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   7239篇
  免费   519篇
  国内免费   320篇
耳鼻咽喉   43篇
儿科学   104篇
妇产科学   30篇
基础医学   1017篇
口腔科学   134篇
临床医学   514篇
内科学   1149篇
皮肤病学   131篇
神经病学   396篇
特种医学   276篇
外科学   499篇
综合类   713篇
现状与发展   1篇
预防医学   222篇
眼科学   229篇
药学   1989篇
中国医学   483篇
肿瘤学   148篇
  2023年   63篇
  2022年   79篇
  2021年   221篇
  2020年   157篇
  2019年   189篇
  2018年   186篇
  2017年   160篇
  2016年   198篇
  2015年   227篇
  2014年   304篇
  2013年   505篇
  2012年   321篇
  2011年   370篇
  2010年   303篇
  2009年   307篇
  2008年   345篇
  2007年   373篇
  2006年   340篇
  2005年   311篇
  2004年   289篇
  2003年   270篇
  2002年   265篇
  2001年   216篇
  2000年   208篇
  1999年   195篇
  1998年   166篇
  1997年   152篇
  1996年   115篇
  1995年   114篇
  1994年   96篇
  1993年   91篇
  1992年   82篇
  1991年   67篇
  1990年   65篇
  1989年   82篇
  1988年   67篇
  1987年   62篇
  1986年   50篇
  1985年   61篇
  1984年   52篇
  1983年   37篇
  1982年   53篇
  1981年   47篇
  1980年   49篇
  1979年   41篇
  1978年   22篇
  1977年   32篇
  1976年   26篇
  1975年   10篇
  1974年   13篇
排序方式: 共有8078条查询结果,搜索用时 375 毫秒
1.
PurposeTo develop and evaluate an automated method to measure the foveal avascular zone (FAZ) area in healthy eyes on Heidelberg Spectralis Optical Coherence Tomography Angiography (HS-OCTA). This method is referred to as the modified Kanno-Saitama macro (mKSM) which is an evolution of the Kanno-Saitama macro (KSM) approach.MethodsThis cross-sectional study included 29 eyes of 25 healthy volunteers who underwent HS-OCTA at the macular area twice at the same time. Regardless of the quality of the images, all of them were included. Macular data on the superficial vascular plexus, intermediate capillary plexus (ICP) and deep capillary plexus were processed by mKSM. The FAZ area was measured twice automatically using the mKSM and KSM and twice manually by two independent examiners.ResultsFrom 174 images, KSM could not measure correctly 31% while mKSM could successfully measure all of them. Intrascan intraclass coefficient ranged from 0.948 to 0.993 for manual measurements and was 1 for mKSM method. Despite that the difference between human examiners is smaller than between human examiners and mKSM according to Bland-Altman plots, the scatterplots show a strong correlation between human and automatic measurements. The best results are obtained in ICP.ConclusionsWith mKSM, the automated determination of the FAZ area in HS-OCTA is feasible and less human-dependent. It solves the inability of KSM to measure the FAZ area in suboptimal quality images which are frequent in daily clinical practice. Therefore, the mKSM processing could contribute to our understanding of the three vascular plexuses.  相似文献   
2.
3.
The objective of this study was to investigate the absorption behavior of chikusetsusaponin IVa (CHS‐IVa) in the rat intestine using single‐pass intestinal perfusion (SPIP) and to classify CHS‐IVa into the biopharmaceutics classification system (BCS). The equilibrium solubility of CHS‐IVa was determined by the shaker method. The absorption mechanism of CHS‐IVa in the intestine was studied by comparing the Peff of different concentrations of CHS‐IVa. The intestinal site dependence of CHS‐IVa absorption was studied by comparing the Peff of the same concentration of CHS‐IVa in different intestinal segments. The relationship between CHS‐IVa and intestinal efflux protein was studied by perfusion with an efflux protein inhibitor. The permeability of CHS‐IVa was investigated by comparing the Peff of CHS‐IVa and the reported value. The solubility of CHS‐IVa over the pH range 1.0–7.5 was 14.4 ± 0.29 to 16.9 ± 0.34 mg/ml. The Peff of CHS‐IVa in the duodenum was 1.76 × 10?3 to 2.00 × 10?3 cm/min. The Peff of CHS‐IVa in the jejunum was 1.26 × 10?3 to 1.39 × 10?3 cm/min. The Peff of CHS‐IVa in the ileum was 1.25 × 10?3 to 1.31 × 10?3 cm/min. The Peff of CHS‐IVa in the colon was 1.02 × 10?3 to 1.08 × 10?3 cm/min. There was no statistical difference of the Peff in the four segments at different CHS‐IVa concentrations. The Peff of CHS‐IVa (0.07, 0.7 and 7.0 mg/ml) were all notably smaller than the reported Peff (3.00 × 10?3 cm/min) in the jejunum. The Peff of CHS‐IVa was not influenced by verapamil (P‐gp inhibitor), indomethacin (MRP inhibitor) and pantoprazole (BCRP inhibitor). CHS‐IVa was classified as high solubility, low permeability and BCS III. The main absorptive tracts were the upper intestinal tracts and the rank order of intestinal permeability was duodenum > jejunum ≈ ileum > colon. The transport mechanism of CHS‐IVa in all intestinal segments might be primarily passive transport. CHS‐IVa was not a substrate of P‐gp, MRP and BCRP.  相似文献   
4.
Studying skin barrier function is central to our understanding of many skin disorders. The past decade has seen a surge of skin barrier related investigative work. Genetic, biochemical and cell biology experiments have added much evidence to the importance of the barrier in disease pathogenesis of a variety of disorders including ichthyosis, atopic dermatitis and psoriasis. However, functional assays prove ever more important to demonstrate relevance of any of these findings. A paper published by Monash and Blank 60 years ago describes a stress test of the skin barrier, measuring skin barrier recovery, a functional test of tremendous implications. This seminal paper has not been cited for almost 15 years, time to acknowledge its critical importance and to review the relevance of this method today.  相似文献   
5.
目的了解丽水市呼吸道病原体感染情况及流行病学特征,为呼吸道传染病诊疗与防控提供科学依据。方法回顾性分析2020年3月至2021年12月丽水市人民医院收治的4035例呼吸道感染患者13项呼吸道病原体PCR毛细电泳核酸检测结果,并分析病原体感染分布特征。结果呼吸道病原体感染患者阳性检出率为32.24%(1301/4035),检出率前5位分别是HRV(16.60%)、HRSV(7.09%)、HPIV(2.87%)、HMPV(2.21%)、HADV(1.96%)。混合感染阳性占比为7.61%(99/1301),Boca病毒(76.0%)与Ch(46.15%)易与其它病原体形成混合感染。不同性别呼吸道病原体感染率差异无统计学意义(P>0.05)。虽然不同季节呼吸道病原体整体感染率差异无统计学意义(P>0.05),但HRV好发于春秋两季,而HPIV在春秋两季感染率较低,春季HRSV感染率较低,HADV在夏秋两季感染率较低,HMPV在冬季较为流行。未成年人呼吸道病原体感染率较高,HRSV、HRV、HPIV、HADV和Boca主要发生于未成年人组,InfB和HMPV在未成年和青年人群感染率都较高。结论未成年人群是呼吸道病原体易感人群,应加强未成年人呼吸道传染病防控。  相似文献   
6.
目的:观察胰腺癌病人肠道通透性和营养状况的改变,初步探讨它们之间的关系. 方法:选取胰腺癌首次入院确诊的病人及健康志愿者各15例,作为试验组和对照组.分别测定尿乳果糖/甘露醇(L/M)比值、血清肿瘤坏死因子(TNF-α)、清蛋白(ALB)、转铁蛋白(TF)和前清蛋白(PA),并对试验组的肠道通透性与血清TNF-α水平、血清蛋白之间的相关性进行分析. 结果:试验组尿L/M比值显著高于对照组(0.331±0.343 vs 0.129± 0.136,P< 0.05).试验组血清TNF-α显著高于对照组,(4.98±6.46)ng/L vs (1.25±2.35)ng/L,P <0.05.试验组ALB、TF、PA浓度均较对照组显著降低(P <0.05).试验组尿L/M比值与血清TNF-α水平呈极显著正相关(P< 0.01)而与ALB、TF、PA均呈极显著的负相关(P<0.01). 结论:胰腺癌病人肠道通透性增加与血清TNF-α水平升高呈显著正相关,与血清蛋白下降呈显著负相关.  相似文献   
7.
建立了顶空毛细管GC法测定吉非罗齐中甲酸乙酯、THF和甲基环己烷3种有机溶剂的残留量。采用HP-1毛细管柱,溶剂DMA,内标乙酸乙酯。平均同收率分别为99.8%、100.3%、100.0%,RSD分别为0.71%、1.51%和1.76%。  相似文献   
8.
The purpose of this work was to investigate the use of an intravascular contrast agent to determine perfusion kinetics in skeletal muscle. A two-compartment kinetic model was used to represent the flux of contrast agent between the intravascular space and extravascular extracellular space (EES). The relationship between the image signal-to-noise ratio (SNR) and errors in estimating permeability surface area product (Ktrans), interstitial volume (ve), and plasma volume (vp) for linear and nonlinear curve-fitting methods was estimated from Monte Carlo simulations. Similar results were obtained for both methods. For an image SNR of 60, the estimated errors in these parameters were 10%, 22%, and 17%, respectively. In vivo experiments were conducted in rabbits to examine physiological differences between these parameters in the soleus (SOL) and tibialis anterior (TA) muscles in the hind limb. Values for Ktrans were significantly higher in the SOL (3.2+/-0.9 vs. 2.0+/-0.5x10(-3) min-1), as were values for vp (3.4+/-0.8 vs. 2.1+/-0.7%). Differences in ve for the two muscles (8.7+/-2.2 vs. 8.5+/-1.6%) were not found to be significant. These results demonstrate that relevant physiological metrics can be calculated in skeletal muscle using MRI with an intravascular contrast agent.  相似文献   
9.
豚鼠耳蜗微血管内皮细胞体外通透性的研究   总被引:1,自引:0,他引:1  
目的 研究豚鼠耳蜗微血管内皮细胞的体外通透性特征。方法 在成功建立豚鼠耳蜗微血管内皮细胞体外通透性模型的基础上 ,研究该体外模型跨细胞电阻及对12 5I 牛血清白蛋白的通透性。结果 ①耳蜗微血管内皮细胞在培养增殖过程中其跨细胞电阻呈动态变化过程 ,以 5× 10 4/cm2 的细胞密度接种时 ,7d左右电阻到达峰值 ,其跨细胞电阻峰值大小为 (118 9± 18 5 )Ω/cm2 ;②体外模型中加入12 5I 牛血清白蛋白后 ,其通透性呈上升期抛物线型曲线 ,90min内几乎呈直线。结论 跨细胞电阻及对12 5I 牛血清白蛋白变化曲线能反映体外耳蜗微血管内皮细胞的通透性特征  相似文献   
10.
本实验探讨了内源性速激肽是否参与白三烯C4(LTC4)的气道效应.LTC4(0.5μgkg-1,iv)可增高豚鼠肺内压(IPP)和气道内依文思蓝渗出。速激肽NK-1受体拮抗剂CP-96345{(2S,3S)-顺式-2-(二苯甲基)-N-[(2-甲氧苯)-甲基]-1-杂氮双环[2.2.2]辛烷-3-胺}1mgkg-1,iv,可减弱LTC4诱导的依文思蓝渗出;NK-2受体拮抗剂SR-48968{(S)-N-甲基-N-[4-(4-乙酰氨基-4-苯基哌啶)-2-(3,4-二氯苯基)丁基]苯甲酰胺},1mgkg-1,iv,可抑制IPP的增高.白三烯拮抗剂ONO-1078(0.03mgkg-1,iv)可阻断这两种反应.结果说明内源性速激肽增强LTC4的气道作用,其中NK-1受体介导微血管渗漏,NK-2受体介导支气管收缩.  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