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   79758篇
  免费   4161篇
  国内免费   501篇
耳鼻咽喉   954篇
儿科学   1689篇
妇产科学   1902篇
基础医学   9828篇
口腔科学   3702篇
临床医学   5981篇
内科学   21433篇
皮肤病学   1784篇
神经病学   6838篇
特种医学   1929篇
外科学   11949篇
综合类   389篇
一般理论   22篇
预防医学   5024篇
眼科学   1380篇
药学   4407篇
中国医学   242篇
肿瘤学   4967篇
  2024年   51篇
  2023年   518篇
  2022年   1115篇
  2021年   2755篇
  2020年   1472篇
  2019年   2132篇
  2018年   2696篇
  2017年   1792篇
  2016年   1972篇
  2015年   2285篇
  2014年   3257篇
  2013年   4125篇
  2012年   6474篇
  2011年   6547篇
  2010年   3709篇
  2009年   3196篇
  2008年   5451篇
  2007年   5597篇
  2006年   5289篇
  2005年   5195篇
  2004年   4574篇
  2003年   4096篇
  2002年   3654篇
  2001年   451篇
  2000年   316篇
  1999年   491篇
  1998年   633篇
  1997年   531篇
  1996年   470篇
  1995年   459篇
  1994年   351篇
  1993年   264篇
  1992年   241篇
  1991年   180篇
  1990年   153篇
  1989年   118篇
  1988年   106篇
  1987年   96篇
  1986年   116篇
  1985年   119篇
  1984年   127篇
  1983年   119篇
  1982年   137篇
  1981年   112篇
  1980年   131篇
  1979年   70篇
  1978年   81篇
  1977年   80篇
  1976年   62篇
  1974年   48篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
32.
33.
<正>Individuals with Marinesco-Sj?gren syndrome(MSS;OMIM 248800),a genetic disease of infancy,suffer various disabilities,including loss of motor coordination due to cerebellar degeneration,and skeletal muscle weakness.After a progressive phase,symptoms stabilize and patients live to old age.Therefore,any pharmacological treatment that delays or attenuates cerebellar degeneration and/or muscle pathology can significantly improve their quality of life.We recently found that inhibiting the protein kinase RNA-like endoplasmic reticulum kinase  相似文献   
34.
BACKGROUND Accurate detection of gastric infection by Helicobacter pylori(H.pylori) and premalignant lesions are important for effective provision of treatment,preventing the development of gastric neoplasia.Optical enhancement systems with optical magnification improved the identification of mucosal superficial and vascular patterns in patients with dyspepsia.AIM To evaluate an optical enhancement system with high-definition magnification,for diagnosis of normal gastric mucosa,H.pylori-associated gastritis,and gastric atrophy.METHODS A cross-sectional,nonrandomized study from November 2015 to April 2016 performed in a single-tertiary academic center from Ecuador.Seventy-two consecutive patients with functional dyspepsia according to the Rome III criteria,were tested for H.pylori using a stool antigen test and were assigned to an Hp+group or an Hp-control group.Esophagogastroduodenoscopy with highdefinition optical magnification and digital chromoendoscopy was performed,and patients were classified into 4 groups,in accordance to the microvasculararchitecture pattern of the mucosa.Interobserver and intraobserver agreement among operators were calculated.RESULTS Of the 72 participants,35 were Hp+ and 37 were Hp-.Among 10 patients with normal mucosal histology in biopsy samples,90% had a Type I pattern of microvascular architecture by endoscopy.Among participants with type IIa and type IIb patterns,significantly more were Hp+ than Hp-(32 vs 8),and most(31 out of 40) had histological diagnoses of chronic active gastritis.Two of the three participants with a histological diagnosis of atrophy had a type III microvascular pattern.The type I pattern predicted normal mucosa,type IIa–IIb predicted H.pylori infection,and type III predicted atrophy with sensitivities of 90.0%,91.4%,and 66.7%,respectively.The intraobserver and interobserver agreements had kappa values of 0.91 and 0.89,respectively.CONCLUSION High-definition optical magnification with digital chromoendoscopy is useful for diagnosis of normal gastric mucosa and H.pylori-associated gastritis with high accuracy,but further studies are needed to determine whether endoscopic diagnosis of gastric atrophy is feasible.  相似文献   
35.
36.
37.
38.
Isotactic polypropylenes (iPP) with different melt flow indexes (MFI) were used to fabricate nanocomposites (NCs) with 10 wt % loadings of multi-wall carbon nanotubes (MWCNTs) using ultrasound-assisted extrusion methods to determine their effect on the morphology, melt flow, and electrical properties of the NCs. Three different types of iPPs were used with MFIs of 2.5, 34 and 1200 g/10 min. Four different NC fabrication methods based on melt extrusion were used. In the first method melt extrusion fabrication without ultrasound assistance was used. In the second and third methods, an ultrasound probe attached to a hot chamber located at the exit of the die was used to subject the sample to fixed frequency and variable frequency, respectively. The fourth method is similar to the first method, with the difference being that the carbon nanotubes were treated in a fluidized air-bed with an ultrasound probe before being used in the fabrication of the NCs with no ultrasound assistance during extrusion. The samples were characterized by MFI, Optical microscopy (OM), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), electrical surface resistivity, and electric charge. MFI decreases in all cases with addition of MWCNTs with the largest decrease observed for samples with the highest MFI. The surface resistivity, which ranged from 1013 to 105 Ω/sq, and electric charge, were observed to depend on the ultrasound-assisted fabrication method as well as on the melt flow index of the iPP. A relationship between agglomerate size and area ratio with electric charge was found. Several trends in the overall data were identified and are discussed in terms of MFI and the different fabrication methods.  相似文献   
39.
The concept of participation was reviewed as a component of children's citizenship in order to promote a programme for Integral Development. A narrative revision of the literature was carried out as well as a group discussion was organized along with the staff of an Integral Care Programme, in order to identify notions of democracy and child citizenship related to care and rearing. Some elements that favoured the child participation and some parenting skills were identified. Among the elements that must be encouraged in children are: the development of emotional, cognitive and communicative skills and promotion of decision-making; among the parent skills development included are: sensitivity and responsivity; establishing routines and participation experiences. It is important to stand out that the identified elements to promote child participation and parental competences should be adapted to every specific cultural context.  相似文献   
40.
The ban of lead in many electronic products and the expectation that, sooner or later, this ban will include the currently exempt piezoelectric ceramics based on Lead-Zirconate-Titanate has motivated many research groups to look for lead-free substitutes. After a short overview on different classes of lead-free piezoelectric ceramics with large strain, this review will focus on Bismuth-Sodium-Titanate and its solid solutions. These compounds exhibit extraordinarily high strain, due to a field induced phase transition, which makes them attractive for actuator applications. The structural features of these materials and the origin of the field-induced strain will be revised. Technologies for texturing, which increases the useable strain, will be introduced. Finally, the features that are relevant for the application of these materials in a multilayer design will be summarized.  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