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   153篇
  免费   6篇
  2023年   1篇
  2022年   2篇
  2021年   2篇
  2019年   1篇
  2018年   2篇
  2017年   2篇
  2016年   2篇
  2015年   3篇
  2014年   4篇
  2013年   4篇
  2012年   14篇
  2011年   7篇
  2010年   4篇
  2009年   8篇
  2008年   6篇
  2007年   4篇
  2006年   3篇
  2005年   5篇
  2004年   6篇
  2003年   8篇
  2002年   4篇
  2001年   7篇
  2000年   2篇
  1999年   8篇
  1998年   1篇
  1997年   3篇
  1996年   1篇
  1995年   2篇
  1992年   2篇
  1991年   2篇
  1990年   3篇
  1989年   1篇
  1988年   7篇
  1987年   2篇
  1986年   3篇
  1985年   1篇
  1984年   3篇
  1983年   2篇
  1982年   2篇
  1981年   2篇
  1980年   1篇
  1979年   2篇
  1977年   2篇
  1975年   1篇
  1974年   2篇
  1973年   3篇
  1971年   1篇
  1970年   1篇
排序方式: 共有159条查询结果,搜索用时 15 毫秒
21.
Adelphocorisella australis sp. n. is described from north Queensland. This, the first representative of the genus known from Australia, is compared with the two previously described species, both from Japan.  相似文献   
22.
Thyroid hormones are essential for vertebrate development. There is a characteristic rise in thyroid hormone levels in blood during critical periods of thyroid hormone-regulated development. Thyroid hormones are lipophilic compounds, which readily partition from an aqueous environment into a lipid environment. Thyroid hormone distributor proteins are required to ensure adequate distribution of thyroid hormones, throughout the aqueous environment of the blood, and to counteract the avid partitioning of thyroid hormones into the lipid environment of cell membranes. In human blood, these proteins are albumin, transthyretin and thyroxine-binding globulin. We analyzed the developmental profile of thyroid hormone distributor proteins in serum from a representative of each order of marsupials (M. eugenii; S.crassicaudata), a reptile (C. porosus), in two species of salmonoid fishes (S. salar; O. tshawytsch), and throughout a calendar year for sea bream (S. aurata). We demonstrated that during development, these animals have a thyroid hormone distributor protein present in their blood which is not present in the adult blood. At least in mammals, this additional protein has higher affinity for thyroid hormones than the thyroid hormone distributor proteins in the blood of the adult. In fish, reptile and polyprotodont marsupial, this protein was transthyretin. In a diprotodont marsupial, it was thyroxine-binding globulin. We propose an hypothesis that an augmented thyroid hormone distributor protein network contributes to the rise in total thyroid hormone levels in the blood during development.  相似文献   
23.
The present review explores sexual differentiation in three non-conventional species: the spotted hyena, the elephant and the tammar wallaby, selected because of the natural challenges they present for contemporary understanding of sexual differentiation. According to the prevailing view of mammalian sexual differentiation, originally proposed by Alfred Jost, secretion of androgen and anti-Mullerian hormone (AMH) by the fetal testes during critical stages of development accounts for the full range of sexually dimorphic urogenital traits observed at birth. Jost's concept was subsequently expanded to encompass sexual differentiation of the brain and behavior. Although the central focus of this review involves urogenital development, we assume that the novel mechanisms described in this article have potentially significant implications for sexual differentiation of brain and behavior, a transposition with precedent in the history of this field. Contrary to the "specific" requirements of Jost's formulation, female spotted hyenas and elephants initially develop male-type external genitalia prior to gonadal differentiation. In addition, the administration of anti-androgens to pregnant female spotted hyenas does not prevent the formation of a scrotum, pseudoscrotum, penis or penile clitoris in the offspring of treated females, although it is not yet clear whether the creation of masculine genitalia involves other steroids or whether there is a genetic mechanism bypassing a hormonal mediator. Wallabies, where sexual differentiation occurs in the pouch after birth, provide the most conclusive evidence for direct genetic control of sexual dimorphism, with the scrotum developing only in males and the pouch and mammary glands only in females, before differentiation of the gonads. The development of the pouch and mammary gland in females and the scrotum in males is controlled by genes on the X chromosome. In keeping with the "expanded" version of Jost's formulation, secretion of androgens by the fetal testes provides the best current account of a broad array of sex differences in reproductive morphology and endocrinology of the spotted hyena, and androgens are essential for development of the prostate and penis of the wallaby. But the essential circulating androgen in the male wallaby is 5alpha androstanediol, locally converted in target tissues to DHT, while in the pregnant female hyena, androstenedione, secreted by the maternal ovary, is converted by the placenta to testosterone (and estradiol) and transferred to the developing fetus. Testicular testosterone certainly seems to be responsible for the behavioral phenomenon of musth in male elephants. Both spotted hyenas and elephants display matrilineal social organization, and, in both species, female genital morphology requires feminine cooperation for successful copulation. We conclude that not all aspects of sexual differentiation have been delegated to testicular hormones in these mammals. In addition, we suggest that research on urogenital development in these non-traditional species directs attention to processes that may well be operating during the sexual differentiation of morphology and behavior in more common laboratory mammals, albeit in less dramatic fashion.  相似文献   
24.
A study on historical range and movement patterns of the African savannah elephants (Loxodonta africana africana) in Ethiopia was made from December 2004 to November 2008. Babile Elephant Sanctuary is one of the strongholds of elephants in the country, where it now supports approximately 27% of the elephant population in Ethiopia. Elephant movement routes and ranges were identified based on interviews of local people and by tracking the animals in the field. Elephants of the Sanctuary were categorized into two distinctive groups or clans based on their movement patterns and their associations to each other. Three major valleys, namely Gobele, Erer and Dakata, were crossed by elephants. Elephants in the population had an estimated annual range of 3014 km2. Of this, 85.7% (2583 km2) was inside the Sanctuary and 14.3% (430 km2) outside but adjacent to the Sanctuary. Elephant use outside of the Sanctuary included three different areas: Upper Erer Valley (8 km2), Upper Gobele Valley (48 km2) and west of Gobele Valley (374 km2). The extent of range varied seasonally. During the wet season, elephant range was restricted to Erer Valley and its tributaries (1266 km2 and a density of approximately 0.25 animal km?2), or 42% smaller than the dry season range (1417 km2, 0.23 elephant km?2). Range use was smallest (332 km2) in October to November and from April to May. During the dry season, elephants were found in two distinctive groups, one using Gobele Valley and the other Erer Valley.  相似文献   
25.
Promoter-Specific Expression and Imprint Status of Marsupial IGF2   总被引:1,自引:0,他引:1  
  相似文献   
26.
27.
28.
29.
30.
Proteins in the uterus of the marsupial Macropus eugenii differ qualitatively and quantitatively from proteins in the maternal serum, peritoneal fluid, and lymph. Some similarities are found which suggest that selection occurs as well as synthesis. In delayed and early gestation, the main components are albumin and prealbumin fractions, but during later pregnancy, α- and β-globulins are found as well as the albumins. Progesterone injection to anestrous animals can stimulate the production of secretion, but the secretory condition is maintained in the presence of a developing embryo only after progesterone treatment has been withdrawn. In both normal and progesterone-treated animals total concentration of protein and volume of secretion increases during the gestation period; the nonpregnant uterus always contains less protein than the pregnant. It is suggested that conditions for supporting the growth of the blastocyst and embryo require not only an increase in the total protein content of the uterine fluid but also the production of specific proteins.  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