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   225766篇
  免费   6715篇
  国内免费   4218篇
耳鼻咽喉   1572篇
儿科学   7110篇
妇产科学   3498篇
基础医学   21793篇
口腔科学   2415篇
临床医学   18596篇
内科学   37155篇
皮肤病学   1170篇
神经病学   18661篇
特种医学   10779篇
外国民族医学   20篇
外科学   33695篇
综合类   13695篇
现状与发展   10篇
一般理论   2篇
预防医学   22369篇
眼科学   3992篇
药学   15149篇
  40篇
中国医学   4691篇
肿瘤学   20287篇
  2024年   193篇
  2023年   741篇
  2022年   1892篇
  2021年   2611篇
  2020年   2100篇
  2019年   1805篇
  2018年   23569篇
  2017年   19025篇
  2016年   21072篇
  2015年   3399篇
  2014年   3679篇
  2013年   3543篇
  2012年   10435篇
  2011年   24731篇
  2010年   21420篇
  2009年   13535篇
  2008年   21790篇
  2007年   24367篇
  2006年   3109篇
  2005年   4394篇
  2004年   5838篇
  2003年   7396篇
  2002年   5221篇
  2001年   2505篇
  2000年   1853篇
  1999年   1170篇
  1998年   843篇
  1997年   801篇
  1996年   481篇
  1995年   462篇
  1994年   404篇
  1993年   240篇
  1992年   241篇
  1991年   256篇
  1990年   275篇
  1989年   215篇
  1988年   155篇
  1987年   129篇
  1986年   91篇
  1985年   93篇
  1984年   44篇
  1983年   41篇
  1982年   35篇
  1980年   49篇
  1938年   60篇
  1937年   25篇
  1935年   22篇
  1934年   30篇
  1932年   56篇
  1930年   46篇
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
991.
Local injection of a mixture of beta-aminopropionitril fumarate (BAPN-f) and sodium hyaluronate (NaH+) together with controlled exercise were evaluated for treatment of superficial digital flexor tendon (SDFT) injuries in horses. Fourteen mixed breed horses with subacute SDF tendon injuries in forelimbs were randomly assigned to two groups. One group received BAPN-f (0.7 mg/ml) and the other received NaH+ (10 mg/ml) all by intratendinous injection. Controlled exercise started during the first week after intratendinous treatment and continued for 12 weeks. Cross-sectional area (CSA) of the SDFT, diameter of the SDFT, and relative area of the lesion (presence of CSA) were measured by ultrasonographic examination. Lesions were semiquantitatively graded for echogenicity on a scale of 0 to 4. The lesion severity in CSA was significantly reduced by BAPN and NaH compared to those horses treated by BAPN only (p < 0.05). Lesion echogenicity score was significantly higher in horses treated with BAPN and NaH+ at day 0 compared to horses treated with BAPN (p < 0.05). At the end of the study, lesion echogenicity score was significantly reduced in the horses treated with BAPN and NaH+ compared to horses treated by BAPN only (p < 0.05). According to the results of the present study, a combination of BAPN-f and NaH+ has a greater beneficial effect on tendon healing and remodeling in horses, as assessed by sonographic examination, compared to treatment with single drugs.  相似文献   
992.
The search for a marsupial XIC reveals a break with vertebrate synteny   总被引:1,自引:0,他引:1  
X-chromosome inactivation (XCI) evolved in mammals to deal with X-chromosome dosage imbalance between the XX female and the XY male. In eutherian mammals, random XCI of the soma requires a master regulatory locus known as the ‘X-inactivation center’ (XIC/Xic), wherein lies the noncoding XIST/Xist silencer RNA and its regulatory antisense Tsix gene. By contrast, marsupial XCI is imprinted to occur on the paternal X chromosome. To determine whether marsupials and eutherians share the XIC-driven mechanism, we search for the sequence equivalents in the genome of the South American opossum, Monodelphis domestica. Positional cloning and bioinformatic analysis reveal several interesting findings. First, protein-coding genes that flank the eutherian XIC are well-conserved in M. domestica, as well as in chicken, frog, and pufferfish. However, in M. domestica we fail to identify any recognizable XIST or TSIX equivalents. Moreover, cytogenetic mapping shows a surprising break in synteny with eutherian mammals and other vertebrates. Therefore, during the evolution of the marsupial X chromosome, one or more rearrangements broke up an otherwise evolutionarily conserved block of vertebrate genes. The failure to find XIST/TSIX in M. domestica may suggest that the ancestral XIC is too divergent to allow for detection by current methods. Alternatively, the XIC may have arisen relatively late in mammalian evolution, possibly in eutherians with the emergence of random XCI. The latter argues that marsupial XCI does not require XIST and opens the search for alternative mechanisms of dosage compensation.  相似文献   
993.
Fiber tracking allows the in vivo reconstruction of human brain white matter fiber trajectories based on magnetic resonance diffusion tensor imaging (MR-DTI), but its application in the clinical routine is still in its infancy. In this study, we present a new software for fiber tracking, developed on top of a general-purpose DICOM (digital imaging and communications in medicine) framework, which can be easily integrated into existing picture archiving and communication system (PACS) of radiological institutions. Images combining anatomical information and the localization of different fiber tract trajectories can be encoded and exported in DICOM and Analyze formats, which are valuable resources in the clinical applications of this method. Fiber tracking was implemented based on existing line propagation algorithms, but it includes a heuristic for fiber crossings in the case of disk-shaped diffusion tensors. We successfully performed fiber tracking on MR-DTI data sets from 26 patients with different types of brain lesions affecting the corticospinal tracts. In all cases, the trajectories of the central spinal tract (pyramidal tract) were reconstructed and could be applied at the planning phase of the surgery as well as in intraoperative neuronavigation.  相似文献   
994.

Background  

Residents play an important role in teaching of medical undergraduate students. Despite their importance in teaching undergraduates they are not involved in any formal training in teaching and leadership skills. We aimed to compare the teaching skills of residents with faculty in facilitating small group Problem Based Learning (PBL) sessions.  相似文献   
995.
目的 观察表皮生长因子 (EGF)与细胞增殖核抗原 (PCNA)在人胎儿睾丸发生过程中的表达特征 ,探讨两者在睾丸发生中的作用。 方法 用SP免疫细胞化学技术检测了人胎儿 12~ 32周睾丸间质细胞、支持细胞、生殖细胞EGF、PCNA阳性细胞表达率。 结果 EGF在胎儿 12周龄睾丸组织未见表达 ,16~ 32周龄睾丸间质细胞呈阳性表达 ,16~ 2 0周为表达高峰 ,随着胎龄的增长呈逐渐下降趋势 (P <0 0 1) ;PCNA在胎儿睾丸间质细胞、支持细胞和生殖细胞均有不同程度表达 ,16~ 2 0周为表达高峰 ,随着胎龄的增长呈逐渐下降趋势 (P <0 0 1)。 结论 EGF与PCNA在人胎儿睾丸发育过程中有不同程度的表达 ,表明EGF与PCNA在睾丸发育过程中起着一定的作用  相似文献   
996.
目的 :研究内毒素血症中诱生型一氧化氮合酶 (induciblenitricoxidesyhthases,iNOS)抑制剂硫酸甲基异硫脲(S Methy1isothioureasulfate,SMT)对大鼠肠系膜淋巴管一氧化氮合酶 (nitricoxidesyhthase,NOS)表达的影响。探讨在内毒素血症中一氧化氮 (nitricoxide,NO)对肠系膜淋巴微循环的影响。方法 :利用NADPH 黄递酶组织化学染色方法观察NOS在大鼠肠系膜淋巴管的表达 ,用硝酸还原酶法测定血清中NO的含量。结果 :脂多糖(lipopolysaccharide,LPS)组大鼠随时间延长肠系膜淋巴管染色强度明显加深 ,血清NO含量显著升高。LPS SMT组染色强度比LPS组降低 ,血清NO含量显著下降。结论 :在内毒素血症中 ,SMT可能通过抑制NOS的活性而起保护作用。  相似文献   
997.
利用木瓜蛋白酶分别制备了抗汉坦病毒鼠源性单克隆抗体(mAb)3G1和3D8F(ab′)2片段。通过WaterDEAE40HR阴离子交换色谱柱纯化后,非还原型SDSPAGE呈现单一条带,相对分子质量(Mr)约100000。两种F(ab′)2片段均具有良好的血凝抑制活性、病毒中和活性及对汉坦病毒感染乳鼠的保护作用  相似文献   
998.
目的观察人膜联蛋白Ⅴ(Human Annexin Ⅴ,HAⅤ)在乙肝病毒感染胎盘、正常中、晚孕胎盘及早孕绒毛中的表达并探讨其意义.方法用SP法检测HBsAg阳性孕妇足月分娩胎盘、HBV血清标志物阴性的正常早孕、中孕和足月胎盘各20例HAⅤ的表达、分布并进行定量分析.结果中孕、足月胎盘和HBV感染的胎盘组织中HAⅤ呈不均一的棕黄色颗粒状染色,泛存在于胎盘组织各类细胞胞浆、胞膜和核膜上.滋养细胞呈强阳性染色,绒毛间质细胞和毛细血管内皮细胞呈弱阳性染色.早孕绒毛HAⅤ棕黄色颗粒主要分布于外层滋养细胞的胞浆、胞膜和核膜上,最内层滋养细胞和间质偶见表达;比较HBV感染组和正常足月组胎盘HAⅤ表达的量,前者的平均灰度比后者明显增高,差异具有显著性(P<0.01),中孕组与足月组HAⅤ表达的量没有差别(P>0.05),早孕和中孕组、足月组HAⅤ表达的量的比较,前者显著低于后两者(P<0.05).结论HAⅤ可能作为受体介导了HBV对胎盘的感染.  相似文献   
999.

Aim  

External quality assurance (EQA) is an extremely valuable resource for clinical pathologists to maintain high standards, improve diagnostic skills, and possibly revalidate medical license. The aim of this study was to participate in and compare four international slide survey programs (UK, IAP-Germany, USA-Canada, Australasia) in pediatric histopathology for clinical pathologists with the aim to use it as a revalidation method.  相似文献   
1000.

Background  

Recruiting and retaining GPs for research can prove difficult, and may result in sub-optimal patient participation where GPs are required to recruit patients. Low participation rates may affect the validity of research.  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