全文获取类型
收费全文 | 50500篇 |
免费 | 20874篇 |
国内免费 | 45845篇 |
专业分类
测绘学 | 4769篇 |
大气科学 | 23337篇 |
地球物理 | 15733篇 |
地质学 | 43631篇 |
海洋学 | 17678篇 |
天文学 | 1450篇 |
综合类 | 6028篇 |
自然地理 | 4593篇 |
出版年
2024年 | 317篇 |
2023年 | 802篇 |
2022年 | 1582篇 |
2021年 | 2009篇 |
2020年 | 2882篇 |
2019年 | 6138篇 |
2018年 | 6526篇 |
2017年 | 6064篇 |
2016年 | 6219篇 |
2015年 | 5695篇 |
2014年 | 5261篇 |
2013年 | 5877篇 |
2012年 | 5675篇 |
2011年 | 5513篇 |
2010年 | 5451篇 |
2009年 | 4635篇 |
2008年 | 3860篇 |
2007年 | 3799篇 |
2006年 | 3304篇 |
2005年 | 3023篇 |
2004年 | 3219篇 |
2003年 | 2883篇 |
2002年 | 2696篇 |
2001年 | 2424篇 |
2000年 | 2029篇 |
1999年 | 2133篇 |
1998年 | 2132篇 |
1997年 | 2109篇 |
1996年 | 1732篇 |
1995年 | 1611篇 |
1994年 | 1482篇 |
1993年 | 1360篇 |
1992年 | 1138篇 |
1991年 | 859篇 |
1990年 | 822篇 |
1989年 | 668篇 |
1988年 | 564篇 |
1987年 | 444篇 |
1986年 | 357篇 |
1985年 | 289篇 |
1984年 | 291篇 |
1983年 | 173篇 |
1982年 | 219篇 |
1981年 | 152篇 |
1980年 | 125篇 |
1979年 | 124篇 |
1978年 | 47篇 |
1977年 | 45篇 |
1971年 | 53篇 |
1970年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
The geodynamic mechanism of the late Early Cretaceous magmatic flare‐up in the collisional zone between the Lhasa and Qiangtang terranes in Tibet is controversial because of a scarcity of robust evidence. To address this problem, we report geochronological, geochemical and Hf isotopic data for the newly discovered Gufeng gabbros from the Duolong Cu–Au mineral district of the western Bangong–Nujiang Suture Zone (BNSZ). The gabbro samples, dated at 126.3 ± 1.8 Ma, show geochemical similarities to typical ocean island basalt (OIB) and have positive εHf(t) values of +3.3 to +6.9. The gabbros were generated by decompression melting of deep upwelling asthenosphere. This event is best explained by slab break‐off and the resultant development of a slab window beneath central Tibet. 相似文献
2.
A formula for the thickness of a shear band formed in saturated soils under a simple shear or a combined stress state has been proposed. It is shown that the shear band thickness is dependent on the pore pressure properties of the material and the dilatancy rate, but is independent of the details of the combined stress state. This is in accordance with some separate experimental observations. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
3.
Lu Sun 《国际地质力学数值与分析法杂志》2003,27(1):69-84
A closed‐form deflection response of a beam rest is presented in this paper using the integral transform method. The theory of linear partial differential equations is used to represent the deflection of beam subjected to a moving harmonic line load in integration form. The solution is finally carried out using the inverse Fourier transform. To evaluate the integration analytically, poles of the integrand are identified with the help of algebraic equation theory. Residue theorem is then utilized to represent the integration as a contour integral in the complex plane. Closed‐form deflections and numerical results are provided for different combinations of load frequency and velocity. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
4.
同时采用4个台站的国际超导重力仪长期连续重力观测资料和国际地球自转服务中心提供的同步地球自转参数,研究了极移引起的地球重力场变化特征。利用自回归模型估计了各序列的功率谱密度和积谱密度,结果表明极移导致的重力效应的主要能量集中在Chandler摆动和周年项附近,叠积后实际重力观测与极移重力信号理论值之间的差异分别为0.4%和3.9%,说明超导重力仪可有效监测极移导致的重力变化。 相似文献
5.
对1995年至2001年《Natue》和《Science》上发表的天文学论文的统计表明,行星天文学领域的论文数量明显超过天文学的其它分支学科,占天文学总论文数的1/3左右。从这个角度来看,行星天文学是天文学最活跃和重要的分支学科之一。对这些论文具体内容的分析可以给出当前行星天文学领域的若干热点问题。相比之下,我国对这一重要领域的关注和投入还远远不够。 相似文献
6.
7.
介绍了云南天文台天体测量工作的发展过程,论述了在空间时代地面光学基本天体测量的必要性和应具备的条件,并且叙述了在新的要求和条件下,地面光学基本天体测量工作应该发挥的作用和广阔的发展前景。 相似文献
8.
9.
The ordinary kriging method, a geostatistical interpolation technique, was applied for developing contour maps of design storm depth in northern Taiwan using intensity–duration–frequency (IDF) data. Results of variogram modelling on design storm depths indicate that the design storms can be categorized into two distinct storm types: (i) storms of short duration and high spatial variation and (ii) storms of long duration and less spatial variation. For storms of the first category, the influence range of rainfall depth decreases when the recurrence interval increases, owing to the increasing degree of their spatial independence. However, for storms of the second category, the influence range of rainfall depth does not change significantly and has an average of approximately 72 km. For very extreme events, such as events of short duration and long recurrence interval, we do not recommend usage of the established design storm contours, because most of the interstation distances exceed the influence ranges. Our study concludes that the influence range of the design storm depth is dependent on the design duration and recurrence interval and is a key factor in developing design storm contours. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
10.
A new species,Clathrocorys gracilis nov. spec. of Tripocyrtidae (Radiolarians: Nassellaria) from surface water in northern South China Sea, is described in this
paper. The new species has four radial beams arising from the cephalic base centre, each foot with cup-shaped structure and
ramified bar in the proximal section (near cephalic base), and each wing with a large mesh in the middle, a medium mesh and
a small mesh on each side respectively.
Project supported by the NSFC (No. 40276044) and the Chinese Academy of Sciences (No. KSCX2-SW-101B). 相似文献