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   148170篇
  免费   8217篇
  国内免费   129篇
林业   5696篇
农学   4342篇
基础科学   908篇
  16882篇
综合类   28543篇
农作物   5973篇
水产渔业   6902篇
畜牧兽医   76458篇
园艺   1778篇
植物保护   9034篇
  2019年   1351篇
  2018年   1990篇
  2017年   2274篇
  2016年   2032篇
  2015年   1785篇
  2014年   2237篇
  2013年   5437篇
  2012年   4081篇
  2011年   4954篇
  2010年   3198篇
  2009年   3269篇
  2008年   4838篇
  2007年   4605篇
  2006年   4405篇
  2005年   4106篇
  2004年   3947篇
  2003年   4012篇
  2002年   3751篇
  2001年   4569篇
  2000年   4543篇
  1999年   3639篇
  1998年   1499篇
  1997年   1440篇
  1996年   1350篇
  1995年   1570篇
  1994年   1407篇
  1993年   1440篇
  1992年   2976篇
  1991年   3162篇
  1990年   3025篇
  1989年   3061篇
  1988年   2702篇
  1987年   2835篇
  1986年   2942篇
  1985年   2849篇
  1984年   2249篇
  1983年   2032篇
  1982年   1431篇
  1979年   2071篇
  1978年   1639篇
  1977年   1407篇
  1975年   1438篇
  1974年   1831篇
  1973年   1862篇
  1972年   1843篇
  1971年   1766篇
  1970年   1700篇
  1969年   1552篇
  1968年   1299篇
  1967年   1348篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
The application of 2-chloroethylphosphonic acid (CEPA) at 750 or 1500 ppm improved the colour of early harvested Worcester Pearmain apples but greatly increased pre-harvest drop. The drop-promoting effect of CEPA could be overcome by applying succinic acid 2,2-dimethyl hydrazide (aminozide) at 2000 ppm or a-(2,4,5-trichlorophenoxy)-propionic acid (2,4,5-TP) at 20 ppm. The combination of CEPA 750 ppm+2,4,5-TP 20 ppm appeared to be particularly promising for improving the attractiveness, flavour and texture of Worcester Pearmain picked on 1st September and 7th September. No damage was seen on the trees either in the year of application or the following year.  相似文献   
102.
The results are reported of an investigation into the effects of sowing on different dates on the emergence and growth of various cultivars of Phaseolus vulgaris and P. coccineus under field conditions. In 1969 five cultivars of French bean and three of runner bean were sown in the field at fortnightly intervals from April onwards. The experiment was repeated, with the addition of two cultivars, in 1970. Consistent differences were found between and within species for a number of growth parameters.

(1) Especially in the early sowings, seedlings of runner beans emerged before those of French beans, and small-seeded cultivars of French bean (in particular Comtesse de Chambord) before larger-seeded cultivars.

(2) The mean relative growth rates measured after emergence were greater in French beans than in runner beans, but differences within species were not significant. Very early sowing appeared to have a lasting depressive effect on the growth rates of seedlings of both species.

(3) The estimated weights of seedlings at emergence (estimated from regressions of seedling weight on time since emergence and on seed weight) were lower in the early sowings than in later sowings, and especially so in the cultivar Comtesse de Chambord.

The main results in each year were similar, but some differences in detail were found. In particular there were differences between years in the emergence of cultivars as affected by soil temperature. The discrepancies were attributed to a difference in the temperature regimes of the two sites.  相似文献   
103.
Plant growth regulators were applied to the foliage and immature fruit clusters of the stenospermic grape selection ‘C35-33’ at various periods before bloom to stimulate viable seed development. In the 1987 season five different plant growth regulators were used, but in 1988 the growth retardants Cycocel and XE-1019 were used exclusively. Chemical treatments applied 35 days after bud break increased significantly germination percentage. Experimental results indicate that the use of certain plant growth regulators may aid in increasing the efficiency of seedless grape breeding by providing an alternative to in-ovulo embryo culture.  相似文献   
104.
Water, Air, &; Soil Pollution - This paper presents a study of Pb contamination of soil at a clay target shooting facility in Canterbury, New Zealand. The spatial distribution of Pb...  相似文献   
105.
The kinetics of the thermal hydrolysis of the fructans of Agave salmiana were determined during the cooking step of mezcal production in a pilot autoclave. Thermal hydrolysis was achieved at different temperatures and cooking times, ranging from 96 to 116 °C and from 20 to 80 h. A simple kinetic model of the depolymerization of fructans to monomers and other reducing sugars and of the degradation of reducing sugars to furans [principally 5-(hydroxymethyl)furfural, HMF] was developed. From this model, the rate constants of the reactions were calculated, as well as the pre-exponential factors and activation energies of the Arrhenius equation. The model was found to fit the experimental data well. The tradeoff between a maximum fructan hydrolysis and a critical furan concentration in allowing for the best ethanol yield during fermentation was investigated. The results indicated that the thermal hydrolysis of agave was optimal, from the point of view of ethanol yield in the ensuing fermentation, in the temperature range of 106-116 °C and the cooking range time of 6-14 h. The optimal conditions corresponded to a fructan hydrolysis of 80%, producing syrups with furan and reducing sugar concentrations of 1 ± 0.1 and 110 ± 10 g/L, respectively.  相似文献   
106.
107.
108.
109.
110.
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