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   3153454篇
  免费   247787篇
  国内免费   5650篇
耳鼻咽喉   45753篇
儿科学   101364篇
妇产科学   85103篇
基础医学   445617篇
口腔科学   89849篇
临床医学   286475篇
内科学   614045篇
皮肤病学   65684篇
神经病学   260561篇
特种医学   125608篇
外国民族医学   1301篇
外科学   476431篇
综合类   74114篇
现状与发展   2篇
一般理论   1237篇
预防医学   252448篇
眼科学   73749篇
药学   235878篇
  6篇
中国医学   5946篇
肿瘤学   165720篇
  2018年   32469篇
  2017年   24869篇
  2016年   27436篇
  2015年   30978篇
  2014年   44299篇
  2013年   67566篇
  2012年   91765篇
  2011年   97108篇
  2010年   57391篇
  2009年   54837篇
  2008年   92249篇
  2007年   98363篇
  2006年   99022篇
  2005年   96332篇
  2004年   93227篇
  2003年   90240篇
  2002年   88693篇
  2001年   145986篇
  2000年   151171篇
  1999年   128141篇
  1998年   37092篇
  1997年   33620篇
  1996年   33484篇
  1995年   32297篇
  1994年   30271篇
  1993年   28279篇
  1992年   103084篇
  1991年   100175篇
  1990年   96795篇
  1989年   93196篇
  1988年   86307篇
  1987年   85037篇
  1986年   80260篇
  1985年   76776篇
  1984年   58221篇
  1983年   49555篇
  1982年   29820篇
  1981年   26754篇
  1979年   54234篇
  1978年   37979篇
  1977年   32139篇
  1976年   30201篇
  1975年   32101篇
  1974年   39134篇
  1973年   37293篇
  1972年   34769篇
  1971年   31993篇
  1970年   30294篇
  1969年   28031篇
  1968年   25525篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
Bernard–Soulier syndrome (BSS) is a rare autosomal recessively inherited bleeding disorder. Pregnancy in patients with BSS is characterized by ante‐, intra‐, or postpartum haemorrhage, which may be delayed and severe. There is no consensus in the management of BSS in pregnancy and so far only 16 pregnancies in nine patients have been described. We report a further three pregnancies in two women with the syndrome. We also outline our management of pregnant patients with BSS.  相似文献   
53.
Multi-day signals, generally with duration of 2-10 days, are a prominent temporal variation type of radon (Rn) in geogas in the unsaturated zone. Rare multi-day Rn signals have been found which are characterized by: (a) a declining limb lasting up to 10 days which conforms to the radioactive decay of Rn, (b) recurs at the same location and (c) is recorded in diverse situations-volcanic and seismogenic. It suggested that a Rn blob is injected at a lower level on a steady upward flow of geogas whereby the rise and final fall of the signal are attributed to the edges of the blob while the central Rn-decay segment records the passing of the decaying blob itself. Rn-decay signals are a small subset of multi-day Rn signals which are considered as highly irregular and unusable for the understanding of geophysical processes. In difference, it is concluded that multi-day Rn signals are probably proxies of subtle geodynamic processes at upper crustal levels and are therefore significant for studying such processes.  相似文献   
54.
SPECT with 99mTc-labeled agents is better able to detect viability after nitrate administration. Nitrates induce vasodilation and may increase blood flow to severely hypoperfused but viable myocardium, thereby enhancing tracer delivery and improving the detection of viability. Quantitative data on the changes in blood flow are lacking in SPECT but can be provided by PET. The aim of the present study was to use PET to evaluate whether nitrate administration increases blood flow to chronically dysfunctional but viable myocardium. METHODS: 13N-Ammonia PET was used to quantitatively assess blood flow, and 18F-FDG PET was used as the gold standard to detect viable myocardium. Twenty-five patients with chronic ischemic left ventricular dysfunction underwent 13N-ammonia PET at rest and after nitrate administration. RESULTS: A significant increase in nitrate-enhanced blood flow was observed in viable segments (from 0.55 +/- 0.15 to 0.68 +/- 0.24 mL/min/g, P < 0.05). No statistically significant change in blood flow was observed in nonviable segments (0.60 +/- 0.20 vs. 0.55 +/- 0.18 mL/min/g). A ratio of at least 1.1 for nitrate-enhanced flow to resting flow allowed optimal detection of viable myocardium, yielding a sensitivity of 82% with a specificity of 100%. CONCLUSION: 13N-Ammonia PET showed a significant increase in nitrate-enhanced blood flow in viable myocardium, whereas blood flow remained unchanged after nitrate administration in nonviable myocardium. Nitrate use during myocardial perfusion imaging will lead to improved assessment of myocardial viability.  相似文献   
55.
BACKGROUND AND PURPOSE: There is concern about the increase of radiation-induced malignancies with the application of modern radiation treatment techniques such as intensity-modulated radiotherapy (IMRT) and proton radiotherapy. Therefore, X-ray scatter and neutron radiation as well as the impact of the primary dose distribution on secondary cancer incidence are analyzed. MATERIAL AND METHODS: The organ equivalent dose (OED) concept with a linear-exponential and a plateau dose-response curve was applied to dose distributions of 30 patients who received radiation therapy of prostate cancer. Three-dimensional conformal radiotherapy was used in eleven patients, another eleven patients received IMRT with 6-MV photons, and eight patients were treated with spot-scanned protons. The treatment plans were recalculated with 15-MV and 18-MV photons. Secondary cancer risk was estimated based on the OED for the different treatment techniques. RESULTS: A modest increase of 15% radiation-induced cancer results from IMRT using low energies (6 MV), compared to conventional four-field planning with 15-MV photons (plateau dose-response: 1%). The probability to develop a secondary cancer increases with IMRT of higher energies by 20% and 60% for 15 MV and 18 MV, respectively (plateau dose-response: 2% and 30%). The use of spot-scanned protons can reduce secondary cancer incidence as much as 50% (independent of dose-response). CONCLUSION: By including the primary dose distribution into the analysis of radiation-induced cancer incidence, the resulting increase in risk for secondary cancer using modern treatment techniques such as IMRT is not as dramatic as expected from earlier studies. By using 6-MV photons, only a moderate risk increase is expected. Spot-scanned protons are the treatment of choice in regard to secondary cancer incidence.  相似文献   
56.
Conclusion  Several quality-control measures take place before (patient and camera preparation) and during SPECT acquisition to achieve high-quality images. Not uncommonly, technologists and physicians are left with suboptimal images that have to be addressed to reach the “right answer” for patient diagnosis and hence management. In many cases patients may be reimaged, especially if the problem is detected early, but in other cases either the patient has left the nuclear laboratory or there is an inevitable problem that, even with reimaging, will not be resolved. In these situations the technologist and physician have to seek the available techniques to obtain the best images possible. These resources are discussed in this issue as an aid in quality control to obtain the best possible images.  相似文献   
57.
58.
59.

Background  

The Association of Surgeons of Great Britain and Ireland (ASGBI) devised the electronic surgical logbook (version 2.4) for higher trainees in General Surgery enabling trainees to compile a uniform data set of their operative and training experience. This is in use by higher surgical trainees (HST) in the United Kingdom. This logbook permits trainees to submit data centrally into a Regional Analysis Database (RAD). With the implementation of the European Working Time Directive (EWTD) there is need for reliable data to assess the effects of the directive on training. In order to draw meaningful conclusions from the database the quality of data needs to be validated. We critically analysed the RAD in the Yorkshire region for a one-year period.  相似文献   
60.
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