全文获取类型
收费全文 | 13190篇 |
免费 | 2364篇 |
国内免费 | 4774篇 |
专业分类
测绘学 | 276篇 |
大气科学 | 2811篇 |
地球物理 | 2225篇 |
地质学 | 7175篇 |
海洋学 | 3067篇 |
天文学 | 23篇 |
综合类 | 941篇 |
自然地理 | 3810篇 |
出版年
2024年 | 99篇 |
2023年 | 272篇 |
2022年 | 682篇 |
2021年 | 606篇 |
2020年 | 683篇 |
2019年 | 783篇 |
2018年 | 663篇 |
2017年 | 646篇 |
2016年 | 659篇 |
2015年 | 696篇 |
2014年 | 914篇 |
2013年 | 851篇 |
2012年 | 951篇 |
2011年 | 921篇 |
2010年 | 674篇 |
2009年 | 864篇 |
2008年 | 829篇 |
2007年 | 883篇 |
2006年 | 913篇 |
2005年 | 815篇 |
2004年 | 802篇 |
2003年 | 714篇 |
2002年 | 646篇 |
2001年 | 536篇 |
2000年 | 518篇 |
1999年 | 484篇 |
1998年 | 370篇 |
1997年 | 366篇 |
1996年 | 296篇 |
1995年 | 253篇 |
1994年 | 242篇 |
1993年 | 179篇 |
1992年 | 153篇 |
1991年 | 114篇 |
1990年 | 70篇 |
1989年 | 69篇 |
1988年 | 46篇 |
1987年 | 34篇 |
1986年 | 12篇 |
1985年 | 6篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1979年 | 4篇 |
1954年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
岩石圈中热压系数的计算 总被引:2,自引:0,他引:2
中国中西部地区发育众多前陆冲断带,它们具有构造变形复杂、油气潜力大和有别于经典前陆盆地的沉积和油气地质特征,但其成因过程和动力学并不清楚。文中利用中西部盆地区的地温、岩石热物性参数和地热学模拟技术,分析该区岩石圈热状态和流变学特征,进一步结合其他地质、地球物理资料,揭示盆地区的深部构造特征和岩石圈性质。研究表明,中西部各主要盆地的岩石圈具有厚度大、强度高、地温低等热-流变学特征,表现为刚硬块体;而其周缘和造山带区却表现为温度高、强度低和厚度小等特征,是构造变形的易发区。在此基础上讨论了岩石圈性质和变形过程等深部构造对前陆盆地成因演化的控制作用,进而初步归纳这类陆内再生前陆盆地的成因演化机制:发育于小型克拉通块体的边缘,其就位受控于岩石圈热-流变学非均质性和构造继承性,其动力来源是新生代印度-欧亚大陆碰撞及其持续的挤压作用。上述研究为探讨中国中西部地区的前陆盆地成因机制提供了深部资料和岩石圈热-流变学约束。 相似文献
192.
Takeshi Ohno Tsuyoshi Komiya Yuichiro Ueno Takafumi Hirata Shigenori Maruyama 《Gondwana Research》2008,14(1-2):126
We measured both mass-dependent isotope fractionation of δ88Sr (88Sr/86Sr) and radiogenic isotopic variation of Sr (87Sr/86Sr) for the Neoproterozoic Doushantuo Formation that deposited as a cap carbonate immediately above the Marinoan-related Nantuo Tillite. The δ88Sr and 87Sr/86Sr compositions showed three remarkable characteristics: (1) high radiogenic 87Sr/86Sr values and gradual decrease in the 87Sr/86Sr ratios, (2) anomalously low δ88Sr values at the lower part cap carbonate, and (3) a clear correlation between 87Sr/86Sr and δ88Sr values. These isotopic signatures can be explained by assuming an extreme greenhouse condition after the Marinoan glaciation. Surface seawater, mixed with a large amount of freshwater from continental crusts with high 87Sr/86Sr and lighter δ88Sr ratios, was formed during the extreme global warming after the glacial event. High atmospheric CO2 content caused sudden precipitation of cap carbonate from the surface seawater with high 87Sr/86Sr and lighter δ88Sr ratios. Subsequently, the mixing of the underlying seawater, with unradiogenic Sr isotope compositions and normal δ88Sr ratios, probably caused gradual decrease of the 87Sr/86Sr ratios of the seawater and deposition of carbonate with normal δ88Sr ratios. The combination of 87Sr/86Sr and δ88Sr isotope systematics gives us new insights on the surface evolution after the Snowball Earth. 相似文献
193.
The Anzishan ophiolite, a typical ophiolitic block of early Carboniferous age in the Mian-Lue suture zone of the Qinling Mountains, central China, consists of amphibolites/metabasalts, gabbros and gabbroic cumulates. All of these rocks, as well as those in the Hunshuiguan-Zhuangke (HZ) block, have compositions similar to normal MORB and back-arc basin basalts (BABB) with high εNd(t) values, indicating that they were derived from a depleted mantle source. The Mian-Lue suture zone also contains blocks of other lithologies, e.g., rift volcanic rocks in the Heigouxia block and arc volcanic rocks in the Sanchazi block. Although they are in fault contact with each other, the presence of these different blocks in the Mian-Lue suture zone may represent a complete Wilson cycle, from initial rifting to open ocean basin to final subduction and continent-continent collision, during the late Paleozoic-early Triassic. In this region, the North and South China Cratons were separated by Paleo-Tethys at least until the early Carboniferous, and final amalgamation of both cratons along the Qinling orogenic belt took place in the Triassic. 相似文献
194.
The best planting alternatives for satisfying high water use demands of forage and fodder crops in a region of Inner Mongolia, China, were determined by a multiobjective distributed-parameter groundwater management model. These alternatives took account of different cropping patterns and pumping decisions associated with both temporal and spatial aspects of water allocation. The model was developed for phreatic, homogenous, and isotropic aquifers using the response matrix technique of quadratic programming theory and, in this case, using the alternative direction implicit (ADI) scheme. Model solutions using effective rainfall with a probability of 50%, show that average water table drawdown in the planning period (2006–2017) is 0.22 m and the groundwater fluctuation in each pumping well is very low. In order to evaluate the pumping decisions under an effective rainfall with a probability of 75%, a sensitive analysis was also conducted. Analysis shows that it is useful to apply the results from the proposed model to control the landscape degradation due to overgrazing and overpumping activities. 相似文献
195.
山东莒南地质公园发现小型兽脚类恐龙
足迹化石Minisauripus 总被引:2,自引:0,他引:2
在山东省莒南地质公园内发现6个小型恐龙足迹化石,被归入足迹属Minisauripus。化石产于下白垩统大盛群田家楼组.时代为早白垩世巴列姆(Barremian)-阿普特期(Apdan)。5个较大,长约6cm,产于下部“主”层面上,其中4个组成2节行迹:1个较小,长约3cm,位于“主”层面30cm之上的上部层面上。山东Minisauripus的特征是:足迹个体小(长3.1~5.6cm,宽2.0~3.7cm),三趾型,略不对称;足迹纵长,各趾近平行,趾垫较清晰;趾末端较钝,但爪迹较尖。Ⅲ趾比Ⅳ趾略长,而Ⅳ趾比Ⅱ趾略长且窄。此外,步幅较长,足长与步长之比约为10:1。与四川、韩国Minisau却淞不同之处是:足迹个体较大,长约是它们的2倍。继中国四川和韩国之后,山东是Minisau而淞在全球的第三个发现点。 相似文献
196.
Glaciers, formed by snowfall and characterized by movement and size, are the most sensitive indicators to climate change.
The ice formation of glaciers (the processes, mechanisms and results of transformation from snow to ice) can indicate the
growth condition, the formation process and the physical characteristics of glaciers. Its spatial variation can also reflect
glacier change, and further reveal climate change. Studies on ice formation of glaciers in China were initiated in 1962, when
Xie and others studied the ice formation of Glacier No.1 at the Urumqi River head, Tianshan Mountain. Other researchersfollowed
suit and did studies on ice formation of glaciers in Qilian Mountain. As time goes by, the concept of ice formation came into
being in China. This paper reviews the development history of glacier zones, and the studies of ice formation of glaciers
in China since the 1960s. These studies mainly focus on Qilian Mountain, Tianshan Mountain, Altay Mountain, and the western
Kunlun Mountain, Himalaya Mountain, the southeastern Tibetan and Hengduan Mountains. The paper also discusses the significance
of ice formation studies, the limitation and deficiency of previous studies, and the prospects and suggestions for future
studies.
__________
Translated from Advances in Earth Science, 2007, 22(4): 386–395 [译自: 地球科学进展] 相似文献
197.
Wenguang Yang Hongbo Zheng Ke Wang Xin Xie Guocheng Chen Xi Mei 《Frontiers of Earth Science》2008,2(2):170-176
Sediments with high sedimentation rate at site MD05-2905 in the Northeastern slope of the South China Sea provide unique materials
for a high-resolution study on the paleoenvironment. Based on precise dating of AMS 14C, grain size analysis of terrigenous debris at core MD05-2905 was conducted after organic matter, biological carbonate and
biogenic opal were removed. The results show that 15.5–63.5 μm coarse grain size ingredients may indicate East Asian winter
monsoon changes and that 2–9 μm fine grain size ingredients may be used as a proxy of evolution of the East Asian summer monsoon.
The results of grain size analysis, which suggest East Asian monsoon intensity, reveal that a winter monsoon dominated the
glacial regime and a summer monsoon dominated the Holocene regime. It was also shown that the summer monsoon increased gradually,
experienced several abrupt changes and reached a culmination in the early Holocene (11200–8500 a B.P.) since 36 ka. Controlled
by precession periodicity, it may be related with the amount of solar radiation at the highest stage, which needs further
study.
__________
Translated from Advances in Earth Science, 2007, 22(10): 1012–1018 [译自: 地球科学进展] 相似文献
198.
199.
200.
成矿理论与勘探实践证明,东部一些老矿由于勘探深度、范围的限制以及认识上的局限,在矿区深部、周边仍有一些矿未能发现和查明,其中相当一部分仍具有找矿潜力;而寻找西部新的煤炭资源是国家“稳定东部发展西部”战略需要。针对中国东西部不同的地质条件和勘探目标,其地震勘探野外施工方法及资料处理原则有所差异;而资料解释在东部以查明地层赋存形态、煤层赋存范围、构造发育特征为主,西部则以寻找煤系地层波阻抗差异明显、连续性好的反射波组为解释重点。地震勘探技术在中国东西部的二个典型地震时间剖面佐证了其在深部找矿的应用效果。 相似文献