全文获取类型
收费全文 | 78519篇 |
免费 | 13301篇 |
国内免费 | 17305篇 |
专业分类
测绘学 | 9737篇 |
大气科学 | 10162篇 |
地球物理 | 18165篇 |
地质学 | 40665篇 |
海洋学 | 9434篇 |
天文学 | 2499篇 |
综合类 | 5812篇 |
自然地理 | 12651篇 |
出版年
2024年 | 271篇 |
2023年 | 812篇 |
2022年 | 2254篇 |
2021年 | 2729篇 |
2020年 | 2963篇 |
2019年 | 3466篇 |
2018年 | 2735篇 |
2017年 | 3195篇 |
2016年 | 3383篇 |
2015年 | 3670篇 |
2014年 | 4354篇 |
2013年 | 4864篇 |
2012年 | 4751篇 |
2011年 | 5077篇 |
2010年 | 4218篇 |
2009年 | 5006篇 |
2008年 | 5062篇 |
2007年 | 5493篇 |
2006年 | 5253篇 |
2005年 | 4610篇 |
2004年 | 4259篇 |
2003年 | 3951篇 |
2002年 | 3506篇 |
2001年 | 3101篇 |
2000年 | 2821篇 |
1999年 | 2631篇 |
1998年 | 2316篇 |
1997年 | 2063篇 |
1996年 | 1840篇 |
1995年 | 1589篇 |
1994年 | 1532篇 |
1993年 | 1300篇 |
1992年 | 978篇 |
1991年 | 709篇 |
1990年 | 604篇 |
1989年 | 473篇 |
1988年 | 394篇 |
1987年 | 235篇 |
1986年 | 158篇 |
1985年 | 118篇 |
1984年 | 63篇 |
1983年 | 35篇 |
1982年 | 44篇 |
1981年 | 32篇 |
1980年 | 39篇 |
1979年 | 37篇 |
1978年 | 51篇 |
1977年 | 31篇 |
1975年 | 4篇 |
1954年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
172.
173.
174.
In this paper the second order characteristic (discontinuous bifurcation) condition is derived for the granular flow (fully plastic) equations. This second order bifurcation equation is shown to be formally identical to the first order localization requirement during steady elastoplastic deformation provided the elastic compliance tensor is substituted for the product of the plastic multiplier with the flow Hessian. For isotropic yield and flow functions the invariant form of the characteristic condition is given in detail, as well as an alternative expression in adapted co‐ordinates. The characteristic condition can be regarded as defining a hardening function which is maximized to identify the critical angles. When the method is applied to 3D Coulomb flow, Mohr's 3D fracture plane conditions are obtained uniquely. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
175.
从胶东所处的板块构造位置和区域控热构造入手,根据地热传导理论,对胶东温泉的地热属性进行分析研究,认为胶东半岛温泉地热属性为毗邻板块边缘高温地热带的板内中低温地热系统,它以偏高的大地热流值为地热背景,以局部控热构造聚敛的大地热流为热源,以地形高差影响和相应的水力压差作用为动力,入渗的大气降水被岩石中的热量加热,并沿断裂出露形成温泉地热水。根据山东半岛温泉地热属性的特点和地热水开发中所面临的问题,提出保持胶东温泉可持续开发的相关对策。 相似文献
176.
A new analysis of all 346 published 14C dated Holocene alluvial units in Britain offers a unique insight into the regional impacts of global change and shows how surprisingly sensitive British rivers have been to relatively modest but repeated changes in climate. Fourteen major but probably brief periods of flooding are identified bracketed within the periods 400–1070, 1940–3940, 7520–8100 and at ca. 10 420 cal. yr BP. There is a strong correspondence between climatic deteriorations inferred from mire wet shifts and major periods of flooding, especially at ca. 8000 cal. yr BP and since ca. 4000 cal. yr BP. The unusually long and complete British record also demonstrates that alterations in land cover have resulted in a step change in river basin sensitivity to variations in climate. This has very important implications for assessing and mitigating the impact of increasing severe flooding. In small and medium‐sized river basins land use is likely to play a key role in either moderating or amplifying the climatic signal. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
177.
The equilibrium of a self gravitating cylindrical polytrope with a general magnetic field and rotation has been discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
178.
179.
180.
Lightning discharge generated in the protoplanetary nebula is viewed as a temporally isolated surge in the flow of electrically charged particles, similar to that of terrestrial lightning. If the current is intense enough, a powerful circular impulse magnetic field is generated around the instantaneous virtual electric conductor. Such magnetic field is capable of magnetizing dust grains containing ferromagnetic components present in its vicinity to their saturation levels. As a result, dust grains attract one another, forming the aggregates. This magnetically driven attraction suggests an important process possibly operational at an early stage of the planetary accretion. Based on both a classical model for electric conductor, and the theory of Lienard–Wiechert electromagnetic potentials, our calculations show that the magnetic impulse due to a discharge channel of a few cm in diameter transferring a charge of about 104 electrons reaches as high as 10 T. At these magnetic fields, the ferromagnetic dust grains, and possibly the already-formed larger aggregates as well, are easily magnetized to the saturation levels, producing compact clusters exhibiting permanent magnetic moments. 相似文献