全文获取类型
收费全文 | 524篇 |
免费 | 24篇 |
专业分类
林业 | 33篇 |
农学 | 32篇 |
基础科学 | 3篇 |
123篇 | |
综合类 | 77篇 |
农作物 | 8篇 |
水产渔业 | 20篇 |
畜牧兽医 | 226篇 |
园艺 | 5篇 |
植物保护 | 21篇 |
出版年
2023年 | 4篇 |
2022年 | 10篇 |
2021年 | 13篇 |
2020年 | 7篇 |
2019年 | 7篇 |
2018年 | 11篇 |
2017年 | 12篇 |
2016年 | 13篇 |
2015年 | 15篇 |
2014年 | 14篇 |
2013年 | 16篇 |
2012年 | 37篇 |
2011年 | 35篇 |
2010年 | 15篇 |
2009年 | 18篇 |
2008年 | 28篇 |
2007年 | 27篇 |
2006年 | 34篇 |
2005年 | 31篇 |
2004年 | 22篇 |
2003年 | 24篇 |
2002年 | 19篇 |
2001年 | 7篇 |
2000年 | 10篇 |
1999年 | 8篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 6篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1972年 | 7篇 |
1971年 | 12篇 |
1970年 | 2篇 |
1969年 | 6篇 |
1968年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有548条查询结果,搜索用时 15 毫秒
1.
2.
Denis J. Sonwa Ousmane Coulibaly A. Akinwumi Adesina Stephan F. Weise Mathurin Tchatat 《Integrated Pest Management Reviews》2002,7(3):191-199
Imports of pesticides have long been subsidised for use in the cocoa agroforests of the humid forest zone of southern Cameroon.
With the liberalisation of the cocoa and pesticides sectors and the devaluation of the local currency (CFA franc), farmers
are facing fluctuations in the price paid for cocoa and the high cost of farm inputs. Without the support of the extension
services, they themselves have developed traditional integrated control methods based on the use of plant extracts mixed with
conventional pesticides. From a survey of 300 cocoa farmers, the study assesses the farmers' command of these methods, the
pests controlled, the problems encountered and the institutional constraints in the definition and dissemination of integrated
control methods. The study concludes with recommendations for research and development towards the better definition and dissemination
of integrated control methods.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
4.
5.
Jan StuckensSebinasi Dzikiti Willem W. Verstraeten Stephan Verreynne Rony Swennen Pol Coppin 《Agricultural and Forest Meteorology》2011,151(7):1002-1015
Hyperspectral remote sensing for monitoring horticultural production systems requires the understanding of how plant physiology, canopy structure, management and solar elevation affect the retrieved canopy reflectance during different stages of the phenological cycle. Hence, the objective of this study was to set up and to interpret a hyperspectral time series for a mature and healthy citrus orchard in the Western Cape province of South Africa considering these effects. Based on the remotely sensed data, biophysical parameters at the canopy level were derived and related to known observed physiological and phenological changes at the leaf level and to orchard management. Fractions of mature fruit, flowers, and sunburnt leaves were considered, and indices related to canopy structure chlorophyll content and canopy water status were calculated.Results revealed small cover fractions of mature fruit, flowers and sunburnt leaves of respectively 2.1%, 3.1% and 7.0%, but the high spectral contrast between flowers and leaves allowed a successful classification of flowering intensity. Furthermore, it was shown that canopy level time series of vegetation indices were sensitive to changes in solar elevation and soil reflectance which could be reduced by applying an empirical soil line correction for the most affected indices. Most trends in vegetation indices at the canopy level could be explained by a combination of changes at the leaf level (chlorophyll, carotenoids, dry matter), changes in canopy structure (leaf area index and leaf angle distribution) and changes in cover fractions of vegetative flushes, flowers and sunburnt leaves. The transformed chlorophyll absorption ratio index over the optimised soil adjusted vegetation index (MCARI/OSAVI) was best related to leaf level trends in chlorophyll content. Seasonal changes in the photochemical reflectance index (PRI) were linked to inverse changes in the carotenoid-to-chlorophyll ratio. Canopy structure indices (the modified triangular vegetation index or MTVI2 and the standardized leaf area index determining index or sLAIDI) were sensitive to changes in leaf area index, average leaf angle as well to management interactions (pruning and harvest). Canopy water status was highly impacted during the spring flush due to expanding leaves that concealed trends in the underlying mature leaves. Seasonal trends in soil and weeds reflectance were related to changes in volumetric soil water content and to the earlier and reduced growth period of non-irrigated weeds. 相似文献
6.
Sebinasi Dzikiti Stephan J. VerreynneJan Stuckens Albert StreverWillem W. Verstraeten Rony SwennenKaren I. Theron Pol Coppin 《Agricultural and Forest Meteorology》2011,151(8):1035-1044
This study describes the diurnal and seasonal dynamics of the canopy reflectance, water use and water status of Midknight Valencia citrus trees under semi-arid conditions. Hyperspectral canopy reflectance data was collected on 30 trees at monthly intervals over a period of 16 months in a commercial orchard in South Africa. The mean canopy reflectance in the wavelength range 350-2500 nm followed a clear seasonal trend influenced by environmental conditions and tree phenology. Mean monthly reflectance peaked in summer (∼22%) while the lowest value (∼15%) was reached in winter with the seasonal changes in the sun's position accounting for a significant proportion of the variations. A sensitivity analysis of a Penman-Monteith transpiration model showed that water use by individual trees changed by up to 13% when the canopy reflectance was varied over the seasonal range of measured values. This suggested that the seasonal changes in tree water use influenced the seasonal trend of the canopy reflectance. Thus monitoring the canopy reflectance of citrus trees could offer information on the tree water status. To test this, sap flow data of water uptake and loss by the trees were compared with the canopy spectra. Sap flow data showed a heavy reliance by the citrus trees on the internally stored water with up to 25% of the daily total transpiration withdrawn from the trees’ internal water storage pools when soil water was limited. This depletion of internally stored water, and hence the change in tree water status, was detected using spectral indices based on the first order derivatives of the canopy reflectance centered at two and, at most, four spectral bands. We conclude that even if citrus trees are evergreen, their canopy reflectance changes significantly throughout the year with a considerable impact on tree energy balance and water use. In addition, the contribution of the internally stored water to daily transpiration is a possible indicator of drought stress for citrus trees detectable from changes in canopy reflectance and it has potential applications in irrigation scheduling using canopy level spectral information. 相似文献
7.
Journal of Plant Diseases and Protection - The following text summarizes the different perspectives of presenters participating in the section Plant Protection in the Tropics and Subtropics, 61st... 相似文献
8.
Juan P. Fuentes David F. Bezdicek Markus Flury Stephan Albrecht Jeffrey L. Smith 《Soil & Tillage Research》2006,88(1-2):123-131
Under conventional farming practices, lime is usually applied on the soil surface and then incorporated into the soil to correct soil acidity. In no-till (NT) systems, where lime is surface applied or only incorporated into the soil to very shallow depth, lime will likely not move to where it is required within reasonable time. Consequently, lime may have to be incorporated into the soil by mechanical means. The objective of this laboratory study was to characterize the effect of lime, incorporated to different depths, on chemical and biological soil properties in a long-term NT soil. Soil samples taken from the 0–5, 0–10, and 0–20 cm depths were analyzed in incubation studies for soil pH, nitrate, CO2 respiration, and microbial biomass-C (MBC). Lime (CaCO3) was applied at rates equivalent to 0, 4.4, 8.8, and 17.6 Mg ha−1. Application of lime to both 0–10 and 0–20 cm depths increased soil pH from about 4.9 by 1, 1.7, and 2.8 units for the low, medium, and high liming rates, respectively. Soil nitrate increased over time and in proportion to liming rate, suggesting that conditions were favorable for N-mineralization and nitrification. Greater respiration rates and greater MBC found in lime-treated than in non-limed soils were attributed to higher soil pH. Faster turnover rates and increased mineralization of organic matter were found in lime-treated than in non-limed soils. These studies show that below-surface lime placement is effective for correcting soil acidity under NT and that microbial activity and nitrification can be enhanced. 相似文献
9.
De Wilde T De Meulenaer B Mestdagh F Govaert Y Vandeburie S Ooghe W Fraselle S Demeulemeester K Van Peteghem C Calus A Degroodt JM Verhé R 《Journal of agricultural and food chemistry》2005,53(16):6550-6557
A number of parameters linked to storage of potatoes were evaluated with regard to their potential to influence the acrylamide formation in French fries. Acrylamide, which is a potential human carcinogen, is reported to be formed during the frying of potatoes as a result of the reactions between asparagine and reducing sugars. This study was conducted using three potato varieties (Bintje, Ramos, and Saturna) typically used in Belgium, The Netherlands, and the northern part of France for French fry and crisp production. Saturna, mainly used in crisp production, appeared to be the least susceptible for acrylamide formation during frying. Especially storage at low temperatures (4 degrees C) compared to storage at 8 degrees C seemed to enhance acrylamide formation due to a strong increase in reducing sugars caused by low-temperature storage. Because of the reversible nature of this physiological reaction, it was possible to achieve a significant reduction of the reducing sugars after a reconditioning of the cold-stored potatoes for 3 weeks at 15 degrees C. All changes in acrylamide concentrations could mainly be explained by the reducing sugar content of the potato (R2 = 0.84, n = 160). This means that, by ensuring a low reducing sugar content of the potato tuber, the risk for acrylamide formation will largely be reduced. Finally the use of a sprout inhibitor did not influence the composition of the potato, and thus acrylamide formation was not susceptible to this treatment. 相似文献
10.
Olivier M Aggarwal A Allen J Almendras AA Bajorek ES Beasley EM Brady SD Bushard JM Bustos VI Chu A Chung TR De Witte A Denys ME Dominguez R Fang NY Foster BD Freudenberg RW Hadley D Hamilton LR Jeffrey TJ Kelly L Lazzeroni L Levy MR Lewis SC Liu X Lopez FJ Louie B Marquis JP Martinez RA Matsuura MK Misherghi NS Norton JA Olshen A Perkins SM Perou AJ Piercy C Piercy M Qin F Reif T Sheppard K Shokoohi V Smick GA Sun WL Stewart EA Fernando J Tejeda Tran NM Trejo T Vo NT Yan SC Zierten DL Zhao S 《Science (New York, N.Y.)》2001,291(5507):1298-1302
We have constructed a physical map of the human genome by using a panel of 90 whole-genome radiation hybrids (the TNG panel) in conjunction with 40,322 sequence-tagged sites (STSs) derived from random genomic sequences as well as expressed sequences. Of 36,678 STSs on the TNG radiation hybrid map, only 3604 (9.8%) were absent from the unassembled draft sequence of the human genome. Of 20,030 STSs ordered on the TNG map as well as the assembled human genome draft sequence and the Celera assembled human genome sequence, 36% of the STSs had a discrepant order between the working draft sequence and the Celera sequence. The TNG map order was identical to one of the two sequence orders in 60% of these discrepant cases. 相似文献