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   184篇
  免费   1篇
林业   15篇
农学   8篇
基础科学   2篇
  33篇
综合类   15篇
农作物   15篇
水产渔业   13篇
畜牧兽医   39篇
园艺   25篇
植物保护   20篇
  2023年   1篇
  2022年   9篇
  2021年   4篇
  2020年   8篇
  2019年   9篇
  2018年   13篇
  2017年   12篇
  2016年   10篇
  2015年   2篇
  2014年   12篇
  2013年   10篇
  2012年   12篇
  2011年   14篇
  2010年   15篇
  2009年   8篇
  2008年   7篇
  2007年   6篇
  2006年   6篇
  2005年   9篇
  2004年   7篇
  2003年   3篇
  2002年   3篇
  2000年   1篇
  1996年   1篇
  1990年   1篇
  1988年   1篇
  1970年   1篇
排序方式: 共有185条查询结果,搜索用时 328 毫秒
151.
Determination of temporal and spatial distribution of water use (WU) within agricultural land is critical for irrigation management and could be achieved by remotely sensed data. The aim of this study was to estimate WU of dwarf green beans under excessive and limited irrigation water application conditions through indicators based on remotely sensed data. For this purpose, field experiments were conducted comprising of six different irrigation water levels. Soil water content, climatic parameters, canopy temperature and spectral reflectance were all monitored. Reference evapotranspiration (ET0), crop coefficient Kc and potential crop evapotraspiration (ETc) were calculated by means of methods described in FAO-56. In addition, WU values were determined by using soil water balance residual and various indexes were calculated. Water use fraction (WUF), which represents both excessive and limited irrigation applications, was defined through WU, ET0 and Kc. Based on the relationships between WUF and remotely sensed indexes, WU of each irrigation treatments were then estimated. According to comparisons between estimated and measured WU, in general crop water stress index (CWSI) can be offered for monitoring of irrigated land. At the same time, under water stress, correlation between measured WU and estimated WU based on CWSI was the highest too. However, canopy-air temperature difference (Tc − Ta) is more reliable than others for excessive water use conditions. Where there is no data related to canopy temperature, some of spectral vegetation indexes could be preferable in the estimation of WU.  相似文献   
152.
The consumer acceptance and the quality standard of agricultural products such as apple are determined mostly by their colour. Colour is measured with a colorimeter and quantified using the C.I.E. L*, a*, b* colour space system. It is used commonly by researchers for the classification and identification of apple fruit. To the best of our knowledge, the present study is the first study investigating the prediction of some colour properties of six apple varieties through artificial neural networks (ANN). The apple varieties are ‘Amasya’, ‘Starking’, ‘Granny Smith’, ‘Pink Lady’, ‘Golden Delicious’, ‘Arapk?z?’ and the colour properties are L* (lightness), a* (redness), b* (yellowness), C* (chroma), h* (hue angle), CI (chroma index). General Regression Neural Networks (GRNN) and Adaptive Neuro Fuzzy Interface System (ANFIS) structures were employed to predict the colour properties. According to the experimental and simulation results, the proposed ANFIS predictor had a superior performance in prediction of these colour parameters.  相似文献   
153.
An alternative approach to application of chitosan based on layer by layer (LbL) assembled technique is studied in this paper. For this aim, chitosan (CHT) was used as a bio-based cationic polyelectrolyte and pentasodium tripolyphosphate (TPP) and poly(sodium 4-styrene sulfonate) (PSS) were selected as anionic polyelectrolyte. TPP/CHT and PSS/CHT based bilayers were fabricated on the cationized woven cotton fabrics via layer-by-layer self-assembly technique. The characterization of coatings on the fabric surface in terms of surface appearance, atomal content, and chemical bondings were made in detail through SEM, XPS, and FTIR-ATR analysis. Also, the antibacterial activity, air permeability, and water contact angle were measured. Surface analyses demonstrate the interaction between TPP, PSS and chitosan separately. XPS spectra also showed the existence of LbL deposition over cotton substrates in terms of both elemental composition and the presence of different types of bondings on the fabric surface. The antibacterial activity analysis revealed that the modified cotton fabric with the addition of CHT/TPP and CHT/PSS bilayers could increase the degree of inhibition on K. pneumanie and S. aureus bacteria.  相似文献   
154.
以渭干河-库车河三角洲绿洲连作5、10、15、20 a和25 a的棉田土壤为研究对象,对棉田土壤的理化性质和酶活性进行分析。结果表明: 随着棉花连作年限的增长棉田土壤容重增大、孔隙度下降,粗砂和细沙含量增加,粘粒含 量下降,其变化连作15 a极为明显; 随着连作年限的增长盐分含量和pH值逐渐降低,有机质和碱解氮含量大幅度升高,速效磷比较稳定或略有减小,而钾的含量显著下降,致使氮、磷、钾比例失调,其增减变化连作15 a极为显著; 随着连作年限的增长脲酶、过氧化氢酶和转化酶的活性呈现先升后降的趋势,连作15 a都达到最高值,蛋白酶和磷酸酶活性也呈现先升后降的趋势,但其活性连作20 a达到最高值。 由研究结果可以得出研究区棉花连作年限不宜超过15 a,棉花连作年限超过15 a时,会导致土壤容重增大、孔隙度下降,土体紧实板结,结构性差,土壤养分含量失衡,酶活性降低,土壤质量下降等连作障碍,使得棉花产出和效益受到影响。  相似文献   
155.

The objective of this study was to determine the effect of 18% thinning on streamflow nutrient flux from a mature oak–beech forest ecosystem by paired watershed approach. Two experimental watersheds including control (W-I) and treatment (W-IV) watersheds were used in the study. The experimental watersheds were monitored about 6 years from 2006 to 2011 for the calibration period and 4 years from 2012 to 2015 for the treatment period. The forest in the treatment watershed was thinned between October and December in 2011, and the forest in the control watershed was left untreated. Water grab samples were collected from the streams in the watersheds on weekly basis during both the calibration and treatment periods and analyzed for calcium (Ca2+), magnesium (Mg2+), Kjeldahl nitrogen (KN), sodium (Na+), potassium (K+), iron (Fe3+), aluminum (Al3+), ammonium nitrogen (NH4 +-N), and sulfate (SO4 2−). The simple linear regression equations were developed between mean monthly nutrient fluxes of two watersheds in the calibration period with significantly high correlation coefficients, and they were used to estimate nutrient fluxes from the treatment watershed during the treatment period as if thinning had not been applied. The changes in the monthly nutrient fluxes were estimated as the differences between measured and values calculated with the linear regression equations. Results showed that removal of 18% standing timber volume did not significantly change nutrient exports except for KN and Na+ from the treatment watershed.

  相似文献   
156.
Sunagoke moss Rachomitrium japonicum is a good potential for greening material. One of the primary determinants of Sunagoke moss growth is water availability. Too much or too little water can cause water stress in plants. Water stress in plants can be detected by imaging. This study is part of on-going research aimed at developing machine vision-based precision irrigation system in a closed bio-production system for cultured Sunagoke moss. The objective of this study is to propose nature-inspired feature selection techniques to find the most significant set of Textural Features (TFs) suitable for predicting water content of cultured Sunagoke moss. The proposed Feature Selection (FS) methods include Neural-Intelligent Water Drops (N-IWD), Neural-Simulated Annealing (N-SA), Neural-Genetic Algorithms (N-GAs) and Neural-Discrete Particle Swarm Optimization (N-DPSO). TFs consist of 120 features extracted from grey, RGB, HSV, HSL and Lab colour spaces using ten Haralick’s textural equations. Back-Propagation Neural Network (BPNN) model performance was tested successfully to describe the relationship between water content of Sunagoke moss and TFs. Red Colour Co-occurrence Matrix (CCM) TFs, L CCM TFs, grey CCM TFs, value(HSV) CCM TFs, green CCM TFs and lightness(HSL) CCM TFs are recommended as individual feature-subset to be used for predicting water content of Sunagoke moss using Artificial Neural Networks. However, FS methods improve the prediction performance. The results show a significant difference between model using FS and models using individual feature-subsets or without FS. Comparative analysis shows the superiority of Neural-Intelligent Water Drops (N-IWD) compared to the other FS methods, since it achieve better prediction performance. The best N-IWD’s fitness function converged with the lowest validation-set Root Mean Square Error (RMSE) of 1.07 × 10−2 when using 36 TFs.  相似文献   
157.
Utilization from bio fertilization is well known a considerable tool to improve the yield and fruit quality of various crop fruits through the increasing emphasis on maintain of soil health, minimize environmental pollution and decrease the use of chemical fertilization. In this study, in order to improve wine grape quality features of cv. Shiraz, four different doses of foliar microbial fertilizer, including 0, 1000, 2000 and 3000?ppm were applied at two different terms as Term I (mostly; pre-bloom applications) and Term II (mostly; post-bloom applications). However, there were no influences of application terms of foliar microbial fertilizer treatments; treatment doses had considerable effects on yield and quality parameters. The lowest p-values, meaning the highest berry quality, from doses of foliar microbial fertilizer were obtained from 2000?ppm (105.08?μW), 1000?ppm (110.40?μW), 3000?ppm (112.97?μW) and 0?ppm (119.58?μW). Comparing the applications of foliar microbial fertilizer, it was observed that doses of 2000?ppm (3155.56?mg/kg), 1000?ppm (3000.92?mg/kg) and 3000?ppm (2530.19?mg/kg) exhibited higher total phenolic compounds content when compared with 0?ppm treatment (2206.97?mg/kg). Berries from grapevines applied with the doses of 2000, 1000 and 3000?ppm foliar microbial fertilizer respectively shown higher total anthocyanin content such as 1230.19, 1160.85 and 865.86?mg/kg compared to 0?ppm (637.37?mg/kg). As a result, research the findings indicated that 2000 and 1000?ppm doses of foliar microbial fertilizer were obviously effective on wine grape quality features of cv. Shiraz in terms of electrochemical property, total phenolic compounds content and total anthocyanin content.  相似文献   
158.
International Aquatic Research - Shrimp is an important traded fishery commodity. When subjected to stress, shrimp usually suffers from oxidative stress, which leads to cell injury, senescence, and...  相似文献   
159.
The experimental results of orthogonal cutting of maple and the modeling of the cutting mechanics are presented. The tool cutting forces were measured for different feed rates. A set of equations relating the tangential and feed forces to the tool edge width and feed rate (chip thickness) to calculate the chip and edge cutting force coefficients was developed. Then the chip force and edge force coefficients were calculated from experimentally obtained cutting forces and were plotted in a polar-coordinate system with respect to the fiber orientation of the maple disk. The polar-coordinate presentation of the cutting force results and the calculated cutting force coefficients provides an excellent visual appreciation of the relation between the cutting forces and the wood fiber orientation. Chips were also collected from various sectors of the wood disk. This analysis further identified the effects of fiber orientation and cutting forces on the types of chip formed and hence the cutting mechanics involved. By applying the calculated cutting coefficients for each tool orientation (in respect to the grain) it is possible to predict the feed and tangential forces for any feed rates. There is good agreement between the predicted and measured cutting forces.  相似文献   
160.
以西昆仑山2个海拔样点的土样为对象,利用(LB和TSA)2种培养基,基于16S rRNA基因序列的系统发育,采用纯培养法对其可培养细菌多样性进行研究。2样点中共分离到91株细菌,分为25个属,52个种。厚壁菌门(Firmicutes)占总菌数的48.75%,放线菌门(Actinobacteria)占36.25%,γ-变...  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