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   42840篇
  免费   2052篇
  国内免费   190篇
耳鼻咽喉   691篇
儿科学   803篇
妇产科学   783篇
基础医学   5549篇
口腔科学   1256篇
临床医学   2978篇
内科学   10101篇
皮肤病学   569篇
神经病学   3437篇
特种医学   1503篇
外科学   7475篇
综合类   193篇
一般理论   2篇
预防医学   1540篇
眼科学   735篇
药学   3549篇
中国医学   81篇
肿瘤学   3837篇
  2023年   213篇
  2022年   458篇
  2021年   769篇
  2020年   376篇
  2019年   551篇
  2018年   657篇
  2017年   509篇
  2016年   608篇
  2015年   678篇
  2014年   878篇
  2013年   1142篇
  2012年   1818篇
  2011年   1967篇
  2010年   1119篇
  2009年   977篇
  2008年   1831篇
  2007年   2040篇
  2006年   1951篇
  2005年   1914篇
  2004年   1879篇
  2003年   1884篇
  2002年   1821篇
  2001年   1627篇
  2000年   1784篇
  1999年   1513篇
  1998年   500篇
  1997年   395篇
  1996年   372篇
  1995年   317篇
  1994年   294篇
  1993年   260篇
  1992年   1109篇
  1991年   924篇
  1990年   901篇
  1989年   947篇
  1988年   832篇
  1987年   833篇
  1986年   782篇
  1985年   771篇
  1984年   528篇
  1983年   425篇
  1982年   220篇
  1979年   483篇
  1978年   275篇
  1977年   253篇
  1975年   207篇
  1974年   224篇
  1971年   230篇
  1969年   230篇
  1968年   216篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
A 13-year-old girl who had severe brain damage due to unknown prenatal cause presented rhabdomyolysis triggered by a mild viral infection. Her muscle biopsy revealed mild variation in fiber size and type 2 fiber atrophy without excess lipid storage. Biochemical analysis of the biopsied material showed decreased carnitine palmitoyltransferase (CPT) activity (15% of the control). Serum and urinary carnitine levels were normal. Skeletal muscle CT scanning showed multiple low density spots. The patient was diagnosed as having CPT deficiency. She recovered from rhabdomyolysis without renal failure after a month with conservative therapy. CPT deficiency is usually found in young healthy persons. This is the first case report of CPT deficiency which presented severe psychomotor retardation since neonatal period.  相似文献   
42.
Febrifugine and isofebrifugine alkaloid mixtures extracted from the leaves and buds of Hydrangea macrophylla var. Otaksa, collected during different months, in Japan, were quantified using high-performance liquid chromatography. Leaves collected during the flowering season, namely from June to August, contained 0.16–0.31 mg/g of the alkaloid mixture, whereas those collected from September to December had less than 0.03 mg/g of the mixture. However, extracts of buds harvested from October to February contained a consistently larger amount (more than 0.49 mg/g) of the alkaloids. Hot-water extracts from the leaves and buds collected during different seasons were evaluated for antimalarial activity against Plasmodium yoelii 17XL in mice. The extract of leaves collected in August demonstrated high antimalarial activity, and all mice that received the extract survived the infection. In contrast, the extract of leaves collected in December showed little activity. The extract of buds collected in December cleared parasites, but with subsequent mortality to mouse. The present results show that the amount of antimalarial agent—febrifugine and isofebrifugine mixture—in H. macrophylla var. Otaksa is both part- and season-dependent, suggesting that the choice of plant parts and their harvesting season are important factors worth considering in the pharmacological use of medicinal plants.  相似文献   
43.
With the development of fast scan techniques and technical advances in software, cardiac MRI can now be used for morphological and functional evaluation of the heart with good reliability and high spatial and temporal resolution. Cardiac MRI is employed at many institutions, mainly for assessing ischemic heart disease. Cardiac MRI can be used to identify coronary artery stenosis, evaluate myocardial viability, assess left ventricular wall motion and function, measure coronary blood flow and flow reserve, and obtain other useful information for the diagnosis of ischemic heart disease in a single examination, serving as a true comprehensive cardiac study. With regard to the evaluation of coronary artery stenosis, new techniques, such as whole-heart coronary MRA, permit visualization of the coronary arteries to their peripheral branches without contrast agent. Good results have been reported for whole-heart MRA as compared with X-ray coronary angiography (CAG). Attempts to evaluate plaque characteristics by visualizing the walls of the coronary arteries have also been reported recently. Technical improvements have been made in myocardial perfusion MRI to detect myocardial ischemia and in delayed contrast-enhanced MRI to assess myocardial viability, and some researchers have recently reported that the diagnostic capabilities of these techniques match or surpass those of cardiac nuclear medicine studies. We outline the features of the latest MR imaging techniques for the diagnosis of ischemic heart disease, discuss their practical applications, and compare them with other imaging modalities.  相似文献   
44.
Background: Buried bumper syndrome (BBS) is a rare complication of percutaneous endoscopic gastrostomy (PEG). Along with the widespread use of the button‐type kit, BBS is encountered frequently. Methods: In the present study, we examined causes and treatments for BBS among 1400 patients who had undergone PEG. Results: The causes of BBS after PEG were classified into two categories: early causes consisted of wound infection, inappropriate size of kit and severe lordosis, while late causes were inappropriate exchange of kit, rough management or weight gain. The treatments for BBS could be determined by the degree of wound infection, fistula and burial of the bumper. Conclusion: We prepared a flowchart for replacement, by which BBS can be managed safely and quickly without surgical or endoscopic intervention.  相似文献   
45.
OBJECTIVES: Laparoscopic surgery for kidney treatment is a common procedure. However, the efficacy of this procedure in patients with several comorbidities has not been well investigated. We conducted a retrospective comparison of results of laparoscopic surgery between patients with several comorbidities and patients with no comorbidity to access the efficacy and safety of this procedure. METHODS: The subjects were 20 patients with three or more comorbidities (group A) and 46 patients with less than three comorbidities (group B). These 66 patients were 48 men and 18 women with a mean age of 62.3 years (age range, 24-83 years). The data from these two groups were compared for American Society of Anesthesiology (ASA) physical status score, previous surgical history, duration of surgery, estimated blood loss, tumor size, complications during and after surgery, conversion rates, time to oral intake, and length of hospital stay. RESULTS: The initial ASA score and age were significantly higher for the patients with comorbidities (P < 0.0001, P = 0.0008, respectively). All other variables before, during, and after surgery were similar for both laparoscopic groups. However, the incidence of atelectasis of laparoscopy was higher than that of open surgery. CONCLUSIONS: Laparoscopic nephrectomy for patients with comorbidities is safe and minimally invasive. Further investigation to prevent atelectasis is necessary.  相似文献   
46.
The presence of blood in the ejaculate is called hematospermia or hemospermia. While often perceived as a symptom of little significance, hematospermia can cause great concern to men who experience it. We report an unusual case of hematospermia associated with pelvic arteriovenous malformation (AVM). A 60-year-old man who visited our hospital complaining of hematospermia and pollakisuria was found to have AVM and aneurysmal changes in the left side of the pelvis using computed tomography (CT). The patient was treated with steel coil embolization of the left inferior gluteal artery, and after the procedure the hematospermia and pollakisuria remained absent without flare-ups.  相似文献   
47.
BACKGROUND: The objective of this study was to evaluate the clinical outcome after surgical management of renal cell carcinoma (RCC) extending to the inferior vena cava (IVC). METHODS: This study included a total of 55 patients (41 men and 14 women; mean age, 59.3 years) with RCC (39 right- and 16 left-sided tumors) involving the IVC, who underwent radical nephrectomy and tumor thrombectomy between 1983 and 2005 at a single institution in Japan. The level of thrombus was classified as follows: level I, infrahepatic; level II, intrahepatic; level III, suprahepatic; and level IV, extending to the atrium. Clinicopathological data from these patients were retrospectively reviewed to identify factors associated with survival. RESULTS: There were 11 and 18 patients who were diagnosed as having lymph node and distant metastases, respectively. Twenty-two patients had tumor thrombus in level I, 20 in level II, 10 in level III, and 3 in level IV. Pathological examinations demonstrated that 34 and 21 patients had clear cell carcinoma and non-clear cell carcinoma, respectively, 42, 9 and 4 were pT3b, pT3c and pT4, respectively, and 6, 35 and 14 were Grades 1, 2 and 3, respectively. Cancer-specific 1-, 3- and 5-year survival rates of these 55 patients were 74.5%, 51.4% and 30.3%, respectively. Among several factors examined, clinical stage (P = 0.047), lymph node metastasis (P = 0.016), histological subtype (P = 0.034) and tumor grade (P < 0.001) were significantly associated with cancer-specific survival by univariate analysis. Furthermore, multivariate analysis demonstrated clinical stage (P = 0.037) and tumor grade (P < 0.001) as independent predictors of cancer-specific survival irrespective of other significant factors identified by univariate analysis. CONCLUSIONS: In patients with RCC involving the IVC, biological aggressiveness characterized by tumor grade rather than tumor extension would have more potential prognostic importance; therefore, more intensive multimodal therapy should be considered in patients with high grade RCC with tumor thrombus extending into the IVC.  相似文献   
48.
BACKGROUND: Oral submucous fibrosis (OSF) is a chewing habit-related pre-cancerous condition of the oral mucosa affecting predominantly south Asians. It is histopathologically characterized by epithelial atrophy and fibrosis of the subepithelial connective tissue. Fibrosis extends all the way into the muscle layer, leading to difficulty in mouth opening. However, the dynamics of extracellular matrix (ECM) remodeling with OSF progression is largely unknown. METHODS: Forty biopsy specimens of OSF and 10 of normal buccal mucosa were examined for expression/deposition modes of eight ECM molecules by histochemistry, immunohistochemistry, and in situ hybridization. RESULTS: In the early stage of OSF, tenascin, perlecan, fibronectin, collagen type III were characteristically enhanced in the lamina propria and the submucosal layer. In the intermediate stage, the ECM molecules mentioned above and elastin were extensively and irregularly deposited around muscle fibers. In the advanced stage, such ECM depositions decreased and were entirely replaced with collagen type I only. Their gene expression levels varied with progression of fibrosis, but the mRNA signals were confirmed in fibroblasts in the submucosal fibrotic areas. CONCLUSIONS: The results indicate that the ECM remodeling steps in OSF are similar to each phase of usual granulation tissue formation. Restricted mouth opening may be a result of loss of variety of ECM molecules including elastin into the homogeneity of collagen type I replacing muscle fibers.  相似文献   
49.
The immunohistochemical localization of manganese (Mn)-superoxide dismutase (Mn-SOD) was studied in the rat basal forebrain using polyclonal antibodies to Mn-SOD. Neurons of the basal forebrain exhibit a high density of Mn-SOD immunoreactivity. Double immunostaining with a monoclonal antibody to choline acetyltransferase demonstrated that both cholinergic and non-cholinergic neurons in the basal forebrain are intensely immunoreactive for Mn-SOD.  相似文献   
50.
Y Yoshiike  S Suzuki  Y Watanuki    T Okubo 《Thorax》1995,50(2):139-142
BACKGROUND--The effects of beta 2 adrenergic agonists on chemoreceptors remain controversial. This study was designed to examine whether fenoterol, a beta 2 adrenergic agonist, increases the ventilatory responses to hypercapnia (HCVR) and hypoxia (HVR) in normal subjects. METHODS--HCVR was tested with a rebreathing method and HVR was examined with a progressive isocapnic hypoxic method in 11 normal subjects. Both HCVR and HVR were assessed by the slope of occlusion pressure (P0.1) or ventilation (VE) plotted against end tidal carbon dioxide pressure and arterial oxygen saturation, respectively. Respiratory muscle strength, spirometric values and lung volume were measured. After a single oral administration of 5 mg fenoterol or placebo HCVR and HVR were evaluated. RESULTS--Fenoterol treatment did not change the specific airway conductance or forced expiratory volume in one second. Respiratory muscle strength did not change. Fenoterol increased the slope of the HCVR of both P0.1 (from 0.251 (0.116) to 0.386 (0.206) kPa/kPa, average increase 71%) and VE (from 10.7 (3.4) to 15.1 (4.2) l/min/kPa, average increase 52%), and shifted the response curves to higher values. For the HVR fenoterol increased the slopes of both P0.1 and VE (from -4.06 (2.00) x 10(-3) to -7.99 (4.29) x 10(-3) kPa/%, an average increase of 83%, and from -0.221 (0.070) to -0.313 (0.112) l/min/%, a 44.5% increase, respectively), and shifted the response curves to higher values. CONCLUSION--Acute administration of fenoterol increases the ventilatory responses to both hypercapnia and hypoxia in normal subjects.  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