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排序方式: 共有143条查询结果,搜索用时 15 毫秒
71.
许顺富 《湖南农业大学学报(自然科学版)》2003,(5)
湖南绅士是中国近代史上极具典型意义的特殊社会群体。近代湖南绅士虽分布于全省各地 ,但又呈现出其独特的地域性特征 ,它不仅与各地的政治、经济、文化的发展程度有着较大的关系 ,而且还受湘军和各时期的领袖人物的影响甚大 ,从而造成了近代湖南绅士分布极不均匀的现象。绅士的分布不均 ,直接导致了湖南近代的政治、经济和文化呈现畸形发展的态势 ,绅士相对集中的地区政治空气浓厚 ,经济发展较快 ,文化教育事业相对繁荣 ;而绅士分布薄弱的地区 ,政治空气沉闷 ,经济发展迟缓 ,文化教育事业落后。 相似文献
72.
73.
Total lipid, lipid classes and their associated fatty acids have been measured in whole halibut, Hippoglossus hippoglossus (L.) larvae and in dissected animals separated into yolk and body compartments. At hatching the larval body contained 17 μg ind?1 of lipid (11% of larval body dry weight), while the yolk contained 190 μg ind?1. Phosphatidylcholine (PC) accounted for 57% of total yolk lipids while phosphatidylethanolamine (PE), triacylglycerol (TAG), cholesterol and sterol ester (SE) accounted for 12%, 12%, 9% and 6% respectively. The main fatty acids in the PC fraction were 22:6n-3 (25.6 μg ind?1), 16:0 (19.2 μg ind?1) and 20:5n-3 (12.6 μg ind?1). Between hatch and 200 day-degrees post hatch (D°PH) a net decline in total lipids of 29% was seen. There seemed to be some, but relatively minor, changes in the relative composition of lipids in the yolk throughout development, which are indicative of a non-selective endocytotic bulk uptake of lipids from the yolk. Towards first-feeding there was a selective catabolism of PC and a net synthesis of PE in the developing body, resulting in a shift in the lipid class composition in the body compared with that of the yolk. The fatty acids released from lipid hydrolysis were mainly used as energy substrates by the growing halibut larvae; 22:6n-3 was quantitatively one of the most important fatty acid fuel in energy metabolism. At the same time 38% and 23% of the 22:6n-3 released from PC was retained by the PE and neutral lipids in the growing larval body respectively. Except for 20:5n-3 (2%, 14%) no similar retention was seen in any of the other fatty acids. The observed net synthesis of PE in developing yolk-sac larvae of Atlantic halibut and the preferential retention of 22:6n-3 into it, increasing from 28% at hatching to 45% at 200 D°PH, may point to a high biological value of this compound. 相似文献
74.
A. FIGUEIREDO-SILVA E. ROCHA J. DIAS P. SILVA P. REMA E. GOMES & L.M.P. VALENTE 《Aquaculture Nutrition》2005,11(2):147-155
A 12‐week feeding trial was conducted to evaluate the effects of fish oil replacement by soybean oil, on lipid distribution and liver histology of two commercially important finfish species: rainbow trout (Oncorhynchus mykiss) and European sea bass (Dicentrarchus labrax). Sea bass (16.2 ± 0.5 g; mean ± SD) and rainbow trout (52.1 ± 0.5 g) juveniles were fed one of three isonitrogenous (500 g kg?1 CP) and isoenergetic (19 kJ g?1) diets, containing 0% (control, diet A), 25% (diet B) and 50% (diet C) soybean oil. At the end of the experiment, lipid deposition was evaluated in muscle, liver and viscera. Cholesterol and triglycerides levels were also determined in plasma. Tissue total, neutral and polar lipid composition (g kg?1 total lipids) showed no significant differences within species, regardless the dietary treatment. The same trend was observed for plasma parameters (P > 0.05). Viscera were the preferential tissue of lipid deposition, with 252–276 and 469–513 g kg?1 total lipid content in trout and sea bass, respectively. Dietary fish oil replacement had no effect on either hepatic lipid droplets accumulation or degree and pattern of vacuolization in the observed liver sections. These data suggest that both sea bass and trout can be fed diets containing up to 50% soybean oil without adverse effects on tissue lipid composition or liver histology. 相似文献
75.
Gabriel Mourente César Megina Esther Díaz-Salvago 《Fish physiology and biochemistry》2001,24(4):351-363
Total lipids, lipid classes, fatty acids and vitamin E contents were measured in ovary, liver, dark muscle, white muscle and
mesenteric perigonadal fat in four maturational stages of Atlantic female northern buefin tuna (Thunnus thynnus thynnus L.) during migration to Mediterranean spawning grounds through the Strait of Gibraltar. Ovary lipid content increased significantly
by 37.6-fold from inmature to spawning stage, accumulating large quantities of steryl/wax esters, whereas the ratio of mesenteric
perigonadal fat (primarily triacylglycerols) weight to ovary weight decreased linearly throughout maturation. In contrast,
liver, dark red and white muscles lipid content did not show a major depletion during maturation compared to that of perigonadal
fat. The fatty acid composition of ovary from bluefin tuna showed that docosahexaenoic acid (DHA; 22:6n-3) was the most abundant
fatty acid and DHA: EPA: AA and DHA: EPA ratios were 19.3/4.3/1 and 4.5/1, respectively. Neutral lipids predominated over
polar lipids (2-3:1) in ovary and triacylglycerol and steryl/wax ester were major lipid classes. In general, fatty acid composition
of most tissues examined were similar to each other but, in contrast, the fatty acid profile of perigonadal fat was rich in
monoenes such as 18:1n-9, 20:1n-9 and 22:1n-11, and DHA decreased significantly at spawning stage. The total lipid balance
suggested for the disappearance of lipid from perigonadal fat depots and, to a lesser degree, from muscle and liver depots,
reflected lipid utilization for gonadal development on the one hand and non-gonadal metabolism in the other. The former included
lipid transferred to the gonad and lipid catabolized to provide metabolic energy for the biosynthesis of gonadal constituents
and the later was likely to be lipid catabolism to provide energy for swimming during spawning migration.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
76.
Jos Enrique Larios‐Lpez Carlos Alonso Gonzlez Miguel Galiana‐García Jos Manuel Tierno de Figueroa 《Ecology of Freshwater Fish》2021,30(1):4-17
The classical debate about the roles of endogenous factors and external drivers in regulating populations continues to be a very active area of scientific research, and these roles are even more complex in populations located in geographically marginal areas. We tested three hypotheses on two separate brown trout populations inhabiting the southernmost basins of the Iberian Peninsula, with the aims of determining the relationships among (a) rainfall and air temperature for each season preceding fish sampling and the observed age group densities; (b) environmental synchrony and density synchrony for all possible pairs of sites; and (c) physical habitat similarity and the similarity of the density response to climatic drivers among pairs of sites. For this purpose, demographic series (98 surveys at 14 sampling sites), climatic conditions (rainfall and air temperature) and site habitat characteristics (physiogeographic and quality index values) were analysed between 2006 and 2014. The results show how the synchrony in the study populations is the result of a Moran effect directed mainly by winter precipitation and conditioned by the habitat similarity (highlighting the altitude, the distance to the upper limit and IHF index, along with the Euclidian distance among pairs of sites of the whole set of habitat variables). Preserving the heterogeneity of these habitat characteristics will increase the resilience of trout populations that inhabit this rear edge of distribution. The current context of global climate warming predicts extremely drastic changes in the dynamics of external drivers that regulate the trout populations in the study region. 相似文献
77.
塔里木河中游胡杨群落结构特征分析 总被引:2,自引:2,他引:0
为了了解生长状况良好的胡杨群落,在塔里木河中游沿岸选择具有代表性胡杨群落,设立1 hm2固定样地,调查分析胡杨林群落结构特征。结果表明:胡杨群落垂直层次优势种较为明显,形成以胡杨+柽柳+芦苇、假苇拂子茅为优势种的荒漠河岸林群落类型;胡杨种群属于稳定型种群,个体数量在不同径级之间分布合理;在不同尺度下,胡杨种群均处于集群分布;胡杨种群在不同发育阶段分布格局由聚集分布向随机分布转变。 相似文献
78.
侵染食用菌的线虫主要来源于各种培养料、复土和污水,从食用菌床及菌体中分离到的线虫有Aphelenchoides composticola,Ditylenchus myceliophagus,Paraphelenchus myceliophthorus和3种杆型线Rhabditida、app.在蘑菇栽培期的9月中旬至10日上旬和翌年的4月下旬至5月上、中旬发生危害最重,各有一次发生高峰。用克线磷和甲醛处理培养料,蘑菇可分别平均增产2.4%~31.0%。 相似文献
79.
Richard L Mayden 《Fish and Fisheries》2002,3(3):171-196
I am a realist and argue that biological species exist in nature. I also argue that the validity of findings of the many disciplines within the natural sciences employing biological species in their endeavours of inquiry are unequivocally linked to the accuracy of the species used in experiments. Few scientists today see the fundamental importance of taxonomic and systematic studies in both addressing accuracy of diversity and the delineation of species diversity for other areas of science. The basic controversial issues in the debate revolve around opinions regarding the nature of species as either Individuals or Classes, confusion of Species as a taxonomic category and as entities in nature, the varied practitioners studying diversity, a general lack of a Lineage perspective and a gross chauvinistic perspective on the types of data worthy of exposing and delineating diversity. I argue that species in nature are Individuals and form Lineages. As Individuals, they cannot be defined but can only be diagnosed in time. The category Species is a Class with a definition. The difficulties realised by scientists studying biodiversity in ‘defining’ a species hinges upon the fact that as natural entities they cannot be defined. Recognizing and understanding the origins of characters in species is further complicated if one views species in nature as Classes and lacks an appreciation for the Lineage and the origin and retention of traits through time. This forms an interesting paradox that many scientists have fallen victim to wherein species are viewed as Classes (hence definable, but immutable) yet are used to understand the process of descent that involves lineages and Individuals! The pre‐Darwinian Class perspective of species, combined with a common chauvinistic perspective on characters ultimately delays progress and places a ‘glass ceiling’ on species diversity for planet Earth. One resolution to the species and species concept issue is to view the concepts in a hierarchical manner of primary (theoretical) and secondary (operational) concepts. Interestingly, the issue of Individuals versus Classes for naturally occurring entities is much more widespread and exists in many other scientific fields. Thus, a hierarchical perspective of having a primary, nonoperational concept for natural entities and multiple operational concepts serving as ‘tools’ for discovering natural things consistent with the primary concept is a heuristic methodology that is applicable to the advancement of many areas of science. 相似文献
80.