全文获取类型
收费全文 | 1998篇 |
免费 | 341篇 |
国内免费 | 539篇 |
专业分类
测绘学 | 219篇 |
大气科学 | 425篇 |
地球物理 | 459篇 |
地质学 | 909篇 |
海洋学 | 299篇 |
天文学 | 75篇 |
综合类 | 213篇 |
自然地理 | 279篇 |
出版年
2024年 | 19篇 |
2023年 | 47篇 |
2022年 | 121篇 |
2021年 | 152篇 |
2020年 | 145篇 |
2019年 | 140篇 |
2018年 | 127篇 |
2017年 | 113篇 |
2016年 | 125篇 |
2015年 | 132篇 |
2014年 | 159篇 |
2013年 | 143篇 |
2012年 | 145篇 |
2011年 | 100篇 |
2010年 | 88篇 |
2009年 | 107篇 |
2008年 | 91篇 |
2007年 | 96篇 |
2006年 | 67篇 |
2005年 | 79篇 |
2004年 | 36篇 |
2003年 | 60篇 |
2002年 | 49篇 |
2001年 | 41篇 |
2000年 | 49篇 |
1999年 | 61篇 |
1998年 | 49篇 |
1997年 | 45篇 |
1996年 | 51篇 |
1995年 | 41篇 |
1994年 | 33篇 |
1993年 | 33篇 |
1992年 | 33篇 |
1991年 | 17篇 |
1990年 | 12篇 |
1989年 | 16篇 |
1988年 | 11篇 |
1987年 | 7篇 |
1986年 | 13篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1975年 | 2篇 |
1958年 | 1篇 |
排序方式: 共有2878条查询结果,搜索用时 15 毫秒
941.
942.
943.
2019年12月2日01时沈阳国家基本气象站(沈阳站)气温1 h内异常回升了6.5℃,利用常规和加密地面观测站实况、NCEP再分析及沈阳站逐小时风廓线雷达资料,从系统配置、热力学诊断、城市热岛效应等方面对此次异常升温事件成因进行精细分析。结果表明:沈阳站异常升温阶段,超低空到近地面暖脊过境造成辽宁大部分地区出现气温回升,暖脊过境是引发沈阳站午夜时分异常升温的原因之一;沈阳站位于沈阳市的东南部,当地面风为西北风时,风从温度相对较高的城区吹向郊区,造成沈阳南部郊区各站气温回升,与北部郊区对比得出升温幅度约为3—4℃。城市热岛中心向下风方漂移是沈阳站气温骤升又一原因。值得注意的是,气温回升前的温度基础值对气温回升幅度存在一定程度影响,回升前的基础温度越低,则回升后造成的升温幅度越大。 相似文献
944.
Deuterium and oxygen 18 in precipitation and atmospheric moisture in the upper Urumqi River Basin, eastern Tianshan Mountains 总被引:2,自引:1,他引:1
Fang Feng Zhongqin Li Mingjun Zhang Shuang Jin Zhiwen Dong 《Environmental Earth Sciences》2013,68(4):1199-1209
The contribution of stable isotopes in meteorological, climatological and hydrological research is well known. This study analyzed the deuterium and oxygen 18 contents (δD and δ18O) of precipitation in event-based samples at three stations (Glacier No. 1, Zongkong, Houxia) along the upper Urumqi River Basin from May 2006 to August 2007. The δ18O in precipitation revealed a wide range and a distinct seasonal variation at all three stations, with enriched values occurring in summer and depleted values in winter. A statistically significant positive correlation was observed between the δ18O and δD and local surface air temperature, and better linear relationship existed between δ18O and air temperature than that of δD. This suggests that paleoclimatic archives relating to precipitation δ18O and δD can be useful for qualitative temperature reconstruction. The d-excess in precipitation also exhibited a seasonal variability. Based on NCEP/NCAR reanalysis data, three-dimensional isentropic back-trajectories in HYSPLIT model were employed to determine the moisture source for each precipitation event. Results indicate a dominant effect of westerly air masses in summer and the integrated influence of westerly and polar air masses in winter, and d-excess can be used as a sensitive tracer of the moisture transport history. 相似文献
945.
Gamma-ray bursts are most luminous explosions in the universe. Their ejecta are believed to move towards Earth with a relativistic speed. The interaction between this “relativistic jet” and a circumburst medium drives a pair of (forward and reverse) shocks. The electrons accelerated in these shocks radiate synchrotron emission to power the broad-band afterglow of GRBs. The external shock theory is an elegant theory, since it invokes a limit number of model parameters, and has well predicted spectral and temporal properties. On the other hand, depending on many factors (e.g. the energy content, ambient density profile, collimation of the ejecta, forward vs. reverse shock dynamics, and synchrotron spectral regimes), there is a wide variety of the models. These models have distinct predictions on the afterglow decaying indices, the spectral indices, and the relations between them (the so-called “closure relations”), which have been widely used to interpret the rich multi-wavelength afterglow observations. This review article provides a complete reference of all the analytical synchrotron external shock afterglow models by deriving the temporal and spectral indices of all the models in all spectral regimes, including some regimes that have not been published before. The review article is designated to serve as a useful tool for afterglow observers to quickly identify relevant models to interpret their data. The limitations of the analytical models are reviewed, with a list of situations summarized when numerical treatments are needed. 相似文献
946.
947.
We performed ion irradiation of mineral samples with 50 keV He+, aimed to investigate ion irradiation effects on diagnostic spectral features. Reflectance spectra of samples in 0.375–2.5 μm are measured before and after ion irradiation. Silicates, including Luobusha olivine, plagioclase and basaltic glass, have shown reddening and darkening of reflectance spectra at the VIS–NIR range. Olivine is more sensitive to ion irradiation than plagioclase and basaltic glass. Irradiated Panzhihua ilmenite exhibits higher reflectance and stronger absorption features, which is totally different from lunar soil and analog silicate materials in other experiments. Using continuum removal and MGM fit, we extracted and compared absorption features of olivine spectra before and after irradiation. Ion irradiation can induce band strength decrease of olivine but negligible band centers shift. We estimate band centers shift caused by ion irradiation are quite limited, even less than variations due to chemical composition in silicates. It provides one possible explanation for no systematic shift in band positions in lunar soil. Irradiated Luobusha olivine spectrum matches spectra of olivine-dominated asteroids. Our results suggest space weathering should be new clues to explain the subtle difference between A-type asteroid spectra and laboratory spectra of olivine. 相似文献
948.
Jeffrey L. Carlin Sebastien Lepine Heidi Jo Newberg Li-Cai Deng Timothy C. Beers Yu-Qin Chen Norbert Christlie Xiao-Ting Fu Shuang Gao Carl J. Grillmair PuragraGuhathakurta Zhan-Wen Han Jin-Liang Hou Hsu-Tai Lee Jing Li Chao Liu Xiao-Wei Liu Kai-Ke Pan J. A. Sellwood Hong-Chi Wang Fan Yang Brian Yanny Yue-Yang Zhan Zheng Zheng Zi Zhu 《天体物理学报》2012,(7):755-771
949.
950.
Systematic differences in the duration and frequency content of ground motions from the hanging wall and footwall during the 2008 Wenchuan earthquake are investigated,focusing on the influence of these differences on structural input energy based on the elastic and inelastic energy responses of structures.A comparison of the input energy spectra between the hanging wall and the footwall reveal that the structural input energy on the hanging wall is not amplified due to the short duration and low peak ground velocity to acceleration ratio(V/A).However,the larger demand of structural input energy on the footwall in the range of medium and long periods is observed and the demand increases up to 50% relative to the average level of structural input energy for rupture distances larger than 30 km.The importance of considering the footwall effect on structural input energy when comparing ground motions in the range of medium and long periods is recognized. 相似文献