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   13257篇
  免费   1536篇
  国内免费   26篇
耳鼻咽喉   108篇
儿科学   301篇
妇产科学   350篇
基础医学   2283篇
口腔科学   229篇
临床医学   1468篇
内科学   2859篇
皮肤病学   170篇
神经病学   906篇
特种医学   703篇
外科学   1752篇
综合类   312篇
一般理论   7篇
预防医学   1373篇
眼科学   208篇
药学   997篇
中国医学   11篇
肿瘤学   782篇
  2021年   233篇
  2020年   128篇
  2019年   198篇
  2018年   246篇
  2017年   179篇
  2016年   187篇
  2015年   216篇
  2014年   303篇
  2013年   436篇
  2012年   625篇
  2011年   664篇
  2010年   406篇
  2009年   330篇
  2008年   567篇
  2007年   599篇
  2006年   606篇
  2005年   552篇
  2004年   518篇
  2003年   487篇
  2002年   462篇
  2001年   420篇
  2000年   419篇
  1999年   406篇
  1998年   169篇
  1997年   148篇
  1996年   162篇
  1995年   178篇
  1994年   150篇
  1993年   156篇
  1992年   334篇
  1991年   341篇
  1990年   278篇
  1989年   288篇
  1988年   240篇
  1987年   265篇
  1986年   256篇
  1985年   277篇
  1984年   226篇
  1983年   177篇
  1982年   127篇
  1981年   113篇
  1980年   94篇
  1979年   157篇
  1978年   125篇
  1977年   97篇
  1976年   99篇
  1975年   96篇
  1974年   110篇
  1973年   108篇
  1972年   95篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Contact dermatitis in patients with leg ulcers   总被引:3,自引:2,他引:1  
100 patients with leg ulcers were patch tested against a standard battery of allergens. The readings were carried out daily from the 2nd to the 7th days. 55 patients showed positive reactions to one or more allergens. 32% of positive reactions developed for the first time after 48 h and 11% after 72 h. No single day or combination of two days gave 100% positive results. A single reading on the 4th day gave the highest number of positive reactions at 92%. The prevalence of positive patch tests was significantly higher in patients with surrounding eczema, and in patients with positive patch tests the ulcer duration was significantly longer than in those with negative patch tests. The total number of positive results in individuals increased linearly with the duration of the ulcer. Of allergens to which the ulcer was exposed, the occurrence of multiple sensitivity was significantly greater than predicted from the prevalence of individual sensitivities. However, there was no association between medicaments and metal sensitivity. This, together with the absence of an exponential rise in the number of allergens with the duration of ulcer, does not support the theory of systemic ampliative allergy.  相似文献   
72.
BACKGROUND: Multicolored Asian lady beetles (Harmonia axyridis) have been used as a biological control agent against crop-destroying aphids in the United States. Outside their natural habitat, H. axyridis seeks refuge in homes during fall and winter, leading to patient complaints and symptoms of rhinitis, wheezing, and urticaria on exposure to the beetles. OBJECTIVE: To gain a better understanding of the character and spectrum of allergic disease provoked by exposure to home-infesting lady beetles. METHODS: Eight patients with allergic symptoms suspected of being caused by H. axyridis and consistent with an IgE-mediated process were identified and interviewed. A whole-body extract from H. axyridis was prepared. Western blots using the patients' serum identified specific IgE antibodies in the extract. Through a novel technique, immunohistochemical analysis using beetle sections overlayed with patient serum was performed. A random survey of allergists from across the United States was also performed to evaluate experience with cases of lady beetle allergy. RESULTS: Western blots revealed IgE binding to 5 proteins with molecular weights of approximately 8.6, 21, 28, 31, and 75 kDa. Specific IgE bound to proteins localized in the beetle's mouth and leg areas. The allergist survey revealed positive responses in North Central, Mid-Atlantic and New England states. CONCLUSION: In 8 patients with allergic symptoms on exposure to high levels of lady beetles, specific IgE bound to proteins from H. axyridis. There was also an increased frequency of suspected cases of lady beetle allergy in endemic areas.  相似文献   
73.
74.
Computerised videokeratography is increasing in sophistication and accuracy. The Orbscan II Videokeratographer combines the advantages of Placido derived and slit-scanning derived topography, to acquire shape information on the posterior surface of the cornea. The purpose of this paper is to construct a model of slit-scanning elevation topography and highlight potential sources of variation in this methodology. Ray tracing calculations were performed on a defined, theoretical, spherical model to obtain a pachymetric measurement. These calculations were tested by comparing the pachymetry measurement derived from the model, over a refractive index shift from 1.376 to 1.400 with the pachymetry measurement obtained by Orbscan II, of a human eye, with an identical alteration in refractive index. The two methods of measurement differed by only 0.157 microm, suggesting that the model is a good representation of slit-scanning elevation topography, and that refractive index variations have only a minimal effect on Orbscan II pachymetry measurement.  相似文献   
75.
BACKGROUND: Inflammatory bowel disease is associated with increased mucosal release of eicosanoids. Among these, thromboxane A2 has been proposed as a possible inflammatory mediator; its suppression may be a useful therapeutic option. METHODS: Using a tissue incubation technique, we compared release of immunoreactive thromboxane B2 by colonic biopsies from patients with ulcerative colitis, Crohn's disease and controls, and assessed the inhibitory effect of picotamide, a thromboxane synthesis inhibitor-receptor antagonist, which has been widely used in Italy for management of ischaemic heart and cerebrovascular disease. RESULTS: Increased amounts of thromboxane B2 were released from biopsies from patients with active ulcerative colitis (median 238 pg/20 min/mg wet weight (interquartile range 147- 325), n = 12) and active Crohn's disease (252 (174-450), 6) compared with those from patients with quiescent ulcerative colitis (95 (61- 140), 12) or Crohn's disease (105 (57-201), 13), or controls (136 (64- 206), 8). Incubation with picotamide at concentrations between 100 microM and 1 mM reduced thromboxane B2 release (IC50 890 microM). CONCLUSION: Since increased thromboxane A2 production may have pathogenetic importance, thromboxane synthesis inhibitor-receptor antagonists such as picotamide merit therapeutic trial in the management of inflammatory bowel disease.  相似文献   
76.
We compared changes from 1965 to 1987 in patients accepted to chronic dialysis, in a Swedish and a US dialysis center, by medical and clinical parameters at the start of dialysis and by duration of the dialysis. We also studied cause of death, outcome, and cumulative survival and tried to relate them to changes in patients and procedures. Finally, we studied how cumulative survival of dialysis patients was dependent on acceptance rates and transplant rates in five European regions and the United States. At both centers, the number of patients accepted grew, but since 1980, the only patient group that has increased has been older patients with many other diseases; these comorbid conditions have increased from approximately 1.2 to 1.4. In both centers, the number of patients with systemic disease, diabetes, and nephrosclerosis doubled. Cause of death showed a decrease in cardiovascular deaths and an increase in deaths due to stopping dialysis. The hemoglobin level increased from 70 to 90 g/L (7.0 to 9.0 g/dL) and the diastolic blood pressure decreased from 100 to 90 mmHg. The creatinine level decreased 30%, with an unchanged urea. Cumulative 3-year survival for patients without complications increased from 60% to approximately 90% and in patients with complications, it improved from 20% to 60% in Sweden and remained at approximately 60% in the US center. In the United States, many more patients were accepted to dialysis and the transplant rate was high. Cumulative survival on dialysis was inversely correlated both to the acceptance rates to dialysis and to the percent of patients transplanted. These factors explained over 90% of the differences in dialysis survival.  相似文献   
77.
There is controversy whether the short-term and long-term results of coronary artery bypass grafting in elderly patients justify performing the procedure. Between January 1977 and December 1986, 4580 patients underwent coronary artery bypass grafting, of whom 222 (4.9%) were 75 years old or older (mean 77 years). There were 143 men and 79 women and 139 (63%) were in New York Heart Association class IV. One hundred forty-six patients (66%) had had at least one preoperative myocardial infarction. Myocardial revascularization was performed under emergency conditions in 17 patients (18%). The mammary artery was used in 43%, 96% of the patients received two or more grafts. The mean number of bypass grafts was 3.1 per patient. The overall hospital mortality rate was 10.8% (24/222), 3.6% for elective procedures, 14.9% in urgent cases, and 35% in emergencies. In contrast, the overall early mortality rate was 3.1% in 4358 patients less than 75 years old. Complications occurred in 83 patients (37%). Of the patients discharged from the hospital, 198 were followed up for a mean of 48 months (1 to 130). Actuarial probability of survival was 75% at 48 months. Postoperatively 70% were in New York Heart Association class I or II and only 21% were rehospitalized for cardiac problems. During the follow-up period 77% of the patients were free from angina, and of those experiencing angina the mean time from operation to the first episode was 75 months. Although elderly patients have a somewhat increased operative mortality rate, particularly if operated on urgently or emergently, long-term survival and freedom from angina are excellent and justify continued performance of coronary bypass grafting in selected patients over 75 years of age.  相似文献   
78.
BACKGROUND: Myocardial perfusion imaging (MPI) is a well-established diagnostic method for evaluation and risk stratification of coronary artery disease (CAD).We undertook this study to validate both the positive predictive value (when compared to cardiac catheterization) and the prognosis afforded by MPI in a group of minority women patients. MATERIAL/METHODS: The database of our Nuclear Imaging and Catheterization Laboratory was retrospectively queried for consecutive minority (African-American, Hispanic and Asian) women patients who underwent MPI and cardiac catheterization within 90 days of each other. Patients with recent revascularization were excluded. Attenuation/scatter correction was utilized in the final interpretation of the study. RESULTS: Of the 54 women patients who underwent MPI, 7 underwent exercise stress testing, 26 had stress testing with adenosine, 18 with dipyridamole and 3 with dobutamine. Eighteen patients (53%) had same number of vessels predicted by MPI and coronary angiography (7 patients with triple vessel disease, 7 with 2-vessel disease and 4 with single vessel disease). Five (3 with intermediate and 2 with high risk scans) out of the 54 patients (9.3%) were dead at 2 years. The sensitivity, specificity and positive predictive value of MPI as compared to angiography were 87.2%, 26.7%, 75.6% and 44.4% respectively. CONCLUSIONS: The sensitivity of MPI in this group of patients is comparable to the general population though the specificity is lower in spite of using attenuation and scatter correction. Low risk perfusion scan signifies favorable prognosis at 2 years with regards to mortality.  相似文献   
79.
80.
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