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   4580篇
  免费   204篇
  国内免费   14篇
耳鼻咽喉   105篇
儿科学   196篇
妇产科学   216篇
基础医学   696篇
口腔科学   33篇
临床医学   285篇
内科学   1033篇
皮肤病学   71篇
神经病学   425篇
特种医学   76篇
外科学   221篇
综合类   28篇
预防医学   388篇
眼科学   120篇
药学   595篇
中国医学   13篇
肿瘤学   297篇
  2024年   7篇
  2023年   32篇
  2022年   203篇
  2021年   305篇
  2020年   105篇
  2019年   138篇
  2018年   148篇
  2017年   129篇
  2016年   157篇
  2015年   159篇
  2014年   201篇
  2013年   294篇
  2012年   368篇
  2011年   380篇
  2010年   201篇
  2009年   151篇
  2008年   239篇
  2007年   312篇
  2006年   280篇
  2005年   266篇
  2004年   197篇
  2003年   196篇
  2002年   155篇
  2001年   19篇
  2000年   16篇
  1999年   14篇
  1998年   7篇
  1997年   12篇
  1996年   10篇
  1995年   6篇
  1992年   7篇
  1991年   4篇
  1990年   7篇
  1989年   6篇
  1988年   8篇
  1987年   5篇
  1986年   6篇
  1984年   2篇
  1983年   8篇
  1982年   5篇
  1981年   2篇
  1979年   3篇
  1978年   7篇
  1977年   5篇
  1976年   2篇
  1975年   3篇
  1974年   6篇
  1973年   1篇
  1972年   1篇
  1969年   1篇
排序方式: 共有4798条查询结果,搜索用时 31 毫秒
41.

Objective

The aim of this study was to analyze the prevalence of HPV and EBV in oral and oropharyngeal squamous cell carcinoma in south-eastern Poland. The correlation between viral infection, OSCC, alcohol use, tobacco smoking, demographic data (gender, age, place of residence), anatomic location, pre-treatment staging, evidence of metastases to lymph nodes, and grading was also investigated.

Methods

The examination samples were collected from paraffin tissue blocks, from 154 patients. Viral DNA was amplified by the nested-PCR method.

Results

HPV DNA was detected in 29.2 % of the tested samples (in 27.4 % of oropharyngeal and in 30.4 % of oral cavity). The HPV type 16 was detected in 15.6 % of all samples, and in 53.3 % of HPV-positive group. In HPV-positive samples from oropharyngeal HPV 16 constitute 76.5 %, and in HPV-positive samples from oral cavity HPV 16 constitute 39.3 %. Mixed infection (more than one type of HPV) was observed in 23.5 and 60.7 %, respectively, and in 46.7 % of all HPV-positive samples, and in 12.3 % of the whole study group. EBV DNA was detected in 27.3 % of the cases and HPV-EBV co-infection in 7.8 % of samples.

Conclusions

In major patients from Southeastern region of Poland with oropharyngeal cancer HPV type 16 was detected but in oral cavity cancer other mixed infections were observed (i.e. 51, 52, 59, 66, 68, 71, 74). HPV 16 was detected more often among patients younger than 50 years of age, whereas the mixed HPV in the group aged 50–59. The pathogenesis of oral squamous cell carcinoma may be connected with EBV infection. Future studies on the mechanisms of HPV/EBV co-infection and/or superinfection and their role in oral squamous cell carcinoma are necessary.
  相似文献   
42.
In this study, the influence of carbonate lake sediments (Polylactide/Carbonate Lake Sediments–PLA/CLS) on the mechanical and structural properties of polylactide matrix composites was investigated. Two fractions of sediments originating from 3–8 and 8–12 m were analysed for differences in particle size by distribution (Dynamic Light Scattering–DLS), phase composition (X-ray Diffraction–XRD), the presence of surface functional groups (Fourier Transform-Infrared–FT-IR), and thermal stability (Thermogravimetric Analysis–TGA). Microscopic observations of the composite fractures were also performed. The effect of the precipitate fraction on the mechanical properties of the composites before and after conditioning in the weathering chamber was verified through peel strength, flexural strength, and impact strength tests. A melt flow rate study was performed to evaluate the effect of sediment on the processing properties of the PLA/CLS composite. Hydrophobic-hydrophilic properties were also investigated, and fracture analysis was performed by optical and electron microscopy. The addition of carbon lake sediments to PLA allows for the obtention of composites resistant to environmental factors such as elevated temperature or humidity. Moreover, PLA/CLS composites show a higher flow rate and higher surface hydrophobicity in comparison with unmodified PLA.  相似文献   
43.
The effectiveness of protective coatings based on 3-(2,2,3,3,4,4,5,5-octafluoropentyloxy)propyltriethoxysilane (OFTES) in protecting concrete surfaces against water was tested. For the synthesis of OFTES, 2,2,3,3,4,4,5,5-octafluoropentanol, which is a by-product in the synthesis of poly(tetrafluoroethylene), was used. The proposed silane is a cheaper alternative to the fluorinated organosilicon compounds currently used. The coatings were deposited by the sol-gel method. As a result of the creation of chemical bonds between the concrete surface and the silane, a coating was created that permanently increases the hydrophobicity of the concrete. Fluorine chains attached to silicon atoms are an effective barrier that prevents access to water and limits its impact on the concrete surface. As a result of the proposed silanization, the concrete surface obtained a hydrophobic character at contact angles of up to 126°, and the water absorption of the concrete decreased by up to 96%.  相似文献   
44.
This paper presents the results of tests on the railway disc brake with regard to the weight wear of friction pads. The tests were carried out at a certified brake test bench where the friction-mechanical characteristics of the railway brake were determined. The test stand was additionally equipped with a thermal imaging camera to observe the contact between the brake pads and the brake disc. The scientific goal of the test is to evaluate the relationship between the weight wear of friction pads and the quantities characterizing the braking process. The quantities characterizing the braking process included pad-to-disc contact area, friction pad thickness, pad-to-disc pressure, and braking speed. A regression model to estimate the friction pad wear on the basis of a single braking with the given input quantities was determined. The greatest influence on the increase in weight wear of friction pads has the braking velocity, which was confirmed by the value of the correlation coefficient of the regression model at value 0.81. The pressure of the friction pad to the disc and the friction pad thickness do not have a significant effect on the weight wear described by the regression model, and the obtained correlation coefficient for these parameters was lower than the value of 0.2.  相似文献   
45.
In the presented research, we investigated Ammonium Nitrate Fuel Oil (ANFO), with the addition of variously modified zeolite Y as an attractive explosive. Analysis of both blasting tests and thermodynamic models of blasting properties led to the conclusion that the addition of zeolite Y enhanced the detonation properties of such prepared ANFO via the growth of the detonation pressure, temperature, compression energy, and heat of the explosion. Generally, the modification of ANFO with variously prepared zeolite Y also reduced the volume of (COx + NOx) post-blast fumes. Furthermore, it was found that the ANFO’s velocity of detonation (VOD) could be controlled by the choice of the way of zeolite Y modification. Namely, for zeolite Y without Mg, as well as Mg-Y prepared via the impregnation method, the VOD rose. The opposite effect was observed when ANFO was modified with Mg-Y, obtained from the deposition of Mg over zeolite Y via the ultrasonic-assisted procedure.  相似文献   
46.
The incidence of Non-Alcoholic Fatty Liver Disease (NAFLD) has been rapidly increasing during the last decade. It is a relevant health problem that affects 25% of the general population. NAFLD involves an extensive array of clinical conditions. So far, no approved pharmacological therapy for NAFLD has been developed. Multiple bioactive compounds have been proposed to treat NAFLD. One of the most promising is Berberine (BBR). Its pleiotropic effect positively impacts various cardiometabolic aspects. In this review, we summarize NAFLD, its metabolic and cardiovascular complications, the hepatoprotective effects of BBR due to its broad spectrum of pharmacological effects, and the potential role of BBR in NAFLD therapy. BBR ameliorates NAFLD by affecting numerous abnormalities. It inhibits lipogenesis and gluconeogenesis, improves insulin resistance and lipid profile, and modulates gut microbiota. The exact mechanism underlying these effects is not yet entirely explained. A growing amount of evidence confirming the positive effects of BBR on multiple metabolic pathways, such as lipids and glucose metabolism, energy homeostasis, or gut microbiota modulation, allows us to speculate about the importance of this natural bioactive substance for NAFLD therapy.  相似文献   
47.
A rise in the incidence of infections with severe acute respiratory syndrome coronavirus 2 has sparked the search for protective strategies against the new pathogen. It is known that individual food components can interact with different immune cells, modulating the immune response of the body. The aim of this study was to develop an index assessing the immunomodulatory potential of diet (POLA index) and to test its utility for the prediction of coronavirus disease 2019 (COVID-19) in a group of healthy young people following a traditional or vegetarian diet. Data on body composition, anthropometric measurements, physical activity, dietary intake, and gut microbiota were obtained from 95 adults (mean age, 34.66 ± 5.76 years). There was a strong correlation between the dietary inflammatory index and the POLA index (r = 0.90; p < 0.0001). Based on Cohen’s kappa statistic, there was a good agreement in qualitative interpretation between the two indices (kappa = 0.61; p < 0.0001). People on a diet with beneficial immunomodulatory effects had a lower risk of COVID-19 of approximately 80%, as compared with those on a diet with highly unbeneficial immunomodulatory effects. In daily practice, the POLA index might serve as a useful tool for dietitians to identify individuals whose diet is deficient in ingredients for optimal immune system function and change their dietary behavior to ensure optimal immune function that reduces the risk of infection.  相似文献   
48.
49.
IntroductionDetection of abnormalities in the KRAS, NRAS and BRAF genes is extremely important for proper qualification of colorectal cancer (CRC) patients for therapy with anti-EGFR (epidermal growth factor receptor) monoclonal antibodies. However, data about prevalence of mutations in these genes, in different localizations of CRC tumors, are limited.Material and methodsWe examined the frequency of mutations in the KRAS, NRAS and BRAF genes in 500 Caucasian CRC patients (200 women and 300 men, median age 66 years). DNA was isolated from formalin-fixed, paraffin-embedded (FFPE) tissues using a Qiagen QIAamp DNA FFPE-kit. Analysis of mutations was carried out using the KRAS/BRAF, NRAS and BRAF Mutation Analysis Kit for Real-Time PCR (EntroGen) with the Cobas 480 real-time PCR apparatus (Roche Diagnostics).ResultsKRAS mutations were detected in 190 (38%) patients, NRAS mutations in 20 (4%) patients, and BRAF mutations in 24 (4.8%) patients. There were no associations between age of CRC patients and frequency of KRAS, NRAS and BRAF gene mutations. These mutations were significantly more often diagnosed in women (55.5%) than in men (41%, p < 0.005). Tumors of the rectum and sigmoideum were the most often observed in both groups of CRC patients – with and without KRAS, NRAS and BRAF gene mutations. However, transverse colon, ascending colon and cecum cancers were the most often affected by mutations.ConclusionsOur study showed that the occurrence of mutations in the KRAS, NRAS and BRAF genes is not accidental and depends on the location of CRC tumors.  相似文献   
50.
The spread of antibiotic-resistant pathogens and the resurgence of tuberculosis disease are major motivations to search for novel antimicrobial agents. Some promising candidates in this respect are cationic polymers, also known as synthetic mimics of antimicrobial peptides (SMAMPs), which act through the membrane-lytic mechanism. Development of resistance toward SMAMPs is less likely than toward currently employed antibiotics; however, further studies are needed to better understand their structure–activity relationship. The main objective of this work is to understand the cross-influence of hydrophobicity, main-chain flexibility, and the topology of ionenes (polycations containing a cationic moiety within the main-chain) on activity. To fulfill this goal, a library of ionenes was developed and compared with previously investigated molecules. The obtained compounds display promising activity against the model microorganisms and drug-resistance clinical isolates, including Mycobacterium tuberculosis. The killing efficiency was also investigated, and results confirm a strong effect of hydrophobicity, revealing higher activity for molecules possessing the flexible linker within the polymer main-chain.

A high significance of the main chain flexibility and an unexpected effect of hydrophobicity on the biological activity in series of ionenes was observed. The most potent among the tested polycations showed high activity toward clinical bacterial isolates.  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