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   1230篇
  免费   47篇
  国内免费   4篇
林业   65篇
农学   25篇
基础科学   18篇
  239篇
综合类   160篇
农作物   61篇
水产渔业   94篇
畜牧兽医   480篇
园艺   36篇
植物保护   103篇
  2023年   6篇
  2022年   11篇
  2021年   15篇
  2020年   18篇
  2019年   24篇
  2018年   23篇
  2017年   15篇
  2016年   14篇
  2015年   21篇
  2014年   18篇
  2013年   60篇
  2012年   72篇
  2011年   87篇
  2010年   62篇
  2009年   56篇
  2008年   80篇
  2007年   80篇
  2006年   86篇
  2005年   69篇
  2004年   72篇
  2003年   78篇
  2002年   85篇
  2001年   13篇
  2000年   13篇
  1999年   13篇
  1998年   16篇
  1997年   11篇
  1996年   12篇
  1995年   10篇
  1994年   9篇
  1993年   10篇
  1992年   5篇
  1991年   7篇
  1990年   4篇
  1989年   6篇
  1988年   10篇
  1987年   9篇
  1986年   11篇
  1985年   11篇
  1984年   9篇
  1983年   10篇
  1982年   6篇
  1980年   7篇
  1979年   2篇
  1978年   4篇
  1976年   2篇
  1975年   6篇
  1974年   3篇
  1973年   2篇
  1967年   2篇
排序方式: 共有1281条查询结果,搜索用时 281 毫秒
261.
ABSTRACT A marked-isolate, release-recapture experiment was conducted to assess the relative contributions of seed-transmitted (released isolates) versus all other inocula to foliar and grain populations of Phaeosphaeria nodorum in winter wheat rotated with nonsusceptible crops in New York and Georgia, United States. Seed infected with two distinct groups of marked isolates of P. nodorum containing rare alleles (identified by amplified fragment length polymorphisms [AFLPs]) and balanced for mating type were planted in experimental field plots in two locations in each state. Recapture was done by isolating P. nodorum from leaves showing necrotic lesions at spring tillering and flowering stages, and mature grains from spikes showing glume blotch. Isolates from these samples were genotyped by AFLPs and categorized as released or nonreleased to infer sources of inoculum. Both infected seed and other sources of the pathogen contributed significant primary inocula to populations recovered from leaves and harvested grain. Seed-transmitted genotypes accounted for a total of 57% of all isolates recovered from inoculated plots, with a range of 15 to 90% of the populations of P. nodorum collected over the season in individual, inoculated plots at the four locations. Plants in the noninoculated control plots also became diseased and 95% or more of the isolates recovered from these plots were nonreleased genotypes. Although other potential sources of P. nodorum within and adjacent to experimental plots were not ruled out, nonreleased genotypes likely were derived from immigrant ascospores potentially from sources at a considerable distance from the plots. Our results suggest that, although reduction of seedborne inoculum of P. nodorum may delay foliar epidemics, this strategy by itself is unlikely to result in high levels of control in eastern North America because of the additional contribution from alternative sources of inoculum.  相似文献   
262.
The US Army Veterinary Corps is composed of approximately 420 active-duty and 200 reserve-component veterinary officers, with 40 to 45 new veterinarians joining the active ranks each year. This article briefly summarizes the training that members of the veterinary corps receive in preparation for their diverse range of duties in service to the United States.  相似文献   
263.
Increased competition for veterinary school admission has created a need to determine whether individual students are likely to be successful candidates for veterinary school admission early in their undergraduate careers. Students invest considerable time and money in pre-veterinary courses of study, hoping for acceptance into professional veterinary school. A forecasting model was developed to predict the likelihood of students with particular characteristics gaining acceptance. Characteristics such as gender, age, size of high school, and ACT, are known upon entrance into college and can be used to determine the likelihood of an individual's being accepted. Data were gathered from the Louisiana State University College of Veterinary Medicine (LSU-CVM) admissions for all students applying to veterinary school for the classes of 2006 through 2008 from the top two agricultural programs in the state in terms of quantity of applicants to veterinary school: Louisiana State University and Louisiana Tech University. A one-way ANOVA was used to examine whether there were any statistical differences between known demographic and performance variables and acceptance into veterinary school. A logit forecasting model was then estimated to predict the likelihood of gaining acceptance into veterinary school based only on variables known early in the student's undergraduate career. Age, gender, and ACT scores were determined to be important variables in determining the likelihood of gaining admission. Overall, the forecasting model is of use in assigning probabilities of acceptance into veterinary school for specific student profiles, which can assist in one-on-one assistance from advisor to student.  相似文献   
264.
BACKGROUND: Lactoferrin is a colostral glycoprotein with antimicrobial properties. HYPOTHESES: (1) Serum lactoferrin and immunoglobulin G (IgG) concentrations are correlated and increase in healthy foals after ingestion of colostrum; (2) compared to healthy foals, ill foals will have lower lactoferrin concentrations that correlate with their IgG concentration, neutrophil count, the diagnosis of sepsis, and survival; and (3) plasma concentrations of lactoferrin will be less than serum concentrations. ANIMALS: Healthy foals (n = 16), mature horses (n = 10), and ill foals 1-4 days old (n = 111) that were examined for suspected sepsis were used for blood collection. Colostrum was obtained from 10 healthy mares unrelated to the foals. METHODS: Blood was obtained from the healthy foals at birth and 1-3 days of age and from the ill foals at admission. Serum IgG was quantified by single radial immunodiffusion (SRID). Lactoferrin concentrations in colostrum and blood were determined by an enzyme-linked immunosorbant assay. The sepsis score, blood culture results, neutrophil counts, and survival were obtained on ill foals. RESULTS: The mean colostral lactoferrin concentration was 21.7 microg/mL. Compared to values at birth, serum IgG (18+/-2 versus 2,921+/-245 mg/dL, SEM) and lactoferrin (249+/-39 versus 445+/-63 ng/mL, SEM) concentrations were significantly greater in healthy foals 1-3 days old. Serum lactoferrin concentration in 1-3-day-old healthy foals was not different from mature horses or ill foals. IgG and lactoferrin concentrations were significantly correlated only in healthy foals. Serum lactoferrin concentrations were significantly lower in ill neutropenic foals. The serum IgG concentration was significantly lower in ill foals as compared to healthy foals. Only serum IgG was significantly less in ill foals with a positive sepsis score and in nonsurvivors, Plasma lactoferrin concentrations were lower than serum concentrations, although values were significantly correlated. CLINICAL IMPORTANCE: Although both serum IgG and lactoferrin concentrations increase in healthy foals after ingestion of colostrum, only serum IgG is significantly correlated with the sepsis score and outcome.  相似文献   
265.
266.
267.
268.
Because of the large number of cultivars that require examination in the development of spring wheat (Triticum aestivum L.) cultivars, breeding programs use predictive methods to test end use quality. The Mixograph is a widely used predictive test with which end use quality of many genotypes can be assessed in a short time. By comparison, the Mixolab is a relatively new device with additional capability that might be used for the same purpose. Our objective was to document variability of, and relationships among, 20 parameters obtained from Mixolab, Mixograph, and bake tests. Tests were performed on flour from 18 genotypes grown in 20 environments. Both genotype and environment had significant effects on quality parameter values. Several Mixograph and Mixolab parameters were highly significantly correlated, particularly when genotype mean values over environments were considered. Correlations between loaf volume and Mixolab parameters within environments were inconsistent and suggest that average genotype values over environments will be most useful. For example, the correlation between Mixolab stability and loaf volume (r = 0.25, P < 0.001) was much higher when genotype averages (r = 0.70, P < 0.001) were considered. Our results show that selection for Mixolab stability and water absorption should help delineate and improve the selection of genotypes with greater loaf volume.  相似文献   
269.
270.
Forest fires release substantial amounts of carbon (C). Much of it is emitted to the atmosphere, but some is deposited within ash on the ground. Little is known about amount and types of C deposited in ash. Here, we quantify total C, and total inorganic, water-soluble and particulate organic fractions deposited in ash during the catastrophic 2009 ‘Black Saturday’ wildfires in Australia. These fires coincided with the highest air temperatures and lowest humidity ever recorded in the local area, which, combined with high fuel loads of mostly long unburnt eucalypt forests, generated extreme burning conditions. In three mixed-species eucalypt forest sites sampled, the canopy, understorey and litter fuels were almost completely consumed, resulting in substantial ash deposition (mean, 81.9 t ha?1), with 5.9 t ha?1 of C being transferred from vegetation to the forest floor. In five temperate rainforest sites sampled, the canopy was not burnt and ash deposition was lower (mean, 48.3 t ha?1) than in the mixed-species eucalypt forest, but overall their higher C content resulted in higher C deposition (8.1 t ha?1). In all cases, most C contained in ash was organic and its pyrogenic nature infers increased resistance to degradation. Pyrogenic C is viewed by many as an important C sink, which could contribute to long-term C sequestration when incorporated into soils or sediments. Our results highlight the potential importance of the pyrogenic C pool in freshly deposited ash and, therefore, the necessity of a systematic and detailed analysis of ash deposition and C forms in ash to improve our understanding of C fluxes by forest fires.  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