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   2795篇
  免费   162篇
  国内免费   10篇
耳鼻咽喉   60篇
儿科学   150篇
妇产科学   69篇
基础医学   335篇
口腔科学   86篇
临床医学   204篇
内科学   618篇
皮肤病学   53篇
神经病学   233篇
特种医学   85篇
外科学   453篇
综合类   39篇
一般理论   1篇
预防医学   207篇
眼科学   73篇
药学   152篇
肿瘤学   149篇
  2024年   4篇
  2023年   32篇
  2022年   40篇
  2021年   81篇
  2020年   40篇
  2019年   81篇
  2018年   145篇
  2017年   86篇
  2016年   104篇
  2015年   101篇
  2014年   159篇
  2013年   181篇
  2012年   240篇
  2011年   205篇
  2010年   107篇
  2009年   83篇
  2008年   166篇
  2007年   147篇
  2006年   150篇
  2005年   155篇
  2004年   116篇
  2003年   117篇
  2002年   116篇
  2001年   43篇
  2000年   47篇
  1999年   54篇
  1998年   3篇
  1997年   8篇
  1996年   5篇
  1995年   3篇
  1994年   3篇
  1993年   7篇
  1992年   17篇
  1991年   17篇
  1990年   18篇
  1989年   10篇
  1988年   8篇
  1987年   13篇
  1986年   12篇
  1985年   7篇
  1984年   3篇
  1983年   4篇
  1977年   3篇
  1975年   3篇
  1973年   4篇
  1971年   2篇
  1968年   3篇
  1966年   3篇
  1965年   1篇
  1962年   1篇
排序方式: 共有2967条查询结果,搜索用时 0 毫秒
91.
The aim of this study was to evaluate the effect of a mixture of vitamins and minerals on oxidative DNA damage and the resistance of DNA to H(2)O(2)-induced DNA strand breaks in lymphocytes from 80 elderly volunteers ex vivo by means of Comet assay. The intervention with vitamin complex decreased significantly the levels of DNA damage. Our results demonstrate that the vitamin complex was able to decrease H(2)O(2)-induced DNA breakage. Our data suggest that the consumption of some vitamins may reduce the effects of oxidative DNA damage and may be useful for attaining healthy aging.  相似文献   
92.
Persistent colonization of the human stomach by Helicobacter pylori is a risk factor for the development of gastric cancer and peptic ulcer disease. H. pylori secretes a toxin, VacA, that targets human gastric epithelial cells and T lymphocytes and enhances the ability of H. pylori to colonize the stomach in a mouse model. To examine how VacA contributes to H. pylori colonization of the mouse stomach, we investigated whether murine T lymphocytes were susceptible to VacA activity. VacA inhibited interleukin-2 (IL-2) production by a murine T-cell line (LBRM-33), similar to its effects on a human T-cell line (Jurkat), but did not inhibit IL-2 production by primary murine splenocytes or CD4+ T cells. VacA inhibited activation-induced proliferation of primary human CD4+ T cells but did not inhibit the proliferation of primary murine CD4+ T cells. Flow cytometry studies indicated that the levels of VacA binding to primary murine CD4+ T cells were significantly lower than levels of VacA binding to human CD4+ T cells. This suggests that the resistance of primary murine CD4+ T cells to VacA is attributable, at least in part, to impaired VacA binding to these cells.  相似文献   
93.
Tumor growth and metastasis need new vessel formation by angiogenesis provided by mature endothelial cells and postnatal vasculogenesis provided by endothelial progenitor cells (EPCs). Emerging data suggest a coordinated interaction between EPCs and hematopoietic progenitor cells (HPCs) in these processes. The complexity of the mechanisms governing the new vessel formation by postnatal vasculogenesis has increased by new evidence that not only bone marrow derived EPCs and HPCs seem to be involved in this process but also local progenitors residing within the vascular wall are mobilized and activated to new vessel formation by tumor cells. This review attempts to bring these systemic and local players of postnatal vasculogenesis together and to highlight their role in tumor growth and mestastasis.  相似文献   
94.
Nosemosis is one of the most widespread of the adult honey bee diseases and causes major economic losses to beekeepers. Two microsporidia have been described infecting honey bees worldwide, Nosema apis and Nosema ceranae, whose seasonality and pathology differ markedly. An increasing prevalence of microsporidian infections in honey bees has been observed worldwide during the last years. Because nosemosis has detrimental effects on both strength and productivity of the infected colonies, an accurate and reliable method to evaluate the presence of Nosema in honey bee colonies is needed. In this study a high degree of variability in the detection of microsporidia depending on the random subsample analyzed was found, suggesting that both sample size and the time of collection (month and day of sampling) notably affect the diagnosis.  相似文献   
95.
Glioblastoma (GBM) causes poor survival in patients even when applying aggressive treatment. Temozolomide (TMZ) is the standard chemotherapeutic choice for GBM treatment, but resistance always ensues. In previous years, efforts have focused on new therapeutic regimens with conventional drugs to activate immune responses that may enhance tumor regression and prevent regrowth, for example the “metronomic” approaches. In metronomic scheduling studies, cyclophosphamide (CPA) in GL261 GBM growing subcutaneously in C57BL/6 mice was shown not only to activate antitumor CD8+ T‐cell response, but also to induce long‐term specific T‐cell tumor memory. Accordingly, we have evaluated whether metronomic CPA or TMZ administration could increase survival in orthotopic GL261 in C57BL/6 mice, an immunocompetent model. Longitudinal in vivo studies with CPA (140 mg/kg) or TMZ (range 140–240 mg/kg) metronomic administration (every 6 days) were performed in tumor‐bearing mice. Tumor evolution was monitored at 7 T with MRI (T2‐weighted, diffusion‐weighted imaging) and MRSI‐based nosological images of response to therapy. Obtained results demonstrated that both treatments resulted in increased survival (38.6 ± 21.0 days, n = 30) compared with control (19.4 ± 2.4 days, n = 18). Best results were obtained with 140 mg/kg TMZ (treated, 44.9 ± 29.0 days, n = 12, versus control, 19.3 ± 2.3 days, n = 12), achieving a longer survival rate than previous group work using three cycles of TMZ therapy at 60 mg/kg (33.9 ± 11.7 days, n = 38). Additional interesting findings were, first, clear edema appearance during chemotherapeutic treatment, second, the ability to apply the semi‐supervised source analysis previously developed in our group for non‐invasive TMZ therapy response monitoring to detect CPA‐induced response, and third, the necropsy findings in mice cured from GBM after high TMZ cumulative dosage (980–1400 mg/kg), which demonstrated lymphoma incidence. In summary, every 6 day administration schedule of TMZ or CPA improves survival in orthotopic GL261 GBM with respect to controls or non‐metronomic therapy, in partial agreement with previous work on subcutaneous GL261.  相似文献   
96.
In order to develop small-diameter vascular grafts, it is necessary to evaluate endothelialization, especially, in the center part at early stage. For implantation of vascular grafts of 1 cm in length to abdominal aortae of rat, endothelial cells can be formed easily by stretching anastomosis. We evaluated the endothelialization in the center part of vascular grafts by implanting vascular grafts using transgenic (TG) silk fibroin (SF) of 3 cm in length. Vascular grafts were prepared 1.5 mm in diameter and 1 and 3 cm in length using wild type (WT) SF and TG SF by braiding structure, respectively. The grafts were removed after 2 weeks or 3 months and evaluated pathologically. Endothelialization was not confirmed totally after 3 months of implantation. However, endothelialization in the center part of grafts was significantly higher in TG SF than in WT SF. No significant difference was found regarding tissue infiltration and internal diameter. The TG SF revealed migration of the endothelial cells into the center part of the vessels at the early stage. Also, tissue infiltration and remodeling is expected using SF. The 3 cm length vascular grafts can be evaluated as a new experimental system.  相似文献   
97.
Background: Glutathione S-transferases (GSTs) are drug-metabolising enzymes involved in biotransformation of carcinogens, drugs, xenobiotics and oxygen free radicals. Polymorphisms of GST genes contribute to inter-individual and population variability in the susceptibility to environmental risk factors, cancer predisposition and pharmacotherapy responses. However, data about GST variability in Argentina are lacking.

Aim: The purpose was to determine the prevalence of GSTM1, GSTT1 and GSTP1 polymorphisms in the general population from a central region of Argentina and to perform inter-population comparisons.

Subjects and methods: GSTM1 and GSTT1 gene deletions and GSTP1 c.313A?>?G were genotyped by PCR assays in 609 healthy and unrelated Argentinians.

Results: The frequencies of variant genotypes in Argentinians were GSTM1-null (45%), GSTT1-null (17%) and GSTP1-GG (11%). GSTM1-present genotype was significantly associated with GSTP1-AG or GSTP1-GG variants (p?=?0.037; p?=?0.034, respectively). Comparison with worldwide populations demonstrated that the GST distributions in Argentina are similar to those reported for Italy and Spain, whereas significant differences were observed regarding Asian and African populations (p?Conclusion: This study has determined, for the first time, the normative profile of three pharmacogenetically relevant polymorphisms (GSTM1, GSTT1 and GSTP1) in the largest Argentinian cohort described to date, providing the basis for further epidemiological and pharmacogenetic studies in this country.  相似文献   
98.
Current evidence strongly suggests that aberrant activation of the nuclear factor kappa B (NF-kB) signaling cascade is connected to carcinogenesis. The matrix metalloproteinases (MMP) which are also the key agents for tumor metastasis may be potent candidates for tumor diagnosis in clinics. In this in vitro study, we hypothesized that metformin with an effective dose can inhibit tumor cell proliferation and metastasis by modulating the expressions of MMP-2 and -9 and interfering with NF-kB signaling in primary breast cancer cells (PBCCs). 300 000 cells per ml were obtained from biopsies of breast tumors from five human donors. The cell viability and proliferation were tested. Immunocytochemistry was performed for MMP-2, MMP-9, and NF-kB, and enzyme-linked immunosorbent assay for NF-kB activity, quantitative real-time PCR for RELA/p65, IkBα, MMP-2, and MMP-9. Three different doses of metformin (5, 10, and 25 mM) (Met) reduced the viability and proliferation of PBCCs in a dose-dependent manner, maximum inhibition was observed at 25 mM Met. The expression of RELA/p65 was not affected by 25 mM Met. Nuclear immunoreactivity and activity of NF-kB reduced while cytoplasmic NF-kB (p65) elevated by 25 mM Met compared to non-treatment (P < 0.05). The expression and immunoreactivity of MMP-9 but not MMP-2 were decreased by 25 mM Met treatment, compared with the non-treatment (P < 0.05). Metformin may have an essential antitumor role in the invasion and metastasis pathways of PBCCs by downregulating the MMP-9 expression blocking both the activity and nuclear translocation of NF-kB.  相似文献   
99.

Background

Hereditary angioedema (HAE) attacks can be provoked with psychological factors. The aim of this study was to assess the effects of anxiety, depression and stress related to COVID-19 pandemic on disease activity of HAE patients during the quarantine period (QP) and the return to normal period (RTNP).

Methods

This study was conducted between March 2020 and September 2020 in four allergy centres. Demographic, clinical features and mental health status were evaluated in QP (from March to the beginning of June) and RTNP (from June to the beginning of September) applied by the government. The 10-point visual analogue scale (VAS10) was used to define the severity of HAE attacks. Depression, Anxiety and Stress Scales-21 (DASS-21) and Fear of COVID-19 (FC-19) scale were performed to assess mental health status.

Results

139 HAE patients were included in the study. In QP, median attack numbers and median VAS10 scores were 5 (min-max: 0–45) and 6 (min-max: 0–10), respectively. HAE attack numbers, DASS-21 stress, anxiety, depression and total DASS-21 scores, and FC-19 scores were higher in QP than RTNP (p = 0.001, p < 0.001, p = 0.001, p < 0.001, p < 0.001, p < 0.001, respectively). However, there was no difference in attack severity scores between the two periods (p > 0.05).

Conclusions

This study revealed that the restriction measures during COVID-19 outbreak cause an increase in the number of HAE attacks in relation to anxiety, depression, stress and fear of COVID-19 pandemic. Therefore, it is important to provide psychological support to HAE patients during the pandemic.
  相似文献   
100.
Frequency of Mycoplasma pneumoniae among atypical pneumonia of childhood   总被引:2,自引:0,他引:2  
We aimed to investigate the frequency of Mycoplasma pneumoniae among atypical pneumonia of childhood that is acquired from the community and to determine a practical approach to the diagnosis of these patients. In this prospective study, 55 patients (31 male and 24 female) with atypical pneumonia were investigated with conventional laboratory and radiological methods as well as culture and polymerase chain reaction (PCR) on throat swab. In addition, serum of the patients was tested for M. pneumoniae specific IgM. The patients were reevaluated clinically at 3-5 days and 3-4 weeks and serologically at 3-4 weeks. The data on patients with M. pneumoniae pneumonia were compared with the other patients with atypical pneumonia and controls. All patients were treated with macrolide antibiotics. The mean age of the patients was 7.8+/-2.9 years. The frequency of M. pneumoniae by this method was 34.5%. Neither clinical, laboratory, or epidemiological data nor response to macrolide antibiotics was useful in detecting the etiology of atypical pneumonia. Diagnostic sensitivity and specificity of IgM+IgG antibodies plus PCR on throat swab were estimated as 100%. M. pneumoniae was an important microorganism in the etiology of atypical pneumonia of childhood in our community. In order to prevent loss of time with beta-lactamase antibiotics, which are usually started in severe pneumonia, serologic tests and PCR must be done during the initial evaluation of the patient for the reliable diagnosis of M. pneumoniae, which will increase the chance of early and appropriate therapy.  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