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   387369篇
  免费   36829篇
  国内免费   26682篇
耳鼻咽喉   3102篇
儿科学   5172篇
妇产科学   4279篇
基础医学   42053篇
口腔科学   6467篇
临床医学   54295篇
内科学   50550篇
皮肤病学   4297篇
神经病学   18270篇
特种医学   14584篇
外国民族医学   224篇
外科学   34103篇
综合类   74888篇
现状与发展   96篇
一般理论   31篇
预防医学   28800篇
眼科学   10765篇
药学   42532篇
  441篇
中国医学   26256篇
肿瘤学   29675篇
  2024年   894篇
  2023年   5106篇
  2022年   10911篇
  2021年   18760篇
  2020年   14820篇
  2019年   12016篇
  2018年   12509篇
  2017年   12201篇
  2016年   11122篇
  2015年   17492篇
  2014年   21816篇
  2013年   20196篇
  2012年   30122篇
  2011年   33810篇
  2010年   23248篇
  2009年   19013篇
  2008年   22936篇
  2007年   22521篇
  2006年   21474篇
  2005年   20267篇
  2004年   13430篇
  2003年   12818篇
  2002年   10409篇
  2001年   8914篇
  2000年   8611篇
  1999年   8481篇
  1998年   5275篇
  1997年   5086篇
  1996年   3970篇
  1995年   3722篇
  1994年   3157篇
  1993年   2041篇
  1992年   2431篇
  1991年   2127篇
  1990年   1797篇
  1989年   1558篇
  1988年   1287篇
  1987年   1141篇
  1986年   941篇
  1985年   677篇
  1984年   371篇
  1983年   271篇
  1982年   145篇
  1981年   170篇
  1980年   115篇
  1979年   154篇
  1978年   73篇
  1977年   53篇
  1974年   42篇
  1972年   37篇
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
991.
BACKGROUND: Optimal feeding practice in the first year of life is crucial for the survival and health of infants, and has long-term consequences in later life. However, non-optimal feeding practices exist widely. The present study aims to explore various constraints to optimal feeding practices in the first year of life of infants in urban areas of Beijing, China. METHODS: A cross-sectional study was conducted in urban areas of Beijing from 4 July to 20 August, 1998. Two hundred and fifty-one mothers of infants aged 6-12 months were chosen from six child health centers in three different urban districts in Beijing. A self-administered structured questionnaire was used to collect data regarding feeding practices and potentially related factors. RESULTS: Feeding practice for most of the infants was in accordance with the national and international recommendations. However, the rate of incidence of exclusive breast-feeding at 3 months of age was lower than that recommended by the World Health Organisation (WHO) (55.8%), and the introduction of solid/semisolid food before 4 months of age was found in approximately 19.3% of the infants. Cow's milk was given to 21.2% of infants from 6 months of age as the sole source of milk or as a supplement. Maternal education level (OR = 2.44, 95% CI: 1.42-4.19, P < 0.05), employment (OR = 2.05, 95% CI: 1.13-3.74, P < 0.05) and antenatal nonexclusive breast-feeding plans (OR = 4.10, 95% CI: 2.24-7.50, P < 0.001) were found to be correlated to inappropriate feeding practices. CONCLUSIONS: The feeding practices for most of the urban infants was found to be in accordance with the Chinese government and WHO recommendations; however, non-optimal feeding practices presenting as the early cessation of breast-feeding and the introduction of solid/semisolid foods existed. Information regarding optimal feeding practices should be disseminated to mothers and medical professionals in China, to ensure optimal infant health.  相似文献   
992.
输尿管镜在输尿管梗阻中的诊治价值   总被引:1,自引:0,他引:1  
目的探讨输尿管镜在输尿管梗阻诊治中的价值.方法应用输尿管镜对52例非结石性输尿管梗阻进行诊治.结果输尿管狭窄35例(行输尿管镜硬性扩张19例,气囊扩张13例,腹腔镜下输尿管成形术3例),输尿管息肉13例行钬激光切除,输尿管癌3例改行开放手术,腔静脉后输尿管1例改行输尿管成形术.手术并发黏膜明显裂伤或黏膜下假道2例,输尿管穿孔1例,其它并发症.结论输尿管镜术能明确输尿管梗阻的病因,并能采取相应治疗.  相似文献   
993.
目的:观察奥沙利铂(L-OHP)并5-氟脲嘧啶、甲酰四氢叶酸钙(5-Fu/LV)配合放疗治疗晚期复发直肠癌患者的增效作用与毒性反应。方法:23例无法手术的晚期复发直肠癌患者进行盆腔放疗,在放疗的第1、5同前一天开始给予L-OHP30mg/m。静滴0.5h,LV100mg/m^2和5-Fu375mg/m^2静滴4h,连用4d。25例单纯放疗者为对照组。结果:放疗结束时,观察组局部症状缓解率较对照组高,尤其对会阴区下坠疼的改善明显(P〈0.05),且转移症状亦有所缓解。两组有效率分别为78.3%、48%(P〈0.05),完全缓解分别为8.7%、4.0%。主要毒副反应是消化道反应、神经毒性、静脉炎,骨髓抑制。结论:利用低剂量L-OHP并5-Fu/LV的增敏作用配合放疗治疗晚期、复发直肠癌可提高近期疗效,改善症状,尤其对于伴远外转移者,为理想、安全的治疗手段。  相似文献   
994.
腹腔镜辅助下大隐静脉隔绝术治疗大隐静脉曲张60例   总被引:1,自引:0,他引:1  
目的探讨腹腔镜辅助下大隐静脉隔绝术的疗效。方法2000年1月~2004年1月对60例66条大隐静脉曲张腹腔镜辅助下行大隐静脉隔绝术,腹腔镜辅助下高位结扎、电灼大腿段大隐静脉,阻断其小腿段所有属支及交通支,使大隐静脉与体循环隔绝。结果手术时间30~60min,(50±9)min;术后住院时间3~5d,(3.5±0.6)d。60例随访1~36个月,平均28个月,无复发。结论腹腔镜辅助下大隐静脉隔绝术创伤小,疗效好,复发率低,是治疗大隐静脉曲张的理想术式。  相似文献   
995.
目的通过动物实验观察不同骨水泥强化松质骨螺钉的生物力学和组织学变化动态,为骨质疏松骨折患者内固定提供理论基础。方法在10只杂种犬胫骨近端制作松质骨螺钉植入的动物模型,分别采用碳酸化羟基磷灰石水泥(CHC)和聚甲基丙烯酸甲酯(PMMA)强化,分别于术后5d、4、8、12和16周处死动物,观察螺钉拔出的生物力学和组织学变化。结果CHC强化的螺钉拔出力随手术后时间的延长而逐渐升高,16周时达到(512.5 14.5)N,而PMMA强化组螺钉拔出力则随手术后时间的延长而逐渐降低。CHC-骨界面结合紧密,并且随时间延长出现CHC降解和骨长入,而PMMA-骨界面形成一层纤维组织。结论CHC强化能够提高松质骨螺钉植入体内的稳定性,并且随植入时间延长而逐渐升高。  相似文献   
996.
目的探讨腹膜后脓肿的病因,诊断和治疗。方法回顾性分析了1990-2004年诊断和治疗腹膜后脓肿33例的临床资料。结果急性坏死性胰腺炎后20例,胆囊切除胆总管探查术后4例,十二指肠损伤2例,阑尾穿孔3例,肾结石4例。超声检查确诊80%(20/25),CT检查确诊100%(22/22)。经腹部腹膜后脓肿切开置管引流25例,手术1~4次不等,后腰部切开引流8例。手术后并发应激性胃粘膜损伤致消化道出血7例,成人呼吸窘迫综合征(ARDS)5例,急性肾功能衰竭3例,死亡4例。治愈时间1~6个月,平均3.5个月。结论及时明确诊断,进行有效引流并加强营养支持是治疗成功的关键。  相似文献   
997.
Small bowel transplantation (SBT) is associated with a high incidence of infectious complications because of ischemia/reperfusion (I/R) mucosal injury concomitant with potent immunosuppression. In this study, we evaluated whether the cavitary two-layer method (cTLM) could reduce I/R injury and allow early mucosal restoration, particularly after prolonged preservation and transplantation. Canine heterotopic segmental SBT was performed immediately without preservation (group 1), after 24-h preservation in UW solution (group 2) or by the cTLM (group 3). The graft samples were taken 1 h after reperfusion and on days 1, 4 and 7. We assessed graft mucosa with detailed microscopic and electromicroscopic analyses. In Group 3, histological injury and cell apoptosis after transplantation were significantly alleviated and rapidly recovered to a similar level of group 1. The mucosal restoration was morphologically completed within 4 days. In contrast, in group 2, more pronounced mucosal injury and delayed recovery were noted. Crypt cell proliferation activity was well maintained in groups 1 and 3 throughout the experimental period. Our ultrastructural analysis suggested that mitochondrial integrity achieved by the cTLM was a basal mechanism under the prompt mucosal restoration. The cTLM could reduce I/R injury, facilitate mucosal regeneration and restore the nearly normal structure early after SBT.  相似文献   
998.
This study compared the osteogenic differentiation of F-MDSCs and M-MDSCs. Interestingly, M-MDSCs expressed osteogenic markers and underwent mineralization more readily than F-MDSCs; a characteristic likely caused by more osteoprogenitor cells within the M-MDSCs than the F-MDSCs and/or an accelerated osteogenic differentiation of M-MDSCs. INTRODUCTION: Although therapies involving stem cells will require both female and male cells, few studies have investigated whether sex-related differences exist in their osteogenic potential. Here, we compared the osteogenic differentiation of female and male mouse skeletal muscle-derived stem cells (F- and M-MDSCs, respectively), a potential cell source for orthopedic tissue engineering. MATERIALS AND METHODS: F- and M-MDSCs were stimulated with bone morphogenetic protein (BMP)4, followed by quantification of alkaline phosphatase (ALP) activity and expression of osteogenic genes. F- and M-MDSCs were also cultured as pellets in osteogenic medium to evaluate mineralization. Single cell-derived colonies of F- and M-MDSCs were stimulated with BMP4, stained for ALP, and scored as either Low ALP+ or High ALP+ to detect the presence of osteoprogenitor cells. F- and M-MDSCs were transduced with a BMP4 retrovirus (MDSC-BMP4 cells) and used for the pellet culture and single cell-derived colony formation assays. As well, F- and M-MDSC-BMP4 cells were implanted in the intramuscular pocket of sex-matched and sex-mismatched hosts, and bone formation was monitored radiographically. RESULTS AND CONCLUSIONS: When stimulated with BMP4, both F- and M-MDSCs underwent osteogenic differentiation, although M-MDSCs had a significantly greater ALP activity and a larger increase in the expression of osteogenic genes than F-MDSCs. In the pellet culture assay, M-MDSCs showed greater mineralization than F-MDSCs. BMP4 stimulation of single cell-derived colonies from M-MDSCs showed higher levels of ALP than those from F-MDSCs. Similar results were obtained with the MDSC-BMP4 cells. In vivo, F-MDSC-BMP4 cells displayed variability in bone area and density, whereas M-MDSC-BMP4 cells showed a more consistent and denser ectopic bone formation. More bone formation was also seen in male hosts compared with female hosts, regardless of the sex of the implanted cells. These results suggest that M-MDSCs may contain more osteoprogenitor cells than F-MDSCs, which may have implications in the development of cellular therapies for bone healing.  相似文献   
999.
目的 研究pcDU6载体质粒介导的转化生长因子β1(TGF-β1)短发夹RNA(shRNA)对人血清白蛋白(HSA)致人肾近曲小管上皮细胞(HK2细胞)增殖,TGF-β1、结缔组织生长因子(CTGF)和纤连蛋白(FN)表达的影响,并探讨有关机制。方法 构建TGF-β1shRNA的pcDU6载体质粒,体外培养HK2细胞株。采用脂质体转染将表达TGF-β1shRNA的pcDU6质粒载体(pcDU6-A1-A2和peDU6-B1-B2)分别导人实验组细胞。用HSA(5g/L)刺激HK2细胞12h或24h。四甲基偶氮唑盐(MTF)比色法测定细胞增殖水平。RT-PCR半定量分析HK2细胞中TGF-β1、CTGF和FNmRNA的表达水平;双抗夹心酶联免疫吸附法检测HK2细胞培养液中TGF-β1及FN蛋白质水平。结果 HK2细胞在HSA刺激下,其TGF-β1、CTGF及FNmRNA的表达明显上调,培养液中TGF-β1和FN的蛋白质含量亦明显升高(P〈0.05)。与pcDU6空载体组比较,pcDU6载体质粒介导的TGF-β1shRNA干扰组TGF-β1、CTGF及FNmRNA的表达明显下调(P〈0.05)。TGF-β1shRNA转染HK2细胞后12h或24h,细胞培养液中TGF-β1和FN蛋白质含量明显下降,HK2细胞增殖被部分抑制(P〈0.05)。在细胞增殖、TGF-β1、CTGF及FN基因表达方面,TGF-β1shRNA干扰组组间比较,以及pcDU6空载体转染组与HSA刺激组比较,差异均无统计学意义。结论 peDU6载体质粒介导的TGF-β1shRNA能够明显抑制HSA刺激下HK2细胞增殖、TGF-β1、CTGF和FN基因的表达。HSA刺激HK2细胞增殖及CTGF和FN基因的过表达可能通过TGF-β1介导。  相似文献   
1000.
目的 探讨组织工程心瓣膜常用人工基质材料--明胶发生降解后的产物对大鼠真皮成纤维细胞增殖及Ⅰ型胶原蛋白分泌的影响. 方法 利用酶组合技术制备明胶降解物(gelatin hydrolysate, GH),采用超滤的方法分离出低分子量明胶降解物组分(gelatin hydrolysate fraction, GHF),用于5只SD大鼠真皮成纤维细胞的体外培养.采用CCK-8活细胞计数试剂盒(Cell Counting Kit-8)检测细胞的增殖情况,ELISA试剂盒检测细胞I型胶原蛋白的分泌情况. 结果 ①GHF对细胞增殖作用的浓度效应:在0.125~1.0 mg/ml浓度范围内,GHF对细胞的促增殖作用呈现先增强后减弱的趋势,在0.25 mg/ml时,细胞增殖率最大,达到(47.54±16.35)%;②GH与GHF对细胞增殖影响比较:GH与GHF均具有促进细胞增殖的作用,且在浓度为0.25 mg/ml时,促细胞增殖作用无显著差异[(27.04±15.21)% vs (39.22±15.55)%, P=0.177];③GH与GHF对细胞分泌Ⅰ型胶原蛋白影响比较:GHF组第3天时Ⅰ型胶原分泌量为(28.06±5.60)pg/105,与空白对照的(18.24±4.52)pg/105相比,有显著差异(P=0.006),而GH组直至第6天时Ⅰ型胶原蛋白分泌量,与空白对照相比,无统计学意义(P=0.103). 结论 分子量大小不同的明胶降解物GH与GHF均具有促进大鼠真皮成纤维细胞增殖的作用,且分子量较小的GHF还具有促进细胞I型胶原分泌的功能.  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