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   702篇
  免费   90篇
  792篇
  2021年   14篇
  2020年   16篇
  2019年   5篇
  2018年   13篇
  2017年   8篇
  2016年   18篇
  2015年   32篇
  2014年   32篇
  2013年   41篇
  2012年   54篇
  2011年   33篇
  2010年   31篇
  2009年   18篇
  2008年   35篇
  2007年   25篇
  2006年   24篇
  2005年   27篇
  2004年   30篇
  2003年   30篇
  2002年   28篇
  2001年   17篇
  2000年   16篇
  1999年   17篇
  1998年   7篇
  1997年   5篇
  1996年   11篇
  1995年   7篇
  1994年   5篇
  1993年   7篇
  1992年   10篇
  1991年   9篇
  1990年   5篇
  1989年   6篇
  1987年   11篇
  1986年   11篇
  1984年   9篇
  1983年   6篇
  1982年   11篇
  1981年   7篇
  1979年   7篇
  1978年   9篇
  1977年   7篇
  1976年   7篇
  1975年   5篇
  1974年   9篇
  1973年   6篇
  1972年   7篇
  1971年   5篇
  1969年   7篇
  1937年   4篇
排序方式: 共有792条查询结果,搜索用时 15 毫秒
741.
742.
743.
The aim of this study was to assess trends in captive breeding of threatened and endangered bird species in British zoos. The measures we recorded were: 1) the total number of species held, 2) the percentage of species held that are listed in the IUCN Red List, 3) the percentage of endangered species breeding, and 4) the number of species in managed breeding programs. These data were gathered from the bird inventories of 10 representative British zoos for the years 1988 and 1997. The data for measures 1–3 were compared between the 2 years using a Wilcoxon matched‐pairs test. We found that the zoos maintained the same number of species (W=10.5; n=10; P=0.093; median=87.5 and 78 for 1988 and 1997, respectively). However, there was a significant increase in the number of birds held that fit each of the IUCN's conservation categories (Endangered: W=43.0; n=10; P<0.05, median=1.48 and 6.64 for 1988 and 1997, respectively; Vulnerable: W=53.0; n=10; P<0.05, median=3.33 and 10.05 for 1988 and 1997, respectively; and Rare: W=55.0; n=10; P<0.01, median=0.00 and 8.33 for 1988 and 1997, respectively). Overall, the percentage of threatened species kept in zoos increased from a median of 4.81 in 1988 to 25.02 in 1997. During this period there was an increase in the number of species in each category of the IUCN Red List. No difference was found in the number of threatened species breeding between 1988 and 1997. Zoo Biol 23:85–89, 2004. © 2004 Wiley‐Liss, Inc.  相似文献   
744.
This study addresses the hypothesis that decreases in lung perfusion rate independently worsen gas exchange efficiency in an isolated left lower lobe in zone 2 conditions. In seven anesthetized dogs, the left lower lobe was isolated, leaving the bronchus and bronchial vasculature intact. Blood was taken from the femoral arteries and reinfused at a controlled rate into the pulmonary artery of the left lower lobe. The flow rate was varied between 100 and 400 ml/min. The multiple inert gas elimination technique was used to quantitate the matching of ventilation to perfusion. Reduction in lobe blood flow resulted in a significant increase in perfusion-related indexes of alveolar ventilation-perfusion heterogeneity, such as the log standard deviation of the perfusion distribution, the retention component of the arterial-alveolar difference area, and the retention dispersion index. The increased heterogeneity suggests a worsening of the intraregional matching between the ventilation and the perfusion when perfusion is less than normal.  相似文献   
745.
Porcine pancreatic hydrolases in juice and homogenate surveyed by electrophoretic separation in agarose gel, at pH 8.6 and subsequently characterized using substrates of various specificity, either directly in the gel or after transfer to nitrocellulose (enzymoblotting) showed: Anodal and cathodal trypsin with Bz-Arg-pNA. Chymotrypsin A, B, and C with similar, but not identical, activities to Suc-Ala-Ala-Pro-Phe-pNA, Bz-Tyr-pNA, Suc-Phe-pNA and Ac-Phe-beta NE and with differences in their molecular weights and electrophoretical charges. Elastase I and protease E with Suc-(Ala)3-pNA and MeO-Suc-Ala-Ala-Pro-Val-pNA and elastase I also with elastin. Elastase II with the chymotrypsin substrates and with elastin. Carboxypeptidase A with CN-Phe. Amylase with blue starch polymer.  相似文献   
746.
Investigating claims that a clothed person's mass loss does not always represent their evaporative heat loss (EVAP), a thermal manikin study was performed measuring heat balance components in more detail than human studies would permit. Using clothing with different levels of vapor permeability and measuring heat losses from skin controlled at 34 degrees C in ambient temperatures of 10, 20, and 34 degrees C with constant vapor pressure (1 kPa), additional heat losses from wet skin compared with dry skin were analyzed. EVAP based on mass loss (E(mass)) measurement and direct measurement of the extra heat loss by the manikin due to wet skin (E(app)) were compared. A clear discrepancy was observed. E(mass) overestimated E(app) in warm environments, and both under and overestimations were observed in cool environments, depending on the clothing vapor permeability. At 34 degrees C, apparent latent heat (lambda(app)) of pure evaporative cooling was lower than the physical value (lambda; 2,430 J/g) and reduced with increasing vapor resistance up to 45%. At lower temperatures, lambda(app) increases due to additional skin heat loss via evaporation of moisture that condenses inside the clothing, analogous to a heat pipe. For impermeable clothing, lambda(app) even exceeds lambda by four times that value at 10 degrees C. These findings demonstrate that the traditional way of calculating evaporative heat loss of a clothed person can lead to substantial errors, especially for clothing with low permeability, which can be positive or negative, depending on the climate and clothing type. The model presented explains human subject data on EVAP that previously seemed contradictive.  相似文献   
747.
The multifunctional zinc‐finger protein CCCTC‐binding factor (CTCF) is a very strong candidate for the role of coordinating the expression level of coding sequences with their three‐dimensional position in the nucleus, apparently responding to a “code” in the DNA itself. Dynamic interactions between chromatin fibers in the context of nuclear architecture have been implicated in various aspects of genome functions. However, the molecular basis of these interactions still remains elusive and is a subject of intense debate. Here we discuss the nature of CTCF‐DNA interactions, the CTCF‐binding specificity to its binding sites and the relationship between CTCF and chromatin, and we examine data linking CTCF with gene regulation in the three‐dimensional nuclear space. We discuss why these features render CTCF a very strong candidate for the role and propose a unifying model, the “CTCF code,” explaining the mechanistic basis of how the information encrypted in DNA may be interpreted by CTCF into diverse nuclear functions.  相似文献   
748.
ABSTRACT: BACKGROUND: Use of inappropriate drugs is common among institutionalized older people. Rigorous trials investigating the effect of the education of staff in institutionalized settings on the harm related to older people's drug treatment are still scarce. The aim of this trial is to investigate whether training professionals in assisted living facilities reduces the use of inappropriate drugs among residents and has an effect on residents' quality of life and use of health services. Methods and design During years 2011 and 2012, a sample of residents in assisted living facilities in Helsinki (approximately 212) will be recruited, having offered to participate in a trial aiming to reduce their harmful drugs. Their wards will be randomized into two arms: one, those in which staff will be trained in two half-day sessions, including case studies to identify inappropriate, anticholinergic and psychotropic drugs among their residents, and two, a control group with usual care procedures and delayed training. The intervention wards will have an appointed nurse who will be responsible for taking care of the medication of the residents on her ward, and taking any problems to the consulting doctor, who will be responsible for the overall care of the patient. The trial will last for twelve months, the assessment time points will be zero, six and twelve months. The primary outcomes will be the proportion of persons using inappropriate, anticholinergic, or more than two psychotropic drugs, and the change in the mean number of inappropriate, anticholinergic and psychotropic drugs among residents. Secondary endpoints will be, for example, the change in the mean number of drugs, the proportion of residents having significant drug-drug interactions, residents' health-related quality of life (HRQOL) according to the 15D instrument, cognition according to verbal fluency and clock-drawing tests and the use and cost of health services, especially hospitalizations. DISCUSSION: To our knowledge, this is the first large-scale randomized trial exploring whether relatively light intervention, that is, staff training, will have an effect on reducing harmful drugs and improving QOL among institutionalized older people Trial registration ACTRN12611001078943.  相似文献   
749.
750.
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