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   5466篇
  免费   231篇
  国内免费   23篇
耳鼻咽喉   17篇
儿科学   106篇
妇产科学   105篇
基础医学   674篇
口腔科学   61篇
临床医学   316篇
内科学   1382篇
皮肤病学   171篇
神经病学   428篇
特种医学   131篇
外科学   1006篇
综合类   19篇
一般理论   1篇
预防医学   90篇
眼科学   41篇
药学   261篇
中国医学   18篇
肿瘤学   893篇
  2023年   52篇
  2022年   80篇
  2021年   113篇
  2020年   80篇
  2019年   86篇
  2018年   96篇
  2017年   88篇
  2016年   113篇
  2015年   108篇
  2014年   147篇
  2013年   198篇
  2012年   287篇
  2011年   412篇
  2010年   217篇
  2009年   172篇
  2008年   360篇
  2007年   390篇
  2006年   323篇
  2005年   387篇
  2004年   380篇
  2003年   350篇
  2002年   313篇
  2001年   42篇
  2000年   49篇
  1999年   80篇
  1998年   95篇
  1997年   85篇
  1996年   88篇
  1995年   76篇
  1994年   73篇
  1993年   45篇
  1992年   39篇
  1991年   39篇
  1990年   27篇
  1989年   20篇
  1988年   26篇
  1987年   14篇
  1986年   14篇
  1985年   12篇
  1984年   14篇
  1983年   7篇
  1982年   7篇
  1981年   13篇
  1980年   22篇
  1979年   8篇
  1978年   14篇
  1977年   13篇
  1976年   6篇
  1975年   11篇
  1973年   6篇
排序方式: 共有5720条查询结果,搜索用时 15 毫秒
991.
To investigate the molecular mechanisms of the high incidence of carcinogenesis in the biliary epithelium of patients with pancreaticobiliary maljunction, we examined p53 gene mutations, loss of heterozygosity of p53, and overexpression of p53 gene product in the cancerous and noncancerous biliary epithelium of 27 patients with pancreaticobiliary maljunction. Mutations of the p53 gene were examined by polymerase chain reaction-single strand conformation polymorphism and a direct sequencing method. Loss of heterozygosity of the p53 gene was determined using a double-targeted fluorescence in situ hybridization method. Expression of p53 gene product was examined using immunohistochemical staining. Mutations of the p53 gene were found in 4 of 5 biliary carcinomas (80%) and in 10 of 26 noncancerous biliary lesions (38.5%). Point mutations of the p53 gene were detected at codons 207, 212, and 217 on exons 5 through 8. The incidence of p53 gene mutations on exons 5, 6, 7, and 8 was 12.9%, 36.4%, 0.0%, and 13.8%, respectively. Loss of heterozygosity of p53 was shown in 72% of the cells obtained from the cancerous lesion, and in an average of 14% obtained from the noncancerous lesions. Overexpression of p53 protein was found in 57.1% of carcinoma, and in 31.3% of the noncancerous lesions. These results suggest that p53 gene mutations are involved in the carcinogenesis of biliary epithelium in patients with pancreaticobiliary maljunction. Received for publication on Feb. 5, 1999; accepted on March 29, 1999  相似文献   
992.
Fasting induced a reduction in neuronal nitric oxide synthase (nNOS) mRNA in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) of rats. The effect of intracerebroventricular (i.c.v.) administration of leptin on the nNOS mRNA level in the PVN and SON of fasting rats was studied by in situ hybridization histochemistry. Leptin (10 microg/kg b.wt) or vehicle was administered i.c.v. at 1700 h on two successive days fasting for 2 days. Fasting for 2 days with i.c.v. administration of vehicle induced a significant reduction of nNOS mRNA in the PVN and SON. Central administration of leptin prevented the fasting-induced reduction of nNOS mRNA in the PVN and SON. Administration of leptin also prevented the fasting-induced reductions of thyrotropin-releasing hormone (TRH) and corticotropin-releasing hormone (CRH) mRNAs in the parvocellular division of the PVN. These results suggest that leptin is associated with fasting-induced reduction of nNOS mRNA in the PVN and SON as well as TRH and CRH mRNAs in the PVN.  相似文献   
993.
994.
995.
Objective This study evaluated cases of pruritus, which is known to be associated with sleep disorder, in chronic liver disease (CLD) patients. Methods Questionnaires were given to 339 enrolled CLD outpatients in winter (November 2019 to March 2020) and again in summer (April to October 2020) (median interval: 104 days). Relative changes in symptoms shown by a visual analogue scale (VAS) and Kawashima''s pruritus score between winter and summer were evaluated in Study 1 (n=199), while Study 2 examined the clinical features of patients with sleep disorder based on the results of the second questionnaire (n=235, median age 70 years old; 141 men, liver cirrhosis 37%). Results Study 1. There was a significant relationship in VAS between daytime and nighttime for each season, as well as between winter and summer for each time period (p<0.001). A comparison of Kawashima''s pruritus scores for the daytime and nighttime showed no significant seasonal differences (p=0.436 and 0.828, respectively). When Kawashima''s score increased, so did the average VAS for both daytime (0:1:2:3:4=0.4±0.2:1.4±0.9:3.0±1.8:5.9±2.1:6.2±2.3) and nighttime (0:1:2:3:4=0.3±0.1:1.4±1.5:3.5±2.3:6.7±2.6:6.9±1.8) (p<0.001 for both). Study 2. Twenty subjects (8.5%) complained of sleep disorder. An elevated FIB-4 index (≥3.07) showed a good predictive value for sleep disorder (p<0.01). The cut-off for the daytime and nighttime VAS values for existing sleep disorder were 1.6 [area under the curve (AUC) 0.901] and 3.4 (AUC 0.931). The respective sensitivity, specificity, and positive and negative predictive values for sleep disorder based on Kawashima''s score (≥2) were 0.85, 0.28, 0.10, and 0.95 for the daytime and 1.00, 0.29, 0.12, and 1.00 for the nighttime. Conclusion Intervention against pruritus is recommended in CLD patients with a high Kawashima''s score (≥2) in any season, especially with an elevated FIB-4 index.  相似文献   
996.
Objective Viral pneumonia is not rare in community-acquired pneumonia (CAP). Mixed or secondary pneumonia (coinfection) can be seen in viral pneumonia; however, its frequency in coronavirus disease 2019 (COVID-19) has only been investigated in a few studies of short duration, and its significance has not been fully elucidated. We investigated the frequency and significance of co-infection in patients with COVID-19 over a 1-year study period. Methods Coinfection was investigated via multiplex polymerase chain reaction (PCR), culture of respiratory samples, rapid diagnostic tests, and paired sera. We used logistic regression analysis to analyze the effect of coinfection on severity at admission and Cox proportional-hazards model analysis to analyze the effect of coinfection on need for high-flow nasal cannula, invasive mandatory ventilation use, and death, respectively. Patients We retrospectively investigated 298 patients who suffered CAP due to severe acute respiratory syndrome coronavirus-2 infection diagnosed by PCR and were admitted to our institution from February 2020 to January 2021. Results Primary viral pneumonia, and mixed viral and bacterial pneumonia, accounted for 90.3% and 9.7%, respectively, of COVID-19-associated CAP, with viral coinfection found in 30.5% of patients with primary viral pneumonia. Influenza virus was the most common (9.4%). Multivariable analysis showed coinfection not to be an independent factor of severity on admission, need for high-flow nasal cannula or invasive mandatory ventilation, and mortality. Conclusion Viral coinfection was common in COVID-19-associated CAP. Severity on admission, need for high-flow oxygen therapy or invasive mandatory ventilation, and mortality were not affected by coinfection.  相似文献   
997.
The induction of postsynaptic structures by presynaptic terminals is suggested in a teleost brain. Neurons in the nucleus pretectalis superficialis pars magnocellularis (PSm) in the common carp are known to send fibers to the corpus mamillare (CM) and the nucleus lateralis valvulae (NLV). Individual axons of PSm neurons bifurcate (or give off an axon collateral), both of which reach the target areas in the CM and NLV. The morphology of horseradish peroxidase-labeled terminals in the CM and NLV appears quite different in light microscopy. Terminals in the CM appear as a fine network of beaded (2–4 μm in diameter) fibers, while those in the NLV are larger (8–12 μm in transverse diameter) and cup-shaped, partially enveloping the soma of individual NLV neurons. In electron microscopy, however, these synapses in the CM and NLV share several ultrastructural similarities. Small (0.2 to 0.4-μm thick, 0.4 to 0.7-μm long) spine-like protrusions arising from dendrites in the CM, and from cell bodies in the NLV, invaginate into the axon terminals, and the synaptic junctions are always formed at the base of the protrusion in both areas. Development of this unusual morphology is inferred to be directed from the presynaptic side. The morphological similarity of the spine-like protrusions to the “spinule,” which is thought to be formed in response to synaptic activation, is discussed. J. Comp. Neurol. 378:379–388, 1997. © 1997 Wiley-Liss, Inc.  相似文献   
998.
999.
1000.
This study aimed to develop a questionnaire on the quality of working life among female medical and healthcare professionals and examine its validity and reliability. The questionnaire was developed from an item pool drawing on the literature. The four trait scales included 40 items, covering female-specific stress in continuing a career, stress of lifestyle in maintaining personal values, job satisfaction and social support network. The questionnaire’s validity and reliability were assessed using data from 1,784 female doctors, dentists, and nurses. Validity was examined using exploratory factor analysis on each trait for construct validity, and multitrait scaling analysis for convergent and discriminant validity. Reliability was tested using Cronbach’s alpha for trait subscales and scales. Exploratory factor analysis on each trait was convergent. One trait derived three subscales, and another two. The remaining two traits were convergent for one factor. Multitrait scaling analysis showed that all scales and subscales were independent. The questionnaire was therefore internally consistent and had construct validity. Cronbach’s alpha was 0.85 for the total and between 0.72 and 0.83 for the subscales. These results validate the four-trait combination questionnaire and suggest that it would be suitable for use in future research, perhaps in combination with other existing scales.  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