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   30301篇
  免费   1282篇
  国内免费   8篇
林业   1070篇
农学   892篇
基础科学   174篇
  4561篇
综合类   3980篇
农作物   1165篇
水产渔业   1146篇
畜牧兽医   16486篇
园艺   338篇
植物保护   1779篇
  2021年   224篇
  2020年   265篇
  2019年   331篇
  2018年   600篇
  2017年   664篇
  2016年   566篇
  2015年   364篇
  2014年   552篇
  2013年   1664篇
  2012年   863篇
  2011年   1117篇
  2010年   808篇
  2009年   762篇
  2008年   1077篇
  2007年   1053篇
  2006年   890篇
  2005年   713篇
  2004年   721篇
  2003年   661篇
  2002年   584篇
  2001年   744篇
  2000年   743篇
  1999年   544篇
  1998年   244篇
  1997年   227篇
  1995年   269篇
  1992年   400篇
  1991年   415篇
  1990年   432篇
  1989年   440篇
  1988年   344篇
  1987年   353篇
  1986年   383篇
  1985年   342篇
  1984年   331篇
  1983年   303篇
  1979年   481篇
  1978年   328篇
  1977年   370篇
  1976年   468篇
  1975年   485篇
  1974年   523篇
  1973年   480篇
  1972年   438篇
  1971年   355篇
  1970年   372篇
  1969年   434篇
  1968年   441篇
  1967年   447篇
  1966年   438篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
62.
63.
64.
Methods used to prepare antigens from caprine syncytial retrovirus (CSR) for use in the agarose gel immunodiffusion test (AGID) or an indirect enzyme-linked immunosorbent assay (ELISA) are described. Caprine and ovine sera were tested for antibody to CSR using the AGID test and ELISA incorporating a caprine system (CSR antigen and rabbit anti-goat IgG) or an ovine system (maedi-visna virus antigen and rabbit anti-sheep IgG). Good correlation was achieved in the results of the 3 tests when sera were devoid of antibody or were strongly positive. Variations in the results on weakly positive sera were considered to be more a matter of interpretation than due to basic differences in the reagents employed.  相似文献   
65.
66.
The ionic composition of the of the intracellular content of the alcohol yeast Saccharomyces cerevisiae R. 1039 biomass was studied for confirmation of their use perspectiveness as a mediator to enable the management the mineral content of food in the manufacture of food and feed additives. The ionic composition of the obtained extracts were identified using the method of capillary electrophoresis. It is found that the quantitative ion content in the cell extracts depends on the concentration of the nutrient medium. When the yeast S. cerevisiae R. 1039 was cultivated on the medium with the soluble solids concentration of 30%, the intracellular ion content in the extracts was 1.3 times higher than when the yeast was cultivated on 12% wort by increasing the concentration of chlorides, sulfates, formates, potassium ions, and calcium. The yield of the yeast S. cerevisiae R. 1039 biomass increased 1.6 times per unit of volume of the medium with increase of the soluble solids concentrations from 12% to 30%.  相似文献   
67.
Twelve anestrous adult Greyhound bitches were used to study a regimen for induction of estrus. Once daily, 7 bitches were given diethylstilbestrol (DES; 5 mg, PO) until sanguineous vaginal discharge and vulvar edema were observed (designated as day 1 of proestrus) and for 2 days thereafter. If no response was elicited after 7 days, a doubled DES dose was given for up to an additional 7 days. Luteinizing hormone (5 mg, IM) was given on day 5 of proestrus, and follicle-stimulating hormone (10 mg, IM) was given on days 9 and 11 of proestrus. Bitches were bred once on day 13. Five bitches were used as a control group; they were given candy tablets for 7 days (first day on tablets, treatment day 1) and 0.9% NaCl (1.0 ml, IM) on treatment days 12, 16, and 18. The 7 bitches treated with DES had a mean proestrus period of 7.7 days and a mean estrus period of 5.7 days up to the day of mating. After mating, they had a mean gestation interval of 64 days and delivered a mean of 4 pups/litter. In 5 bitches, initial treatment with 5 mg of DES/day induced proestrus within 7 days; however, in 2 bitches, additional treatment with 10 mg of DES/day was needed for 5 and 6 days, respectively. Serum estradiol-17 beta and progesterone concentrations remained at base line during the period of DES treatment. Concentrations of both hormones increased after injection with luteinizing hormone and remained high for the next 4 days.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
68.
69.
Verticillium dahliae, the causal agent of Verticillium wilt of tomato, causes serious damage to crops grown in unheated greenhouses. To control this disease, growers are obliged to employ strong soil disinfestants. The possibility of controllingV. dahliae by using soil solarization during the months of June — August was examined. The soil was covered with transparent polyethylene sheets for 10 weeks. The pathogen could not be isolated from the solarized soil, whereas the inoculum level in the nonsolarized soil remained high (1379–1806 propagules/g soil). The yield from the solarized soil was increased by 112.4% in comparison with the control, and no infected plants were observed. The percentage of infected roots was very low (0.3–0.4%) in relation to the nonsolarized soil (66.7–67.1%). From these results it was concluded that solarization can effectively control Verticillium wilt of greenhouse-grown tomato under the summer conditions in Crete.  相似文献   
70.
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