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   795篇
  免费   62篇
林业   85篇
农学   30篇
基础科学   7篇
  196篇
综合类   38篇
农作物   39篇
水产渔业   117篇
畜牧兽医   249篇
园艺   23篇
植物保护   73篇
  2023年   10篇
  2022年   26篇
  2021年   33篇
  2020年   47篇
  2019年   62篇
  2018年   39篇
  2017年   32篇
  2016年   40篇
  2015年   28篇
  2014年   40篇
  2013年   47篇
  2012年   66篇
  2011年   52篇
  2010年   48篇
  2009年   33篇
  2008年   44篇
  2007年   50篇
  2006年   28篇
  2005年   21篇
  2004年   27篇
  2003年   22篇
  2002年   19篇
  2001年   3篇
  2000年   7篇
  1999年   4篇
  1998年   3篇
  1997年   2篇
  1996年   4篇
  1995年   2篇
  1990年   2篇
  1989年   4篇
  1988年   5篇
  1986年   1篇
  1985年   1篇
  1983年   1篇
  1982年   3篇
  1978年   1篇
排序方式: 共有857条查询结果,搜索用时 515 毫秒
741.
ABSTRACT

Broccoli sprouts (Brassica oleraceae var. italica) have been attributed health protective effects based on their glucosinolate content, and thus, are recommended in diets. However, no information is available on the mineral content of this novel product and how fertilization might influence it. The influence of nitrogen (N) and sulfur (S) applications (0, 14, and 28 mg· N dish?1 and 0, 4.5, and 9 mg· S dish?1) on the mineral content [N, S, potassium (K), calcium (Ca), magnesium (Mg), sodium (Na), chloride (Cl), and silicon (Si)] of broccoli sprouts (Brassica oleraceae var. italica cv. ‘Marathon’) was determined 11 d after sowing. It was found that N and S fertilization significantly (P < 0.001) influenced the uptake of all elements except phosphorus (P). Sulfur concentrations in broccoli sprouts varied between 11.4 and 15.2 mg· g?1 (dw), while the Ca, Mg, P, K, and Na concentrations were below 10 mg· g?1 (dw). The Cl contents ranged from 13.6 to 23.1 mg· g?1 (dw). The highest S concentration was found when 9 mg· dish?1 S and 14 mg· dish?1 N was applied. A higher N rates of 28 mg· dish?1, N yielded no higher S uptake. The significantly (P < 0.05) highest Ca, Mg, and Na concentrations were found in the control treatments, while this effect proved to be not consistent for P. The results clearly revealed that N and S fertilization increased biomass production even in the early growth stages. With view to maintaining high Ca concentrations an application in the form of ammonium sulfate would be preferable.  相似文献   
742.
The objective of this growth chamber study was to evaluate the effect of adding N-(n-butyl) thiophosphoric triamide (NBPT) and dicyandiaminde (DCD) to urea fertilizer, on the physiology and growth of cotton (Gossypiumhirsutum L.) under normal and high temperatures. Treatments consisted of two day temperature regimes, 30°C and 38°C, and five nitrogen fertilization applications: unfertilized control, 125 kg ha?1 of urea, 93 kg ha?1 of urea, 93 kg ha?1 urea + NBPT, and 93 kg ha?1 urea + NBPT + DCD. The addition of NBPT to urea fertilizer had positive effects on leaf chlorophyll, leaf area, dry matter, nitrogen (N) uptake, and N use efficiency. The absence of a significant interaction effect indicated that N fertilization was not influenced by temperature. Deficiency of N significantly decreased leaf chlorophyll, increased glutathione reductase, decreased protein and increased leaf nitrate reductase. Physiological changes under high temperature included increased plant N uptake, glutamine synthetase, leaf chlorophyll, protein content, plant height and leaf area were due to high N uptake and utilization.  相似文献   
743.
Faced with new challenges, such as emerging diseases, shortening of orchard longevity, and larger social and environmental demands from consumers, practices such as rootstock diversification, irrigation and high density plantings have become relevant for the Brazilian citrus industry. This research had the objective to evaluate the performance of irrigated and non-irrigated ‘Tahiti’ lime trees grafted on 12 rootstocks and one interstock. Plots were distributed following a randomized block design, with four replicates and one plant per plot. Rootstocks influenced plant vigor, especially ‘Flying Dragon’ trifoliate, which reduced tree height by approximately 47% compared to the ‘Rangpur’ lime. Trees that were budded on more vigorous rootstocks showed higher yield when grown without irrigation than with irrigation. The ‘1646’ citradia and ‘Morton’ citrange rootstocks performed particularly well. On the other hand, the plants on less vigorous rootstocks showed better performance in terms of yield under irrigation than the same combinations without irrigation, especially those grafted on the tetraploid ‘Carrizo’ and ‘Troyer’ citranges, ‘Swingle’ citrumelo, ‘Davis A’ trifoliate and ‘Flying Dragon’ trifoliate. Plants budded on the ‘1708’ citradia had high yields under irrigated and non-irrigated conditions. The effect of interstock on plant vigor was dependent of rootstock. Interstocked plants on ‘Davis A’ trifoliate were higher than those without interstock. On the other hand, interstocked plants on Catania 2 ‘Volkamer’ lemon were less vigorous than those without interstock.  相似文献   
744.
We herein describe the partial nucleotide sequencing and phylogenetic analysis of the B2L gene of seventeen Brazilian orf viruses (ORFV). Seventeen viruses were recovered from outbreaks of contagious ecthyma in sheep and goats in four states in Southern and Northeast country, and three from commercial vaccines. Most analyzed viruses were associated with outbreaks of classical contagious ecthyma, with lip, nostrils and labial commissure involvement, yet udder/teat, feet, vulvar and disseminated lesions were also reported in some cases. Nucleotide sequence analysis revealed a high degree of B2L similarity among sheep sequences (>99%) regardless the geographic origin, and a remarkable high identity for the two goat isolates (>99.8%), with similarity dropping to below 99% when comparing viruses from the two species. A phylogenetic tree grouped most sheep and goat viruses on different branches. In addition, sequence alignment allowed the identification of up to six scattered nucleotide changes that were predominant and more consistent in goat isolates, including a number of sequences from other continents. Thus, in spite of the high nucleotide similarity, different degrees of similarity and discrete nucleotide changes in the B2L gene may help in grouping ORFV viruses according to host species.  相似文献   
745.
The practice of covering in herds is often used in Crioulo breeding farms, thus not allowing the determination of ovulation dates and the early detection of pregnancies. This fact complicates the estimation of gestational age after 70 days of conception. This study aimed to evaluate the diameter of the fetal orbits of Crioulo mares to develop a formula to estimate a gestational date. Measurements of 164 fetal ocular orbits were performed in 124 Crioulo mares with gestational ages ranging between 119 and 341 days. The current study observed a linear growth pattern of Crioulo fetal orbits up to 341 days of gestation. Thus, obtaining a suitable linear regression model to determine the gestational age of Crioulo mares based on fetal ocular orbit diameter measure is possible. The obtained model was y = 8.3756x + 11.90, where y represents the gestational age in days, and x represents the diameter of the fetal ocular orbit in millimeters. This formula had an r2 of 0.985 (P < .001). We conclude that this model allows researchers and veterinarians to accurately estimate the gestational age of Crioulo mares between 4 and 11 months of pregnancy.  相似文献   
746.
Abstract— In this work a larval shrimp diet was spray-dried using a ratio of 75% whey protein concentrate and 25% mesquite gum as wall material, where the sole protein contribution to the diet was the whey protein concentrate. The microencapsulated diet exhibited the following physical properties: mean volumetric particle size of 49.3 om, characteristic floatability time 225.3 min, and density of 606 g/L. Its outer morphology was characterized by a dimpled spherical shape with no evident surface pores or cracks. Inner microstructure showed a central void, with the feed components finely embedded in the wall matrix. Two bioassays were performed with zoea of white shrimp Litopenaeus vannamei . In the first study, microencapsulated diet, and microencapsulated diet plus a single dose of live algae, were compared with a live algae control diet; in the second study, three co-feeding regimes consisting of microencapsulated diet + 10,30 and 60C. muellericellaL, respectively, were compared with the live algae control diet. In overall terms, the co-feeding regime with 30 cells/ OL produced larvae with carapace length (0.74-mm CL) and development index (4.5 DI) significantly superior to that of the live algae treatment (0.70-mm CL, 4.1 DI; respectively), and yielded similar individual dry weight (34-Og DW) and survival rate (58%). These results indicate that microencapsulated diets supplemented with live algae can produce responses similar to those of live feed. These results  相似文献   
747.
748.
749.
This paper reports experiences of the Australian Centre for International Agricultural Research (ACIAR) Smallholder Forestry Project in the establishment of working relationships with a people’s organisation in Leyte Province, Philippines. Strategies adopted in building a partnership with the organisation through the establishment of a community nursery, conduct of field trial research and the emerging practical impacts on smallholders are specifically discussed. Information presented in this paper is the outcome of documented field experiences during the research as well as informal discussions with members of the people’s organisation. This project illustrates that within-community research can be an effective extension tool if local people are given the chance to participate in all stages of planning and implementation. Mere participation in research activities, however, is not enough. Continuing interaction between the researchers and the local people is crucial in paving the way to partnership building. The developmental partnership that was established has created practical impacts which may lead to more widespread adoption and promotion of farm and community forestry in Leyte Province.  相似文献   
750.
The main agroforestry systems in Venezuela are the multispecies plant associations in integrated coffee production system and the silvopastoral system. This paper describes the functional and structural aspects of these systems. The multilayered coffee production systems are practised mainly in the premontane moist forest of the Andes region, but are also found in other areas of the country. Various tree species are used for shade and as fence in big coffee plantations, whereas in small units with traditional production pattern, coffee is planted along with many other species, often constituting a 3–4 layer canopy. Available data are presented on the production as well as some socioeconomic aspects.The silvopastoral systems are found in the tropical dry forest (savannas) and in the very dry tropical forest of the semiarid zones of the country. A large number of trees and shrubs are found in these pastoral areas where they play both productive (fodder and feed) and service (shelter) roles.Although both these systems are practised over large areas of the country, practically no research has been done to improve them. In order to strengthen national capability to undertake such research, international support of cash and as well as technical advice is needed.
Resumen Los principales sistemas agroforestales en Venezuela son el Sistema integrado de producción de café y el sistema silvopastoril. En el presente trabajo se describen aspectos funcionales y estructurales de esos sistemas. El sistema de producción multi-estratificado de café es practicado principalmente en el bosque húmedo premontano de la región andina, per también es frecuentemente observado en áreas del país. Diferentes especies de árboles son utilizados como sombra y como cercos vivos en las grandes plantaciones de café, mientras que en las pequenas unidades con un patrón de producción tradicional, el café es plantado junto con una gran diversidad de especies constituyendo un dosel vegetativo de 3–4 estratos.Información disponible sobre producción y algunos aspectos socio-económicos es presentada en el trabajo.Los sistemas silvopastoriles son encontrados en el bosque seco tropical (sabanas o llanos) y en el bosque muy seco tropical de las zonas semiaridas del país. Un gran número de árboles y arbustos se encuentran en esas áreas de pastoreo donde juegan un doble rol, producción (forraje ya alimento) y servicio (refugio y abrigo).Aunque ambos sistemas son practicados en grandes áreas del país, practicamente ninguna investigación se ha llevado a cabo para mejoralos. Con el objeto de fortalecer la capacidad en el país de llevar a cabo tal tipo de investigación, se hace necessario recursos economicós y asesaría técnica por parte de organizaciones internacionales.
  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