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   3817篇
  免费   699篇
  国内免费   36篇
耳鼻咽喉   80篇
儿科学   144篇
妇产科学   67篇
基础医学   487篇
口腔科学   108篇
临床医学   469篇
内科学   992篇
皮肤病学   62篇
神经病学   227篇
特种医学   175篇
外科学   538篇
综合类   118篇
一般理论   1篇
预防医学   246篇
眼科学   110篇
药学   272篇
中国医学   33篇
肿瘤学   423篇
  2023年   28篇
  2022年   47篇
  2021年   103篇
  2020年   112篇
  2019年   242篇
  2018年   198篇
  2017年   182篇
  2016年   189篇
  2015年   235篇
  2014年   260篇
  2013年   284篇
  2012年   224篇
  2011年   226篇
  2010年   251篇
  2009年   174篇
  2008年   177篇
  2007年   161篇
  2006年   141篇
  2005年   130篇
  2004年   127篇
  2003年   116篇
  2002年   112篇
  2001年   54篇
  2000年   46篇
  1999年   38篇
  1998年   52篇
  1997年   45篇
  1996年   56篇
  1995年   38篇
  1994年   31篇
  1993年   31篇
  1992年   34篇
  1991年   37篇
  1990年   32篇
  1989年   33篇
  1988年   40篇
  1987年   34篇
  1986年   22篇
  1985年   18篇
  1984年   20篇
  1983年   19篇
  1982年   13篇
  1981年   17篇
  1980年   14篇
  1979年   9篇
  1977年   14篇
  1976年   13篇
  1975年   10篇
  1974年   8篇
  1972年   10篇
排序方式: 共有4552条查询结果,搜索用时 18 毫秒
991.
PURPOSE: Hepatocellular carcinoma (HCC), the most common form of liver cancer, is a leading cause of cancer death worldwide. We previously showed that aberrant mRNA splicing of the liver intestine-cadherin gene CDH17 in liver tissues was triggered by the specific constellation of two CDH17 single nucleotide polymorphisms (651T and IVS6+35G). CDH17 aberrant splicing was highly associated with tumor dissemination and shorter survival of HCC patients. Consequently, it is highly relevant to assess whether the presence of these single nucleotide polymorphisms in the general population represents a risk to the development of HCC. EXPERIMENTAL DESIGN: We conducted a case-control study including 164 HCC and 99 cirrhosis patients and 293 healthy controls. Genotyping was done by PCR and direct sequencing. Odds ratio (OR) and chi2 analysis were used to analyze genotypes and haplotypes. RESULTS: Genotypes 651TT [OR, 2.62; 95% confidence interval (95% CI), 1.34-5.03] and IVS6+35 GG (OR, 1.95; 95% CI, 1.04-3.62) were highly associated with HCC disease. The 651T (C>T) and IVS6+35G (A>G) alleles were also overrepresented in HCC patients and, in particular, the T-G haplotype was the most prevalent in HCC patients when compared with healthy controls (OR, 1.57; 95% CI, 1.167-2.109; P=0.004), which was in agreement with the aberrant splicing observed in tumor tissues. There was no significant difference in genotype and allele frequencies between cirrhosis patients and controls. CONCLUSION: The functional T-G haplotype of CDH17 (651 C>T and IVS6+35A>G) is a genetic susceptibility factor for the development of HCC in a Chinese population.  相似文献   
992.

BACKGROUND.

Older age has historically been an adverse prognostic factor in pediatric acute myeloid leukemia (AML). To the authors' knowledge, the impact of age relative to that of other prognostic factors on the outcome of patients treated in recent trials is unknown.

METHODS.

Clinical outcome and causes of treatment failure of 351 patients enrolled on 3 consecutive protocols for childhood AML between 1991 and 2008 were analyzed according to age and protocol.

RESULTS.

The more recent protocol (AML02) produced improved outcomes for patients aged 10 years to 21 years compared with 2 earlier studies (AML91 and AML97), with 3‐year rates of event‐free survival (EFS), overall survival (OS), and cumulative incidence of refractory leukemia or recurrence (CIR) for this group being similar to those of patients aged birth to 9 years: EFS: 58.3% ± 5.4% versus 66.6% ± 4.9% (P = .20); OS: 68.9% ± 5.1% versus 75.1% ± 4.5% (P = .36); and CIR: 21.9% ± 4.4% versus 25.3% ± 4.2% (P = .59). The EFS and OS estimates for patients aged 10 to 15 years overlapped those for patients aged 16 to 21 years. However, the cumulative incidence of toxic death was significantly higher for patients aged 10 to 21 years compared with younger patients (13.2% ± 3.6% vs 4.5% ± 2.0%; P = .028).

CONCLUSIONS.

The survival rate for older children with AML has improved on the results of a recent trial and is now similar to that of younger patients. However, deaths from toxicity remain a significant problem for patients in the older age group. Future trials should focus on improving supportive care while striving to develop more effective antileukemic therapy. Cancer 2012. © 2012 American Cancer Society.  相似文献   
993.
994.
Although a second age‐related peak of human papillomavirus (HPV) infection is observed in many populations, it does not seem to have any impact on cervical screening policies. We examined the age‐specific prevalence of HPV infection among 2,604 women enrolled for cervical screening and correlated the age at diagnosis of 2,491 cervical intraepithelial neoplasia Grade 2/3 (CIN2/3) lesions and 801 invasive cervical cancers (ICC). Two peaks of HPV infection were detected at 26–30 and 46–50 years, respectively. The first infection peak was followed by a CIN2/3 peak and an ICC peak at 5–15 and 15 years later, respectively. The second infection peak was followed by an ICC peak 20 years later, but strikingly no CIN2/3 peak was detected in between and thus eliminated an opportunity of treating the lesions at preinvasive stages. The most plausible explanation is that women at the expected second CIN2/3 peak (50–65 years) are not having Pap smears under the current opportunistic screening program. Furthermore, women of this age may have physiological retraction of the transformation zone, and CIN lesions may remain undetected if an adequate Pap smear sample is not obtained. To combat this problem, the screening program in Hong Kong needs to focus on women aged 50 years and older and a mop‐up screening up to 75 years is necessary. Bimodal peaks of HPV infection and cervical cancer are seen in many countries and the analysis of population‐specific age distribution of CIN2/3 should be an integral exercise in evaluating the effectiveness of a screening program.  相似文献   
995.
Limited availability of in vitro and in vivo model systems has hampered efforts to understand tumor biology and test novel therapies for ependymoma, the third most common malignant brain tumor that occurs in children. To develop clinically relevant animal models of ependymoma, we directly injected a fresh surgical specimen from a 9-year-old patient into the right cerebrum of RAG2/severe complex immune deficiency (SCID) mice. All five mice receiving the initial transplantation of the patient tumor developed intracerebral xenografts, which have since been serially subtransplanted in vivo in mouse brains for 4 generations and can be cryopreserved for long-term maintenance of tumorigenicity. The xenograft tumors shared nearly identical histopathological features with the original tumors, harbored 8 structural chromosomal abnormalities as detected with spectral karyotyping, maintained gene expression profiles resembling that of the original patient tumor with the preservation of multiple key genetic abnormalities commonly found in human ependymomas, and contained a small population (<2.2%) of CD133+ stem cells that can form neurospheres and display multipotent capabilities in vitro. The permanent cell line (BXD-1425EPN), which was derived from a passage II xenograft tumor and has been passaged in vitro more than 70 times, expressed similar differentiation markers of the xenograft tumors, maintained identical chromosomal abnormalities, and formed tumors in the brains of SCID mice. In conclusion, direct injection of primary ependymoma tumor cells played an important role in the generation of a clinically relevant mouse model IC-1425EPN and a novel cell line, BXD-1425EPN. This cell line and model will facilitate the biological studies and preclinical drug screenings for pediatric ependymomas.  相似文献   
996.
Oncogenic activation of the Wnt signaling pathway is common in cancers, but mutation of β‐catenin in ovarian cancer is rare. In addition to genetic events, epigenetic modification of secreted frizzled‐related protein (SFRP) family has been shown to be important in regulating Wnt signaling. Although high degree of homology is observed in the same family, different SFRPs may have opposing effects on the same process. We reported recently that a Wnt antagonist, SFRP5, is downregulated frequently through promoter hypermethylation and that this hypermethylation is associated with overall survival in ovarian cancer. The aim of this study was to analyze the function of SFRP5 in ovarian cancer. Functional assays including measuring cell proliferation, invasion, colony formation and xenograft were performed using ovarian cancer cell lines with overexpression of SFRP5 or a short hairpin RNA silencing. The methylation status of SFRP5 in relation to cisplatin resistance in ovarian cancer patients was analyzed. Restoration of the expression of SFRP5 attenuated Wnt signaling in ovarian cancer cells and suppressed cancer cell growth, invasion of cells and tumorigenicity in mice. These effects were independent of the canonical pathway. The expression of SFRP5 inhibited epithelial–mesenchymal transition (EMT). The restoration of SFRP5 downregulated AKT2 and sensitized ovarian cancer cells to chemotherapy. These effects are consistent with the poor response to platinum‐based chemotherapy in patients with methylation of SFRP5. Our data suggested that epigenetic silencing of SFRP5 leads to oncogenic activation of the Wnt pathway and contributes to ovarian cancer progression and chemoresistance through the TWIST‐mediated EMT and AKT2 signaling.  相似文献   
997.
998.
The diagnosis of hemophagocytic lymphohistiocytosis (HLH) is delayed by most physicians. This study aimed to identify early parameters and suitable scoring systems for the risk of HLH. Clinical and laboratory data collected ≤3 days after admission were defined as early parameters and used to calculate the number of HLH‐2004 criteria met and bone marrow (BM) score. Between January 2006 and February 2016, 233 immunocompetent adults with naïve fever of unknown origin who underwent a BM study were enrolled to mimic patients at risk of HLH and randomly assigned into the developmental or validation cohort. Hemophagocytic lymphohistiocytosis was finally diagnosed in 47 patients, with non‐Hodgkin lymphoma as the major etiology (51.1%). Upon admission, four‐fifths of patients who developed subsequent HLH fulfilled ≤3 of 8 HLH‐2004 criteria, and 6 early parameters were independent predictors of HLH: anemia (hemoglobin < 10 g/dL), thrombocytopenia (platelet count < 100 × 103/μL), leukoerythroblastosis, hyperbilirubinemia (total bilirubin > 2 × upper normal limit), hyperferritinemia (ferritin > 1000 ng/mL), and splenomegaly. Compared with the HLH criteria met upon admission, the BM score was an independent predictor (odds ratio = 1.621; 95% confidence interval, 1.355‐1.940) with excellent discrimination (area under the receiver operating characteristic curve = 0.920; 95% confidence interval, 0.883‐0.958). The sensitivity and specificity for a BM score cutoff of 10 points were 95% and 75%, respectively. When approaching immunocompetent adults with a continuously high fever, the BM score at initial admission assists with early identification of patients at risk of HLH.  相似文献   
999.
Sodium alginate, a biopolymer, was employed in the formulation of matrix tablets. They cracked or laminated at acidic pH, compromising their dissolution performance. Improved mechanical strength and reduced barrier permeability of calcium alginate gel provided the rationale for cross-linking the alginate matrix to sustain drug release. Studies had suggested that the incorporation of soluble calcium salts in alginate matrix tablets could sustain drug release at near-neutral pH due to in situ cross-linking. However, results from the present study showed otherwise when gastrointestinal pH conditions were simulated. Significant reduction in drug release rate was only observed when an external calcium source was utilized at low concentration. High calcium ion concentrations caused matrix disintegration. In contrast, matrices pre-coated by calcium alginate could sustain drug release at pH 1.2 followed by pH 6.8 for over 12h. The presence of cross-linked barrier impeded matrix lamination and preserved matrix structure, contributing to at least three-fold reduction in drug release at pH 1.2. Zero order release as well as delayed burst release could be achieved by employing appropriate grade of alginate and cross-linking conditions.  相似文献   
1000.
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