全文获取类型
收费全文 | 89篇 |
免费 | 8篇 |
国内免费 | 16篇 |
专业分类
测绘学 | 18篇 |
大气科学 | 3篇 |
地球物理 | 20篇 |
地质学 | 51篇 |
海洋学 | 6篇 |
天文学 | 3篇 |
综合类 | 6篇 |
自然地理 | 6篇 |
出版年
2024年 | 1篇 |
2022年 | 5篇 |
2021年 | 3篇 |
2019年 | 4篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2016年 | 4篇 |
2015年 | 4篇 |
2014年 | 4篇 |
2013年 | 5篇 |
2012年 | 10篇 |
2011年 | 3篇 |
2010年 | 6篇 |
2009年 | 4篇 |
2008年 | 4篇 |
2007年 | 2篇 |
2006年 | 5篇 |
2005年 | 3篇 |
2004年 | 6篇 |
2003年 | 5篇 |
2002年 | 3篇 |
2001年 | 10篇 |
2000年 | 5篇 |
1999年 | 3篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有113条查询结果,搜索用时 109 毫秒
51.
无特定病原中国对虾种群选育的研究 总被引:16,自引:1,他引:16
报道了无特定病原中国对虾种群(SPF)选育的结果,主要介绍1999-2000年选育子3代和子4代的养殖结果。1999年选育对虾子3代养殖平均1788kg/ha,对虾平均体长13.69cm。而对照池中暂养池对虾体长3-4cm发病死亡,养殖池对虾体长6cm发病死亡;2000年选育对虾子4代养殖平均3168kg/ha,对虾平均体长15.00cm;对照池产量为3450kg/ha,对虾平均体长13.30cm。说明经过连续几代的人工选育,对虾生长速度明显加快。 相似文献
52.
53.
54.
Climatic and environmental change in Yanchi Lake, Northwest China since the Late Glacial: A comprehensive analysis of lake sediments 总被引:1,自引:0,他引:1
Modern climate research has shown that the Asian summer monsoon water vapor transport is limited to the eastern part of the Qilian Mountains. On the Holocene millennial-scale, whether the northwest boundary of the summer monsoon varies according to climate change is a key scientific issue. Yanchi Lake is located in the northern Qilian Mountains and the middle of the Hexi Corridor, where the modern climate is less affected by the Asian summer monsoon. It is a key research area for examining the long-term variations of the Asian summer monsoon. Paleoclimatic data, including AMS ^14C dates of pollen concentrates and bulk organic carbon, lithology, grain-size, mineral composition and geochemical proxies were acquired from sediments of Yanchi Lake. The chronological results show that the lower part of the lacustrine section is formed mainly in the Late Glacial and early Holocene period, while the proxies' data indicate the lake expansion is associated with high content of mineral salts. The middle part of this section is formed during the transitional period of the early and middle Holocene. Affected by the reworking effect, the pollen concentrates AMS^14C dates from the middle part of the section are generally older than those from the lower part. Since the mid-Holocene, Yanchi Lake retreated significantly and the deposition rate dropped obvi- ously. The Yanchi Lake record is consistent with the Late Glacial and Holocene lake records in the Qinghai-Tibet Plateau and the climatic records in typical monsoon domain, which indicate the lake expansion and the strong Asian summer monsoon during the Late Glacial and early Holocene. The long-term monsoonal pattern is different from the lake evolution in Central Asia on the Holocene millennial-scale. This study proves the monsoon impacts on the northwestern margin of the summer monsoon, and also proves the fact that the northern boundary of the summer monsoon moves according to millennial-scale climate change. 相似文献
55.
为评估黄土高原地区地震滑坡致灾区域,提出一种基于模糊信息优化处理的地震滑坡滑距预测方法。在野外调查、室内试验和分析的基础上,对黄土高原的地震滑坡类型、性质和影响因素进行分析。以摩根斯坦-普莱斯法计算黄土边坡的稳定性,建立边坡最小安全系数与影响因素的关系,其影响因素主要包括地震烈度、比高、坡角、容重、内黏聚力、内摩擦角等,并在此基础上得到纯黄土地震滑坡滑距的影响关系。将黄土高原地区数次大震中采集到的93个样本数据进行归纳分析,建立模糊信息优化处理模型。所得的计算结果通过误差校验和与其他滑坡滑距预测方法进行对比,来证明本模型有较高的准确性。最后对天水市22个潜在滑坡的边坡进行滑距预测。 相似文献
56.
对靖西县高山广播电视转播发射台发生雷灾事故的原因进行分析,提出高山广播电视转播发射台应该采取的防雷措施。 相似文献
57.
对土石坝心墙掺砾黏土开展模拟心墙单元小主应力方向加载的真三轴试验,首先对试样进行不同围压条件下等向固结,然后保持小主应力恒定,通过调整大主应力和中主应力,以模拟土石坝竣工后的初始三向应力状态。试验过程中保持大主应力和中主应力恒定,从小主应力方向单向加载,以模拟土石坝蓄水过程中心墙单元所经历的应力路径。试验结果与常规三轴试验以及复杂应力条件下大主应力方向真三轴加载试验结果都有显著不同。不同初始应力条件下,不同主应力方向的初始切线模量和初始切线泊松比的变化规律非常复杂,应力–应变显现出明显的各向异性。在心墙堆石坝施工过程及蓄水过程中,心墙单元所经历的应力路径明显不同,合理的土体本构模型应该对这种由于加荷路径不同所引起的不同方向模量和泊松比进行合理描述。 相似文献
58.
为了向用图者较好地传递统计数据信息,从量化的角度探讨了对统计地图的图面设计和符号设计的优化问题,并在一个实例中加以实现。 相似文献
59.
The results from Raman spectroscopy analysis of salt aqueous solutions at −170°C demonstrate that for those clearly sharp
iron peaks whose Raman wavenumber is close to each other such as NO
3
−
and CO
3
2−
, their original shape could be restorable by the stripping technique, and that ice’s sharp characteristic peak 3090–3109
cm−1) is steady, while the spectrum band of the complex compound (nCl−-[H+-OH−]n) chlorine ion combined chemically with water molecule is 3401–3413 cm−1. On the other hand, the research shows that the higher the negative iron concentration, the stronger its Raman characteristic
peak intensity and the smaller the ice’s. Based on the number of data and theoretical work, the strong correlation of the
molar concentration of negative ion with the S
i/S
H
2O band area ratio is built up. Moreover, the developed Raman method is successfully used in the component analysis of the
field fluid inclusions from Silurian sandstone in Tarim basin. 相似文献
60.
The results from Raman spectroscopy analysis of salt aqueous solutions at -170℃ demonstrate that for those clearly sharp iron peaks whose Raman wavenumber is close to each other such as and , their original shape could be restorable by the stripping technique, and that ice's sharp characteristic peak (3090-3109 cm-1) is steady, while the spectrum band of the complex compound (nCl--[H+-OH-]n) chlorine ion combined chemically with water molecule is 3401-3413 cm-1. On the other hand, the research shows that the higher the negative iron concentration, the stronger its Raman characteristic peak intensity and the smaller the ice's. Based on the number of data and theoretical work, the strong correlation of the molar concentration of negative ion with the band area ratio is built up. Moreover, the developed Raman method is successfully used in the component analysis of the field fluid inclusions from Silurian sandstone in Tarim basin. 相似文献