全文获取类型
收费全文 | 87680篇 |
免费 | 4253篇 |
国内免费 | 8079篇 |
专业分类
林业 | 8938篇 |
农学 | 8285篇 |
基础科学 | 4693篇 |
12409篇 | |
综合类 | 44246篇 |
农作物 | 4676篇 |
水产渔业 | 2317篇 |
畜牧兽医 | 7106篇 |
园艺 | 2013篇 |
植物保护 | 5329篇 |
出版年
2024年 | 544篇 |
2023年 | 1279篇 |
2022年 | 1933篇 |
2021年 | 2109篇 |
2020年 | 2149篇 |
2019年 | 2676篇 |
2018年 | 1591篇 |
2017年 | 2690篇 |
2016年 | 3359篇 |
2015年 | 3016篇 |
2014年 | 4028篇 |
2013年 | 4349篇 |
2012年 | 6248篇 |
2011年 | 6499篇 |
2010年 | 5384篇 |
2009年 | 5390篇 |
2008年 | 4988篇 |
2007年 | 6036篇 |
2006年 | 5291篇 |
2005年 | 4549篇 |
2004年 | 3444篇 |
2003年 | 3055篇 |
2002年 | 2361篇 |
2001年 | 2151篇 |
2000年 | 1949篇 |
1999年 | 1554篇 |
1998年 | 1376篇 |
1997年 | 1224篇 |
1996年 | 1236篇 |
1995年 | 1164篇 |
1994年 | 1096篇 |
1993年 | 987篇 |
1992年 | 942篇 |
1991年 | 756篇 |
1990年 | 694篇 |
1989年 | 604篇 |
1988年 | 474篇 |
1987年 | 323篇 |
1986年 | 169篇 |
1985年 | 60篇 |
1984年 | 45篇 |
1983年 | 24篇 |
1982年 | 31篇 |
1981年 | 31篇 |
1980年 | 28篇 |
1979年 | 24篇 |
1978年 | 26篇 |
1977年 | 17篇 |
1976年 | 23篇 |
1962年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
21.
黄邦华 《安徽农业大学学报》2001,(2):52-54
青少年违法犯罪是当前的严重问题,造成这一局面有青少年自身的原因,也有社会环境的影响。预防青少年违法犯罪己成为迫在眉睫的问题,必须坚持学校、社会和家庭的配合,建立社会化防治网络,形成良好的外部环境,才能使青少年得以健康成长。 相似文献
22.
本文报道广东南岭国家级自然保护区大东山管理站所辖林区广翅目1科2属2种,脉翅目3科8属10种,长翅目1科1属1种,鳞翅目(蛾类)27科213属299种的昆虫名录。 相似文献
23.
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
24.
江立 《仲恺农业技术学院学报》1996,9(2):1-4,19
本文述了“广东山区开发理论与实践研讨会”所达成共识的观点:广东山区开发具有重要的战略意义,广东山区开发必须走可持续肆展,农业产业化经营、工业化道路,同时必须搞好基础设施建设,组织好商品流通工作,优化资源配置。 相似文献
25.
26.
青藏高原西部狮泉河宽谷区的荒漠化过程 总被引:2,自引:0,他引:2
狮泉河宽谷区的荒漠化过程以整个青藏高原的环境演化为背景,受人为的资源利用不合理而强化。今天的宽谷景观一方面隐含了高原宽谷的变化,一方面显示出干旱,退化的主导特征,较之西北干旱区,生态系统更具脆弱性,荒漠化的治理应在发挥区内水资源优质的同时强调生态系统自身的稳定。 相似文献
27.
28.
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
29.
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
30.