根分泌物及其生态效应

根分泌物是个古老而年轻的研究领域。早在18,19世纪,人们(Plenk,1795;Decandolle,1830)就观察到根分泌物对邻近植株的促生和抑制作用,1904年Hilter提出“根际”的概念,标志着人们对根分泌物及其生态效应的进一步认识。此后人们对根分泌物研究逐步展开。Lyon和Willson(1920)发现,生长于无菌水培液中的植物能释放有机物,为深入研究奠定了基础。但很长一段时间这个研究领域一     

苔藓植物的生物多样性及其保护

苔藓植物的生物多样性及其保护曹同高谦付星路勇（中国科学院沈阳应用生态研究所,１１００１５）ＤｉｖｅｒｓｉｔｙｏｆＢｒｙｏｐｈｙｔｅｓａｎｄＴｈｅｉｒＣｏｎｓｅｒｖａｔｉｏｎ．ＣａｏＴｏｎｇ,ＧａｏＱｉａｎ,ＦｕＸｉｎｇ,ＬｕＹｏｎｇ（Ｉｎｓｔｉｔｕｔ...     

Managed-care plans. Their future under national health insurance.

The nation''s health maintenance organizations, preferred-provider organizations, independent practice associations, and similar managed-care efforts are not well positioned to take a leadership role in a nationwide universal access or national health insurance plan. They--with the possible exception of some large staff and group health maintenance organizations--have been unable to show uniformly that they can contain costs, provide better access or higher quality of care, and achieve greater patient satisfaction than fee-for-service endeavors. As the United States pursues universal access as a step toward national health insurance, the managed-care plans will continue to increase their numbers of subscribers. They will not, however, be able to enroll large numbers of the young, low-income employees and their dependents who account for most of the 63 million people uninsured sometime during each year. Under national health insurance, there might be an option for some health maintenance organizations to negotiate capitated payments. The vast majority of the nation''s physicians, however, will reluctantly embrace a centrally managed fee-for-service approach rather than a salary or capitated reimbursement method, leaving only a trace of the competitive managed-care plan theme in a future, primarily monolithic, national health care system.     

Insulin-responsive cultured foetal-rat hepatocytes. Their preparation and characterization.

An improved non-perfusion method for the preparation of cultured foetal-rat hepatocytes is described. Digestion of the liver with collagenase and deoxyribonuclease I gave yields of 40 X 10(6) hepatocytes/g of liver. The plating efficiency of hepatocytes in medium with 10 microM-cortisol was 50%. Cell morphology and metabolism were maintained through 3 days of monolayer culture, with minimal contamination by haematopoietic cells or fibroblasts. The cultured cells bound and degraded 125I-insulin in a time- and dose-dependent manner. The estimated ED50 for competitive binding at 37 degrees C was 1.1 nM. Curvilinear Scatchard plots were observed, with estimates of 16 500 high-affinity sites (Kd = 813 pM) and 53 000 low-affinity sites (Kd = 23 nM) per cell. The cultured cells demonstrated a glycogenic response to insulin, with an estimated ED50 of 120 pM. The degree of glycogenic response to insulin varied with time in culture: 500% above basal on day 1, 200% on day 2, and only 150% on day 3. Cultured foetal cells also exhibited a time-dependent uptake of 2-aminoisobutyric acid, which, in contrast with previous reports with adult cells, was not stimulated by the presence of 10 nM-insulin. Cultured foetal hepatocytes may provide an interesting model with which to study the relationship between insulin-receptor binding and insulin action.     

Characteristics of Shelter-Relinquished Animals and Their Owners Compared With Animals and Their Owners in U.S. Pet-Owning Households

Animal shelters in the United States annually receive millions of relinquished dogs and cats, and risk factors for relinquishment are not fully understood. Investigators sponsored by the National Council on Pet Population Study and Policy interviewed people who relinquished dogs and cats at 12 shelters in four regions. We collected similar data from a sample of U.S. households with companion animals. Data collected included nonhuman animal characteristics such as age, sex, and frequency of selected behaviors. We also obtained data on keepers' (owners') age, sex, and level of education as well as their general knowledge of pet care and behavior. We found that relinquishment was associated with physical and behavioral characteristics of the animals and owner characteristics and knowledge. Relinquished animals were more likely to be intact, younger, and mixed bred. People relinquishing animals were significantly more likely to be men and younger than 35 years. Duration of ownership was significantly shorter for relinquished animals.     

Characteristics of Shelter-Relinquished Animals and Their Owners Compared With Animals and Their Owners in U.S. Pet-Owning Households

Animal shelters in the United States annually receive millions of relinquished dogs and cats, and risk factors for relinquishment are not fully understood. Investigators sponsored by the National Council on Pet Population Study and Policy interviewed people who relinquished dogs and cats at 12 shelters in four regions. We collected similar data from a sample of U.S. households with companion animals. Data collected included nonhuman animal characteristics such as age, sex, and frequency of selected behaviors. We also obtained data on keepers' (owners') age, sex, and level of education as well as their general knowledge of pet care and behavior. We found that relinquishment was associated with physical and behavioral characteristics of the animals and owner characteristics and knowledge. Relinquished animals were more likely to be intact, younger, and mixed bred. People relinquishing animals were significantly more likely to be men and younger than 35 years. Duration of ownership was significantly shorter for relinquished animals.     

论宝鸡农业生态问题及对策

保持良好的农业生态环境,创造丰富的农产品,是摆在人们面前的一项紧迫任务。现就位于我国西部的陕西省宝鸡市农业生态环境存在的问题及应当采取的对策作分析和探讨。一、宝鸡市农业生态环境存在的问题(一) 消大于长,森林覆盖率下降宝鸡市辖十县二区,三面环山,南依秦岭,西为关山,北为千山余脉。山区面积1.3324×10~4 km~2,占全市总面积72.68%,森林面积