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   2611篇
  免费   185篇
  国内免费   18篇
耳鼻咽喉   28篇
儿科学   98篇
妇产科学   55篇
基础医学   403篇
口腔科学   34篇
临床医学   185篇
内科学   420篇
皮肤病学   50篇
神经病学   211篇
特种医学   118篇
外科学   267篇
综合类   20篇
预防医学   123篇
眼科学   79篇
药学   203篇
中国医学   9篇
肿瘤学   511篇
  2023年   20篇
  2022年   44篇
  2021年   71篇
  2020年   42篇
  2019年   49篇
  2018年   53篇
  2017年   58篇
  2016年   75篇
  2015年   79篇
  2014年   99篇
  2013年   99篇
  2012年   196篇
  2011年   193篇
  2010年   124篇
  2009年   104篇
  2008年   150篇
  2007年   180篇
  2006年   147篇
  2005年   138篇
  2004年   132篇
  2003年   112篇
  2002年   112篇
  2001年   53篇
  2000年   48篇
  1999年   44篇
  1998年   33篇
  1997年   23篇
  1996年   16篇
  1995年   16篇
  1994年   18篇
  1993年   13篇
  1992年   20篇
  1991年   25篇
  1990年   22篇
  1989年   24篇
  1988年   22篇
  1987年   23篇
  1986年   27篇
  1985年   22篇
  1984年   19篇
  1983年   6篇
  1982年   6篇
  1981年   5篇
  1979年   7篇
  1978年   6篇
  1977年   8篇
  1974年   4篇
  1972年   5篇
  1971年   4篇
  1969年   4篇
排序方式: 共有2814条查询结果,搜索用时 31 毫秒
151.
BACKGROUND: Serum creatinine level (Cr) is extensively used as an index of glomerular filtration rate (GFR) with bedside patients. As serum Cr level differ by the muscle volume, the use of serum Cr as an index of GFR has long been considered problematic in children. METHODS: The subjects of this study were 135 healthy children aged from 1 to 15-years-old. As a pathological condition, the changes in serum cystatin C (Cys-C) in the children whose blood urea nitrogen exceeded 20 mg/dL during the acute stage of dehydration were also investigated. RESULTS: The mean serum Cys-C value was 0.67 +/- 0.19 mg/L on the whole. There was not any male-female difference. The mean serum Cys-C values of the 12 cases in the acute stage and the recovery stage were 0.61 +/- 0.12 mg/L and 0.64 +/- 0.14 mg/L, respectively, indicating no significant difference. CONCLUSION: Serum Cys-C is considered as a favorable index of GFR in children because it is not influenced by age and sex. As it is not influenced by the prerenal factors either, serum Cys-C is useful in children over 1-years-old.  相似文献   
152.
Hypermethylation of the 5' upstream region (5' region) of the human p16(CDKN2A) (p16) gene is known to cause silencing, which is involved in a wide range of human cancers. For the rat p16 gene, its 5' region has not been cloned, and it is uncertain whether surrogate use of exon 1 alpha is adequate for analysis of p16 silencing. In this study, we observed that methylation analysis of exon 1 alpha gave false positive results in three samples of normal rat mammary epithelia and in two of six primary mammary carcinomas. Therefore, we determined the nucleotide sequence of the 5' region of the rat p16 gene. To confirm that methylation status of the 5' region is correlated with p16 expression, the methylation status was analyzed by bisulfite sequencing and methylation-specific PCR in three samples of normal mammary glands, six samples of mammary carcinomas and four cell lines. The 5' region was demethylated in all of the three normal and six carcinoma samples that fully expressed p16. On the other hand, the 5' region was highly methylated in the 3Y1 cell line, which lacked p16 expression, but without deletion. These results showed that the methylation status of the 5' region was more closely correlated with p16 expression than that of the exon 1 alpha and analysis of the methylation status is useful in examining p16 silencing in various rat tumors.  相似文献   
153.
Dendritic cell appearance and differentiation during early and late stages of rat stomach carcinogenesis were studied in the pyloric mucosa. Young male rats were given drinking water with or without N-methyl-N'-nitro-N-nitrosoguanidine (MNNG; 100 mg/liter) for 14 days. Use of competitive RT-PCR and northern blotting showed that MNNG exposure induced 3- to 4-fold greater expression of the genes for integrin beta7 and integrin alphaE2 (identical with antigen OX-62, a dendritic cell marker), as well as three cytokines, IL-4, GM-CSF and TNFalpha, in the stomach pyloric mucosa of resistant Buffalo rats compared to sensitive ACI rats. These genes were minimally expressed in control animals. The results confirm the appearance of dendritic cells in the target pyloric mucosa and suggest the possibility that dendritic cell differentiation and maturation are induced by various cytokines, at least in Buffalo rats. Competitive RT-PCR showed expression of integrin alphaE2 and beta7, MHC class II-associated invariant chain (Ii), MHC class II, B7-1, CD28, GM-CSF and TNFalpha genes in all 12 examined stomach adenocarcinomas and adenomas induced in male Lewis and WKY rats with 30 weeks' MNNG exposure, suggesting the presence of dendritic cells in tumors. OX-62 staining and western blotting for OX-62 also confirmed the presence of dendritic cells in tumors. However, the population of dendritic cells in tumors was less than that in the pyloric mucosa after 14 days' MNNG exposure. The present results suggest that immune defense involving dendritic cells is marshaled from the very early initiation stage during rat stomach cancer development, but is downgraded in developed tumors.  相似文献   
154.
OBJECTIVE: To describe growth before and after menarche. DESIGN: Nine hundred five fourth grade school girls were identified as a closed cohort from the first semester of 1993 for the observational study of the onset of menarche and its predictive factors. SETTINGS: Eight elementary schools in Taipei City and Taipei County, Taiwan. MAIN OUTCOME MEASURES: Data were collected from self-administered questionnaires and school records. Height and weight were measured in September, January, February, and June, or only in September and February of each year. RESULTS: All subjects remained in the cohort until sixth grade, 410 of whom had their first menstruation before graduating from elementary school. Height, weight, and body mass index (calculated as weight in kilograms divided by the square of height in meters) at each time point were plotted against 2 time scales: chronological age and time from the onset of menarche. Growth velocity of height and weight across the onset of menarche was assessed with slope change using the mixed-effect model analysis. CONCLUSIONS: The results support the hypothesis that height velocity reaches a peak 1 year before menarche but height velocity stopped increasing within 1 year after menarche. The change in weight velocity reveals no obvious growth spurt at age of menarcheal onset.  相似文献   
155.
156.
157.
We examined a 34-year-old premenopausal woman who had noticed a left-breast lump a month previously. She had no past history of malignancies but had a family history of breast and ovarian cancers. Her mother had suffered from ovarian cancer when aged 47 years and had died of the disease at age 52. The younger two of the patient's four aunts had developed breast cancer when they were 37 and 48 years old. A physical examination showed an ill-defined mass, 1.5 cm in diameter, located in the upper outer quadrant of the patient's left breast. Mammography revealed diffuse microcalcification in both breasts but ultrasonography revealed an irregular tumorous lesion only in the left breast. Aspiration breast cytology revealed adenocarcinoma of the left breast. Modified radical mastectomy of the left breast and excision of a biopsy specimen from the right breast were carried out simultaneously. Histopathologically the left-breast tumor was an atypical medullary carcinoma with cartilaginous metaplasia, of histological grade 3, and the right-breast specimen showed fibrocystic changes with atypical ductal hyperplasia. Estrogen receptors were positive, but progesterone receptor was not detected on the tumor cells, which were immunopositive for nuclear p53 although c-erbB-2 overexpression was not observed. A nonsense germline mutation of the BRCA1 gene (exon5) was detected. The patient has been well since the operation (10 months). These findings may provide useful information about the carcinogenesis and biological behavior of BRCA1-associated breast cancers.  相似文献   
158.
Background: Acute inflammatory reactions cause neuronal damage in cerebral ischemia-reperfusion. Urinary trypsin inhibitor (UTI), a serine protease inhibitor, is cytoprotective against ischemia-reperfusion injury in the liver, intestine, kidney, heart, and lung through its antiinflammatory activity. Neuroprotective action of UTI on transient global cerebral ischemia has been documented. This is the first study to determine whether UTI is neuroprotective against transient focal cerebral ischemia.

Methods: Adult male Wistar rats were randomly assigned to the following treatment groups: 0.9% saline (control, n = 9); 100,000 U/kg UTI (n = 9); and 300,000 U/kg UTI (n = 9). Treatments were performed intravenously 10 min before right middle cerebral artery occlusion for 2 h and subsequent reperfusion. Ninety-six hours after the onset of reperfusion, the motor neurologic deficit and the cerebral infarct size were evaluated. Furthermore, immunohistochemical staining for myeloperoxidase and nitrotyrosine to count infiltrating neutrophils and nitrated cells, respectively, was performed on the brain sections.

Results: Infarct volume in the 300,000 U/kg UTI group was smaller than in the 100,000 U/kg UTI and saline control groups (P < 0.05). Treatment with 300,000 U/kg UTI showed a trend to improve neurologic outcome but did not reach statistical significance (P = 0.0693). The significant decrease in neutrophil infiltration was observed in the ischemic hemisphere treated with 300,000 U/kg UTI compared with saline control (P < 0.05). Nitrotyrosine deposition in the ischemic hemisphere was significantly reduced in the 300,000 U/kg UTI group compared with saline control and 100,000 U/kg UTI groups (P < 0.05).  相似文献   

159.
160.
Aberrant DNA methylation has been shown to play an important role during multistage carcinogenesis in various human organs. The aim of the present study was to evaluate the significance of DNA methyltransferase 1 (DNMT1) protein expression during pancreatic carcinogenesis. Immunohistochemical analysis of DNMT1 in 48 peripheral pancreatic duct epithelia showing no remarkable histological findings without an inflammatory background (DE), 54 peripheral pancreatic duct epithelia with an inflammatory background (DEI), 188 pancreatic intraepithelial neoplasias (PanIN), and 220 areas of invasive ductal carcinoma from surgical specimens resected from 100 patients, was carried out. The average incidence of DNMT1 immunoreactivity increased progressively from DE to DEI (P = 0.003), from DE and DEI to PanIN (P < 0.0001), among PanIN with different grades of dysplasia (from PanIN I to PanIN II, P = 0.0012), from PanIN to invasive ductal carcinomas (P < 0.0001) and among invasive ductal carcinomas with different grades of histological differentiation (from well or moderately to poorly differentiated adenocarcinomas, P < 0.0001). High-level DNMT1 protein expression in invasive ductal carcinomas was correlated significantly with an advanced t category (P = 0.0224) and an advanced stage (P = 0.0294). Moreover, patients with invasive ductal carcinomas showing high-level DNMT1 protein expression had a poorer outcome (P = 0.0469). These data suggest that increased DNMT1 protein expression participates in multistage pancreatic carcinogenesis from the precancerous stage to malignant progression of ductal carcinomas and may be a biological predictor of poor prognosis.  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