全文获取类型
收费全文 | 541篇 |
免费 | 108篇 |
国内免费 | 123篇 |
专业分类
测绘学 | 77篇 |
大气科学 | 106篇 |
地球物理 | 117篇 |
地质学 | 268篇 |
海洋学 | 77篇 |
天文学 | 12篇 |
综合类 | 40篇 |
自然地理 | 75篇 |
出版年
2024年 | 3篇 |
2023年 | 9篇 |
2022年 | 31篇 |
2021年 | 37篇 |
2020年 | 33篇 |
2019年 | 40篇 |
2018年 | 35篇 |
2017年 | 50篇 |
2016年 | 39篇 |
2015年 | 39篇 |
2014年 | 49篇 |
2013年 | 41篇 |
2012年 | 35篇 |
2011年 | 40篇 |
2010年 | 36篇 |
2009年 | 32篇 |
2008年 | 27篇 |
2007年 | 34篇 |
2006年 | 19篇 |
2005年 | 15篇 |
2004年 | 15篇 |
2003年 | 13篇 |
2002年 | 19篇 |
2001年 | 20篇 |
2000年 | 8篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 5篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有772条查询结果,搜索用时 42 毫秒
1.
Two small satellites of Pluto, S/2005 P1 (hereafter P1) and S/2005 P2 (hereafter P2), have recently been discovered outside the orbit of Charon, and their orbits are nearly circular and nearly coplanar with that of Charon. Because the mass ratio of Charon-Pluto is ∼0.1, the orbits of P2 and P1 are significantly non-Keplerian even if P2 and P1 have negligible masses. We present an analytic theory, with P2 and P1 treated as test particles, which shows that the motion can be represented by the superposition of the circular motion of a guiding center, the forced oscillations due to the non-axisymmetric components of the potential rotating at the mean motion of Pluto-Charon, the epicyclic motion, and the vertical motion. The analytic theory shows that the azimuthal periods of P2 and P1 are shorter than the Keplerian orbital periods, and this deviation from Kepler's third law is already detected in the unperturbed Keplerian fit of Buie and coworkers. In this analytic theory, the periapse and ascending node of each of the small satellites precess at nearly equal rates in opposite directions. From direct numerical orbit integrations, we show the increasing influence of the proximity of P2 and P1 to the 3:2 mean-motion commensurability on their orbital motion as their masses increase within the ranges allowed by the albedo uncertainties. If the geometric albedos of P2 and P1 are high and of order of that of Charon, the masses of P2 and P1 are sufficiently low that their orbits are well described by the analytic theory. The variation in the orbital radius of P2 due to the forced oscillations is comparable in magnitude to that due to the best-fit Keplerian eccentricity, and there is at present no evidence that P2 has any significant epicyclic eccentricity. However, the orbit of P1 has a significant epicyclic eccentricity, and the prograde precession of its longitude of periapse with a period of 5300 days should be easily detectable. If the albedos of P2 and P1 are as low as that of comets, the large inferred masses induce significant short-term variations in the epicyclic eccentricities and/or periapse longitudes on the 400-500-day timescales due to the proximity to the 3:2 commensurability. In fact, for the maximum inferred masses, P2 and P1 may be in the 3:2 mean-motion resonance, with the resonance variable involving the periapse longitude of P1 librating. Observations that sample the orbits of P2 and P1 well on the 400-500-day timescales should provide strong constraints on the masses of P2 and P1 in the near future. 相似文献
2.
基于ARP协议的网络主机地址的识别技术研究 总被引:3,自引:0,他引:3
从移动IPv6工作原理入手,IP地址管理器是针对越来越严重的IP地址盗用现象而设计的一套有效的监控和管理IP地址的方案。分析与研究IP地址管理器中的信息收集模块后,以Winpcap为开发工具,利用ARP,附等协议完成对网络中活动主机的扫描以及信息(主机名、MAC、操作系统)的收集和识别。模块实现了对网络的自动实时监控,有效地提高了管理效率。 相似文献
3.
在Gaussian波场基础上,推导出以P-M谱和平均JONSWAP谱代表的充分成长和有限风区的深水风浪平均波长与平均波周期之间的关系为.推导中运用了Rice跨零点问题的解并通过滑动时间平均技术估计4阶谱矩.在风浪水槽进行了实验,实验结果与有限风区下推导出的关系相比较,符合较好. 相似文献
4.
V. I. Man’kovsky 《Physical Oceanography》2001,11(5):491-494
We present the parameters of empirical relationships between the depth of visibility of Secchi disk and optical and biological
characteristics of the Black-Sea surface waters.
Translated by Peter V. Malyshev and Dmitry V. Malyshev 相似文献
5.
Young-Ok Kim Eun Jin Yang Jung-Hoon Kang Kyoungsoon Shin Man Chang Cheol Soo Myung 《Ocean Science Journal》2007,42(1):9-17
The summer distributions of planktonic microbial communities (heterotrophic and phtosynthetic bacteria, phtosynthetic and
heterotrophic nanoflagellates, ciliate plankton, and microphytoplankton) were compared between inner and outer areas of Lake
Sihwa, divided by an artificial breakwater, located on the western coast of Korea, in September 2003. The semienclosed, inner
area was characterized by hyposaline surface water (<17 psu), and by low concentrations of dissolved oxygen (avg. 0.4 mg L1) and high concentrations of inorganic nutrients (nitrogenous nutrients >36 μM, phosphate <4 μM) in the bottom layer. Higher
densities of heterotrophic bacteria and nanoflagellates also occurred in the inner area than did in the outer area, while
microphytoplankton (mainly diatoms) occurred abundantly in the outer area. A tiny tintinnid ciliate, Tintinnopsis nana, bloomed
into more than 106 cells L1 at the surface layer of the inner area, while its abundance was much lower (103-104 cells L1) in the outer area of the breakwater. Ciliate abundance was highly correlated with heterotrophic bacteria (r = 0.886, p <
0.001) and heterotrophic flagellates (r = 0.962, p < 0.001), indicating that rich food availability may have led to theT. nana bloom. These results suggest that the breakwater causes the eutrophic environment in artificial lakes with limited flushing
of enriched water and develops into abundant bacteria, nanoflagellates, and ciliates. 相似文献
6.
伴随模式同化系统在修正模式地形中的应用 总被引:7,自引:1,他引:7
任何模式都只是实际大气的一种近似模拟,存在误差。鉴于传统的四维资料伴随模式同化系统都是假设模式完全正确仅对初始场进行修正。将伴随模式同化系统应用于修正模式地形误差,通过对不同初始地形的修正试验表明,MM5伴随模式同化系统能很好地对地形误差进行修正,能够反演出与初始气象要素场分辨率相匹配、与模式更协调的地形场,为伴随模式同化系统的广泛应用提供了一种新的思路。 相似文献
7.
8.
9.
10.