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981.
基于再生核Hilbert空间小波核函数支持向量机的高光谱遥感影像分类 总被引:1,自引:0,他引:1
针对支持向量机用于高光谱遥感影像分类存在的分类精度不高、参数选择困难等问题,提出一种再生核Hilbert空间的小波核.其可以逼近任意非线性函数,能够有效改进参数估计的效果,进而实现基于再生核Hilbert空间的小波核函数支持向量机(小波支持向量机).并选取北京昌平地区的国产高光谱数据operational modula... 相似文献
982.
983.
984.
本文为验证SVM对高维特征的适应性和可靠性,针对不同特征提取方法与特征组合,以国产OMISⅡ传感器获得的北京昌平地区高光谱遥感据为例,对SVM分类器中特征维数对分类准确率的影响进行了试验,通过对主成分分析、最小噪声分离算法、相关系数分组后特征提取、导数光谱等的分析,表明SVM分类器的分类精度随着特征维数波动,其中主成分分析降维后提取的特征具有用于分类能够获得最高的准确率。通过与最大似然法和光谱角制图分类算法的比较,说明在同样的特征输入情况下SVM分类算法分类的准确率高于最大似然法和光谱角制图分类器。 相似文献
985.
星载GPS GEO卫星定轨的太阳光压宏观模型 总被引:1,自引:0,他引:1
提出了基于太阳光压宏观模型的星载GPS定轨方法,用于在星上确定地球静止卫星轨道.融合卫星运动学信息和星载GPS观测,采用积分滤波法得到连续的轨道解;针对星上太阳光压难以建模的问题,利用宏观模型方法计算GEO卫星所受的光压力.给出了作用在平面板、球形和圆柱形上的光压计算公式,并以“风云四号”卫星为例,建立了相应的宏观模型... 相似文献
986.
Xiaofeng Guo Kun Yang Long Zhao Wei Yang Shenghai Li Meilin Zhu Tandong Yao Yingying Chen 《Boundary-Layer Meteorology》2011,139(2):307-332
We present a field investigation over a melting valley glacier on the Tibetan Plateau. In the ablation zone, aerodynamic roughness
lengths (z
0M
) vary on the order of 10−4–10−2 m, whose evolution corresponds to three melt phases with distinct surface cover and moisture exchange: snow (sublimation/evaporation),
bare ice (deposition/condensation), and ice hummocks (sublimation/evaporation). Bowen-ratio similarity is validated in the
stably stratified katabatic winds, which suggests a useful means for data quality check. A roughness sublayer is regarded
as irrelevant to the present ablation season, because selected characteristics of scalar turbulence over smooth snow are quite
similar to those over hummocky ice. We evaluate three parametrizations of the scalar roughness lengths (z
0T
for temperature and z
0q
for humidity), viz. key factors for the accurate estimation of sensible heat and latent heat fluxes using the bulk aerodynamic
method. The first approach is based on surface-renewal models and has been widely applied in glaciated areas; the second has
never received application over an ice/snow surface, despite its validity in (semi-)arid regions; the third, a derivative
of the first, is proposed for use specifically over rough ice defined as z
0M
> 10−3 m or so. This empirical z
0M
threshold value is deemed of general relevance to glaciated areas (e.g. ice sheet/cap and valley/outlet glaciers), above
which the first approach gives notably underestimated z
0T,q
. The first and the third approaches tend to underestimate and overestimate turbulent heat/moisture exchange, respectively,
frequently leading to relative errors higher than 30%. Comparatively, the second approach produces fairly low errors in energy
flux estimates both in individual melt phases and over the whole ablation season; it thus emerges as a practically useful
choice to parametrize z
0T,q
in glaciated areas. Moreover, we find all three candidate parametrizations unable to predict diurnal variations in the excess
resistances to humidity transfer, thus encouraging more efforts for improvement. 相似文献
987.
Dejuan Jiang Kun Wang Zhi Li Qiuxian Wang 《Theoretical and Applied Climatology》2011,104(3-4):501-509
The variability of extreme summer precipitation over Circum-Bohai-Sea region during 1961?C2008 was investigated based on the daily precipitation data of 63 meteorological stations using the linear regression method, the non-parametric Mann?CKendall test, and the continuous wavelet transform method. The results showed that there were large spatial differences in the trends of extreme summer precipitation indices. Decreasing trends were found in summer total precipitation, extreme precipitation frequency, intensity and proportion, the maximum consecutive wet days (CWD), and the maximum 1- and 5-day precipitation, and the largest decrease was observed in the central coast area (except CWD), although the trends were not statistically significant at the 5% level at most places. Inversely, the maximum consecutive dry days exhibited non-significant increasing trends. Additionally, the significant 2?C4-year periods were detected for eight indices, showing the significant interannual variability of extreme summer precipitation. Overall, the results of this study indicated that in the last 48?years, there was severe water stress over Circum-Bohai-Sea region, especially in the central coast area, which exerted negative effects on economic development and natural ecosystems. 相似文献
988.
Based on the dynamic triaxial test system and using the fitted wave of the Wenchuan earthquake and 1 Hz constant amplitude sinusoid,the paper compares the results of tests on undisturbed loess samples under different loads and vibration modes but under same saturated conditions.Results of the comparative experiment show:The stress-strain curves have a similar trend under random seismic loading and constant amplitude sinusoidal loading,but the random seismic loading is more sensitive to failure strength of the undisturbed loess samples under the same stress. 相似文献
989.
甘肃文县上城台地的地震记录分析 总被引:1,自引:0,他引:1
选取文县上城台地三个不同高程强震台同时记录到的汶川大地震的9次余震记录,研究场地的地震反应和波的传播效应。通过对比峰值加速度、地震反应谱、加速度时程等地震动参数,全面分析了地震动放大效应与地形的关系以及地震动特征与震源的关系。结果表明:相对于山脚,山顶的峰值加速度明显放大,并且山顶的地震动在场地卓越周期附近放大最显著;多数地震记录显示山顶处垂直白水江河谷分量的峰值加速度比值大于平行河谷分量比值;地震动绝对持时从山脚、山腰到山顶依次增长。总之,地形条件和其上覆松散层共同作用造成了上城台地的地震动放大。 相似文献
990.