全文获取类型
收费全文 | 2377篇 |
免费 | 392篇 |
国内免费 | 644篇 |
专业分类
测绘学 | 295篇 |
大气科学 | 924篇 |
地球物理 | 334篇 |
地质学 | 630篇 |
海洋学 | 276篇 |
天文学 | 58篇 |
综合类 | 163篇 |
自然地理 | 733篇 |
出版年
2024年 | 8篇 |
2023年 | 41篇 |
2022年 | 108篇 |
2021年 | 124篇 |
2020年 | 133篇 |
2019年 | 145篇 |
2018年 | 98篇 |
2017年 | 113篇 |
2016年 | 119篇 |
2015年 | 94篇 |
2014年 | 143篇 |
2013年 | 193篇 |
2012年 | 158篇 |
2011年 | 151篇 |
2010年 | 132篇 |
2009年 | 145篇 |
2008年 | 154篇 |
2007年 | 192篇 |
2006年 | 163篇 |
2005年 | 137篇 |
2004年 | 122篇 |
2003年 | 101篇 |
2002年 | 98篇 |
2001年 | 75篇 |
2000年 | 67篇 |
1999年 | 66篇 |
1998年 | 55篇 |
1997年 | 58篇 |
1996年 | 41篇 |
1995年 | 47篇 |
1994年 | 33篇 |
1993年 | 22篇 |
1992年 | 22篇 |
1991年 | 17篇 |
1990年 | 8篇 |
1989年 | 3篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有3413条查询结果,搜索用时 15 毫秒
991.
Huang Jiayou 《大气科学进展》2000,17(2):184-192
To reveal climatic variation over North China, the climatic jumps in summer in Beijing are analyzed using the data of precipitation of summer (June, July, August) during the period of 1841-1993, in which those missed before 1950 were reconstructed by the stepwise regression method with minimum forecast error. The climatic jumps at different scales are analyzed using different diagnostic methods with different decade (10-100 years) windows. Some new methods and ideas are proposed. The variance difference, the linear tendency difference, and the difference of power spectral distribution between the samples before and after the period at the moving point in the center of the series are compared with other methods (for example, Mann-Kendall test, t-test, and accumulative anomaly etc.). Considering the differences among the statistics above, a synthetic jump index is also proposed in order to get the definite jump points in the moving series. The results show that the climatic jumps in the area occurred in the 1890’s, the 1910s and the 1920s, and mostly in the 1920s, which suggests that the local climatic jumps in North China have a simultaneous response to the global warming in the hundred-year scales. 相似文献
992.
993.
Adding Local Accuracy to Direct Sequential Simulation 总被引:3,自引:0,他引:3
Jef Caers 《Mathematical Geology》2000,32(7):815-850
Geostatistical simulations are globally accurate in the sense that they reproduce global statistics such as variograms and histograms. Kriging is locally accurate in the minimum local error variance sense. Building on the concept of direct sequential simulation, we propose a fast simulation method that can share these opposing objectives. It is shown that the multiple-point entropy of the resulting simulation is related to the univariate entropy of the local conditional distributions used to draw simulated values. Adding local accuracy to conditional simulations does not detract much from variogram reproduction and can be used to increase multiple-point entropy. The methods developed are illustrated using a case study. 相似文献
994.
Local music policies within a global music industry: cultural quarters in Manchester and Sheffield 总被引:4,自引:0,他引:4
This paper will explore the relationship between the local and the global in the music industry through the lens of place-based cultural policies.The first part of the paper will outline current debates around the complex interaction of the local and the global in culture in general and the popular music industry in particular. Alongside the continuous expansion of globalisation has been a reassertion of ‘place', of ‘locality'. Whilst this has been investigated to some extent at the level of local music scenes it has never been fully addressed in terms of music industry policy as part of an economic development strategy. Yet it is here that the particular values of ‘place' are asserted in the face of some ‘global' music industry with a view to developing (or at least retaining some of the benefits of) a local music industry.Whilst situating itself within these debates about the relationship of local and global musical production and consumption, the paper explores the different strategies of two northern English cities and their attempts to promote culture, and music, within each cities ‘cultural quarter': Sheffield's Cultural Industries Quarter and Manchester's Northern Quarter. The paper analyses the role and appropriateness of local authority policy intervention, the importance of ‘soft' networks within local music scenes and the different ways in which authorities in each example have tried to overcome dichotomies of art and industry, cultural and economy. 相似文献
995.
996.
新生代构造抬升对地表化学风化和全球气候变化的影响 总被引:9,自引:0,他引:9
全球新生代构造抬升 ,特别是南亚喜马拉雅青藏高原和南美安底斯山脉和Altiplano高原在新生代的抬升对地表化学风化和全球气候变化产生了重要影响。它对地表化学风化的影响主要表现为引起造山带地区化学风化能力的提高 ;而它对全球气候变化的影响则主要表现在两个方面 ,一是直接的物理影响 ,即通过对大气和海洋循环的影响来对大气变化产生作用 ;一是通过对地表硅酸盐岩石的化学风化造成大气CO2 变化和全球温度的改变 ,从而对气候变化产生间接的生物化学效应。目前看来 ,新生代构造抬升造成的大气CO2 浓度减少是造成全球新生代气候变冷的重要原因。这已得到了近 10年来计算机大气环流模型 (GCMs)数值模拟和野外实验研究的支持 ,但在关于地表化学风化的主要控制因素 ,以及海洋Sr同位素是否可作为反映地表化学风化速率变化的替代性标志和气候变化反馈机制等方面 ,还需要作进一步研究。 相似文献
997.
ABRUPT CHANGE OF LAKE ENVIRONMENT IN WEST CHINA: AN EVIDENCE FOR GLOBAL CLIMATE WARMINGtheNational(G19980 4 0 80 2 )andCAS’sKeyProjectonTibetanPlateauResearch(KZ951 A1 2 0 4 ) 相似文献
998.
冰川消融对气候变化的响应——以乌鲁木齐河源1号冰川为例 总被引:19,自引:10,他引:9
目前气候变暖导致的冰川退缩,引起了广泛关注.以新疆天山乌鲁木齐河源1号冰川为例,根据1959年以来的观测资料,研究了冰川消融对气候变化的响应.结果表明:近50 a来冰川在表面粒雪特征、成冰带、冰川温度、面积、厚度及末端位置等方面发生了显著变化,而这些变化均与气温的升高有着密切的联系;冰川的退缩自20世纪80年代后,尤其是近10 a来出现了加速趋势.其原因除夏季气温升高外,还有两个重要因素,一是冰川温度升高造成冷储的减少,二是冰川表面反射率下降导致辐射能量接收的增强.冰川物质平衡在1986年之前由气温和降水共同决定,之后主要受气温控制. 相似文献
999.
1000.
New and important roles for DMSP in marine microbial communities 总被引:4,自引:0,他引:4
The algal osmolyte dimethylsulfoniopropionate (DMSP) is recognised as the major precursor of marine dimethylsulfide (DMS), a volatile sulfur compound that affects atmospheric chemistry and global climate. Recent studies, using 35S-DMSP tracer techniques, suggest that DMSP may play additional very important roles in the microbial ecology and biogeochemistry of the surface ocean. DMSP may serve as an intracellular osmolyte in bacteria that take up phytoplankton-derived DMSP from seawater. In addition, DMSP appears to support from 1 to 13% of the bacterial carbon demand in surface waters, making it one of the most significant single substrates for bacterioplankton so far identified. Furthermore, the sulfur from DMSP is efficiently incorporated into bacterial proteins (mostly into methionine) and DMSP appears to be a major source of sulfur for marine bacterioplankton. Assimilatory metabolism of DMSP is via methanethiol (MeSH) that is produced by a demethylation/demethiolation pathway which dominates DMSP degradation in situ. Based on the linkage between assimilatory metabolism of DMSP and bacterial growth, we offer a hypothesis whereby DMSP availability to bacteria controls the production of DMS by the competing DMSP lyase pathway. Also linked with the assimilatory metabolism of DMSP is the production of excess MeSH which, if not assimilated into protein, reacts to form dissolved non-volatile compounds. These include sulfate and DOM–metal–MeSH complexes, both of which represent major short-term end-products of DMSP degradation. Because production rates of MeSH in seawater are high (3–90 nM d−1), reaction of MeSH with trace metals could affect metal availability and chemistry in seawater. Overall, results of recent studies provide evidence that DMSP plays important roles in the carbon, sulfur and perhaps metal and DOM cycles in marine microbial communities. These findings, coupled with the fact that the small fraction of DMSP converted to DMS may influence atmospheric chemistry and climate dynamics, draws attention to DMSP as a molecule of central importance to marine biogeochemical and ecological processes. 相似文献