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   8163篇
  免费   472篇
  国内免费   35篇
耳鼻咽喉   68篇
儿科学   283篇
妇产科学   198篇
基础医学   1248篇
口腔科学   173篇
临床医学   723篇
内科学   1684篇
皮肤病学   246篇
神经病学   865篇
特种医学   167篇
外科学   631篇
综合类   67篇
一般理论   3篇
预防医学   669篇
眼科学   185篇
药学   770篇
中国医学   11篇
肿瘤学   679篇
  2024年   8篇
  2023年   65篇
  2022年   215篇
  2021年   351篇
  2020年   203篇
  2019年   216篇
  2018年   281篇
  2017年   195篇
  2016年   275篇
  2015年   273篇
  2014年   320篇
  2013年   465篇
  2012年   691篇
  2011年   668篇
  2010年   352篇
  2009年   301篇
  2008年   483篇
  2007年   525篇
  2006年   501篇
  2005年   460篇
  2004年   482篇
  2003年   408篇
  2002年   382篇
  2001年   48篇
  2000年   47篇
  1999年   43篇
  1998年   50篇
  1997年   51篇
  1996年   39篇
  1995年   23篇
  1994年   26篇
  1993年   22篇
  1992年   19篇
  1991年   17篇
  1990年   10篇
  1989年   20篇
  1988年   12篇
  1987年   7篇
  1986年   7篇
  1985年   9篇
  1984年   9篇
  1983年   12篇
  1982年   13篇
  1981年   9篇
  1980年   6篇
  1978年   6篇
  1977年   7篇
  1976年   4篇
  1975年   4篇
  1974年   6篇
排序方式: 共有8670条查询结果,搜索用时 15 毫秒
61.
PURPOSE:Prostanoids are important mediators of pulmonary vaso- and bronchotone regulation and strongly influence inflammatory reactivity. The product of cyclooxygenase (Cox), prostaglandin H(2), is further metabolized via downstream enzymes into the different effective metabolites. The specific cellular equipment with certain downstream enzymes crucially determines the cellular reactivity by generation of functionally different prostanoid metabolites. EXPERIMENTAL DESIGN: To elucidate the role of arachidonic acid metabolism via the cyclooxygenase pathway in different human lung tumors, expression of cyclooxygenase isoenzymes (Cox-1 and Cox-2) and downstream enzymes of prostanoid metabolism was investigated in human non-small cell lung cancer and normal human lung tissue by immunohistochemical techniques. RESULTS: In comparison to strong Cox-1 reactivity in airways and endothelial cells of normal lung specimens, only 4 of 15 adenocarcinomas showed infrequent Cox-1 expression. All lung cancer specimens displayed an increased Cox-2 immunostaining pattern with strong reactivity in adenocarcinomas and lower reactivity in squamous cell carcinomas. Adenocarcinomas and squamous cell carcinomas were also positive for thromboxane A(2) synthase, prostaglandin D(2) synthase, and prostaglandin E(2) synthase, but not for prostacyclin synthase. Endothelial cells of vessels found within or near the tumor show extensive immunostaining of Cox-2 and thromboxane A(2) synthase, whereas endothelial cells of normal lung specimens, in contrast, expressed Cox-1 and prostacyclin synthase. CONCLUSIONS: We conclude that non-small cell lung cancer shows a specific Cox-/downstream-enzyme expression pattern, which is specifically altered in lung tumor cells and tumor supplying vessels in contrast to normal lung tissue. This may have major impact on tumor progression and tumor-associated inflammation via an altered prostanoid metabolism with consecutive tumor-associated blood flow distribution.  相似文献   
62.
63.
PURPOSE: A phase III study to determine whether a weekly docetaxel schedule improves the therapeutic index compared with the classic 3-weekly schedule. PATIENTS AND METHODS: Patients with stage IIIB-IV non-small-cell lung cancer (NSCLC) were randomly assigned to docetaxel 75 mg/m2 on day 1 every 3 weeks (3-weekly) and 35 mg/m2 on days 1, 8, and 15 (weekly) for < or = eight cycles. End points included survival (primary), toxicity, and response. RESULTS: Of 215 patients enrolled, 208 (103 in the 3-weekly arm and 105 in the weekly arm) were assessable for response. At baseline, 24.5% of patients (51 out of 208) had received prior paclitaxel therapy and 43.3% of patients (90 out of 208) had been progression-free for more than 3 months after first-line therapy. After 12 months' follow-up, median survival was 6.3 months (95% CI, 4.68 to 7.84 months) with 3-weekly docetaxel and 9.2 months (95% CI, 5.83 to 12.59 months) with weekly docetaxel (P = .07) after a median of four (range, one to eight) and two (range, one to eight) treatment cycles, respectively. Overall, response rates were 12.6% v 10.5% with 3-weekly versus weekly docetaxel. Significantly fewer patients reported grade 3 to 4 toxicities with weekly docetaxel versus 3-weekly docetaxel (P < or = .05). There were significantly lower rates of grade 3 to 4 anemia (P < or = .05), leucopenia (P < .0001), and neutropenia (P < or = .001) with weekly versus 3-weekly treatment. No grade 3 to 4 thrombocytopenia or mucositis was reported. CONCLUSION: Weekly docetaxel 35 mg/m2 demonstrated similar efficacy and better tolerability than standard 3-weekly docetaxel 75 mg/m2 and can be recommended as a feasible alternative second-line treatment option for patients with advanced NSCLC.  相似文献   
64.
The aim of this study was to assess the possibilities to use brewer’s spent grains (BSGs) left over from beer production for energy purposes, and to determine its calorific value and chemical composition. The research materials were samples of wet spent grain from a brewery in Poland. Three samples, that are different in ingredient composition, were examined. The examined samples of BSGs were characterised by humidity that is typical for this product (approx. 77–80%). Convective drying of the spent grain contributed to a reduction in the water content in the biomass to below 10%. Samples of dry spent grain that were examined contained a similar amount of ash (3.8–4.1% d.m.) and organic matter (91.0–91.9% d.m.). All the examined spent grain samples demonstrated similar volatile matter content—approx. 77.8–78.7% d.m. and calorific value—approx. 15.6–15.9 MJ/kg. The estimated calorific value for wet samples (approx. 1.4–2.0 MJ/kg) indicated that it is necessary to lower water content in the biomass in order to improve its energy properties.  相似文献   
65.
Rich in polyphenols, cranberry juice (CJ) with high antioxidant activity is believed to contribute to various health benefits. However, our knowledge of the neuroprotective potential of cranberries is limited. Previously, we have demonstrated that CJ treatment controls oxidative stress in several organs, with the most evident effect in the brain. In this study, we examined the capability of CJ for protection against Parkinson’s disease (PD) in a rotenone (ROT) rat model. Wistar rats were administered with CJ in a dose of 500 mg/kg b.w./day (i.g.) and subcutaneously injected with ROT (1.3 mg/kg b.w./day). The experiment lasted 45 days, including 10 days pre-treatment with CJ and 35 days combined treatment with CJ and ROT. We quantified the expression of α-synuclein and apoptosis markers in the midbrain, performed microscopic examination, and assessed postural instability to evaluate the CJ neuroprotective effect. Our results indicate that the juice treatment provided neuroprotection, as evidenced by declined α-synuclein accumulation, Bax and cleaved/active caspase-9 expression, and normalized cytochrome c level that was accompanied by the enhancement of neuronal activity survival and improved postural instability. Importantly, we also found that long-term administration of CJ alone in a relatively high dose may exert a deleterious effect on cell survival in the midbrain.  相似文献   
66.
Neural bases of cognitive reappraisal may depend on the direction of regulation (up- or downregulation) and stimulus valence (positive or negative). This study aimed to examine this using a cognitive reappraisal task and conjunction analysis on a relatively large sample of 83 individuals. We identified regions in which activations were common for all these types of emotion regulation. We also investigated differences in brain activation between the ‘decrease’ and ‘increase’ emotional response conditions, and between the regulation of negative and positive emotions. The common activation across conditions involved mainly the prefrontal and temporal regions. Decreasing emotions was associated with stronger involvement of the dorsolateral prefrontal cortex, while increasing with activation of the amygdala and hippocampus. Regulation of negative emotions involved stronger activation of the lateral occipital cortex, while regulation of positive emotions involved stronger activation of the anterior cingulate cortex extending to the medial prefrontal cortex. This study adds to previous findings, not only by doing a conjunction analysis on both emotional valences and regulation goals, but also doing this in a bigger sample size. Results suggest that reappraisal is not a uniform process and may have different neural bases depending on regulation goals and stimulus valence.  相似文献   
67.
68.
69.

Purpose

Two Demodex species (eyelash mites)—D. folliculorum and D brevis—are believed to be associated with human skin and eye diseases. However, the clinical significance of infection with Demodex species remains controversial.

Study design

The aim of this study was to estimate the prevalence of ocular demodicosis in patients with blepharitis as compared with the prevalence in the healthy population in Poland.

Methods

This case-control prospective study was carried out from 2007 to 2016. The enrolled patients (668) were divided into 2 groups: the study group, comprising 553 patients with blepharitis (349 women and 204 men, aged 17–88 years), and the control group, comprising 115 healthy volunteers without a history of ocular pathologies (78 women and 37 men, aged 17–88 years). A sample of 10 eyelashes was taken aseptically from each eye of the examined person and later studied under a light microscope.

Results

Demodex species were found in 62.4% (345/544) of the patients in the study group and in 24.3% (28/100) of the controls (P = .001, OR = 0.006). The overall prevalence was 55.8% (373/668) in all the examined participants. The presence of Demodex infection increased with age in both groups. No association of Demodex infection with gender was found (119/204 vs 226/349; P > .05, OR 1.086). A high mean number of mites was present more frequently in patients aged older than 50 years and in those who complained especially about itching (P < .05).

Conclusion

The prevalence of ocular demodicosis is significantly correlated with blepharitis and increases with age.
  相似文献   
70.
A hitherto unknown glutathione-S-transferase in human erythrocytes displays polymorphism: three quarters of the population (conjugators) possess, whereas one quarter (non-conjugators) lack this specific activity. A standard method for the identification of conjugators and non-conjugators with the use of methyl bromide and gas chromatography (head space technique) is described. Three substrates of the polymorphic enzyme, methyl bromide, ethylene oxide and dichloromethane (methylene chloride), were incubated in vitro with individual whole blood samples of conjugators and non-conjugators. All three substances led to a marked increase of sister chromatid exchanges (SCE) in the lymphocytes of the non-conjugators but not in those of conjugators. A protective effect of the glutathione-S-transferase activity in human erythrocytes for the cytogenetic toxicity of these chemicals in vitro is thus confirmed. Since the enzyme activity is not found in erythrocytes of laboratory animals, species extrapolations for risk assessment of methyl bromide, ethylene oxide and dichloromethane should be reconsidered.  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