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991.
992.
The Zgorzelec-Wiżajny profile cuts through the main European geotectonic units of the Palaeozoic Western and Central European
Platform and the East European Craton, including the connecting Trans-European Suture Zone. The paper summarises 40 years
of research on geomagnetic secular variations along the Zgorzelec-Wiżajny profile since 1966. It discusses methods of processing
measurement records and presenting their results. The latter are presented against the background of the local geology and
the crustal deep magnetic structure data.
The hitherto method of variation analysis was modified to address a new trend in the geomagnetic secular variations that has
emerged in the East European Craton during the last five years (2001–2005). 相似文献
993.
1885年以来长江中下游梅雨期在70年代末发生了一次强年代际突变:从1958-1978年的弱梅雨时段突变为1979-1999年的强梅雨时段.后21年梅雨量比前21年平均增加了66%,长江中下游夏涝年出现率显著增长.此两时段梅雨由弱转强和出梅/入夏期由偏早转为延迟呈密切联系,这在相当程度上反映中国东部夏季气候-水资源分布的突变.进一步分析,发现两时段内影响梅雨盈亏年际变化的前期因子也很不同.研究了两时段梅雨盛行趋势突变的成因,发现与显著增强的人类活动有关:20世纪70年代末,我国工业开始大发展,大气污染的增长导致地面太阳辐射减少,中国北方沙化土地面积又迅速扩大.同时温室效应的增长也表现在我国暖冬(尤其是2月).此外,长江中下游1月降水量增多;厄尔尼诺事件从20世纪70年代末开始也明显增多.由上述5因子组成的相关点聚图凸显出前后两时段处于截然不同的地-气环境位相.从2000年开始,长江中下游梅雨又进入新的偏少期,中国东部夏季水资源分布正面临新的变化. 相似文献
994.
中国降水年内分配的时空演变特征之新法研究 总被引:4,自引:0,他引:4
利用中国160站50a月降水资料,分别用降水量序列法、降水量方差法及降水量离差法定量计算了全年降水的聚集程度(聚集度)和最大降水对应的聚集时间(聚集期),并利用计算出的聚集度和聚集期分析了中国降水年内时空变化的气候特征,验证并比较了3种新方法的合理性;挑选长江中下游作为关键区,对该区的聚集度进行了区域平均的趋势分析和小波分析,结果发现,该区的降水聚集度具有明显的年际变化,而年代际变化则表现得比较稳定。 相似文献
995.
中国近50 a地温的变化特征 总被引:20,自引:2,他引:20
利用1954-2001年中国532站的月平均0.8m层地温资料,对我国及其不同区域地温的变化特征进行了分析。结果表明,近50a,全国年平均地温的年代际变化大致为下降阶段,相对气候冷期及上升阶段。地温的区域变化特征显著,90年代后东北地区地温增温最显著,西南东部地区地温下降趋势明显,青藏高原东部地温在1980年前后发生一次急剧下降的突变过程。地温季节变化中,冬季地温年代际变化特征与其他季节相比差异较显著,而春季地温年际变化出现异常的频率最大。 相似文献
996.
Seismic studies of the lowermost mantle suggest that the core-mantle boundary (CMB) region is strongly laterally heterogeneous
over both local and global scales. These heterogeneities are likely to be associated with significant lateral viscosity variations
that may influence the shape of the long-wavelength non-hydrostatic geoid. In the present paper we investigate the effect
of these lateral viscosity variations on the solution of the inverse problem known as the inferences of viscosity from the
geoid. We find that the presence of lateral viscosity variations in the CMB region can significantly improve the percentage
fit of the predicted data with observations (from 42 to 70% in case of free-air gravity) while the basic characterisics of
the mantle viscosity model, namely the viscosity increase with depth and the rate of layering, remain more or less the same
as in the case of the best-fitting radially symmetric viscosity models. Assuming that viscosity is laterally dependent in
the CMB region, and radially dependent elsewhere, we determine the largescale features of the viscosity structure in the lowermost
mantle. The viscosity pattern found for the CMB region shows a high density of hotspots above the regions of higher-than-average
viscosity. This result suggests an important role for petrological heterogeneities in the lowermost mantle, potentially associated
with a post-perovskite phase transition. Another potential interpretation is that the lateral viscosity variations derived
for the CMB region correspond in reality to lateral variations in the mechanical conditions at the CMB boundary or to large-scale
undulations of a chemically distinct layer at the lowermost mantle. 相似文献
997.
Air samples were collected covering a full diurnal cycle during each month of the year 2002 at a mountaintop of Mt. Abu (24.6^∘ N, 72.7^∘ E, 1680 amsl). These samples were analyzed for C2−C4 NMHCs using a gas chromatograph (GC) equipped with flame ionization detector (FID). The seasonally averaged diurnal distributions of these NMHCs do not show significant variations in the summer season. While sharp peaks in the diurnal variation of some species during evening hours are additional features apart from higher levels in all NMHCs in the winter season. The seasonal variations in relatively long lived species (e.g. ethane, propane and acetylene) are observed to be more pronounced compared to those in reactive species (e.g. ethene, propene and butanes). The seasonal changes in transport patterns seem to be more dominant factor at this site for the observed variations in NMHCs than changes in OH radical concentration. The annual mean mixing ratios of ethane, ethene, propane, propene, i-butane, acetylene, and n-butane are 1.22 ± 0.58, 0.34 ± 0.24, 0.46
± 0.20, 0.17 ± 0.14, 0.21 ± 0.18, 0.41 ± 0.43, and 0.31 ± 0.35 ppbv, respectively. Only few pairs of NMHCs are observed to show good correlations, mainly due to transport of air masses with different degree of photochemical processing. A comparison of this measurement with data reported for other remote sites of the globe indicates lower levels of light NMHCs in the tropical sites. The annual mean mixing ratios of various C2−C4 NMHCs at Mt. Abu are lower by factors ranging between 3 to 9 compared to a nearest urban site of Ahmedabad. The annual mean propylene (propene) equivalent concentrations of about 1.12 and 8.62 ppbC were calculated for Mt. Abu and Ahmedabad, respectively. 相似文献
998.
The methods were discussed to calculate the gravity variation due to crustal deformation based on a model of dis-location on a finite rectangular plane.Taking the Lijiang Ms=7.0 earthquake as an example the calculating princi-ple of fault parameters were determined,and the results were given.Of particular interests were the characteristics of the gravity variations in different dislocation types.With comparison between the calculated results and the practical measurements,it was found that the model could to some extent account for the observations.But it failed to give explanations to the more far spatial gravity variation. 相似文献
999.
1000.
利用1998年1月至2000年5月美国新墨西哥州Starfire Optic Range (SOR:35°N,106.5°W)钠风场、温度激光雷达共46个观测夜的数据,分析大气中间层钠层结构的季节变化特征. 结果表明,钠层丰度变化显示出很强的年振荡现象,其平均值为5.06×109cm-2,最大值出现在11月份,最小值出现在6月和7月份. 钠层均方根宽度的平均值为4.30km,中心高度的平均值为91.60km. 均方根宽度和中心高度变化显示出较明显的半年振荡特征. 年平均钠层夜间变化显示出潮汐的影响,丰度夜间变化在午夜前最小,日出前达到最大. 白天光离化作用和夜间复合过程,与潮汐动力学一起,导致钠层丰度发生较大的夜间变化. 相似文献