全文获取类型
收费全文 | 5956篇 |
免费 | 300篇 |
国内免费 | 647篇 |
专业分类
林业 | 788篇 |
农学 | 897篇 |
基础科学 | 429篇 |
910篇 | |
综合类 | 1732篇 |
农作物 | 407篇 |
水产渔业 | 233篇 |
畜牧兽医 | 958篇 |
园艺 | 183篇 |
植物保护 | 366篇 |
出版年
2024年 | 24篇 |
2023年 | 77篇 |
2022年 | 191篇 |
2021年 | 254篇 |
2020年 | 209篇 |
2019年 | 221篇 |
2018年 | 148篇 |
2017年 | 217篇 |
2016年 | 242篇 |
2015年 | 268篇 |
2014年 | 281篇 |
2013年 | 339篇 |
2012年 | 395篇 |
2011年 | 397篇 |
2010年 | 405篇 |
2009年 | 331篇 |
2008年 | 272篇 |
2007年 | 333篇 |
2006年 | 308篇 |
2005年 | 241篇 |
2004年 | 151篇 |
2003年 | 133篇 |
2002年 | 170篇 |
2001年 | 141篇 |
2000年 | 139篇 |
1999年 | 132篇 |
1998年 | 117篇 |
1997年 | 105篇 |
1996年 | 101篇 |
1995年 | 88篇 |
1994年 | 85篇 |
1993年 | 77篇 |
1992年 | 67篇 |
1991年 | 81篇 |
1990年 | 39篇 |
1989年 | 37篇 |
1988年 | 31篇 |
1987年 | 16篇 |
1986年 | 7篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有6903条查询结果,搜索用时 265 毫秒
991.
Ming-Daw Su Mei-Chun Lin Chun-Hung Lin Shih-Fu Wang Tzai-Hung Wen Hsin-I Hsieh 《Paddy and Water Environment》2012,10(1):31-39
As irrigation demands usually take the largest share of water supply, paddy fallow is considered as a drought relieving measure
in some Asian paddy growing countries by transferring the water saved to the municipal and industrial sectors. But the relationship
between fallow area and irrigation demand reduction is not necessarily linear, there may be more than dozens combinations
of fallow farm that can meet the same amount of irrigation demand reduction requirement. The Joint Count Statistics (JCS),
an index commonly used in spatial analysis to measure the spatial coherence among cells was modified as a spatial aggregation
index for evaluating the irrigation demand reduction effectiveness from a spatial perspective. This Modified JCS is supposed
to identify the degree of spatial aggregation by taking underlying irrigation network into considerations. The modified JCS
was proved to be effective to identify better fallow pattern through a case study in Taiwan. 相似文献
992.
PH Hong YD Su JH Su YH Chen TL Hwang CF Weng CH Lee ZH Wen JH Sheu NC Lin YH Kuo PJ Sung 《Marine drugs》2012,10(5):1156-1168
Two new briarane diterpenoids, briarenolides, F (1) and G (2), were isolated from an octocoral identified as Briareum sp. The structures of briaranes 1 and 2 were established by spectroscopic methods and by comparison of the spectroscopic data with those of known briarane analogues. Briarenolide F was proven to be the first 6-hydroperoxybriarane derivative and this compound displayed a significant inhibitory effect on the generation of superoxide anion by human neutrophils. 相似文献
993.
A novel 15C compound, pseudoalteromone B (1), possessing a novel carbon skeleton, was obtained from a marine bacterium Pseudoalteromonas sp. CGH2XX. This bacterium was originally isolated from a cultured-type octocoral Lobophytum crassum, that was growing in cultivating tanks equipped with a flow-through sea water system. The structure of 1 was established by spectroscopic methods. Pseudoalteromone B (1) displayed a modestly inhibitory effect on the release of elastase by human neutrophils. 相似文献
994.
Choo-Aun Neoh Robert Y.-L. Wang Zhong-Hao Din Jui-Hsin Su Yu-Kuei Chen Feng-Jen Tsai Shun-Hsiang Weng Yu-Jen Wu 《Marine drugs》2012,10(12):2893-2911
Sinulariolide, an isolated compound from the soft coral Sinularia flexibilis, possesses the anti-proliferative, anti-migratory and apoptosis-inducing activities against the TSGH bladder carcinoma cell. The anti-tumor effects of sinulariolide were determined by 3-(4,5-cimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay, cell migration assay and flow cytometry, respectively. Sinulariolide inhibited the growth and migration of bladder carcinoma cells in a dose-dependent manner, as well as induced both early and late apoptosis as determined by the flow cytometer. Also, the sinulariolide-induced apoptosis is related to the mitochondrial-mediated apoptosis via caspase-dependent pathways, elucidated by the loss of mitochondrial membrane potential, release of cytochrome C, activation of caspase-3/-9, Bax and Bad, as well as suppression of Bcl-2/Bcl-xL/Mcl-1. Detection of the PARP-1 cleaved product suggested the partial involvement of caspase-independent pathways. Moreover, inhibition of p38MAPK activity leads to the rescue of the cell cytotoxicity of sinulariolide-treated TSGH cells, indicating that the p38MAPK pathway is also involved in the sinulariolide-induced cell apoptosis. Altogether, these results suggest that sinulariolide induces apoptosis against bladder cancer cells through mitochondrial-related and p38MAPK pathways. 相似文献
995.
Li-Hsueh Wang Jyh-Horng Sheu Shih-Yao Kao Jui-Hsin Su Yung-Husan Chen Yu-Hsin Chen Yin-Di Su Yu-Chia Chang Lee-Shing Fang Wei-Hsien Wang Yang-Chang Wu Ping-Jyun Sung 《Marine drugs》2012,10(11):2415-2434
The structures, names, bioactivities and references of 105 natural products obtained from gorgonian corals belonging to the family Plexauridae with an Indo-Pacific distribution are described in this review. All compounds mentioned in this review were obtained from gorgonian corals belonging to the genera Astrogorgia, Bebryce, Echinomuricea, Euplexaura and Menella. 相似文献
996.
2011-2015年河南省农业机械总动力的预测 总被引:1,自引:0,他引:1
农业机械总动力是衡量农业机械化水平的一项重要指标。对河南省农业机械总动力进行预测,将为农业机械化部门制定合理的发展规划提供一定的理论支持,同时也为农机企业了解未来市场需求状况提供一定的参考。以1991-2010年间的河南省农业机械总动力统计数据为基础,利用BP神经网络建立了河南省农业机械总动力的预测模型。该模型采用3层BP神经网络,输入层、隐含层和输出层的神经元数目分别为5,13和1。隐含层和输出层的激励函数分别为正切型与对数型Sigmoid函数。采用分步预测的思想,利用自适应学习速率训练方法对该网络进行了训练,获得了该模型中各层之间的连接权值和各层神经元的阈值。利用该模型对现有数据进行了仿真预测,结果表明,该模型具有较高的预测精度。在此基础上,对河南省"十二五"期间的农业机械总动力进行了预测,并给出了预测数据。 相似文献
997.
998.
999.
1000.
针对螺旋离心泵轴向力求解时,数学模型建立和方程难以封闭等问题,为了实现螺旋离心泵轴向力的定量求解,研究其轴向力受介质的影响和随介质的变化规律,以150×100LN-32型螺旋离心泵为研究对象,选用清水和两相流含沙水作为介质,应用计算流体力学软件Fluent,建立相对坐标系下的时均连续方程及Navier-Stocks方程,并采用标准k-ε方程湍流模型和SIM-PLE算法进行数值模拟,得到螺旋离心泵内流场的压力分布后计算出轴向力,从而避开了单纯数学上定量求解螺旋离心泵轴向力的许多难题.在此前提下,通过研究在固液两相流介质中,颗粒体积分数、颗粒直径及不同的流量对轴向力的影响和变化规律,结果表明:螺旋离心泵的轴向力随两相流介质体积分数的增大而增大;随流量和颗粒粒径的增大反而减小.该结论对于提高螺旋离心泵的稳定性和延长其使用寿命具有重要意义. 相似文献