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   530篇
  免费   21篇
  国内免费   1篇
林业   14篇
农学   10篇
基础科学   10篇
  79篇
综合类   58篇
农作物   28篇
水产渔业   29篇
畜牧兽医   267篇
园艺   8篇
植物保护   49篇
  2023年   3篇
  2021年   8篇
  2020年   8篇
  2019年   10篇
  2018年   8篇
  2017年   12篇
  2016年   9篇
  2015年   6篇
  2014年   9篇
  2013年   16篇
  2012年   31篇
  2011年   28篇
  2010年   11篇
  2009年   11篇
  2008年   25篇
  2007年   33篇
  2006年   35篇
  2005年   38篇
  2004年   48篇
  2003年   38篇
  2002年   36篇
  2001年   11篇
  2000年   5篇
  1999年   5篇
  1998年   9篇
  1997年   7篇
  1996年   9篇
  1995年   5篇
  1994年   5篇
  1993年   8篇
  1992年   4篇
  1991年   4篇
  1990年   5篇
  1989年   4篇
  1988年   3篇
  1987年   2篇
  1986年   1篇
  1985年   5篇
  1984年   2篇
  1983年   5篇
  1982年   3篇
  1981年   1篇
  1979年   4篇
  1977年   5篇
  1976年   2篇
  1975年   3篇
  1974年   5篇
  1972年   2篇
  1971年   3篇
  1966年   1篇
排序方式: 共有552条查询结果,搜索用时 15 毫秒
61.
OBJECTIVE: To evaluate the use of multifrequency bioelectrical impedance analysis (MF-BIA) for estimating total body water (TBW), extracellular fluid volume (ECFV), and intracellular fluid volume (ICFV) in horses. ANIMALS: 9 healthy mares. PROCEDURE: TBW and ECFV were measured by use of deuterium oxide and sodium bromide dilution techniques, respectively. Intracellular fluid volume was calculated as the difference between TBW and ECFV. Concurrently, MF-BIA recordings were obtained by use of 4 anatomic electrode positions and 3 measurements of length. Models for MF-BIA data were created for all combinations of length and anatomic electrode position. Models were evaluated to determine the position-length configuration that provided the most consistent estimates of TBW, ECFV, and ICFV, compared with values determined by use of the dilution techniques. RESULTS: Positioning electrodes over the ipsilateral carpus and tarsus and use of height at the tuber sacrale for length provided the closest estimate between values for TBW, ECFV, and ICFV predicted by use of MF-BIA and measured values obtained by dilutional techniques. This model had the narrowest 95% limits of agreement. CONCLUSIONS AND CLINICAL RELEVANCE: MF-BIA techniques have been used to predict changes in TBW, ECFV, and ICFV in healthy and diseased humans. Results reported in this study provide an equine-specific model to serve as the basis for further evaluation of MF-BIA in horses with altered fluid states. The MF-BIA techniques have a number of potential applications for use in horses, including evaluation of exercise physiology, pharmacologic studies, and critical-care management.  相似文献   
62.
OBJECTIVE: To characterize an outbreak of West Nile virus (WNV) infection in horses in North Dakota in 2002, evaluate vaccine effectiveness, and determine horse characteristics and clinical signs associated with infection. DESIGN: Retrospective study. ANIMALS: 569 horses. PROCEDURE: Data were obtained from veterinary laboratory records, and a questionnaire was mailed to veterinarians of affected horses. RESULTS: Affected horses were defined as horses with typical clinical signs and seroconversion or positive results of virus isolation; affected horses were detected in 52 of the 53 counties and concentrated in the eastern and northeastern regions of the state. Among affected horses, 27% (n = 152) were vaccinated against WNV, 54% (309) were not, and 19% (108) had unknown vaccination status; 61 % (345) recovered, 22% (126) died, and 17% (98) had unknown outcome. The odds of death among nonvaccinated horses were 3 and 16 times the odds among horses that received only 1 or 2 doses of vaccine and horses that were vaccinated according to manufacturer's recommendations, respectively. Horses with recumbency, caudal paresis, and age > 5 years had higher odds of death, whereas horses with incoordination had lower odds of death, compared with affected horses without these characteristics. CONCLUSIONS AND CLINICAL RELEVANCE: Vaccination appears to have beneficial effects regarding infection and death caused by WNV.  相似文献   
63.
64.
CASE DESCRIPTION: 2 dogs and 5 cats were evaluated for treatment of ureteroliths. CLINICAL FINDINGS: Spontaneous retrograde movement of 1 or more ureteroliths was detected by radiography, ultrasonography, fluoroscopy, and a combination of fluoroscopy and ultrasonography. The ureteroliths moved retrograde up to 4 centimeters. Retrograde movement of ureteroliths into the renal pelvis resulted in improved renal function in some patients but made complete surgical removal of all uroliths more difficult. TREATMENT AND OUTCOME: Medical management was not successful, and ureteroliths were surgically removed. Surgical management of ureteroliths was complicated by retrograde movement of ureteroliths in the perioperative period. CLINICAL RELEVANCE: Ureteroliths can move retrograde within the ureter and even back into the renal pelvis. Retrograde movement of ureteroliths may make surgical planning more difficult.  相似文献   
65.
The transnational agrarian movement La Via Campesina (LVC) seeks to reestablish food sovereignty authority within national borders by removing agriculture from the WTO system. The WTO is a membership organization of participating nation-states that have agreed to abide by the rules of the WTO governance regime. Nominally, at least, changes in these governance rules must be approved by the nation-state members. This paper examines the extent to which South Korean affiliate organizations of LVC, the Korean Peasant League and the Korean Women Peasants Association, have been successful in placing food sovereignty issues on the national agri-food policy agenda in South Korea that challenge the WTO??s neoliberal global governance regime for agriculture. In effect, the success of transnational movements like LVC in challenging global institutions may rest on how well their member affiliates are able to play domestic agri-food politics.  相似文献   
66.
67.
Developing sustainable rangeland management strategies requires solution-driven research that addresses ecological issues within the context of regionally important socioeconomic concerns. A key sustainability issue in many regions of the world is conserving habitat that buffers animal populations from climatic variability, including seasonal deviation from long-term precipitation or temperature averages, and that can establish an ecological bottleneck by which the landscape-level availability of critical resources becomes limited. We integrated methods to collect landscape-level animal occurrence data during severe winter conditions with estimation and validation of a resource selection function, with the larger goal of developing spatially explicit guidance for rangeland habitat conservation. The investigation involved greater sage-grouse (Centrocercus urophasianus) that occupy a landscape that is undergoing human modification for development of energy resources. We refined spatial predictions by exploring how reductions in the availability of sagebrush (as a consequence of increasing snow depth) may affect patterns of predicted occurrence. Occurrence of sage-grouse reflected landscape-level selection for big sagebrush, taller shrubs, and favorable thermal conditions and avoidance of bare ground and anthropogenic features. Refinement of spatial predictions showed that important severe winter habitat was distributed patchily and was constrained in spatial extent (7–18% of the landscape). The mapping tools we developed offer spatially explicit guidance for planning human activity in ways that are compatible with sustaining habitat that functions disproportionately in population persistence relative to its spatial extent or frequency of use. Increasingly, place-based, quantitative investigations that aim to develop solutions to landscape sustainability issues will be needed to keep pace with human-modification of rangeland and uncertainty associated with global climate change and its effects on animal populations.  相似文献   
68.
69.
Background odors produced by plants in the environment can interfere with the response of insects to a point-releasing attractant, especially when their compositions overlap. In this study, a series of binary choice tests was conducted in a wind tunnel to investigate whether background odors emitted from cherry, blueberry, blackberry, or raspberry fruits would affect the level of Drosophila suzukii (Matsumura) attraction to its symbiotic yeast, Hanseniaspora uvarum (Niehaus) (Saccharomycetales: Saccharomycetaceae). Whether an increase in the intensity of background odors would affect the attractiveness of H. uvarum to D. suzukii was also investigated, either by increasing the number of cherry or raspberry fruit per cup or by increasing the number of fruit cups surrounding the cup baited with the yeast. In wind tunnel assays, background fruit odors interfering with D. suzukii attraction to the yeast varied among fruit types. Raspberry odor inhibited the attractiveness of H. uvarum to the fly the most, followed by blackberry odor, whereas cherry and blueberry odors had no significant impact on the attraction. An increase in the intensity of odors by adding more cherry or raspberry fruit per cup did not increase the impact of fruit odor on the attraction; however, adding more raspberry cups around H. uvarum linearly decreased its attractiveness, suggesting that background host fruit abundance and likely increase in host odor may influence D. suzukii attraction to yeast odor depending on host species.  相似文献   
70.
The difference in yields of cultivars may be causing difference in soybean yield between Japan and the USA. The objective of this study was to identify the effect of the cultivar on dry matter production and to reveal the key factors causing the differences in yield by focusing utilization of solar radiation in recent Japanese and US soybean cultivars. Field experiments were conducted during two seasons in Takatsuki, Japan (34°50′), and in a single season in Fayetteville (36°04′), AR, USA. Five Japanese and 10 US cultivars were observed under near-optimal conditions in order to achieve yields as close to their physiological potential as possible. The seed yield and total aboveground dry matter (TDM) were measured at maturity as long as radiation was intercepted by the canopy. The seed yield ranged from 3.10t ha?1 to 5.91t ha?1. Throughout the three environments, the seed yield of US cultivars was significantly higher than that of Japanese cultivars. The seed yield correlated with the TDM rather than the HI with correlation coefficients from .519 to .928 for the TDM vs. .175 to .800 for the HI, for each of the three environments. The higher TDM of US cultivars was caused by a higher radiation use efficiency rather than higher total intercepted radiation throughout the three environments. The seasonal change in the TDM observed in four cultivars indicated that dry matter productivity was different between cultivars, specifically during the seed-filling period.  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