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   2126篇
  免费   104篇
  国内免费   1篇
林业   109篇
农学   132篇
基础科学   3篇
  372篇
综合类   147篇
农作物   281篇
水产渔业   186篇
畜牧兽医   844篇
园艺   33篇
植物保护   124篇
  2023年   14篇
  2022年   39篇
  2021年   52篇
  2020年   34篇
  2019年   40篇
  2018年   53篇
  2017年   64篇
  2016年   61篇
  2015年   64篇
  2014年   92篇
  2013年   122篇
  2012年   162篇
  2011年   170篇
  2010年   111篇
  2009年   116篇
  2008年   141篇
  2007年   137篇
  2006年   152篇
  2005年   85篇
  2004年   84篇
  2003年   78篇
  2002年   77篇
  2001年   67篇
  2000年   38篇
  1999年   26篇
  1998年   12篇
  1997年   3篇
  1996年   3篇
  1995年   7篇
  1994年   5篇
  1993年   4篇
  1992年   10篇
  1991年   3篇
  1990年   13篇
  1989年   12篇
  1988年   7篇
  1987年   4篇
  1985年   6篇
  1981年   3篇
  1978年   3篇
  1976年   2篇
  1975年   3篇
  1974年   7篇
  1973年   10篇
  1971年   3篇
  1970年   2篇
  1968年   2篇
  1966年   4篇
  1949年   2篇
  1929年   2篇
排序方式: 共有2231条查询结果,搜索用时 0 毫秒
981.
K Yu    S. J. Park  V. Poysa 《Plant Breeding》2000,119(5):411-415
The possibility of using random amplified polymorphic DNA (RAPD) markers previously mapped in the common bean PC50/XANI59 population to select for resistance to common bacterial blight (CBB) in different populations was examined. Two out of 02 selected RAPD markers were polymorphic in HR56 and W0633d, the parental lines used in this experiment. Cosegregation analysis of the two polymorphic markers and disease reaction in a recombinant inbred (RI) population derived from HR67/W1744d confirmed that one of the two RAPD markers, BC420900, was significantly associated with a major quantitative trait locus‐conditioning resistance to CBB in HR67. This locus accounted for approximately 51) of the phenotypic variation. The RAPD marker was transformed into a sequence characterized amplified region (SCAR) marker and used for selection in a different population derived from ‘Envoy’/HR67. Prediction for resistance to CBB with the BC420.990 SCAR marker was 94.2% accurate in this population. A comparison between marker‐assisted selection (MAS) and conventional greenhouse screening showed that the cost of MAS is about one‐third less than that of the greenhouse test.  相似文献   
982.
蓝色系草本植物有很高的观赏价值,它不仅是园林景观中的稀有素材,也是育种研究的重要种质资源。北京周边山区有丰富的蓝色系草本资源,但目前应用于园林绿化的种类较少,城区花坛、花境所用素材多为国外引入的园艺品种。根据2年实地调查研究,总结了北京松山、百花山、东灵山等高山地区的蓝色系草本植物种类,统计结果为19科41属59种。针对目前研究及应用现状,对部分有较高观赏价值种类提出引种建议,为今后的开发和利用提供依据。  相似文献   
983.
试验旨在测定运用油副产品的有效方法。该油副产品来自红花籽油中共轭亚油酸(CLA)的纯化过程,其中的共轭亚油酸为甘油酯形式。共轭亚油酸副产品(CBP)添加到产蛋鸡饲粮中,以提高共轭亚油酸在卵黄中的积累。试验设3种不同饲粮,分别为:对照饲粮,添加共轭亚油酸副产品2%的饲粮,添加共轭亚油酸-80(含80%游离型共轭亚油酸)2%的饲粮。从3个不同饲粮组获取卵黄,通过气相色谱法分析卵黄脂肪酸,测定蛋品质。在饲养试验阶段,试验组蛋品质和产蛋量几乎没有变化,各试验组间也没有显著差异。添加共轭亚油酸副产品的试验组,在饲养第1周,卵黄中共轭亚油酸含量显著增加;在整个饲养试验阶段,与其他试验组相比,其卵黄中共轭亚油酸含量最高。而添加共轭亚油酸-80试验组,卵黄中共轭亚油酸含量在第3周增加。此外,热处理48h后,共轭亚油酸-80和共轭亚油酸副产品中,总共轭亚油酸异构体含量分别被降低12.92%和0.51%;亚油酸-80(含80%游离型亚油酸)和亚油酸副产品中,亚油酸(LA)异构体含量分别被降低19.63%和5.78%。试验证实共轭亚油酸副产品中脂肪主要是酯化形式,然而共轭亚油酸-80和亚油酸-80中的脂肪由游离脂肪酸构成。油副产品对蛋品质和产蛋量没有影响,作为动物性功能食品来源应用是很有意义的。  相似文献   
984.
Genome sequences for most metazoans and plants are incomplete because of the presence of repeated DNA in the heterochromatin. The heterochromatic regions of Drosophila melanogaster contain 20 million bases (Mb) of sequence amenable to mapping, sequence assembly, and finishing. We describe the generation of 15 Mb of finished or improved heterochromatic sequence with the use of available clone resources and assembly methods. We also constructed a bacterial artificial chromosome-based physical map that spans 13 Mb of the pericentromeric heterochromatin and a cytogenetic map that positions 11 Mb in specific chromosomal locations. We have approached a complete assembly and mapping of the nonsatellite component of Drosophila heterochromatin. The strategy we describe is also applicable to generating substantially more information about heterochromatin in other species, including humans.  相似文献   
985.
986.
Glutamine metabolism is an important metabolic pathway for cancer cell survival, and there is a critical connection between tumour growth and glutamine metabolism. Because of their similarities, canine mammary carcinomas are useful for studying human breast cancer. Accordingly, we investigated the correlations between the expression of glutamine metabolism‐related proteins and the pathological features of canine mammary tumours. We performed immunohistochemical and western blot analysis of 39 mammary tumour tissues. In immunohistochemical analysis, the expression of glutaminase 1 (GLS1) in the epithelial region increased according to the histological grade (P < .005). In the stromal region, complex‐type tumours displayed significantly higher GLS1 intensity than simple‐type tumours. However, glutamate dehydrogenase expression did not show the same tendencies as GLS1. The western blot results were consistent with the immunohistochemical findings. These results suggest that the expression of GLS1 is correlates with clinicopathological factors in canine mammary tumours and shows a similar pattern to human breast cancer.  相似文献   
987.
An enzyme-linked immunosorbent assay (ELISA) using bulk tank milk samples was evaluated as a screening test for bovine tuberculosis (TB), a contagious chronic disease of cattle. An ELISA with MPB70, a major antigen of Mycobacterium bovis was performed using paired sets of milk and sera samples from 33 tuberculin-positive and 43 tuberculin-negative cattle. Anti-MPB70 antibodies were detected in milk samples and there was a significant correlation between seroreactivities of milk and sera samples (R2 = 0.83). Using the tuberculin skin test as the reference test, the sensitivities of ELISA using milk and sera samples were 87.8% and 81.8%, respectively, and the specificities were 97.7% and 100%, respectively.In the screening test using bulk tank milk samples from 931 dairy herds in Whasung, Gyeonggi-do, Korea, the positive rate for anti-MPB70 antibody was 4.5% (42/931) and the tuberculin-positive rate was 2.8% (26/931). Individual milk samples (n = 253) were collected from randomly selected 8 problematic and 3 negative herds (positive and negative in the screening test by MPB70 ELISA using bulk tank milk samples, respectively) and tested by MPB70 milk ELISA. In the problematic herds, positive rates were 10.5% (20/190) for anti-MPB70 antibodies in milk ELISA and 2.1% (4/190) in the tuberculin skin test. More than one dairy cows were positive by milk ELISA among the problematic herds, and all tuberculin-positive dairy cows were positive in the milk ELISA. Further, no positive cows were detected in negative herds both by milk ELISA and tuberculin skin test. These results suggest that an ELISA, using bulk tank milk samples, might be a potential efficient screening test for bovine TB of dairy cows.  相似文献   
988.
BackgroundBovine tuberculosis (TB) is caused by Mycobacterium bovis, a well-known cause of zoonotic tuberculosis in cattle and deer, and has been investigated in many physiological and molecular studies. However, detailed genome-level studies of M. bovis have not been performed in Korea.ObjectivesTo survey whole genome-wide single-nucleotide polymorphism (SNP) variants in Korean M. bovis field isolates and to define M. bovis groups in Korea by comparing SNP typing with spoligotyping and variable number tandem repeat typing.MethodsA total of 46 M. bovis field isolates, isolated from laryngopharyngeal lymph nodes and lungs of Korean cattle, wild boar, and Korean water deer, were used to identify SNPs by performing whole-genome sequencing. SNP sites were confirmed via polymerase chain reaction using 87 primer pairs.ResultsWe identified 34 SNP sites with different frequencies across M. bovis isolates, and performed SNP typing and epidemiological analysis, which divided the 46 field isolates into 16 subtypes.ConclusionsThrough SNP analysis, detailed differences in samples with identical spoligotypes could be detected. SNP analysis is, therefore, a useful epidemiological tracing tool that could enable better management of bovine TB, thus preventing further outbreaks and reducing the impact of this disease.  相似文献   
989.
Feline calicivirus (FCV) is a highly infectious pathogen in cats and widely distributed worldwide with high genetic variation. Full-length open reading frame 2 of 5 from recently isolated Korean FCV isolates were sequenced and compared with those of global isolates. The results of phylogenetic analysis supported dividing global FCV isolates into two genogroups (type I and II) and demonstrated the presence of genogroup II in Korea, indicating their geographic spread in East Asia. High sequence variations in region E of the FCV isolates emphasizes that a novel vaccine needs to be developed to induce protective immunity against various FCV strains.  相似文献   
990.
Limb contact variables of the gaits of superior dressage horses were determined for competitors at the 1988 Seoul Summer Olympic Games in the finals of the Individual Dressage competition. Two 16-mm motion picture cameras were aimed perpendicular to the plane of motion along the HXF and KXM diagonals of the standard dressage arena, and filmed at 100 fps. Nineteen of the horses selected as finalists for individual dressage medals were filmed during the Grand Prix Special test executing one-stride canter lead changes, two-stride canter lead changes and the left lead extended canter. Velocities, stride lengths and stride durations were 7.03±.07 m/s, 4.15±.05 m and .592±.004 s for the extended canter. Across all stride frequencies, score was optimized with extended canter strides of the greatest length, with no upper limit detected to optimal stride length. Canter strides with lead changes had lower velocities, shorter strides and longer durations than strides without a lead change, with velocities, stride lengths and stride durations, respectively, of 3.36±.05 m/s, 2.08±.04 m and .617±.003 s for one-stride canter lead change strides; 3.65±.07 m/s, 2.21±.04 m and .605±.003 s for pre-change canter two-stride lead change strides; and 3.95±.07 m/s, 2.44±.04 m and .621±.004 s for post-change canter two-stride lead change strides. This study provided the first objective documentation of the canter limb contact patterns of world-class dressage horses.  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