全文获取类型
收费全文 | 7693篇 |
免费 | 1798篇 |
国内免费 | 3125篇 |
专业分类
测绘学 | 1196篇 |
大气科学 | 1160篇 |
地球物理 | 1406篇 |
地质学 | 5549篇 |
海洋学 | 1378篇 |
天文学 | 205篇 |
综合类 | 658篇 |
自然地理 | 1064篇 |
出版年
2024年 | 109篇 |
2023年 | 251篇 |
2022年 | 518篇 |
2021年 | 591篇 |
2020年 | 471篇 |
2019年 | 525篇 |
2018年 | 458篇 |
2017年 | 432篇 |
2016年 | 475篇 |
2015年 | 535篇 |
2014年 | 538篇 |
2013年 | 560篇 |
2012年 | 682篇 |
2011年 | 724篇 |
2010年 | 637篇 |
2009年 | 647篇 |
2008年 | 605篇 |
2007年 | 672篇 |
2006年 | 589篇 |
2005年 | 461篇 |
2004年 | 339篇 |
2003年 | 250篇 |
2002年 | 283篇 |
2001年 | 273篇 |
2000年 | 211篇 |
1999年 | 125篇 |
1998年 | 92篇 |
1997年 | 95篇 |
1996年 | 54篇 |
1995年 | 63篇 |
1994年 | 43篇 |
1993年 | 55篇 |
1992年 | 31篇 |
1991年 | 32篇 |
1990年 | 25篇 |
1989年 | 26篇 |
1988年 | 21篇 |
1987年 | 17篇 |
1986年 | 13篇 |
1985年 | 9篇 |
1984年 | 20篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 6篇 |
1976年 | 2篇 |
1975年 | 5篇 |
1973年 | 4篇 |
1958年 | 2篇 |
1957年 | 3篇 |
1954年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
对采自东南极普里兹湾海区沉积物NP93-2柱样系统的磁组构分析,结果表明:1.普里兹湾海洋沉积物具有较大的磁化率各向异性,较好地指示了沉积过程中水动力过程的变化;2.由磁化率各向异性主轴方向确定的古水流方面主要为近EW向及NS向,分别对应着南极绕极环流的方向及由融冰水的大量生成而导致的南极底层水形成的方向,这两种不同方向的水流在该海区不同时段的表现各不相同;3.依据表征磁组构的参数及古水流方向的变化,可将12700aB.P.以来的南极地区的古气候分成5个古气候变化带. 相似文献
12.
阿尔金群为阿尔金构造带的古老变质基底,由于缺乏精确的同位素测年数据,对其形成时代尚存争议。运用LA-ICP-MS 锆石U-Pb 定年分析方法,对阿尔金山南缘清水泉地区阿尔金群中的斜长角闪岩进行了年代学测定,并初步探讨其地质意义。锆石CL图像具有多晶面面状结构,无岩浆锆石具有的震荡环带和核边结构,Th/U比值大多都较低(<0.1),显示变质锆石的特点。18个锆石颗粒的19个测点给出的207Pb/206Pb年龄介于(1786±16)~(1877±12)Ma之间,加权平均值为(1827±13)Ma(MSWD=4.4,1σ)。区域地质与同位素年代学新资料表明,阿尔金山南缘清水泉地区在古元古代晚期存在一期构造-热事件,本期事件与吕梁运动的时限相吻合,在全球尺度上可能是古元古代哥伦比亚超大陆汇聚-裂解事件在该地区的响应,也证明阿尔金山存在新太古代—古元古代的变质基底,并且为探讨阿尔金构造带前寒武纪构造-热事件和演化历史提供了新证据。 相似文献
13.
14.
The relationship between the length of the solar cycle, a good indicator of long-term change in solar activity, and natural disasters (drought, flood, and strong earthquakes) in China during the last 108 years is analyzed. The results suggest that the length of solar cycle may be a useful indicator for drought/flood and strong earthquakes. When the solar activity strengthens, we see the length of the solar cycle shorten and more floods occur in South China and frequent strong earthquakes happen in the Tibetan Plateau,but the droughts in East China as well as the strong earthquakes in Taiwan and at the western boundary of China are very few. The opposite frequencies occur when the solar activity weakens. The current study indicates that the solar activity may play an important role in the climate extremes and behavior in the lithosphere. 相似文献
15.
16.
17.
Wendy L. Mao Yue Meng Ho-kwang Mao 《Physics of the Earth and Planetary Interiors》2010,180(3-4):203-208
We report experimental observation of a sizable elastic anisotropy in a polycrystalline sample of ferromagnesian silicate in post-perovskite (ppv) structure. Using a novel composite X-ray transparent gasket to contain and synthesize ppv in a panoramic diamond-anvil cell along with oblique X-ray diffraction geometry, we observed the anisotropic lattice strain and {1 0 0} or {1 1 0} slip-plane texture in the sample at 140 GPa. We deduced the elasticity tensor (cij), orientation-dependent compressional wave velocities, polarization-dependent shear-wave velocities, and the velocity anisotropy of the silicate ppv. Our results are consistent with calculations and indicate that with sufficient preferred orientation, the elastic anisotropy of this phase can produce large shear-wave splitting. 相似文献
18.
The South China Sea is rich in oil and gas resources. With the increasing exploration of oil and gas resources in the northern South China Sea and the increasing demand for energy in the world, The central‐southern South China Sea have become important constituencies for oil and gas resources. The central‐southern basins of South China Sea can be divided into three types of basin groups, namely, the southern basin group (Zengmu Basin, Brunei‐Sabah Basin), the western basin group (Wan'an Basin, Zhong jiannan Basin) and the Central Basin Group (Liyue Basin, Beikang Basin, Nanweixi Basin and Palawan Basin). At present, the degree of exploration is relatively low, and the source rock has not yet formed a understanding of the system. The main source rock development time, source rock characteristics, hydrocarbon generation potential and control factors of each basin group are still unclear, which seriously restricts the exploration of oil and gas. Based on the sedimentary facies distribution and sedimentary filling evolution, combined with the geoche mical characteristics of the source rocks, the source age, organic matter type, hydrocarbon generation potential and main controlling factors of the basins in the central‐southern basins are discussed. By the detailed research on delta scale, provenance system, paleoclimate conditions, ancient vegetation development and hydroca rbon generation parent material, the main controlling factors of hydrocarbon generation potential of source rocks in each basin group are revealed. 相似文献
19.
Holocene environmental evolution recorded by core sediments of Judian Lake in the east of Lubei Plain,Shandong Province 下载免费PDF全文
Judian Lake in the east of Lubei Plain is located in the monsoon area of northern China,which is sensitive to global climate change and provides abundant lake sedimentary data for the study of the past climate and environment evolution in the land-sea interaction area. Based on the sporopollen identification,grain size analysis and AMS14C dating of core sediments from the drilling hole of the Judian Lake,the evolutional process of climate and environment since 8900 cal a BP in the northern Lubei Plain was discussed. The results show that: 8900-7625cal a BP,the temperature and precipitation increased and the climate changed from cold-dry to warm-wet;7625—6810 cal a BP,the overall climate was becoming cooler and drier;6810—4435cal a BP,the temperature rose and the precipitation increased,showing an overall warm and humid climate in the middle Holocene;4435—3150cal a BP,the climate was generally cold and humid with some low-amplitude fluctuations of cold and warm. During the middle Holocene,there were two obvious cold and dry events in 5450—5280cal a BP and 4160—4090cal a BP,which was consistent with the geological and climatic records in China and even in the world. It may be due to the southward movement of the equatorial convergence zone caused by the change of solar radiation,the change of ocean surface temperature and the feedback of surface vegetation. 相似文献
20.