全文获取类型
收费全文 | 157篇 |
免费 | 28篇 |
国内免费 | 16篇 |
专业分类
测绘学 | 19篇 |
大气科学 | 6篇 |
地球物理 | 15篇 |
地质学 | 44篇 |
海洋学 | 82篇 |
天文学 | 11篇 |
综合类 | 19篇 |
自然地理 | 5篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2018年 | 3篇 |
2017年 | 8篇 |
2016年 | 1篇 |
2015年 | 6篇 |
2014年 | 9篇 |
2013年 | 8篇 |
2012年 | 6篇 |
2011年 | 11篇 |
2010年 | 4篇 |
2009年 | 10篇 |
2008年 | 14篇 |
2007年 | 23篇 |
2006年 | 16篇 |
2005年 | 7篇 |
2004年 | 15篇 |
2003年 | 6篇 |
2002年 | 6篇 |
2001年 | 10篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 5篇 |
1997年 | 4篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1987年 | 1篇 |
排序方式: 共有201条查询结果,搜索用时 78 毫秒
101.
本文通过进行魁蚶吊笼养殖试验,研究分析了不同入笼规格、挂养水层及放养密度对魁蚶的生长及存活率的影响,比较了魁蚶吊笼养殖与底播养殖模式的不同差异。试验表明,吊笼魁蚶的最适入笼规格为1.5 cm;越冬最适挂养水层为3.5 m以上,度夏最适水层为2.5~3 m;第一次越冬最适密度为1 000粒/层,第一次度夏最适密度为500粒/层,第二次越冬最适密度为200粒/层,第二次度夏最适密度为100粒/层;通过吊笼养殖至3~4 cm规格后进行底播养殖,能够有效提高魁蚶成活率,由此可见,吊笼—底播接力养殖,是提高魁蚶养殖效益的一种有效养殖模式。 相似文献
102.
Climate change affects the environment and natural resources immensely. Rainfall, temperature and evapotranspiration are major parameters of climate affecting changes in the environment. Evapotranspiration plays a key role in crop production and water balance of a region, one of the major parameters affected by climate change. The reference evapotranspiration or ET0 is a calculated parameter used in this research. In the present study, changes in the future rainfall, minimum and maximum temperature, and ET0 have been shown by downscaling the HadCM3 (Hadley Centre Coupled Model version 3) model data. The selected study area is located in a part of the Narmada river basin area in Madhya Pradesh in central India. The downscaled outputs of projected rainfall, ET0 and temperatures have been shown for the 21st century with the HADCM3 data of A2 scenario by the Least Square Support Vector Machine (LS-SVM) model. The efficiency of the LS-SVM model was measured by different statistical methods. The selected predictors show considerable correlation with the rainfall and temperature and the application of this model has been done in a basin area which is an agriculture based region and is sensitive to the change of rainfall and temperature. Results showed an increase in the future rainfall, temperatures and ET0. The temperature increase is projected in the high rise of minimum temperature in winter time and the highest increase in maximum temperature is projected in the pre-monsoon season or from March to May. Highest increase is projected in the 2080s in 2081–2091 and 2091–2099 in maximum temperature and 2091–2099 in minimum temperature in all the stations. Winter maximum temperature has been observed to have increased in the future. High rainfall is also observed with higher ET0 in some decades. Two peaks of the increase are observed in ET0 in the April–May and in the October. Variation in these parameters due to climate change might have an impact on the future water resource of the study area, which is mainly an agricultural based region, and will help in proper planning and management. 相似文献
103.
104.
Steven W. Ellingson 《Experimental Astronomy》2004,17(1-3):261-267
Radio frequency interference (RFI) has plagued radio astronomy from its inception. The Workshop on the Mitigation of Radio Frequency Interference in Radio Astronomy (RFI2004) was held in Penticton, BC, Canada in July 2004 in order to consider the prognosis for the RFI problem, in particular as it impacts the planned Square Kilometre Array (SKA). This paper concludes that RFI is unlikely to be a “showstopper” in achieving SKA science goals, but that improved RFI mitigation technology may nevertheless be essential in order to take advantage of the vastly improved sensitivity, bandwidth, and field of view. Reported results provide some optimism that the desired improvements in RFI mitigation technology are possible, but indicate that much more work is required. 相似文献
105.
T. J. Cornwell 《Experimental Astronomy》2004,17(1-3):329-343
I investigate the problem of high dynamic range continuum synthesis imaging in the presence of confusing sources, using scaling arguments and simulations. I derive a quantified cost equation for the computer hardware needed to support such observations for the EVLA and the SKA. This cost has two main components – from the data volume, scaling as D−6 (where D is the antenna diameter), and from the non-coplanar baselines effect, scaling as D−2, for a total scaling of D−8. A factor of two in antenna diameter thus corresponds to 12 years of Moore’s law (18 month doubling time) cost reduction in computing hardware. For a SKA built with 12.5 m antennas observing with 1 arcsecond at 1.4 GHz, I find the computing load to be about 150 Petaflops (costing about $500 million in 2015). For 25 m antennas, the load is about 256 times lower, costing $2 million in 2015. This new cost equation differs from that of Perley and Clark (2003), which has scaling as D−6. This is because I find that the excellent Fourier plane coverage of the small antenna design does not significantly change the convergence rate of the Clean algorithm, which is already satisfactory in this regime.The National Radio Astronomy Observatory is operated by Associated Universities, Inc., under cooperative agreement with the National Science Foundation. 相似文献
106.
结合工程实例介绍了灌注桩工程中有关成孔体积、混凝土灌注量与钢筋笼重量等内容的精确计算公式,这些公式对灌注桩前期概算及施工后期工程量计算具有指导意义。 相似文献
107.
108.
109.
详细推导了电偶源频率测深单分量电场定义的视电阻率数字滤波计算公式,并且应用最小二乘法设计了只有30个系数的滤波器,编制出适用于袖珍计算机的视电阻率计算程序,使计算速度大为提高.与用均匀半空间的精确公式计算的视电阻率对比,最大相对误差<2%. 相似文献
110.