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   1108103篇
  免费   82505篇
  国内免费   2931篇
耳鼻咽喉   14476篇
儿科学   37354篇
妇产科学   30345篇
基础医学   159551篇
口腔科学   29915篇
临床医学   101288篇
内科学   216682篇
皮肤病学   24580篇
神经病学   89833篇
特种医学   41931篇
外国民族医学   309篇
外科学   165480篇
综合类   25477篇
现状与发展   1篇
一般理论   539篇
预防医学   87925篇
眼科学   25282篇
药学   79669篇
  5篇
中国医学   2179篇
肿瘤学   60718篇
  2019年   9072篇
  2018年   12570篇
  2017年   9804篇
  2016年   11100篇
  2015年   12693篇
  2014年   17468篇
  2013年   26738篇
  2012年   35810篇
  2011年   38197篇
  2010年   22660篇
  2009年   21452篇
  2008年   35903篇
  2007年   38041篇
  2006年   38369篇
  2005年   37279篇
  2004年   36151篇
  2003年   34953篇
  2002年   33515篇
  2001年   47972篇
  2000年   48831篇
  1999年   41343篇
  1998年   12683篇
  1997年   11373篇
  1996年   11205篇
  1995年   10821篇
  1994年   9938篇
  1993年   9346篇
  1992年   32898篇
  1991年   32060篇
  1990年   31594篇
  1989年   30436篇
  1988年   27674篇
  1987年   27790篇
  1986年   25908篇
  1985年   25181篇
  1984年   19144篇
  1983年   16261篇
  1982年   10331篇
  1981年   9323篇
  1979年   17272篇
  1978年   12737篇
  1977年   10808篇
  1976年   10164篇
  1975年   10544篇
  1974年   12645篇
  1973年   12113篇
  1972年   11079篇
  1971年   10232篇
  1970年   9496篇
  1969年   8831篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
OBJECTIVE: To establish reference intervals for the fetal right, left and total lung volumes and heart volume between 12 and 32 weeks of gestation. METHODS: Fetal lung and heart volumes were measured using three-dimensional (3D) ultrasound in 650 normal singleton pregnancies at 12-32 weeks. The VOCAL (Virtual Organ Computer-aided AnaLysis) technique was used to obtain a sequence of six sections of each lung and the heart around a fixed axis, each after a 30 degrees rotation from the previous one. The rotation axis for the lungs extended from the apex to the upper limit of the diaphragm dome, and the rotation axis for the heart extended from its apex to its connection to the great vessels. The contour of each of these organs was drawn manually in the six different rotation planes to obtain the 3D volume measurement. In 60 cases the fetal lungs and heart volumes were measured by the same sonographer twice and also by a second sonographer once in order to compare the measurements and calculate intra- and interobserver agreement. RESULTS: The total lung volume and heart volume increased with gestation, from respective mean values of 1.6 and 0.6 mL at 12 weeks to 10.9 and 4.3 mL at 20 weeks and 49.3 and 26.6 mL at 32 weeks. The right to left lung volume ratio did not change significantly with gestation (median, 0.7), whereas the heart to total lung volume ratio increased with gestation from about 0.3 at 12 weeks to 0.5 at 32 weeks. In the Bland-Altman plot, the difference between paired measurements by two sonographers was, in 95% of the cases, less than 0.05, 0.5 and 1.9 mL for each lung at 12-13, 19-22 and 29-32 weeks, respectively, and the corresponding values for the heart volumes were 0.04, 0.4 and 2.3 mL. CONCLUSIONS: In normal fetuses the lung and heart volumes increase between 12 and 32 weeks of gestation. The extent to which in pathological pregnancies possible deviations in these measurements from normal prove to be useful in the prediction of outcome remains to be determined.  相似文献   
32.
OBJECTIVE: To explore the impact of timing and type of ultrasound, particularly three-dimensional (3D), exposure on maternal-fetal attachment and maternal health behavior during pregnancy. METHODS: Subjects were 68 women aged 18 years or older expecting their first child who presented for a routine ultrasound scan at around either 12 or 18 weeks' gestation in Nepean Hospital, Western Sydney. Women completed questionnaires assessing maternal-fetal attachment and health behavior, and were then allocated arbitrarily to either two-dimensional (2D) or 3D ultrasound examination. Repeat questionnaires were completed 1 week later. RESULTS: Maternal-fetal attachment increased after both 2D and 3D ultrasound exposure, and the effect was moderated by the timing of exposure, with women receiving their first ultrasound examination at around 12 weeks showing the greatest change. Alcohol consumption was the only behavior to show significant change following ultrasound exposure, with a reduction in the reported average number of drinks per week. There was no significant difference in the pattern of change for 2D compared with 3D ultrasound exposure, and no effect of ultrasound exposure on maternal perception of the fetus. CONCLUSIONS: Ultrasound has a positive impact on maternal-fetal attachment, particularly in the first trimester. 3D ultrasound did not offer enhanced benefits. Associations between ultrasound exposure and alcohol consumption warrant further investigation. Larger samples are needed to clarify the moderating effects of gestational age and type of ultrasound exposure.  相似文献   
33.
The increased number of lymphocytes in airways during an asthmatic response is believed to be the result of increased recruitment of these cells. However, it is possible that a decreased apoptotic rate could also contribute to the increased number. The aim of the present study was to investigate whether allergen airway provocation influences the apoptotic phenotype of lung and peripheral blood lymphocytes (PBL) in subjects with atopic asthma. Bronchoalveolar lavage (BAL) lymphocytes and PBL from 12 asthmatic subjects previously challenged with allergen (n = 7) or saline (n = 5) were exposed to the apoptotic stimulus tributyltin (TBT) in vitro and assayed for apoptosis. Airway allergen provocation resulted in decreased sensitivity of BAL lymphocytes to TBT-induced apoptosis, with 42.2% (range 33.9-62.5%) apoptotic cells before challenge versus 23.5% (range 15.3-42.4%) after challenge, while PBL were unaffected. The increased apoptosis resistance correlated with higher numbers of Bcl-2-expressing lymphocytes. Interestingly, baseline caspase-3-like activity was significantly elevated in viable BAL lymphocytes compared with viable PBL, and was unaltered by allergen exposure. In conclusion, allergen inhalation renders bronchoalveolar lavage lymphocytes more resistant to apoptosis while peripheral blood lymphocytes were not influenced at all, indicating that the apoptotic phenotype of airway lymphocytes may play a role in asthmatic inflammation.  相似文献   
34.
35.
36.
PURPOSE: In children with locally advanced or recurrent malignant tumours, prognosis can be improved by regional deep hyperthermia (RHT) in combination with platin-based chemotherapy. However, because of the increasing number of patients that achieve long-time remission with this therapy, it is necessary to evaluate long-term sequelae of thermochemotherapy. During the years 1993-2004 one has observed avascular osteonecrosis (AON) of the femoral head after RHT in seven children with pelvic germ cell tumours or rhabdomyosarcomas. METHODS: Although AON may develop in patients with malignancies treated with chemo- or radiotherapy alone, RHT might nevertheless contribute to the occurrence of AON. In order to determine potential risk factors for AON after RHT, this study analysed the relationship of AON to the patient's age, medical history and treatment parameters such as thermal dose equivalent and power output. RESULTS AND CONCLUSIONS: In the present study AON was associated with young age as well as intensity of hyperthermia indicated by high power levels that exceed 20 W per kg body weight and/or application of eight or more heat sessions as well as additional radiotherapy. Based on this observation, it was assumed that an optimized three dimensional thermal field modelling may be helpful to avoid hazardous temperatures in the femoral heads during RHT treatment and to reduce AON of the femoral heads.  相似文献   
37.
Severe persistent asthma can have a substantial impact on a patient's health-related quality of life (HRQL), both as a result of symptoms and from side effects of treatment. The HRQL impact of two doses (400 and 800 microg twice daily) of mometasone furoate dry powder inhaler (MF DPI) was compared with placebo in patients with severe persistent asthma previously maintained on oral steroids as a component of a previously published randomized, 12-week, double-blind, placebo-controlled, multicenter trial. A 9-month open-label extension (OLE), with all patients treated with MF DPI, followed. Patients 12 years of age or older completed a generic HRQL measure, the Medical Outcomes Trust Short Form-36 (SF-36), and an asthma-specific measure, the Marks Asthma Quality of Life Questionnaire (AQLQ-M), at baseline, at endpoint (last evaluable visit) of the double-blind phase (EODBP), and after the first 3 months of the OLE. Of 132 patients enrolled in the study, 128 provided HRQL data at baseline and at EODBP. Mean SF-36 scores at baseline showed significant HRQL impairment compared with U.S. general population norms. With treatment, the reduction in oral corticosteroid (OCS) requirements of the MF-DPI-treated groups was accompanied by significant (p < 0.05) improvement over placebo in the physical domain of HRQL (SF-36 physical component summary score and the physical function subscale) at EODBP. MF-DPI-treated patients also showed significant improvements at EODBP in each of the four subscales of the AQLQ-M (p<0.05). From EODBP to the OLE 3-month endpoint, patients treated with MF DPI twice daily maintained, or improved, SF-36 scores in most domains. Symptomatic improvement and reduction in OCS use with MF DPI were accompanied by significant improvement in HRQL in patients with severe persistent asthma. These improvements were maintained during the 3-month period of the OLE in which HRQL was evaluated.  相似文献   
38.
A 17-year-old man presented with signs of peritonitis. Laparotomy revealed gangrene of the stomach without obvious cause. The patient underwent total gastrectomy with esophago-jejunal anastomosis with formation of jejunal pouch. Bacterial culture of the peritoneal fluid grew Strept. pyogenes and E. coli. The patient was discharged on day 21 after a stormy postoperative course.  相似文献   
39.
Patients with multiple system atrophy (MSA) present large changes in blood pressure (BP) due to autonomic disturbances. We analyzed how this change may influence dynamic cerebral autoregulation (DCA). Simultaneous recordings of arterial BP (Finapres) and middle cerebral artery (MCA) blood flow velocity (BFV) (transcranial Doppler) were performed in 10 patients with MSA (61 +/- 12 yr of age) and 12 healthy volunteers (61 +/- 11 yr of age): cerebral BFV response to oscillations in mean BP was studied in the supine position by cross-spectral analysis of mean BP and mean MCA BFV. The DCA was also studied during the decrease in BP the first seconds when standing up from a sitting position by the assessment of the cerebrovascular resistance index (CR; mean BP/mean MCA BFV ratio). The MCA BFV/BP cross-spectral analysis showed a phase for the mid-frequency band (0.07-0.2 Hz) significantly larger in MSA, suggesting more active autoregulation in response to larger changes in BP. Changes in CR reflecting the rate of autoregulation, when standing did not differ between the two groups. These data suggest that dynamic cerebral autoregulation is preserved in MSA.  相似文献   
40.
There is increasing evidence that the assessment of eosinophilic airway inflammation using induced sputum and measurement of airway hyperresponsiveness provides additional, clinically important information concerning asthma control. The aim of this study was to directly compare the effects of different treatments on these markers in patients with asthma and persistent symptoms, despite the use of low-dose inhaled corticosteroids. A double-blind four-way crossover study was performed, which compared a 1-month treatment with budesonide 400 mug b.i.d., additional formoterol, additional montelukast and placebo in 49 patients with uncontrolled asthma despite budesonide 100 mug b.i.d., with each treatment separated by a 4-week washout period. The change in sputum eosinophil count with formoterol (2.4 to 3.8% change, 0.6-fold reduction, 95% confidence interval (CI) 0.5-0.9) differed significantly from placebo (2.8 to 2.5% change, 1.1-fold reduction, 95% CI 0.7-1.6) and high-dose budesonide (2.7 to 1.6% change, 1.6-fold reduction, 95% CI 1.2-2.2). The effects of montelukast did not differ from placebo. The changes in methacholine airway responsiveness were small and did not differ between treatments. High-dose budesonide had the broadest range of beneficial effects on other outcomes, including symptom scores, morning peak expiratory flow and forced expiratory volume in one second. In conclusion, treatment given in addition to low-dose inhaled corticosteroids results in modest benefits. Formoterol and high-dose budesonide have contrasting effects on eosinophilic airway inflammation.  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