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   614篇
  免费   46篇
林业   45篇
农学   10篇
基础科学   9篇
  93篇
综合类   80篇
农作物   25篇
水产渔业   33篇
畜牧兽医   303篇
园艺   17篇
植物保护   45篇
  2023年   5篇
  2022年   8篇
  2021年   14篇
  2020年   28篇
  2019年   15篇
  2018年   26篇
  2017年   28篇
  2016年   38篇
  2015年   15篇
  2014年   20篇
  2013年   37篇
  2012年   34篇
  2011年   43篇
  2010年   22篇
  2009年   28篇
  2008年   31篇
  2007年   20篇
  2006年   15篇
  2005年   14篇
  2004年   16篇
  2003年   15篇
  2002年   15篇
  2001年   6篇
  2000年   10篇
  1999年   9篇
  1998年   16篇
  1997年   10篇
  1996年   6篇
  1995年   5篇
  1994年   9篇
  1993年   8篇
  1992年   9篇
  1991年   10篇
  1990年   6篇
  1989年   7篇
  1988年   9篇
  1983年   3篇
  1982年   2篇
  1979年   2篇
  1978年   2篇
  1972年   5篇
  1971年   3篇
  1967年   2篇
  1966年   2篇
  1954年   2篇
  1953年   2篇
  1952年   3篇
  1943年   2篇
  1940年   2篇
  1901年   2篇
排序方式: 共有660条查询结果,搜索用时 125 毫秒
51.
52.
Digestion of green plants in the gastrointestinal (GI) tract produces degradation products from chlorophyll that cause ingesta and feces to be highly fluorescent. This property was exploited for development and construction of instruments to noninvasively detect minute quantities of feces on meat samples in real time. The presence of feces on meat products is a primary source of foodborne pathogens, such as Escherichia coli O157:H7 and Salmonella. This new technology provides a rapid and accurate alternative to the practice of visual inspection and augments more time-consuming biological testing methods. This innovation can assist meat processors and government inspectors in their efforts to provide safe and wholesome food to consumers.  相似文献   
53.
Understanding the effects of oil contamination on the composition and function of soil microbiota entails investigation of the effects of a mixture of hydrocarbons at the community level in a complex environmental matrix. One approach to this difficult problem is to ally a community-level fingerprinting approach with bioassays that have a physiological or functional implication. Two contrasting refined oils (paraffin and motor oil) were used to contaminate soil microcosms, and a simulated bioremediation treatment with nutrient-addition was applied. The indigenous microorganisms were monitored over 103 d using complementary community-level techniques (carbon source physiological profiling using Biolog® microplates, and phospholipid fatty acid (PLFA) profiling). Changes in the toxicity of the applied oils were monitored using luminescent bacterial bioassays, including Vibrio fischeri and a hydrocarbon-degrading Pseudomonas putida strain. Distinct shifts in microbial community structure and C source utilization profiles were observed as a result of oil contamination. There was some evidence that bioremediated soils were returning to control values by the end of the experiment. This was supported by the bioassay results which showed an initial increase in toxicity as a result of the oil addition which had then decreased by the conclusion of the experiment. The two oils exhibited markedly different toxicity towards the bioassay organisms, with species-specific differences in response. This oil-specific difference was also found in the PLFA profiles which showed the two oil types selected different microbial communities.  相似文献   
54.
55.
56.
Risk assessment of dietary exposure to pesticides using a Bayesian method   总被引:2,自引:0,他引:2  
Risk assessment of pesticides can be a statistically difficult problem because pesticides occur only occasionally, but they may occur on multiple components in the diet. A Bayesian statistical model is presented which incorporates multivariate modelling of food consumption and modelling of pesticide measurements which are for a large part below a measurement threshold. It is shown that Bayesian modelling is feasible for a limited number of food components, and that in a data-rich situation the model compares well with an empirical Monte Carlo modelling.  相似文献   
57.
58.
OBJECTIVE: To determine whether urine protein-to-creatinine ratio (UP:C) > or = 1.0 at initial diagnosis of chronic renal failure (CRF) is associated with greater risk of development of uremic crises, death, and progression of renal failure in dogs. DESIGN: Prospective cohort study. ANIMALS: 45 dogs with CRF PROCEDURE: Dogs were prospectively assigned to 2 groups on the basis of initial UP:C < 1.0 or 2 > or = 1.0. The association between magnitude of proteinuria and development of uremic crises and death was determined before and after dogs with initial UP:C > or =1.0 were assigned to 3 subgroups and compared with dogs with initial UP:C < 1.0. Changes in reciprocal serum creatinine concentration were used to estimate decrease in renal function. RESULTS: Initially, dogs had similar clinical characteristics with the exception of systolic blood pressure and UP:C. Relative risks of development of uremic crises and death were approximately 3 times higher in dogs with UP:C > or =1.0, compared with dogs with UP:C < 1.0. Relative risk of adverse outcome was approximately 1.5 times higher for every 1-unit increment in UP:C. The decrease in renal function was of greater magnitude in dogs with UP:C > or =1.0, compared with dogs with UP:C < 1.0. CONCLUSIONS AND CLINICAL RELEVANCE: Initial UP:C > or =1.0 in dogs with CRF was associated with greater risk of development of uremic crises and death, compared with dogs with UP:C < 1.0. Initial determinations of UP:C in dogs with naturally occurring CRF may be of value in refining prognoses.  相似文献   
59.
Indices of renal function: reference values in normal horses   总被引:1,自引:0,他引:1  
Urine and blood samples were taken at the same time from normal adult horses presented for routine investigations to establish reference values for a variety of parameters reported to be useful in the clinical evaluation of renal function. Blood biochemical values were consistent with previous studies and had well-defined normal ranges. Parameters representing urine concentration and electrolyte excretion however, varied widely reflecting the ability of the healthy kidney to change the composition of urine in response to differences in environment and management. Percent creatinine clearance ratios for potassium in particular were lower than those reported in normal horses in previous studies. Rational interpretation of these latter measurements should accept a wide range of normal values and management conditions must be considered in this interpretation.  相似文献   
60.
That pesticide use in public areas in Denmark has been significantly reduced during the period 1995 to 2002 is shown when comparing three surveys carried out by the Danish Forest and Landscape Research Institute (DFLRI) with funding from the Danish Environmental Protection Agency. During that period, the total registered public use of pesticides was reduced from 28.8 tonnes active ingredients to 6.3 tonnes, corresponding to a 78% reduction. In 2002, the Danish counties and state institutions had reduced their total pesticide use by 80% and 73%, respectively, compared to 1995 figures. Similarly, the Danish municipalities reduced their use by 83% from 1995 to 2002. Surveys of municipal pesticide use carried out in 1995, 2000 and 2002 have been used as the basis for determining the factors that have influenced municipal reductions of pesticide use. The 2000 and 2002 trends can be explained partly on the basis of the figures for 1995 use. The trend for 2002 can also be partially explained by the political parties in power in the municipalities during the phase-out period. The models used account for up to 30% of the total variations, meaning that the pesticide use of individual municipalities is very much influenced by other, non-definable factors such as tradition.  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