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   50篇
  免费   1篇
废物处理   6篇
环保管理   5篇
综合类   10篇
基础理论   8篇
污染及防治   15篇
评价与监测   2篇
灾害及防治   5篇
  2023年   2篇
  2022年   2篇
  2021年   1篇
  2018年   2篇
  2017年   2篇
  2016年   5篇
  2015年   1篇
  2014年   1篇
  2013年   4篇
  2012年   2篇
  2011年   3篇
  2010年   3篇
  2009年   1篇
  2008年   4篇
  2007年   1篇
  2006年   1篇
  2005年   1篇
  2003年   2篇
  2002年   2篇
  2000年   1篇
  1998年   1篇
  1997年   1篇
  1994年   2篇
  1991年   1篇
  1987年   2篇
  1983年   1篇
  1980年   1篇
  1964年   1篇
排序方式: 共有51条查询结果,搜索用时 15 毫秒
11.
12.
13.
In the present work the effect of Hg2+ and Cu2+ on the level of cytosolic Ca2+ in mussel (Mytilus edulis L.) haemolymph cells were investigated by confocal microscopy and spectrofluorimetry utilizing the fluorescent dye Fluo3. In the blood cells of marine molluscs, exposure to Cu2+ and Hg2+ in the nanomolar and micromolar range causes a time-and concentration-dependent increase in the cytosolic Ca2+ level. Both the presence of a low-calcium containing medium and pretreatment of the cells with the channel blocker Verapamil greatly reduced the effects of higher (50 M) Hg2+ concentrations, this indicating that Hg2+ enhances the influx of extracellular Ca2+ partly through activation of voltage-dependent Ca2+ channels. Low concentrations of Hg2+ (1 M) and also of Cu2+ (0.5 M), an essential element, were able to induce a sustained increase in cytosolic Ca2+, which was not affected either by Verapamil pretreatment or by lowering the extracellular calcium concentration. These data indicate that in mussel haemocytes heavy metal cations impair Ca2+ homeostasis not only by affecting Ca2+ channels, but also by interfering with other mechanisms of calcium transport across cellular membranes, such as the Ca2+-ATPases. The resulting increase in cytosolic Ca2+ could activate Ca-dependent processes which may be involved in many of the biochemical and physiological alterations observed in the cells of metal-exposed mussels. Specimens used in these experiments were collected from the river Linker near Plymouth, U.K. in June 1991.  相似文献   
14.
Plasma concentration of androgens and gonad development were studied in wild cooperatively breeding bell miners (Manorina melanophrys) of different age, sex and social status. Plasma levels of androgens increased with age of birds. For sexually mature (SM) bell miners, androgen levels were higher in breeders than in nonbreeding (NB) helpers (P < 0.005), and they were marginally higher in females than in males (P < 0.10). Thus female breeders showed the highest plasma levels of androgens. This pattern may be explained by an asymmetry between the sexes in the levels of competition needed to reach and defend breeding status; the degree of intra-sexual competition seems to be higher among female bell miners than among males. In general, male breeders had larger gonads than male SMNB helpers; male breeder gonads produced spermatozoa whereas most helpers' gonads did not. However, old (i.e. 34 months) SMNB male helpers had large gonads producing spermatozoa in spite of having low plasma levels of androgens. We suggest that young male bell miners may be under a voluntary mechanism of reproductive suppression perhaps favoured by inbreeding avoidance; although some aggressive interactions observed between very young helpers (about 2 months) and adult members of the breeding unit suggests that a certain degree of imposition also occurs at young ages. Older male helpers may avoid aggression with the male breeder and imposed reproductive suppression, hence the low circulating levels of androgens, but they have the potential to sneak extra-pair copulations. Gonad size decreased during the non-breeding season in both sexes.  相似文献   
15.
Complexity of seminal fluid: a review   总被引:2,自引:0,他引:2  
The seminal fluid is a complex medium containing a great variety of molecules, mainly produced by sex accessory glands, and also cells other than spermatozoa (e.g. leucocytes). In this paper, I review current knowledge on composition of seminal fluid in both vertebrates (mainly mammals) and invertebrates (mainly insects) with internal fertilisation, in the light of possible benefits of seminal fluid components to males (e.g. sperm capacitation, sperm competition and fertilisation), possible costs to males (e.g. autoimmunity, antigenic effects), potential benefits to females being inseminated (e.g. food, immunostimulation and antibiotic effects) and potential costs to females (e.g. transmission of venereal diseases). The diversity of microorganismal, cellular and molecular components of seminal fluids can be interpreted in the light of emergence of co-adapted complexes, host–parasite coevolution, male–female arms races, sperm competition, pleiotropy and redundancy of function.  相似文献   
16.
17.
Atlantic bluefin tuna (BFT; Thunnus thynnus) is a migrating species straddling the North Atlantic Ocean and Mediterranean Sea. It is assumed that this species is divided into a western and an eastern stock, which spawn in the Gulf of Mexico and the Mediterranean Sea, respectively. To learn more about the reproductive behavior of the eastern BFT stock, we tracked gonadal development in adult fish that were sampled between April and July during three consecutive years (2003–2005). Sampling campaigns were carried out using common fishing methods at selected locations within the Mediterranean Sea, namely Levantine Sea, Malta, and Balearic Islands. An additional sampling point, Barbate, was situated northwest of the Straits of Gibraltar along the Atlantic coast. Morphometric parameters such as the total body mass (M B) and the weights of the gonads (M G) were recorded, and the respective gonadosomatic index (GSI) values were calculated. The data collected revealed two important trends: (1) GSI values are higher in fish caught in the eastern rather than the western locations across the Mediterranean Sea, and (2) the GSI reaches maximum values between late May and early June in Levantine Sea (eastern Mediterranean Sea), and only 2 and 4 weeks later in the central (Malta) and western (Balearic Islands) locations, respectively. The advanced gonadal development in BFT correlates well with higher sea surface temperatures. Our findings also distinguish the northern Levantine Sea BFT population (mean M B 78.41 ± 4.13 kg), and the Barbate BFT population with the greatest M B (all fish sampled > 100 kg). These data reflect a situation in which the eastern Mediterranean basin may function as a habitat for young BFT, until they gain a larger M B and are able to move to the Atlantic Ocean. However, the existence of genetically discrete BFT populations in the Mediterranean Sea cannot be ruled out.  相似文献   
18.
19.
20.
ABSTRACT: There is considerable controversy inthe Northeast surrounding the extent to whcih public drinking water reservoirs should be used for recreational purposes. This paper reports the results of two integrated studies of (1) recreation users of Quabbin Reservation, the largest inland water source in New England and (2) the general public of Massachusetts. Data were obtained by conducting on-site interviews of Quabbin users and through state-wide telephone interviews of the general public; both studies focused on assessing attitudes toward the recreational use of drinking water reservoirs in Massachusetts. Unlike the findings of a 1969 study conducted by Baumann, results showed that the majority of Massachusetts residents do not favor recreation-prohibiting laws for most activities. Most favored at least moderate use of reservoirs for recreational purposes. In addition, over all views were not as restrictive as present legislation would suggest. Finally, these findings suggest that current recreation-prohibiting laws should be reassessed in light of pugblic opinion which favors the use of these valuable resources.  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