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   198338篇
  免费   18632篇
  国内免费   10904篇
耳鼻咽喉   1874篇
儿科学   3059篇
妇产科学   3636篇
基础医学   20524篇
口腔科学   3743篇
临床医学   25806篇
内科学   27705篇
皮肤病学   2870篇
神经病学   8698篇
特种医学   7215篇
外国民族医学   50篇
外科学   19046篇
综合类   34248篇
现状与发展   49篇
一般理论   19篇
预防医学   16066篇
眼科学   5048篇
药学   21049篇
  253篇
中国医学   12724篇
肿瘤学   14192篇
  2024年   546篇
  2023年   2413篇
  2022年   5943篇
  2021年   8688篇
  2020年   6654篇
  2019年   5532篇
  2018年   6020篇
  2017年   6040篇
  2016年   5350篇
  2015年   8695篇
  2014年   10717篇
  2013年   11464篇
  2012年   16938篇
  2011年   17474篇
  2010年   12900篇
  2009年   10905篇
  2008年   12611篇
  2007年   12298篇
  2006年   11086篇
  2005年   9972篇
  2004年   7330篇
  2003年   6872篇
  2002年   5724篇
  2001年   4481篇
  2000年   3847篇
  1999年   3020篇
  1998年   1511篇
  1997年   1451篇
  1996年   1166篇
  1995年   1010篇
  1994年   934篇
  1993年   581篇
  1992年   1032篇
  1991年   887篇
  1990年   796篇
  1989年   691篇
  1988年   624篇
  1987年   599篇
  1986年   470篇
  1985年   386篇
  1984年   274篇
  1983年   231篇
  1982年   130篇
  1981年   134篇
  1980年   107篇
  1979年   219篇
  1978年   163篇
  1977年   104篇
  1976年   111篇
  1975年   106篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
目的: 应用超声心动图评价急性心肌梗死患者行Ⅱ期心脏康复前后心功能及同步性改变。方法: 对20例急性心肌梗死患者Ⅱ期心脏康复前后使用脉冲多普勒结合心电图计算主肺动脉射血前时间差,即心室间机械延迟时间(IVMD)。于心尖四腔心切面,使用M型超声心动图,计算出三尖瓣环收缩期位移(TAPSE)。使用实时三维超声心动图获取心尖四腔心全容积图像,在Qlab 9.0软件下获得心率、左室射血分数(LVEF)、左室舒张末容积(LVEDV)、左房最大容积(LAVmax)和左房射血分数(LAEF)。软件自动计算出左室16节段达收缩期最小容积点时间最大时间差(Tmsv16 Dif)心率校正值,即LVTmsv16 Dif/R R(%),以及左房16节段达收缩期最小容积点时间最大时间差(Tmsv16 Dif)心率校正值,即LATmsv16 Dif/R R(%)。结果: 急性心肌梗死患者Ⅱ期心脏康复后心率、LATmsv16 Dif/R R(%)明显低于康复前(P<0.001和P<0.05),LVEF、LAEF明显高于康复前(P<0.001和P<0.05),康复前后IVMD、TAPSE、LVEDV、LAVmax、LVTmsv16 Dif/R R(%)比较差异无统计学意义(P均>0.05)。结论: 急性心肌梗死患者行Ⅱ期心脏康复后左心收缩功能及左房同步性较康复前改善。  相似文献   
992.
作者根据现代免疫学观点,自1989年起采用自制中药“90增血剂”治疗ITP46例。期间,应用间接免疫荧光技术检测了患者外周血T淋巴细胞亚群,结果表明病例组全T细胞(CD_3)、T辅助/诱导细胞(CD_4)降低,T抑制/细胞毒细胞(CD_8)增高,CD_4/CD_8比值明显降低。治疗后,患者T亚群恢复常态,血小板数上升,骨髓产板型巨核细胞数增加,临床总有效率达91.2%,明显优于激素组(71.4%)。提示中药具有显著的疗效和良好的免疫调节作用。同时,动态观察ITP患者T细胞亚群的变化,对帮助临床判断治疗反应和预后有很大意义。  相似文献   
993.
We measured the concentrations of the three major monoamine neurotransmitters noradrenaline, dopamine, and serotonin, their metabolites, and receptor binding sites in autopsied brain of three patients with narcolepsy. As compared with the controls, concentrations of the noradrenaline and serotonin metabolites MHPG and 5-HIAA, respectively, were markedly elevated in cerebral cortical subdivisions of the narcolepsy patients together with a trend for above-normal neurotransmitter/metabolite "turnover" ratio. A moderately reduced number of alpha 1-adrenoceptors, as judged by the reduced levels of 3H-prazosin binding, was observed in cerebral cortex of two of the three patients with narcolepsy. Mean striatal levels of dopamine and its metabolite homovanillic acid were normal, whereas the concentration of dopamine's second metabolite, dihydroxyphenylacetic acid, was markedly reduced by 50% or greater. This was accompanied by a marked increase (+125%) in mean 3H-spiperone binding to the D2 dopamine receptor in both caudate and putamen; in contrast, the levels of 3H-SCH 23390 binding to the striatal D1 dopamine receptor were in the normal range. Our data provide evidence for altered brain monoaminergic neurotransmitter function in human narcolepsy.  相似文献   
994.
Two clinicians and the nursing sisters working in the ICU evaluated the chance of survival of ICU patients every day. Patients were assessed either as "outcome unknown or will die." These predictions were compared with those made by computerized trend analysis of daily acute physiology and chronic health evaluation (APACHE II) scores corrected for the presence and duration of major organ system failure. The predictions were not acted upon during the study. Comparing the predictions with actual hospital outcome, the doctors and nurses had a false-positive diagnosis rate for dying of between 7.7% and 16.7%, while there were no false predictions by the computer model. The patients predicted to die by the doctors and nurses were not completely identical to those predicted by the computer. Predictions of doctors and nurses that were confirmed by the computer had a sensitivity of 20% and no false predictions of death.  相似文献   
995.
Summary A human glioma cell line (YKG1), which was positively identified for glial fibrillary acidic (GFA) and S-100 proteins, was established from a surgical specimen of a patient with glioblastoma. Chromosome analysis of the cells revealed a homogeneously staining region (HSR) on a marker chromosome. The assay for transforming growth factors (TGFs) in the conditioned medium of the cell line revealed that it contained high levels of - and -type TGFs, which might regulate the growth of glioblastoma and influence on the peritumoral tissues.  相似文献   
996.
本实验观察了大鼠全身照射不同剂量(4~25Gy)及全腹部照射(10Gy)后胃酸分泌的变化并用RIA方法测定照射后胃窦及血清中胃泌素水平.结果表明,全身8~25Gy照射后第3天,腹部10Gy照射后1~6周,胃酸分泌明显抑制.主现表现为胃液中[H~+]分泌的抑制,致使照射后胃液酸度降低.10Gy以上剂量照射使胃泌素释放增加,表现为血清胃泌素明显升高,胃窦胃泌素明显减少,导致照射引起的"低胃酸、高胃泌素血症".这种表现与人的某些萎缩性胃炎或恶性贫血的状况相似.  相似文献   
997.
Summary The plasma pharmacokinetic profile of 4-epidoxorubicin (epirubicin) was investigated in 28 patients with nasopharyngeal carcinoma (NPC) after single i.v. rapid infusions. All patients had normal liver and renal functions. Plasma concentrations of the parent compound were specifically determined by a high-performance liquid chromatographic (HPLC) method, with UV detection at 254 nm. Plasma levels of the compound were fitted to a three-compartment open model; a triexponential decrease in plasma concentrations with a long terminal plasma halflife (44.8±21.2 h) was observed in 27 patients. The respective mean (±SD) serum concentration at 72 h and the AUC, plasma clearance, and terminal elimination rate constant in complete responders were 7.67±1.98 ng/ml, 4,002±3,080 ng· h/ml, 26.6±12.9 l/h·m2, and 0.009±0.007 l/h, whereas those in nonresponders were 4.96±1.8 ng/ml, 1,88±652.8 ng·h/ml, 44.4±15 l/h·m2, and 0.017±0.006 l/h, respectively; these differences were significant (P(0.05). Epirubicin produced a 52% response rate, including 6 patients with a complete response, 8 with a partial response, 11 with no change, and 2 with progressive disease. No relationship could be found between the various pharmacokinetic parameters and either leukopenia, age, or sex. These observations strongly suggest that plasma clearance may be one of the determining factors affecting the response or nonresponse of NPC patients to epirubicin, and a dose adjustment according to plasma clearance would probably increase the response rate.  相似文献   
998.
组织工程心脏瓣膜研究进展   总被引:1,自引:0,他引:1  
目前组织工程心脏瓣膜研究已在支架的选材、种子细胞的选择、种子细胞的种植与瓣膜构建方法三个方面取得进展,并已构建出三种代表性组织工程心脏瓣膜。对它们各自的特点进行综述。  相似文献   
999.
陡脉冲电场对荷瘤BALB/c小鼠癌细胞杀伤效应的实验研究   总被引:1,自引:0,他引:1  
观测陡脉冲电场对荷瘤BALB/c小鼠癌细胞的杀伤效应。处理后的癌细胞在光镜下表现为细胞核固缩、核碎裂、核溶解;在电镜下表现为异染色质增加,边集,呈团块样改变,细胞质肿胀,脂滴数量增加,质膜破裂;核固缩,碎裂,线粒体肿胀。实验揭示了陡脉冲电场能有效地杀伤癌细胞,明显抑制了荷瘤小鼠恶性肿瘤的生长、增殖,有着良好的应用前景。  相似文献   
1000.
Differential expression of multiple osteogenic factors may be responsible for the different osteoinductivity of osteosarcoma cell lines. We compared in vivo osteoinductivity of human osteosarcoma cell lines (Saos-2 vs. U-2 OS) in nude mice, and their in vitro expression of various osteogenic factors of protein level by quantitative immunocytochemistry and mRNA level by RT-PCR and/or in situ hybridization. Saos-2 cells, but not U-2 OS, were osteoinductive in vivo. Significantly higher expression (independent t-test, all p < 0.005) of osteogenic factors were observed in Saos-2 cells compared with U-2 OS, which included bone morphogenetic proteins (particularly BMPs-2, 3, 4, and 7), transforming growth factor-beta (TGF-beta), BMP receptor (BMPR)-1A, receptor-regulated Smads (R-Smads), Smads 1, 2, and 5, and common-mediator Smad (Co-Smad), Smad 4. In contrast, U-2 OS cells expressed higher levels of inhibitory Smad 6 (I-Smad) protein than Saos-2 cells (p < 0.001). These results suggest that a combination of osteogenic factors (BMPs, TGF-beta, BMPRs, and R/Co-Smads) against I-Smad may play important roles in the Saos-2 cell osteoinductivity. This may have a clinical implication in selecting key osteogenic factors for combined therapy for bone defect diseases. The characterized cell lines can be used as positive and negative controls for the assessments of both in vitro and in vivo bone formation capabilities of designed tissues or biomaterials.  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