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   77篇
  免费   6篇
  国内免费   24篇
测绘学   1篇
地球物理   5篇
地质学   5篇
海洋学   65篇
综合类   16篇
自然地理   15篇
  2023年   2篇
  2020年   1篇
  2019年   4篇
  2018年   4篇
  2017年   4篇
  2016年   9篇
  2015年   4篇
  2014年   3篇
  2013年   14篇
  2012年   5篇
  2011年   6篇
  2010年   1篇
  2009年   5篇
  2008年   5篇
  2007年   2篇
  2006年   4篇
  2005年   2篇
  2004年   5篇
  2003年   3篇
  2002年   2篇
  2001年   4篇
  2000年   3篇
  1998年   2篇
  1997年   1篇
  1996年   1篇
  1995年   2篇
  1994年   4篇
  1992年   1篇
  1991年   2篇
  1989年   1篇
  1984年   1篇
排序方式: 共有107条查询结果,搜索用时 31 毫秒
101.
近年来,基于性的“浪漫”与“亲密关系”受到国际学术界的广泛关注,并业已成为旅游学术研究中的热点话题。文章围绕国际旅游学术研究中的相关话题,从性旅游相关概念、旅游者特征、性旅游中的性工作者、旅游影响及公共管理等方面对国外相关研究文献进行了归纳和评析。研究表明,国外性旅游研究较为成熟,并开始形成较为完善的知识体系。通过本研究试图唤起中国学术界对性旅游的关注,并借鉴吸取国外经验,以期尽快提升中国性旅游研究水平和旅游公共管理的能力。  相似文献   
102.
Calanus sinicus is a calanoid copepod widely distributed in coastal waters of China and Japan, and oversummering strategies may have major impacts on their population dynamics which in turn affect local marine food web structure. The abundance, stage composition, and sex composition of the planktonic copepod C. sinicus were studied from August to October 2002 in the southern Yellow Sea to understand how its population recovers from the over-summering state. Results showed that C. sinicus had low reproduction in August due to high temperature, except in waters near the Cheju Island with rich food and moderate bottom temperature, but the reproduction rates here decreased in September–October as food availability declined. When temperature dropped in September–October, C. sinicus actively propagated in coastal shallow waters. However, reproduction rates of C. sinicus individuals inhabiting the Yellow Sea Cold Water Mass(YSCWM) remained low during the three months of the study. The percentage of C. sinicus females was high during the reproductive period, which suggests that the sex composition of adult C. sinicus may reflect whether or not the population is in the reproductive mode.Numerous fifth copepodite stage(CV) C. sinicus aggregated in the YSCWM in a suspended developmental stage during the three months of this study, and they potentially served as the parental individuals for population development when conditions became optimal for reproduction later in the year.  相似文献   
103.
104.
105.
氨基脲(semicarbazide,SEM)作为新型环境污染物已在海洋、食品和人体尿液中检出,其对环境和生物体可能带来的影响越来越受到人们的关注。研究采用1、10、100、1 000μg/L的SEM急性暴露96h的成年雄性斑马鱼,对性腺指数、17β-雌二醇(E2)和睾酮(T)的含量、性激素合成酶以及HPG轴相关的基因相对表达量进行测定,探究SEM急性暴露对雄性斑马鱼的内分泌干扰效应。结果表明,低剂量1μg/LSEM急性暴露通过抑制下丘脑中HPG轴起始因子s型促性腺激素释放激素(sGnRH)sGnRHmRNA相对表达量,进一步抑制促卵泡激素(FSH)FSHβ、促黄体激素(LH)LHβ、细胞色素P450 19B (CYP19B) CYP19B基因相对表达量,中高剂量10、100、1 000μg/L的SEM急性暴露下调下丘脑sGnRHmRNA的表达却上调c型促性腺激素释放激素(cGnRH)cGnRH、CYP19B的表达;而不同浓度的SEM暴露均会下调精巢内3β-羟类固醇脱氢酶(3β-HSD) 3β-HSD、细胞色素P450 17(CYP17) CYP17、细胞色素P450 11A (CYP1...  相似文献   
106.
Fiddler crabs are known as the most conspicuous bioturbating animals in mangrove forest, which by their burrowing activities promote nutrient cycling in ecosystems. Mangroves, crabs and bacteria are connected in the form of positive feedback loop, whereby an increase in the activity of any participant will tend to increase the activity of all others as well. Population structure, growth, mortality, recruitment, biomass and production of fiddler crabs as dominant species of deposit-feeder crabs have been investigated from May 2005 to March 2006 in the Sirik mangrove estuary in the eastern part of Strait of Hormuz. Ten 1 m2 squares of the substrate were randomly sampled during low tide. There was a significant change in organic content in the sampling area during study period. The sex ratio was significantly deviated from 1:1 ratio in large sizes, where males were dominated year around. Fiddler crabs showed seasonal growth pattern during a year, which the maximum growth was observed during autumn and early summer and ceased during winter by low temperature. Growth parameters were estimated by Appeldoorn's method and fitted with seasonalized von Bertalanffy growth models. The Kimura likelihood ratio test revealed significant differences in the overall growth curves between males and females, originated from the differences in kk and LL between sexes. Males were found to exhibit higher growth rate and larger size than females, this could be attributed to the higher investment of energy for reproduction in females. Reproduction was restricted to spring and early summer, while recruitment occurs at the end of summer. Total annual production of males and females was 37.90 and 10.05 g dry weight/10 m2 respectively and major production took place during early summer. Because of impact of temperature on the activity of fiddler crabs in subtropical regions, density of crabs has significant positive correlation with temperature (P < 0.01), while growth rate shows significant negative correlation with organic matter of sediment (P < 0.05). In conclusion these crabs showed lower mortality and production rate with the seasonal growth and recruitment in comparison with tropical species.  相似文献   
107.
We investigated, with a series of field and laboratory observations, the possible effect of the starfish Marthasteria glacialis predation on the operational sex ratio (OSR), i.e. the number of sexually mature males divided by the total number of sexually mature adults of both sexes at any one time, of the edible sea urchin Paracentrotus lividus . The OSR was estimated three times during the sea urchin summer spawning period (July 2004, June 2005 and July 2006) on barren substrates of Ustica Island Marine Protected Area (Southern Tyrrhenian Sea, Italy). Four sites were selected: two characterized by high M. glacialis density (take zone C) and two controls with low starfish density (no-take zone A). Mature sea urchins were independently collected by SCUBA diving and sexed. The adult sex ratio was skewed towards males at high M. glacialis density sites, whereas it was balanced (1:1) at predator low-density sites. Results of sex-selective feeding experiments in the laboratory showed that females of P. lividus were more vulnerable to M. glacialis predation. These outcomes underline the possible importance of M. glacialis in regulating the OSR of P. lividus populations.  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