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   274篇
  免费   49篇
  国内免费   6篇
  2023年   4篇
  2022年   3篇
  2021年   9篇
  2020年   8篇
  2019年   17篇
  2018年   14篇
  2017年   28篇
  2016年   17篇
  2015年   20篇
  2014年   21篇
  2013年   34篇
  2012年   23篇
  2011年   22篇
  2010年   8篇
  2009年   9篇
  2008年   10篇
  2007年   10篇
  2006年   12篇
  2005年   11篇
  2004年   6篇
  2003年   2篇
  2002年   6篇
  2001年   4篇
  2000年   5篇
  1999年   4篇
  1998年   2篇
  1997年   3篇
  1995年   2篇
  1994年   1篇
  1993年   1篇
  1991年   2篇
  1990年   1篇
  1989年   1篇
  1988年   2篇
  1987年   2篇
  1986年   1篇
  1985年   2篇
  1983年   1篇
  1982年   1篇
排序方式: 共有329条查询结果,搜索用时 156 毫秒
1.
A new dissimilarity measure, Uppsala dissimilarity, is proposed. It is a Manhattan-type measure in between the Canberra and Gower measures, based on the differences between scores in relevés compared, but it also takes both the sums of scores and the difference between maximum and minimum score into account. The measure is considered realistic for phytosociological material.A new optimality criterion has been developed after unsatisfactory results had been obtained with the DOL criterion (Popma et al. 1983) which was developed previously by our group. Problems with DOL were especially met when the criterion was applied to the distribution of only one species over the cluster array obtained. The new criterion takes both internal cluster homogeneity and between-cluster dissimilarity into account. Between-cluster dissimilarity is calculated for all other clusters and not only for the nearest neighbour, as in DOL. The new criterion has both an unweighted form: SOM, and a form with weighting for cluster size: SWOM.This new criterion was successfully applied to the evaluation of the sharpness of distribution of individual species over cluster arrays, under the name of SIM: species indication measure and SWIM, species weighted indication measure.The measures were applied to some test data. Differences between the unweighted and weighted forms were found which could not be easily interpreted.Some remarks are made on the coherence of d-SAHN and h-SAHN approaches in agglomerative clustering within the new strategy proposed.Abbreviations DOL = Detection of Optimal Level - S(W)IM = Species (Weighted) Indication Measure - S(W)OM = Standardized (Weighted) Optimality Measure - UD = Uppsala Dissimilarity measure - WPGMA = Weighted Pair-Group Method Average linking clustering - SAHN = Sequential Agglomerative Hierarchical Non-overlapping clustering  相似文献   
2.
术语是科学概念的约定性语言符号,是科技信息交流的工具。中国的灵长类学研究虽然起步较晚,但发展迅速。在研究过程中,学者们广泛参阅、借鉴国际同行的研究成果,并引入了一些灵长类学专业术语。科学、规范、准确、明晰的表达理应成为学者们的共识,而这对信息的沟通与交流至关重要。本文阐述了科学研究术语规范化表述的重要性,并基于文献梳理,介绍了非人灵长类社会中α-雄性更替(α-male replacement)的主要类型之术语及其含义,建议国内研究者使用:(1)取代(Takeover);(2)等级反转(Rank reversal);(3)继承(Succession);(4)补缺(Waltz-in);(5)分群(Fission)。文中还讨论了影响α-雄性更替的主要因素。  相似文献   
3.
毛彬彬  张巧仙  方云  林尽 《蛇志》2021,(1):74-76
目的探讨PDCA循环在提高肿瘤患者输液港护理依从性的应用效果。方法选取2018年2~8月我院收治的504例输液港置管的肿瘤患者按随机分配原则分为对照组240例和观察组264例,对照组给予一般治疗和常规管理,观察组在对照组基础上实施PDCA循环管理,观察两组患者的并发症发生情况、输液港护理依从性,并进行统计分析。结果观察组的并发症发生率明显低于对照组,差异有统计学意义(P<0.05);观察组的输液港护理依从性明显高于对照组,差异有统计学意义(P<0.05)。结论运用PDCA循环能优化维护流程,降低并发症,提高患者输液港护理依从性,值得临床应用。  相似文献   
4.

Background

Many studies have reported the associations of polymorphic CAG repeats in androgen receptor (AR) gene with PCOS risk, but with inconsistent results. So, the aim of present meta-analysis was to clarify such inconsistence, so as to provide more conclusive results.

Methods

PubMed was searched for the eligible reports published until February 2012 without language limitation. The studies reporting the relationship between CAG repeat length and PCOS were selected for the meta-analysis according to the inclusion criteria. Two reviewers independently extracted the data and evaluated the study quality.

Principal findings

As for the relationship between CAG repeat length and PCOS risk, the pooled results showed that the biallelic mean was not significantly different between PCOS and controls (SMD − 0.03, 95% CI − 0.16–0.10, P = 0.603), and that the ORs of PCOS were not demonstrated for the individuals with the biallelic mean less than median (OR 0.96, 95% CI 0.68–1.35, P = 0.794), with the short CAG allele (OR 0.94, 95% CI 0.80–1.10, P = 0.424), or with the X-weighted biallelic mean (OR 0.81, 95% CI 0.46–1.41, P = 0.447). Further, as for the relationship between CAG repeat length and T levels in PCOS patients, the biallelic mean was not significantly different between PCOS patients with high T and those with low T (SMD 0.79, 95% CI − 0.12–1.70, P = 0.088), while the summary correlation r indicated that the CAG biallelic mean appeared to be positively associated with T levels in PCOS (r 0.20, 95% CI 0.11–0.30, p = 0.000).

Conclusions

This meta-analysis demonstrates no evident association between the CAG length variations in AR gene and PCOS risk, while the CAG length appears to be positively associated with T levels in PCOS patients.  相似文献   
5.
Seasonal effects on shift‐work tolerance were assessed using the Standardized Shiftwork Index and the 21‐item Hamilton Depression Scale. Participants (N=88) mainly worked a two‐day, two‐night, four‐off rotation with 12 h shifts changing at 06∶00 and 18∶00 h in Vancouver, Canada. At this latitude (~49° N), daylength varies seasonally from ~16 to ~8 h, and both daily commutes occur in the dark in mid‐winter and in sunlight in mid‐summer. Questionnaires were completed twice, near the summer and winter solstices (order counterbalanced). Outcome variables were mood, general psychological health, sleep quality, chronic fatigue, physical health, job satisfaction, and social and domestic disruption. Of these, general psychological health and mood were significantly worse in winter, while sleep was more disturbed in summer. In winter, 31% exceeded the cutoff for psychological distress, and >70% scored in the higher than normal range for depressive symptoms. In summer, the proportions dropped to 19% and 53%, respectively. Measures of physical health and psychosocial well‐being showed no seasonal effects. Relationships among explanatory and outcome variables, assessed by linear regression and canonical correlations, were also stable across season. Neuroticism was the strongest predictor of tolerance to shift work. Age was predictive only of sleep disturbance in both summer and winter. These results indicate that time of year can affect important outcome measures in shift‐work assessment and intervention studies. The high average scores on measures of psychological distress and depression in winter suggest that at northern latitudes, some shift schedules may increase the risk of seasonal‐type depression.  相似文献   
6.
This paper contextualizes racial and ethnic identities in shaping African women’s work lives in the USA. While the literature on black immigrant groups has posited that ethnic identities are often deployed to shield black immigrants from racism, my findings indicate that for a group of African women, their racial and ethnic identities are viewed as potential sources of discrimination. As black immigrant women from middle-class backgrounds in their home countries, they also articulate experiences with racism and downward social and occupational mobility. Accounting for how race and ethnicity intersect in the lives of black immigrant groups can nuance our understanding of racial identities and highlight diversity in experiences among national and regional groups. Focusing on particular health-care settings further suggests the importance of professional contexts in shaping the identity formations of recent black immigrants.  相似文献   
7.
In 2008, one of the worst public health crises occurred in the state of Nevada, where authorities discovered up to 63,000 patients were potentially exposed to hepatitis C infection, largely due to substandard infection control and other negligent practices at two endoscopy clinics in Las Vegas. In the subsequent grand jury proceedings that followed, it was discovered that several clinic employees not only participated in these egregious practices, but doctors, nurses, and other health care professionals witnessed yet failed to report these incidents, largely due to fears of whistleblower retaliation. In response, the Nevada state legislature attempted to strengthen whistleblower protection laws, but it remains unclear if such laws actually protect employees who attempt to report patient safety concerns. As the push for quality patient outcomes becomes more prominent with health care reform, whistleblower concerns must be effectively addressed to ensure that health care professionals can report patient safety concerns without fear of retaliation.  相似文献   
8.
In the late 1940s, epidemics of antibiotic-resistant strains of Staphylococcus aureus began to plague postpartum nurseries in hospitals across the United States. Exacerbated by overcrowding and nursing shortages, resistant S. aureus outbreaks posed a novel challenge to physicians and nurses heavily reliant on antibiotics as both prophylaxis and treatment. This paper explores the investigation of the reservoir, mode of transmission, and virulence of S. aureus during major hospital outbreaks and the subsequent implementation of novel infection control measures from the late 1940s through the early 1960s. The exploration of these measures reveals a shift in infection control policy as hospitals, faced with the failure of antibiotics to slow S. aureus outbreaks, implemented laboratory culture routines, modified nursery structure and layout, and altered nursing staff procedures to counter various forms of S. aureus transmission. Showcasing the need for widespread epidemiologic surveillance, ultimately manifesting itself in specialized “hospital epidemiology” training promoted in the 1970s, the challenges faced by hospital nurses in the 1950s prove highly relevant to the continued struggle with methicillin-resistant Staphylococcus aureus (MRSA) and other resistant nosocomial infections.  相似文献   
9.
Recently, we established a protocol for the cultivation of primary porcine oviduct epithelial cells (POEC), which promoted tissue-like morphology for a prolonged culture period. The present study focuses on developing this model into a comprehensive, standardized culture system, as a candidate tool for reproductive toxicity testing and basic research. We cultivated POEC isolated from 25 animals in our culture system for both 3 and 6 weeks and systematically analyzed effects of medium conditioning, supplementation with standardized sera, and culture duration in both freshly isolated and cryopreserved cells. The differentiation status was evaluated via histomorphometry, transepithelial electrical resistance (TEER) measurement, and expression analyses. The culture system possessed high reproducibility, more than 95% of cultures achieved a fully differentiated phenotype. Cells recapitulated in vivo–like morphology and ultrastructure from 3 to 6 weeks. Cryopreservation of the cells prior to cultivation did not affect culture quality of POEC. Employment of conditioned medium ensured optimal promotion of POEC differentiation, and different standardized sera induced fully differentiated phenotypes. Consistent TEER establishment indicated the presence and maintenance of cell type–specific intercellular junctions. The functionality of POEC was proven by consistent mucin secretion and stable expression of selected markers over the whole culture duration. We conclude that POEC are suitable for experiments from 3 weeks up to at least 6 weeks of culture. Therefore, this culture system could be used for in vitro estrous cycle simulation and long-term investigation of toxic effects on oviduct epithelium.  相似文献   
10.
?????? 目的 从目前护理人员承担的工作量出发,探讨临床科室护理人员配置理想床护比,为医院护理人力配置提供依据。方法 以工作量测算法作为核心研究方法,采用工现场观察法对西安市某大型综合医院42个临床科室护士的工作量进行测算,并使用Excel、SPSS17.0统计软件进行公式运算和统计分析。结果 (1)临床科室护理人员的工作时间超过标准工作时间6小时;(2)所调研科室现有床护比仅为1: 0.46,缺编41.50%;(3)依据目前的工作量需要,内科病房的床护比应为1:0.62,外科病房床护比应为1:0.63,监护科室为1:2.08,平均床护比1:0.78。结论 临床科室医师人员配备亟待补充,医院应根据实际工作量进行合理测算后配置护理人员,通过工时测定提出了的理想床护比可为其他医院提供参考。  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