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   24042篇
  免费   1468篇
  国内免费   72篇
耳鼻咽喉   265篇
儿科学   603篇
妇产科学   511篇
基础医学   4286篇
口腔科学   545篇
临床医学   2165篇
内科学   4721篇
皮肤病学   603篇
神经病学   2272篇
特种医学   1255篇
外国民族医学   2篇
外科学   3779篇
综合类   132篇
一般理论   10篇
预防医学   1175篇
眼科学   406篇
药学   1435篇
中国医学   26篇
肿瘤学   1391篇
  2023年   129篇
  2022年   305篇
  2021年   605篇
  2020年   340篇
  2019年   425篇
  2018年   512篇
  2017年   437篇
  2016年   614篇
  2015年   618篇
  2014年   807篇
  2013年   974篇
  2012年   1402篇
  2011年   1361篇
  2010年   770篇
  2009年   769篇
  2008年   1179篇
  2007年   1124篇
  2006年   1063篇
  2005年   1018篇
  2004年   895篇
  2003年   853篇
  2002年   817篇
  2001年   582篇
  2000年   523篇
  1999年   490篇
  1998年   199篇
  1997年   191篇
  1996年   171篇
  1995年   134篇
  1994年   135篇
  1993年   122篇
  1992年   243篇
  1991年   309篇
  1990年   268篇
  1989年   282篇
  1988年   256篇
  1987年   239篇
  1986年   249篇
  1985年   252篇
  1984年   169篇
  1983年   161篇
  1979年   197篇
  1978年   133篇
  1977年   123篇
  1976年   110篇
  1975年   149篇
  1974年   152篇
  1973年   136篇
  1972年   133篇
  1971年   117篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Hepatitis B virus (HBV) DNA is detectable in a number of liver transplant candidates who are negative for hepatitis B surface antigen (HBsAg). After liver transplantation (LT), such patients may have molecular and/or serologic evidence of HBV replication. However, clinical disease from reactivation of occult HBV infection after LT has not been described. We report a patient who underwent LT for cryptogenic cirrhosis and had to be retransplanted twice for hepatic artery thrombosis. The patient was negative for HBsAg and positive for anti-hepatitis B core (HBc) and anti-HBs before all LT procedures and developed acute hepatitis B shortly after receiving the third graft. The HBV strain isolated at that time exhibited an unusual in frame insertion of a CAG motif within the HBV polymerase (HBV(INS+)). HBV(INS+) was detected retrospectively as a minor species in pretransplantation sera and the explanted native liver by insertion-specific polymerase chain reaction. This case in an occult HBV carrier shows that clinically apparent, endogenous reinfection of the graft may occur with minor HBV variants that are not detectable in pretransplantation samples by standard diagnostic procedures. This has implications for the analysis of sources of acute hepatitis B in patients after LT and possibly for consideration of antiviral prophylaxis in anti-HBc/anti-HBs/HBV DNA-positive patients.  相似文献   
32.
We found that naive (CD45RA+) CD4 T cells have a lower capacity of adhesion to Epstein-Barr virus (EBV) immortalized B cells than memory (CD45RO+) CD4 T cells, as judged by conjugate formation. This would appear to be due to differences in the expression of adhesion molecules [lymphocyte function-associated antigen (LFA)-1, CD2]. However, kinetic studies showed that the degree of adhesion of naive T cells to B cells was stable over 60 min while that of memory T cells, like that of unseparated CD4 T cells, was characterized by a rapid formation and rapid dissociation of conjugates. This could be explained by a difference in the sensitivity of naive and memory CD4 T cells to down-regulation of antigen-independent adhesion by CD4-MHC class II interaction. Indeed, memory T cells also adhered stably to MHC class II(-) B cells. The adhesion of memory T cells, but not naive T cells, to MHC class II(+) B cells was sensitive to inhibition by OKT4a an anti-CD4 antibody, human immunodeficiency (HIV) gp160 (env) protein and a 12-mer peptide encompassing the 35-46 sequence of the HLA, DR beta 1 domain and previously shown to inhibit activation of HLA class II-restricted CD4 T cell responses. Since MHC class II expression did not influence the degree of conjugate formation by naive or memory CD4 T cells with B cells, CD4-MHC class II interaction does not appear to be involved in binding itself, but may down-regulate the adhesion of memory but not naive CD4 T cells.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
33.
Cranial sonography provides a noninvasive, portable method for imaging the infant brain. This study describes the time-dependent, sonographic findings of infantile cerebral infarction, as well as computed tomographic (CT) scan and neuropathologic confirmation. Three hundred ninety-five infants under 18 months of age were sonogrammed over a period of 18 months. Three infants were diagnosed by cranial sonography and confirmed by CT scan and/or autopsy to have acute ischemic cerebral infarcts. The cases were followed with serial cranial sonograms for up to 18 months of age. The acute sonographic findings included a hyperechoic zone around the infarcted tissue. The subacute infarct had a checkerboard pattern, while the chronic infarcts were anechoic.  相似文献   
34.
The effect of histamine on the phosphoinositide turnover andintracellular free calcium activity [Ca2+]i was examined inhuman glomerular epithelial cells in culture. Addition of histamineto glomerular epithelial cells resulted in formation of inositolphosphates in a time- and dose-dependent manner. A transientmaximum of inositol trisphosphate (InsP3) was observed within10 s. Stimulation of protein kinase C by short-term pretreatment(15 mm) of glom erular epithelial cells with phorbol 12-mynstate13-acetate caused a dose-dependent inhibition of the histamine-inducedinositol phosphate accumulation. The baseline of [Ca2+]i inthe cells was 115 ±2.7 nmol/l (n=103). Histamine (ED50:approx. 2x10–7mol/l) caused a rapid and transient increasein [Ca2+]i, as detected by fura-2 microfluorimetry studies.In a calcium-free extracellular solution the rapid increaseof [Ca2+]i was still present. The H1 receptor antagonist mepyramine(IC50: approx. 8 x 10–9 mol/l) inhibited the histamine(10–6 mol/l) response on [Ca2+]i Cimetidine, a potentH2 receptor antagonist, showed no effect. This data indicates that H1 receptor activation causes hydrolysisof phosphatidylinositol 4, 5-bisphosphate by phospholipase Cactivation, and consecutive mobil ization of intracellular calcium.Since histamine is a mediator of inflammation, antigen responseand cellular injury, these findings could be of importance forthe understanding of glomerular epithelial cell pathology.  相似文献   
35.
AIMS. Comparison of the degradation of poly(D,L)lactide (Resorb X) or poly(lactide-co-glycolide) (LactoSorb) in vivo. MATERIAL AND METHODS. LactoSorb and Resorb X osteosynthesis plates were fixed at the lateral aspect of the femora of 26 Chinchilla rabbits using the respective osteosynthesis screws. After intraperitoneal injection of fluorochromes the screw plate bone blocks were resected after 1, 6, 12, 14, 16, 21, 26 months and radiologic, histologic as well as fluorescence microscopic examinations were carried out. RESULTS. Newly formed bone was detectable above and beneath the polymers 1 month after the implantation. The implants were totally covered by newly formed bone after 6 months. While the LactoSorb screws were found to be as birefringent as after 1 month, in the Resorb X screws a continuous resorption by phagocytizing marrow cells starting from the periphery was detectable. Resorb X was totally resorbed in histologic slides 12 months after implantation, while total resorption of LactoSorb lasted 14 months; both polymers were replaced by marrow cells. Bone remodeling was not finished 26 months after implantation in both polymers. CONCLUSION. Resorption of Resorb X was finished earlier than the resorption of LactoSorb. Both materials were found by fluorescence microscope to be completely resorbed after 12 or 14 months, but bone remodeling of the screw holes was not yet finished 26 months after implantation.  相似文献   
36.
37.
38.
39.
40.
For cardio-pulmonary resuscitation there are standardized treatment concepts, but there have been few prospective investigations examining the efficacy of prehospital advanced trauma life support and its effect on the outcome in patients with severe head injury and multiple trauma treated within the German emergency system. The results of this study underline the importance of intensive prehospital treatment and highlight some problems that should be taken into account in future in the training of emergency physicians. Methods. A total of 179 patients with cerebral trauma were investigated. Data obtained included demographic and logistic data of the patients and the emergency physicians, diagnoses and treatment at the scene of the accident and state of the patient on admission in each case. Having divided the patients into three groups by severity of the trauma, we distinguished between sufficient and insufficient treatment and assessed infusion therapy, ventilatory support, positioning and immobilization, and analgesic and sedative therapy. For statistical analysis of the data we used χ2-test and Fisher's exact test. P<0.05 was considered significant. Results. There were 102 patients who had sustained a cerebral trauma without other life-threatening lesions (score 1), 40 with multiple trauma (score 2) and 37 with multiple trauma (score 3). On average 2.4?IV lines were established and the patients received 1186±765?cc of crystalloid in addition to 801±411?cc of colloid fluids. In all groups, patients who received adequate infusion therapy had a better outcome; even in the group with score 1 significantly fewer had a fatal outcome. In all, 167 (93%) patients had endotracheal tubes placed, and in 150 cases (84%) ventilatory therapy was considered sufficient. The proportion of score 1 patients with sufficient ventilatory support who had a fatal outcome was significantly lower than that in the group with insufficient treatment. In patients with multiple trauma we could not separate the benefits of sufficient respiratory therapy and infusion therapy. In only 54% of the cases a vacuum mattress was used and in only 41% the patients were positioned with the upper part of the body elevated by 30°. These were 28 patients (16%) who received neither analgesics nor sedatives. Regardless of the quality of prehospital treatment of isolated head injury, a Glasgow Coma Scale (GCS) score lower than 5 involved a very high mortality and all patients with a GCS score of 9 or more survived. In the group with GCS scores between 5 and 8, however, significantly more of the patients who received adequate treatment survived (82.5% vs 40%). Conclusions. The present study confirms that sufficient advanced trauma life support can improve the outcome of trauma victims with cerebral trauma. Adequate infusion and respiratory therapy reduce the mortality among such patients significantly. In patients with multiple trauma a clear positive effect of generous infusion therapy also is evident. The clearest effect of sufficient prehospital treatment is seen in patients with isolated cerebral trauma and a GCS score between 5 and 8. These results demonstrate the importance of advanced trauma life support and show emphatically that the so-called scoop-and-run strategy should be abandoned when resources are available for extended preclinical emergency treatment. On the other hand, we detected some problem areas in the prehospital treatment of trauma victims, such as positioning, immobilization and drug therapy with analgesics and sedatives. These findings allow us to pinpoint specific points that should be stressed in the training of emergency physicians and paramedics.  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