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   410篇
  免费   43篇
  国内免费   68篇
测绘学   2篇
地球物理   38篇
地质学   37篇
海洋学   388篇
天文学   1篇
综合类   43篇
自然地理   12篇
  2024年   3篇
  2023年   6篇
  2022年   13篇
  2021年   7篇
  2020年   22篇
  2019年   20篇
  2018年   12篇
  2017年   10篇
  2016年   14篇
  2015年   12篇
  2014年   16篇
  2013年   44篇
  2012年   6篇
  2011年   18篇
  2010年   11篇
  2009年   20篇
  2008年   34篇
  2007年   24篇
  2006年   29篇
  2005年   15篇
  2004年   16篇
  2003年   8篇
  2002年   21篇
  2001年   17篇
  2000年   16篇
  1999年   12篇
  1998年   11篇
  1997年   14篇
  1996年   16篇
  1995年   5篇
  1994年   6篇
  1993年   10篇
  1992年   7篇
  1991年   2篇
  1990年   1篇
  1989年   1篇
  1988年   1篇
  1987年   2篇
  1986年   7篇
  1985年   1篇
  1984年   3篇
  1983年   2篇
  1982年   2篇
  1981年   3篇
  1980年   1篇
排序方式: 共有521条查询结果,搜索用时 15 毫秒
121.
122.
123.
David  Mook. 《Marine Ecology》1986,7(2):105-113
Abstract. .The absorption efficiencies of the intertidal mangrove dwelling mollusk Melampus coffeus and the rocky intertidal dwelling mollusk Acanthopleura granulata were calculated by a modification of CONOVER'S (1966) equation. M. coffeus tended to consume fresh mangrove leaves indicating that M. coffeus may obtain much of its energy from the actual substrate material rather than from associated bacteria and meiofauna on decaying leaves. Obtaining energy directly from the substrate may be a mechanism for M. coffeus to utilize its food source more efficiently. In contrast, chitons (A. granulata) may utilize the higher energy components of their limited intertidal microflora! food source. Using the high energy component of a food source may be an additional mechanism by which organisms efficiently utilize a food source.  相似文献   
124.
Abstract.  Harpacticoid copepod food is patchily distributed and individuals must episodically move to new food patches. Key questions in harpacticoid feeding ecology include how individuals detect food patches and how rapidly they move toward patches. Based on literature reports, we hypothesized that harpacticoids locate food parcels by sensing a water-borne cue. We tested this idea using individuals of Leptastacus coulli Huys, 1992 and Praeleptomesochra similis Lang, 1965 from a sandy beach in north Florida (29.948° N, 84.341° W). Individuals from both species selected seawater that had been exposed to food significantly more frequently than they selected control seawater. The rate of movement of these species was millimeters per second, which agreed with previous reports.  相似文献   
125.
Abstract. Samples of Blennius incognitus from three differently polluted locations on the Istrian west coast (Adriatic Sea, Yugoslavia) were collected in early July during the spawning season. The gut content was analyzed employing the occurrence and point (relative volumetric) method. This fish grazes the surface of the rocky substratum. Inhabiting small benthic animals are ingested together with algae and detritus. The diet depends on the composition and condition of the covering phytal and its inhabiting fauna. A decrease of available animal food seems to intensify grazing on the substrate. A sexual dimorphism in the feeding habit during the reproductive period exists. Females feed more on animals; males feed more on substrate and in cases also on eggs of their own species.  相似文献   
126.
方斑东风螺早期发育过程中几种消化酶的活性   总被引:4,自引:0,他引:4  
将方斑东风螺Babylonia areolata(Link)的早期发育从早期面盘幼体到变态后15d的稚贝分成6个阶段,分别测定各阶段蛋白酶(P)、脂肪酶(L)、淀粉酶(A)和纤维素酶(C)活性。研究结果表明,随着幼体发育的推进,蛋白酶比活力逐渐减小,脂肪酶比活力逐渐增加,淀粉酶和纤维素酶比活力则在变态前逐渐增加,而变态后逐渐减小。比较A/P和(A C)/(P L)两种指标指示方斑东风螺幼体发育过程中的食性变化,提出(A C)/(P L)用于指示方斑东风螺食性变化更合理、准确。综合比较幼体发育各阶段4种消化酶活性,发现在面盘幼体向稚贝变态期间,幼体消化能力最弱,原因与幼体的变态过程有关。实验结果也验证了贝类具有分泌纤维素酶的能力,该酶在东风螺对纤维素分解中占主导地位。  相似文献   
127.
The food choice of juvenile flounder (Platichthys flesus) and turbot (Scophthalmus maximus) was studied in the northern Baltic Sea during the years 1988, 1989, 1994 and 1995. The diet included organisms from 30 species/taxa in flounder (n = 306) and 10 species/taxa in turbot (n = 41). Flounder 45 mm mainly consumed meiofauna (dominating taxon: Harpacticoida, Copepoda) and larger fish (46–101 mm) consumed macrofauna (dominating taxa: Oligochaeta, Amphipoda and Chironomidae). In terms of biomass, macrofauna dominated for all sizes of flounders, and meiofauna was important only for the smallest fish. A strong seasonal variation could be detected in the diet. In spring, macrofauna dominated for all size classes of fish (only fish > 30 mm were caught in spring), while in summer and autumn meiofauna dominated the diets for fish 45 mm in size. Juvenile turbot (22–88 mm) consumed macrofauna and small fish. Turbot 30 mm consumed mainly amphipods, while > 30 mm turbot consumed mysid shrimps, amphipods and fish.The ontogenetic shift from meio- to macrofauna-sized prey in flounders occurs at a larger fish size in the northern Baltic Sea than reported in other areas, possibly depending on the increased relative importance of meiofauna in the northern Baltic. The seasonal variation in the diet could be due to seasonally changing abundances in the zoobenthos, or for the small fish (1-group, spring), to switching from meio- to macrofauna in order to optimize their energy gain. The 0-group flounders consumed meiofauna for a long period, possibly due to a learning-process or simply due to easy availability of meiofauna. Turbot has a much larger mouth gap than flounders, thus allowing them to consume macrofauna from the beginning of their benthic life.  相似文献   
128.
Abstract. This study of the enteropneust, Balanoglossus aurantiacus , in Bogue Sound, NC, provides information on the general structure and variability in geometry of its burrow, B. aurantiacus employs a funnel at the anterior end of its burrow to cave in surface sediments. It ingests, processes, then deposits these sediments back on the surface as fecal castings. Measurements made on resin casts of burrows and on photographs of surface features (burrow openings and funnels) revealed a new and consistent pattern of burrow construction. This pattern distinguishes B. aurantiacus burrows from those reported for other funnel feeders and enteropneusts (except, perhaps, for B. clavigerus). Laboratory and field observations revealed that, within its burrow, B. aurantiacus is elongated, can double-back on itself, and can use anterior burrow openings for subsequent fecal castings. Tests for significant changes in location of surface features gave estimates of how frequently individuals in aquaria and field populations abandon old burrow locations and construct new burrows. Field observations showed that B. aurantiacus will reopen a blocked burrow opening.  相似文献   
129.
Neuropeptide Y(NPY) is a 36-amino acid peptide of the neuropeptide Y family that plays key roles in the regulation of food intake. In this study,we focused on NPY m RNA expression changes around feeding time and during food deprivation in olive flounder. The olive flounder NPY m RNA levels were analyzed in different tissues and a high level of expression was detected in the brain. We also demonstrated a correlation between NPY expression levels in the brain and feeding schedule. NPY expression levels in olive flounder maintained on a daily scheduled feeding regimen increased shortly before feeding and decreased after the scheduled feeding time. Compared with the-1 h group before feeding,NPY expression in the 3 h group after feeding decreased significantly( P <0.05). Food deprivation led to an 81.7% decrease in NPY m RNA levels in the 24 h fasted group(P <0.05) and a 91.7% decrease in the 48 h fasted group(P <0.05). Therefore,our study demonstrates that NPY expression is associated with food intake in olive flounder. This result reveals the function of NPY in regulating food intake and its potential importance in olive flounder aquaculture.  相似文献   
130.
Effect of salinity on survival,feeding behavior and growth of juvenile swimming crab P ortunus trituberculatus was investigated under 5 salinity levels of 5,10,20,30 and 40. The results show that the crab juveniles fed 2 or 3 times at the salinity 20 and 30,each lasted for about 25 minutes,for a total feeding time of 73.2±22.65 minutes per day. At these salinities,there were significantly higher in the frequency of feeding and in total feeding time than those at lower salinities of 5 and 10. All crab juveniles moulted when reared at a salinity of 20 during the 5 days duration of the experiment,which is significantly higher than those at other salinities. All juveniles survived at salinity 20,and the survivorship was not significantly different from that at 30,but was signif icantly higher than those at other salinities. The crab juveniles reared at a salinity of 20 had the highest value of food ration of 0.190 8±0.011 3 g/g BW,average body weight gain of 0.796±0.128 g,gain rate of 87%–96%,and food conversion ratio of 1.20±0.09. There was no significant difference in the values found between 20 and 30 but these values were significantly lower than that at the other salinities( P 0.05). Highest activities of digestive enzymes(Amylase,Protease,Lipase) and lowest activities of protective enzymes(SOD,PO,CAT) were also obtained on crab juveniles reared at salinity of 20.  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