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   510篇
  免费   35篇
林业   14篇
农学   13篇
基础科学   2篇
  52篇
综合类   53篇
农作物   22篇
水产渔业   20篇
畜牧兽医   323篇
园艺   10篇
植物保护   36篇
  2023年   2篇
  2022年   6篇
  2021年   5篇
  2020年   12篇
  2019年   13篇
  2018年   5篇
  2017年   8篇
  2016年   16篇
  2015年   4篇
  2014年   9篇
  2013年   16篇
  2012年   16篇
  2011年   40篇
  2010年   23篇
  2009年   20篇
  2008年   29篇
  2007年   42篇
  2006年   37篇
  2005年   45篇
  2004年   45篇
  2003年   32篇
  2002年   36篇
  2001年   4篇
  2000年   3篇
  1999年   5篇
  1998年   4篇
  1997年   5篇
  1996年   5篇
  1995年   3篇
  1994年   5篇
  1993年   3篇
  1992年   4篇
  1991年   7篇
  1990年   4篇
  1989年   5篇
  1987年   2篇
  1986年   4篇
  1985年   4篇
  1984年   1篇
  1983年   2篇
  1982年   2篇
  1981年   1篇
  1980年   1篇
  1979年   2篇
  1975年   2篇
  1973年   1篇
  1972年   2篇
  1970年   2篇
  1968年   1篇
排序方式: 共有545条查询结果,搜索用时 31 毫秒
101.
Thoracolumbar disc herniation was diagnosed in a two-year-old ferret using a myelogram followed by a computed tomography scan. The ferret was paraplegic with no control over urination and defecation. Conservative treatment that included cage rest and passive range of motion exercises for three weeks followed by extensive physiotherapy and hydrotherapy resulted in full recovery two months after the onset of treatment. Although intervertebral disc disease has been reported previously in four ferrets, this is the first report in which a postmyelogram computed tomography was used to demonstrate the herniated disc, and physiotherapy was used as principal treatment modality.  相似文献   
102.
Streptococcus uberis, strain 0140J, contains a single copy sortase A (srtA), encoding a transamidase capable of covalently anchoring specific proteins to peptidoglycan. Unlike the wild-type, an isogenic mutant carrying an inactivating ISS1 insertion within srtA was only able to infect the bovine mammary gland in a transient fashion. For the first 24 h post challenge, the srtA mutant colonised at a similar rate and number to the wild type strain, but unlike the wild type did not subsequently colonise in higher numbers. Similar levels of host cell infiltration were detected in response to infection with both strains, but only in those mammary quarters infected with the wild type strain were clinical signs of disease evident. Mutants that failed to express individual sortase substrate proteins (sub0135, sub0145, sub0207, sub0241, sub0826, sub0888, sub1095, sub1154, sub1370, and sub1730) were isolated and their virulence determined in the same challenge model. This revealed that mutants lacking sub0145, sub1095 and sub1154 were attenuated in cattle. These data demonstrate that a number of sortase anchored proteins each play a distinct, non-redundant and important role in pathogenesis of S. uberis infection within the lactating bovine mammary gland.  相似文献   
103.
The records of 31 cats and eight dogs undergoing surgical correction of peritoneopericardial diaphragmatic hernia (PPDH) from 2000 through 2007 were reviewed. Weimaraners and long-haired cats of varying breeds, particularly Maine Coon cats, appear to be at higher risk of PPDH. Presenting complaints were most commonly related to the respiratory and gastrointestinal tracts in both dogs and cats, although respiratory signs were more prevalent in cats, and gastrointestinal signs were more common in dogs. The most common herniated organs were liver, gallbladder, and small intestine. Mortality associated with surgical repair of PPDH in cats and dogs was low in the first 2 weeks postoperatively, and prognosis for return to normal function was excellent. Peri-and postoperative complications were typically minor and self-limiting.  相似文献   
104.
Bacterial communities in sediments underneath milkfish cages and adjacent off‐cage areas in Bolinao, Lingayen Gulf, West Philippine Sea were characterized using PCR‐denaturing gradient gel electrophoresis to assess influence of the fish farming to the sediments. The sediments in the fish cage (FC) area showed anoxic conditions [redox potential of ?165 to ?213 mV and acid‐volatile sulphide‐sulphur (AVS‐S) of 0.55–1.88 mg g?1 (dry weight)] compared to the relatively oxic off‐cage area [redox potential of 72–81 mV and AVS‐S of 0.09–0.14 mg g?1 (dry weight)]. The composition of the microbial populations revealed influence of the fish feed sedimentation with higher dominance of putative sulphate‐reducing bacteria (SRB) in the FC area. Compositions of the bacterial taxa showed dominance of the Bacteroidetes group and Deltaproteobacteria. The results suggest that the fish feeds created a new suitable environment, in which reductive microorganisms such as SRB, ferric‐ion‐reducing bacteria and nitrate‐reducing bacteria can thrive. Organic load from the feed and quantity of its leftover constituents may be the key factors that influence the structure of the bacterial community in the sediments of the milkfish farms.  相似文献   
105.
Numerical investigation of irrigation scheduling based on soil water status   总被引:2,自引:1,他引:1  
Improving the sustainability of irrigation systems requires the optimization of operational parameters such as irrigation threshold and irrigation amount. Numerical modeling is a fast and accurate means to optimize such operational parameters. However, little work has been carried out to investigate the relationship between irrigation scheduling, irrigation threshold, and irrigation amount. Herein, we compare the results of HYDRUS 2D/3D simulations with experimental data from triggered drip irrigation, and optimize operational parameters. Two field experiments were conducted, one on loamy sand soil and one on sandy loam soil, to evaluate the overall effects of different potential transpiration rates and irrigation management strategies, on the triggered irrigation system. In both experiments, irrigation was controlled by a closed loop irrigation system linked to tensiometers. Collected experimental data were analyzed and compared with HYDRUS 2D/3D simulations. A system-dependant boundary condition, which initiates irrigation whenever the matric head at a predetermined location drops below a certain threshold, was implemented into the code. The experimental model was used to evaluate collected experimental data, and then to optimize the operational parameters for two hypothetical soils. The results show that HYDRUS 2D/3D predictions of irrigation events and matric heads are in good agreement with experimental data, and that the code can be used to optimize irrigation thresholds and water amounts applied in an irrigation episode to increase the efficiency of water use.  相似文献   
106.
This retrospective study evaluated the incidence of meniscal injury in cats with cranial cruciate ligament (CCL) ruptures. Medical records for cats diagnosed with CCL ruptures treated by a lateral fabellotibial suture (LFS) were reviewed for signalment, history, physical examination and surgical findings. Ninety-five cats (98 stifles) met the inclusion criteria. The incidence of meniscal injuries in feline CCL deficient stifles was 67%. Isolated medial meniscal injuries were found in 55 stifles (56%), isolated lateral meniscal injuries were found in 5 stifles (5%), and lateral and medial meniscal injuries were found in 6 stifles (6%). There was no correlation between the presence of a meniscal injury and age, breed, sex, weight, duration of lameness, presence of concurrent medial patellar luxation, degree of degenerative joint disease, or presenting side of lameness. Given the high rate of meniscal pathology in cats with CCL ruptures, exploratory surgery for meniscal assessment and concurrent stifle stabilization should be considered in feline patients.  相似文献   
107.
108.
Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental pollutants produced by incomplete combustion sources such as home heating, biomass burning, and vehicle emissions. PAH concentrations in soils are influenced by source inputs and environmental factors that control loss processes and soil retention. Many studies have found higher concentrations of these pollutants in soils within cities of temperate climates that have a centralized urban core. Less is known about the factors regulating PAH abundance in warm, arid urban ecosystems with low population densities but high traffic volumes. The relative importance of sources such as motor vehicle traffic load and aridland ecosystem characteristics, including temperature, silt, and soil organic matter (SOM) were explored as factors regulating PAH concentrations in soils near highways across the metropolitan area of Phoenix, AZ (USA). Highway traffic is high compared with other cities, with an average of 155,000 vehicles/day. Soils contained low but variable amounts of SOM (median 2.8?±?1.8% standard deviation). Across the city, median PAH concentrations in soil were low relative to other cities, 523?±?1,886 ??g/kg, ranging from 67 to 10,117 ??g/kg. Diagnostic ratio analyses confirmed that the source of PAHs is predominantly fuel combustion (i.e., vehicle emissions) rather than petrogenic, biogenic, or other combustion sources (coal, wood burning). However, in a multiple regression analysis including traffic characteristics and soil properties, SOM content was the variable most strongly related to PAH concentrations. Our research suggests that dryland soil characteristics play an important role in the retention of PAH compounds in soils of arid cities.  相似文献   
109.
110.
To prepare for a carbon (C) constrained economy, crop production energy audits or life cycle analysis (LCA) must be conducted. However, energy audits may not maximize profitability. This study conducted simultaneous production, economic, and energy audits to evaluate differences among these assessments. The 2005 and 2006 South Dakota field experiment contained two nitrogen (N; 0 and 224 kg N ha?1) rates, two corn population levels (76,500 and 149,000 plants ha?1), and two simulated landscape positions (upper backslope and lower backslope). The energy inputs, outputs, and net energy gain for corn grain used in ethanol production were calculated using the Nebraska Biofuel Energy Simulator (BESS) version 2008.3.1. For LC analysis, corn grain was used in ethanol production and dry distiller's grain was used as a livestock feed. Manure was not applied to the field. A partial economic analysis to examine profitability was conducted where seed, N fertilizer, and corn values were $312 (100,000 seeds)?1, $1.25 (kg N)?1, and $158 (Mg grain at 15.5% moisture)?1, respectively. Results showed that: 1) to maximize profitability and energy gains, inputs must closely match crop needs for a site; 2) increasing the population level from 74,500 to 149,000 plants ha?1 increased energy input and output, increased yield and energy gain by 11%, but did not influence profitability; 3) increasing N from 0 to 224 kg N ha?1 increased yield 7%, reduced profit by $145/ha, increased energy input and output values, but did not impact energy gain; and 4) corn grown in high yielding areas of landscapes may have higher yields (P = 0.08), profitability (P = 0.08), and energy gains (P = 0.08) than other areas. These calculations demonstrate that yield, profitability, and energy audits may have divergent results.  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