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   815篇
  免费   24篇
  国内免费   2篇
耳鼻咽喉   5篇
儿科学   68篇
妇产科学   10篇
基础医学   144篇
口腔科学   15篇
临床医学   108篇
内科学   168篇
皮肤病学   28篇
神经病学   8篇
特种医学   145篇
外科学   26篇
综合类   9篇
预防医学   39篇
眼科学   9篇
药学   34篇
肿瘤学   25篇
  2021年   8篇
  2019年   7篇
  2018年   8篇
  2016年   6篇
  2015年   10篇
  2014年   9篇
  2013年   14篇
  2012年   9篇
  2011年   21篇
  2010年   28篇
  2009年   21篇
  2008年   12篇
  2007年   12篇
  2006年   16篇
  2005年   11篇
  2003年   14篇
  2002年   6篇
  2001年   5篇
  2000年   6篇
  1999年   10篇
  1998年   35篇
  1997年   47篇
  1996年   47篇
  1995年   38篇
  1994年   20篇
  1993年   24篇
  1992年   10篇
  1991年   18篇
  1990年   15篇
  1989年   27篇
  1988年   36篇
  1987年   27篇
  1986年   41篇
  1985年   21篇
  1984年   9篇
  1983年   11篇
  1982年   7篇
  1981年   15篇
  1980年   9篇
  1979年   18篇
  1978年   15篇
  1977年   13篇
  1976年   11篇
  1975年   16篇
  1971年   8篇
  1970年   7篇
  1969年   6篇
  1968年   11篇
  1967年   10篇
  1966年   8篇
排序方式: 共有841条查询结果,搜索用时 0 毫秒
41.
Volumetric rendering is a new approach to three-dimensional (3D) imaging that overcomes many of the drawbacks of currently available surface-rendering systems. Its application on the Pixar Imaging System in two cases of acetabular fracture was assessed to illustrate the features of the technique. The fast-computing architecture and large memory of this system allow rapid generation of a series of high-quality 3D images in each plane of rotation (x or spinal axis, z or somersaulting axis) that can be viewed as independent static images or as an animated real-time video loop. Editing to remove the normal contralateral hemipelvis enhances appreciation of acetabular abnormalities. Every pixel of computed tomographic data is preserved, allowing representation of both soft tissue and bone as translucent overlap. The presentation of data also allows detection of subtle abnormalities and features and minimizes the artifact generation common in surface-rendered images.  相似文献   
42.
43.
Myocardial tagging in polar coordinates with use of striped tags   总被引:1,自引:0,他引:1  
Bolster  BD  Jr; McVeigh  ER; Zerhouni  EA 《Radiology》1990,177(3):769-772
Regional deformation abnormalities in the heart wall provide a good indicator of ischemia. Myocardial tagging with magnetic resonance imaging is a new method of assessing heart wall motion during contraction. Current methods of myocardial tagging either do not provide two-dimensional information or lack a coordinate system well adapted to the morphology of the heart. In this article, the authors describe a new tagging method that provides a true polar coordinate system, with both radial and angular dimensions. This is accomplished with use of a section-selective version of spatially modulated magnetization resulting in striped tags (STAGs). These STAG planes are placed in the myocardium in a star pattern so that they intersect on the long axis of the heart and stripes appear through the width of the heart wall. In the short-axis view during contraction, rotation around the long axis yields angular information such as shear and twist, while separation of the stripes within the myocardium permits measurement of radial thickening. Therefore, this method provides a coordinate system for calculating two-dimensional strain that is adapted to the morphology of the left ventricle.  相似文献   
44.
45.
The immediate-spin (IS) crossmatch is used to detect ABO incompatibility between donor red cells (RBCs) and the serum of the intended recipient. However, this test may be positive in the absence of ABO incompatibility (false positive) or it may be negative when ABO incompatibility exists (false negative). During a 25-month study, the rates of both false-positive and false-negative IS crossmatch results were evaluated, and the sensitivity and specificity of the IS crossmatch were determined. During the study period, 53,656 IS crossmatches were performed for patients without significant RBC antibodies. Fifty-five patients had positive IS crossmatches, and no false-negative reactions were found. In tests of 55 patients with positive IS crossmatches, 77 false-positive and 5 true-positive reactions were noted. The causes of the false-positive reactions were rouleaux (36 patients), cold-reactive antibodies (8 patients), a combination of rouleaux and cold-reactive antibodies (2 patients), fibrin clot (1 patient), and undetermined (3 patients). The sensitivity and specificity of the IS crossmatch were 100 and 99.86 percent, respectively. Laboratory personnel should be aware that the IS crossmatch may have false-positive or false-negative results, and they should develop written protocols to distinguish quickly between true-positive and false-positive reactions.  相似文献   
46.
BACKGROUND: Hospitals and blood centers throughout the United States use a variety of reagents and methods to perform pretransfusion testing. A survey was developed to determine the reagents and methods in use and their relative prevalence in different work settings. STUDY DESIGN AND METHODS: A national survey on pretransfusion testing was conducted. Surveys were distributed to state and regional blood bank associations, which then distributed them to hospitals and blood centers within their region. In most instances, the blood centers distributed the survey to the local hospitals. Completed surveys were returned to the authors for review, and all information was entered into a database for analysis. RESULTS: Analysis of the data shows that the majority of blood banks use monoclonal reagents for ABO testing and monoclonal-polyclonal blended reagents for Rh testing. The data show that anti-IgG and polyclonal antihuman globulin reagents are used almost equally for antibody screening (detection) tests and that most blood banks use a three-cell antibody-screening test. Slightly more than 50 percent of hospitals use an immediate-spin crossmatch in the absence of unexpected antibodies. CONCLUSION: A number of approved reagents and methods are used by blood bank laboratories for pretransfusion testing. Facility size (number of beds) and type tend to influence the choice of methods and reagents employed. This survey provides an opportunity for blood bank laboratories to compare their current practices with those of their peers.  相似文献   
47.
Excluding studies from Brechot and co-workers, little supporthas been found for a role of the hepatitis B virus in the pathogenesisof HBsAg seronegative patients with predominantly chronic liverdiseases, including primary liver cancer. In this study liverDNA from 59 predominantly British patients (four cases withpaired biopsies, 6–12 months apart) with different, mostlychronic, liver diseases was analysed by molecular hybridization.All were seronegative for HBsAg and serum hepatitis B virusDNA (dot blot hybridization) and their liver diseases were believedto be unrelated to hepatitis B virus infection. Hepatitis Bvirus DNA was detected in liver of 11 (18.6 per cent) patients;nine had episomal(3.2 Kb) DNA and eight had higher molecularweight bands suggesting integrated forms. Six patients werealso seronegative for anti-HBc. Patients of UK and non-UK originwere equally represented. Hepatitis B virus DNA was detectedin serum of six of nine patients tested using the polymerasechain reaction. The detection of hepatitis B virus DNA in liverand in serum by this assay in a significant proportion of patientswith chronic liver disease, hitherto unsuspected of being hepatitisB virus-related, suggests a possible role for this virus inlow- as well as high-prevalence countries.  相似文献   
48.
Discrepancies in reverse ABO typing due to prozone   总被引:5,自引:0,他引:5  
Three group O sera manifesting prozone in reverse ABO tests are reported. All were implicated in erroneous blood typing results. One sample failed to react with A1 red cells (RBCs) in immediate-spin (IS) tests, had anti-A and -B titers of 8192 and 2048, respectively, by indirect antiglobulin technique (IAT), and was from a diabetic patient; the parenteral administration of A substance present in porcine insulin is a possible cause of hyperimmunity in this case. The second sample was from the recipient of a single unit of group B fresh-frozen plasma; the serum anti-A and -B titers were 10,240 by IAT, but only weak reactions with A1 and B RBCs were noted in routine IS reverse typing tests; the hyperimmunity in the patient concerned was likely due to crossreacting anti-A, B stimulated by B-active glycoproteins and/or glycolipids in the transfused plasma. The third serum also had anti-A and anti-B IAT titers of 10,240 but did not react with A1 and B RBCs by IS; the hyperimmunity in this case may be related to sepsis from intestinal flora carrying A- and/or B-like antigens. These antibodies lysed A1 and/or B RBCs in tests incubated at room temperature (RT) and strongly agglutinated those RBCs by IS when diluted 10-fold with saline. The absence of the prozone phenomenon in tests with RBCs suspended in diluents containing EDTA is consistent with the previously published mechanism for anti-A prozone: namely, the steric hindrance of agglutination by the C1 component of human complement.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
49.
Background: This article describes standard operating procedures (SOPs) for a computer crossmatch to replace the immediate-spin crossmatch for ABO incompatibility between patient blood samples submitted for pretransfusion testing and the blood component selected for transfusion. These SOPs were developed following recent changes to the Standards for Blood Banks and Transfusion Services of the American Association of Blood Banks (AABB). Study Design and Methods: SOPs were developed, utilizing currently available software, for pretransfusion testing. The SOP for donor unit processing entails bar code entry of the unit number, component name, and ABO/Rh type; computer entry and interpretation of serologic reactions; warning of discrepancies between bar code-entered blood type and result interpretation; and quarantine of the donor unit in such instances. The SOP for patient sample testing requires bar code entry of specimen accession number, which accesses patient demographics; computer entry and interpretation of ABO/Rh tests; repeat blood typing at the time of crossmatch if only one patient blood type is on record; and warning if there are nonconcordant current and historical blood types. The computer crossmatch SOP requires bar code entry of specimen accession and donor unit numbers; release of group O red cells pending resolution of discrepancies; and immediate-spin crossmatch during computer downtime. Tables validated on- site prompt warning messages and prevent both computer crossmatch and release if blood components of the wrong ABO type are selected. Results: These SOPs meet the requirements of the 15th edition of the AABB Standards. Projected annual time savings at this institution are > 100,000 workload recording units. Further benefits include reduced patient sample volume requirements, less handling of biohazardous material, and elimination of unwanted positive or negative reactions associated with the immediate-spin crossmatch. Release of incompatible blood components when the wrong patient blood type is on record is addressed by requiring the use of group O red cells in the absence of two concordant blood types, one of which must be from a current sample. Conclusion: A combination of existing computer programs and carefully developed SOPs can provide a safe and efficient means of detecting donor-recipient incompatibility without performance of serologic crossmatch.  相似文献   
50.
Bulletin of Experimental Biology and Medicine - A common method of modeling urolithiasis is the use of 1 and 0.75% ethylene glycol, or a combination of ethylene glycol with other lithogens, but too...  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