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   271篇
  免费   15篇
林业   13篇
农学   8篇
基础科学   4篇
  16篇
综合类   51篇
农作物   4篇
水产渔业   9篇
畜牧兽医   151篇
园艺   1篇
植物保护   29篇
  2023年   3篇
  2021年   3篇
  2019年   7篇
  2018年   2篇
  2017年   7篇
  2016年   4篇
  2015年   5篇
  2014年   5篇
  2013年   20篇
  2012年   12篇
  2011年   11篇
  2010年   4篇
  2009年   9篇
  2008年   6篇
  2007年   13篇
  2006年   8篇
  2005年   12篇
  2004年   4篇
  2003年   8篇
  2002年   12篇
  2001年   6篇
  2000年   11篇
  1999年   8篇
  1998年   4篇
  1997年   7篇
  1996年   2篇
  1995年   5篇
  1993年   2篇
  1992年   4篇
  1991年   3篇
  1990年   6篇
  1989年   4篇
  1988年   2篇
  1987年   3篇
  1985年   4篇
  1984年   3篇
  1983年   3篇
  1979年   3篇
  1978年   6篇
  1977年   4篇
  1976年   4篇
  1972年   3篇
  1971年   3篇
  1970年   7篇
  1969年   3篇
  1967年   4篇
  1966年   2篇
  1937年   2篇
  1935年   1篇
  1934年   1篇
排序方式: 共有286条查询结果,搜索用时 31 毫秒
251.
Moldy corn in diets of gestating and lactating swine   总被引:1,自引:0,他引:1  
Moldy corn was substituted for normal corn in four dietary treatments to provide 0, 2.1, 3.7 and 4.8 ppm of zearalenone. The diets were fed to gilts from the day after first observed estrus through two gestation-lactation periods. Each diets was fed to 11 gifts initially. Overall reproductive performance appeared to decrease as the level of moldly corn in the diet increased, with fewer sows completing two parities and fewer piglets weaned per litter, especially from sows fed the highest level of moldy corn. Three-week-old gilts that nursed sows fed the highest level of moldy corn had increased weight of reproductive tracts. In 35-d-old gilts, symptoms of estrogenism increased as the level of moldy corn in the diet increased, even though there were no symptoms of estrogenism in the mature gilts or sows fed the same diets. Neither zearalenone nor its metabolites (alpha- and beta-zearalenol) were detected in milk obtained 1 or 14 d postpartum.  相似文献   
252.
Analyte comparisons between 2 clinical chemistry analyzers   总被引:1,自引:0,他引:1       下载免费PDF全文
The purpose of this study was to assess agreement between a wet reagent and a dry reagent analyzer. Thirteen analytes (albumin, globulin, alkaline phosphatase, alanine aminotransferase, amylase, urea nitrogen, calcium, cholesterol, creatinine, glucose, potassium, total bilirubin, and total protein) for both canine and feline serum were evaluated. Concordance correlations, linear regression, and plots of difference against mean were used to analyze the data. Concordance correlations were excellent for 8 of 13 analytes (r > or = 0.90); the correlations for albumin, potassium, and calcium were clinically unreliable. The linear regression analysis revealed that several analytes had slopes significantly different from unity, which was likely related to methodological differences. Compared to the wet reagent analyzer, the dry reagent analyzer showed excellent agreement for alkaline phosphatase, alanine aminotransferase, amylase (feline), urea nitrogen, cholesterol, creatinine, glucose, total bilirubin (canine), and total protein. However, it showed only slight to substantial agreement for amylase (canine), calcium, albumin, potassium, and total bilirubin (feline).  相似文献   
253.
Recent public concern about air pollution from pork production units has prompted more research to develop methods to reduce and control odors. Masking agents, enzymes and bacterial preparations, feed additives, chemicals, oxidation processes, air scrubbers, biofilters, and new ventilation systems have been studied. Research relating the effects of the swine diet on manure odors has been scarce. Introducing feed additives to bind ammonia, change digesta pH, affect specific enzyme activity, and mask odors has been either costly or not consistently successful. Recent research emphasis has focused on manipulating the diet 1) to increase the nutrient utilization of the diet to reduce excretion products, 2) to enhance microbial metabolism in the lower digestive tract to reduce excretion of odor-causing compounds, and 3) to change the physical characteristics of urine and feces to reduce odor emissions. Primary odor-causing compounds evolve from excess degradable proteins and lack of specific fermentable carbohydrates during microbial fermentation. Reductions in ammonia emissions by 28 to 79% through diet modifications have been reported. Limited research on reduction of other odorous volatile organic compounds through diet modifications is promising. Use of synthetic amino acids with reduced intact protein levels in diets significantly reduces nitrogen excretions and odor production. Addition of nonstarch polysaccharides and specific oligosaccharides further alters the pathway of nitrogen excretion and reduces odor emission. Continued nutritional and microbial research to incorporate protein degradation products, especially sulfur-containing organics, with fermentable carbohydrates in the lower gastrointestinal tract of pigs will further control odors from manure.  相似文献   
254.
Both P(n), and S(n), phases recorded at distances greater than 3000 kilometers in the western Pacific have substantial amounts of energy at high frequencies, in sorne instances as high as 12 hertz for P(n) and 15 hertz for S(n), A comparison of P(n) and S(n) spectra reveals generally higher energy levels and higher proportions of high-frequency to low-frequency energy for S(n) than for P(n). Estimates of the effective quality factor, Q, indicate that the efficiency of S(n) propagation may be two or three times that of P(n). First arrivals of Pn and Sn have apparent velocities in agreement with values for the uppermost mantle, whereas maximum-energy arrivals have apparent velocities in agreement with values for the lower crust.  相似文献   
255.
Covalent Maillard products of the reactions of carbonyl compounds with proteins are often described in the literature, but, until recently, evidence for their existence has been indirect. Cyclotene (2-hydroxy-3-methylcyclopent-2-enone), a common flavor compound, was incubated with a model food protein, ribonuclease, and found to cross-link the protein. Size exclusion high-performance liquid chromatrography and electrospray mass spectrometry of the early stages of the reaction provide strong evidence for covalent adducts that we believe to be intermediates in the cross-linking reaction.  相似文献   
256.
Ampicillin formulations were assayed by microbiological and hydroxylamine methods to determine whether thehydroxylamine analytical method is a suitable substitute for the microbiological method. Paired assay results by the 2 analytical methods were obtained on different strengths of tablet, capsule, and suspension, formulations containing ampicillin and ampicillin degradation compounds. Several statistical tests were used to assess the equivalence of the paired assay results. The data analyses indicate that the hydroxylamine method is a suitable substitute for the microbiological method for potency assays and stability studies of ampicillin formulations. The hydroxylamine method yielded slightly higher assay results than the microbiological method for severely degraded formulations.  相似文献   
257.
Infestations of aphids(Macrosiphum rosae L.) and of twospotted spider mites(Tetranychus urticae Koch) were examined in relation to growth and sporulation ofClonostachys rosea andBotrytis cinerea, and to suppression of the pathogen by the agent, in green rose leaves. Leaves were infested artificially with 10 aphids/leaflet for 3 h, or naturally with 15-30 aphids/leaflet for 7-12 days or with undetermined numbers of mites for 10-12 days. Leaves that had or had not been infested were inoculated withC. rosea, withB. cinerea, or withC. rosea plusB. cinerea. Germination incidence and germ tube growth ofC. rosea andB. cinerea on the phylloplane in most instances were much greater in leaves previously infested with aphids or mites compared with noninfested leaves. After combined inoculation,C. rosea suppressed germination ofB. cinerea from 47% to 19% in noninfested leaves, but in leaves that had been infested the agent was ineffective and germination incidence of the pathogen increased to 75-93%. Previous infestation with naturally introduced aphids or mites, but not brief infestations of artificially introduced aphids, markedly increased sporulation ofC. rosea after the leaves died during an initial 7-15 days of incubation on a paraquat agar medium, regardless of whether or notB. cinerea was present. Sporulation ofB. cinerea was similarly increased when inoculated alone. After 15-20 days, however, conidiophores of the agent or pathogen covered most of the leaf surface in these treatments. In leaves inoculated withC. rosea plusB. cinerea, the agent suppressed sporulation of the pathogen almost completely in both previously infested and noninfested leaves. Thus, aphid and mite infestations did not compromise the ability ofC. rosea to suppress inoculum production byB. cinerea in the leaves. Increased nutrient availability on the phylloplane through exudation or as honeydew or frass is proposed as a basis to explain effects of the pest infestations onC. rosea andB. cinerea.  相似文献   
258.
ABSTRACT Morphological characteristics and vegetative compatibility groups (VCGs) of 486 isolates of Glomerella cingulata, Colletotrichum gloeosporioides, and C. acutatum collected from apple leaves with Glomerella leaf spot (GLS) symptoms and fruit with bitter rot symptoms in the United States and Brazil were studied. From this collection, 155 isolates of G. cingulata (93 from fruit, 61 from leaves, and 1 from buds), 42 isolates of C. gloeosporioides from fruit, and 14 isolates of C. acutatum (10 from fruit and 4 from leaves) were studied using mitochondrial (mt)DNA restriction fragment length polymorphism (RFLP) haplotypes. A subset of 24 isolates was studied by examining the sequence of a 200-bp intron of the glyceraldehyde 3-phosphate dehydrogenase (GDPH) nuclear gene. In addition, 98 isolates were tested for pathogenicity on leaves of cvs. Gala and Golden Delicious in the greenhouse, and 24 isolates were tested for pathogenicity on fruit of cv. Gala in growth chambers. In total, 238 and 225 isolates of G. cingulata were separated into four distinct morphological types and six VCGs, respectively. Five morphological types and six VCGs were identified among 74 and 36 isolates of C. gloeosporioides, respectively. Three morphological types and four VCGs were identified among 74 and 23 isolates of C. acutatum, respectively. Seven different mtDNA RFLP haplotypes were observed within isolates of G. cingulata, two within isolates of C. gloeosporioides, and two within isolates of C. acutatum. Phylogenetic trees, inferred based on maximum likelihood and maximum parsimony methods using the intron sequence, produced similar topologies. Each species was separated into distinct groups. All isolates tested were pathogenic on fruit, though only isolates with specific VCGs and haplotypes were pathogenic to leaves. Vegetative compatibility was a better tool than molecular characters for distinguishing isolates of G. cingulata pathogenic on both leaves and fruit from the ones pathogenic only on fruit. Isolates of G. cingulata capable of causing both GLS and bitter rot were included in haplotypes and groups based on the sequence analysis of the 200-bp intron that also included isolates capable of causing bitter rot only. Additionally, isolates of G. cingulata from the United States and Brazil which cause GLS were included in different haplotypes and sequence analysis groups. Therefore, one hypothesis is that isolates of G. cingulata from the United States capable of causing both GLS on foliage and bitter rot on fruit may have arisen independently of Brazilian isolates of G. cingulata capable of causing both GLS and bitter rot, and the two groups of isolates may represent distinct populations.  相似文献   
259.
Applications of biotechnology for forest regeneration   总被引:4,自引:0,他引:4  
Grossnickle  Steven C.  Sutton  Ben C.S. 《New Forests》1999,17(1-3):213-226
The Forest Biotechnology Centre is an interdisciplinary research group dedicated to the development and application of advanced technology for the enhancement of forest regeneration. The Centre carries out contracts on behalf of clients in forest-related industries and government agencies. In addition, there are a number of long-term, in-house projects aimed at the development of proprietary technologies in genetics and propagation, and seedling production and establishment. Technical capabilities include: tissue culture, molecular genetics, pathology and microbial inoculants, and ecophysiology. These techniques are also being used to improve nursery culture regimes, disease assessment, planting regimes, and new product development for a variety of conifer species. Additional programs relate population genetics to adaptive traits, and develop clonal testing within elite families from tree-breeding programs.  相似文献   
260.
Sutton  William R.J. 《New Forests》1999,17(1-3):95-110
Ten thousand years ago our 5 million hunter-gatherer ancestors used, over the period of a year, about 200 species of local food items. Now, the nearly 6 billion global population gets 70 percent of its food from nine species of plants, one species of bird, and two species of mammals. This is despite global access to about 50,000 edible plants, as well as large numbers of bird and other animal species. We have concentrated our agricultural efforts on those species which are the most desirable, the most convenient, the most productive, and the most easily stored. Of equal importance, the species must be responsive to both genetic improvement and to management manipulation (i.e., domestication). Globally, very little of our food, except fish, now comes from wild sources.Although we use at least as much wood as we do food, wood supply (which still comes mostly from natural forests) is only now becoming limiting. There are no energy-efficient or environmentally acceptable substitutes for wood. The most likely means we have of satisfying the increasing global demand for wood is to obtain more of our wood from deliberately planted forests. Management of planted forests will increasingly parallel intensive agriculture. One consequence is that, of the 1,000 tree species we now use globally, we may eventually get most of our wood from four or five species. One of these tree species will be radiata pine (Pinus radiata D. Don). Radiata grows fast on a wide range of sites, has desirable wood properties, and responds well to both genetic improvement and stand management. The planted forest technology for radiata pine is probably the most advanced of any potential tree species. The evolution and success of radiata pine in New Zealand has major implications and lessons for the rest of the world.  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