全文获取类型
收费全文 | 5152篇 |
免费 | 1407篇 |
国内免费 | 2182篇 |
专业分类
测绘学 | 941篇 |
大气科学 | 822篇 |
地球物理 | 1340篇 |
地质学 | 3471篇 |
海洋学 | 987篇 |
天文学 | 59篇 |
综合类 | 422篇 |
自然地理 | 699篇 |
出版年
2024年 | 86篇 |
2023年 | 202篇 |
2022年 | 407篇 |
2021年 | 471篇 |
2020年 | 396篇 |
2019年 | 428篇 |
2018年 | 401篇 |
2017年 | 370篇 |
2016年 | 377篇 |
2015年 | 408篇 |
2014年 | 368篇 |
2013年 | 414篇 |
2012年 | 504篇 |
2011年 | 503篇 |
2010年 | 459篇 |
2009年 | 382篇 |
2008年 | 412篇 |
2007年 | 396篇 |
2006年 | 337篇 |
2005年 | 317篇 |
2004年 | 229篇 |
2003年 | 142篇 |
2002年 | 149篇 |
2001年 | 139篇 |
2000年 | 120篇 |
1999年 | 90篇 |
1998年 | 39篇 |
1997年 | 25篇 |
1996年 | 32篇 |
1995年 | 18篇 |
1994年 | 15篇 |
1993年 | 9篇 |
1992年 | 15篇 |
1991年 | 13篇 |
1990年 | 11篇 |
1989年 | 7篇 |
1987年 | 5篇 |
1985年 | 4篇 |
1982年 | 3篇 |
1980年 | 2篇 |
1979年 | 6篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1966年 | 2篇 |
1965年 | 3篇 |
1957年 | 4篇 |
1954年 | 4篇 |
1934年 | 2篇 |
1928年 | 3篇 |
1925年 | 3篇 |
排序方式: 共有8741条查询结果,搜索用时 31 毫秒
81.
Although Eddy Covariance (EC) technique is one of the best methods for estimating the energy and mass exchanges between underlying surface and atmosphere in micrometeorology, errors and uncertainties still exist without necessary corrections. In this paper, we will focus on the effect of coordinate system on the eddy fluxes. Based on the data observed over four sites (one farmland site, one grassland site and two forest sites), the effects of three coordinate system transforming methods (Double Rotation-DR, Triple Rotation-TR and Planar Fit-PF)on the turbulent fluxes are analyzed. It shows that (i) the corrected fluxes are more or less than the uncorrected fluxes, which is related mainly to the sloping degree of surface, wind speed and wind direction; and (ii) pitch angle has a sinusoidal dependence on wind direction, especially in the regular sloping terrain; and (iii) PF method is something like the simplification of TR or DR,and there are not obvious distinctions in correction in sloping grassland and flat farmland, but PF method is not suitable for uneven and irregular forest sites. 相似文献
82.
新疆阿尔泰造山带构造作用的锆石裂变径迹分析 总被引:1,自引:0,他引:1
在新疆阿尔泰造山带所获得的19个锆石裂变径迹年龄变化于155-243Ma之间,明显地分为2组,分别对应于2个构造活动期,早期为155-189Ma,晚期为189-243Ma。这与磷灰石裂变径迹年龄反映的62-100Ma和100-160Ma两个构造期完全一致。早期和晚期构造活动期持续的时间分别为54-60Ma和34-38Ma,而这两个构造期之间的间隔时间,则从早到晚由83-89Ma变为89-93Ma。同时,锆石裂变径迹年龄与距特斯巴汗断裂和巴寨断裂的距离有关,反映这两条断裂带对区域构造演化的控制作用。 相似文献
83.
84.
85.
86.
87.
Zhongwu Li Hao Peng Binggeng Xie Chun Liu Xiaodong Nie Danyang Wang Mei Huang Haibing Xiao Lin Shi Xuqin Zhang Jieyu Jiang 《水文研究》2020,34(6):1446-1459
Exploring the chemical characterization of dissolved organic matter (DOM) is important for understanding the fate of laterally transported organic matter in watersheds. We hypothesized that differences in water-extractable organic matter (WEOM) in soils of varying land uses and rainfall events may significantly affect the quality and the quantity of stream DOM. To test our hypotheses, characteristics of rainfall-runoff DOM and WEOM of source materials (topsoil from different land uses and gullies, as well as typical vegetation) were investigated at two adjacent catchments in the Loess Plateau of China, using ultraviolet–visible absorbance and excitation emission matrix fluorescence with parallel factor analysis (PARAFAC). Results indicated that land-use types may significantly affect the chemical composition of soil WEOM, including its aromaticity, molecular weight, and degree of humification. The PARAFAC analysis demonstrated that the soils and stream water were dominated by terrestrial/allochthonous humic-like substances and microbial transformable humic-like fluorophores. Shifts in the fluorescence properties of stream DOM suggested a pronounced change in the relative proportion of allochthonous versus autochthonous material under different rainfall patterns and land uses. For example, high proportions of forestland could provide more allochthonous DOM input. This study highlights the relevance of soils and hydrological dynamics on the composition and fluxes of DOM issuing from watersheds. The composition of DOM in soils was influenced by land-use type. Precipitation patterns influenced the proportion of terrestrial versus microbial origins of DOM in surface runoff. Contributions of allochthonous, terrestrially derived DOM inputs were highest from forested landscapes. 相似文献
88.
89.
研究了移动测量系统宽幅影像的拼接与量测算法。通过建立三幅影像柱面全景投影的几何关系,能够直接拼接完成宽幅影像。利用宽幅影像和原始影像间反投影变换关系以及三幅原始影像的同、异步立体像对,可建立宽幅影像与物方空间坐标间一一对应关系,从而实现宽幅影像目标的量测算法。宽幅影像的投影拼接和量测实验表明,利用柱面全景投影拼接得到宽幅影像的方法可应用于移动测量平台宽幅影像序列的拼接;在原始影像具备同步立体像对的条件下,宽幅影像量测的绝对精度可达1 m以内,相对精度可达0.2 m以内,满足城市环境实景目标量测的精度需求。 相似文献
90.