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   28713篇
  免费   1518篇
  国内免费   12篇
林业   1208篇
农学   827篇
基础科学   173篇
  4277篇
综合类   4144篇
农作物   1076篇
水产渔业   1702篇
畜牧兽医   14642篇
园艺   386篇
植物保护   1808篇
  2021年   284篇
  2020年   304篇
  2019年   398篇
  2018年   561篇
  2017年   620篇
  2016年   602篇
  2015年   431篇
  2014年   598篇
  2013年   1159篇
  2012年   1050篇
  2011年   1266篇
  2010年   854篇
  2009年   821篇
  2008年   1221篇
  2007年   1166篇
  2006年   1026篇
  2005年   931篇
  2004年   818篇
  2003年   894篇
  2002年   745篇
  2001年   833篇
  2000年   818篇
  1999年   667篇
  1998年   300篇
  1997年   299篇
  1995年   273篇
  1992年   442篇
  1991年   535篇
  1990年   451篇
  1989年   423篇
  1988年   413篇
  1987年   414篇
  1986年   374篇
  1985年   396篇
  1984年   354篇
  1983年   293篇
  1982年   251篇
  1979年   387篇
  1978年   295篇
  1977年   293篇
  1976年   304篇
  1975年   319篇
  1974年   338篇
  1973年   302篇
  1972年   293篇
  1971年   251篇
  1969年   289篇
  1968年   272篇
  1967年   327篇
  1966年   308篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
Waters unusually rich in ammonia, boron, carbon dioxide, hydrogen sulfide, and hydrocarbons are found in more than 100 localities along the Pacific coast of the United States. The waters are believed to be products of low-grade metamorphism of marine sediments. The marine sedimentary rocks would have to be tectonically emplaced below crystalline rocks in many places. Mercury ore deposits are probably also products of the low-grade metamorphism.  相似文献   
12.
Induced (traumatic) resin in white spruce (Picea glauca (Moench) Voss) leaders resistant or susceptible to the white pine weevil (Pissodes strobi Peck) was analyzed for volatile terpenes and diterpene resin acids after simulated white pine weevil damage. Leaders from 331 trees were wounded just below the apical bud with a 1-mm diameter drill, coinciding with the natural time of weevil oviposition in the spring. Leaders were removed in the fall, and the bark and xylem from the upper and lower regions of the leader extracted and analyzed by gas chromatography. Unwounded trees had low amounts of resin in xylem compared with bark. In response to wounding, volatile terpenes and diterpene resin acids increased in the upper xylem (area of wounding), with resistant trees showing a greater increase than susceptible trees. Wounding caused monoterpenes in particular to decrease in the lower region of the leader (away from the drilled area) in greater amounts in susceptible trees than in resistant trees. In response to wounding, the proportion of monoterpene to resin acid increased in the upper and lower xylem of resistant trees, and slightly increased in the upper xylem of susceptible trees. Monoterpene-enriched resin is more fluid than constitutive resin, and probably flows more readily into oviposition cavities and larval mines, where it may kill immature weevils. Loss of resin components in the lower xylem suggested catabolism and transport of these materials to the site of wounding; however, energetic and regulatory data are necessary to confirm this hypothesis. This study provides a basis for measuring the ability of a tree to undergo traumatic resinosis that could be used to screen for resistance to white pine weevil.  相似文献   
13.
14.
The effect of boiling and baking in either a convential or microwave oven on the lipid content of potatoes was investigated. The crude lipid content of potatoes was lowered significantly by all methods of cooking. The loss was highest in potatoes cooked in a microwave oven, least in boiled tubers, and intermediate in tubers baked in a conventional oven. Similar trends were observed for both cortex and pith tissues. Generally, the phospholipid content followed the same trend as the crude lipid, the exception being the cortex tissue of tubers baked in the conventional oven, in which the greatest loss of phospholipid occurred. Cooking did not significantly alter the fatty acid composition of tubers. A possible relationship between the degree of cell rupturing, known to be influenced by different mechanisms of heat transfer, and the amounts of tuber lipid associated with different cooking methods was discussed.  相似文献   
15.
16.
A synthetic hexaploid, Triticum timofeevii×T. tauschii, was used to transfer disease resistance genes to the commercial cultivar Saratovskaya 29 (S29) by backcrossing. After five backcrosses the resulting derivatives still showed some traits of the synthetic, namely brown spike glumes and several gliadin components. Genetic analysis showed that the derived forms had inherited the Gli-D1 allele of the synthetic, which was found to be tightly linked to a gene for glume colour. Recombination percentages between these genes was estimated to be 2.5 ± 1.7%. The development of the derivatives was also accompanied by a rearrangement within the Gli-B1 locus, resulting in the formation of a new variant of the allele in S29.  相似文献   
17.
18.
After the observation of 2 horses with uveitis on a horse farm in the Minnesota River valley, 100 horses from this geographic area were given ophthalmologic examinations and were evaluated serologically for leptospirosis. A statistically significant (P less than 0.001) association was observed between the finding of antibodies against Leptospira interrogans serovar pomona and uveitis.  相似文献   
19.
20.
Malignant lymphoma involving bone and heart was diagnosed in a 4-year-old Whippet, using radiography, histologic examination, nuclear scintigraphy of the skeleton and heart, and cardiac ultrasonography.  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