脑左右两侧壳核、苍白球的表观扩散系数(ADC)值、部分各向异性(FA)值及扩散张量特征值λ1、λ2、λ3。分析不同年龄组间ADC、FA、λ1、λ2、λ3值的差异及与年龄的相关性。结果I、Ⅱ、Ⅲ组的壳核ADC值分别为:(6.68±0.40)×10^-4、(6.47±0.36)×10^-4、(6.44±0.34)×10^-4mm^2/s,苍白球ADC值分别为:(6.13±0.50)×10^-4、(6.05±0.33)×10^-4、(6.05±0.52)×10$-4mm^2/s。I、Ⅱ、Ⅲ组的壳核FA值分别为:0.20±0.03、0.23±0.03、0.25±0.03,苍白球FA值分别为:0.35±0.03、0.36±0.03、0.37±0.04。各年龄组内壳核ADC值大于苍白球,而FA值小于苍白球。壳核FA值的组问差异有统计学意义(F=10.082,P=0.000),壳核I、Ⅱ、Ⅲ组入,值分别为(5.35±0.45)×10^-4、(5.04±0.46)×10^-4、(4.90±0.44)×10^-4mm^2/s,差异亦有统计学意义(F=5.675,P=0.005);壳核FA值与年龄呈正相关(r=0.555,P〈0.01),λ3值与年龄呈负相关(r=-0.440,P〈0.01)。结论壳核FA值随年龄的增长而上升,λ3值随年龄的增长而下降。  相似文献   
24.
OBJECTIVES: To present a series of women with recurrent molar pregnancies, including rare familial cases, and discuss etiology and treatment options. METHODS: We performed a detailed clinical evaluation and pedigree analysis of five Egyptian women with recurrent pregnancy loss due to molar pregnancy. RESULTS: The women had a history of four to nine consecutive hydatidiform moles but of no viable pregnancies. Two of the women had molar pregnancies with different husbands who themselves had viable offspring from previous wives; and three of them, who belonged to a family with extensive intermarriage, had a pedigree consistent with an autosomal recessive maternal-effect mutation. CONCLUSIONS: Recurrent pregnancy loss due to habitual molar pregnancy is uncommon and familial cases are extremely rare. The etiology of this disorder is not well understood but likely results from a maternal-effect mutation. Management options are limited, especially for couples who desire to have their own genetic offspring.  相似文献   
25.
范永前  梁承伟  沈海敏 《上海医学》2004,27(8):578-580,F006
目的 评价腰椎管减压、后外侧植骨和椎弓根螺钉内固定治疗退行性腰椎滑脱的临床疗效。方法  1993年 1月~ 2 0 0 2年 9月对 74例腰椎退行性滑脱的患者行腰椎管减压、后外侧植骨和椎弓根螺钉内固定 ,采用的椎弓根内固定技术包括Dick 8例、Steffee 10例、RF 9例、Socon 2 5例、Tenor 2 0例、Moss Miami 2例。滑脱水平在L4的患者有 4 4例、L3 有 9例、L5有 16例 ,两节水平的滑脱有 5例。Ⅰ°滑脱 37例 ,Ⅱ°31例 ,Ⅲ°6例。患者平均年龄为 5 3.6岁 (30~ 79岁 )。根据手术前、后日本骨科协会 (TDA)评分评价临床症状改善的程度。结果 平均随访时间为 4 4个月 (12~ 10 4个月 ) ,所有患者最后随访的JOA评分中客观症状为 (6 .7± 1.0 )分 ,临床体征为 (4 .7± 1.1)分 ,日常活动为 (11.8± 1.9)分 ,总评分为 (2 3.0± 2 .5 )分。手术前、后的JOA评分比较 ,术后主观症状改善 70 % ,临床体征改善 6 8% ,日常活动改善 77%。根据患者的年龄分为A组 (30~ 39岁 )、B组 (4 0~ 4 9岁 )、C组 (5 0~ 5 9岁 )、D组 (≥ 6 0岁 ) ,以JOA的评分结果 >2 5分定为满意 ,A、B、C、D组的满意率分别为91%、75 %、6 9%、6 1%。结论 椎板减压、后外侧植骨融合和椎弓根螺钉内固定是治疗不稳定腰椎滑脱的一种有效方法 ,临床疗效  相似文献   
26.
This study aimed to evaluate human antibody responses to diphtheria toxin subunits in various age groups. Antibodies against the intact diphtheria toxin and the diphtheria toxin subunits A and B were evaluated in 1319 individuals using a double-antigen ELISA. Although high levels of protection (83.6%, 95% CI 79.2-87.4) were found in children and adolescents, the middle-aged adult population was less protected (28.8%, 95% CI 24.3-33.6). An increase in age was associated with a decrease in the frequency of protected individuals in the 0-39-year age group (p <0.001). Anti-subunit B levels correlated well (p <0.01) with levels of antibodies against the intact toxin. In children aged < or =16 years, the intervals at which the peaks in geometric mean titres of anti-subunit B antibodies were observed were found to correlate with the ages at which booster doses are administered. Overall, males appeared to be more protected than females (OR 1.67, 95% CI 1.34-2.08, p <0.001). A small group of individuals had antibody levels of > or =0.1 IU/mL against the intact toxin, but did not have protective antibody against subunit B. Determination of anti-subunit B antibody levels should help in evaluating the effectiveness of diphtheria boosters and other aspects of diphtheria immunity.  相似文献   
27.
R. B. Martin 《BONE》1991,12(6):391-400
This paper quantifies the relative contributions of the remodeling space and the accumulation of Haversian canals to bone porosity at various ages. It also examines the importance of variations in the rate of bone remodeling that occur during growth and aging, and as a result of trauma and disease. The dependence of the remodeling space (cavities due to resorbing, reversing, and refilling BMUs) and the Haversian canal components of porosity on the Basic Multicellular Unit (BMU) activation frequency are mathematically formulated. A graph is developed using data for the cortex of the human rib which shows the extent to which porosity is primarily due to the remodeling space in children, and to accumulated Haversian canals in adults. It is shown that the diminution of activation frequency between birth and age 35 contributes to the concurrent increase in bone volume fraction, and the increase in activation frequency after age 35 contributes to the subsequent decline of bone volume fraction. An equation is derived for determining the time rate of change of activation frequency using two fluorochrome labels.  相似文献   
28.
Objectives: This study examines the efficacy of the predicting power for hospital mortality and functional outcome of three different scoring systems for head injury in a neurosurgical intensive care unit (NICU). Design: On the day of admission, data were collected from each patient to compute the Acute Physiology, Age, and Chronic Health Evaluation (APACHE) II and III, and Glasgow Coma Scale (GCS) scores. Hospital mortality was defined as the deaths of patients before discharge from hospital. Early mortality was defined as death before the 14th day after admission. Late mortality was defined as death after the 15th day from admission. Functional outcome was evaluated by Index of Independence in Activities of Daily Living (Index of ADL). Setting: An 8-bed NICU in a 1270-bed medical center in Taichung Veterans General Hospital. Patients and participants: Two hundred non-selected patients with acute head injury were included in our study in a consecutive period of 2 years. Patients less than 14 years old were not included. Interventions: None. Measurements and results: Sensitivity, specificity and correct prediction outcome were measured by the chi-square method in three scoring systems. The Youden index was also obtained. The best cut-off point in each scoring system was determined by the Youden index. The difference in Youden index was calculated by Z score. A difference was also considered if the probability value was less than 0.05. The area under Receiver Operating Characteristic (ROC) curve was computed. Then the area under ROC of each scoring system was compared by Z score. There was statistical significance if p was less than 0.05. For prediction of hospital mortality, the best cut-off points are 55 for APACHE III, 17 for APACHE II and 5 for GCS. The correct prediction outcome is 82.4% in APACHE III, 78.4% in APACHE II and 81.9% in the GCS. The Youden index has best cut-off points at 0.68 for APACHE III, 0.59 for APACHE II, and 0.56 for GCS. The area under Receiver Operating Characteristic (ROC) curve is 0.90 in the APACHE III, 0.84 in the APACHE II and 0.86 in the GCS. There are no statistical differences among APACHE III and II, and GCS in terms of correct prediction outcome, Youden Index and the area under the ROC curve. Other physiological variables excluding GCS in APACHE III and II (AP III-GCS, AP II-GCS) have less statistical value in the determination of mortality for acute head injury. For the prediction of late mortality, APACHE III and II yield significantly better results in the area under the ROC curve, correct prediction and Youden index than those of GCS. Other physiological variables (AP III-GCS and AP II-GCS) play an important role in the prediction of late mortality in APACHE scores. For prediction of the functional outcome of surviving patients with acute head injury, the APACHE III yields the best results of correct prediction outcome, Youden index and the area under the ROC curve. Conclusion: The APACHE III and II may not replace the role of GCS in cases of acute head injury for hospital or early mortality assessment. But for prediction of the late mortality, the APACHE III and II have better accuracy than GCS. Other physiological variables excluding GCS in the APACHE system play a crucial contribution for late mortality. GCS is simple, less time-consuming and economical for patients with acute head injury for the prediction of hospital and early mortality. The APACHE III provides better prediction for severe morbidity than GCS and APACHE II. Therefore, the APACHE III provides a good assessment not only for hospital and late mortality, but also for functional outcome. Received: 22 May 1995 Accepted: 2 September 1996  相似文献   
29.
New markers have been used to monitor the changes of bone turnover occurring during growth. Data on bone turnover rate during the perinatal period are, however, very scarce. In the present study we evaluated bone turnover rate, assessed by the measurement of urinary N-terminal telopeptide of type I collagen (NTx) concentrations, at different gestational ages, and we documented the trend of bone turnover rate occurring in the first days after birth. Urine samples were obtained from 83 healthy full term newborn infants, 16 preterm, and 17 infants of diabetic mothers (IDMs). The first miction after birth was collected. Urine samples were also collected 24 and 48 h after birth. NTx was measured by an enzyme-linked immunosorbent assay (Osteomark®, Ostex International, Inc. Seattle, WA). The relationship between NTx at birth and all the other variables has been evaluated using multiple regression analysis. The changes of NTx excretion over time and the effect of the groups were studied by multivariate analysis of variance (MANOVA) for repeated measures. We found a remarkable association between gestational age and NTx concentrations at birth (R = 0.56; p < 0.00001). NTx concentrations showed a progressive decrement, reaching a nadir between the 38th and the 42nd week of gestation. The NTx concentrations changed significantly during the first 48 h of life in the three groups. Moreover, preterm infants had NTx excretion values at birth significantly higher than full term infants (p < 0.001), whereas NTx excretion rates of IDMs were not different from those of the other two groups of subjects. In conclusion, gestational age seems to be the major determinant of bone turnover in neonates; NTx excretion rate is higher before term, it slows in proximity of delivery, and it increases significantly during the first 48 h of life. Preterm infants have higher bone turnover rate than full term infants. NTx excretion rate of IDMs was comparable with those of the control subjects.  相似文献   
30.
葡萄糖筛选试验在妊娠期糖尿病诊断及治疗中的价值   总被引:5,自引:1,他引:4  
目的 探讨 5 0 g葡萄糖筛选试验 (GCT)在妊娠期糖尿病 (GDM )诊断及治疗中的价值。 方法 选择 2 0 0 0年 1月~ 2 0 0 3年 6月在我院行产前检查并分娩的 5 0 gGCT异常的孕妇 36 8例 ,按血糖值分为 5组 :≥7.8~ <8.0mmol/L为Ⅰ组 ,≥ 8.0~ <9.0mmol/L为Ⅱ组 ,≥ 9.0~ <10 .0mmol/L为Ⅲ组 ,≥ 10 .0~ <11.0mmol/L为Ⅳ组 ,≥ 11.0mmol/L为Ⅴ组。比较 5组 75 g口服葡萄糖耐量试验 (OGTT)异常的比例及需用胰岛素治疗的病例数的差异。结果  5组GDM的发生率分别为 6 .9%、8.5 %、2 1.3%、4 7.8%和 85 .0 % ,75 gOGTT异常的发生率分别为 19.0 %、2 4 .2 %、5 1.1%、87.0 %和 90 .0 % ,且用胰岛素治疗的病例数随 5 0 gGCT血糖值的上升而增加。结论  5 0 gGCT在GDM的诊断及治疗方案的预测方面均有重要价值。  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