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   100557篇
  免费   10208篇
  国内免费   4932篇
耳鼻咽喉   2420篇
儿科学   591篇
妇产科学   1816篇
基础医学   11920篇
口腔科学   3425篇
临床医学   7599篇
内科学   12641篇
皮肤病学   2037篇
神经病学   529篇
特种医学   4457篇
外国民族医学   130篇
外科学   14960篇
综合类   17892篇
现状与发展   23篇
预防医学   2289篇
眼科学   584篇
药学   5101篇
  24篇
中国医学   1321篇
肿瘤学   25938篇
  2024年   138篇
  2023年   1445篇
  2022年   2255篇
  2021年   4035篇
  2020年   3583篇
  2019年   3369篇
  2018年   3186篇
  2017年   3615篇
  2016年   4096篇
  2015年   4613篇
  2014年   6709篇
  2013年   5951篇
  2012年   6014篇
  2011年   6506篇
  2010年   5191篇
  2009年   5098篇
  2008年   5324篇
  2007年   5597篇
  2006年   5230篇
  2005年   4666篇
  2004年   3712篇
  2003年   3286篇
  2002年   2805篇
  2001年   2661篇
  2000年   2291篇
  1999年   1842篇
  1998年   1662篇
  1997年   1505篇
  1996年   1345篇
  1995年   1170篇
  1994年   1050篇
  1993年   763篇
  1992年   670篇
  1991年   590篇
  1990年   495篇
  1989年   438篇
  1988年   407篇
  1987年   334篇
  1986年   294篇
  1985年   316篇
  1984年   251篇
  1983年   176篇
  1982年   212篇
  1981年   187篇
  1980年   172篇
  1979年   125篇
  1978年   103篇
  1977年   80篇
  1976年   58篇
  1975年   29篇
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
991.
Normal hyperplastic and malignant endometrial specimens were labelled in vitro with bromodeoxyuridine (BrdU). S-phase cells were stained after DNA denaturation, using a monoclonal antibody to BrdU and an indirect immunoperoxidase method. Various conditions for BrdU uptake, DNA denaturation, and staining were tested. BrdU labelling was compared with autoradiography using tritiated thymidine, with good correlation. Glandular labelling indices of proliferative endometrium were significantly higher than both secretory and hyperplastic endometrium but were similar to carcinoma. Stromal labelling showed the same trend but the differences were not statistically significant.  相似文献   
992.
We describe a case of hepatocellular carcinoma in which a tumor embolus in the portal vein and 3 of 4 intrahepatic metastases were necrosed completely by Lipiodol transcatheter chemo-embolization (Lipiodol-TCE). Tumor emboli in the portal vein and intrahepatic metastases usually cannot be necrosed by conventional transcatheter chemo-embolization alone, because small nodules such as intrahepatic metastases and tumor emboli in the portal vein are supplied blood from the portal vein. However, in this case, Lipiodol-TCE was effective against tumor emboli in the portal vein and intrahepatic metastases. ACTA PATHOL JPN 38: 1363-1367, 1988.  相似文献   
993.
Immunohistochemical studies were performed to clarify the significance of the expression or overexpression of epidermal growth factor (EGF), EGF-receptor (EGFR), p53, v- erb B, ras p21 in 23 cases each of tubular adenoma and adenocarcinoma. The expression of EGF, EGFR, p53, v- erb B, and ras p21 in paraffin-embedded tissues, from 46 patients with colorectal tumors (adenoma: 23 cases; 14 mild dysplasia, six moderate dysplasia, three severe dysplasia, adenocarcinoma: 23 cases; 17 well differentiated, two moderately differentiated, three poorly differentiated, one mucinous carcinoma was analyzed immunohistochemically using anti-EGF, EGFR, p53, v- erb B and ras p21 antibodies. The EGF and ras p21 tended to express more strongly in carcinoma cases than in the adenoma cases, and in severe and moderate dysplasia than in mild dysplasia (EGF: stained positive in five adenomas [21.74%] and 17 adenocarcinomas [73.91%]; ras p21: stained positive in six adenomas [26.09%] and 14 adenocarcinomas [60.87%]. The EGFR stained positive in two adenomas (8.70%) and two adenocarcinomas (8.70%). The p53 and v- erb B showed positive staining only in the carcinoma cases (p53: stained positive in four cases [17.39%]; v- erb B: stained positive in eight cases [34.78%]). This study suggests that these factors seem to have some role in the progression of colon neoplasms. It suggests that genetic alteration is not always equal to the overexpression of protein products, but that it reflects them well, and that the staining makes some contribution to differential diagnosis in colorectal neoplasms.  相似文献   
994.
FAS receptor (FAS, CD95) and FAS ligand (FAS-L, CD95-L) are complementary members of a particular apoptotic pathway that plays a major role in immune regulation. The activation of FAS-L may trigger cytotoxic mechanisms leading to the death of FAS-expressing cells. Tumor cells and tumor-infiltrating lymphocytes (TIL) may express FAS and FAS-L in various proportions, and their interplay may affect tumor behavior. In the present study, we explored the expression of FAS and FAS-L in 28 mammary carcinomas (19 ductal and 9 lobular) and in their lymph node metastases. The expression of these mediators in immunostained sections was graded and evaluated comparatively between normal and neoplastic mammary epithelium, between tumor cells and TILs, and between mammary carcinoma cells and their lymph node metastases. We demonstrated the coexpression of FAS and FAS-L by breast carcinoma cells and TIL, with FAS expressed more strongly by normal epithelial cells and TIL than tumor cells. FAS-L was better stained on tumor cells than on TIL. There was equal or greater expression of FAS and FAS-L in the primary tumors and their TIL than in the metastatic counterparts. Comparing the expression of FAS with that of FAS-L, we recorded FAS equal or stronger than FAS-L in the primary mammary tumors and the reversal of their expression, FAS-L greater than FAS in the lymph node metastases. These results are consistent with reports of studies with other tumors, suggesting that the upregulated FAS-L indicates an increased ability of tumor cells to induce apoptosis in TIL and in the normal tissues invaded. However, it is understood that the FAS/FAS-L system, although essential for apoptosis, is only a contributing factor to the complex process of tumor invasion and antitumor defense.  相似文献   
995.
AIMS: Malignant thymic tumour histologically resembling a soft tissue sarcoma is extremely rare and defined as sarcomatoid carcinoma in the recent World Health Organization (WHO) classification. We report two such cases in which the tumour cells showed a prominent rhabdomyoblastic differentiation and analyse whether these tumours retain an epithelial nature at least in part. METHODS AND RESULTS: One tumour occurred in a 51-year-old man (Case 1) and the other in a 40-year-old woman (Case 2). Microscopically, both tumours consisted essentially of two types of tumour cells: spindle and large round cells, with no apparent epithelial components. Osteosarcomatous small foci were also found in Case 2. Immunohistochemically, desmin and muscle-specific actin were positive in the majority of both types of tumour cells, whereas myogenin was predominant in the spindle cells and myoglobin in the large round cells. Some of both types of cells expressed cytokeratin with co-expression of myoglobin in the large round cells, but with no myogenin in the spindle cells. Some cytokeratin-positive spindle cells were also negative for desmin. Ultrastructural examination of a recurrent tumour in Case 2 revealed some epithelial features among the spindle cells. Cytogenetic study of the same tumour showed a complex abnormality including der(16)t(1;16)(q12;q12.1), an identical pattern previously reported in a case of thymic squamous cell carcinoma. CONCLUSIONS: The findings support the definition in the WHO classification of sarcomatoid carcinoma that includes purely sarcomatous tumour as in the present cases. Occurrence of this type of tumour may indicate a relationship between thymic epithelial cells and myoid cells and/or a potential for divergent differentiation in thymic epithelial tumours.  相似文献   
996.
Alterations in tissue zinc levels have been documented in patients with gastrointestinal tract malignancies and more frequently, in those with colonic cancer. However, the precise role of tissue zinc in carcinogenesis is not well elucidated. This study, using a well-established colon cancer model in rats, was designed to investigate the relationship of tissue zinc to the carcinogenic process. The aim was to examine tissue zinc levels in the preneoplastic tissues and to study the changes that occur during transition of mucosa from normal to preneoplastic state. Six-week old rats were given a single dose subcutaneous injection of azoxymethane (AOM) (30mg/kg body weight) and sacrificed after 1, 2, 5, and 9 months of the treatment. Plasma zinc levels showed a significant decrease (p<0.05) at 9 months compared with controls. Tissue zinc levels showed a significant decrease in the large intestine at 1 and 2 months (p<0.05) and at 5 and 9 months (p<0.01), in the small intestine at 2, 5, and 9 months (p<0.05), and in the stomach at 5 and 9 months (p<0.05). The maximum percent decrease (45%) in tissue zinc was observed in the large intestine at 9 months. Tissue copper zinc super oxide dismutase (CuZnSOD) activity was assessed in the body of the stomach, small intestine, and large intestine and compared with the control group. There was a significant fall in CuZnSOD levels in the small intestine at 9 months (p<0.05) and in the large intestine at 5 and 9 months (p<0.01). Two of these six rats showed histological evidence of precancerous lesions in the mucosa of the colon. This study suggests that the decrease in plasma zinc, tissue zinc and activity of CuZnSOD is associated with development of preneoplastic lesions in the colonic mucosa.  相似文献   
997.
时间分辨荧光免疫分析方法学评价   总被引:19,自引:0,他引:19  
秦卫仕  田蓉 《免疫学杂志》2002,18(5):397-399,405
目的:通过内质控的定量分析,对时间分辨荧光分析的方法学进行客观评价。方法:以促甲状腺激素检测为例,对系统探测灵敏度 ,低、中、高持控血清的批内和批间精密度,批间稳定性参数Slope、ED20、ED50、ED80等4项指标,系统探测的准确度(回收试验),系统探测的有效性(平行试验),受试者工作特性曲线(receiver operator characteristic,ROC)等进行定量测定和描述。结果;TSH的最小测定值为0.002μU/mL.低、中、高3种质控样品批内和批间变异系数均小于5%,批间稳定性参数各变异系数均小于5%,与统计学要求相一致,且符合标准曲线质控参数的重现性。回收试验满足临床要求,符合检验统计结果。理论值与实测值间作回归分析,相关系数r=0.999。ROC显示,甲亢诊断的最佳阈值为0.3μU/mL,甲低诊断的最佳阈值为5.0μU/mL。甲亢敏感度为89.3%,特异度为93.3%,准确度为90.1%,阳性似然比为13.4,甲低敏感度为83.8%,特异率为90.9%,准确度为86.4%,阳性似然比为9.2。结论:时间分辨荧光免疫分析方法是一种效果好、准确度高、灵敏度高、特异性强、测试精度良好的自动化免疫分析方法。  相似文献   
998.
We investigated the reaction of the cellular immune system of liver and blood in the C57BL/6 mouse to a metastasizing Lewis lung carcinoma. The cellular immune system of the liver consists of mature and immature macrophages, B-cells, T-cells including their subpopulations, and natural killer cells, and their percentage frequencies differ significantly from those in the corresponding mononuclear blood cell (MBC) compartment. This suggests that the hepatic immune cells represent a system with autonomous function showing a typical homing of its members. Imminent metastasis to the liver is signalled by impressive alterations in the percentage frequencies of nonparenchymal liver cells (NPLC). There are a dramatic loss of mature macrophages, an increase in immature macrophages, a reduction of T-helper cells leading to a low CD4/CD8 ratio, and an increase in natural killer cells. In the blood, the corresponding precursor cells show comparable changes with a delay of at least 2 days. Early metastasis is accompanied by a significant increase in mononuclear NPLC producing tumour necrosis factor . The alterations in percentage frequencies of the NPLC during tumour metastasis differ markedly from the changes in these cells in the liver during endotoxinaemia.  相似文献   
999.
Oesophageal squamous cell carcinoma with lymphoid stroma   总被引:4,自引:0,他引:4  
Summary We treated a 70-year-old Japanese man with squamous cell carcinoma of the oesophagus with evidence of lymphoid stroma. The tumour consisted of a main lesion invading the muscular layer of the oesophagus, in association with wide areas of carcinoma in situ. The tumour stroma of the lesion was nondesmoplastic and was uniformly infiltrated mainly by abundant lymphocytes and plasma cells. Immunohistochemically, the lymphocytes consisted of a large number of T lymphocytes and a small number of B lymphocytes. S-100 protein positive cells were marked in the tumour cell nests and necrotic change of tumour cells was frequent. Abundant infiltration of lymphocytes and plasma cells was also wide-spread beneath the carcinoma in situ, together with the lymphoid follicles. Carcinoma with lymphoid stroma can occur not only in the breast, uterine cervix, nasopharynx and stomach but also in the oesophagus.  相似文献   
1000.
One hundred and seven smears demonstrating a low-grade squamous intraepithelial lesion (LSIL) were analyzed for features predicting subsequent biopsy confirmation. Twelve (29%) of 41 smears showing few LSIL cells were biopsy confirmed compared to 33 (60%) of 55 containing an intermediate number of LSIL cells and 9 (82%) of 11 displaying many LSIL cells (P < 0.002). Thirty-seven (47%) of 78 smears showing mainly condylomatous atypia (CA), 7 (54%) of 13 revealing predominantly cervical intraepithelial neoplasia 1 (CIN 1), and 10 (63%) of 16 displaying both CA and CIN 1 were histologically confirmed (N.S.). Biopsy confirmation was obtained in 35 (65%) of 54 women whose repeat smears obtained at colposcopy demonstrated SIL compared to four (15%) of 26 patients whose repeat smears were normal or contained atypical squamous cells of undetermined significance (P < 0.001). These results suggest that the number of diagnostic cells in an LSIL smear predicts biopsy confirmation and affirm the validity of combining CA and CIN 1 under the category of LSIL in the Bethesda System. © 1994 Wiley-Liss, Inc.  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