全文获取类型
收费全文 | 17039篇 |
免费 | 34篇 |
国内免费 | 1篇 |
专业分类
林业 | 3666篇 |
农学 | 1324篇 |
基础科学 | 138篇 |
2806篇 | |
综合类 | 730篇 |
农作物 | 2124篇 |
水产渔业 | 1823篇 |
畜牧兽医 | 1442篇 |
园艺 | 1121篇 |
植物保护 | 1900篇 |
出版年
2023年 | 3篇 |
2022年 | 6篇 |
2021年 | 31篇 |
2020年 | 14篇 |
2019年 | 32篇 |
2018年 | 2750篇 |
2017年 | 2713篇 |
2016年 | 1194篇 |
2015年 | 94篇 |
2014年 | 40篇 |
2013年 | 45篇 |
2012年 | 832篇 |
2011年 | 2167篇 |
2010年 | 2115篇 |
2009年 | 1273篇 |
2008年 | 1359篇 |
2007年 | 1609篇 |
2006年 | 74篇 |
2005年 | 138篇 |
2004年 | 140篇 |
2003年 | 197篇 |
2002年 | 89篇 |
2001年 | 13篇 |
2000年 | 62篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 13篇 |
1992年 | 9篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 7篇 |
1988年 | 12篇 |
1987年 | 1篇 |
1979年 | 1篇 |
1977年 | 4篇 |
1972年 | 1篇 |
1969年 | 1篇 |
1968年 | 4篇 |
1967年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 796 毫秒
51.
52.
53.
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
54.
55.
56.
57.
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
58.
The effects of ammonia and nitrite on vigour, survival rate, moulting rate of zoea of blue swimming crab, Portunus pelagicus, were studied. A total of five nitrite-N treatments (26.67, 53.34, 106.68, 213.36, 426.72 mg/l) and a control (no nitrite-N added) were
set up for the acute nitrite-N toxicity experiment; a total of five ammonia-N treatments (8.43, 16.86, 33.72, 67.44, 134.88 mg/l)
and a control (no ammonia-N added) were set up for the acute ammonia-N toxicity experiment. The results showed that the vigour,
survival rate and moulting rate of zoea of the blue swimming crabs exposed to over 53.34 mg/l were significantly different
(P < 0.05) from the control group. The zoea LC50 values (mg/l) of nitrite-N were 179.47, 76.56, 66.70, 37.49, 25.01, 25.35, 25.34 mg/l for 24, 36, 48, 60, 72, 84, 96 h, respectively.
The vigour, survival rate and moulting rate of zoea of the blue swimming crabs exposed to over 16.86 mg/l were significantly
different (P < 0.05) from the control group. The zoea LC50 values (mg/l) of ammonia-N were 51.04, 39.62, 38.72, 24.43, 16.90, 13.42, 11.16 mg/l for 24, 36, 48, 60, 72, 84, 96 h, respectively.
The zoeae are highly sensitive to ammonia and nitrite, and the toxicity of ammonia and nitrite on Portunus pelagicus decrease with development of this crab. 相似文献
59.
60.
Yukino TAMAMURA-ANDOH Nobuyuki TANAKA Keisuke SATO Yoshino MIZUNO Nobuo ARAI Ayako WATANABE-YANAI Masato AKIBA Masahiro KUSUMOTO 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》2021,83(5):754
We examined the antimicrobial susceptibility of 848 Escherichia coli isolates from 237 feces samples of wild sika deer (Cervus nippon) captured between 2016 and 2019 in 39 of the 47 prefectures of Japan. Five of the 237 wild sika deer (2.1%) carried E. coli with resistance to at least one antimicrobial, and all the resistant isolates showed resistance to tetracycline. The resistant isolates contained antimicrobial resistance genes that were similar to those in E. coli derived from humans and farm animals. Although wild sika deer are not currently likely to be a source for the transmission of antimicrobial resistance in Japan, they can potentially mediate antimicrobial resistance spread by coming into contact with humans, animals, and their surroundings. 相似文献