全文获取类型
收费全文 | 1633篇 |
免费 | 261篇 |
国内免费 | 202篇 |
专业分类
测绘学 | 23篇 |
大气科学 | 322篇 |
地球物理 | 743篇 |
地质学 | 361篇 |
海洋学 | 196篇 |
天文学 | 364篇 |
综合类 | 37篇 |
自然地理 | 50篇 |
出版年
2024年 | 7篇 |
2023年 | 17篇 |
2022年 | 31篇 |
2021年 | 21篇 |
2020年 | 33篇 |
2019年 | 58篇 |
2018年 | 22篇 |
2017年 | 37篇 |
2016年 | 41篇 |
2015年 | 42篇 |
2014年 | 65篇 |
2013年 | 81篇 |
2012年 | 58篇 |
2011年 | 71篇 |
2010年 | 61篇 |
2009年 | 129篇 |
2008年 | 125篇 |
2007年 | 127篇 |
2006年 | 116篇 |
2005年 | 97篇 |
2004年 | 97篇 |
2003年 | 87篇 |
2002年 | 75篇 |
2001年 | 69篇 |
2000年 | 68篇 |
1999年 | 64篇 |
1998年 | 64篇 |
1997年 | 46篇 |
1996年 | 49篇 |
1995年 | 54篇 |
1994年 | 59篇 |
1993年 | 31篇 |
1992年 | 29篇 |
1991年 | 13篇 |
1990年 | 10篇 |
1989年 | 16篇 |
1988年 | 11篇 |
1987年 | 8篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有2096条查询结果,搜索用时 15 毫秒
61.
地震活动时序谱的涨落统计特征与地震活跃期 总被引:1,自引:0,他引:1
为寻求地震活动演化的统计判据,本文采用多项式拟合法展示地震时序谱之涨落谱,以分维函数法判断最小邻间距(NNS)分布的Poisson性,然后采用MKS无参量法判别涨落谱之统计稳定性,确定NNS分布的转变区,具体研讨了四川、云南若干震区地震活动时序谱的涨落统计分布,发现地震活跃期到来时NNS分布表现出非Poisson化的特征。进一步通过改变和调节时序数据样本集之震级下限,并逐段前推进行统计计算的方式进一步验证结果的可靠性,客观地确定了这些震区地震活动时序涨落谱统计特征的转变期,使根据该统计法判断地震活跃期的方法论渐趋完善。 相似文献
62.
利用三维非静力能量闭合(E-ε)的边界层模式,以深圳海岸复杂地形进行了实际模拟。结果给出了该地区海陆风情形下气流和湍流孤变化特征。在海风发展盛期,气流方向由大面积的水域和内陆的位置决定,不规则海岸线对局地气流影响不大,夜间陆风时,不规则海岸线对局地气流影响较大,湍流能量高值颁在陆地上空的不稳定层内,水面上湍能很小。模拟结果与实测结果上比较吻合。 相似文献
63.
阿拉善活动块体的划分及归宿 总被引:15,自引:0,他引:15
通过对阿拉善地区地震活动图象呈现显著的条带状、新构造变形表现为块体的隆升和向北的掀斜、周缘的内部性质各异的断裂活动状况、结晶基底与基底内推覆和滑脱构造发育等构造特征的分析,以及与相邻块体的比较,论证了阿拉善活动块体的存在,对其边界作了厘定,并将其归属到华北亚板块,强调了阿拉善块体为一活动构造,其内部存在一个NE向的阿拉善地震带,归属于华北地震区。该地区的地震危险性不可低估。 相似文献
64.
利用14C、热释光(TL)样品年代及扩散方程计算结果,结合区域黄土剖面中古土壤年龄,对毛毛山地区晚第四纪各级地貌年龄进行了对比研究。根据毛毛山活动断裂水平位移和垂直位移分布明显的分组特征,求得毛毛山断裂带不同段落不同时段的平均滑动速率。大约自中更新世晚期以来,毛毛山断裂走滑段的平均水平滑动速率为2.3~3.9mm/a,垂直滑动速率为0.07~0.19mm/a;天祝盆地倾滑段垂直滑动速率为0.11~0.86mm/a。沿断裂带滑动速率具明显的非均匀性特点,表现为自东向西水平位移具累积滑动亏损特征,垂直位移则具补偿性 相似文献
65.
66.
Kusuma G. Rao V. N. Lykossov A. Prabhu S. Sridhar E. Tonkacheyev 《Journal of Earth System Science》1996,105(3):227-260
An attempt has been made here to study the sensitivity of the mean and the turbulence structure of the monsoon trough boundary
layer to the choice of the constants in the dissipation equation for two stations Delhi and Calcutta, using one-dimensional
atmospheric boundary layer model withe-ε turbulence closure. An analytical discussion of the problems associated with the constants of the dissipation equation is
presented. It is shown here that the choice of the constants in the dissipation equation is quite crucial and the turbulence
structure is very sensitive to these constants. The modification of the dissipation equation adopted by earlier studies, that
is, approximating the Tke generation (due to shear and buoyancy production) in theε-equation by max (shear production, shear + buoyancy production), can be avoided by a suitable choice of the constants suggested
here. The observed turbulence structure is better simulated with these constants. The turbulence structure simulation with
the constants recommended by Aupoixet al (1989) (which are interactive in time) for the monsoon region is shown to be qualitatively similar to the simulation obtained
with the constants suggested here, thus implying that no universal constants exist to regulate dissipation rate.
Simulations of the mean structure show little sensitivity to the type of the closure parameterization betweene-l ande-ε closures. However the turbulence structure simulation withe-ε. closure is far better compared to thee-l model simulations. The model simulations of temperature profiles compare quite well with the observations whenever the boundary
layer is well mixed (neutral) or unstable. However the models are not able to simulate the nocturnal boundary layer (stable)
temperature profiles. Moisture profiles are simulated reasonably better. With one-dimensional models, capturing observed wind
variations is not up to the mark. 相似文献
67.
M. R. Handy 《International Journal of Earth Sciences》1996,85(4):832-851
The Zone of Samedan is part of a fossil, early Mesozoic rift system originally situated in the distal, Lower Austro-Alpine
domain of the Adriatic passive continental margin. An early Mesozoic configuration of asymmetrical rift basins bounded by
relative structural highs compartmentalized Late Cretaceous active margin tectonics; Jurassic half-grabens were folded into
arcuate synclines, whereas relative structural highs engendered thin, imbricated thrust sheets. West-directed thrusting and
folding initiated at the surface and continued to depths favoring mylonitization under lower greenschist-facies conditions.
At this time Liguria-Piemontese ophiolites were accreted to Lower Austro-Alpine units directly underlying the Zone of Samedan.
Late Cretaceous orogenic collapse of the Adriatic active margin involved the reactivation of west-directed thrusts as low-angle,
top-to-the-east, normal faults. These faults accommodated extensional uplift of Liguria-Piemontese ophiolites and Lower Austro-Alpine
units beneath and within the Zone of Samedan. During Paleogene collision, some Late Cretaceous faults in the Zone of Samedan
were reactivated under lower anchizonal conditions as north-directed thrusts. The latter stages of this early Tertiary thickening
were transitional to brittle, high-angle normal faulting associated with top-to-the-east extension and spreading above the
warm, uplifting Lepontine dome. 相似文献
68.
研究了1995年7月22日甘肃永登5.8级地震地电、水化学、水动态、地应力、地形变等5种前兆的异常特征,得到如下结论:①该次地震中短期(1年尺度)和短临异常空间分布符合“异常震源地点发震机制主要活断层”之间的特定关系,近2~3年的中期异常集中分布在西秦岭北缘北西向断裂带和海原通渭武都南北向断裂带上;②震前约1年时间尺度震源区发育起来了北北西南南东向挤压变化突出的附加应力场,并引起断层错动;③源兆集中分布在本次地震震源周围,场兆集中分布在上述两条活动断裂带上.源兆占异常的大多数,场兆占少数.在时间上场兆出现在先,源兆在后. 相似文献
69.
Zhang Xiaoliang 《中国地震研究》2004,18(2):161-170
On the basis of Discontinuous Deformation Analysis (DDA), and considering the moderate intrusion of specific block boundaries to different extents, the first-order block motion model is established for the northeastern margin of Qinghai-Xizang(Tibet) block and the kinematical model for depicting deformation of small regions as well by using GPS observations of three periods (1991, 1999 and 2001). By simulating, we obtained the motion features of the firstorder blocks between the large WWN faults on the sides of the studied region, the distribution features of the principal strain rate field and the inhomogeneous motion features with spacetime of the faults in the northern boundary of the Qinghai-Xizang (Tibet) block. 相似文献
70.