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   2784篇
  免费   158篇
  国内免费   27篇
耳鼻咽喉   9篇
儿科学   74篇
妇产科学   62篇
基础医学   490篇
口腔科学   103篇
临床医学   236篇
内科学   541篇
皮肤病学   33篇
神经病学   285篇
特种医学   114篇
外科学   224篇
综合类   19篇
预防医学   259篇
眼科学   30篇
药学   218篇
中国医学   22篇
肿瘤学   250篇
  2024年   2篇
  2023年   36篇
  2022年   100篇
  2021年   139篇
  2020年   89篇
  2019年   89篇
  2018年   98篇
  2017年   84篇
  2016年   96篇
  2015年   79篇
  2014年   135篇
  2013年   157篇
  2012年   254篇
  2011年   243篇
  2010年   130篇
  2009年   131篇
  2008年   183篇
  2007年   184篇
  2006年   167篇
  2005年   139篇
  2004年   86篇
  2003年   117篇
  2002年   97篇
  2001年   15篇
  2000年   8篇
  1999年   11篇
  1998年   11篇
  1997年   10篇
  1995年   13篇
  1994年   5篇
  1993年   10篇
  1992年   6篇
  1991年   3篇
  1990年   7篇
  1989年   2篇
  1988年   2篇
  1986年   2篇
  1985年   3篇
  1984年   3篇
  1983年   3篇
  1982年   2篇
  1980年   3篇
  1976年   2篇
  1975年   1篇
  1973年   1篇
  1972年   2篇
  1971年   1篇
  1970年   1篇
  1964年   1篇
  1932年   1篇
排序方式: 共有2969条查询结果,搜索用时 12 毫秒
91.
Journal of Autism and Developmental Disorders - Behavioural phenotype and autism-related traits of 38 patients affected by Cornelia de Lange syndrome (CdLS) were assessed using a specific...  相似文献   
92.
93.
BACKGROUND: The T cell-mediated immune response to human cytomegalovirus (HCMV) after primary infection, as well as the determinants of intrauterine transmission, are poorly understood. METHODS: Sequential peripheral blood leukocyte samples from 74 pregnant women and 29 nonpregnant individuals with primary infection were examined for HCMV-specific CD4+ T cells by cytokine flow cytometry (CFC) and lymphoproliferative response (LPR) analysis. Immunological results for 19 transmitter and 21 nontransmitter mothers were compared. RESULTS: Comparison of CFC and LPR analysis results showed that (1) there was no difference between pregnant and nonpregnant individuals; (2) HCMV-specific CD4+ T cells were detected by CFC, in the absence of an LPR to HCMV, in the great majority or the totality (according to different intervals) of samples collected from both pregnant and nonpregnant individuals during follow-up; and (3) LPR to HCMV was significantly (P<.001) lowered or delayed in transmitter mothers, compared with that in nontransmitter mothers. CONCLUSIONS: Pregnancy does not influence the HCMV-specific immune response. A dissociation between CFC response and LPR is commonly observed in patients with primary infections, and ad hoc studies aimed at understanding the mechanism(s) of the reduced LPR in transmitter mothers are warranted.  相似文献   
94.
Autism spectrum disorders (ASD) are characterized by a broad range in clinical presentation. Although a definite genetic cause has not yet been fully demonstrated, family based studies suggest that a multigenic pattern may be responsible for susceptibility, but most results are conflicting and have yet to be replicated. The purpose of this investigation was to analyze the linkage of the human leukocyte antigen (HLA) and the human serotonin transporter coding (5-HTTLPR) genes with ASD in a group of 37 families of Sardinian ethnicity in insular Italy. In 50% of these families, ASD is linked to HLA, and in the other 50% it is linked to 5-HTTLPR polymorphic genes; in other words, linkage to one or the other was evident in all cases. Despite a very homogenous genetic pattern being generally reported for Sardinians, the linkage observed with HLA and 5-HTTLPR genetic regions indicated a statistically defined heterogeneity (p=0.002). No allelic HLA or 5-HTTLPR polymorphisms were specifically associated with ASD, suggesting these loci as markers of other genes mapped in their close proximity that may be more directly involved and thus may merit further analytical studies.  相似文献   
95.
Huntington's disease (HD) is caused by mutated huntingtin (htt), a toxic protein ubiquitously expressed in nervous and non-nervous system tissues. Fragmentation of htt by caspases and further accumulation in cells of protein aggregates contribute to cell dysfunction and death. In the attempt to elucidate whether this mechanism depends on patients' genotype, we analysed the pattern of htt fragmentation, the caspase 3, 8 and 9 activities and their variation in lymphoblasts with heterozygous and homozygous CAG mutation and in controls. Cells homozygous for expanded mutation showed greater amount of mutated fragments than heterozygotes and controls, caspase 3, 8 and 9 activities greater in mutated than control cell lines, after cyanide treatment, the caspase 3 and 8 particularly increased in homozygotes. This data offers a biological explanation to the clinical in-patients evidence of mutation homozygosity associated with more severe phenotype.  相似文献   
96.
97.
Prostaglandins play a critical role in tumor development and growth by regulating numerous biologic processes, including tumor angiogenesis, with clear prognostic and therapeutic implications. The aim of this study was to investigate the prognostic relevance of cyclooxygenase-2 (COX-2) pathway activation in head and neck squamous cell carcinoma (HNSCC). COX-2 activity was analyzed in 52 consecutive patients by assessing protein expression and prostaglandin E(2) (PgE(2)) levels and was then correlated to vascular endothelial growth factor (VEGF) expression and tumor angiogenesis. We evaluated the prognostic impact of these parameters by Kaplan-Meier and Cox survival analysis. COX-2 expression by tumor cells was closely correlated to VEGF expression and to tumor vascularization. According to Kaplan-Meier analysis, patients with COX-2 tumor overexpression and with higher PgE(2) tumor levels had significantly shorter overall survival estimates (P = 0.022 and P = 0.033, respectively). Analogously, patients with more-vascularized tumors had worse survival than those with less-vascularized cancers (P = 0.032). Cox multivariate analysis demonstrated that the most significant prognostic factors were presence of lymph node metastasis, tumor vascularization, COX-2 protein expression, and PgE(2) tumor levels. This study demonstrates a close correlation between COX-2 pathway, VEGF expression, and tumor angiogenesis in HNSCC. In addition, COX-2 overexpression and higher tumor vascularization appear to predict a shorter survival in patients with head and neck cancer.  相似文献   
98.
The susceptibility of certain inbred mouse strains to murine cytomegalovirus (MCMV) is related to their inability to generate a strong natural killer (NK) cell response. We addressed here whether the MCMV susceptibility of the BALB/c strain is due to viral functions that control NK cell activation in a strain-specific manner. MCMV expresses two proteins, gp48 and gp40, that are encoded by the genes m06 and m152, respectively; they down-regulate major histocompatibility complex (MHC) class I expression at the plasma membrane. Using MCMV deletion mutants and revertants, we found that gp40 but not gp48 controls NK cell activation. Absence of gp40 improved antiviral NK cell control in BALB/c, but not C57BL/6, mice. Down-regulation of H-60, the high-affinity ligand for the NKG2D receptor, was the mechanism by which gp40 modulates NK cell activation. Thus, a single herpesvirus protein has a dual function in inhibiting both the adaptive as well as the innate immune response.  相似文献   
99.
Withdrawal and infusion of blood via umbilical catheters can affect cerebral blood flow in preterm infants. We compared the effects on cerebral perfusion of 3 ml/kg blood withdrawal and infusion via umbilical arterial (UAC) and venous (UVC) catheters in 16 infants < or =32 weeks gestation, age <24 h, on mechanical ventilation. Near infrared spectroscopy was used to monitor changes in cerebral oxy- and deoxyhemoglobin, total cerebral hemoglobin (an index of cerebral blood volume; CBV) and HbD (an index of cerebral intravascular oxygenation). In 10 infants the study was repeated 1 h after intravenous administration of 10 mg/kg ibuprofen as prophylaxis against PDA. Withdrawal and infusion via the UVC caused significant MABP and concordant HbD and CBV changes. Smaller modifications were seen following blood withdrawal and infusion via the UAC. Ibuprofen attenuated cerebral hemodynamic changes associated with withdrawal, but not infusion, from UAC and UVC.  相似文献   
100.

Objective

Ovarian cancers comprise several histologically distinct tumour groups with widely different prognosis. We aimed to describe the worldwide distribution of ovarian cancer histology and to understand what role this may play in international variation in survival.

Methods

The CONCORD programme is the largest population-based study of global trends in cancer survival. Data on 681,759 women diagnosed during 1995–2009 with cancer of the ovary, fallopian tube, peritoneum and retroperitonum in 51 countries were included. We categorised ovarian tumours into six histological groups, and explored the worldwide distribution of histology.

Results

During 2005–2009, type II epithelial tumours were the most common. The proportion was much higher in Oceania (73.1%), North America (73.0%) and Europe (72.6%) than in Central and South America (65.7%) and Asia (56.1%). By contrast, type I epithelial tumours were more common in Asia (32.5%), compared with only 19.4% in North America. From 1995 to 2009, the proportion of type II epithelial tumours increased from 68.6% to 71.1%, while the proportion of type I epithelial tumours fell from 23.8% to 21.2%. The proportions of germ cell tumours, sex cord-stromal tumours, other specific non-epithelial tumours and tumours of non-specific morphology all remained stable over time.

Conclusions

The distribution of ovarian cancer histology varies widely worldwide. Type I epithelial, germ cell and sex cord-stromal tumours are generally associated with higher survival than type II tumours, so the proportion of these tumours may influence survival estimates for all ovarian cancers combined. The distribution of histological groups should be considered when comparing survival between countries and regions.  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