全文获取类型
收费全文 | 66439篇 |
免费 | 11973篇 |
国内免费 | 19103篇 |
专业分类
测绘学 | 4169篇 |
大气科学 | 6059篇 |
地球物理 | 8616篇 |
地质学 | 52735篇 |
海洋学 | 6163篇 |
天文学 | 7888篇 |
综合类 | 4585篇 |
自然地理 | 7300篇 |
出版年
2024年 | 327篇 |
2023年 | 1056篇 |
2022年 | 2345篇 |
2021年 | 2758篇 |
2020年 | 2584篇 |
2019年 | 3345篇 |
2018年 | 2449篇 |
2017年 | 2796篇 |
2016年 | 3008篇 |
2015年 | 3213篇 |
2014年 | 4361篇 |
2013年 | 4000篇 |
2012年 | 4543篇 |
2011年 | 4646篇 |
2010年 | 4246篇 |
2009年 | 4875篇 |
2008年 | 4647篇 |
2007年 | 4873篇 |
2006年 | 4566篇 |
2005年 | 4241篇 |
2004年 | 3758篇 |
2003年 | 3460篇 |
2002年 | 2978篇 |
2001年 | 2744篇 |
2000年 | 2642篇 |
1999年 | 2386篇 |
1998年 | 2075篇 |
1997年 | 1663篇 |
1996年 | 1347篇 |
1995年 | 1117篇 |
1994年 | 1018篇 |
1993年 | 840篇 |
1992年 | 637篇 |
1991年 | 520篇 |
1990年 | 369篇 |
1989年 | 291篇 |
1988年 | 230篇 |
1987年 | 142篇 |
1986年 | 102篇 |
1985年 | 81篇 |
1984年 | 41篇 |
1983年 | 29篇 |
1982年 | 26篇 |
1981年 | 17篇 |
1980年 | 22篇 |
1979年 | 12篇 |
1978年 | 26篇 |
1977年 | 19篇 |
1976年 | 5篇 |
1954年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Larisa A. Yakovina Yakiv V. Pavlenko Carlos Abia 《Astrophysics and Space Science》2003,288(3):279-286
Lithium abundances in the atmospheres of the super Li-rich C-giants WZ Cas and WX Cyg are derived by the spectral synthesis
technique using the Li I resonance line at λ670.8 nm and three subordinate lines at λλ 812.6, 610.4 and 497.2 nm. The differences
between the Li abundances derived from the λ670.8 nm line and the λλ 497.2, 812.6 nm lines do not exceed ±0.5 dex. The lithium
line at λ610.4 nm provides typically lower abundances than the resonance line (by ≈ 1 dex). The mean LTE and NLTE Li abundances
from three Li I lines (excluding λ610.4 nm) are 4.7, 4.9 for WZ Cas, and 4.6, 4.8 for WX Cyg, respectively.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
92.
韩玲 《地球科学与环境学报》2003,25(1):74-75
提出了一种基于格网DEM的粗差检测及剔除方法,其基本思想是对每个表面上的点,在坡度上,高程或突变量引起的形状不连续,可能被怀疑有误差,通过坡度上每个点,应用坡度逼近或改变量来计算,考虑坡度变化的相对值,并以这些相对值计算一个统计值为判断该点合法性的阈值,使计算结果更为可靠。 相似文献
93.
94.
95.
We examine possible locations for the primordial disk of the Edgeworth-Kuiper Belt (EKB), using several subsets of the known objects as markers of the total mass distribution. Using a secular perturbation theory, we find that the primordial plane of the EKB could have remained thin enough to escape detection only if it is clustered very closely about the invariable plane of the Solar System. 相似文献
96.
Photometric observations of Pluto in the BVR filter system were obtained in 1999 and in 1990-1993, and observations in the 0.89-μm methane absorption band were obtained in 2000. Our 1999 observations yield lightcurve amplitudes of 0.30 ± 0.01, 0.26 ± 0.01, and 0.21 ± 0.02 and geometric albedos of 0.44 ± 0.04, 0.52 ± 0.03, and 0.58 ± 0.02 in the B, V, and R filters, respectively. The low-albedo hemisphere of Pluto is slightly redder than the higher albedo hemisphere. A comparison of our results and those from previous epochs shows that the lightcurve of Pluto changes substantially through time. We developed a model that fully accounts for changes in the lightcurve caused by changes in the viewing geometry between the Earth, Pluto, and the Sun. We find that the observed changes in the amplitude of Pluto’s lightcurve can be explained by viewing geometry rather than by volatile transport. We also discovered a measurable decrease since 1992 of ∼0.03 magnitudes in the amplitude of Pluto’s lightcurve, as the model predicts. Pluto’s geometric albedo does not appear to be currently increasing, as our model predicts, although given the uncertainties in both the model and the measurements of geometric albedo, this result is not firm evidence for volatile transport. The maximum of methane-absorption lightcurve occurs near the minimum of the BVR lightcurves. This result suggests that methane is more abundant in the brightest regions of Pluto. Pluto’s phase coefficient exhibits a color dependence, ranging from 0.037 ± 0.01 in the B filter to 0.032 ± 0.01 in the R filter. Pluto’s phase curve is most like those of the bright, recently resurfaced satellites Triton and Europa. Although Pluto shows no strong evidence for volatile transport now (unlike Triton), it is important to continue to observe Pluto as it moves away from perihelion. 相似文献
97.
Jianhua FAN Bingfei SHI 《东北亚地学研究》2006,9(2):217-219
Kunming Basin locates middle of Yunnan altiplano and has a particularity in geography,topographic and geological environment.With the urban dilation quickly,add the reason of the unreasonable city layout,conflicts between environment and urban resources consumption become shrill increasingly.It is human being activities that lead to vulnerability and depravation of geological environment in local.Take a few examples on geological environment to expatiate relationship between urban construction and geological environment carrying capacity,and find a way how to make a better plan for urban sustainable development to achieve new balance between man and nature in local. 相似文献
98.
We consider the effects of projection, internal absorption, and gas-or stellar-velocity dispersion on the measured rotation curves of galaxies with edge-on disks. Axisymmetric disk models clearly show that the rotational velocity in the inner galaxy is highly underestimated. As a result, an extended portion that imitates nearly rigid rotation appears. At galactocentric distances where the absorption is low (i.e., it does not exceed 0.3–0.5m kpc?1), the line profiles can have two peaks, and a rotation curve with minimum distortions can be obtained by estimating the position of the peak that corresponds to a higher rotational velocity. However, the high-velocity peak disappears in high-absorption regions and the actual shape of the rotation curve cannot be reproduced from line-of-sight velocity estimates. In general, the optical rotation curves for edge-on galaxies are of little use in reconstructing the mass distribution in the inner regions, particularly for galaxies with a steep velocity gradient in the central region. In this case, estimating the rotation velocities for outer (transparent) disk regions yields correct results. 相似文献
99.
100.