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   2733篇
  免费   179篇
  国内免费   1篇
林业   261篇
农学   93篇
基础科学   47篇
  636篇
综合类   119篇
农作物   167篇
水产渔业   402篇
畜牧兽医   931篇
园艺   58篇
植物保护   199篇
  2024年   4篇
  2023年   18篇
  2022年   58篇
  2021年   102篇
  2020年   96篇
  2019年   120篇
  2018年   113篇
  2017年   108篇
  2016年   120篇
  2015年   99篇
  2014年   148篇
  2013年   194篇
  2012年   197篇
  2011年   232篇
  2010年   120篇
  2009年   135篇
  2008年   161篇
  2007年   159篇
  2006年   134篇
  2005年   113篇
  2004年   113篇
  2003年   111篇
  2002年   63篇
  2001年   21篇
  2000年   14篇
  1999年   20篇
  1998年   15篇
  1997年   12篇
  1996年   9篇
  1995年   5篇
  1994年   12篇
  1993年   7篇
  1992年   8篇
  1991年   3篇
  1990年   3篇
  1989年   7篇
  1988年   5篇
  1987年   8篇
  1986年   4篇
  1985年   4篇
  1984年   8篇
  1983年   2篇
  1982年   3篇
  1981年   6篇
  1980年   5篇
  1976年   4篇
  1972年   2篇
  1970年   2篇
  1969年   2篇
  1954年   1篇
排序方式: 共有2913条查询结果,搜索用时 31 毫秒
991.
This report describes 5 cases of fatal Lawsonia intracellularis-associated ulcerative and necro-hemorrhagic enteritis in weanling Thoroughbred and Standardbred foals. The lesions are similar to those of the L. intracellularis-associated ulcerative and necro-hemorrhagic enteritis syndrome in pigs. Two foals had concurrent severe typhlo-colitis as a result of a large burden of encysted cyathostomes. The clinical, diagnostic, and therapeutic challenges, and the potential complications encountered during the management of such cases are discussed.  相似文献   
992.
BACKGROUND: Tuta absoluta(Meyrick) is one of the most serious pests of tomato recently introduced in the Mediterranean region. A novel bioassay method designed for the accurate determination of insecticide toxicity on T. absoluta (IRAC method No. 022) was validated by three different laboratories [Greece (NAGREF), Italy (UC) and Spain (UPCT)] on European populations. RESULTS: The insecticides indoxacarb and chlorantraniliprole were used as reference products. The IRAC leaf dip method is easy to perform, producing repeatable, homogeneous responses. LC50 values for indoxacarb ranged between 1.8 and 17.9 mg L?1 (NAGREF), 0.93 and 10.8 mg L?1 (UC) and 0.20 and 0.70 mg L?1 (UPCT), resulting in a tenfold, 12‐fold and fourfold difference between the least and most susceptible populations at each laboratory respectively. For chlorantraniliprole, LC50 values ranged between 0.10 and 0.56 mg L?1 (NAGREF), 0.23 and 1.34 mg L?1 (UC) and 0.04 and 0.24 mg L?1 (UPCT), resulting in a sixfold difference in all three cases. Overall, UPCT reported lower mean LC50 to indoxacarb, while UC reported higher LC50 to chlorantraniliprole. CONCLUSIONS: The new bioassay is reliable, providing a useful tool in the design of IRM strategies. Within each country/lab, the variability observed in the results for both indoxacarb and chlorantraniliprole can be attributed to natural variation. Future research is necessary to determine the extent to which it is possible to compare results among laboratories. Copyright © 2012 Society of Chemical Industry  相似文献   
993.
994.
995.
The data set composed by phenolic compound profiles of 83 Citrus juices (determined by HPLC-DAD-MS/MS) was evaluated by chemometrics to differentiate them according to Citrus species (sweet orange, tangerine, lemon, and grapefruit). Cluster analysis (CA) and principal component analysis (PCA) showed natural sample grouping among Citrus species and even the Citrus subclass. Most of the information contained in the full data set can be captured if only 15 phenolic compounds (concentration ≥10 mg/L), which can be quantified with fast and accurate methods in real samples, are introduced in the models; a good classification which allows the confirmation of the authenticity of juices is achieved by linear discriminant analysis. Using this reduced data set, fast and routine methods have been developed for predicting the percentage of grapefruit in adulterated sweet orange juices using principal component regression (PCR) and partial least-squares regression (PLS). The PLS model has provided suitable estimation errors.  相似文献   
996.
Leaf-cutting ants perform a vital role in the cycling of carbon and nutrients in tropical ecosystems. Nests have high levels of organic matter and refuse dumps host up to two times more soil micro-organisms than non-nest soil. The increased levels of organic matter in the soil of nests, however, can affect CO2 emissions from soil and alter the balance of atmospheric CO2. We aimed at assessing the effect of nests of the leaf-cutting ant Acromyrmex balzani on CO2 emissions in a coastal area of Northeast Brazil. Results show that A. balzani nests emitted up to four times more CO2 than the surrounding soil and emissions were positively correlated with soil moisture and soil organic matter (SOM) content. In addition, field experiments demonstrated that refuse material has a lower residence time than the leaf material brought to the colonies. Despite the high density of nests and high content of SOM compared to adjacent control soil, CO2 emissions by A. balzani nests represent only 0.3% of the total CO2 efflux by the studied ecosystem. Although these effluxes account for a relative small portion of the total soil CO2 emission, they are still important for the understanding of C balance, especially when one considers the thousands of tons of CO2 emitted each day, across entire Neotropical regions where leaf-cutting ants occur.  相似文献   
997.
The present work describes a detailed study about the adsorption of malachite green (MG) by a polyether-type polyurethane foam (PUF) using sodium dodecylsulfate (SDS) as a carrier. The adsorption process was based on the formation of a hydrophobic ionic-pair between the MG cationic dye and the dodecylsulfate anion, which presented high affinity for the PUF. The manifold employed in the study was built up by adjusting a cylinder of PUF with 200 mg in the arm of an overhead stirrer, which was soaked (and stirred) in the solution containing the dye and SDS. The adsorption process was characterized in relation to equilibrium and kinetic aspects. Langmuir (r 2 = 0.842) and Freundlich (r 2 = 0.996) isotherms were also employed for modeling the system as well as the Nernst partition law (r 2 = 0.999). A study about the recovery of MG and the PUF regeneration was conducted, and the acetonitrile was the most efficient solvent for the desorption of the adsorbed ionic pair. The obtained results showed that the concentration of SDS added to the medium plays an important role on the adsorption process, which can be better described by employing a second-order kinetic model.  相似文献   
998.
Olive oil mill wastewater (OMW) generates a wide variety of pollutants depending on the production process and other factors such as olive varieties and cultivation system. Efforts to mitigate the impact of these effluents in the environment have been made by developing more efficient treatment systems in terms of removal of chemical oxygen demand (COD), color, organic compounds, and toxicity. This study is the first that reports the potential of a treatment of OMW by biocomposites of silica?Calginate?Cfungi (Pleurotus sajor caju and Trametes versicolor). The treatment by biocomposites can be considered as a three-step process responsible for the removal of the compounds: (1) adsorption of reactants on the monolithic structure and diffusion to the biological active sites, (2) biodegradation by the fungi, and (3) diffusion of the products resulting from the biodegradation. Both treatments tested showed potential capacity to remove organic compounds, color, COD, and toxicity. The T. versicolor biocomposites were the most effective and responsible for the reduction in color (from 38.4 to 44.9?%), COD (from 42.8 to 63.8?%), and total phenolic content (from 85.3 to 88.7?%) after 29?days of treatment. The toxicity reduction on Portuguese OMW was minimal, but the use of composites on the Moroccan OMW caused a 9.5- to 19-fold reduction in toxicity. Furthermore, the biocomposites showed potential for re-utilization for more 29?days of treatment.  相似文献   
999.
1000.
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