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   6914篇
  免费   617篇
  国内免费   189篇
耳鼻咽喉   76篇
儿科学   169篇
妇产科学   121篇
基础医学   743篇
口腔科学   130篇
临床医学   877篇
内科学   883篇
皮肤病学   103篇
神经病学   276篇
特种医学   229篇
外国民族医学   2篇
外科学   789篇
综合类   1084篇
现状与发展   2篇
一般理论   5篇
预防医学   790篇
眼科学   125篇
药学   687篇
  2篇
中国医学   337篇
肿瘤学   290篇
  2023年   41篇
  2022年   123篇
  2021年   194篇
  2020年   144篇
  2019年   104篇
  2018年   96篇
  2017年   122篇
  2016年   105篇
  2015年   172篇
  2014年   241篇
  2013年   290篇
  2012年   463篇
  2011年   514篇
  2010年   453篇
  2009年   418篇
  2008年   433篇
  2007年   426篇
  2006年   426篇
  2005年   298篇
  2004年   240篇
  2003年   194篇
  2002年   173篇
  2001年   167篇
  2000年   185篇
  1999年   108篇
  1998年   45篇
  1997年   49篇
  1996年   39篇
  1995年   39篇
  1994年   50篇
  1993年   39篇
  1992年   72篇
  1991年   71篇
  1990年   66篇
  1989年   59篇
  1988年   71篇
  1987年   58篇
  1986年   49篇
  1985年   56篇
  1984年   66篇
  1983年   60篇
  1982年   38篇
  1980年   49篇
  1979年   64篇
  1978年   39篇
  1977年   43篇
  1976年   43篇
  1975年   44篇
  1973年   37篇
  1972年   40篇
排序方式: 共有7720条查询结果,搜索用时 295 毫秒
71.
Prospective observations on 442 consecutive samples have confirmed that pregnancies with CNS malformations are regularly associated with an abnormal cellular content of amniotic fluid. A crude semiquantitative test of the cell content can give valuable clinical information in relation to borderline amniotic fluid alpha-fetoprotein values, and help to detect false positive AFP's.  相似文献   
72.
BACKGROUND: INN 00835 is a synthetic pentapeptide with a potential for rapid onset of action as an antidepressant. Its efficacy was investigated in a pilot study in patients diagnosed with major depression. METHODS: Fifty two patients received either active drug - INN 00835 (26 patients) - or placebo (26 patients), subcutaneously at 0.2 mg/kg for 5 consecutive days. The patients were evaluated for an additional 4 weeks after treatment. Efficacy was evaluated by the following psychiatric rating scales: HAMD, MADRS, CSRS, CGI, and VAS. The effect of treatment was also evaluated by using a biochemical marker: changes in blood platelet serotonin (5HT) uptake rates in drug-treated patients compared to those in the placebo group. Plasma concentrations of INN 00835 were measured by LC/MS. RESULTS: Statistical analysis indicated a strong pharmacodynamic correlation between plasma drug concentrations at 1 h after dosing and the reduction in the severity of depression as measured by the psychiatric rating scales. A minimum effective plasma concentration (MEC) of INN 00835 was 5 ng/ml. Statistically significant differences in response to treatment (P<0.05) were found between patients with plasma concentrations above MEC and those in the placebo group, as well as between subjects with plasma concentrations above and below the MEC. The peak effect was observed after the 5-day treatment and the response to treatment persisted during the 4-week follow-up period. The change of 5HT uptake rates after treatment was significantly larger in the drug-treated group than in the placebo group. Limitations: This was a pilot study conducted in a relatively small population (52 patients) and the limited number of blood sampling times did not allow a comprehensive pharmacokinetic analysis. There was a relatively large placebo response. The results have to be confirmed in future, large scale studies. CONCLUSIONS: INN 00835 appears to be a promising drug for the treatment of major depression.  相似文献   
73.
目的:检测视黄酸依赖Fas/RARα表达载体转染HL-60细胞启动的凋亡效应。方法:成功构建视黄酸依赖Fas/RARα表达载体,用脂质体转染HL-60白血病细胞,经四甲基偶氮唑盐[3-(4,5-dimethylthiaol-2-yl)-2,5-diphenyl tetrazolium bromide,MTT]、流式细胞、DNA梯形带和透射电镜等方法观测视黄酸处理后细胞凋亡效应的发生。结果:以一定剂量的视黄酸处理HL-60后,细胞增殖受抑,呈凋亡性变。结论:视黄酸及其依赖的融合基因表达可协同诱导HL-60细胞发生凋亡效应。  相似文献   
74.
Pigment production by group B streptococci (GBS) is a useful test for identification of the organisms. The test is positive in 99.5% of beta-haemolytic strains. No false-positives are noted. Non-haemolytic strains do not produce pigment. Islam's media less agar can be used as a one-step broth detector of GBS in mixed cultures. This may have application for the detection of GBS in women in labour. When used as an identification system for GBS, serum-starch broth can be further modified by reduction of serum and starch concentrations by at least 80%.  相似文献   
75.
目的:探讨体外定向分化胚胎干细胞(ESCs)为造血干细胞(HSCs)对体内造血功能的重建作用。方法:将小鼠E14.1胚胎干细胞采用“三步诱导法”在体外分化发育为HSCs,造血克隆形成(CFU)实验观察其体外造血集落形成情况,免疫磁珠分选纯化HSCs移植给经亚致死剂量γ射线照射的雌性SCID小鼠,观察其植入及小鼠造血功能恢复情况。结果: 经过分阶段诱导,多种造血刺激因子联合应用能有效促进ESCs定向分化发育为HSCs,流式细胞仪检测HSCs特异性表面标志物CD34+/Sca-1+表达最高为(58.64±4.20)%,CFU培养能形成较多的红系、粒系/巨噬细胞系及混合细胞集落, Wright-Giemsa 染色显示为原始的造血细胞。此阶段的HSCs经分选纯化后移植给经γ射线照射后的小鼠,移植组小鼠+10 d造血功能开始恢复,观察40 d后除血小板恢复较慢外,白细胞、红细胞、血红蛋白等指标已接近正常,植入率为71.4%,存活率为43.0%,染色体检测证实已由受体鼠的XX转为供体鼠的XY。结论: 采用分阶段诱导的方法,可在体外定向诱导小鼠ESCs分化发育为HSCs,此来源的HSCs可以有效重建体内造血功能。  相似文献   
76.
The ionic selectivity of the hyperpolarizationactivated inward current (i f) channel to monovalent cations was investigated in single isolated sinoatrial node cells of the rabbit using the whole-cell patch-clamp technique. With a 140 mM K+ pipette, replacement of 90% external Na+ by Li+ caused a –24.5 mV shift of the fully activated current/voltage I/V curve without a significant decrease of the slope conductance. With a 140 mM Cs+ pipette, the i f current decreased almost proportionally to the decrease in external [Na+]o as Li+ was substituted. These responses are practically the same as those observed with N-methyl glucamine (NMG+) substitution, suggesting that the relative permeability of Li+ compared with Na+ for the i f channel is as low as that of NMG+. When Cs+ or Rb+ was substituted for internal K+, the fully activated I/V relationship for i f showed strong inward rectification with a positive reversal potential, indicating low permeability of the i f channel for Cs+ and Rb+. These results show that the i f channel is highly selective for Na+ and K+ and will not pass the similar ions Li+ and Rb+. Such a high degree of selectivity is unique and may imply that the structure of the i f channel differs greatly from that of other Na+ and K+ conducting channels.  相似文献   
77.
自然流产模型小鼠蜕膜细胞凋亡及Bcl-2、Bax表达的研究   总被引:1,自引:0,他引:1  
目的:通过比较正常妊娠模型小鼠及自然流产模型小鼠蜕膜细胞凋亡及Bcl-2、Bax蛋白的表达,从细胞及分子水平探讨自然流产的发病机制。方法:建立正常妊娠模型CBAXBALB/c和自然流产模型CBAXDBA/2。用免疫组化SABC法测定两组模型孕13天蜕膜细胞Bcl-2和Bax蛋白的表达,并通过MIAS-2000医用彩色病理图像免疫组化测量系统对其表达进行半定量分析,其结果用平均灰度值表示;同时应用DNA缺口原位末端标记技术(TUNEL)测定两组模型孕13天蜕膜细胞凋亡情况。结果:与正常妊娠模型相比,自然流产模型蜕膜细胞Bcl-2蛋白的表达降低(P〈0.01);Bax蛋白的表达明显升高(P〈0.01)。蜕膜细胞凋亡指数,自然流产模型明显高于正常妊娠模型(P〈0.01)。结论:早孕期蜕膜组织细胞凋亡异常是自然流产的机制之一,Bcl-2/Bax途径可能是诱导早孕期蜕膜细胞凋亡的重要因素。  相似文献   
78.
The long-term biostability of a novel thermoplastic polyurethane elastomer (Elast-Eon 2 80A) synthesized using poly(hexamethylene oxide) (PHMO) and poly(dimethylsiloxane) (PDMS) macrodiols has been studied using an in vivo ovine model. The material's biostability was compared with that of three commercially available control materials, Pellethane 2363-80A, Pellethane 2363-55D and Bionate 55D, after subcutaneous implantation of strained compression moulded flat sheet dumbbells in sheep for periods ranging from 3 to 24 months. Scanning electron microscopy, attenuated total reflectance-Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy were used to assess changes in the surface chemical structure and morphology of the materials. Gel permeation chromatography, differential scanning calorimetry and tensile testing were used to examine changes in bulk characteristics of the materials. The results showed that the biostability of the soft flexible PDMS-based test polyurethane was significantly better than the control material of similar softness, Pellethane 80A, and as good as or better than both of the harder commercially available negative control polyurethanes, Pellethane 55D and Bionate 55D. Changes observed in the surface of the Pellethane materials were consistent with oxidation of the aliphatic polyether soft segment and hydrolysis of the urethane bonds joining hard to soft segment with degradation in Pellethane 80A significantly more severe than that observed in Pellethane 55D. Very minor changes were seen on the surfaces of the Elast-Eon 2 80A and Bionate 55D materials. There was a general trend of molecular weight decreasing with time across all polymers and the molecular weights of all materials decreased at a similar relative rate. The polydispersity ratio, Mw/Mn, increased with time for all materials. Tensile tests indicated that UTS increased in Elast-Eon 2 80A and Bionate 55D following implantation under strained conditions. However, ultimate strain decreased and elastic modulus increased in the explanted specimens of all three materials when compared with their unimplanted unstrained counterparts. The results indicate that a soft, flexible PDMS-based polyurethane synthesized using 20% PHMO and 80% PDMS macrodiols has excellent long-term biostability compared with commercially available polyurethanes.  相似文献   
79.
目的:探讨不同组织病理分级的脑星形细胞瘤中血管内皮生长因子受体3(Flt-4又称VEGFR-3)的表达意义。 方法: 采用免疫组织化学方法,检测50例不同级别脑星形细胞瘤患者手术切除标本中Flt-4、血管内皮生长因子(VEGF)的表达,并用抗FⅧ因子抗体标记瘤组织血管内皮细胞,计算肿瘤内微血管密度(IMVD)。 结果: Flt-4、VEGF总阳性表达率分别为52%(26/50)、60%(30/50)。Flt-4、VEGF均与脑星形细胞瘤病理分级呈显著正相关(等级相关系数分别为0.359、0.360,P<0.05)。 结论: 脑星形细胞瘤中有Flt-4表达,主要表达于血管内皮细胞和部分肿瘤细胞,Flt-4既可是内皮细胞自分泌产生,部分还可来自瘤细胞的旁分泌;脑星形细胞瘤中Flt-4阳性表达的脉管是血管;Flt-4的表达与星形细胞瘤的病理分级相关  相似文献   
80.
Neurosteroids such as dehydroepiandrosterone (DHEA), pregnenolone and 17beta-estradiol are synthesized by cytochrome P450s from endogenous cholesterol. We previously reported a new cytochrome P450 enzyme, CYP7B, highly expressed in rat and mouse brain that metabolizes DHEA and related steroids by hydroxylation at the 7alpha position. Such 7-hydroxylation can enhance DHEA bioactivity in vivo. Here we show that the reaction is conserved across mammalian species: in addition to mouse and rat, DHEA hydroxylation activity was present in brain extracts from sheep, marmoset and human. Northern blotting using a human CYP7B complementary deoxyribonucleic acid (cDNA) probe confirmed the presence of CYP7B mRNA in marmoset and human hippocampus; CYP7B mRNA was present in marmoset cerebellum and brainstem, with lower levels in hypothalamus and cortex. In situ hybridization to human brain revealed higher levels of CYP7B mRNA in the hippocampus than in cerebellum, cortex, or other brain regions. We also measured CYP7B expression in Alzheimer's disease (AD). CYP7B mRNA was significantly decreased (approximately 50% decline; P<0.05) in dentate neurons from AD subjects compared with controls. A decline in CYP7B activity may contribute the loss of effects of DHEA with ageing and perhaps to the pathophysiology of AD.  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