全文获取类型
收费全文 | 59364篇 |
免费 | 3103篇 |
国内免费 | 7211篇 |
专业分类
林业 | 2519篇 |
农学 | 8177篇 |
基础科学 | 2396篇 |
8045篇 | |
综合类 | 25850篇 |
农作物 | 7632篇 |
水产渔业 | 2082篇 |
畜牧兽医 | 6730篇 |
园艺 | 3515篇 |
植物保护 | 2732篇 |
出版年
2024年 | 400篇 |
2023年 | 1154篇 |
2022年 | 2045篇 |
2021年 | 2351篇 |
2020年 | 2357篇 |
2019年 | 2556篇 |
2018年 | 1900篇 |
2017年 | 2578篇 |
2016年 | 3183篇 |
2015年 | 2946篇 |
2014年 | 3584篇 |
2013年 | 3833篇 |
2012年 | 4540篇 |
2011年 | 4217篇 |
2010年 | 3365篇 |
2009年 | 3387篇 |
2008年 | 3002篇 |
2007年 | 3311篇 |
2006年 | 2983篇 |
2005年 | 2584篇 |
2004年 | 1903篇 |
2003年 | 1553篇 |
2002年 | 1246篇 |
2001年 | 1137篇 |
2000年 | 1020篇 |
1999年 | 843篇 |
1998年 | 806篇 |
1997年 | 686篇 |
1996年 | 626篇 |
1995年 | 579篇 |
1994年 | 473篇 |
1993年 | 476篇 |
1992年 | 391篇 |
1991年 | 333篇 |
1990年 | 318篇 |
1989年 | 264篇 |
1988年 | 183篇 |
1987年 | 141篇 |
1986年 | 85篇 |
1985年 | 61篇 |
1984年 | 56篇 |
1983年 | 19篇 |
1982年 | 23篇 |
1981年 | 46篇 |
1980年 | 28篇 |
1979年 | 15篇 |
1978年 | 19篇 |
1977年 | 17篇 |
1976年 | 24篇 |
1962年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
71.
72.
A field experiment was conducted with different nitrogen regimes to assess the growth and yield performance of wheat genotypes which differ in nitrate assimilation potential. Genotypic differences in biomass accumulation were observed at different growth stages. The nitrogen treatment had little effect on biomass accumulation at early stages of growth, while at later stages of growth there was enhanced biomass accumulation when N was applied in more than two splits. On an average, genotypes with high nitrate reductase activity (the 'HNR' genotypes) accumulated 14.2 % more biomass than the genotypes with low nitrate reductase activity ('LNR' genotypes) when an extra dose (40 kg N ha−1 ) of nitrogen was given at the time of anthesis. The application of nitrogen in more than two splits increased grain yield of both 'HNR' and 'LNR' genotypes mainly by increasing grain weight per ear. The application of an extra dose of nitrogen (40 kg N ha−1 ) at the time of anthesis increased grain yield of 'HNR' genotypes by 38.5 % as compared to 'LNR' genotypes. 相似文献
73.
1988~1990年通过一年生苗的高生长、地径与合理密度的观察。兴安落叶松育苗容器材料和规格的研究结果表明,纸容器的苗木无论在苗高、地径上与其它容器比较都具有显著性差异,容器规格选择φ3.8×12.5cm为宜,较理想密度为910株/m~2。 相似文献
74.
花生区组四粒红与根茎区组Arachis glabrata杂交果针经离体培养克服了不亲和性,获得杂种。杂种二代性状出现疯狂分离,但有些性状仍分别倾向双亲。经叶片过氧化物同工酶分析,酶带的条数、宽窄、活性强弱及迁移率,杂种与双亲有明显差异,也有共同之处,初步证明了杂种的真实性。 相似文献
75.
76.
J. Müller 《Journal of Agronomy and Crop Science》1993,171(4):217-235
Dry Matter Production, CO2 Exchange, Carbohydrate and Nitrogen Content of Winter Wheat at Elevated CO2 Concentration and Drought Stress
Methods of mathematical modelling and simulation are being used to an increasing degree in estimating the effects of rising atmospheric CO2 concentration and changing climatic conditions on agricultural ecosystems. In this context, detailed knowledge is required about the possible effects on crop growth and physiological processes. To this aim, the influence of an elevated CO2 concentration and of drought stress on dry matter production, CO2 exchange, and on carbohydrate and nitrogen content was studied in two winter wheat varieties from shooting to milk ripeness. Elevated CO2 concentration leads to a compensation of drought stress and at optimal water supply to an increase of vegetative dry matter and of yield to the fourfold value. This effects were caused by enhanced growth of secondary tillers which were reduced in plants cultivated at atmospheric CO2 concentration. Analogous effects in the development of ear organs were influenced additionally by competitive interactions between the developing organs. The content and the mass of ethanol soluble carbohydrates in leaves and stems were increased after the CO2 treatment and exhausted more completely during the grain filling period after drought stress. Plants cultivated from shooting to milk ripeness at elevated CO2 concentration showed a reduced response of net photosynthesis rate to increasing CO2 concentration by comparison with untreated plants. The rate of dark respiration was increased in this plants. 相似文献
Methods of mathematical modelling and simulation are being used to an increasing degree in estimating the effects of rising atmospheric CO
77.
M. Özgen 《Journal of Agronomy and Crop Science》1991,166(5):318-325
The purpose of this study was to compare responsiveness to environment as well as the stability of newly developed promising lines with traditional commercial cultivars. Subject research was conducted in Ankara between 1983-1989 on common and durum wheat cultivars and lines. Regression coefficient (b) was used as the criterion of genotypes' responsiveness to environment whereas deviation from regression (S2 d) and coefficient of determination (r2 ) were used as stability parameters. Each experiment year was regarded as an environment and yield average of each year was used as the environmental index.
In consequence of the research, it was determined that new varieties with high yield, adaptable to diverse environments could be developed by means of hybridizations between parents having different genetic characteristics which were provided from diverse ecological regions. 相似文献
In consequence of the research, it was determined that new varieties with high yield, adaptable to diverse environments could be developed by means of hybridizations between parents having different genetic characteristics which were provided from diverse ecological regions. 相似文献
78.
79.
Time course of grain filling pattern in two rice (Oryza sativa L.) cultivars, grown under normal and low light intensities, was studied. The number of spikelets, partially filled grains and high density grains were monitored at a 5 day interval during grain filling period from uniform panicles tagged at anthesis. The low light tolerant cultivar Swarnaprabha had more high density grains and less partially filled grains throughout the grain filling period and at harvest compared to cultivar Ratna under both normal and low light intensities. Further, the opening of spikelets in two flushes in Swarnaprabha seemed to result in a more efficient resource allocation and hence better yield as compared to Ratna, in which the opening of spikelets was in a single flush on day 10. 相似文献
80.
室内药效试验表明:麦根宁1号、敌力脱对小麦根腐病菌的生长均有良好的抑制作用。麦根宁Ⅰ号稀释300倍时,平均抑菌圈直径最大;敌力脱稀释800倍时,平均抑菌圈直径最大。同时,麦根宁Ⅰ号、敌力脱Ⅱ号,粉锈宁对小麦全蚀病菌生长也有明显的抑制作用。粉锈宁,麦根宁Ⅰ,Ⅱ号在稀释10000倍时,抑菌率均达100%;敌力脱在稀释15000倍时,平均抑菌率仍达89.7%。 相似文献