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   288篇
  免费   7篇
  国内免费   5篇
林业   40篇
农学   17篇
基础科学   2篇
  44篇
综合类   12篇
农作物   35篇
水产渔业   38篇
畜牧兽医   70篇
园艺   15篇
植物保护   27篇
  2024年   1篇
  2023年   2篇
  2022年   12篇
  2021年   15篇
  2020年   16篇
  2019年   15篇
  2018年   14篇
  2017年   13篇
  2016年   13篇
  2015年   12篇
  2014年   8篇
  2013年   22篇
  2012年   20篇
  2011年   26篇
  2010年   19篇
  2009年   14篇
  2008年   12篇
  2007年   9篇
  2006年   7篇
  2005年   6篇
  2004年   7篇
  2003年   11篇
  2002年   3篇
  2001年   3篇
  2000年   6篇
  1999年   1篇
  1998年   1篇
  1996年   3篇
  1995年   2篇
  1994年   1篇
  1991年   1篇
  1985年   1篇
  1980年   1篇
  1979年   1篇
  1974年   1篇
  1972年   1篇
排序方式: 共有300条查询结果,搜索用时 12 毫秒
141.
This study evaluated the effects of three levels of loading density (200, 300 and 400 g L−1) and four levels of duration (1, 3, 6 and 9 h) on the mortality, plasma cortisol and chloride levels and growth of rohu Labeo rohita fingerlings in a transport simulation. While total immediate mortality was low (4–12%), delayed mortality was high (27–49%). Initial capture and handling were found to constitute the most stressful phase as indicated by elevated plasma cortisol. The levels of cortisol continued to rise at 6 and 9 h after transport, with the highest level observed at 9 h after transport. The level of plasma chloride fell after transport across all density levels and treatment durations. Specific growth rate (SGR, %/day) and total bacterial density (cfu/g) were not different between and within treatments, and between treatments and the controls. This study demonstrates that transport has a profound effect on the stress responses of rohu fingerlings. Although the level of immediate mortality was low, the higher level of delayed mortality has serious implications in terms of production inefficiency for grow-out farmers.  相似文献   
142.
Communication can contribute to the evolution of biodiversity by promoting speciation and reinforcing reproductive isolation between existing species. The evolution of species-specific signals depends on the ability of individuals to detect signal variation, which in turn relies on the capability of the brain to process signal information. Here, we show that evolutionary change in a region of the brain devoted to the analysis of communication signals in mormyrid electric fishes improved detection of subtle signal variation and resulted in enhanced rates of signal evolution and species diversification. These results show that neural innovations can drive the diversification of signals and promote speciation.  相似文献   
143.
Traditionally, chitin is extracted from crustacean shells using chemical methods involving the use of strong acids and alkali. In this study, chitin was extracted from the shrimp shell waste using microbes isolated from the fermented milk and bread. The chitin yield from the shells of Fenneropenaeus semisulcatus was 14.054% and 16.062%, respectively, for shell:bacterial broth ratios of 1:15 and 1:25; whereas, the yield of chitin from the shells of Fenneropenaeus indicus was 14.93% and 13.871%, respectively, at 1:15 and 1:25 broth ratios. The Fourier transform infrared spectra obtained from the chitin samples showed characteristic chitin peaks in both shell to bacterial broth ratio. The X-ray diffraction analysis revealed peaks between 10–15 and 25–30 degrees in the chitin recovered from both species, though some variations between species were observed. In conclusion, results of the present study indicate that application of microorganisms for the extraction of chitin from the shrimp shell waste could be an alternative for the traditional chemical methods.  相似文献   
144.
Tensile strength plays a vital role in determining the mechanical behavior of woven fabrics. In this study, two artificial neural networks have been designed to predict the warp and weft wise tensile strength of polyester cotton blended fabrics. Various process and material related parameters have been considered for selection of vital few input parameters that significantly affect fabric tensile strength. A total of 270 fabric samples are woven with varying constructions. Application of nonlinear modeling technique and appreciable volume of data sets for training, testing and validating both prediction models resulted in best fitting of data and minimization of prediction error. Sensitivity analysis has been carried out for both models to determine the contribution percentage of input parameters and evaluating the most impacting variable on fabric strength.  相似文献   
145.
In order to meet the required strength of a fabric, selection of yarn is difficult because tensile strength of woven fabric depends upon a number of factors. Still, the manufacturers have to use hit and trial method in order to select the yarn for the required tensile strength of fabric. This study was carried out to develop regression equations for the prediction of yarn tensile strength suitable for the predefined strength of cotton woven fabrics. These equations were developed by using empirical data obtained from two hundred and thirty four fabric samples prepared under a systematic plan with different constructions. Prediction proficiency and precision of these regression equations were evaluated by correlation analysis of the predicted and actual warp and weft yarn strength values of another set of thirty six fabric samples. The results show a very strong prediction precision of the equations.  相似文献   
146.
Paddy and Water Environment - Rice is critical to maintaining nutritional demand and food security of many Asian and African nations. The high water demanding rice is traditionally cultivated with...  相似文献   
147.
为了比较不同机器学习算法在干旱半干旱区春小麦叶片水分含量(leaf water content, LWC)遥感监测中的应用效果及筛选最佳波段组合,在田间尺度上,以春小麦冠层高光谱数据为基础,采用两波段组合形式,计算15种光谱参数(比值植被指数RVI、归一化植被指数NDVI、差值植被指数DVI和12种水分植被指数),通过对抽穗期叶片含水量与光谱参数拟合效果进行对比与分析,分别构建了基于机器学习[人工神经网络(artificial neuralnetwork, ANN)、K近邻(K-nearestneighbors, KNN)和支持向量回归(support vector regression, SVR)]和光谱参数的春小麦LWC反演模型,并对模型精度进行验证,以确定有效波段组合。结果表明,小麦抽穗期LWC与冠层高光谱反射率(R784~950)、12种水分植被指数均显著相关(P<0.01);波段组合形式有效地优化了两波段指数的波段组合,在800~1 000 nm区间光谱参数(RVI1046,1057、NDVI1272,1279  相似文献   
148.
Background:Bispecific antibodies represent an important class of mAbs, with great therapeutic potentials due to their ability to target simultaneously two distinct epitopes. The generation of functional bispecific antibodies with the highest possible yields is particularly critical for the production of these compounds on industrial scales. Anti- CD3 × CD19 bsAb is a bispecific T-cell engager (BiTE) currently used for treating ALL. Herein, we have tried to optimize the expression level of this antibody in mammalian hosts. Methods:WPRE sequence was incorporated at the 3’ end of the expression cassette. This modification resulted in a notable about two-fold increase in the expression of the bsAb in the Expi293 cell line. Results & Conclusion:Follow-up flow cytometry analysis demonstrated the binding properties of the produced antibody at acceptable levels, and in vitro bioactivity assays showed that this product is potent enough for targeting and destroying CD19-positive cells. Our findings show that WPRE enhances the expression of this type of bispecific mAbs in HEK-293 family cell lines. This approach can be used in biopharma industry for the mass production of anti-CD3 × CD19 bispecific antibody. Key Words: Acute lymphoblastic leukemia, Bispecific antibodies, Monoclonal antibody  相似文献   
149.
Present research investigates the mechanical properties of jute-coir fiber reinforced hybrid polypropylene (PP) composite with fiber loading variation and observes the effect of chemical treatment of fiber on property enhancement of the composites. Composites were manufactured using hot press machine at four levels of fiber loading (5, 10, 15 and 20 wt%). Fiber ratio’s were varied (jute:coir=1:1, 3:1 and 1:3) for 20 % fiber loaded composites. Both jute and coir fiber was treated using 5 % and 10 % NaOH solutions. Composites were also prepared using treated fiber with jute-coir fiber ratio of 3:1. Tensile, flexural, impact and hardness tests and Fourier transform infrared spectroscopic analysis were conducted for characterization of the composites. Tensile test of composite showed a decreasing trend of tensile strength and increasing trend of the Young’s modulus with increase in fiber loading. During flexural, impact and hardness tests, the flexural strength, flexural modulus, impact strength and hardness values were found to be increased with increase in fiber loading. All these properties enhanced with the enhancement of jute content except impact strength. 5 % NaOH treatment provided an improving trend of properties whereas, 10 % NaOH treatment showed the reverse one. The FTIR analysis of the composites indicated decrease of hemicelluloses and lignin content with alkali treatment.  相似文献   
150.
This paper presents the effects of particle size and mixing ratio on the properties including physical, mechanical, and decay resistance of wood plastic composites (WPCs). In addition, it also presents the effects of immersion temperatures on water absorption (WA) and thickness swelling (TS) of the WPCs. WPCs with a thickness of 6 mm were fabricated from Albizia richardiana King & Prain wood particles and recycled polyethylene terephthalate (PET) by the flat-press method. To prepare the WPCs, two different wood particle sizes (0.5–1.0 and 1.01–2.0 mm) were used along with four different mixing ratios (w/w). Subsequently, the physical properties include density, moisture content, WA, and TS, and mechanical properties include modulus of elasticity (MOE) and modulus of rupture (MOR) of the produced WPCs was evaluated. Furthermore, decay resistance was evaluated by the weight loss percentage method. Moreover, the effects of immersion temperatures on WA and TS of WPCs after 24 h of immersion in water at three different temperatures, i.e., 25, 50, and 75 °C were investigated. Results showed that the wood particle size had impact on WPC’s density (only 6% decreased with the increase of particle size); however, the density decreased by 29% when the wood particle content increased from 40 to 70%. The WA and TS gradually increased with the increase of particle content and decrease of particle size. In addition, WA and TS increased proportionately with increasing immersion temperature from 25 to 75 °C. Furthermore, the highest MOE (2570 N/mm2) was found for the WPCs fabricated from large wood particles having the ration of 50:50 (wood particle:PET). For decay resistance, WPCs consisted of larger particles and higher PET content showed greater resistance against decay. Therefore, it is comprehensible that fabrication of the WPCs from 50% large particles and 50% PET is technically feasible and further improvement of WPC performance like enhancement of MOE and reduction of density using coupling agent and agricultural waste fibers, respectively, in the WPC formulation is recommended.  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