全文获取类型
收费全文 | 13598篇 |
免费 | 2579篇 |
国内免费 | 3373篇 |
专业分类
测绘学 | 975篇 |
大气科学 | 2851篇 |
地球物理 | 3568篇 |
地质学 | 6856篇 |
海洋学 | 1835篇 |
天文学 | 716篇 |
综合类 | 1316篇 |
自然地理 | 1433篇 |
出版年
2024年 | 68篇 |
2023年 | 233篇 |
2022年 | 601篇 |
2021年 | 687篇 |
2020年 | 569篇 |
2019年 | 684篇 |
2018年 | 715篇 |
2017年 | 653篇 |
2016年 | 759篇 |
2015年 | 620篇 |
2014年 | 797篇 |
2013年 | 849篇 |
2012年 | 721篇 |
2011年 | 793篇 |
2010年 | 781篇 |
2009年 | 778篇 |
2008年 | 667篇 |
2007年 | 662篇 |
2006年 | 541篇 |
2005年 | 514篇 |
2004年 | 396篇 |
2003年 | 388篇 |
2002年 | 425篇 |
2001年 | 439篇 |
2000年 | 442篇 |
1999年 | 620篇 |
1998年 | 560篇 |
1997年 | 509篇 |
1996年 | 502篇 |
1995年 | 390篇 |
1994年 | 372篇 |
1993年 | 342篇 |
1992年 | 310篇 |
1991年 | 237篇 |
1990年 | 192篇 |
1989年 | 160篇 |
1988年 | 137篇 |
1987年 | 70篇 |
1986年 | 78篇 |
1985年 | 48篇 |
1984年 | 44篇 |
1983年 | 32篇 |
1982年 | 42篇 |
1981年 | 19篇 |
1980年 | 20篇 |
1979年 | 19篇 |
1978年 | 13篇 |
1977年 | 17篇 |
1976年 | 8篇 |
1958年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
861.
A.?L.?TserklevychEmail author O.?S.?Zayats Ye.?O.?Shylo O.?M.?Shylo 《Kinematics and Physics of Celestial Bodies》2018,34(1):19-36
The computer simulation of the reorientation of the Earth and Mars lithosphere figure has been performed, which due to the dynamic redistribution of masses, allowed to reveal certain regularities of the structure-forming processes. It has been shown that the shape of the lithosphere surface has a different orientation relatively to the geoids’ (aroids) figure. This causes redistribution of masses leading to a strained state of the lithosphere as a result of endogenous and gravitational-rotational forces action in the evolutionary processes of planet’s self-development. The solution of this problem is considered on the example of lithosphere surface heights approximation by a biaxial ellipsoid with seven parameters. The acting horizontal forces in the upper shell of the planet has been calculated, introducing the concept of “evolutionary deviation of the plumb” and assuming that the tangential forces are proportional to the angle, which is defined as the angle between the direction of the plumb line in the past geological epoch and the plumb line direction at a given point. The calculated fields of tangential force vectors show good consistency with the direction of space-time displacement of Earth’s continents and tectonic plates and consistent with the results of the horizontal movements of GNSS stations. This is quite convincing evidence that under the long-term action of vortex rotationalgravitational forces, the lithospheres masses acquire the properties of creep. All this leads to the fact that interacting blocks and plates within the vortex rotational-gravitational model can be interconnected to elastic fields that creates a single planetary geodynamic field that forms the evolutionary state of the geo-environment. 相似文献
862.
深弹发射装置安装在甲板部位,使用环境恶劣,过去均采用传统的试验方法进行环境适应性考核。最近几年,随着三维设计的广泛应用,仿真技术也开始发挥作用,以发射装置接线箱的冲击响应为例,介绍仿真技术在发射装置环境适应性分析中的应用。通过案例分析可知,仿真分析对于发现机械结构设计中的薄弱环节还是非常有效的,它突破了环境试验受限于试验样机和特定环境条件的限制,可以在较短的时间内得到仿真结果,对装备模型进行及时修正。 相似文献
863.
Sacit Özdemir Cahit Yeşilyaprak Bahadır Aktuğ Derya Öztürk Deniz Çoker Recep Balbay 《Experimental Astronomy》2018,46(2):323-336
We present preliminary statistics on the precipitable water vapor (PWV) content over the Karakaya Hills in Erzurum city, where the largest optical and near-infrared astronomical telescope in Turkey will be operated. Since the observatory will observe in the near-infrared (NIR), it is intended to perform PWV measurements of the atmosphere above the site by using signal delays in Global Positioning System (GPS) communication. The analysis of the GPS data recorded on the summit for almost one year shows that the atmosphere over the site of the observatory, which has an altitude of 3170 m, has favorable conditions for NIR observations. From GPS measurements, we report that the site had an average PWV of 3.2 mm and a median PWV of 2.7 mm between October 6, 2016, and June 15, 2017. We also present the time dependency of the PWV content and the correlations between the amount of PWV and the other meteorological records gathered from radiosonde flights and ground-based measurements. 相似文献
864.
865.
Ye. V. Zhuleva 《Oceanology》2010,50(1):107-112
The volumes of formed volcanoes are an important indicator of the formation intensity of the ocean floor volcanogenic morphostructure
under different geodynamic conditions. The distribution of the volumes of volcanoes that formed within the oceanic lithosphere
of different geological ages is considered to analyze the spatial and time dynamics of the scopes of the seamount formation.
The greatest volumes of effused rocks concentrate in volcanoes of different heights on the different-age segments of the lithosphere.
The total volumes of volcanogenic substance growing with increasing age and thickness of the lithosphere is caused by the
increasing range of the heights of the formed volcanoes and the growing number of big seamounts. Despite that the volcanic
seamounts formed within the mid-oceanic ridges, on the divergent boundaries of the lithospheric plates and in the transform
faults most often, half of the volcanogenic material was emitted to the earth’s surface during the spreading of the intraplate
volcanism. A leading part in the formation of the volcanogenic morphostructure of the ocean floor belongs to the formation
of big seamounts with heights of 4–6 km and volumes from 1500 to 5100 km3, respectively, in the provinces with ages from 60 to 90 mln years. 相似文献
866.
867.
868.
869.
870.
雷诺数对圆形渐缩喷嘴湍流射流的影响 总被引:2,自引:0,他引:2
The present study systematically investigates by experiment the influence of Reynolds number (Re) on a turbulent jet issuing from a smoothly-contracting round nozzle. Measurements were performed for seven Reynolds numbers varying from Re = 4,050 to Re = 20,100 using single hot-wire anemometry and over an axial distance of 30 nozzle exit diameters. Although all the exit velocity profiles are of "top-hat" shape, these measurements reveal significant dependence on Re of the exit and downstream flows. The effect of Re on both the mean and turbulent fields is substantial for Re < 10,000 and becomes weak beyond Re = 10,000. The length of the jet’s potential core and the far-field rates of decay and spread all depend significantly on Re. 相似文献