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   1619篇
  免费   92篇
  国内免费   3篇
耳鼻咽喉   8篇
儿科学   53篇
妇产科学   49篇
基础医学   252篇
口腔科学   27篇
临床医学   95篇
内科学   263篇
皮肤病学   31篇
神经病学   115篇
特种医学   20篇
外科学   152篇
综合类   42篇
一般理论   1篇
预防医学   130篇
眼科学   134篇
药学   205篇
中国医学   9篇
肿瘤学   128篇
  2023年   9篇
  2022年   18篇
  2021年   70篇
  2020年   46篇
  2019年   41篇
  2018年   36篇
  2017年   43篇
  2016年   38篇
  2015年   52篇
  2014年   82篇
  2013年   100篇
  2012年   142篇
  2011年   146篇
  2010年   79篇
  2009年   50篇
  2008年   116篇
  2007年   103篇
  2006年   84篇
  2005年   86篇
  2004年   96篇
  2003年   78篇
  2002年   64篇
  2001年   13篇
  2000年   10篇
  1999年   5篇
  1998年   13篇
  1997年   8篇
  1996年   6篇
  1995年   11篇
  1994年   10篇
  1993年   8篇
  1992年   7篇
  1991年   3篇
  1990年   3篇
  1988年   5篇
  1987年   2篇
  1986年   3篇
  1985年   2篇
  1984年   5篇
  1983年   3篇
  1982年   1篇
  1980年   3篇
  1979年   3篇
  1978年   2篇
  1975年   3篇
  1974年   1篇
  1973年   1篇
  1970年   1篇
  1969年   1篇
  1966年   1篇
排序方式: 共有1714条查询结果,搜索用时 15 毫秒
1.
Gallstones are common and their incidence increases with age.1 Fifty per cent of these stones are in the common bile duct (CBD) in the elderly.2 Most of them are silent but with time there is an increasing chance of developing symptoms which are more likely to be serious in the elderly.3 Failure to relieve mechanical obstruction of bile flow may lead to secondary biliary cirrhosis.4 It has been estimated that on average secondary biliary cirrhosis develops some seven years after the onset of obstruction from a stricture, four and half years after gallstone obstruction and 10 months after the onset of malignant stricture.5 The characteristic features are the pathological findings of portal-portal linkages, with a pattern of monolobular cirrhosis and the preservation of normal vascular relationships.6 Secondary biliary cirrhosis may lead to hepatic insufficiency and portal hypertension with the resultant complications, such as bleeding oesophageal varices, hypersplenism with pancytopenia, ascites and encephalopathy. We describe a patient in whom the diagnosis was not suspected until laparotomy and confirmed only at autopsy.  相似文献   
2.
At the present time fine-needle aspiration (FNA) is considered a routine diagnostic procedure in evaluating neoplastic vs. nonneoplastic lesions in many organs, with high sensitivity and specificity. The purpose of this study was to assess the utility of FNA in areas of diagnostic difficulty and its limitations in evaluating bone lesions in patients with a previous history of malignancy. From 1989 to 2000, 249 CT-guided FNAs of bone lesion were performed at our institutions; 187/249 (75.1%) patients had a previous history of malignancy. Aspirated material was air-dried for Diff-Quik stain or fixed in ethanol for Papanicolaou staining. Subsequent surgical tissue was available in 69/187 (36.9%) of the cases. There were 114 males and 73 females, ages 14-86 yr (mean, 64 yr). The primary tumor site was lung 49, genitourinary 46, breast 31, gastrointestinal 28, hematopoietic 26, soft tissue/skin 5, and thyroid 2. There were 125 FNAs of the vertebral spine, 19 from the pelvis, 11 from the ribs, 9 from the sternum, 5 from the femur, and 18 from miscellaneous bone sites. Out of 187, 166 (88.7%) were malignant aspirates confirming the patients' primary malignancies. The most common malignancy encountered was adenocarcinoma, 126/187 (67.4%). Surgical tissue was available for review in 69 patients and the results were in agreement with the FNAs diagnosis in all cases. Nine out of 187 (4.8%) cases were diagnosed as marrow elements on cytological material. These patients have been followed for 1-9 yr and have failed to reveal signs or symptoms of clinical recurrence. Three out of 187 (1.6%) cases showed osteomyelitis. Nine out of 187 (4.8%) were unsatisfactory specimens, with biopsy follow-up available in four cases, showing three metastatic tumors and one case of osteomyelitis. FNA of metastatic bone lesions is a major step in pretreatment diagnosis. On satisfactory specimens, the cytological diagnosis viewed in the clinical-radiological context proves to be similar to surgical diagnosis. FNA is an excellent technique with a high accuracy rate in assessing metastatic bone lesions.  相似文献   
3.
A 4(1/2)-yr-old female presented with right-sided pleural effusion and a retroperitoneal mass. Cytologic analysis of the pleural fluid yielded malignant small round blue cells, which were noncohesive, 3-4 times the size of lymphocytes. The malignant cells had hyperchromatic, pleomorphic nuclei with moderate amounts of vacuolated cytoplasm. A few fiber-shaped cells were also seen. Immunostains for desmin, muscle-specific actin were positive; ultrastructural findings of thick and thin actin-myosin filaments confirmed the diagnosis of embryonal rhabdomyosarcoma. This case illustrates the importance of performing appropriate immunohistochemical stains and ultrastructural studies on cytological material to arrive at a definitive diagnosis.  相似文献   
4.
Movements by a standing person are commonly associated with adjustments in the activity of postural muscles to cause a desired shift of the center of pressure (COP) and keep balance. We hypothesize that such COP shifts are controlled (stabilized) using a small set of central variables (muscle modes, M-modes), while each M-mode induces changes in the activity of a subgroup of postural muscles. The main purpose of this study has been to explore the possibility of identification of muscle synergies in a postural task using the framework of the uncontrolled manifold (UCM) hypothesis employing the following three steps in data analysis: (i) Identification of M-modes: Subjects were asked to release a load from extended arms through a pulley system, resulting in a COP shift forward prior to load release. Electromyographic (EMG) activity of eleven postural muscles on one side of the body was integrated over a 100 ms interval corresponding to the early stage of the COP shift, and subjected to a principal component (PC) analysis across multiple repetitions of each task. Three PCs were identified and associated with a push-back M-mode, a push-forward M-mode and a mixed M-mode. (ii) Calculation of the Jacobian of the system, which relates changes in the magnitude of M-modes to COP shifts using regression techniques: Subjects performed three different tasks (releasing different loads at the back, voluntarily shifting body weight forward and backward, at different speeds) to verify if the relationship between magnitudes of M-modes and COP shifts is task or direction specific. (iii) UCM analysis: Three tasks were chosen (load release in the front, arm movement forward and backward) which were associated with an early shift in COP. A manifold was identified in the M-mode space corresponding to a certain average (across trials) shift of the COP and variance per degree of freedom within the UCM (VUCM) and orthogonal (VORT) to the UCM was computed. Across subjects, VUCM was significantly higher than VORT when analysis at the third step was performed using a Jacobian computed based on a set of tasks associated with a COP shift in the same direction but not in the opposite direction. This result confirms our hypothesis that the M-modes work together as a synergy to stabilize a desired shift of the COP. Forward and backward COP shifts are associated with different synergies based on the same three M-modes.An erratum to this article can be found at  相似文献   
5.
The recently isolated gene for neuroflbromatosls type 2 (NF2)encodes a 595 amlno acid protein, named merlin, which Is relatedto the cytoskeleton-assoclated proteins moesln, ezrin and radlxin.To Identify evolutionarily conserved regions and to providesequence Information necessary for the establishment of a mousemodel for NF2, we have determined the cDNA sequence of the mouseNF2 tumor suppressor gene, and mapped It In the mouse genome.Mouse merlin is a 596 amino acid protein, 98% identical to humanmerlin, but one amlno acid longer due to the Insertion of aproline residue near the C-terminus. Of the nine amlno aciddifferences between mouse and humans, seven occur in the C-termlnal20% of the protein, far from the protein 4. 1 domain that definesthis family. Two of the NF2 cDNA clones reveal evidence of alternativesplicing events that alter the predicted merlin product, oneremoving a 45 amlno acid segment from the middle section ofthe protein and the other changing the C-terminus. The existenceof several different forms of merlin potentially with differentprimary roles will complicate the Identification of the precisefunction that must be disrupted to cause the NF2-assoclatedtumors. The mouse NF2 homologue maps to Chr 11, in a regionhomologous to human Chr 22, but devoid of any mouse mutationswhich could be models of the human disorder.  相似文献   
6.
Background: Posttraumatic stress disorder (PTSD) is common in refugees but its association with longer-term psychosocial dysfunction remains unclear. We examined whether a subgroup of refugees with comorbid PTSD and depression were at particularly high risk of disability. We also investigated whether specific trauma experiences were linked to this comorbid pattern. Methods: Consecutive Bosnians (and one or two compatriots nominated by them) were recruited from a community centre, yielding a total sample of 126 participants (response rate 86%). Measures included a trauma inventory, the Clinician Administered PTSD Scale (CAPS) (Blake et al., 1995) and the depression module of the Structured Clinical Interview (SCID) (First et al., 1997). Results: Three diagnostic groupings emerged: normals (n=39), pure PTSD (n=29), and comorbid PTSD and depression (n=58). Of four trauma dimensions derived from principle components analysis (human rights violations, dispossession and eviction, life threat and traumatic loss), life threat alone was associated with pure PTSD, with life threat and traumatic loss both being associated with comorbidity. Compared to normals and those with pure PTSD, the comorbid group manifested more severe PTSD symptoms as well as higher levels of disability on all indices (global dysfunction: odds RATIO=5.0, P<0.001, distress: odds RATIO=6.0, P<0.001, social impairment: odds ratio 5.9, P<0.001, and occupational disability: odds ratio 5.0, P<0.001). Limitations: Recruitment was not random, the sample size was modest, and trauma event endorsement was based on retrospective accounts. Conclusions: The combination of life threat and traumatic loss may be particularly undermining to the psychological well-being of refugees and consequent comorbidity of PTSD and depression may be associated with longer-term psychosocial dysfunction. The findings raise the question whether the comorbid pattern identified should be given more recognition as a core posttraumatic affective disorder.  相似文献   
7.
It is well established that the activation of T lymphocytes by mitogen/antigen is accompanied by a rise in intracellular free calcium ([Ca2+]i), changes in membrane potential, metabolism of inositol phospholipid, and activation of protein kinase C. Theseearly events of signal transduction culminate inlate events of lymphocyte activation, namely, DNA synthesis, lymphokine production, and cellular proliferation. In this study we examined the effect of human immunodeficiency virus (HIV) on changes in membrane potential and [Ca2+]i levels. The membrane potentials were markedly decreased (depolarized) in T cell lines infected with HIV (H9/HTLV IIIb) and did not respond normally to phytohemagglutinin (PHA) or anti-T3 (anti-CD3) monoclonal antibody compared to uninfected H9 cell line. The basal [Ca2+]i levels in H9/HTLV IIIb cells were increased in comparison to those in H9 cells; however, there was very little further increase in [Ca2+]i in H9/HTLV IIIb cells following activation with PHA or anti-T3 monoclonal antibody. This is in contrast to a significant rise in [Ca2+]i in H9 cells following similar stimulation. These data demonstrate abnormalities in the plasma membrane potential and [Ca2+]i levels in chronically infected T cells with HIV. These abnormalities in signal transduction of the T-cell activation pathway could be responsible for T-cell dysfunction in patients with HIV infection.  相似文献   
8.
9.
10.
Endoscopic biopsies obtained from 275 patients (180 from the upper gastrointestinal tract and 95 from the lower gastrointestinal tract) were studied to compare the accuracy of biopsy imprint cytology and histology in the diagnosis of gastrointestinal lesions, and also to establish the degree of reliability of imprint cytology alone for an early diagnosis of malignancy. Biopsy histology results were found to be correct in 100% cases. Imprint cytology had an overall accuracy of 100%, 96.7%, 95.8% and 95.8% for the diagnosis of malignancies of the oesophagus, stomach, duodenum and colorectum respectively. False negative results were obtained with lymphomas. Regenerative cellular atypia was an important cause for false positive results. It was concluded that imprint cytology can serve as a useful and simple tool for an immediate diagnosis of malignancy. This should be subsequently correlated with histopathology which facilitates exact tumour typing and assessment of tumour invasion.  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