全文获取类型
收费全文 | 17635篇 |
免费 | 53篇 |
国内免费 | 5篇 |
专业分类
林业 | 3709篇 |
农学 | 1320篇 |
基础科学 | 137篇 |
2906篇 | |
综合类 | 780篇 |
农作物 | 2136篇 |
水产渔业 | 1925篇 |
畜牧兽医 | 1729篇 |
园艺 | 1121篇 |
植物保护 | 1930篇 |
出版年
2023年 | 5篇 |
2022年 | 8篇 |
2021年 | 39篇 |
2020年 | 29篇 |
2019年 | 28篇 |
2018年 | 2761篇 |
2017年 | 2720篇 |
2016年 | 1218篇 |
2015年 | 97篇 |
2014年 | 56篇 |
2013年 | 86篇 |
2012年 | 844篇 |
2011年 | 2183篇 |
2010年 | 2125篇 |
2009年 | 1287篇 |
2008年 | 1374篇 |
2007年 | 1624篇 |
2006年 | 91篇 |
2005年 | 157篇 |
2004年 | 157篇 |
2003年 | 209篇 |
2002年 | 106篇 |
2001年 | 69篇 |
2000年 | 92篇 |
1999年 | 36篇 |
1998年 | 11篇 |
1997年 | 5篇 |
1996年 | 10篇 |
1995年 | 4篇 |
1993年 | 14篇 |
1992年 | 29篇 |
1991年 | 18篇 |
1990年 | 23篇 |
1989年 | 27篇 |
1988年 | 21篇 |
1987年 | 20篇 |
1986年 | 11篇 |
1985年 | 14篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1979年 | 8篇 |
1977年 | 4篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1973年 | 5篇 |
1971年 | 4篇 |
1970年 | 4篇 |
1969年 | 3篇 |
1968年 | 5篇 |
1965年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
73.
74.
75.
76.
A new functional porous carbons (PC-WF) is prepared by activation-pyrolysis method use waste cotton fabrics (WF) as an abundant, cheap and available precursor for removal of Brilliant Crocein (BC-GR) and Cationic Red 2GL (CR-GL) from aqueous phase. The PC-WF was characterized by BET, FTIR, SEM, and XRD techniques, the surface area, total pore volume, average pore diameter was found as 1463.5 m2 g-1, 0.783 cm3 g-1 and 2.14 nm, respectively. The influences on BC-GR and CR-GL adsorption of various experimental factors such as initial concentration and temperature were investigated. Adsorption kinetics was found to be best represented by the pseudo-second order model. The adsorption capacity was 319.8 mg g-1 for BC-GR and 842.5 mg g-1 for CR-GL at 30 °C, respectively. The results indicate that for waste cotton fabrics in particular, the practical application of this process to the production of porous carbon would be possible. 相似文献
77.
The eating quality of cooked rice is important and determines its market price and consumer acceptance. To comprehensively describe the variation of eating quality in 183 rice germplasm accessions, we evaluated 33 eating-quality traits including amylose and protein contents, pasting properties of rice flour, and texture of cooked rice grains. All eating-quality traits varied widely in the germplasm accessions. Principal-components analysis (PCA) revealed that allelic differences in the Wx gene explained the largest proportion of phenotypic variation of the eating-quality traits. In 146 accessions of non-glutinous temperate japonica rice, PCA revealed that protein content and surface texture of the cooked rice grains significantly explained phenotypic variations of the eating-quality traits. An allelic difference based on simple sequence repeats, which was located near a quantitative trait locus (QTL) on the short arm of chromosome 3, was associated with differences in the eating quality of non-glutinous temperate japonica rice. These results suggest that eating quality is controlled by genetic factors, including the Wx gene and the QTL on chromosome 3, in Japanese rice accessions. These genetic factors have been consciously selected for eating quality during rice breeding programs in Japan. 相似文献
78.
79.
80.
Mingshi Li Chengquan Huang Wenjuan Shen Xinyu Ren Yingying Lv Jingrui Wang Zhiliang Zhu 《林业研究》2016,27(6):1329-1341
Forest losses or gains have long been recognized as critical processes modulating the carbon flux between the biosphere and the atmosphere. Timely, accurate and spatially explicit information on forest disturbance and recovery history is required for assessing the effectiveness of existing forest management. The major objectives of our research focused on testing the mapping efficacy of the vegetation change tracker (VCT) model over a forested area in China. We used a new version of VCT algorithm built upon the Landsat time series stacks (LTSS). The LTSS consisted of yearly image acquisitions to map forest disturbance history from 1987 to 2011 over the Ning-Zhen Mountains, Jiangsu Province of east China. The LTSS consisted of TM and ETM+ scenes with different projections due to distinct data sources (Beijing remote sensing ground station and the USGS EROS Center). The validation results of the disturbance year maps showed that most spatial agreement measures ranged from 70 to 86 %, comparable with the VCT accuracies reported for many places in USA. Very low accuracies were identified in 1995 (38.3 %) and 1992 (56.2 %) in the current analysis. These resulted from the insensitivity of the VCT algorithm to detect low intensity disturbances and also from the mis-registration errors of the image pairs. Major forest disturbance types existing in our study area were identified as agricultural expansion (39.8 %), urbanization (24.9 %), forest management practice (19.3 %), and mining (12.8 %). In general, there was a gradual decreasing trend in forest cover throughout this region, caused principally by China’s economic, demographic, environmental and political policies and decisions, as well as some weather events. While VCT has largely been used to assess long term changes and trends in the USA, it has great potential for assessing landscape level change elsewhere throughout the world. 相似文献