全文获取类型
收费全文 | 733篇 |
免费 | 244篇 |
国内免费 | 469篇 |
专业分类
测绘学 | 10篇 |
大气科学 | 705篇 |
地球物理 | 185篇 |
地质学 | 144篇 |
海洋学 | 241篇 |
天文学 | 11篇 |
综合类 | 63篇 |
自然地理 | 87篇 |
出版年
2024年 | 5篇 |
2023年 | 11篇 |
2022年 | 30篇 |
2021年 | 34篇 |
2020年 | 39篇 |
2019年 | 44篇 |
2018年 | 55篇 |
2017年 | 59篇 |
2016年 | 51篇 |
2015年 | 54篇 |
2014年 | 53篇 |
2013年 | 87篇 |
2012年 | 62篇 |
2011年 | 44篇 |
2010年 | 47篇 |
2009年 | 59篇 |
2008年 | 68篇 |
2007年 | 64篇 |
2006年 | 51篇 |
2005年 | 72篇 |
2004年 | 41篇 |
2003年 | 58篇 |
2002年 | 53篇 |
2001年 | 43篇 |
2000年 | 36篇 |
1999年 | 33篇 |
1998年 | 47篇 |
1997年 | 19篇 |
1996年 | 17篇 |
1995年 | 15篇 |
1994年 | 21篇 |
1993年 | 23篇 |
1992年 | 20篇 |
1991年 | 11篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1977年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1446条查询结果,搜索用时 15 毫秒
961.
962.
利用1980年1月~1983年12月已滤波的OLR资料,采用经验正交函数分析方法,对1980~1981年(正常年)和1982~1983年(异常年)低纬西太平洋和印度洋地区低频振荡的空间分布及遥相关特征进行了研究.结果表明:正常年与异常年,这些地区低频振荡的强度、空间型及时间系数的变化有较大的差异.此外,还发现正常年这些地区存在3种低频遥相关,即赤道西太平洋型,北热带西太平洋型和赤道印度洋型;异常年则仅存在2种低频遥相关,即赤道西太平洋型和南热带西太平洋型.由于受厄尔尼诺事件的影响,东西向偶极型低频振荡中心的位置和强度都有很大的变化 相似文献
963.
In this study, a modified identification and tracking algorithm for extratropical cyclones is developed. This identification scheme is based on triangular-mesh contouring techniques combined with a connected-component labeling method in order to detect the outer boundaries and spatial domain characteristics of individual cyclones. A new tracking method allowing for the identification of cyclone merging and splitting events, as well as short-lived windstorms, is developed to reduce the uncertainty in the tracking of extratropical cyclones. I also show that this method excludes the tracks of open systems that would have been unnecessarily detected using conventional NCP methods. The climatological features of the distribution of cyclone frequencies are substantially larger over the traditional storm track regions compared to those seen in previous studies. Interestingly, a significant increase in the cyclone density in the Arctic occurs during all four seasons(up to 19%in summer) compared to that seen with a latitude–longitude gridded mesh analysis. I develop two new regional intensity indices(depth and vorticity) based on the cyclonic domain to better quantify the cyclonic activity in the Arctic region, and find that the interannual variabilities in these two indices are highly consistent. The results of this analysis may shed light on high-latitude cyclonic behavior studies via the newly detected 2D cyclone atlas derived from this cyclonic-domain-based algorithm. 相似文献
964.
This paper compares data from linearized and nonlinear Zebiak–Cane model, as constrained by observed sea surface temperature anomaly(SSTA), in simulating central Pacific(CP) and eastern Pacific(EP) El Nio. The difference between the temperature advections(determined by subtracting those of the linearized model from those of the nonlinear model),referred to here as the nonlinearly induced temperature advection change(NTA), is analyzed. The results demonstrate that the NTA records warming in the central equatorial Pacific during CP El Nio and makes fewer contributions to the structural distinctions of the CP El Nio, whereas it records warming in the eastern equatorial Pacific during EP El Nio, and thus significantly promotes EP El Nio during El Nio–type selection. The NTA for CP and EP El Nio varies in its amplitude,and is smaller in CP El Nio than it is in EP El Nio. These results demonstrate that CP El Nio are weakly modulated by small intensities of NTA, and may be controlled by weak nonlinearity; whereas, EP El Nio are significantly enhanced by large amplitudes of NTA, and are therefore likely to be modulated by relatively strong nonlinearity. These data could explain why CP El Nio are weaker than EP El Nio. Because the NTA for CP and EP El Nio differs in spatial structures and intensities, as well as their roles within different El Nio modes, the diversity of El Nio may be closely related to changes in the nonlinear characteristics of the tropical Pacific. 相似文献
965.
The initial errors constitute one of the main limiting factors in the ability to predict the El Nio–Southern Oscillation(ENSO) in ocean–atmosphere coupled models. The conditional nonlinear optimal perturbation(CNOP) approach was employed to study the largest initial error growth in the El Nio predictions of an intermediate coupled model(ICM). The optimal initial errors(as represented by CNOPs) in sea surface temperature anomalies(SSTAs) and sea level anomalies(SLAs) were obtained with seasonal variation. The CNOP-induced perturbations, which tend to evolve into the La Nia mode, were found to have the same dynamics as ENSO itself. This indicates that, if CNOP-type errors are present in the initial conditions used to make a prediction of El Nio, the El Nio event tends to be under-predicted. In particular, compared with other seasonal CNOPs, the CNOPs in winter can induce the largest error growth, which gives rise to an ENSO amplitude that is hardly ever predicted accurately. Additionally, it was found that the CNOP-induced perturbations exhibit a strong spring predictability barrier(SPB) phenomenon for ENSO prediction. These results offer a way to enhance ICM prediction skill and, particularly,weaken the SPB phenomenon by filtering the CNOP-type errors in the initial state. The characteristic distributions of the CNOPs derived from the ICM also provide useful information for targeted observations through data assimilation. Given the fact that the derived CNOPs are season-dependent, it is suggested that seasonally varying targeted observations should be implemented to accurately predict ENSO events. 相似文献
966.
不同太平洋年代际振荡和ENSO位相下大气水分收支变化对北半球冬季太平洋蒸发量的影响 总被引:1,自引:1,他引:0
本文利用OAFlux资料研究了1958~2015年北半球冬季太平洋蒸发量在不同厄尔尼诺—南方涛动(ENSO)和太平洋年代际振荡(PDO)位相下的分布特征,并从水汽收支的角度分析了蒸发量异常的成因,结果表明:ENSO主要影响热带东太平洋、副热带西北太平洋和中纬度北太平洋中部的蒸发量。El Ni?o(La Ni?a)时水汽在北太平洋中部异常辐散(辐合),有利于当地大气水汽含量减小(增大),造成蒸发量增大(减小);副热带西北太平洋异常的水汽辐合(辐散)有利于蒸发量减小(增大);除此以外,蒸发量在热带东太平洋蒸发量增大(减小)则主要是降水量增大(减小)导致。与此同时,ENSO对上述海区蒸发量的影响还受到PDO的调控,当PDO处于暖(冷)位相时,El Ni?o(La Ni?a)造成蒸发量异常程度在中纬度北太平洋中部显著增大,这主要是由降水量增大(减小)引起的大气水汽含量减小(增大)所致,此时对应着风暴轴异常增大(减小);当PDO处于冷(暖)位相时,El Ni?o(La Ni?a)造成的蒸发量异常程度在副热带西北太平洋和热带东太平洋显著增大,而这与湿度变化引起的水汽平流异常程度增大紧密相关。 相似文献
967.
采用1960~2014年西南地区93个站的逐月降水资料以及NCEP/NCAR再分析月平均资料,分析了东部型El Ni?o(EP El Ni?o)和中部型El Ni?o(CP El Ni?o)对我国西南地区冬季降水的不同影响。结果表明,EP ElNi?o年冬季和CP El Ni?o事件中1994/1995年、2002/2003年冬季,我国西南地区受异常偏东风影响,获得来自孟加拉湾和南海的水汽供应。同时,西南地区存在明显的幅合上升运动,上升运动异常增强,对流加强,导致西南地区冬季降水偏多;而CP El Ni?o事件中1968/1969年、1977/1978年,2004/2005年、2009/2010年冬季,我国西南地区受异常西北风影响,来自孟加拉湾和南海的水汽减少。同时,西南地区存在明显的幅散下沉运动,上升运动异常减弱,对流减弱,导致西南地区冬季降水偏少。 相似文献
968.
索马里急流是北半球夏季最为强盛的越赤道气流,南亚高压则是出现在对流层高层、平流层低层最大最稳定的反气旋环流系统,基于近60年NECP/NCAR再分析资料,本文研究了年代际尺度上夏季索马里急流与南亚高压的联系。研究结果表明:年代际尺度上,索马里急流与南亚高压存在显著的正相关关系,当索马里急流偏弱(强)时,夏季南亚高压偏弱西退(偏强东进)。对不同年代际背景下南亚高压东西部的经向垂直环流的分析发现,当索马里急流处于偏弱位相时,南亚高压西半部(20°~70°E)经向垂直环流偏强,而其东半部(75°~120°E)经向垂直环流减弱;反之亦然。南亚高压南北两侧的纬向垂直环流的变化也有差异,索马里急流偏弱(强)时,北部南亚高压(27.5°~35°N)的青藏高原上空纬向垂直环流显著减弱(增强),而南部南亚高压(20°~27.5°N)的伊朗高原上空纬向垂直环流减弱(增强)明显。进一步的研究发现,年代际尺度上索马里急流与南亚高压的联系受到PDO(Pacific Decadal Oscillation)年代际变化的调制。PDO正负位相的转折,首先改变了对流层高层副热带西风急流的强弱变化,从而使得位于其南部的南亚高压强度和热带东风急流发生相应的改变,热带东风急流的变化又通过热带印度洋上空的局地纬向垂直环流将异常信号传递到对流低层,改变热带地区索马里急流的强弱变化。 相似文献
969.
970.
行星运动与厄尔尼诺、东北夏季低温冷害 总被引:1,自引:0,他引:1
利用厄尔尼诺与行星运动的联系,对厄尔尼诺进行了分类。发现东北夏季低温冷害的发生与厄尔尼诺的类型有关:负极值型和负正极值型厄尔尼诺的发生年几乎与冷害年一一对应,其他类型的厄尔尼诺则很少甚至不发生冷害。统计表明:三大行星(火、木、土)冲日时日心黄纬的负极值年的次年和木星的正极值的前一年及当年,有利于冷害的发生;土星运行到日心黄经为19~121°时,会导致冷害群的发生。 相似文献