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   36147篇
  免费   1835篇
  国内免费   169篇
耳鼻咽喉   497篇
儿科学   698篇
妇产科学   405篇
基础医学   4893篇
口腔科学   879篇
临床医学   2406篇
内科学   9142篇
皮肤病学   770篇
神经病学   2408篇
特种医学   1425篇
外国民族医学   1篇
外科学   6264篇
综合类   198篇
一般理论   2篇
预防医学   952篇
眼科学   502篇
药学   2460篇
中国医学   118篇
肿瘤学   4131篇
  2023年   217篇
  2022年   439篇
  2021年   686篇
  2020年   390篇
  2019年   502篇
  2018年   665篇
  2017年   513篇
  2016年   670篇
  2015年   625篇
  2014年   918篇
  2013年   1061篇
  2012年   1795篇
  2011年   1877篇
  2010年   1093篇
  2009年   991篇
  2008年   1731篇
  2007年   1931篇
  2006年   1824篇
  2005年   1935篇
  2004年   1812篇
  2003年   1645篇
  2002年   1633篇
  2001年   1121篇
  2000年   1042篇
  1999年   1007篇
  1998年   477篇
  1997年   345篇
  1996年   343篇
  1995年   297篇
  1994年   245篇
  1993年   274篇
  1992年   682篇
  1991年   612篇
  1990年   575篇
  1989年   572篇
  1988年   563篇
  1987年   526篇
  1986年   482篇
  1985年   444篇
  1984年   337篇
  1983年   277篇
  1982年   177篇
  1979年   251篇
  1977年   195篇
  1973年   183篇
  1972年   192篇
  1971年   194篇
  1970年   180篇
  1969年   190篇
  1968年   170篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Introduction: One of the causes of pain during insertion of the colonoscope is stretching of the mesenterium by loop formation. The degree of pain differs according to the type of loop formation. Our aims were to study the accuracy of the colonoscopist’s assessment of the presence and type of loop formation and to study the degree of pain in relation to the type of loop by administering the visual analog scale (VAS). Methods: Two hundred and fifty‐seven consecutive patients were enrolled. All procedures were performed by two experienced colonoscopists who were blind to magnetic endoscope imaging view. After the colonoscopy, the colonoscopist was asked to assess the presence and type of loop formation. The degree of pain was assessed using the VAS. Results: The accuracy of estimating N loop, alpha loop, absence of loop formation and U loop was each over 70%. The accuracy of estimating gamma and splenic loop was significantly lower than the accuracy of estimating U loop. Colonoscopy was significantly more painful in women than in men. The degree of pain was significantly higher upon formation of reverse alpha loop and gamma and splenic loop than upon formation of N loop and U loop. Conclusions: Upon formation of reverse alpha loop or gamma and splenic loop, patients experienced more pain and it was difficult for the endoscopists to assess these loops. As women had severe pain compared with men, the use of a pediatric colonoscope or higher dosage of sedation in women should be considered.  相似文献   
62.
We reported a case of X-linked lymphoproliferative syndrome (XLP) with multiple nodular lesions in the brain and lungs. A 21-year-old man was admitted because of one month history of low grade fever, headache, nausea, and amnesia. He developed agammaglobulinemia following Epstein-Barr virus infection at 3-year-old, and thereafter was administered 7.5g of immunoglobulin every 3 weeks with a diagnosis of XLP. Physical examination was unremarkable on admission. Neurological examination revealed disorientation of time, and bilateral gaze-evoked nystagmus. Neuropsychological tests demonstrated impairment of recent memory and calculation. Pleocytosis (83/microl) and increase of protein (1269 mg/dl) and IgG (141 mg/dl) in the CSF were observed. Brain MRI showed multiple nodular lesions with high intense signal on T2-weighted images and Gd-DTPA enhancement on T1-weighted images. Chest CT showed multiple nodular lesions in the bilateral lungs. The needle lung biopsy was performed, which showed infiltration of lymphocytes around the vessels. An immunohistochemical study showed that the infiltrating cells were mainly CD8 positive T lymphocytes. B lymphocyte and plasma cells were not seen. The histological findings excluded intravascular malignant lymphoma and lymphomatoid granulomatosis. Therefore we diagnosed lymphoid vasculitis. The patient developed pancytopenia caused by hemophagocytic syndrome 48 days after admission and was treated with 1 g of methylprednisolone per day for 3 days and a tapered dose of steroid (500 mg to 125 mg of methylprednisolone and 60 mg to 10mg of predonisolone) for 21 days, which resulted in the improvement of clinical features (hemophagocytic syndrome and central nervous system symptoms) and the abnormal CSF findings. The multple nodular lesions in the brain and the lungs shrank 1 month after treatment and disappeared 11 months later. There are few reports concerning lymphoid vasculitis with XLP, and no effective treatment has been described. Our case suggests that steroid therapy may be useful for the treatment of lymphoid vasculitis in XLP.  相似文献   
63.
BACKGROUND: Myocardial perfusion single photon emission computed tomography (SPECT) occasionally fails to detect coronary stenosis in patients with coronary artery disease (CAD). We evaluated coronary flow reserve (CFR) using oxygen 15-labeled water in areas with and without ischemia on technetium 99m tetrofosmin stress perfusion SPECT in patients with angiographically documented CAD. METHODS AND RESULTS: Twenty-seven patients with CAD and eleven age-matched normal subjects were studied. Baseline myocardial blood flow (MBF) and MBF during hyperemia induced by intravenous adenosine triphosphate infusion (0.16 mg. kg(-1). min(-1)) were determined with the use of O-15-labeled water positron emission tomography, and the CFR was calculated. Tc-99m tetrofosmin stress/rest SPECT was performed for comparison. On the basis of the results of coronary angiography and SPECT, coronary segments were divided into 3 types: segments with coronary stenosis and a perfusion abnormality on stress SPECT imaging (group A, n = 16), segments with coronary stenosis without a perfusion abnormality (group B, n = 42), and remote segments with no coronary stenosis or perfusion abnormality (group C, n = 18). Baseline MBF values were similar among the 3 groups. CFR in group A was lower (1.82 +/- 0.54) than in group B (2.22 +/- 0.87, P <.05), in group C (2.92 +/- 1.21, P <.01), and in normal segments (3.86 +/- 1.24, P <.001). CFR in group B was lower than in group C (P <.02) and in normal segments (P <.001). CFR in group C was lower than in normal segments (P <.02). CONCLUSIONS: Areas with a perfusion abnormality on stress SPECT had reduced CFR. In the areas without a perfusion abnormality and with coronary stenosis, lowering of CFR was intermediate between the areas with a perfusion abnormality and remote segments. Moreover, CFR was slightly, but significantly, lower in remote segments in patients with CAD compared with normal segments.  相似文献   
64.
65.
The excitatory responses of deflationary slowly adapting pulmonary stretch receptor (SAR) activity to lung deflation ranging from approximately -15 to -25 cm of H(2)O for approximately 5 s were examined before and after administration of flecainide, a Na(+) channel blocker, and K(+) channel blockers, such as 4-aminopyridine (4-AP) and tetraethylammonium (TEA). The experiments were performed in anesthetized, artificially ventilated rats after unilateral vagotomy. The deflationary SARs increased their activity during lung deflation and its effect became more pronounced by increasing the degree of negative pressure. During lung deflation the average values for the deflationary SAR adaptation index (AI) were below 40%. Intravenous administration of veratridine (50 microg/kg), an Na(+) channel opener, stimulated deflationary SAR activity: one maintained excitatory activity mainly during deflation and the other receptors showed a tonic discharge during both deflation and inflation. Despite the difference in deflationary SAR firing patterns after veratridine administration, flecainide treatment (6.0 mg/kg) blocked veratridine-induced deflationary SAR stimulation and also caused strong inhibition of the excitatory responses of deflationary SARs to lung deflation. Under these conditions, the average values for deflationary SAR AI were over 90%. The responses of deflationary SARs and deflationary SAR AI to lung deflation were not significantly altered by pretreatment with either 4-AP (0.7 and 2.0 mg/kg) or TEA (2.0 and 6.0 mg/kg). These results suggest that the excitatory effect of lung deflation on deflationary SAR activity is mediated by the activation of flecainide-sensitive Na(+) channels on the nerve terminals of deflationary SARs.  相似文献   
66.
Pepsinogens are acid protease enzymes of pepsin usually found in gastric mucosa. In the present study, we demonstrated the presence of pepsinogen isozymes in male Syrian golden hamster lung tissues by a combined immunohistochemical and biochemical approach. Immunohistochemically, using rat pepsinogen 1 antibody, pepsinogen positive cells were observed mainly in the epithelia of the terminal bronchioles. They demonstrated morphological features of Clara cells. The pepsinogen isozyme pattern of lung tissue determined by polyacrylamide gel electrophoresis was similar to that of stomach mucosa. Treatment of hamsters with polychlorinated biphenyls at a dose of 500 mg/kg body weight ip caused a 2.8-fold increase in pepsinogen content (p less than 0.01) as well as increase in numbers of pepsinogen positive cells in the lung.  相似文献   
67.
The core sequence of the enhancer of murine leukemia virus (MuLV) long terminal repeat is highly conserved in a large number of MuLV strains and appears to play an essential role when SL3-3 or Moloney strains induce T cell lymphoma in mice. We found by using the electrophoretic mobility shift assay that a polyomavirus enhancer core-binding protein, PEBP2, bound to this core motif of MuLV. We also noted that PEBP2 in several hematopoietic cell lines derived from B lymphocyte, macrophage and myelocyte lineages migrated significantly faster than the authentic PEBP2 detected in NIH3T3 (ibroblasts. Interestingly, PEBP2 detected in the cell lines of T lymphocyte lineage appeared to contain both types, which were indistinguishable in electrophoretic mobility from those of NIH3T3 and of B lymphocyte, macrophage and myelocyte lineages. The treatment of the nuclear extract containing PEBP2 with phosphatase generated PEBP3, which is a subcomponent of PEBP2 and retained the same DNA-binding specificity as PEBP2. The altered mobility of hematopoietic cell-derived or T lymphocyte-derived PEBP2 was found to be due to the alteration of the mobility of PEBP3. Based on the distinct mobility of PEBP2/3 of T lymphocytes from those of other hematopoietic cells, we discuss the implication of PEBP2 in MuLV-induced T cell leukemia and T cell-specific gene expression.  相似文献   
68.
A 52-year-old woman who had had 6 months of chemotherapy using mitomycin C and cisplatin for cervical cancer presented with hemolytic uremic syndrome. Conventional plasmapheresis using whole-plasma fraction was ineffective. However, plasmapheresis using the cryosupernatant fraction dramatically improved symptoms of hemolytic anemia and thrombocytopenia in this case. The activity of factor VIII in the cryosupernatant fraction of plasma as a replacement fluid decreased after removal of cryoprecipitate, indicating effective removal of von Willebrand factor. The pathogenesis of her hemolytic uremic syndrome may have been associated with von Willebrand factor multimers contained in the cryoprecipitate of plasma. Similar use of the cryosupernatant fraction of plasma could not be found in other reports of cases of hemolytic uremic syndrome. Plasmapheresis using the cryosupernatant fraction of plasma may improve refractory hemolytic uremic syndrome.  相似文献   
69.
Protein kinase C (PKC) activity was measured in rat brain with 2 h of middle cerebral artery (MCA) and common carotid artery (CCA) occlusion, using dual autoradiography of [14C]iodoantipyrine (IAP) and [3H]phorbol-12,13-dibutyrate (PDBu). In the ischemic brain, it required more than 120 min of incubation to obtain a plateau in PDBu binding. In contrast, the binding of PDBu in non-ischemic brain reached a plateau with incubation for 60 min. This delay of PDBu binding in the ischemic brain suggests that the affinity of this ligand is reduced due to a change in structure of the cell membrane caused by ischemia. PDBu binding in the ischemic brain increased significantly compared to the non-ischemic brain. This finding provides further evidence that excessive activation of PKC in the ischemic brain may play an important role in ischemic neuronal damage. ©1997 Elsevier Science B.V. All rights reserved.  相似文献   
70.
A case of hepatic infarction with portal thrombosis is reported. A 63-year-old woman with liver cirrhosis and esophageal varices was admitted for treatment of the esophagel varices. Endoscopic variceal ligation (EVL) and endoscopic injection sclerotherapy (EIS) were performed. Two months later, she experienced right hypochondralgia and right flank pain. Serum transaminase levels were suddenly elevated, and computed tomography scans of the liver showed multiple small nodular lesions. Her condition worsened, and she died of hepatic failure. Autopsy revealed splenic and portal vein thrombosis, multiple hepatic infarction, and evidence of chronic pancreatitis. We believe that liver cirrhosis and chronic pancreatitis were the main risk factors for the portal thrombosis, and the treatment for esophageal varices appeared to have triggered the thrombosis. The hepatic infarction was caused by the portal thrombosis.  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