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   20116篇
  免费   1092篇
  国内免费   21篇
林业   1040篇
农学   633篇
基础科学   145篇
  2996篇
综合类   3365篇
农作物   978篇
水产渔业   1195篇
畜牧兽医   9464篇
园艺   286篇
植物保护   1127篇
  2021年   223篇
  2020年   238篇
  2019年   271篇
  2018年   390篇
  2017年   445篇
  2016年   353篇
  2015年   270篇
  2014年   394篇
  2013年   774篇
  2012年   693篇
  2011年   853篇
  2010年   583篇
  2009年   511篇
  2008年   852篇
  2007年   769篇
  2006年   713篇
  2005年   654篇
  2004年   622篇
  2003年   621篇
  2002年   553篇
  2001年   527篇
  2000年   503篇
  1999年   408篇
  1998年   202篇
  1997年   212篇
  1996年   175篇
  1995年   208篇
  1994年   166篇
  1993年   177篇
  1992年   285篇
  1991年   326篇
  1990年   318篇
  1989年   330篇
  1988年   300篇
  1987年   259篇
  1986年   303篇
  1985年   262篇
  1984年   214篇
  1983年   209篇
  1979年   253篇
  1978年   168篇
  1975年   174篇
  1974年   246篇
  1973年   221篇
  1972年   251篇
  1971年   231篇
  1970年   207篇
  1969年   193篇
  1968年   162篇
  1966年   162篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The objectives of this study were to develop primers and a real time PCR protocol for the postharvest biocontrol yeast Cystofilobasidium infirmominiatum (Cim). The application of this technology was developed to quantify Cim on the surfaces of apple, two pear cultivars, and sweet cherry fruit treated over a range of concentrations. Statistically significant relationships were observed between Cim DNA on fruit surfaces, expressed as μg/m2, and CFU/L of dip suspensions for apple, pear, and sweet cherry. In addition, the relationship for each fruit was significantly different from the other three fruits. Threshold values of concentrations of Cim DNA on the fruit surface were calculated based on regression equations and a dose of 2.0 × 1011 CFU/L of dip suspension, the dose for optimum decay control, and were 4.8, 7.0, 16.5, and 25.2 μg/m2 for Bosc pear, Lapins sweet cherry, d’Anjou pear, and Golden Delicious apple, respectively. Monitoring Cim DNA concentration on fruit surfaces will assure that Cim is being properly applied to fruit and that a sufficient number of cells are present for optimum decay control.  相似文献   
992.
993.
Foliar fertilizers (FF) applied at the reproductive growth stage was reported to increase soybean (Glycine max L. Merr.) yield in field trials. But yield increases have not been consistent. Field experiments were conducted on Calloway silt loam soil in 1981—1982 to determine the effect of two foliar fertilizer (FF) formulations, 16N + 4P + 4K + 1 S (Hanway) and 12 N + 4 P + 4 K + 0.5 S (Folian), and time of application, 0800- and 1900-h, on the growth of seven soybean cultivars from maturity groups V, VI, and VII. Foliar fertilizers were applied at a rate of 187 L/ha?1 in water by a backpack CO2 pressure sprayer at R5 to R6 growth stages. Foliar fertilizers caused no crop injury (leaf burn) when applied at 1900-h but caused moderate injury at 0800-h, which caused a yield reduction. The most significant crop injury was caused by Hanway formulation when applied at 0800-h. Yields were significantly reduced by FF in 1981 but not in 1982. Generally, Folian formulation treatments had higher yields than Hanway formulation treatments, but neither formulation increased yield above that of the untreated plants. The Bragg cultivar exhibited the least amount of crop injury and the most positive yield response to FF. Plant height, 100-seed weight and lodging rates were not adversely affected by the foliar applications. Due to the general lack of consistent yield increases or in some instances yield reduction from FF applications, the formulations used cannot be recommended for use by soybean producers.  相似文献   
994.
The effects of variations in the relative sowing time of component crops in okra/maize and okra/cowpea intercropping systems were examined in 1990 and 1991 cropping seasons. Okra was either sown the same day as, or two weeks before or after maize or cowpea. Intercropping reduced the growth and yield of okra, maize and cowpea relative to their sole crops. However, okra yield was depressed more by maize than by cowpea, especially when okra was sown two weeks after maize. Comparative assessment of okra/maize and okra/cowpea mixtures suggests that it is better to grow okra and cowpea together than intercropping okra and maize because yield advantages were always higher in okra/cowpea (67% and 59% in 1990 and 1991 respectively) than in okra/maize (15% and 29%). The results were discussed in light of competitive abilities of the various components in the mixtures.  相似文献   
995.
The severity of lymphoproliferative disease associated with malignant catarrhal fever was extremely variable among 25 animals at the San Diego Wild Animal Park. Severe lymphoproliferative disease was seen in 3 of 10 Formosan Sika deer (Cervus nippon taiouanus), 3 of 6 Indian Axis deer (Cervus a axis), 3 of 6 Barasingha deer (Cervus d duvauceli), and 1 of 3 Nilgai (Boselaphus tragocamelus). Two Sika deer and 2 Barasingha deer had lesions morphologically indistinguishable from lymphosarcoma. Our findings were consistent with the hypothesis that alcelaphine herpesvirus-1 has oncogenic potential.  相似文献   
996.
Tricresyl phosphate (TCP) in contaminated edible oils was extracted using acetonitrile and detected by thin layer chromatography as well as gas chromatography (GC). The chromatoplate was developed with isooctane-ethyl acetate (90 + 10) and visualized by spraying with 2,6-dichloroquinone chloroimide. TCP gives a characteristic blue-violet spot when heated at 100 degrees C for 15 min. The method is direct and sensitive and can be used to detect as low as 2.5 micrograms TCP or TOCP (tri-o-cresyl phosphate). GC was carried out using 10% OV-101 as the stationary phase and flame ionization detection for confirmation and quantitation of TOCP in oils.  相似文献   
997.
998.
Lignosulphonates are formed by the cleavages of the α-O-4 linkages of the “infinite” lignin network in wood, and a sulphonation of the α- and/or γ-positions of the side chains of the C9 units. The resulting lignosulphonate molecule forms a randomly branched polyelectrolyte. The molecule coils in solution to make a more ball-shaped molecule with the sulphonate groups enriched on the surface. The scaling laws for this model of the lignosulphonate polymer as well as for other models of the lignosulphonate have been derived. The scaling laws for the randomly branched polyelectrolyte and microgel are the same for most properties except the polyelectrolyte expansion. The scaling laws are compared with literature experimental values for radii and polyelectrolyte expansion. The randomly branched polyelectrolyte model successfully accounts for the behaviour in solution. The dependence of the polyelectrolyte expansion on the molecular weight demonstrates that the lignosulphonate is not a microgel structure.  相似文献   
999.
1000.
Bacteria were isolated from necrotic lesions on a horse chestnut tree (Aesculus hippocastanum) with bleeding canker in Hamburg, Germany. Sequencing of the rDNA-ITS region revealed great similarity to pathovars of Pseudomonas syringae. Pseudomonas syringae pv. aesculi was identified by sequence homology of the gyrase B gene. This is the first report of P. syringae pv. aesculi in Germany. Phytophthora was not detected.  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