全文获取类型
收费全文 | 2301篇 |
免费 | 260篇 |
国内免费 | 281篇 |
专业分类
测绘学 | 682篇 |
大气科学 | 83篇 |
地球物理 | 553篇 |
地质学 | 849篇 |
海洋学 | 71篇 |
天文学 | 280篇 |
综合类 | 124篇 |
自然地理 | 200篇 |
出版年
2024年 | 11篇 |
2023年 | 24篇 |
2022年 | 52篇 |
2021年 | 43篇 |
2020年 | 77篇 |
2019年 | 86篇 |
2018年 | 46篇 |
2017年 | 59篇 |
2016年 | 85篇 |
2015年 | 84篇 |
2014年 | 101篇 |
2013年 | 155篇 |
2012年 | 106篇 |
2011年 | 118篇 |
2010年 | 119篇 |
2009年 | 148篇 |
2008年 | 170篇 |
2007年 | 128篇 |
2006年 | 156篇 |
2005年 | 113篇 |
2004年 | 89篇 |
2003年 | 88篇 |
2002年 | 97篇 |
2001年 | 89篇 |
2000年 | 91篇 |
1999年 | 86篇 |
1998年 | 59篇 |
1997年 | 64篇 |
1996年 | 55篇 |
1995年 | 37篇 |
1994年 | 39篇 |
1993年 | 34篇 |
1992年 | 15篇 |
1991年 | 27篇 |
1990年 | 19篇 |
1989年 | 15篇 |
1988年 | 13篇 |
1987年 | 17篇 |
1986年 | 10篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有2842条查询结果,搜索用时 0 毫秒
51.
52.
鉴于当前国际上关于自转微椭、非均匀地球(SREHI)的固体潮汐响应的结果之间存在明显分歧,特别是Love数k及重力潮汐因子δ对纬度的依赖情况截然不同,本文借助于摄动法与张量正则分量的广义球谐展开建立起来的侧向非均匀、自转微椭、粘弹地球的潮汐模拟理论,计算了SREHI地球的潮汐形变及相应的引力位变化.结果表明,描述径向位移的Love数的纬度依赖部分系数h+与球对称部分h0+δh0之比不大于1.0‰;对O1波为0.27‰;对M2波为0.19‰;对M3波为0.49‰;对M4波为0.88‰.描述地球引力位变化的Love数的纬度依赖部分系数k+与球对称部分k0+δk0之比小于3.0‰;对O1波为2.67‰;对M2波为1.89‰;对M3波为2.24‰;对M4波为2.70‰. 相似文献
53.
本文研究了液核地球对日月引潮力位球谐函数项的变形响应,即周日固体潮。作为数值结果,计算了1066A地球模型的周日潮汐勒夫数。所建立的周日固体潮理论模型改进了Molodensky液核动力学理论模型。为了比较两者之间的差异,还根据Molodensky理论模型计算了1066A地球模型的周日潮汐勒夫数。 相似文献
54.
Due to the specific dynamics, the probes located at the halo orbits or Lissajous orbits around the Earth-Moon collinear libration point L1 or L2 are always studied in the synodic system to understand their trajectories. In fact, they are also orbiting the Earth in a distant Keplerian ellipse. Because of their intrinsic orbital instability, in the orbit prediction the initial errors propagate more prominently than those of the normal orbiting satellites, this requires special attention in the orbit design, maneuver, and control. Despite of all this, they are similar to the normal orbiting satellites in orbit determination and hardly require other special attentions. In this paper, the quantitative results of error propagation under the unstable dynamics, together with the theoretical analysis are presented. The results of precise orbit determination and short-arc orbit predictions are also shown, and compared with the results from the Beijing Aerospace Control Center. 相似文献
55.
H. Greiner-Mai 《Astronomische Nachrichten》1987,308(3):217-226
The electromagnetic core-mantle coupling is one of the most likely hypotheses to explain the connections between both, the decade fluctuations of the Earth rotation and such of the magnetic field of the Earth. Within this paper, the axial and equatorial electromagnetic torques are computed at time intervals of two years from 1903.5 to 1975.5. They are compared with mechanical torques necessary for the excitation of the decade variations of the rotation of the Earth. The comparison is made with regard to the magnitude of the torques, to their time behaviour and to the periods within the time variations of both types of the torques. The computed electromagnetic torques are comparable with that necessary to excite the variations of the rotation of the Earth. But they are two or three orders less than that necessary to excite the decade variations of the polar motion. Some comparable periods were found within the spectra of the electromagnetic and the mechanical torques. This speaks in favour of the core-mantle coupling. But there are differences between both spectra too hinting at other processes which we cannot describe by a simple model of the core-mantle coupling. 相似文献
56.
57.
The Carboniferous and Permian sedimentary rocks (mainly the Shanxi and Taiyuan formations) in the Linxing region, eastern Ordos Basin, China, host a significant volume of unconventional gas resources (coalbed methane, shale gas and tight sandstone gas). Currently, the in-situ stress state is poorly understood but knowledge of this is extremely important for a range of applications, such as gas exploration and production, fracture stimulation and wellbore stability. The maximum horizontal stress (SHmax), minimum horizontal stress (Shmin) and vertical stress (Sv) magnitudes, and the SHmax orientation in the Linxing region were systematically analyzed for the first time in the present study, which can provide a reference for subsequent numerical simulation and hydraulic fracturing design. Based on borehole breakouts and drilling-induced tensile fractures interpreted from borehole imaging logs, the SHmax orientation rotates from ∼NEE-SWW-trending in the southern part to ∼ NWW-SEE-trending in the northern part of the Linxing region. Both conventional logs and extended leak-off tests were used for stress magnitude determination. The results revealed three types of in-situ stress fields (Sv > SHmax > Shmin, SHmax > Sv > Shmin and SHmax > Sv ≈ Shmin), and a dominant strike-slip stress regime (SHmax > Sv ≥ Shmin) was found for the entire well section in the target Shanxi Formation and Taiyuan Formation in the Linxing region. In addition, differential stress increased with depth in the Linxing region, which indicates that wellbore instability might be a potentially significant problem when drilling wells that are vertical or ∼ N-S-trending. 相似文献
58.
59.
单晶高温合金展现出优越的抗疲劳性能和高温蠕变性能,广泛应用于航空发动机和燃气轮机的热端部件。但是,其制备过程中会产生晶体取向偏离、杂晶等缺陷。目前国际上已经普遍使用X射线劳埃衍射技术对单晶叶片的晶体缺陷进行无损检测,但是这种检测方法主要依赖人工识别,效率低,结果可重复性差,不适合批量化检测。本文结合工程需要,提出对劳埃衍射斑点进行自动识别的算法,主要包括衍射图样的预处理、轮廓检测、轮廓形态筛选及轮廓符合检测等。该算法能够自动检测出衍射图样上的衍射斑点,并最终给出斑点的位置坐标数据及其误差。根据衍射斑点的位置,通过衍射分析算法,计算出单晶叶片上的晶体取向,并最终对叶片的晶体缺陷给出综合评价。 相似文献
60.
Understanding our star, the Sun, is of fundamental interest for life on Earth. In this paper, the status of knowledge in solar physics of roughly two decades ago is summarised, and the most recent developments in this very active field are shown, many of them achieved by means of space based missions. The Sun–Earth connection is described and, finally, an outlook on future solar research is given. 相似文献