全文获取类型
收费全文 | 6038篇 |
免费 | 1156篇 |
国内免费 | 1379篇 |
专业分类
测绘学 | 544篇 |
大气科学 | 1255篇 |
地球物理 | 1699篇 |
地质学 | 2928篇 |
海洋学 | 671篇 |
天文学 | 158篇 |
综合类 | 653篇 |
自然地理 | 665篇 |
出版年
2024年 | 30篇 |
2023年 | 112篇 |
2022年 | 281篇 |
2021年 | 303篇 |
2020年 | 246篇 |
2019年 | 296篇 |
2018年 | 341篇 |
2017年 | 320篇 |
2016年 | 365篇 |
2015年 | 287篇 |
2014年 | 323篇 |
2013年 | 352篇 |
2012年 | 292篇 |
2011年 | 277篇 |
2010年 | 326篇 |
2009年 | 309篇 |
2008年 | 280篇 |
2007年 | 284篇 |
2006年 | 212篇 |
2005年 | 223篇 |
2004年 | 189篇 |
2003年 | 201篇 |
2002年 | 268篇 |
2001年 | 290篇 |
2000年 | 260篇 |
1999年 | 278篇 |
1998年 | 238篇 |
1997年 | 206篇 |
1996年 | 186篇 |
1995年 | 164篇 |
1994年 | 164篇 |
1993年 | 132篇 |
1992年 | 119篇 |
1991年 | 86篇 |
1990年 | 69篇 |
1989年 | 56篇 |
1988年 | 46篇 |
1987年 | 34篇 |
1986年 | 19篇 |
1985年 | 23篇 |
1984年 | 16篇 |
1983年 | 18篇 |
1982年 | 9篇 |
1981年 | 11篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1958年 | 8篇 |
1954年 | 1篇 |
排序方式: 共有8573条查询结果,搜索用时 15 毫秒
81.
通过对辽河群岩石中主要变质矿物的观察和研究,以岩石的变形历史作为变质结晶作用的相对时标,确定了矿物生长的时序特征及其演化过程。发现变质与变形既是有密切联系的又是各自独立的地质作用,辽河期的变形作用存在明显的3个变形幕,而辽河期的变质作用是个连续的完整的过程,无明显的热波动。变质作用高峰和变形作用高峰存在时间差。 相似文献
82.
本文研究了锂、铷、铯三元素在丙酮有机溶剂中的行为,测定条件,干扰离子的影响及消除,使灵敏度分别比在水相中提高为2.5—3.5倍。方法灵敏度高,干扰少,测定范围为0~5PPM,适用于矿石中微量锂、铷、铯三元素同时测定。 相似文献
83.
84.
Zhen Tao Quanzhou Gao Wenping Guo Zhengang Wang Yongling Zhang Chenji Xie Xiakun Huang Hongwei Zhong 《山地科学学报》2011,8(5):694-703
A whole year analysis of riverine dissolved organic carbon (DOC) concentrations in the Xijiang River (XJR), South China, showed that the mean riverine DOC concentration (1.24 mg L-1) in the XJR was notably lower than the averaged value (5.75 mg L-1) of the global riverine DOC concentration in several major rivers. There is an inconspicuous monthly fluctuation of the DOC signal in the XJR, but on a semi-yearly time scale, however, the riverine DOC concentration had significant difference between hydrological... 相似文献
85.
Polycyclic aromatic hydrocarbons (PAHs) contamination of topsoil in Benxi City, Northeast China was investigated in this study,
and sampling sites were located in industrial area and residential area. Results demonstrate that there is high variability
in the total PAHs concentrations, ranging from 783.00 ng/g to 729 076.29 ng/g dry weight in the topsoil of Benxi City and
the pollution in industrial area is the most serious. The results also present that higher molecular weight PAHs (4–6 rings)
contribute substantially (79.03%) to the overall content of PAHs. The PAHs sources were determined with factor analysis by
nonnegative constraints, and the results show that PAHs originating from traffic tunnel, power plant, coke oven and residential
emission sources, account for 27.10%, 40.81%, 20.11% and 11.98%, respectively, of the total. The PAHs pollution is the most
serious around Benxi Iron and Steel Group Corporation, and the PAHs mainly originate from coke oven and traffic tunnel, with
the average contribution rate of 57.40% and 42.60%, respectively. The source apportionment results are basically consistent
with the industry distribution, and the geographical and climatic characteristics of the study area. 相似文献
86.
以位于秦岭—大别造山带之北、华北陆块南部、地跨华北陆块稳定块体、陆块南部边缘变形带的南华北盆地为研究对象,通过对研究区42条不同时代的野外剖面详细观测,运用层序地层学理论,把南华北盆地作为一个整体系统,对青白口系—侏罗系层序界面特征及时空分布规律进行了系统分析,共识别出了8种类型层序界面的物质表现形式,分别是不整合面、渣状层、古喀斯特作用面、冲刷侵蚀面、超覆面、岩性岩相转换面、最大海泛面、最大湖泛面。并重点讨论了各类型界面的时空分布特征。结果表明:在时间演化上,从早到晚由海相—海陆过渡相—陆相,层序界面经历了海相沉积不整合、古喀斯特作用面、渣状层到陆相不整合面、冲刷侵蚀面等;在空间上,同一层序界面在不同相带表现形式不同,同一种类型的界面可在不同相带出现,但不同相带表现特征有一定差异性。 相似文献
87.
基于地磁对电离层的影响,尝试利用GPS信号和Klobuchar模型估计地磁北极在地理坐标系中的位置,并建立了相应的数学模型。理论分析和数据验证了方法的可行性,如果进行Klobuchar模型的区域化改进和算法的完善,将更有利于地磁北极估计的可靠性和估计精度的提高。 相似文献
88.
1INTRODUCTIONEcosystem services can be divided into two major cat-egories, one is system function, and the other is sys-tem services and goods provision, which provide not only materials such as food and medicine, but also support and maintenance of whole system. Ecological services contribute to the whole economic system, both directly and indirectly, and consequently repre-sent parts of the total value of our economy system (COSTANZA etal., 1997; GUO etal., 2001). Sustainable d… 相似文献
89.
?????????????λ??????????????????????????????????t??????????????????????????????????????????????????λ?????GPS????????????????????????????mm/s?????????????1 cm/s?? 相似文献
90.
Debris flows introduced in landslide deposits under rainfall conditions: The case of Wenjiagou gully 总被引:4,自引:2,他引:4
Debris flows often occur in landslide deposits during heavy rainstorms. Debris flows are initiated by surface water runoff and unsaturated seepage under rainfall conditions. A physical model based on an infinitely long, uniform and void-rich sediment layer was applied to analyze the triggering of debris-flow introduced in landslide deposits. To determine the initiation condition for rainfall-induced debris flows, we conducted a surface water runoff and saturated-unsaturated seepage numerical program to model rainfall infiltration and runoff on a slope. This program was combined with physical modeling and stability analysis to make certain the initiation condition for rainfall-introduced debris flows. Taking the landslide deposits at Wenjiagou gully as an example, the initiation conditions for debris flow were computed. The results show that increase height of surface-water runoff and the decrease of saturated sediment shear strength of are the main reasons for triggering debris-flows under heavy rainfall conditions. The debris-flow triggering is affected by the depth of surface-water runoff, the slope saturation and shear strength of the sediment. 相似文献