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   2530篇
  免费   360篇
  国内免费   3篇
林业   110篇
农学   246篇
基础科学   22篇
  370篇
综合类   314篇
农作物   73篇
水产渔业   260篇
畜牧兽医   1190篇
园艺   57篇
植物保护   251篇
  2023年   27篇
  2021年   22篇
  2020年   29篇
  2019年   39篇
  2018年   120篇
  2017年   113篇
  2016年   97篇
  2015年   87篇
  2014年   83篇
  2013年   141篇
  2012年   113篇
  2011年   151篇
  2010年   107篇
  2009年   96篇
  2008年   131篇
  2007年   122篇
  2006年   132篇
  2005年   110篇
  2004年   82篇
  2003年   85篇
  2002年   59篇
  2001年   83篇
  2000年   81篇
  1999年   47篇
  1998年   31篇
  1997年   24篇
  1996年   30篇
  1995年   25篇
  1994年   24篇
  1993年   25篇
  1992年   37篇
  1991年   42篇
  1990年   41篇
  1989年   23篇
  1988年   26篇
  1987年   24篇
  1986年   20篇
  1985年   20篇
  1984年   18篇
  1983年   15篇
  1979年   18篇
  1978年   13篇
  1976年   19篇
  1975年   13篇
  1973年   12篇
  1971年   13篇
  1970年   12篇
  1969年   13篇
  1968年   19篇
  1967年   13篇
排序方式: 共有2893条查询结果,搜索用时 78 毫秒
141.
Antimicrobial resistance is a global challenge that impacts both human and veterinary health care. The resilience of microbes is reflected in their ability to adapt and survive in spite of our best efforts to constrain their infectious capabilities. As science advances, many of the mechanisms for microbial survival and resistance element transfer have been identified. During the 2012 meeting of Antimicrobial Agents in Veterinary Medicine (AAVM), experts provided insights on such issues as use vs. resistance, the available tools for supporting appropriate drug use, the importance of meeting the therapeutic needs within the domestic animal health care, and the requirements associated with food safety and food security. This report aims to provide a summary of the presentations and discussions occurring during the 2012 AAVM with the goal of stimulating future discussions and enhancing the opportunity to establish creative and sustainable solutions that will guarantee the availability of an effective therapeutic arsenal for veterinary species.  相似文献   
142.
143.
Diet plays an important role in maintaining rabbit health. Feeding an incorrect diet, particularly a low fibre diet, has been linked with digestive, dental and urinary tract disease. However, food intake and dietary requirements have been poorly studied in pet rabbits. This study assessed the effects of two commonly fed pet rabbit diets [extruded nuggets with hay (EH) and muesli with hay (MH)] alongside hay only (HO) and muesli only (MO) on food and water intake in 32 Dutch rabbits. Dry matter (DM) intake was greater in the HO group and lower in the MO group than in the EH and MH groups (p < 0.001). The portion of the diet made of hay was greater in the EH group than in the MH group (p < 0.001). Water intake was positively correlated with DM intake and was greatest in the HO group (p < 0.001). Selective feeding occurred in all rabbit groups fed muesli, whether or not hay was also available. Pellets were rejected, and grains and extrudates selected. The presence of selective feeding in all rabbits fed muesli leads to the consumption of an unbalanced diet. In addition, hay intake and water intake were lower when muesli was fed. Conclusions drawn from this study are based on general recommendations for pet rabbits, and clinical disease may have developed by feeding the study diets over a longer time period, as many diet‐related conditions typically present in older rabbits. However, the study demonstrates that the feeding of muesli diets cannot be recommended.  相似文献   
144.
This article reports Salix tetradenia Hand.‐Mazz as a new host of Candidatus phytoplasma and demonstrates its association with witches' broom disease on S. tetradenia plants. Plants exhibited typical visual symptoms of phytoplasma with virescence, abnormality of flowers and witches' broom, and phytoplasma bodies were observed by transmission electron microscopy. Products of 1.2 kb were amplified by nested PCR using phytoplasma universal primer pairs R16F2n/R16R2, but no amplification products were obtained from symptomless plants. The sequence analysis of three 16S rDNA isolates showed 99.84%, 99.68% and 99.76% identify, respectively, with the homologous gene (nc_005303) of member of ‘Candidatus phytoplasma asteris’ (16SrI) group. Phylogenetic and virtual computer‐simulated restriction fragment length polymorphism analysis of the 16S rRNA, tuf and rp gene sequences confirmed that this phytoplasma clustered in the 16SrI‐B subgroup. These results indicated that the diseased S. tetradenia plants were infected by a phytoplasma of the 16SrI group. This is the first report on the occurrence of phytoplasma disease on S. tetradenia worldwide.  相似文献   
145.
The influence of sex ratio, stocking density and age of hybrid tilapia (Oreochromis niloticus X O. aureus) brood fish on seed production in concrete tanks were evaluated in 1992 and 1993. A sex ratio of 1:2 and 1:3 (male: female) and a density of 2 fish m-2 gave the best result with respect to number of seed female-1 day-1 and number of seed kg-1-1 female day-1. Maximum seed production female-1 day-1 was recorded for 3-year-old females and the minimum for 1-year-olds, but in terms of seed kg-1 female day-1 and seed m-2 day-1, 1-year-olds produced the maximum number of seed followed by 2-, 3- and 4-year-old females. Seasonal pattern in seed production was apparently influenced by season and temperature. From the first harvest on 21 April 1993 the production increased gradually, reaching a peak during the third harvest and a second peak during the sixth harvest. Thereafter seed production gradually decreased, reaching a minimum during the tenth harvest on 27 October 1993. No seed were found during the last harvest of 18 November 1993. Maximum production coincided with the highest water temperature of around 28°C.  相似文献   
146.
In the freshwater area of Vietnam's Mekong Delta, Barbodes gonionotus (Bleeker), Cyprinus carpio L. and Oreochromis niloticus (L.) are often reared together in rice fields. The survival rate and specific growth rate (SGR) of C. carpio showed a large variance. To understand the underlying reasons for this variation, we used multiple regressions for the variables SGR and survival rate, using the results of eight experiments in such polycultures at the Co Do rice–fish experimental station. The SGR of C. carpio declined with increasing rice density. Interspecific competition with O. niloticus also had a negative effect on C. carpio SGR. When fertilizer or manure is added to the trench of the rice–fish field or when extra food can be given to the fish, O. niloticus seems more appropriate than C. carpio. The survival rate of C. carpio depended on season, C. carpio stocking weight and density and the biomass of wild fish species. To obtain higher survival rates, one should stock fewer fish but of a larger size, after thorough eradication of wild fish species.  相似文献   
147.
An 8‐week feeding experiment was conducted in floating cages (1.5 × 1.0 × 2.0 m) to determine the potential use of defatted soybean meal (roasted and solvent‐extracted) as a partial replacement of fishmeal in the isonitrogenous (approximately 450 g kg?1 CP [crude protein]) diet for juvenile cobia with an initial average weight of about 8.3 g. Diets were formulated to include 0, 100, 200, 300, 400, 500 and 600 g kg?1 (diets D0, D10, D20, D30, D40, D50 and D60, respectively) of fishmeal protein being substituted by defatted soybean meal without methionine supplementation. The results showed that weight gain rate decreased significantly when the replacement level of fishmeal protein was increased from 400 g kg?1 to 500 g kg?1, and the D60 diet was the lowest in all groups. These results indicate that up to 400 g kg?1 of fishmeal protein can be replaced by defatted soybean meal without causing significant reduction in growth. Feed conversion ratio (FCR) and protein efficiency ratio (PER) were significantly affected by the replacement level of fishmeal protein being substituted by defatted soybean meal, when the replacement level of fishmeal protein was 200 g kg?1 (diet, D20), FCR was the lowest and PER was the highest. There were no significant differences in the moisture, lipid, crude protein and ash content in whole body and muscle, while lipid content in liver increased as the dietary soybean meal replacement levels increased. There were significant differences in haemoglobin, haematocrit, red blood cell, plasma glucose and triglyceride concentration in fish fed diets with different soybean meal replacement levels. Results of this trial indicated that the optimum level of fishmeal protein replacement with defatted soybean meal, determined by quadratic regression analysis was 189.2 g kg?1, on the basis of maximum weight gain.  相似文献   
148.
The tongue sole Cynoglossus semilaevis, an inshore fish in China, has showed great potential in aquaculture recently. However, poor survival was recorded during the period of weaning from live Artemia to artificial diets. In this paper, the influence of co‐feeding larvae with live and inert diet on weaning performance was described. The C. semilaevis larvae were reared at 21 ± 1 °C and fed four different feeding regimes from 6 days post‐hatching (dph): A, Artemia (10 individuals mL?1); B, Artemia (5 individuals mL?1); C, mixed diet (10 Artemia individuals mL?1 and 12 mg L?1 inert diet); and D, mixed diet (5 Artemia individuals mL?1 and 12 mg L?1 inert diet). Rotifers were also supplied in all cases during the first days of feeding. Mixed diets of commercial formulated feed and live prey (rotifers and Artemia) allowed larvae to complete metamorphosis, achieving similar specific growth rate (SGR) (18.5 ± 1.4% and 18.7 ± 1.6%) and survival (40 ± 7.6% and 48.5 ± 6.8%) compared with larvae fed on live feed alone (SGR of 18.3 ± 1.2%, 19.3 ± 1.9% and survival of 41.2 ± 11.3%, 38 ± 4.9%). However, in metamorphosed fish, when live feed was withdrawn on 31 dph, there was significant difference (P < 0.05) in survival and growth among treatments. Metamorphosed fish, previously fed mixture diets during larval stages, had similar survival (62.1 ± 7.6% and 62.8 ± 3.9% for regimes C and D, respectively) but higher than that obtained for fish that previously fed on live feed (49.3 ± 2% and 42.1 ± 3.9% for regimes A and B, respectively) after weaning (day 60). The SGR of weaned fish previously fed live feed was similar (3.1 ± 0.6% and 2.92 ± 0.6% for regimes A and B, respectively) but lower than that recorded for fish that was fed from day 6 to day 30 on the mixed diet (4.5 ± 1.1% and 4.9 ± 0.3% for regimes C and D, respectively). It is suggested that weaning of C. semilaevis from early development would appear to be feasible and larval co‐feeding improves growth and survival.  相似文献   
149.
150.
Source-sink dynamics are an emergent property of complex species–landscape interactions. A better understanding of how human activities affect source-sink dynamics has the potential to inform and improve the management of species of conservation concern. Here we use a study of the northern spotted owl (Strix occidentalis caurina) to introduce new methods for quantifying source-sink dynamics that simultaneously describe the population-wide consequences of changes to landscape connectivity. Our spotted owl model is mechanistic, spatially-explicit, individual-based, and incorporates competition with barred owls (Strix varia). Our observations of spotted owl source-sink dynamics could not have been inferred solely from habitat quality, and were sensitive to landscape connectivity and the spatial sampling schemes employed by the model. We conclude that a clear understanding of source-sink dynamics can best be obtained from sampling simultaneously at multiple spatial scales. Our methodology is general, can be readily adapted to other systems, and will work with population models ranging from simple and low-parameter to complex and data-intensive.  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