全文获取类型
收费全文 | 302篇 |
免费 | 40篇 |
国内免费 | 72篇 |
专业分类
测绘学 | 47篇 |
大气科学 | 19篇 |
地球物理 | 57篇 |
地质学 | 164篇 |
海洋学 | 20篇 |
天文学 | 22篇 |
综合类 | 20篇 |
自然地理 | 65篇 |
出版年
2024年 | 2篇 |
2023年 | 5篇 |
2022年 | 17篇 |
2021年 | 23篇 |
2020年 | 17篇 |
2019年 | 24篇 |
2018年 | 24篇 |
2017年 | 18篇 |
2016年 | 18篇 |
2015年 | 9篇 |
2014年 | 11篇 |
2013年 | 24篇 |
2012年 | 12篇 |
2011年 | 15篇 |
2010年 | 8篇 |
2009年 | 15篇 |
2008年 | 12篇 |
2007年 | 9篇 |
2006年 | 13篇 |
2005年 | 14篇 |
2004年 | 13篇 |
2003年 | 10篇 |
2002年 | 15篇 |
2001年 | 13篇 |
2000年 | 13篇 |
1999年 | 11篇 |
1998年 | 2篇 |
1997年 | 6篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 7篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有414条查询结果,搜索用时 78 毫秒
101.
The stratigraphic division and correlation of the Lower/Middle Cambrian boundary is a global problem that has not yet been solved even up to now. That is because there existed two distinctly different biogeographic regions during the Early and Middle Cambrian[1]—— the Indian-Pacific biogeographic region and the Atlantic biogeographic region. In the Atlantic biogeographic region the traditional Lower/Middle Cambrian boundary was marked by the extinction of Olenellids trilobite and the in… 相似文献
102.
Eddy flux corrections for CO2 exchange in broad-leaved Korean pine mixed forest of Changbai Mountains 总被引:1,自引:0,他引:1
WU Jiabing Guan Dexin SUN Xiaomin YU Guirui Zhao Xiaosong HAN Shijie JIN Changjie 《中国科学D辑(英文版)》2005,48(Z1)
Based on analysis of mechanisms causing energy no-closure and nocturnal low fluxes issues for CO2 exchange studies by eddy covariance method, corrections were done with the raw data sets obtained from Changbai Mountains forest flux site, to evaluate the impacts of sonic anemometer tilt, frequency response limitations and advection on estimation of CO2 exchange, respectively. The results show that the planar fit coordinate transforming method is superior to the streamline coordinate transforming method in tilt correction. The latter could cause a systematical underestimation of eddy fluxes relating with the angle of sensor and terrain tilt. The underestimation of CO2 and energy fluxes for frequency response limitations average 3.0% and 2.0% during daytime, respectively, which increase by 9.0% and 5.5% during nighttime, respectively. The corrections of frequency response limitations are closely related to atmospheric stability. The advection loss of CO2 fluxes is dominated by nocturnal vertical advection, which is at least 18% when the horizontal advection is neglected. It is suggested that more work be done to understand the characteristics of horizontal advection and turbulent eddies under a complexcircumstance. 相似文献
103.
Meteorological control on CO2 flux above broad-leaved Korean pine mixed forest in Changbai Mountains 总被引:2,自引:0,他引:2
Guan Dexin WU Jiabing YU Guirui SUN Xiaomin Zhao Xiaosong HAN Shijie JIN Changjie 《中国科学D辑(英文版)》2005,48(Z1)
The impacts of temperature, photosynthetic active radiation (PAR) and vapor pressure deficit (VPD) on CO2 flux above broad-leaved Korean pine mixed forest in the Changbai Mountains were studied based on eddy covariance and meteorological factors measurements.The results showed that, daytime CO2 flux was mainly controlled by PAR and they fit Michaelis-Menten equation. Meanwhile VPD also had an influence on the daytime flux. Drier air reduced the CO2 assimilation of the ecosystem, the drier the air, the more the reduction of the assimilation. And the forest was more sensitive to VPD in June than that in July and August. The respiration of the ecosystem was mainly controlled by soil temperature and they fit exponential equation. It was found that this relationship was also correlated with seasons; respiration from April to July was higher than that from August to November under the same temperature. Daily net carbon exchange of the ecosystem and the daily mean air temperature fit exponential equation. It was also found that seasonal trend of net carbon exchange was the result of comprehensive impacts of temperature and PAR and so on. These resulted in the biggest CO2 uptake in June and those in July and August were next. Annual carbon uptake of the forest ecosystem in 2003 was -184 gC. m-2. 相似文献
104.
青藏高原湖泊沉积研究及其进展 总被引:3,自引:0,他引:3
青藏高原湖泊沉积研究主要围绕青藏高原隆升和全球变化响应开展的。研究揭示了青藏高原隆升具有整体性、阶段性和后期加速性。中晚更新世以来和末次间冰期-冰期气候演化过程得到重建,并能够与冰芯和深海氧同位素记录对比;同时也存在M IS3阶段强烈暖湿和末次冰盛期冷湿等区域特征;新仙女木事件在湖泊沉积物也有明显记录。全新世研究表明青藏高原早期暖湿并经历冷事件,大暖期普遍出现高水位,后期气候向干冷化方向发展。湖泊沉积环境定量化重建也得到研究。青藏高原湖泊沉积应在高分辨率纹层沉积和环境指标定量分析基础理论方面加强研究。 相似文献
105.
埋藏条件下蒙脱石层间水的稳定性 总被引:3,自引:0,他引:3
王世杰 《矿物岩石地球化学通报》1998,(4)
蒙脱石族矿物广泛存在于地表各种环境中,其层间结构的稳定性对各种表生地质作用的发生和过程起着重要作用。在砂岩成岩作用中,蒙脱石族矿物的脱水作用改变了砂岩孔隙流体的量和成分,同时也降低了油气储蓄层的孔隙度和渗透性。泥、页岩中由于蒙脱石族矿物的脱水作用,在... 相似文献
106.
王世杰 《中国地球化学学报》1996,15(2):105-112
By using the improved trace(50μg) Sr isotope analytical method the ^87Sr/^86Sr ratios of Xiaodukou foraminifera fossils were measured,giving a range of 0.71105-0.71274,apparently higher than the value of contemporaneous seawater(0.709087-0.709147)and also slightly higher than the average value of modern Yellow River(0.7111),demonstrating that the contemporaneous environment where Xiaodukou foraminifera inhabited was an inland lake.Detailed analyses of △ Sr values showed that there occurred an event responsible for environmental changes in the ancient Nihewan Lake area during the time(about 1.0Ma ago)when Xiaodukou foraminifera appeared.Because of strong evaporation the salinity of the lake would increase and a regional salt-water of brackish-water lacustrine environment would be produced,thus providing a suitable and inhabitable environment for foraminiferae.It is concluded that Xiaodukou foraminiferal fossil assemblaes belong to non-marine foraminiferal species. 相似文献
107.
青藏高原可可西里地区现代冰川发育特征 总被引:5,自引:1,他引:5
经野外考察和室内分析计算,青藏可可西里地区发育现代冰川437条,覆盖面积达1552.39km^2,冰储量为162.8349km^3,成为本区众多河湖泊水体的重要补给源泉。 相似文献
108.
A brown fine-grained mineral aggregate in the form of plate and stuffing was found in the Hannuoba spinel-lherzolite. A series
of measurements, including X-ray powder diffraction, infrared spectrometry, DTA and electron microprobe analysis, were made
on this aggregate. The results show that the aggregate consists of the following minerals: hydrous magnesio-silicate minerals,
metamorphic chrysotile, ringwoodite, spinel, rutile, forsterite etc. This is a high-pressure hydrous mineral aggregate never
reported in lherzolite elsewhere.
Based on the compositions and distribution features of the minerals, it is suggested that the fine-grained mineral aggregate
was derived from phlogopite, which had been formed early in the upper mantle and was hydrolyzed during partial melting. 相似文献
109.
110.