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   173篇
  免费   6篇
  国内免费   1篇
林业   8篇
农学   21篇
  31篇
综合类   16篇
农作物   9篇
水产渔业   2篇
畜牧兽医   84篇
园艺   2篇
植物保护   7篇
  2023年   1篇
  2022年   1篇
  2021年   1篇
  2020年   4篇
  2019年   5篇
  2018年   4篇
  2017年   2篇
  2016年   3篇
  2014年   4篇
  2013年   6篇
  2012年   1篇
  2011年   4篇
  2010年   1篇
  2009年   1篇
  2008年   4篇
  2007年   12篇
  2006年   10篇
  2005年   7篇
  2004年   5篇
  2003年   9篇
  2002年   5篇
  2001年   6篇
  2000年   5篇
  1999年   2篇
  1998年   5篇
  1997年   5篇
  1996年   5篇
  1995年   4篇
  1994年   3篇
  1993年   8篇
  1992年   6篇
  1991年   4篇
  1990年   4篇
  1989年   3篇
  1988年   1篇
  1987年   3篇
  1986年   1篇
  1985年   2篇
  1978年   2篇
  1975年   2篇
  1972年   2篇
  1971年   5篇
  1970年   2篇
  1969年   3篇
  1968年   1篇
  1967年   2篇
  1966年   2篇
  1953年   2篇
排序方式: 共有180条查询结果,搜索用时 15 毫秒
71.
Principles for Sustainable Governance of the Oceans   总被引:1,自引:0,他引:1  
Pressures being exerted on the ocean ecosystems through overfishing, pollution, and environmental and climate change are increasing. Six core principles are proposed to guide governance and use of ocean resources and to promote sustainability. Examples of governance structures that embody these principles are given.  相似文献   
72.
随着养殖业的发展,环境污染已逐渐成为畜牧养殖中的主要问题之一。畜禽死淘率的增高和药费支出的加大,已经提出了一个危险的信号,提示我们要加强环境的卫生管理,防止病原体污染,这是防止疫病发生的一个关键措施。  相似文献   
73.
74.
Lupinosis was produced in sheep in four experiments by administering a toxic extract of Phomopsis leptostromiformis by various routes and at various dose rates. The course of the intoxication was followed by plasma biochemical analyses for a number of electrolytes, metabolites and enzymes. Results from these analyses suggested that in addition to being an hepatotoxicity, lupinosis also resulted in injury to muscle, kidney and adrenal cortex. This was confirmed by microscopic examination of these tissues.  相似文献   
75.
S. L. K. Hsam    V. Mohler    L. Hartl    G. Wenzel  F. J. Zeller 《Plant Breeding》2000,119(1):87-89
Powdery mildew and leaf rust resistance genes on the 1RS arm of the T1BL·1RS translocated chromosome were mapped in relation to the Sec‐1 locus and AFLP and restriction fragment length polymorphism markers, respectively, employing segregating F3 populations. Integration of molecular markers indicated that Pm17 lies between the Lr26 and Sec‐1 loci, with both resistance genes allocated distally to the Sec‐1 locus in the satellite of the 1RS arm.  相似文献   
76.
Lombi  E.  Sletten  R. S.  Wenzel  W. W. 《Water, air, and soil pollution》2000,124(3-4):319-332
Five soils from Austria that have high contents of arsenic (As)due to anthropogenic and/or geogenic sources were separated intosand, silt, and clay fractions. The distribution of As among theparticle-size fractions was clay >> silt > sand. Theparticle-size fractions were analysed according to an 8-stepsequential extraction procedure (SEP) designed to assess theprimary reservoirs and extractability of As. Steps 1 and 2,(i.e. NH4NO3 and (NH4)2SO4) extractedthe least As, while considerably greater amounts were extractedin steps 3, 4 and 5 (i.e. NH4H2PO4,NH2OH-HCl, and NH4F). The greatest amounts of As wereextracted in steps 6 and 7, both NH4-oxalate extractantstargeting the amorphous and crystalline oxide fractions. Theresidual fraction (step 8) was typically low. The extraction ofthe clays contained generally more As in steps 3 to 8, while Asrelease in the first two steps was typically highest in the sandand silt fractions. These findings are in accord with factoranalysis indicating that the extractants of the SEP areseparated into weak (steps 1 and 2) and strong (steps 3 to 8)extractants. SEP data along with microprobe analyses (X-raymicroanalyses) indicate that most As is associated with Fe andis therefore not readily mobile. Anyhow, As could be releasedupon changes in redox potential or pH. The greaterextractability of As from sand fractions using weak extractantsmay explain the higher toxicity of As in coarse-textured soils,as found in previous studies.  相似文献   
77.
We report a catalytic system that produces olefin block copolymers with alternating semicrystalline and amorphous segments, achieved by varying the ratio of alpha-olefin to ethylene in the two types of blocks. The system uses a chain shuttling agent to transfer growing chains between two distinct catalysts with different monomer selectivities in a single polymerization reactor. The block copolymers simultaneously have high melting temperatures and low glass transition temperatures, and therefore they maintain excellent elastomeric properties at high temperatures. Furthermore, the materials are effectively produced in economically favorable, continuous polymerization processes.  相似文献   
78.
A commercial vaccine containing modified-live bovine viral diarrhea virus (BVDV; types 1 and 2) was administered to one group of 22 peripubertal bulls 28 days before intranasal inoculation with a type 1 strain of BVDV. A second group of 23 peripubertal bulls did not receive the modified-live BVDV vaccine before intranasal inoculation. Ten of 23 unvaccinated bulls--but none of the vaccinated bulls--developed a persistent testicular infection as determined by immunohistochemistry and polymerase chain reaction. Results of this study indicate that administration of a modified-live vaccine containing BVDV can prevent persistent testicular infection if peripubertal bulls are vaccinated before viral exposure.  相似文献   
79.
Photoperiod response is a major determinant of duration of growing stages in wheat. Conscious selection for these photoperiod response genes in plant breeding programs will yield genotypes with better adaptation to diverse environments. To provide a starting point for the development of molecular markers useful for the selection process, genetic maps around the photoperiod insensitive gene Ppd-B1 were built employing three segregating populations. Of 25 markers that were selected for the Ppd-B1 region, only two could be mapped across all three populations. In pairwise comparisons, the extent of transferable markers ranged from three to eight. Recombination frequencies of markers distal to Ppd-B1 were more homogeneous than those of proximal markers. This finding suggested a closer proximity of Ppd-B1 to the markers that were mapped distal to breakpoint 0.83 in the physical map of chromosome 2BS. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
80.
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