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   750542篇
  免费   53070篇
  国内免费   4909篇
耳鼻咽喉   9548篇
儿科学   23743篇
妇产科学   18211篇
基础医学   115731篇
口腔科学   20938篇
临床医学   69631篇
内科学   140928篇
皮肤病学   16661篇
神经病学   51747篇
特种医学   27432篇
外国民族医学   96篇
外科学   109067篇
综合类   22525篇
现状与发展   17篇
一般理论   166篇
预防医学   54408篇
眼科学   17509篇
药学   58525篇
  31篇
中国医学   5149篇
肿瘤学   46458篇
  2021年   7666篇
  2019年   6874篇
  2018年   9428篇
  2017年   7543篇
  2016年   8149篇
  2015年   9530篇
  2014年   12784篇
  2013年   17539篇
  2012年   23643篇
  2011年   24927篇
  2010年   14804篇
  2009年   13652篇
  2008年   22177篇
  2007年   23772篇
  2006年   24140篇
  2005年   22474篇
  2004年   21661篇
  2003年   20733篇
  2002年   20056篇
  2001年   37666篇
  2000年   38092篇
  1999年   31652篇
  1998年   8749篇
  1997年   7461篇
  1996年   7597篇
  1995年   7205篇
  1994年   6603篇
  1993年   5846篇
  1992年   23306篇
  1991年   23209篇
  1990年   22569篇
  1989年   22286篇
  1988年   20239篇
  1987年   19584篇
  1986年   18611篇
  1985年   17393篇
  1984年   12772篇
  1983年   10773篇
  1982年   5939篇
  1979年   11522篇
  1978年   8130篇
  1977年   6832篇
  1976年   6594篇
  1975年   7269篇
  1974年   8498篇
  1973年   8141篇
  1972年   7658篇
  1971年   7127篇
  1970年   6878篇
  1969年   6307篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
The purpose of this investigation was to characterize noise levels in spaces designated as “effective quiet” areas on a U.S. Navy aircraft carrier. Noise dosimetry samples were collected in 15 designated spaces, representing 15 noise measurements, while at-sea during airwing carrier qualifications. Equivalent sound level (Leq) measurements were collected during flight operations (Leq (flt ops)), non-flight operations (Leq (non-flt ops)), and over 24-hr periods (Leq (24-hr)). These data were compared to the 70 dBA American Conference of Governmental Industrial Hygienists (ACGIH®) Threshold Limit Value (TLV®) for “effective quiet” areas intended for temporary threshold shift recovery when personnel live and work in a potentially noise hazardous environment for periods greater than 24?hr. The monitored areas were selected based on personnel occupancy/use during off-duty time periods. Areas were classified by either (1) leisure areas that included mess (eating areas), gyms, lounges, an internet cafe, and the fantail social area or (2) berthing (sleeping) areas. The Leq measurements in decibels “A” weighted (dBA) were compared to determine significant differences between Leq (flt ops), Leq (non-flt ops), and Leq (24-hr) and were compared between leisure area and berthing area. Measured noise levels according to time period ranged as follows: (1) Leq (24-hr): 70.8–105.4 dBA; (2) Leq (flt ops): 70–101.2 dBA; and (3) Leq (non-flt ops): 39.4–104.6 dBA. All area measurements over the 24-hr period and during flight operations and 46.7% of the areas during the non-flight operation time period exceeded the “effective quiet” 70 dBA ACGIH TLV. Mean Leqs were 15 dBA higher during flight operations compared to non-flight operations in “effective quiet” areas (p?=?0.001). The Leqs in leisure areas were significantly higher than berthing areas by approximately 21 dBA during non-flight operation periods (p?=?0.001). Results suggest noise levels in “effective quiet” areas frequented by aircraft carrier personnel during off-duty hours when at-sea may inhibit auditory recovery from occupational noise exposures that occur on-duty.  相似文献   
3.
BACKGROUND Postoperative liver failure is the most severe complication in cirrhotic patients with hepatocellular carcinoma(HCC) after major hepatectomy. Current available clinical indexes predicting postoperative residual liver function are not sufficiently accurate.AIM To determine a radiomics model based on preoperative gadoxetic acid-enhanced magnetic resonance imaging for predicting liver failure in cirrhotic patients with HCC after major hepatectomy.METHODS For this retrospective study, a radiomics-based model was developed based on preoperative hepatobiliary phase gadoxetic acid-enhanced magnetic resonance images in 101 patients with HCC between June 2012 and June 2018. Sixty-one radiomic features were extracted from hepatobiliary phase images and selected by the least absolute shrinkage and selection operator method to construct a radiomics signature. A clinical prediction model, and radiomics-based model incorporating significant clinical indexes and radiomics signature were built using multivariable logistic regression analysis. The integrated radiomics-based model was presented as a radiomics nomogram. The performances of clinical prediction model, radiomics signature, and radiomics-based model for predicting post-operative liver failure were determined using receiver operating characteristics curve, calibration curve, and decision curve analyses.RESULTS Five radiomics features from hepatobiliary phase images were selected to construct the radiomics signature. The clinical prediction model, radiomics signature, and radiomics-based model incorporating indocyanine green clearance rate at 15 min and radiomics signature showed favorable performance for predicting postoperative liver failure(area under the curve: 0.809-0.894). The radiomics-based model achieved the highest performance for predicting liver failure(area under the curve: 0.894; 95%CI: 0.823-0.964). The integrated discrimination improvement analysis showed a significant improvement in the accuracy of liver failure prediction when radiomics signature was added to the clinical prediction model(integrated discrimination improvement = 0.117, P =0.002). The calibration curve and an insignificant Hosmer-Lemeshow test statistic(P = 0.841) demonstrated good calibration of the radiomics-based model. The decision curve analysis showed that patients would benefit more from a radiomics-based prediction model than from a clinical prediction model and radiomics signature alone.CONCLUSION A radiomics-based model of preoperative gadoxetic acid–enhanced MRI can be used to predict liver failure in cirrhotic patients with HCC after major hepatectomy.  相似文献   
4.
5.
Pharmaceutical Chemistry Journal - An HPLC-MS method for simultaneous quantitative determination of a novel gestagenic pharmaceutical and two of its metabolites in rat and rabbit blood sera was...  相似文献   
6.
Bulletin of Experimental Biology and Medicine - Ammonium, an end-product of catabolism, in low doses can promote adaptation of metabolic pathways in erythrocytes under conditions of extreme...  相似文献   
7.
8.
We report two British cases of liver abscess, due to Klebsiella pneumoniae and associated with synchronous infection elsewhere, which required liver resection for definitive treatment. They illustrate the geographic spread of aggressive K pneumoniae liver infection and demonstrate the importance of early aggressive treatment.  相似文献   
9.
10.
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