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   40507篇
  免费   2760篇
  国内免费   182篇
耳鼻咽喉   370篇
儿科学   1042篇
妇产科学   946篇
基础医学   5228篇
口腔科学   666篇
临床医学   3946篇
内科学   7884篇
皮肤病学   639篇
神经病学   4125篇
特种医学   1575篇
外科学   6541篇
综合类   491篇
现状与发展   1篇
一般理论   35篇
预防医学   3301篇
眼科学   1016篇
药学   2701篇
中国医学   116篇
肿瘤学   2826篇
  2023年   227篇
  2022年   402篇
  2021年   887篇
  2020年   551篇
  2019年   803篇
  2018年   1027篇
  2017年   722篇
  2016年   727篇
  2015年   866篇
  2014年   1339篇
  2013年   1757篇
  2012年   2815篇
  2011年   2932篇
  2010年   1676篇
  2009年   1537篇
  2008年   2677篇
  2007年   2896篇
  2006年   2691篇
  2005年   2637篇
  2004年   2511篇
  2003年   2376篇
  2002年   2178篇
  2001年   390篇
  2000年   345篇
  1999年   400篇
  1998年   511篇
  1997年   468篇
  1996年   480篇
  1995年   371篇
  1994年   355篇
  1993年   313篇
  1992年   240篇
  1991年   205篇
  1990年   175篇
  1989年   180篇
  1988年   200篇
  1987年   184篇
  1986年   179篇
  1985年   179篇
  1984年   154篇
  1983年   169篇
  1982年   206篇
  1981年   180篇
  1980年   157篇
  1979年   93篇
  1978年   126篇
  1977年   124篇
  1976年   100篇
  1975年   102篇
  1974年   77篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
BackgroundUpper gastrointestinal (UGI) bleed is a common surgical disease in sub-Saharan Africa where there is often a lack of diagnostic and interventional adjuncts such as endoscopy. This study sought to characterize the role of endoscopy in management of acute UGI bleeding.Materials and MethodsThis is a prospective observational analysis of adults presenting with an UGI bleed to a tertiary center in Lilongwe, Malawi, over two years. Patients were classified as having no endoscopy, diagnostic endoscopy, or endoscopy with variceal banding. Bivariate, survival analysis, and logistic regression analyses were used to compare intervention cohorts.Results293 patients were included with 49 patients (16.7%) receiving endoscopy with banding, 65 (22.2%) patients receiving diagnostic endoscopy only, and 179 (61.1%) receiving no endoscopy. Upon survival analysis comparing to the no endoscopy group, cox hazard modelling showed an adjusted hazard ratio over 30 days of 0.12 (95% CI 0.02, 0.88, p=0.038) for the endoscopic banding group and a hazard ratio of 0.39 (95% CI 0.13, 1.16, p=0.090) for the diagnostic endoscopy only group. Physical exam findings consistent with cirrhosis and decreasing age were independent predictors of an endoscopic diagnosis of variceal bleeding.ConclusionEsophagogastric varices are a common cause of UGI bleeding in sub-Saharan Africa and can be predicted with age and physical exam findings. Endoscopy with variceal banding has a survival benefit for patients presenting with acute UGI bleed even with relatively low utilization. Appropriately triaging patients with likely variceal bleeding and improving endoscopy capacity would likely have a significant impact on mortality.  相似文献   
993.
Sustainability science has grown as a field of inquiry, but has said little about the role of large-scale private sector actors in socio-ecological systems change. However, the shaping of global trends and transitions depends greatly on the private sector and its development impact. Market-based and command-and-control policy instruments have, along with corporate citizenship, been the predominant means for bringing sustainable development priorities into private sector decision-making. This research identifies conflict as a further means through which environmental and social risks are translated into business costs and decision making. Through in-depth interviews with finance, legal, and sustainability professionals in the extractive industries, and empirical case analysis of 50 projects worldwide, this research reports on the financial value at stake when conflict erupts with local communities. Over the past decade, high commodity prices have fueled the expansion of mining and hydrocarbon extraction. These developments profoundly transform environments, communities, and economies, and frequently generate social conflict. Our analysis shows that mining and hydrocarbon companies fail to factor in the full scale of the costs of conflict. For example, as a result of conflict, a major, world-class mining project with capital expenditure of between US$3 and US$5 billion was reported to suffer roughly US$20 million per week of delayed production in net present value terms. Clear analysis of the costs of conflict provides sustainability professionals with a strengthened basis to influence corporate decision making, particularly when linked to corporate values. Perverse outcomes of overemphasizing a cost analysis are also discussed.Large-scale natural resource extraction projects (including exploration and processing activities) profoundly transform environments, communities, and economies, and often generate social conflict (2, 3). Previous studies of resource extraction and conflict have highlighted the relationship between mining and hydrocarbon resources and broader civil conflict (4, 5) and individual cases of project level conflict (6, 7). In this study, we investigate the importance of company–community conflict in the context of regulation of the sustainability performance of mining and hydrocarbon companies. We estimate the cost of social conflict to companies, determine how companies interpret this conflict, and explain how they respond to conflict. Costs were understood broadly as the negative impacts of company–community conflict on a company’s tangible and intangible assets, including value erosion. Conflict is defined as the coexistence of aspirations, interests, and world views that cannot be met simultaneously, or that actors do not perceive as being subject to simultaneous satisfaction, and is viewed in this assessment as ranging from low-level tension to escalated situations involving a complete relationship breakdown or violence (8).There is growing appreciation that unmitigated environmental and social risks have the potential to negatively influence the financial success of large-scale developments in the extractive industries. A 2008 study of 190 projects operated by the major international oil companies showed that the time taken for projects to come on-line nearly doubled in the preceding decade, causing significant increases in costs (9), although this increase reflects project remoteness, scale, technical difficulty, and input price, as well as social conflict. A follow-up of a subset of those projects found that nontechnical risks accounted for nearly one-half of the total risks faced by these companies, and that risks related to company relationships with other social actors constituted the single largest category (10). A separate empirical study of 19 publicly traded junior gold-mining companies found two-thirds of the market capitalization of these firms was a function of the firm’s stakeholder engagement practices, whereas only one-third was a function of the value of gold in the ground (11).In its analysis of socio-ecological systems (SESs), the sustainability science literature has said little about the large-scale private sector as an important actor within, and regulator of, SES behavior. A review of the 450 sustainability science articles published in PNAS, for example, finds just 23 referring to “corporate,” “industry,” “private sector,” or “company” in their texts. An extensive word cloud produced by a historical review of 20,000 papers related to sustainability science (12) notes just five terms implying a focus on the private sector (“corporate social,” “corporate sustainability,” “social responsibility,” “industrial ecology,” and “supply chain”), with none of these terms invoking core company decision making, culture, or calculations. However, large-scale corporate actors are obviously of central importance to the “major questions” for research in sustainability science (13), and perhaps especially the questions: “What shapes the long-term trends and transitions that provide the major directions for this century?” and “What determines the adaptability, vulnerability, and resilience of human–environment systems?” (13).The relevance of private sector actors is particularly clear in the extractive industries where, given the evolution of technology and industrial structure in these sectors, large enterprises have become highly influential actors in SES dynamics. Dramatic events and disasters, such as the Deepwater Horizon in the Gulf of Mexico, make this clear. Such enterprises can also be critical actors in slower processes of SES change, such as those mediating the relationships among water, agriculture, livelihoods, mining, and climate change (14, 15). Companies in the extractive industries have, to greater or lesser extent, developed policies for sustainable development and used sustainability professionals to respond to the changes induced by their activities on SESs. It is therefore important to understand the drivers of company behavior to build adequate models of socio-ecological change.This study addresses one potential driver of company behavior: conflicts motivated by the social and environmental risks created by, and the impacts of, corporate activities. More specifically, the study understands social conflict as a means through which populations communicate perceptions of risk and which generate costs for companies. The study refers to risk from the perspective of the entity experiencing the risk (i.e., environmental risks are risks to the environment; social risks are risks to society, social groups, or individuals; and business risks are the risks to the business). We ask about the significance of the costs associated with community conflict to companies, how far companies are prepared to respond to these costs by seeking strategies to reduce the environmental and social risk that they generate within SESs, and the conditions that can induce regulatory and strategic change within the corporate sector itself such that it reduces any negative environmental and social impacts.Although the report addresses just one dimension of large-scale private sector activity, the purpose is to suggest the importance of paying far more attention to corporate behavior in studies of socio-ecological dynamics. Emerging research on large-scale land acquisitions, or “land grabs” (16), and the implications for land-change science (17) suggests the same need to attend to corporate actors in sustainability science. In addressing this theme, our primary purpose is to map out, explore, and identify (rather than test) particular relationships between large-scale business and SES dynamics. The intent of the research is to build SES theory in ways that treat corporate behavior as endogenous to these systems.Through in-depth confidential interviews with corporate finance, legal, and sustainability professionals, and empirical case analysis, we investigate the extent to which recognition of the costs of conflict has the potential to change the ways in which companies address the environmental and social risks of mining and hydrocarbon development. Case studies combined desk-based analysis of secondary materials with key informant interviews to confirm or supplement the analysis. Case studies were used to characterize the types of company–community conflicts affecting mining projects, the point at which conflict took effect within the project cycle, and the types of effects that conflict appeared to have on projects. Key informant interviews were used to address how large-scale mining and hydrocarbon companies interpret these conflicts, how they respond to them, the factors determining different types of company response, and the extent to which calculations of the financial costs of conflict change the ways in which companies respond.  相似文献   
994.
Toxoplasma gondii is a leading cause of severe foodborne illness in the United States. Population-based studies have found T. gondii infection to be more prevalent in racial/ethnic minority and socioeconomically disadvantaged groups. Soil contaminated with cat feces, undercooked meat, and congenital transmission are the principal sources of infection. Toxoplasmosis-associated illnesses include congenital neurologic and ocular disease; acquired illness in immunocompetent persons, most notably ocular disease; and encephalitis or disseminated disease in immunosuppressed persons. The association of T. gondii infection with risk for mental illness is intriguing and requires further research. Reduction of T. gondii in meat, improvements in hygiene and food preparation practices, and reduction of environmental contamination can prevent toxoplasmosis, but more research is needed on how to implement these measures. In addition, screening and treatment may help prevent toxoplasmosis or reduce the severity of disease in some settings.  相似文献   
995.
996.

Aims/hypothesis

White cell count has been shown to predict incident type 2 diabetes, but differential white cell count has received scant attention. We examined the risk of developing diabetes associated with differential white cell count and neutrophil:lymphocyte ratio and the effect of insulin sensitivity and subclinical inflammation on white cell associations.

Methods

Incident diabetes was ascertained in 866 participants aged 40–69 years in the Insulin Resistance Atherosclerosis Study after a 5 year follow-up period. The insulin sensitivity index (SI) was measured by the frequently sampled IVGTT.

Results

C-reactive protein was directly and independently associated with neutrophil (p?<?0.001) and monocyte counts (p?<?0.01) and neutrophil:lymphocyte ratio (p?<?0.001), whereas SI was inversely and independently related to lymphocyte count (p?<?0.05). There were 138 (15.9%) incident cases of diabetes. Demographically adjusted ORs for incident diabetes, comparing the top and bottom tertiles of white cell (1.80 [95% CI 1.10, 2.92]), neutrophil (1.67 [1.04, 2.71]) and lymphocyte counts (2.30 [1.41, 3.76]), were statistically significant. No association was demonstrated for monocyte count (1.18 [0.73, 1.90]) or neutrophil:lymphocyte ratio (0.89 [0.55, 1.45]). White cell and neutrophil associations were no longer significant after further adjusting for family history of diabetes, fasting glucose and smoking, but the OR comparing the top and bottom tertiles of lymphocyte count remained significant (1.96 [1.13, 3.37]). This last relationship was better explained by SI rather than C-reactive protein.

Conclusions/interpretation

A lymphocyte association with incident diabetes, which was the strongest association among the major white cell types, was partially explained by insulin sensitivity rather than subclinical inflammation.  相似文献   
997.
998.
999.
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