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   2091篇
  免费   220篇
  国内免费   18篇
耳鼻咽喉   29篇
儿科学   130篇
妇产科学   48篇
基础医学   224篇
口腔科学   49篇
临床医学   267篇
内科学   403篇
皮肤病学   114篇
神经病学   116篇
特种医学   152篇
外国民族医学   2篇
外科学   301篇
综合类   107篇
现状与发展   30篇
预防医学   118篇
眼科学   22篇
药学   98篇
中国医学   4篇
肿瘤学   115篇
  2024年   18篇
  2023年   182篇
  2022年   22篇
  2021年   28篇
  2020年   58篇
  2019年   35篇
  2018年   60篇
  2017年   58篇
  2016年   54篇
  2015年   65篇
  2014年   98篇
  2013年   89篇
  2012年   58篇
  2011年   68篇
  2010年   96篇
  2009年   100篇
  2008年   61篇
  2007年   91篇
  2006年   58篇
  2005年   62篇
  2004年   64篇
  2003年   43篇
  2002年   54篇
  2001年   64篇
  2000年   55篇
  1999年   53篇
  1998年   42篇
  1997年   57篇
  1996年   48篇
  1995年   41篇
  1994年   35篇
  1993年   41篇
  1992年   17篇
  1991年   17篇
  1990年   15篇
  1989年   44篇
  1988年   33篇
  1987年   28篇
  1986年   15篇
  1985年   19篇
  1984年   17篇
  1983年   11篇
  1982年   11篇
  1981年   16篇
  1980年   15篇
  1978年   9篇
  1976年   21篇
  1975年   16篇
  1974年   7篇
  1970年   6篇
排序方式: 共有2329条查询结果,搜索用时 15 毫秒
71.
Background: Restoration of spontaneous circulation after cardiopulmonary resuscitation in cardiac arrest patients does not always signal a completely successful outcome. Functional deficiencies of the nervous system are found in many survivors of cardiac arrest. Objectives: To study the effects of dopamine-induced elevated blood pressure on the hemodynamics, oxygen metabolism, and cerebral resuscitation in different perfusion conditions in a resuscitated animal model. Methods: There were 18 pigs included in the study. Ventricular fibrillation (VF) was induced with a programmed electrical stimulation device. After 4 min of untreated ventricular fibrillation followed by 9 min of CPR, 12 animals were resuscitated successfully, and were then randomly assigned to either the study group (dopamine group) or the control group (normal perfusion group). All animals in the two groups received normal saline through continuous intravenous guttae for 4 h at a rate of 15 mL/kg/h. In the study group, dopamine was added to raise the animals' blood pressure. Four hours of intensive monitoring was performed for all study animals. Finally, 24-h evaluation of neurological function was conducted in surviving animals in accordance with the standard of the Cerebral Performance Category Score. Results: In animals in the dopamine group, the cardiac output, mean aortic pressure, coronary perfusion pressure, oxygen delivery, and oxygen consumption were higher than those found in the animals in the normal perfusion group (p < 0.05). Oxygen metabolism was remarkably improved in animals in the dopamine group. Furthermore, cerebral perfusion was better in the dopamine group than in the control group and thus, results of the evaluation of nervous system function were better in animals treated with dopamine (p < 0.05). Conclusions: Dopamine improved systemic perfusion, cerebral blood supply, and oxygen metabolism after successful resuscitation from VF in a porcine model. All of these factors have profound effects on the cerebral resuscitation.  相似文献   
72.
A comparative study was carried out of emissions from the catalytic combustion of pellets made from furniture board waste and pellets made from wood mixed with Fe2O3. The mass content of the Fe2O3 catalyst in the fuel was varied from 0% to 5%, 10%, and 15% in relation to the total dry mass weight of the pellets. The average flame temperature in the boiler was between 730 and 800 °C. The effect of the catalyst concentration in the fuel was analysed with respect to the contents of O2, CO2, CO, H2, and NOx in the flue gas and the combustion quality of the pellets in the heating boiler. Changes in the CO2 content and the proportion of unburned combustible components in the combustion residue were assessed. It was established that an increase in the Fe2O3 content of the prepared fuels had a positive effect on reducing NOx, CO, and H2 emissions. However, the proportion of iron oxide in the tested fuel pellets did not significantly influence changes in their combustion quality. A strong effect of the addition of Fe2O3 on the reduction of the average NOx content in the flue gas occurred with the combustion of furniture board fuel, from 51.4 ppm at 0% Fe2O3 to 7.7 ppm for an additive content of 15%. Based on the analysis of the residue in the boiler ash pan, the amount of unburned combustibles relative to their input amounts was found to be 0.09–0.22% for wood pellets and 0.50–0.31% for furniture board waste pellets.  相似文献   
73.
74.
Epstein-Barr virus lymphoproliferation after bone marrow transplantation   总被引:16,自引:7,他引:16  
We review 15 cases of secondary B-cell lymphoproliferative disorders that occurred among 2,475 patients who received allogeneic bone marrow transplants (BMTs) at the Fred Hutchinson Cancer Research Center (Seattle) between 1969 and 1987. The histopathologic findings in 14 of the 15 patients spanned a wide spectrum of lymphoproliferative lesions. One patient had features characteristic of angioimmunoblastic lymphadenopathy. Epstein-Barr virus (EBV) genomic sequences were identified by Southern blot analysis in each of the 13 patients evaluated. Ten of the 12 lesions evaluated originated in donor cells. In two patients, who had mixed chimerism after transplantation, the lesions originated in host cells. The combined evidence from immunoglobulin light chain staining and the analysis of immunoglobulin heavy chain gene rearrangement indicated that the lesions in most patients represented polyclonal proliferations that gave rise to clonal subpopulations. The results indicate an overall actuarial incidence of 0.6% for this complication in BMT recipients. Anti-CD3 monoclonal antibody (MoAb) treatment of acute graft-v-host disease (GVHD) and T cell depletion of the donor marrow were statistically significant risk factors, and GVHD appeared to play a contributing role, particularly in the setting of human leukocyte antigen (HLA) disparity. Two patients had no identifiable risk factors. Prophylaxis or treatment with acyclovir had no detectable effect in the patients; all but two died with uncontrolled lymphoproliferation.  相似文献   
75.
Metabolic adaption of pancreatic islet tissue in aging rats   总被引:2,自引:0,他引:2  
A previous report indicating reduced glucose metabolism in pancreatic islets isolated from old as compared with young rats was reinvestigated. With a modified islet isolation procedure it was found that islets from 12- to 18-month-old rats had increased glucose use, elevated glucokinase, phosphofructokinase and glucose-6-phosphate dehydrogenase when compared with islets from 2-month-old controls. Glucose-induced insulin release in vitro of islets from the older rats was also improved by the more careful method of islet isolation but did not achieve rates observed with islets from young rats. The data suggest an age-related activation of pancreatic islet cell metabolism, possibly in response to overstimulation by increased peripheral insulin resistance, characteristic of older obese rats.  相似文献   
76.
Fifty-two of 175 (30%) survivors of allogeneic marrow transplantation developed chronic graft-versus-hose diseases (GVHD). Five with limited chronic GVHD had an indolent clinical course with involvement of only the skin and liver. Forty-seven with extensive chronic GVHD had an unfavorable multiorgan disorder that resembled several autoimmune diseases. Thirteen patients with extensive disease (group I) were not treated and only 2 survive with Karnofsky scores >- 70%. Mortality resulted from infections and morbidity from sica syndrome, pulmonary and hepatic insufficiency, scleroderma-like skin disease, and contractures. Another 13 (group II) received a median of 8 mo prednisone and/or a brief course of antithymocyte globulin, and 3 survive without disability. The other 21 (group III) were treated with a combination of prednisone (1.0 mg/kg/q.o.d.) and either cyclophosphamide, procarbazine, or azathioprine (all 1.5 mg/kg/day) for a median of 13 mo. Combination therapy was well tolerated with only modest myelotoxicity. Fifteen in group III had a good and 4 a fair response to treatment while 2 with no response died. Azathioprine and prednisone was the most effective regimen. All therapy has been discontinued in 12 group III patients: GVHD returned in 5 (including 2 who died in spite of retreatment) while 7 remain free of GVHD for a median of 11 (range 6-30) mo observation. Only I group III survivor is disabled and 16 of the original 21 are alive 2-4 yr after transplant with Karnofsky scores of 70%-100%. Thus, combination immmunosuppression appears to favorably affect and, in some cases, premanently arrest the adverse natural course of extensive chronic GVHD.  相似文献   
77.
78.
The evaluation of gastrointestinal function in diabetic patients   总被引:2,自引:0,他引:2  
Nowadays,anumberofoptionsareavailablefortheasesmentofgastricmotorfunction.Thus,aglobalevaluationofgastricmotorfunctionmaybeob...  相似文献   
79.
We compared the efficiency of immunophenotyping using flow cytometry (FCM) and a combination of morphologic and immunocytochemical studies for detecting malignant cells in 92 effusions. Cytologic results were as follows: carcinoma cells, 43 specimens; benign, 42 specimens; suggestive of nonepithelial malignancy, 7 specimens. After immunocytochemical analysis, 5 benign specimens were reclassified as malignant and 4 malignant epithelial specimens as benign. With FCM, cells positive for Ber-EP4, B 72.3, AH6, and HB-TN were detected in 28 to 36 (64%-82%) of 44 carcinomas but only 2 to 12 (5%-29%) of 41 benign specimens. Significant association was seen for coexpression. Ber-EP4 and AH6 were the most sensitive; Ber-EP4 was the most specific. The presence of cells positive for 3 of 4 markers strongly suggested malignancy (34/44 carcinoma specimens [77%]; 3/41 reactive specimens [7%]). The presence of cells positive for all 4 markers was diagnostic of malignancy (17/44 malignant specimens [39%]; 0/41 reactive effusions [0%]). FCM and immunocytochemical resultsfor Ber-EP4 expression showed excellent association. FCM is a powerful tool for diagnosing difficult effusions and can quantify coexpression of various markers in fresh specimens. By using established cellular markers coupled with biological markers, FCM also has great promise for experimental purposes.  相似文献   
80.
BACKGROUND: Chronic obstructive pulmonary disease (COPD) is a major health problem with an estimated prevalence of 10-15% among smokers. The incidence of moderate COPD, as defined by the Global Initiative for Chronic Obstructive Lung Disease (GOLD), is largely unknown. AIM: To determine the cumulative incidence of moderate COPD (forced expiratory volume in 1 second/forced vital capacity ratio [FEV1/FVC] <0.7 and FEV1 <80% predicted) and its association with patient characteristics in a cohort of male smokers. DESIGN: Prospective cohort study. SETTING: The city of IJsselstein, a small town in the Netherlands. METHOD: Smokers aged 40-65 years who were registered with local GPs, participated in a study to identify undetected COPD. Baseline measurements were taken in 1998 of 399 smokers with normal spirometry (n = 292) or mild COPD (FEV1/FVC <0.7 and FEV1 >or=80% predicted, n = 107) and follow-up measurements were conducted in 2003. RESULTS: After a mean follow-up of 5.2 years, 33 participants developed moderate COPD (GOLD II). This showed an estimated cumulative incidence of 8.3% (95% CI = 5.8 to 11.4) and a mean annual incidence of 1.6%. No participant developed severe airflow obstruction. The risk of developing moderate COPD in smokers with baseline mild COPD (GOLD I) was five times higher than in those with baseline normal spirometry (one in five versus one in 25). CONCLUSIONS: In a cohort of middle-aged male smokers, the estimated cumulative incidence of moderate COPD (GOLD II) over 5 years was relatively high (8.3%). Age, childhood smoking, cough, and one or more GP contacts for lower respiratory tract problems were independently associated with incident moderate COPD.  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