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   1550篇
  免费   121篇
  1671篇
  2023年   5篇
  2022年   9篇
  2021年   18篇
  2020年   12篇
  2019年   14篇
  2018年   19篇
  2017年   28篇
  2016年   32篇
  2015年   66篇
  2014年   59篇
  2013年   82篇
  2012年   109篇
  2011年   101篇
  2010年   64篇
  2009年   65篇
  2008年   70篇
  2007年   94篇
  2006年   83篇
  2005年   88篇
  2004年   67篇
  2003年   82篇
  2002年   74篇
  2001年   18篇
  2000年   19篇
  1999年   25篇
  1998年   30篇
  1997年   16篇
  1996年   18篇
  1995年   24篇
  1994年   29篇
  1993年   24篇
  1992年   25篇
  1991年   16篇
  1990年   17篇
  1989年   25篇
  1988年   11篇
  1987年   13篇
  1986年   19篇
  1985年   13篇
  1984年   12篇
  1983年   9篇
  1982年   4篇
  1981年   7篇
  1980年   8篇
  1979年   6篇
  1978年   11篇
  1977年   10篇
  1976年   4篇
  1972年   3篇
  1970年   3篇
排序方式: 共有1671条查询结果,搜索用时 12 毫秒
51.
52.
53.
Due to the reform of long term care in 2015, there is growing concern about whether groups at risk receive the care they need. People in need of care have to rely more on help from their social network. The increased need for informal care requires resilience and organizational skills of families, but also of volunteers, professionals and employers. What does this mean for the provision of informal care in the next decennia? The symposium ‘The future of informal care’, organized on January 26 2017 by the National Institute for Social Research and the Institute for Societal Resilience of the Vrije Universiteit, addressed possible answers to this question. In her inaugural speech Alice de Boer discussed social inequality as possible determinant and outcome of informal care. Some conclusions:Until 2050 the absolute number of 75-plus doubled to about 3 million persons, but the number of informal caregivers will decrease. In addition to the importance of social and economic resources (the ‘have & have-nots’), the ability to arrange care (the ‘can & can-nots’) gains importance.Almost half of the older employers provides informal care just before retirement. Flexibility in working hours and work location facilitates combining work and care, but about half of the employers indicates that partial retirement and working at home are no options.Informal caregivers and professionals often provide care from comparable perspectives and identities. Addressing similarities rather than differences improves their chances for collaboration.The number of adult children providing household care to older parents increased between 2002 and 2014. This suggests an increase in family solidarity, but current reform policies may increase the gender inequality in caregiving families.Spouses and children remain primary caregivers in the future, preferably supported by many different types of caregivers. Not everybody has the capabilities to organize and direct such a large care network.Providing informal care increases the risk for overburden and absence at work or education. Informal caregivers at risk remain, also in the future, women, spouses, migrants, and younger carers.  相似文献   
54.
Fast-growing, aerobic, heterotrophic bacteria from the root surface of young sugar beet plants were inventoried. Isolation of the most abundant bacteria from the root surface of each of 1,100 plants between the second and tenth leaf stage yielded 5,600 isolates. These plants originated from different fields in Belgium and Spain. All isolates were characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of total cellular proteins. Comparison of protein fingerprints allowed us to inventory the bacteria of individual plants of different fields or leaf stages and to analyze the composition and variability of the rhizobacterial population of young sugar beet plants. Each field harbored a specific population of bacteria which showed a highly hierarchic structure. A small number of bacteria occurring frequently at high densities dominated in each field. The major bacteria were identified as Pseudomonas fluorescens, Xanthomonas maltophilia, Pseudomonas paucimobilis, and Phyllobacterium sp. The former three species showed a high genetic variability as they were represented by different protein fingerprint types on the same or different fields or leaf stages. Twinspan analysis and relative abundance plots showed that the structure and composition of the bacterial populations varied strongly over time. Pseudomonads were typically early colonizers which were later replaced by X. maltophilia or Phyllobacterium sp.  相似文献   
55.
A theoretical analysis of the detachment of bacteria adhering to substratum surfaces upon the passage of an air-liquid interface is given, together with experimental results for bacterial detachment in the absence and presence of a conditioning film on different substratum surfaces. Bacteria (Streptococcus sobrinus HG1025, Streptococcus oralis J22, Actinomyces naeslundii T14V-J1, Bacteroides fragilis 793E, and Pseudomonas aeruginosa 974K) were first allowed to adhere to hydrophilic glass and hydrophobic dimethyldichlorosilane (DDS)-coated glass in a parallel-plate flow chamber until a density of 4 × 106 cells cm−2 was reached. For S. sobrinus HG1025, S. oralis J22, and A. naeslundii T14V-J1, the conditioning film consisted of adsorbed salivary components, while for B. fragilis 793E and P. aeruginosa 974K, the film consisted of adsorbed human plasma components. Subsequently, air bubbles were passed through the flow chamber and the bacterial detachment percentages were measured. For some experimental conditions, like with P. aeruginosa 974K adhering to DDS-coated glass and an air bubble moving at high velocity (i.e., 13.6 mm s−1), no bacteria detached upon passage of an air-liquid interface, while for others, detachment percentages between 80 and 90% were observed. The detachment percentage increased when the velocity of the passing air bubble decreased, regardless of the bacterial strain and substratum surface hydrophobicity involved. However, the variation in percentages of detachment by a passing air bubble depended greatly upon the strain and substratum surface involved. At low air bubble velocities the hydrophobicity of the substratum had no influence on the detachment, but at high air bubble velocities all bacterial strains were more efficiently detached from hydrophilic glass substrata. Furthermore, the presence of a conditioning film could either inhibit or stimulate detachment. The shape of the bacterial cell played a major role in detachment at high air bubble velocities, and spherical strains (i.e., streptococci) detached more efficiently than rod-shaped organisms. The present results demonstrate that methodologies to study bacterial adhesion which include contact with a moving air-liquid interface (i.e., rinsing and dipping) yield detachment of an unpredictable number of adhering microorganisms. Hence, results of studies based on such methodologies should be referred as “bacterial retention” rather than “bacterial adhesion”.  相似文献   
56.
The act of ensuring freshwater is considered the most essential and basic need for humanity. Although the planet is water-rich in some terms, the freshwater sources available for human consumption and beneficial uses are very limited. Excess population growth, industrial development coupled with improving living standards have caused an unprecedented need for freshwater all over the world. Regions once rich in water resources are struggling to meet the ever increasing demands in recent years. In addition, climate change and unsustainable management practices have led to a situation called “drought” in many regions. Water supplies in drought conditions can be addressed by taking two major approaches related to management and technology development. The management approaches include demand mitigation and supply enhancement. Demand mitigation can be done by implementing water conservation practices, and by enforcing a mechanism to influence user-responsible behavior through higher water fares and other billing routes. Supply enhancement can be achieved by utilizing the methods available for water reclamation, reuse and recycle including rain harvesting. This paper provides a critical insight of the causes for drought and the issues caused by persistent drought conditions followed by discussion of management and technological approaches required to maintain adequate water resources around the world. Challenges and opportunities involved in implementation of desalination and water reuse technologies in addressing global water scarcity are discussed in detail with case studies  相似文献   
57.
58.
It has now been recognised that the immune system as a whole can be the target for xenobiotic induced toxicity. The discipline of immuntoxicology encompasses non specific direct immunotoxicity and immunostimulation, and specific responses like hypersensitivity and autoimmunity. Direct immunotoxicity can be determined in tiered studies, TIER 1 being a general toxicity study with emphasis on evaluation of organs belonging to the immune system, TIER 2 investigating the effects of xenobiotics on immune functionality in immunological challenge experiments. In the TIER 1 study, organ weights and histopathological evaluation of immune organs like spleen, thymus, lymph nodes, blood and bone marrow may detect the occurrence of direct immunotoxicity. The follow up studies in the TIER 2 phase can then determine the extent of the immunosuppression and identify which specific parts or cellular components of the immune system are involved. In view of the complexity of the immune system and the multitude of interactions within the immune system in vivo animal experiments are needed to investigate xenobiotics for their potential immunotoxicity. In vitro assays with in vivo exposed cells of the immune system may present additional information on the mechanisms involved in the observed direct immunotoxicity.  相似文献   
59.
Genes controlling antibacterial resistance may be important in the hygiene hypothesis, which states that lack of bacterial infections during childhood would favor development of allergic disease. We, therefore, studied whether Nramp1 (Slc11a1) alleles, which determine susceptibility (Nramp1(s)) or resistance (Nramp1(r)) to intracellular bacteria, affect the efficacy of heat-killed Mycobacterium vaccae in the treatment of allergic asthma in a mouse model. Treatment of OVA-sensitized Nramp1(s) mice with M. vaccae suppressed airway hyperresponsiveness, airway eosinophilia, Ag-specific IgE, and IL-4 and IL-5 production after OVA aerosol challenge. In contrast, M. vaccae hardly affected these parameters in Nramp1(r) mice. In addition, The Nramp1 gene affected both T cell-mediated responses to M. vaccae in vivo and the level of macrophage activation after stimulation with M. vaccae in vitro. In conclusion, the efficacy of M. vaccae in preventing allergic and asthmatic manifestations in a mouse model is strongly affected by Nramp1 alleles. These findings could have important implications for the future use of mycobacteria and their components in the prevention or treatment of allergic asthma. A new link is described between genes, the environment, and the development of allergy, in which the Nramp1 gene fine tunes the hygiene hypothesis.  相似文献   
60.

Objective

Our aim was to investigate whether trends in quality of diabetes care differ between sexes in the Netherlands from 1998 till 2013.

Research Design and Methods

In this prospective observational cohort study quality of care was measured using process and outcome measures in patients with type 2 diabetes in primary care. Trend and absolute differences between sexes were investigated for patients <75 years. Subgroup analyses were performed in patients ≥75 years. 10-year mortality risk was assessed with the Globorisk risk equation in patients without cardiovascular diseases <75 years.

Results

The number of patients increased from 2,644 in 1998 to 62,230 in 2013. In 1998, 51% of the men and 60% of the women <75 years had an HbA1c >53 mmol/mol; this decreased to approximately 29% in both sexes in 2013. Patients having a systolic blood pressure >140 mmHg decreased from 70% to 42%, and from 80% to 40% in men and women <75 years, respectively. In patients ≥75 years it decreased from 72% to 50% in men and 85% to 56% in women. Obesity increased in both sexes, whereas smoking in men and women declined in patients <75 years (men: 34% to 22%; women: 22% to 18%). The number of patients with a mortality risk >20% over 10 years decreased from 15% to 3% in men and from 18% to 3% in women.

Conclusions

Quality of diabetes care has improved considerably in the period 1998–2013 in both sexes. Possibly relevant trend differences between sexes were observed for HbA1c, systolic blood pressure, BMI and smoking. The predicted mortality risk decreased over time in both sexes. Except for BMI in both age groups and systolic blood pressure in patients ≥75 years, no evident poorer risk factor control in women compared to men was found at the end of the study period.  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