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   1185篇
  免费   140篇
  国内免费   12篇
林业   93篇
农学   58篇
基础科学   12篇
  233篇
综合类   115篇
农作物   58篇
水产渔业   131篇
畜牧兽医   570篇
园艺   10篇
植物保护   57篇
  2023年   14篇
  2022年   18篇
  2021年   32篇
  2020年   30篇
  2019年   45篇
  2018年   53篇
  2017年   53篇
  2016年   34篇
  2015年   36篇
  2014年   62篇
  2013年   90篇
  2012年   69篇
  2011年   73篇
  2010年   59篇
  2009年   40篇
  2008年   58篇
  2007年   43篇
  2006年   46篇
  2005年   47篇
  2004年   38篇
  2003年   37篇
  2002年   39篇
  2001年   28篇
  2000年   30篇
  1999年   22篇
  1998年   11篇
  1997年   10篇
  1996年   11篇
  1995年   16篇
  1994年   11篇
  1993年   5篇
  1992年   12篇
  1991年   9篇
  1990年   8篇
  1989年   10篇
  1988年   8篇
  1987年   12篇
  1986年   9篇
  1985年   12篇
  1984年   6篇
  1983年   5篇
  1982年   5篇
  1980年   7篇
  1979年   7篇
  1977年   4篇
  1975年   9篇
  1974年   10篇
  1973年   4篇
  1972年   5篇
  1968年   5篇
排序方式: 共有1337条查询结果,搜索用时 265 毫秒
21.
Plant Foods for Human Nutrition - ADP-glucose pyrophosphorylase (AGPase) is a key enzyme of starch synthesis in seeds, tubers and fruits. UDP-glucose pyrophosphorylase (UGPase) is an important...  相似文献   
22.
Microbial communities can subsist at depth in marine sediments without fresh supply of organic matter for millions of years. At threshold sedimentation rates of 1 millimeter per 1000 years, the low rates of microbial community metabolism in the North Pacific Gyre allow sediments to remain oxygenated tens of meters below the sea floor. We found that the oxygen respiration rates dropped from 10 micromoles of O(2) liter(-1) year(-1) near the sediment-water interface to 0.001 micromoles of O(2) liter(-1) year(-1) at 30-meter depth within 86 million-year-old sediment. The cell-specific respiration rate decreased with depth but stabilized at around 10(-3) femtomoles of O(2) cell(-1) day(-1) 10 meters below the seafloor. This result indicated that the community size is controlled by the rate of carbon oxidation and thereby by the low available energy flux.  相似文献   
23.
A kernel screening assay (KSA) was used to assess the genetic and environmental effects on the vulnerability of maize to aflatoxin accumulation. Kernels of 26 inbred lines that had been grown in seven environments, and 190 lines of the Intermated B73xMo17 (IBM) population grown in one location in the United States, were inoculated with a toxigenic strain of A. flavus and incubated in the dark at 30°C for 6 days. Percent kernel colonization (PKC), sporulation and aflatoxin were influenced by the maize genotypes (G), the location (“ear environment” or E) and the GxE interactions. Overall, low broad‐sense heritabilities were observed for PKC, sporulation and aflatoxin. PKC was significantly correlated with sporulation in all environments. Aflatoxin was positively correlated with colonization for two and with sporulation for all ear environments. Higher grain sulphur or magnesium in IBM was associated with less colonization or aflatoxin. Postharvest susceptibility of maize to aflatoxin is thus influenced by factors that are modulated by the ear environment. In a KSA, sporulation could be a proxy test for aflatoxin accumulation.  相似文献   
24.
25.
Samples from multiple animals may be pooled and tested to reduce costs of surveillance for infectious agents in aquatic animal populations. The primary advantage of pooling is increased population‐level coverage when prevalence is low (<10%) and the number of tests is fixed, because of increased likelihood of including target analyte from at least one infected animal in a tested pool. Important questions and a priori design considerations need to be addressed. Unfortunately, pooling recommendations in disease‐specific chapters of the 2018 OIE Aquatic Manual are incomplete and, except for amphibian chytrid fungus, are not supported by peer‐reviewed research. A systematic review identified only 12 peer‐reviewed aquatic diagnostic accuracy and surveillance studies using pooled samples. No clear patterns for pooling methods and characteristics were evident across reviewed studies, although most authors agreed there is a negative effect on detection. Therefore, our purpose was to review pooling procedures used in published aquatic infectious disease research, present evidence‐based guidelines, and provide simulated data examples for white spot syndrome virus in shrimp. A decision tree of pooling guidelines was developed for use by peer‐reviewed journals and research institutions for the design, statistical analysis and reporting of comparative accuracy studies of individual and pooled tests for surveillance purposes.  相似文献   
26.
A simple apparatus was developed to study metabolic gases in the rice rhizosphere. With this device, a positive rhizosphere effect of rice was demonstrated on three soil microbial activities: N2 fixation, CH4 formation and denitrification.  相似文献   
27.
The stable production of high‐quality fry in marine aquaculture is still hampered by unpredictable mortality caused by infectious diseases during larval rearing. Consequently, the development of new biocontrol agents is crucial for a viable aquaculture industry. The bacterial energy storage compound poly‐β‐hydroxybutyrate (PHB) has been shown to exhibit beneficial properties on aquatic organisms such as enhanced survival, growth, disease resistance and a controlling effect on the gastrointestinal microbiota. However, the effect of PHB on the developing immune system of fish larvae has so far not been investigated. In this study, the effect of feeding PHB‐enriched Artemia nauplii on survival, growth and immune response in European sea bass (Dicentrarchus labrax) postlarvae was examined. Amorphous PHB was administered to 28‐day‐old sea bass postlarvae over a period of 10 days. The survival and growth performance were monitored, and the expression of 29 genes involved in immunity, growth, metabolism and stress‐response was measured. While the expression of the insulin‐like growth factor 1 (igf1), an indicator of relative growth, was upregulated in response to feeding PHB, the larval survival and growth performance remained unaffected. After 10 days of PHB treatment, the expression of the antimicrobial peptides dicentracin (dic) and hepcidin (hep) as well as mhc class IIa and mhc class IIb was elevated in the PHB fed postlarvae. This indicates that PHB is capable of stimulating the immune system of fish early life stages, which may be the cause of the increased resistance to diseases and robustness observed in previous studies.  相似文献   
28.
The current study investigated the effects of oyster mushroom Pleurotus ostreatus, extract on immunological and hematological parameters of rainbow trout, Oncorhynchus mykiss. The fish were fed diets containing 0 (control), 1, and 2% supplementation of the oyster mushroom extract for 6 wk. Blood samples were collected weekly for the first 6 weeks. After 6 wk of feeding, the fish were challenged with Lactococcus garvieae and mortality was recorded. The results of this study showed that feeding rainbow trout an oyster mushroom extract–supplemented diet stimulated phagocytic activity of phagocytic cells, lysozyme activity, and myeloperoxidase activity in serum, but it did not significantly affect the total serum immunoglobulin level. At the same time, a significant increase was found in the number of neutrophils, monocytes, and total white blood cells. Fish fed the diet supplemented with oyster mushroom extract showed reduced mortalities following L. garvieae infection compared with controls. These results show that supplementation of fish diets with oyster mushroom extract at 1 and 2% concentrations significantly imrpoves hematological parameters and modulates the immune response against L. garvieae in rainbow trout.  相似文献   
29.
30.
Fourteen oxime ethers and eleven other unsaturated compounds derived from 2,2-dimethyl-3-(3-phenoxybenzyloxy)propanal were synthesised and their insecticidal activity against Musca domestica, Locusta migratoria, Dysdercus cingulatus, Aedes aegypti, Plutella xylostella, Drosophila melanogaster, Tetranychus urticae and Spodoptera littoralis tested. Structural variations including chain length, branching and unsaturation of the oxime ether O-alkyl group and substituent exchange at the carbon-carbon double bond of the unsaturated compounds were made in order to examine the structure-activity relationship. All biological activities were compared with the activity of the ether pyrethroid MTI-500.  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