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81.
Bioassay-directed isolation and purification of the hexane extract of Apium graveolens L. seeds led to the characterization of three compounds: beta-selinene (1), 3-n-butyl-4,5-dihydrophthalide (2) and 5-allyl-2-methoxyphenol (3). The structures of these compounds were established by using (1)H and (13)C NMR spectral methods. Compounds, 1-3 demonstrated 100% mortality on fourth-instar Aedes aegyptii larvae at 50, 25, and 200 microg mL(-)(1), respectively, in 24 h. Also, 2 inhibited the growth of Candida albicans and Candida kruseii at 100 microg mL(-)(1). It inhibited both topoisomerase-I and -II enzyme activities at 100 microg mL(-)(1). Compound 2 displayed 100% mortality at 12.5 and 50 microg mL(-)(1), respectively, when tested on nematodes, Panagrellus redivivus and Caenorhabditis elegans. The triglyceride, 1,3-di[(cis)-9-octadecenoyl]-2-[(cis,cis)-9, 12-octadecadienoyl]glycerol (4) and 3 were isolated for the first time from A. graveolens seeds, although 4 was not biologically active. 相似文献
82.
WM Itano JJ Bollinger JN Tan B Jelenkovic X Huang DJ Wineland 《Science (New York, N.Y.)》1998,279(5351):686-689
Single crystals of a one-component plasma were observed by optical Bragg diffraction. The plasmas contained 10(5) to 10(6) single-positive beryllium-9 ions (9Be+) at particle densities of 10(8) to 10(9) per cubic centimeter. In approximately spherical plasmas, single body-centered cubic (bcc) crystals or, in some cases, two or more bcc crystals having fixed orientations with respect to each other were observed. In some oblate plasmas, a mixture of bcc and face-centered cubic ordering was seen. Knowledge of the properties of one-component plasma crystals is required for models of white dwarfs and neutron stars, which are believed to contain matter in that form. 相似文献
83.
Farmers' adoption of improved technologies is the ultimate measure of the success of any agricultural innovation. In a joint
project of the International Centre for Research in Agroforestry (ICRAF) and the Department of Research and Specialist Services
of Zimbabwe, the potential for adoption of the improved planted fallow technology using Sesbania sesban was assessed in the Mangwende Communal Area. The study was based on experimental data of maize (Zea mays) yields following 1-, 2- and 3-year improved fallows at Domboshawa Training Center, northern Zimbabwe where the improved
fallows were promising. The data indicated that maize yields were higher after S. sesban fallows than after Cajanus cajan and Acacia angustissima fallows. A five-year linear programming model sensitive to the diversity within households was developed to simulate the
livelihood system of households in the Mangwende Communal Area. Improved fallows of S. sesban were incorporated into the model to determine the potential for their adoption. Model results indicated that there is potential
for the technology to be adopted by 80% of the farmers. According to the model, the new technology on average occupies 60%
of the area under maize. Nevertheless, households continue to use fertilizers and cattle manure. One-year improved fallows
are planted every other year; three-year improved fallows are also planted. Farmers who adopt the fallow technologies realize
an increase in the cash available for discretionary spending. Factors such as composition of the household in terms of fulltime
workers, size of the arable land owned by the farmer, and whether the household differentiates activities by gender, determine
the adoption of the improved-fallow technology.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
84.
Agroforestry Systems Inventory 总被引:2,自引:0,他引:2
P. K. R. Nair 《Agroforestry Systems》1987,5(3):301-317
85.
Brazil accounts for about 20% of the world production of cocoa, and about 95% of cocoa produced in Brazil is from the southeastern part of Bahia State. Traditionally, cacao is grown in monoculture (though under the shade of various other species). But various crop combinations involving cacao have recently been undertaken by the farmers with encouragement from Brazilian government.As a part of the crop diversification programme in the traditional cacao growing areas and their surroundings, extensive areas are being planted to other plantation crops, mainly clove and rubber and, to some extent, coconut too. Crop combinations have been adopted in some of these new plantings and cacao is an important component of most of such combinations. Whereas several other crops are combined with clove trees, cacao is usually the only species grown with mature rubber trees. Young rubber trees are, however, interplanted with a number of other species. Productive coconut areas are found mostly in sandy soils along the coast so that there is little intercropping. However, scattered farms are found where coconuts are underplanted with guarana, black pepper, cacao, cashew, etc. as done commonly in other parts of Northeast Brazil. 相似文献
86.
Land use systems in the Northeast Region of Brazil are dominated by large holdings and extensive cultivation of perennial crops such as cashew, coconut, carnauba wax palm, babaçu palm and so on. The common feature which links these crops is the silvopastoral system of livestock (chiefly cattle, sheep and donkeys) grazing under them. Agrosilvicultural systems involving cultivation of annual subsistence crops, and in some instances other perennials, in the stands of these perennial crops is also common. The paper presents the available information on the management, production, rate of growth, economic importance, etc. of these agroforestry systems involving cashew, coconut and carnauba palm. These systems are of considerable merit in the environmental, agricultural and socio-economic conditions of Northeast Brazil. However, practically no research nor even systematic data collection has been done on these so that there is an almost total lack of information on them. In order to improve the systems, they should be studied in detail and research undertaken on various components (crops, trees and livestock) individually as well as the system as a whole. Selection of suitable species of grass and other herbaceous crops, appropriate management techniques for both overstorey and understorey species in relation to the age of the overstorey species, optimal stocking rates of animals, etc. have to be determined so as to enable plantation owners and operators to realize the full potential of these systems. 相似文献
87.
D. S. Zamora S. Jose P. K. R. Nair J. W. Jones B. J. Brecke et al. 《Agroforestry Systems》1991,13(2):194-194
88.
Understanding the historical development of indigenous systems will provide valuable information for the design of ecologically
desirable agroforestry production systems. Such studies have been relatively few, especially in Amazonia. The agroforestry
systems in Amazonia follow a trail that begins with the arrival of the first hunter-gatherers in prehistoric times, followed
by the domestication of plants for agriculture, the development of complex societies rich in material culture, the decimation
of these societies by European diseases, warfare, and slavery, the introduction of exotic species, and finally, the present-day
scenario of widespread deforestation, in which agroforestry is ascribed a potential role as an alternative land use. Despite
the upheavals which occurred in colonial times, greatly reducing the population of native tribes, a review of anthropological
and ethnobiological literature from recent decades indicates that a great variety of indigenous agroforestry practices still
exist, ranging from deliberate planting of trees in homegardens and fields to the management of volunteer seedlings of both
cultivated and wild species. These practices result in various configurations of agroforestry systems, such as homegardens,
tree/crop combinations in fields, orchards of mixed fruit trees, and enriched fallows. Together they constitute a stock of
knowledge developed over millenia, and represent technologies that evolved along with the domestication of native forest species
and their incorporation into food production systems. This knowledge is the basis for the principal agroforestry practice
employed by farmers in Amazonia today, the homegarden, and has potential to contribute to the development of other agroforestry
systems. 相似文献
89.
Institutional and policy issues are now recognized as high priority items in agroforestry research. However, such studies based on actual field experiences seldom seem to have been undertaken. To help address this deficiency, a study was undertaken in Ecuador to evaluate institutional and policy impacts on agroforestry dissemination using two field projects as case studies.The projects were in contrasting ecological locations: the Amazonian lowlands (the Coca Agroforestry Project), and the Andean highlands (the PROMUSTA project). The impact of policy and institutional constraints (such as land tenure, research and extension support, marketing and pricing, and credit) on the implementation of these projects was assessed based on interviews with farmers and project officials as well as analyses of secondary data. The Coca project was found to be adversely impacted by the lack of extension, product marketing, and credit availability. The principal institutional constraints for the Andean project included legal obstacles to farm-land procurement, inadequate extension, little state-financial assistance, and limited affordable credit. The relevance of these issues was location specific: while access to land was not a serious constraint in the lowlands, it was a major issue in the highlands.The study validates the premise that policy and institutional evaluations should become an essential component of design and implementation of agroforestry projects. Although the components of a sound policy framework might be similar in most developing-country situations, it may not be possible to evolve universally applicable procedures for agroforestry-policy formulation because of the location-specificity of the promoted systems and the institutional issue related to their adoption.Florida Agricultural Experiment Station Journal Series No. R-03861. 相似文献
90.