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   611篇
  免费   22篇
  国内免费   3篇
林业   43篇
农学   28篇
基础科学   4篇
  133篇
综合类   31篇
农作物   71篇
水产渔业   36篇
畜牧兽医   213篇
园艺   18篇
植物保护   59篇
  2023年   7篇
  2022年   8篇
  2021年   20篇
  2020年   20篇
  2019年   27篇
  2018年   34篇
  2017年   42篇
  2016年   27篇
  2015年   12篇
  2014年   31篇
  2013年   57篇
  2012年   43篇
  2011年   34篇
  2010年   26篇
  2009年   21篇
  2008年   24篇
  2007年   27篇
  2006年   13篇
  2005年   15篇
  2004年   15篇
  2003年   9篇
  2001年   7篇
  2000年   9篇
  1999年   4篇
  1998年   4篇
  1997年   4篇
  1996年   5篇
  1993年   2篇
  1992年   5篇
  1991年   9篇
  1990年   10篇
  1989年   6篇
  1988年   6篇
  1987年   6篇
  1986年   6篇
  1985年   3篇
  1984年   4篇
  1983年   2篇
  1981年   2篇
  1980年   4篇
  1979年   4篇
  1977年   1篇
  1976年   1篇
  1975年   5篇
  1974年   1篇
  1972年   1篇
  1971年   1篇
  1970年   3篇
  1969年   3篇
  1964年   1篇
排序方式: 共有636条查询结果,搜索用时 15 毫秒
91.
The aim of this study was to examine whether and to what extent the addition of potassium diformate (pdf) or free organic acids (fpa) to the diet and the grinding intensity might affect the course of infection and the passage of orally applied Salmonella and Escherichia coli in pigs. Experiments were carried out using 80 reared piglets allotted to four groups. Pigs were fed pelleted diets ad libitum (except during a 15 h feed‐withholding‐period before infection). The control diet contained finely ground cereals (2 mm screen). To two test diets (also finely ground) 1.2% pdf, 0.9% organic acids (75% formic and 25% propionic acid, fpa) respectively were added. The fourth diet (without acids) was based on coarsely ground cereals (6‐mm screen). After experimental infection alternately with S. Derby or E. coli, the course of infection was examined (rectal swab technique). Pigs were sacrificed 4–5 h after a further oral application of ~109–1010 CFU S. Derby or E. coli to determine the counts of Salmonella or E. coli in chyme (classical culture methods). Adding pdf or fpa to the diet led to reduced Salmonella shedding and resulted in significantly lower counts of Salmonella and E. coli in the stomach content indicating an improved efficacy of the stomach barrier. In the distal parts of the digestive tract, the effect was less obvious concerning counts of E. coli, whereas counts of Salmonella were reduced markedly as well. The diet based on coarsely ground cereals failed to demonstrate positive effects concerning infection and passage of orally applied bacteria as well, but this diet was also pelleted and showed unintentionally, comparable amounts of fine particles. Results obtained in this study allow the recommendation of using pdf or organic acids as additives when dietary measures against Salmonella or E. coli in pigs are required.  相似文献   
92.
As part of the Sino-Pak trans-boundary cooperation for conservation and sustainable development in Pamir border region,World Wild Fund (WWF)-Pakistan conducted a preliminary social,economic and ecological survey in the Shimshal-Pamir Lakes area in July 2009.The purpose of the study was to explore potentials and opportunities for future collaborative conservation of some species,habitats and high altitude ecosystems in the border region between China and Pakistan.The two-week herpetological study in the Shimshal Pamir area of Khunjerab National Park (KNP) along Pakistan-China border was an integral part of the survey,conducted exclu-sively to document reptilian fauna with a special emphasis on investigating their occurrence,distribution and status in the study area.Field investigations were performed during daytime when it was hot enough and reptiles were active,basking or feeding.A total of 15 specimens belonging to four species of the Agamidae family were captured by striking stones and beating bushes with sticks.Collected specimens were preserved using 10% formalin solution,tagged with field information and stored in Zoological Survey Department,Karachi for future reference.Laboratory investigations were carried out for pholidosic counts and morphometric measurements.A detailed review of relevant literature,habitat characteristics and laboratory investigations revealed the occurrence of Laudakia himalayana,L.pakistanica,L.tuberculata and L.badakhshana at 4,082 m,4,172 m,4,005 m and 4,240 m asl,respectively,which are much higher altitudes as compared to the previously reported heights of 3,353 m,3,200 m,2,500 m and 2,400 m asl.The terrain offers a variety of ecological barriers,in the form of fast and freezing running waters and massive glaciers with peculiar harsh climatic conditions prevailing for nine months of the year,which restricts species migration and thus increases endemism.Although one of the four species recorded from the study area,i.e.L.pakistanica is endemic to Pakistan,L.tuberculata and L.badakhshana are new records from Shimshal,Pakistan,so a detailed investigation is suggested for further herpetological records from the study area.  相似文献   
93.
Potassium (K+) and nitrogen [N, as the form of ammonium (NH4+)] are major nutrients for plant growth. Although there have been a number of studies on the kinetic fixation of potassium and ammonium ions in soils and clays, however, investigations on the kinetics of competitive fixation of these ions have been few, if any, especially by taking into account silt component of the soils. In this study, the kinetics of potassium and ammonium fixation were examined in the silt components of several soil samples. The results revealed that considerable amounts of K+ and in lesser amounts, NH4+ ions were fixed by silt components of the soils. Potassium fixation was strongly preferred over ammonium. To describe the fixation kinetics, seven mathematically models were evaluated. A comparison of the models showed that pseudo-second-order equation properly described the fixation of these ions by the silt components.  相似文献   
94.
The objective of this study was to evaluate carob pods and their effect on growth performance, antioxidant activities, carcass and caecal characteristics and equilibrium modification of the caecal microbiota population of growing NZW rabbits. Eighty weaned rabbits (initial body weight: 625.00 ± 26.46 g) were randomly allocated into four dietary groups of 20 rabbits each until 90 days of age. Dietary groups were as follows: C (basal diet with no supplementation), CP1 (basal diet + 2.5% carob pods), CP2 (basal diet + 5% carob pods) and CP3 (basal diet + 10% carob pods). Rabbits given the CP2 diet had significantly higher daily and final body weights compared with the other experimental groups. The increase in inclusion rate of carob pods significantly decreased feed intake, whereas carob pods at 5% in the CP2 group recorded the best value of feed conversion ratio. Rabbits in the CP3 group showed the worst slaughter weight and carcass dressing percentage weight. No significant effect was found on meat protein and ash contents. Cholesterol, low‐density lipoprotein, high‐density lipoprotein and triglycerides decreased significantly (p < 0.05) in rabbits treated with carob pods compared with the control. Because of high content of the antioxidant compounds in CP2 and CP3 groups, the activities of glutathione peroxidase, glutathione S‐transferase, catalase and superoxide dismutase increased, whereas the concentration of thiobarbituric acid‐reactive substance decreased significantly. Rabbits given the CP2 diet had a significantly higher volatile fatty acid concentration and a lower pH in content of the caecum compared to the other groups. The data of microbial analysis for C group showed a significant increase in Escherichia coli and Clostridium counts. Lactobacillus and Bacillus counts increased significantly more in the CP2 and CP3 groups than in the other groups. In conclusion, 5% of carob pods in the diet stimulated the performance of growing rabbits, and thus, it has potential as an unconventional feed resource for rabbits without any adverse effects.  相似文献   
95.
The objective of this research was to evaluate the biodegradation of chloroform by using biotrickling filter (BTF) and determining the dominant bacteria responsible for the degradation. The research was conducted in three phases under anaerobic condition, namely, in the presence of co-metabolite (phase I), in the presence of co-metabolite and surfactant (phase II), and in the presence of surfactant but no co-metabolite (phase III). The results showed that the presence of ethanol as a co-metabolite provided 49% removal efficiency. The equivalent elimination capacity (EC) was 0.13 g/(m3 h). The addition of Tomadol 25-7 as a surfactant in the nutrient solution increased the removal efficiency of chloroform to 64% with corresponding EC of 0.17 g/(m3 h). This research also investigated the overall microbial ecology of the BTF utilizing culture-independent gene sequencing alignment of the 16S rRNA allowing identification of isolated species. Taxonomical composition revealed the abundance of betaproteobacteria and deltaproteobacteria with species level of 97%. Azospira oryzae (formally dechlorosoma suillum), Azospira restrica, and Geobacter spp. together with other similar groups were the most valuable bacteria for the degradation of chloroform.  相似文献   
96.
Sunflower is an important oilseed crop, which shows susceptibility to heat stress. In this study, 63 single cross hybrids were evaluated under heat stress condition for 2 years and compared with the two commercial hybrids. Genotype and genotype × environment (GGE) was used to differentiate single cross hybrids on the basis of multiple traits. GGE biplot showed that several single cross hybrids had higher seed yield potential than standard check. Moreover, seed yield per plant (SYP) was related to pollen viability percentage, showing that achene yield was the product of high gametophytic fertility under heat stress. Hybrids having high seed yield potential under heat stress had lower cell membrane injury. GGE biplot for SYP and its components showed that single cross hybrids were characterized into two major groups. Group I was further characterized into two sub group. Group Ia included hybrids with high 100-SW, while group Ib had the hybrids with high number of seeds per head and head diameter. Group II had the hybrids with high kernel weight and kernel to seed ratio. The hybrids could be recommended according to their potential utilization in the seed industry.  相似文献   
97.
Cadmium (Cd) is a nonessential and toxic element because it inhibits the growth and development of plants and is dangerous for end consumer. It enters in the human food chain through food crops. Application of plant nutrients such as zinc (Zn) and gypsum is a viable and cheap strategy to minimize its accumulation in edible plant portions. Therefore, this investigation was conducted to determine the effectiveness of Zn and gypsum against Cd accumulation in wheat. The results showed that Cd toxicity considerably decreased the plant growth, physiological activities, and yield attributes and increased the Cd accumulation in root, shoot, and grain, while application of Zn and gypsum remarkably increased the growth and yield and decreased the Cd accumulation in plant parts in Cd-contaminated soil. The results also depicted that application of Zn showed better results as compared to gypsum. In conclusion, we can say that application of Zn and gypsum remarkably ameliorated the Cd toxicity and decreased its accumulation in wheat, grown in Cd-contaminated soil.  相似文献   
98.
Betaine is found ubiquitously in plants, animals, microorganisms, and rich dietary sources including seafood, spinach, and wheat bran. The chief physiological role of betaine is to function as a methyl donor and an osmolyte. Betaine also acts as an osmolyte, to maintain the avian’s cellular water and ion balance to improve the avian’s capacity against heat stress via preventing dehydration and osmotic inactivation. It helps in maintaining the protective osmolytic activity, especially in heat-stressed birds. Betaine may promote various intestinal microbes against osmotic variations and thus improve microbial fermentation activity. Previous studies showed that dietary supplementation of betaine in poultry diets could positively affect nutrients’ digestibility, reduce abdominal fat weight, and increase breast meat yield. In addition, betaine has been reported to protect internal organs and boost their performance. Its inclusion in poultry diet is sparing essential amino acids like choline and methionine. In addition, it may play an important role in lean meat production by positively affecting the lipid metabolism with increased fatty acids catabolism and thus reducing carcass fat deposition. The aim of this review article was to broaden the knowledge regarding betaine and its importance in the poultry industry to cope with the heat stress problem. Moreover, it should be added to the diet as a natural anti-stressor through different routes (water/feed) to overcome the heat stress problem. However, further studies need to be conducted at the genetic and molecular basis to elucidate the mechanism behind the betaine as a natural anti-heat agent to decrease the heat stress problem in the poultry industry.  相似文献   
99.
The optimum dose of gamma radiation for sterilizing the red date palm weevil was determined using newly emerged weevils obtained from colonies established on four date palm cultivars in the laboratory. Male weevils from each date palm cultivar were treated with gamma radiation doses of 10, 15, 20, 25 or 30 Gray (Gy) and then mated with similar aged females to determine egg hatchability and male lifespan. Hatchability percent was significantly reduced at 15 Gy and above, and male lifespan was decreased at 10–15 Gy and above. Date palm cultivar significantly affected average male lifespan as well as egg hatchability, and the interaction between radiation dose and date palm cultivar was significant for both parameters. These results indicate that 15 Gy of gamma radiation to be an optimum dose for sterilizing red date palm weevil.  相似文献   
100.
Cultivated peanut, the second most economically important legume crop throughout the United States and the third most important oilseed in the world, is consistently threatened by various diseases and pests. Sclerotinia minor Jagger (S. minor), the causal agent of Sclerotinia blight, is a major threat to peanut production in the Southwestern U.S., Virginia, and North Carolina and can reduce yield by up to 50% in severely infested fields. Although host plant resistance would provide the most effective solution to managing Sclerotinia blight, limited sources of resistance to the disease are available for use in breeding programs. Peanut germplasm collections are available for exploration and identification of new sources of resistance, but traditionally the process is lengthy, requiring years of field testing before those potential sources can be identified. Molecular markers associated with phenotypic traits can speed up the screening of germplasm accessions, but until recently none were available for Sclerotinia blight resistance in peanut. This study objective of this study was to characterize the US peanut mini-core collection with regards to a recently discovered molecular marker associated with Sclerotinia blight resistance. Ninety-six accessions from the collection were available and genotyped using the SSR marker and 39 total accessions from spanish, valencia, runner market types were identified as new potential sources of resistance and targeted for further evaluation in field tests for Sclerotinia blight resistance.  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