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   38488篇
  免费   1859篇
  国内免费   300篇
耳鼻咽喉   281篇
儿科学   696篇
妇产科学   443篇
基础医学   5179篇
口腔科学   1045篇
临床医学   2315篇
内科学   9590篇
皮肤病学   877篇
神经病学   2619篇
特种医学   1339篇
外科学   6803篇
综合类   154篇
一般理论   2篇
预防医学   1126篇
眼科学   726篇
药学   2350篇
中国医学   127篇
肿瘤学   4975篇
  2023年   199篇
  2022年   439篇
  2021年   916篇
  2020年   471篇
  2019年   681篇
  2018年   894篇
  2017年   683篇
  2016年   826篇
  2015年   838篇
  2014年   1141篇
  2013年   1427篇
  2012年   2326篇
  2011年   2718篇
  2010年   1546篇
  2009年   1260篇
  2008年   2326篇
  2007年   2563篇
  2006年   2433篇
  2005年   2607篇
  2004年   2514篇
  2003年   2524篇
  2002年   2512篇
  2001年   475篇
  2000年   427篇
  1999年   532篇
  1998年   603篇
  1997年   471篇
  1996年   457篇
  1995年   384篇
  1994年   337篇
  1993年   311篇
  1992年   286篇
  1991年   251篇
  1990年   249篇
  1989年   234篇
  1988年   183篇
  1987年   175篇
  1986年   160篇
  1985年   138篇
  1984年   150篇
  1983年   126篇
  1982年   93篇
  1981年   104篇
  1980年   98篇
  1979年   96篇
  1978年   60篇
  1977年   39篇
  1975年   45篇
  1974年   29篇
  1973年   32篇
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
111.
112.
Several reports claim that portal hypertension after living-donor liver transplantation (LDLT) adversely affects graft function, but few have assessed the impact of portal venous pressure (PVP) on graft regeneration. We divided 32 adult LDLT recipients based on mean PVP during the 1st 3 days after LDLT into a group with a PVP > or = 20 mm of Hg (H Group; n = 17), and a group with a PVP < 20 mm of Hg (L Group; n = 15). Outcome in the H Group was poorer than in the L Group (58.8 vs. 92.9% at 1 year). Peak peripheral hepatocyte growth factor (HGF) during the 1st 2 weeks was higher in the H Group (L: 1,730 pg/mL, H: 3,696 pg/mL; P < .01), whereas peak portal vascular endothelial growth factor (VEGF) level during the 1st week was higher in the L Group (L: 433 pg/mL, H: 92 pg/mL; P < .05). Graft volume (GV) / standard liver volume (SLV) was higher in the H Group (L / H, at 2, 3, and 4 weeks, and at 3 months: 1.02 / 1.24, .916 / 1.16, .98 / 1.27, and .94 / 1.29, respectively; P < .05). Peak serum aspartate aminotransferase, bilirubin levels, and international normalized ratio after LDLT were significantly higher in the H Group, as was mean ascitic fluid volume. In conclusion, early postoperative PVP elevation to 20 mm of Hg or more was associated with rapid graft hypertrophy, higher peripheral blood HGF levels, and lower portal VEGF levels; and with a poor outcome, graft dysfunction with hyperbilirubinemia, coagulopathy, and severe ascites. Adequate liver regeneration requires an adequate increase in portal venous pressure and flow reflected by clearance of HGF and elevated VEGF levels.  相似文献   
113.
114.
Summary A case of a solid parotid tumour in a 16-year-old boy is presented. Histologically, the tumour demonstrated some peculiar findings. An acinar pattern was predominant although every component seen in the normal salivary gland was present, namely, serous and mucous gland acini, ducts, myoepithelial cells, adipose and lymphoid tissue. Large eosinophilic granules were abundant in the large acinar cell cytoplasm. Immunohistochemically, the tumour demonstrated the proteins which are present in the normal parotid gland, for example, amylase, lactoferrin and lysozyme. Electron microscopic features were quite similar to those of normal parotid tissue except for accumulation of a large number of cytoplasmic granules in the acinar cells. There has been no previous report of a tumour with the same features as seen in this case. Our pathological diagnosis is hamartoma, although the possibility of hyperplasia or neoplasia can not be excluded.  相似文献   
115.
This study was conducted to compare the midline incision right retroperitoneal approach for repairing abdominal aortic aneurysms (AAA) with the transperitoneal approach. The intra- and postoperative course of 15 patients who underwent AAA repair using the transperitoneal approach between 1987 and 1991 and another 15 patients who underwent AAA repair using the retroperitoneal approach between 1991 and 1994 were evaluated. The incidence of postoperative wound complications was also assessed. There was no operative or hospital death in either group. Although a significantly longer interval was required from the incision to the aortic clamp using the extraperitoneal method, there were no statistical differences in the aortic clamping time, total operation time, or blood loss between the two groups. On the other hand, there was a statistically significant improvement in bowel function and a significant reduction in the length of postoperative hospitalization following the extraperitoneal procedure. Furthermore, no wound complications such as those associated with the left flank incision developed after the extraperitoneal procedure. Thus, we recommend the midline incision right retroperitoneal approach for AAA as it does not involve muscle division and is associated with fewer complications.  相似文献   
116.
Recent genetic and molecular technology have shown that genetic abnormalities related to the cardiac ion channels can be a cause of some hereditary arrhythmic diseases. Until now, advanced analysis has proceeded especially in congenital long QT syndrome, and six different subtypes have been identified in Romano-Ward syndrome and 2 subtypes in Jervell & Lange-Nielsen syndrome. Since the mechanism of QT interval prolongation in each subtype is based on the malfunction of different cardiac ion channels, the same pharmacological treatment may show different antiarrhythmic effects for each subtype. In this paper, we review some of the hereditary arrhythmic diseases and discuss the possibility of gene-specific treatment in such diseases.  相似文献   
117.
CTGF/CCN2, a hypertrophic chondrocyte-specific gene product, possessed the ability to repair damaged articular cartilage in two animal models, which were experimental osteoarthritis and full-thickness defects of articular cartilage. These findings suggest that CTGF/CCN2 may be useful in regeneration of articular cartilage. INTRODUCTION: Connective tissue growth factor (CTGF)/CCN2 is a unique growth factor that stimulates the proliferation and differentiation, but not hypertrophy, of articular chondrocytes in vitro. The objective of this study was to investigate the therapeutic use of CTGF/CCN2. MATERIALS AND METHODS: The effects of recombinant CTGF/CCN2 (rCTGF/CCN2) on repair of damaged cartilage were evaluated by using both the monoiodoacetic acid (MIA)-induced experimental rat osteoarthritis (OA) model and full-thickness defects of rat articular cartilage in vivo. RESULTS: In the MIA-induced OA model, quantitative real-time RT-PCR assays showed a significant increase in the level of CTGF/CCN2 mRNA, and immunohistochemical analysis and in situ hybridization revealed that the clustered chondrocytes, in which clustering indicates an attempt to repair the damaged cartilage, produced CTGF/CCN2. Therefore, CTGF/CCN2 was suspected to play critical roles in cartilage repair. In fact, a single injection of rCTGF/CCN2 incorporated in gelatin hydrogel (rCTGF/CCN2-hydrogel) into the joint cavity of MIA-induced OA model rats repaired their articular cartilage to the extent that it became histologically similar to normal articular cartilage. Next, to examine the effect of rCTGF/CCN2 on the repair of articular cartilage, we created defects (2 mm in diameter) on the surface of articular cartilage in situ and implanted rCTGF/CCN2-hydrogel or PBS-hydrogel therein with collagen sponge. In the group implanted with rCTGF/CCN2-hydrogel collagen, new cartilage filled the defect 4 weeks postoperatively. In contrast, only soft tissue repair occurred when the PBS-hydrogel collagen was implanted. Consistent with these in vivo effects, rCTGF/CCN2 enhanced type II collagen and aggrecan mRNA expression in mouse bone marrow-derived stromal cells and induced chondrogenesis in vitro. CONCLUSION: These findings suggest the utility of CTGF/CCN2 in the regeneration of articular cartilage.  相似文献   
118.
We report a 47-year-old alcoholic man with alcoholic pellagra encephalopathy (APE) showing myoclonus and ataxia as chief complaints. He had been a heavy drinker for 30 years. He had noticed appetite loss and subsequently showed a subacutely progressive gait disturbance. He had no history of diarrhea, dementia, or dermatitis. On admission, he showed severe alcoholic liver cirrhosis with a large amount of ascites, limbs and truncal ataxia, myoclonus of the limbs and areflexia, although his consciousness was alert and there were no sign of dermatitis. Though the plasma level of ammonia was normal, we started administration of amino acids suspecting hepatic encephalopathy. Symptoms showed no improvement, and subsequent administration of thiamine was also ineffective. A decreased serum level of niacin was demonstrated. After administration of nicotinamide, the symptoms improved gradually. This patient received a diagnosis of APE. Endemic pellagra, characterized by the classical triad of dermatitis, diarrhea and dementia, is known to be caused by a dietary deficiency of the niacin, and has now become very rare in developed countries. At present, pellagra is encountered most often in patients with chronic alcoholism, which is called APE. APE patients often show only disturbance of consciousness. Although several reports has described ataxia and myoclonus in patients with APE, APE patients with myoclonus and ataxia as chief complaints have not previously been reported. On autopsy cases, central chromatolysis of neurons in the dentate nucleus of the cerebellum, gracile and cuneate nuclei, and the Clarke's column has been demonstrated. The APE patients would show myoclonus and ataxia as their first symptoms. In conclusion, we would like to emphasize that administration of niacin should be started for the treatment of chronic alcoholic patients showing myoclonus and ataxia even without the classical triads found in endemic pellagra patients.  相似文献   
119.
Adenoid cystic carcinoma, a relatively uncommon tumor of salivary glands, is characterized by a prolonged clinical course and a fatal outcome. The molecular events underlying their progression are unknown. In this study, we examined the methylation status of E-cadherin gene and its protein expression in 23 cases of adenoid cystic carcinoma and correlated the results with the clinicopathologic factors to determine its role in these tumors. We also analyzed the effect of 5-azacytidine on the re-expression in a methylated cell line of adenoid cystic carcinoma for this gene. In our study, E-cadherin immunoreactivity, although heterogeneous, showed a progressive reduction with high histological grade and in metastatic and recurrent lesions. Promoter methylation was detected in 16 of 23 cases (70%), but there was no correlation with the histological grade or patient prognosis. Microdissection of immuno-negative cells in heterogeneous tumors showed positive methlyation. In the cell line from salivary adenoid cystic carcinoma with methylated E-cadherin, 5-azacytidine restored the E-cadherin expression. Our results indicate that: (1) E-cadherin gene promoter is frequently methylated in adenoid cystic carcinoma, leading to reduced E-cadherin expression, (2) variable E-cadherin expression might result from the intratumoral heterogeneity, and (3) increased extent of methylated areas may be associated with progression and advancement of the disease.  相似文献   
120.
Background: A lung-protecting strategy is essential when ventilating acute lung injury/acute respiratory distress syndrome patients. Current emphasis is on limiting inspiratory pressure and volume. This study was designed to investigate the effect of peak inspiratory flow on lung injury.

Methods: Twenty-four rabbits were anesthetized, tracheostomized, ventilated with a Siemens Servo 300, and randomly assigned to three groups as follows: 1) the pressure regulated volume control group received pressure-regulated volume control mode with inspiratory time set at 20% of total cycle time, 2) the volume control with 20% inspiratory time group received volume-control mode with inspiratory time of 20% of total cycle time, and 3) the volume control with 50% inspiratory time group received volume-control mode with inspiratory time of 50% of total cycle time. Tidal volume was 30 ml/kg, respiratory rate was 20 breaths/min, and positive end-expiratory pressure was 0 cm H2O. After 6 h mechanical ventilation, the lungs were removed for histologic examination.

Results: When mechanical ventilation started, peak inspiratory flow was 28.8 +/- 1.4 l/min in the pressure regulated volume control group, 7.5 +/- 0.5 l/min in the volume control with 20% inspiratory time group, and 2.6 +/- 0.3 l/min in the volume control with 50% inspiratory time group. Plateau pressure did not differ significantly among the groups. Gradually during 6 h, Pao2 in the pressure regulated volume control group decreased from 688 +/- 39 to a significantly lower 304 +/- 199 mm Hg (P < 0.05) (mean +/- SD). The static compliance of the respiratory system for the pressure regulated volume control group also ended significantly lower after 6 h (P < 0.05). Wet to dry ratio for the pressure regulated volume control group was larger than for other groups (P < 0.05). Macroscopically and histologically, the lungs of the pressure regulated volume control group showed more injury than the other groups.  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