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   866篇
  免费   64篇
  国内免费   21篇
林业   87篇
农学   73篇
基础科学   16篇
  113篇
综合类   332篇
农作物   45篇
水产渔业   22篇
畜牧兽医   215篇
园艺   14篇
植物保护   34篇
  2023年   5篇
  2021年   5篇
  2020年   3篇
  2019年   7篇
  2018年   22篇
  2017年   18篇
  2016年   16篇
  2015年   16篇
  2014年   11篇
  2013年   52篇
  2012年   41篇
  2011年   93篇
  2010年   31篇
  2009年   38篇
  2008年   33篇
  2007年   56篇
  2006年   46篇
  2005年   70篇
  2004年   63篇
  2003年   40篇
  2002年   61篇
  2001年   23篇
  2000年   17篇
  1999年   34篇
  1998年   17篇
  1997年   10篇
  1996年   14篇
  1995年   5篇
  1994年   11篇
  1993年   7篇
  1992年   15篇
  1991年   12篇
  1990年   7篇
  1989年   10篇
  1988年   7篇
  1987年   3篇
  1986年   5篇
  1985年   3篇
  1984年   2篇
  1983年   3篇
  1968年   1篇
  1967年   1篇
  1963年   1篇
  1954年   1篇
  1948年   2篇
  1947年   1篇
  1946年   1篇
  1945年   1篇
  1937年   1篇
  1934年   1篇
排序方式: 共有951条查询结果,搜索用时 62 毫秒
1.
2.
Χ灾绷吹矸酆康挠跋焓钦?,直接影响比间接影响大。Study on the correlation between rice quality and agronomic traits of quality riceNIE Cheng rong, WEN Yu hui, WANG Yun bo, CHEN Ming zhong,LI Mei, LIU Dao quan(Agronomy Department, Foshan University , Nanhai 528231,China)The correlative analy  相似文献   
3.
Some Physical Properties of Linseed   总被引:1,自引:0,他引:1  
  相似文献   
4.
1. An experiment was conducted to determine the effect of different dietary protein contents on the performance of naked neck (Na/na) and normally feathered (na/na) broilers.

2. Chicks from the two genotypes were reared in wire‐floored cages and divided at random into 3 groups. Birds were fed on high protein (HP, 12.99 MJ ME, 238 g crude protein/kg and 12.94 MJ ME, 216 g crude protein/kg from 0 to 3 and 3 to 7 weeks, respectively), medium protein (MP, 12.99 MJ ME, 219 g crude protein/kg and 12.87 MJ ME, 201 g crude protein/kg from 0 to 3 and 3 to 7 weeks), and low protein (LP, 12.94 MJ ME, 205 g crude protein/kg and 12.75 MJ ME, 184 g protein/kg from 0 to 3 and 3 to 7 weeks) diets.

3. The LP diets resulted in a significantly lower daily body weight gain of males from 0 to 3 weeks. Dietary protein content had no effect on body weight gain from 3 to 7 weeks, body weight at 7 weeks, and the food intake of birds. Carcase composition of birds from both genotypes was unaffected by dietary protein.

4. Naked neck birds had significandy higher body weights at 7 weeks. Yields of carcase and breast of Na/na males were significantly higher than those of na/na males. There were no significant differences between females from the two genotypes as regards carcase yield.

5. It was concluded that the dietary protein requirements of naked neck birds were similar to those for normally feathered birds.  相似文献   

5.
Isozyme analysis and sequence analysis of the internal transcribed spacer regions (ITS-1 and ITS-2) and the 5.8S subunit of the ribosomal DNA gene repeat were used to examine whether isolates of Phytophthora porri from Allium and Brassica represent a single homogeneous species. Twenty-six strains of P. porri, 16 strains isolated from the genus Allium, and 10 strains isolated from the genus Brassica, were analyzed using malate dehydrogenase (MDH), isocitrate dehydrogenase (IDH) and lactate dehydrogenase (LDH), represented altogether by four putative loci (Mdh-2, Idh-1, Idh-2, and Ldh-2). Isozyme analysis revealed that strains isolated from Allium contained five private alleles at three isozyme loci (Ldh-2 83, Ldh-2 104, Idh-1 108, Idh-1 112, and Idh-2 98), whereas six different alleles were observed at four isozyme loci (Ldh-2 85, Ldh-2 100, Ldh-2 114, Idh-1 100, Idh-2 100, and Mdh-2 111) in strains obtained from Brassica. The heterozygosity at the Ldh-2 locus, differing in allele composition, however, between strains from Allium and Brassica, was present in all strains, indicating that it is probably fixed. Sequence analysis of the ITS regions and the 5.8S subunit showed consistent differences between isolates from Allium and isolates from Brassica. Based on isozyme data, ITS sequence analysis and formerly published differences in restriction enzyme patterns of mitochondrial DNA, morphology and pathogenicity, it was concluded that the isolates of P. porri Foister did not represent a homogeneous species. Isolates from Brassica constitute a distinct species which is described here as P. brassicae sp. nov. It was inferred from isozyme patterns, which were in no case intermediate between the two species, that P. porri and P. brassicae do not hybridize and are reproductively isolated by barriers to gene flow.  相似文献   
6.
The majority of information on oncology therapies has been reported in humans, canine, and feline patients, and laboratory animals with experimentally induced tumors. A variety of treatments,including radiation therapy, chemotherapy, photodynamic therapy, and others have been used with exotic animals. There are many species of exotic pets, and anatomic differences, as well as husbandry and nutritional requirements, must be taken into account to provide optimal care. By providing a broad overview of therapies and considerations for treatment, this article is intended to provide the practitioner with an overview of approach and options when addressing oncology cases in exotic animals.  相似文献   
7.
8.
The need for a better understanding of the interaction between irrigation practices and the elevation and quality of the water table is of paramount importance for developing irrigation management strategies to ameliorate the regional problems of elevated saline water tables in the San Joaquin Valley, California. An area of approximately 3000 ha which includes portions of the Diener Ranch and the adjacent University of California, Westside Research and Extension Center, located south of Five Points in the Westlands Water District on the west side of the San Joaquin Valley was chosen for extensive field measurements. Field work consisted of four main activities namely, field instrumentation, collection of records of field activities, periodic data collection, and analyses of field data. Field measurements of water table carried out during 1994 indicated that the water table elevation was sensitive to the irrigation practices. There was a general increase in the area with a water table close to the surface during the irrigation season, and a return to water table elevations similar to the starting conditions at the end of the season. During the study period, the surface water quality deteriorated more in areas irrigated with reuse water and persisted through the end of the season. Depth averaged electrical conductivity for the study area over 6.5 m decreased between December 1993 and December 1994. Vertical hydraulic gradients in the saturated zone, were found to be an order of magnitude larger than horizontal gradients. The direction of vertical gradients changed, with downward gradients following pre-irrigations and upward gradients later in the season, when crop water requirements increased. Based on the results of the field study, it can be concluded that the irrigation management practices have a direct effect on local water table response as well as on water quality. Therefore, irrigation practices that promote less deep percolation losses may be helpful in controlling the water table rise.  相似文献   
9.
平江县位于湖南省东北部,是一个典型的"老、山、边、穷、大"五位一体的农业大县,也是国家级贫困县。近几年来,平江县农业综合开发办公室不断总结经验教训,努力探索农业综合开发的新途径,逐步完善有关政策,使平江县农业综合开发迈上了一个新的台阶。  相似文献   
10.
Plant Foods for Human Nutrition - St. John’s wort has been used for centuries in traditional medicine of many cultures, and nowadays it is well-known as a clinically important antidepressant...  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