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   499篇
  免费   34篇
林业   43篇
农学   29篇
基础科学   3篇
  103篇
综合类   33篇
农作物   55篇
水产渔业   82篇
畜牧兽医   133篇
园艺   8篇
植物保护   44篇
  2024年   1篇
  2023年   1篇
  2022年   16篇
  2021年   26篇
  2020年   29篇
  2019年   29篇
  2018年   45篇
  2017年   35篇
  2016年   33篇
  2015年   25篇
  2014年   23篇
  2013年   37篇
  2012年   36篇
  2011年   42篇
  2010年   21篇
  2009年   16篇
  2008年   19篇
  2007年   5篇
  2006年   9篇
  2005年   7篇
  2004年   9篇
  2003年   5篇
  2002年   6篇
  2001年   6篇
  2000年   5篇
  1999年   6篇
  1998年   2篇
  1997年   5篇
  1996年   2篇
  1995年   2篇
  1994年   2篇
  1993年   2篇
  1992年   2篇
  1990年   2篇
  1989年   2篇
  1988年   3篇
  1987年   3篇
  1986年   3篇
  1985年   2篇
  1984年   6篇
  1983年   1篇
  1982年   1篇
  1980年   1篇
排序方式: 共有533条查询结果,搜索用时 31 毫秒
121.
Saudi Arabia is an arid and the largest country in the middle east with a total land area of 2.253 x 10(6) km2. Recent urban and rural expansion has shown manifold increases in water use in various sectors. Water resources are limited and non-renewable coupled with unpredicted scanty rainfall. In order to meet the rising water needs, evaluation of water quality is important for allocation to various uses. A total of 101 well water samples were collected from Al-Ahsa Oasis. Water samples were analyzed for total salt concentration, pH, Ca, Mg, Na, K, HCO3, Cl, SO4, NO3, F and B contents. Soil Salinity Development (SSD), adjusted sodium adsorption ratio (adj.SAR), adjusted sodium adsorption ratio (adj. R(Na)) and Exchangeable Sodium Percentage (ESP) were calculated. The EC of groundwater ranged between 1.23 and 5.05 dS m(-1). Sodium was the most abundant cation followed by Ca, Mg and K in descending order. Chloride was the most abundant anion followed by SO4 and HCO3 in groundwater of Al-Ahsa Oasis. A significant correlation was found between Na and Cl (R2 = 0.936). Thermodynamics calculation revealed that an appreciable amount of Ca and Mg is associated with Cl and SO4 ions. The SAR and ESP values are within the permissible limits according to Ayers and Westcot, 1985. The NO3 concentration is within safe limits for drinking purpose according to WHO (1998) standards. The Saturation Indices (SI) indicated that groundwater is under-saturated (negative SI) with respect to certain minerals (for example: calcite, dolomite, gypsum, anhydrite, halite, pyrite, fluorite and aragonite) and oversaturated (positive SI) with respect to some other minerals (For example: Goethite, Siderite and hematite). The negative saturation index (SI) reveals that most of minerals are in un-saturated state and will dissolve more Ca and Mg into the soil solution after irrigation. A good relationship exists between Cl and other ions (Na, Ca and Mg) as well as between SO4 and Ca and Mg ion of groundwater. The salinity and sodicity hazards of groundwater of Al-Ahsa Oasis were classified as C3S1 and C4S2 i.e., high salinity with medium sodicity problems. The predicted soil salinity suggested application of 15-20% leaching requirements to keep soil salinity within permissible limits. Cultivation of slight to moderate salt and sodium tolerant crops is recommended for optimal agricultural production and efficient water use.  相似文献   
122.
The digestion and Volatile Fatty Acid (VFA) production from rice straw and oil palm fronds by cellulolytic bacteria isolated from the termite Coptotermes curvignathus were investigated. The bacteria were Acinetobacter strain Raminalimon, Enterobacter aerogenes strain Razmin C, Enterobacter cloacae strain Razmin B, Bacillus cereus strain Razmin A and Chryseobacterium kwangyangense strain Cb. Acinetobacter strain Raminalimon is an aerobic bacterium, while the other species are facultative anaerobes. There were significant differences (p<0.05) among the bacteria for Dry Matter (DM) lost and acetic acid production from rice straw and Acinetobacter strain Raminalimon showed the highest activity. The facultative bacteria C. kwangyangense strain Cb (cfu mL(-1) 231 x 10(-6), OD: 0.5), E. cloacae (cfu mL(-1) 68 x 10(-7), OD: 0.5) and E. aerogenes (cfu mL(-1) 33 x 10(-7), OD: 0.5) were used for digestion study with the rumen fluid microflora. The in vitro gas production technique was applied for the comparative study and the parameters measured were pH, gas (volume), dry matter lost, acetic acid, propionic acid and butyric acid concentrations. pH was not significantly (p<0.05) different among the five treatments. The bacterium C. kwangyangense strain Cb showed the highest activity (p<0.05) for DM lost, acetic acid, propionic acid and butyric acid production from rice straw when compared to the other bacterial activities. There was no significance (p<0.05) difference between the three bacteria for the dry matter lost of oil palm fronds but the production of Volatile Fatty Acids (VFA) was significantly (p<0.05) high in the treatment which was inoculated with C. kwangyangense strain Cb. The Gen Bank NCBI/EMBL accession numbers for the bacterial strains are EU332791, EU305608, EU305609, EU294508 and EU169201.  相似文献   
123.
Coconut palm ( Cocos nucifera ), oil palm ( Elaeis guineensis ), Bermudagrass ( Cynodon dactylon ) and Madagascar periwinkle ( Catharanthus roseus ) with symptoms indicative of phytoplasma disease were collected from different locations in Malaysia. PCR assays employing phytoplasma universal rRNA gene primers P1/P7 alone or P1/P7 followed by R16F2n/R16R2 detected phytoplasmas in eight out of 20 Malayan Red Dwarf (MRD), nine out of 12 Malayan Yellow Dwarf (MYD) and 12 out of 12 Malayan Tall (MT) coconut palms displaying coconut yellow decline symptoms. Positive detections were also obtained from six out of six oil palm seedlings showing symptoms of yellowing and necrosis, from 10 out of 10 Bermudagrass samples with white leaf symptoms, and from eight out of eight periwinkle plants showing phyllody, virescence, little leaf, proliferation and foliar yellowing. Phytoplasmas were not detected in any of the symptomless plants tested. Sequencing and phylogenetic analysis of PCR products determined that phytoplasmas infecting both MRD and MT coconuts and Bermudagrass in Serdang, Selangor State, were all members of the 16SrXIV ' Candidatus Phytoplasma cynodontis' group, whereas isolates in periwinkle in Serdang were all members of the 16SrI ' Ca. Phytoplasma asteris' group. However, the phytoplasmas detected in MYD coconuts and oil palms from Banting, Selangor State, and in periwinkle from Putrajaya were collectively very similar (99%), but shared <97·5% similarity with 16S rDNA sequences of all other known phytoplasmas, indicating that they represent a novel taxonomic group. Thus, at least two phylogenetically distinct phytoplasmas are associated with the coconut yellow decline syndrome in Malaysia, both of which were also detected in other plant species.  相似文献   
124.
Abstract.— Amino acid profiles of freshwater prawn Macrobrachium rosenbergii were determined during early larval stages (I-IX) to provide some baseline biochemical information of the growing larvae. The larvae obtained from several females were stocked into three 250-L tanks at a density of 30 larvae/L. The feeding regime consisted of newly hatched Artemia nauplii and egg custard containing 5% cod liver oil. For each developmental stage, larval samples from each experimental tank were pooled, freeze dried and after acid hydrolysis, the quantification of amino acids was done by a reverse phase high performance liquid chromatography ( N = 2). The highest represented of the total amino acids were for glutamic acid and phenylalanine (with cystine) with ranges from 13.4–16.6 and 9.7–11.5%, respectively, whereas tryptophan (1.4–1.6%). methionine (1.4–2.7%) and histidine (2.9–4.2%) were relatively lower. The levels of the following essential amino acids did not significantly change during larval development: arginine, leucine, phenylalanine (plus cystine), threonine, tryptophan and valine. Despite statistically significant changes that were observed in levels of some amino acids, amino acid composition appeared to be relatively unchanged during the larval growth. The results may suggest that the amino acid requirements of the freshwater prawn is relatively constant during larval life and can be satistied by a suitable protein source that resembles the larval amino acid profile.  相似文献   
125.
NADPH-dependent inhibition of hepatic microsomal carboxylesterase by a derivative of monocrotophos (coded as RPR-5) was studied in rat and Japanese quail as a measure of monooxygenase-catalysed activation of RPR-5. There was NADPH-dependent inhibition of hepatic microsomal α-naphthyl acetate esterase (carboxylesterase) both in rat and quail, indicating monooxygenase-catalysed formation of an oxon that subsequently phosphorylated α-NaE. The pattern of in-vitro metabolism of 14C-labelled RPR-5 by 11000g supernatant (11-S), microsomes and 105000g supernatant (105-S) fractions of rat and quail livers suggested the involvement of microsomal monooxygenases and carboxylesterases. A radiolabelled metabolite (M2) was tentatively identified as an acid produced by carboxyl esterase attack. In rat, metabolism by microsomal and cytosolic (105-S) carboxylesterases appeared to predominate with relatively little oxidative metabolism. In quail, putative microsomal carboxylesterase hydrolysis of RPR-5 was much lower than in the rat with almost neglible hydrolysis by cytosolic fractions. Also, production of M2 by quail microsomes was substantially reduced after addition of NADPH, suggesting inhibition of a carboxyl esterase by the oxon of RPR-5. Differences in this detoxification of RPR-5 between rat and quail may be an important factor in determining selective toxicity and the results underline the importance of relating metabolism to toxicity when selecting animal models for toxicity testing.  相似文献   
126.
Journal of Crop Science and Biotechnology - Flash flood causes a serious damage to rice crops in northern and eastern parts of Bangladesh almost every year. This study was designed to identify...  相似文献   
127.
Leaf blight is a common disease affecting Sansevieria trifasciata in many countries, including Malaysia. In the present study, Fusarium isolates were consistently recovered from the diseased leaves collected from various locations throughout the country. Based on morphology and multigene phylogenetic analysis using mitochondrial small subunit (mtSSU), intergenic spacer region (IGS) and translation elongation factor 1-α (TEF1-α) gene sequences, seven Fusarium species were identified, with F. oxysporum being the most prevalent (67.6%) among 34 isolates. Pathogenicity tests resulted in the discovery of pathogenic isolates that belonged to F. oxysporum, F. proliferatum, and F. pseudocircinatum, whereas all isolates of F. brachygibbosum, F. concentricum, F. mangiferae, and F. solani were nonpathogenic. The results suggest that several Fusarium species are accountable for causing disease on S. trifasciata in Malaysia.  相似文献   
128.
The influence of fever, induced by different agents, on the disposition kinetics of imidocarb was determined in goats. Escherichia coli endotoxin (0.2 microgram/kg), Trypanosoma evansi (10(7) in 1 ml sterile glucose citrate), and Infectious Bovine Rhinotracheitis virus (10(6.5)TCID50) were the agents administered to induce the febrile state. In control and febrile animals the two-compartment model was used to describe the disposition kinetics of the drug. Fever caused significant changes to occur in the apparent volume of distribution and the body (systemic) clearance of imidocarb, but the half-life remained unchanged. The statistical significance of the changes in these pharmacokinetic parameters varied with the etiology of the febrile state. E. coli endotoxin and IBR virus caused corresponding decreases in apparent volume of distribution and clearance of imidocarb, while fever induced with T. evansi caused highly significant increases in both pharmacokinetic parameters. It was concluded that the alterations in the disposition kinetics of imidocarb that occurred in the febrile goats were related not only to the febrile reaction per se but also to the pathophysiology of the disease condition.  相似文献   
129.
Mondal  Santu  Bhakat  M.  Singh  A.  Mohanty  T. K.  Abdullah  M.  Yadav  S. K.  Kumar  R. 《Tropical animal health and production》2019,51(7):1823-1827

Zebu bulls are a shy breeder and they exhibit optimum libido in the presence of females with estrus phase. Continuous semen collection with the use of male dummy leads to lack of adequate sexual stimulation. Therefore, the present study was designed to test the effect of estrus-specific molecule(s) for effective sexual preparation of donor bulls. The bulls were divided into normal and poor libido group, five bulls in each group by taking 1-month control study data after collecting the information of individual bull’s sexual behaviour during semen collection by regular semen collector. The bulls were never being exposed to female animals and semen was collected by an artificial vagina. The ten animals were exposed to a glycerol-water solution (50/50 v:v) as control and then exposed to estrus-specific molecules one by one. The estrus-specific molecules like squalene, 1-iodoundecane, acetic acid, coumarin, propionic acid, oleic acid, and 2-butanone were purchased from Sigma-Aldrich Company, USA, and the molecules were solubilised individually in a non-pressurised aerosol dispenser as 1.0% concentration in glycerol-water solution (50/50, v:v). Identical bulls were used as the control and exposed to each molecule one by one by giving a refractory period of 14 days. A nasal spray of acetic acid or 2-butanone significantly (p < 0.05) reduced reaction time (RT) and total time taken to ejaculate (TTTE) in normal libido bull group. Semen volume, sperm concentration, and the total number of sperm per ejaculation obtained did not show significant improvement in the normal libido group of bulls after the application of estrus-specific molecules as compared to the control. In poor libido group, acetic acid, oleic acid, and 2-butanone application showed significant (p < 0.01) improvement in RT and TTTE as compared to the control group, whereas semen production variables like sperm concentration and total sperm output per ejaculation increased significantly (p < 0.05) except semen volume. There was significant (p < 0.01) reduction in RT (%) and TTTE (%) after the application of acetic acid followed by 2-butanone and oleic acid. The sperm concentration and total sperm output per ejaculation were more after the application of each molecule but significant increase (p < 0.05) in sperm concentration was observed with 2-butanone (11.42%), acetic acid (11.42%), and oleic acid (10.13%), whereas total sperm output per ejaculation increased significantly (p < 0.05) only after the application of acetic acid and 2-butanone (24.75% and 26.84%). Hence, it can be concluded that acetic acid, 2-butanone, and oleic acid are effective for better sexual preparation of Sahiwal bulls and total sperm output per ejaculation.

  相似文献   
130.
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