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   3418篇
  免费   410篇
  国内免费   50篇
耳鼻咽喉   41篇
儿科学   151篇
妇产科学   49篇
基础医学   383篇
口腔科学   88篇
临床医学   304篇
内科学   870篇
皮肤病学   57篇
神经病学   126篇
特种医学   273篇
外国民族医学   1篇
外科学   297篇
综合类   139篇
一般理论   1篇
预防医学   562篇
眼科学   56篇
药学   265篇
中国医学   7篇
肿瘤学   208篇
  2023年   23篇
  2021年   53篇
  2020年   46篇
  2019年   47篇
  2018年   43篇
  2017年   68篇
  2016年   65篇
  2015年   63篇
  2014年   114篇
  2013年   130篇
  2012年   113篇
  2011年   106篇
  2010年   107篇
  2009年   115篇
  2008年   96篇
  2007年   161篇
  2006年   131篇
  2005年   120篇
  2004年   124篇
  2003年   100篇
  2002年   101篇
  2001年   98篇
  2000年   74篇
  1999年   81篇
  1998年   110篇
  1997年   93篇
  1996年   85篇
  1995年   91篇
  1994年   82篇
  1993年   79篇
  1992年   81篇
  1991年   70篇
  1990年   72篇
  1989年   75篇
  1988年   72篇
  1987年   72篇
  1986年   59篇
  1985年   66篇
  1984年   43篇
  1983年   51篇
  1982年   34篇
  1981年   29篇
  1980年   26篇
  1979年   28篇
  1978年   27篇
  1977年   28篇
  1976年   45篇
  1975年   30篇
  1973年   25篇
  1971年   22篇
排序方式: 共有3878条查询结果,搜索用时 15 毫秒
71.

Introduction

Humans are widely exposed to estrogenically active phthalates, parabens, and phenols, raising concerns about potential effects on breast tissue and breast cancer risk. We sought to determine the association of circulating serum levels of these chemicals (reflecting recent exposure) with mammographic breast density (a marker of breast cancer risk).

Methods

We recruited postmenopausal women aged 55 to 70 years from mammography clinics in Madison, Wisconsin (N = 264). Subjects completed a questionnaire and provided a blood sample that was analyzed for mono-ethyl phthalate, mono-butyl phthalate, mono-benzyl phthalate, butyl paraben, propyl paraben, octylphenol, nonylphenol, and bisphenol A (BPA). Percentage breast density was measured from mammograms by using a computer-assisted thresholding method.

Results

Serum BPA was positively associated with mammographic breast density after adjusting for age, body mass index, and other potentially confounding factors. Mean percentage density was 12.6% (95% confidence interval (CI), 11.4 to 14.0) among the 193 women with nondetectable BPA levels, 13.7% (95% CI, 10.7 to 17.1) among the 35 women with detectable levels below the median (<0.55 ng/ml), and 17.6% (95% CI, 14.1 to 21.5) among the 34 women with detectable levels above the median (>0.55 ng/ml; Ptrend = 0.01). Percentage breast density was also elevated (18.2%; 95% CI, 13.4 to 23.7) among the 18 women with serum mono-ethyl phthalate above the median detected level (>3.77 ng/ml) compared with women with nondetectable BPA levels (13.1%; 95% CI, 11.9 to 14.3; Ptrend = 0.07). No other chemicals demonstrated associations with percentage breast density.

Conclusions

Postmenopausal women with high serum levels of BPA and mono-ethyl phthalate had elevated breast density. Further investigation of the impact of BPA and mono-ethyl phthalate on breast cancer risk by using repeated serum measurements or other markers of xenoestrogen exposure are needed.  相似文献   
72.
This study examined attitudes to human papillomavirus (HPV) testing among a purposively selected sample of women from four ethnic groups: white British, African Caribbean, Pakistani and Indian. The design was qualitative, using focus group discussion to elicit women's attitudes towards HPV testing in the context of cervical cancer prevention. The findings indicate that although some women welcomed the possible introduction of HPV testing, they were not fully aware of the sexually transmitted nature of cervical cancer and expressed anxiety, confusion and stigma about HPV as a sexually transmitted infection. The term 'wart virus', often used by medical professionals to describe high-risk HPV to women, appeared to exacerbate stigma and confusion. Testing positive for HPV raised concerns about women's sexual relationships in terms of trust, fidelity, blame and protection, particularly for women in long-term monogamous relationships. Participation in HPV testing also had the potential to communicate messages of distrust, infidelity and promiscuity to women's partners, family and community. Concern about the current lack of available information about HPV was clearly expressed and public education about HPV was seen as necessary for the whole community, not only women. The management of HPV within cervical screening raises important questions about informed participation. Our findings suggest that HPV testing has the potential to cause psychosocial harm to women and their partners and families.  相似文献   
73.
Cerebral blood flow is a finely tuned process dependent on coordinated changes in arterial tone. These changes are strongly tied to smooth muscle membrane potential and inwardly rectifying K+ (KIR) channels are thought to be a key determinant. To elucidate the role of KIR2.1 in cerebral arterial tone development, this study examined the electrical and functional properties of cells, vessels and living tissue from tamoxifen-induced smooth muscle cell (SMC)-specific KIR2.1 knockout mice. Patch-clamp electrophysiology revealed a robust Ba2+-sensitive inwardly rectifying K+ current in cerebral arterial myocytes irrespective of KIR2.1 knockout. Immunolabeling clarified that KIR2.1 expression was low in SMCs while KIR2.2 labeling was remarkably abundant at the membrane. In alignment with these observations, pressure myography revealed that the myogenic response and K+-induced dilation were intact in cerebral arteries post knockout. At the whole organ level, this translated to a maintenance of brain perfusion in SMC KIR2.1−/− mice, as assessed with arterial spin-labeling MRI. We confirmed these findings in superior epigastric arteries and implicated KIR2.2 as more functionally relevant in SMCs. Together, these results suggest that subunits other than KIR2.1 play a significant role in setting native current in SMCs and driving arterial tone.  相似文献   
74.
75.
76.
Jean L. Koff MD  MS  Edmund K. Waller MD  PhD 《Cancer》2019,125(6):838-842
In an article published in this issue of Cancer, D’Arcy et al link the incidence of cancer among recipients of solid organ transplantation (SOT) in the Scientific Registry of Transplant Recipients with data from regional and statewide cancer registries to examine cancer-specific mortality for common malignancies in SOT recipients. This analysis helps to illuminate the role of immune surveillance across a broad range of malignancies and compares the incidence of cancers due to virally mediated oncogenesis (lymphoma, squamous cell carcinoma of the aerodigestive epithelium, and hepatitis-induced liver cancer) with the incidence of other malignancies. The authors’ central finding is that cancer-specific mortality is significantly increased in SOT recipients in comparison with nontransplant recipients for multiple cancers, and the increased cancer incidence is not limited to the effects of viral oncogenesis. The authors document a significant increase in common epithelial malignancies that are currently treated with immune checkpoint antibodies, including melanoma, bladder cancer, colorectal cancer, cancers of the oral cavity/pharynx, kidney cancer, and lung cancer, and this supports the hypothesis that post-SOT immunosuppression affects immune surveillance in these cancers. Provocatively, the authors also document increases in the incidence and mortality of cancers not typically responsive to immune checkpoint therapies, including breast cancer and pancreatic cancer. The findings of D’Arcy et al suggest that immune surveillance controls oncogenesis and tumor progression in a broad range of malignancies and that breast cancer and pancreatic cancer could be sensitive to drugs targeting immune surveillance pathways other than those treated with currently Food and Drug Administration–approved antibodies to CTLA4 and PD-1/PD-L1.  相似文献   
77.
78.

Background

Multifocal pheochromocytoma/paraganglioma presenting at an early age is commonly associated with a hereditary syndrome.

Case Report

A 29-year-old woman was referred for evaluation of multifocal pheochromocytoma/paraganglioma. Interestingly, her family history did not include pheochromocytoma/paraganglioma, and comprehensive genetic testing for the well-documented pheochromocytoma/paraganglioma susceptibility genes was negative. Of note, this patient had a history of a complex cardiac defect resulting in cyanotic congenital heart disease and had never undergone operative repair. Thus she lived in a chronic hypoxic state with a baseline oxygen saturation of about 80%. Laboratory evaluation found marked increases in plasma norepinephrine and normetanephrines with normal epinephrine and metanephrines. Imaging revealed 4 aortocaval masses and a right adrenal mass. After appropriate preoperative preparation she underwent successful resection of each of the neoplasms, with pathologic testing revealing multifocal pheochromocytoma/paraganglioma.

Discussion

This case highlights a growing recognition of the potential development of pheochromocytoma/paraganglioma in patients with cyanotic congenital heart disease. The underlying pathophysiology and phenotypic similarities between pheochromocytoma/paraganglioma in patients with cyanotic congenital heart disease and those with mutations that lead to cellular pseudohypoxia are reviewed.  相似文献   
79.
Merck & Co., Inc., Kenilworth, NJ, USA, is undergoing a transformation in the way that it prosecutes R&D programs. Through the adoption of a “model-driven” culture, enhanced R&D productivity is anticipated, both in the form of decreased attrition at each stage of the process and by providing a rational framework for understanding and learning from the data generated along the way. This new approach focuses on the concept of a “Design Cycle” that makes use of all the data possible, internally and externally, to drive decision-making. These data can take the form of bioactivity, 3D structures, genomics, pathway, PK/PD, safety data, etc. Synthesis of high-quality data into models utilizing both well-established and cutting-edge methods has been shown to yield high confidence predictions to prioritize decision-making and efficiently reposition resources within R&D. The goal is to design an adaptive research operating plan that uses both modeled data and experiments, rather than just testing, to drive project decision-making. To support this emerging culture, an ambitious information management (IT) program has been initiated to implement a harmonized platform to facilitate the construction of cross-domain workflows to enable data-driven decision-making and the construction and validation of predictive models. These goals are achieved through depositing model-ready data, agile persona-driven access to data, a unified cross-domain predictive model lifecycle management platform, and support for flexible scientist-developed workflows that simplify data manipulation and consume model services. The end-to-end nature of the platform, in turn, not only supports but also drives the culture change by enabling scientists to apply predictive sciences throughout their work and over the lifetime of a project. This shift in mindset for both scientists and IT was driven by an early impactful demonstration of the potential benefits of the platform, in which expert-level early discovery predictive models were made available from familiar desktop tools, such as ChemDraw. This was built using a workflow-driven service-oriented architecture (SOA) on top of the rigorous registration of all underlying model entities.  相似文献   
80.
Tackling alcohol-related harms crosses agency and professional boundaries, requiring collaboration between health, criminal justice, education and social welfare institutions. It is a key component of most multi-component programmes in the United States, Australia and Europe. Partnership working, already embedded in service delivery structures, is a core mechanism for delivery of the new UK Government Alcohol Strategy. This article reports findings from a study of alcohol partnerships across England. The findings are based on a mix of open discussion interviews with key informants and on semi-structured telephone interviews with 90 professionals with roles in local alcohol partnerships. Interviewees reported the challenges of working within a complex network of interlinked partnerships, often within hierarchies under an umbrella partnership, some of them having a formal duty of partnership. The new alcohol strategy has emerged at a time of extensive reorganisation within health, social care and criminal justice structures. Further development of a partnership model for policy implementation would benefit from consideration of the incompatibility arising from required collaboration and from tensions between institutional and professional cultures. A clearer analysis of which aspects of partnership working provide ‘added value’ is needed.  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