首页 | 官方网站   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   8548篇
  免费   518篇
  国内免费   337篇
医药卫生   9403篇
  2024年   7篇
  2023年   74篇
  2022年   126篇
  2021年   260篇
  2020年   231篇
  2019年   200篇
  2018年   192篇
  2017年   255篇
  2016年   220篇
  2015年   282篇
  2014年   452篇
  2013年   651篇
  2012年   577篇
  2011年   638篇
  2010年   476篇
  2009年   409篇
  2008年   472篇
  2007年   524篇
  2006年   474篇
  2005年   370篇
  2004年   325篇
  2003年   282篇
  2002年   237篇
  2001年   210篇
  2000年   156篇
  1999年   144篇
  1998年   118篇
  1997年   104篇
  1996年   108篇
  1995年   91篇
  1994年   102篇
  1993年   68篇
  1992年   74篇
  1991年   64篇
  1990年   68篇
  1989年   46篇
  1988年   52篇
  1987年   37篇
  1986年   35篇
  1985年   42篇
  1984年   31篇
  1983年   11篇
  1982年   33篇
  1981年   25篇
  1980年   16篇
  1979年   14篇
  1978年   10篇
  1977年   3篇
  1975年   3篇
  1970年   1篇
排序方式: 共有9403条查询结果,搜索用时 468 毫秒
1.
Lung and female breast cancers are highly prevalent worldwide. Although the association between exposure to ambient fine particulate matter (PM2.5) and lung cancer has been recognized, there is less evidence for associations with other common air pollutants such as nitrogen dioxide (NO2) and ozone (O3). Even less is known about potential associations between these pollutants and breast cancer. We conducted a population-based cohort study to investigate the associations of chronic exposure to PM2.5, NO2, O3 and redox-weighted average of NO2 and O3 (Ox) with incident lung and breast cancer, using the Ontario Population Health and Environment Cohort (ONPHEC), which includes all long-term residents aged 35–85 years who lived in Ontario, Canada, 2001–2015. Incident lung and breast cancers were ascertained using the Ontario Cancer Registry. Annual estimates of exposures were assigned to the residential postal codes of subjects for each year during follow-up. We used Cox proportional-hazards models adjusting for personal- and neighborhood-level covariates. Our cohorts for lung and breast cancer analyses included ~4.9 million individuals and ~2.5 million women, respectively. During follow-up, 100,146 incident cases of lung cancer and 91,146 incident cases of breast cancer were diagnosed. The fully adjusted analyses showed positive associations of lung cancer incidence with PM2.5 (hazard ratio [HR] = 1.02 [95% CI: 1.01–1.05] per 5.3 μg/m3) and NO2 (HR = 1.05 [95% CI: 1.03–1.07] per 14 ppb). No associations with lung cancer were observed for O3 or Ox. Relationships between PM2.5 and NO2 with lung cancer exhibited a sublinear shape. We did not find compelling evidence linking air pollution to breast cancer.  相似文献   
2.
In this study, the carbonic anhydrase (CA) enzyme was purified from Black Sea trout (Salmo trutta Labrax Coruhensis) kidney with a specific activity of 603.77 EU/mg and a yield of 35.5% using Sepharose-4B-l-tyrosine- sulphanilamide affinity column chromatography. For determining the enzyme purity and subunit molecular mass, sodiumdodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) was performed and single band was observed. The molecular mass of subunit was found approximately 29.71 kDa. The optimum temperature, activation energy (Ea), activation enthalpy (ΔH) and Q10 values were obtained from Arrhenius plot. Km and Vmax values for p-nitrophenyl acetate of the purified enzyme were calculated from Lineweaver-Burk graphs. In addition, the inhibitory effects of different heavy metal ions (Fe2+, Pb2+, Co2+, Ag+ and Cu2+) on Black Sea trout kidney tissue CA enzyme activities were investigated by using esterase method under in vitro conditions. The heavy metal concentrations inhibiting 50% of enzyme activity (IC50) were obtained. Finally Ki values and inhibition types were calculated from Lineweaver-Burk graphs.  相似文献   
3.
目的 分析乌司他丁与连续性血液净化联用对热射病患者所产生的影响。方法 选取2017年5月—2019年2月在海南医学院第二附属医院进行治疗的88例热射病患者作为研究对象,将其分为研究组和常规组,常规组患者接受常规治疗,研究组患者在常规治疗基础上,将乌司他丁与连续性血液净化联用。分析两种治疗措施的效果。结果 治疗前两组患者的IL-17、TNF-α、cTnⅠ、β2-MG、PT、D-D、ET和TM水平,差异无统计学意义(P>0.05)。经治疗两组患者的上述指标水平都表现出下降的趋势,相对于常规组,研究组患者下降水平更明显,差异具有统计学意义(P<0.05)。研究组治疗的总有效率为95.5%,高于常规组的72.7%,差异具有统计学意义(P<0.05)。结论 运用乌司他丁与连续性血液净化联用的疗法对热射病患者进行治疗,可获得十分理想的治疗效果,可在临床工作中推广。  相似文献   
4.

Introduction

For never-smokers (smoked <100 lifetime cigarettes), lung cancer (LC) has emerged as an important issue. We aimed to investigate the effects of prevalence changes in tobacco smoking and particulate matter (PM) 2.5 (PM2.5) levels on LC in Taiwan, in relation to contrasting PM2.5 levels, between Northern Taiwan (NT) and Southern Taiwan (ST).

Methods

We reviewed 371,084 patients with LC to assess smoking prevalence and correlations between the incidence of adenocarcinoma lung cancer (AdLC) and non-AdLC. Two subsets were selected to assess different AdLC stage trends and the effect of PM2.5 on survival of patients with AdLC.

Results

From 1995 to 2015, the proportion of male adult ever-smokers decreased from 59.4% to 29.9% whereas the female smoking rate remained low (3.2% to 5.3%). AdLC incidence in males and females increased from 9.06 to 23.25 and 7.05 to 24.22 per 100,000 population, respectively. Since 1993, atmospheric visibility in NT improved (from 7.6 to 11.5 km), but deteriorated in ST (from 16.3 to 4.2 km). The annual percent change in AdLC stages IB to IV was 0.3% since 2009 (95% confidence interval [CI]: -1.9%–2.6%) in NT, and 4.6% since 2007 (95% CI: 3.3%–5.8%) in ST; 53% patients with LC had never smoked. Five-year survival rates for never-smokers, those with EGFR wild-type genes, and female patients with AdLC were 12.6% in NT and 4.5% in ST (hazard ratio: 0.79, 95% CI: 0.70–0.90).

Conclusions

In Taiwan, greater than 50% of patients with LC had never smoked. PM2.5 level changes can affect AdLC incidence and patient survival.  相似文献   
5.
The activation of the innate and adaptive immune systems by SARS-CoV-2 causes the release of several inflammatory cytokines, including IL-6. The inflammatory hypercytokinemia causes immunopathological changes in the lungs including vascular leakage, and alveolar edema. As a result of these changes in the lungs, hypoxia and acute respiratory distress syndrome occur in patients with COVID-19. Even though there are clinical trials on the development of therapeutics and vaccines, there are currently no licensed vaccines or therapeutics for COVID-19. Pharmacological approaches have shown poor results in sepsis-like syndromes caused by the hypercytokinemia. Suppressing the cytokine storm is an important way to prevent the organ damage in patients with COVID-19. Extracorporeal blood purification could be proposed as an adjunctive therapy for sepsis, aiming to control the associated dysregulation of the immune system, which is known to protect organ functions. Several extracorporeal blood purification therapies are now available, and most of them target endotoxins and/or the cytokines and aim improving the immune response. For this purpose, plasmapheresis and immunoadsorption may be an important adjunctive treatment option to manage the complications caused by cytokine storm in critically ill patients with COVID-19.  相似文献   
6.
Immunoglobulins (Igs) are major serum proteins which play important roles in immunity. Both untargeted and targeted proteomic workflows can be applied to investigate antigen-binding sites and the glycosylation profiles of Igs. For a more-comprehensive picture of IgG from human serum, we developed an IgG purification process and coupled the standardized method to untargeted and targeted proteomic workflows for IgG investigations. Parameters such as the type of purification beads, volume of the bead slurry, incubation conditions, and binding capacities were evaluated in this study. Only 2 μL of human serum was required for each sample. The performance of coupling the purification process to untargeted proteomics in the IgG analysis was evaluated by comparing normalized abundances of IgG subclass-specific peptides with quantification results from an ELISA. Pearson's correlation values were all >0.82. Targeted proteomic workflow was applied to serum samples from patients with autoimmune pancreatitis and from healthy controls, and the results corresponded to clinical findings that IgG4-related peptides/glycopeptides showed higher abundances in the diseased group. The developed IgG purification process is simple and requires small sample volume, and it can be coupled to targeted and untargeted proteomic workflows for clinical investigations in the future.  相似文献   
7.
8.
9.
生物安全柜是重要的一级屏障设备,适当的控制方式对生物安全柜的防护能力是很重要的。文中主要介绍了生物安全柜的控制要点和几种控制方式及其特点。  相似文献   
10.
闽产木立芦荟多糖的分离纯化及初步分析   总被引:14,自引:2,他引:12  
目的 分离纯化及初步分析产木立芦荟中的多糖。方法 芦荟经沸水提取,醇沉,Sevage法去除蛋白质,Sephadex G-200柱色谱分离纯化,制得闽产木立芦荟多糖,以硫酸-苯酚法测定其总糖含量。结果 闽产木立芦荟多糖经紫外吸收光谱扫描具有多糖特征吸收峰,未见核酸和蛋白质吸收峰,多糖含量可达89.7%,初步分析由D-甘露糖和D-葡萄糖等单糖组成。结论 从闽产木立芦荟中可提取分离纯度较高的杂多糖。  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-23

京公网安备 11010802026262号