全文获取类型
收费全文 | 35023篇 |
免费 | 121篇 |
国内免费 | 137篇 |
专业分类
测绘学 | 945篇 |
大气科学 | 2390篇 |
地球物理 | 5969篇 |
地质学 | 15939篇 |
海洋学 | 2599篇 |
天文学 | 6137篇 |
综合类 | 203篇 |
自然地理 | 1099篇 |
出版年
2022年 | 144篇 |
2021年 | 206篇 |
2020年 | 193篇 |
2019年 | 229篇 |
2018年 | 3538篇 |
2017年 | 3253篇 |
2016年 | 2090篇 |
2015年 | 318篇 |
2014年 | 453篇 |
2013年 | 619篇 |
2012年 | 1566篇 |
2011年 | 3300篇 |
2010年 | 3071篇 |
2009年 | 3249篇 |
2008年 | 2587篇 |
2007年 | 3254篇 |
2006年 | 543篇 |
2005年 | 798篇 |
2004年 | 689篇 |
2003年 | 749篇 |
2002年 | 550篇 |
2001年 | 278篇 |
2000年 | 294篇 |
1999年 | 180篇 |
1998年 | 187篇 |
1997年 | 174篇 |
1996年 | 128篇 |
1995年 | 136篇 |
1994年 | 124篇 |
1993年 | 102篇 |
1992年 | 80篇 |
1991年 | 104篇 |
1990年 | 109篇 |
1989年 | 86篇 |
1988年 | 88篇 |
1987年 | 105篇 |
1986年 | 89篇 |
1985年 | 117篇 |
1984年 | 101篇 |
1983年 | 114篇 |
1982年 | 91篇 |
1981年 | 104篇 |
1980年 | 127篇 |
1979年 | 89篇 |
1978年 | 95篇 |
1977年 | 81篇 |
1976年 | 70篇 |
1975年 | 67篇 |
1974年 | 75篇 |
1973年 | 70篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
We observed near-Main-Sequence B-stars in the Magellanic Clouds with the 3.6 m telescope and CASPEC at La Silla. We obtained spectra of high resolution and high S/N-ratio. The stars are members of the blue globular clusters NGC 1818 (LMC) and NGC 330 (SMC). The spectra are used for differential abundance analyses using HER as galactic reference star. Apart from CNO the metals are underabundant by about a factor of three and four for the LMC and SMC star, respectively. The CNO pattern is interesting since in both stars oxygen is considerably more abundant than carbon.Based on observations collected at ESO, La Silla and on Calar Alto, Spain and on observations made with the International Ultraviolet Explorer. 相似文献
42.
V. Nagasubramanian P. V. Radhadevi R. Ramachandran R. Krishnan 《Journal of the Indian Society of Remote Sensing》2008,36(1):27-35
Rational Function Model (RFM) is the alternate sensor Model to the rigorous sensor model that allows end user to perform sensor-independent
photogrammetric processing. Nowadays, commercial off-the-shelf (COTS) digital photogrammetric work stations have incorporated
RFM as a method for image restitution. It is technically applicable to all types of airborne and space borne sensors. In this
paper, we describe the derivations of the algorithmic procedure for third order inverse and forward RFM method for 3-D reconstruction.
Model accuracy is evaluated for aerial image, TK-350 Russian image and IRS-1C PAN image. The results ensure that properly
constructed RFM are accurate enough to be used in place of the original rigorous models. The test results are reported and
summarised. 相似文献
43.
R. Raaj M. Ramalingam S. K. Ghosh U. C. Kothyari 《Journal of the Indian Society of Remote Sensing》2008,36(1):61-68
This article reports a preliminary work in which two site specific seasonal algorithms have been proposed for estimating the
suspended sediments concentration (SSC) from the digital numbers recorded on Indian Remote sensing Satellite, IRS-P4 Ocean
Colour Monitor (OCM) sensor. For estimation of SSC, the proposed algorithms utilize dark pixel deduction atmospheric correction
technique. The computations are performed with respect to north east monsoon phase situations of Palk Strait coastal stretch.
The algorithms performance was satisfactory during the north east monsoon period. Although the results obtained cannot be
generalized, we suggest that the authority of proposed algorithms can be extended to other seasons with the addition of more
temporal experimental validation data sets and with numeric constants adjusted to present existing conditions. (As this area
was severely affected by Tsunami, it may have dissimilar conditions at present). 相似文献
44.
K. S. Rao Y. S. Rao H. K. Al Jassar 《Journal of the Indian Society of Remote Sensing》2008,36(2):123-136
Spaceborne Imaging Radar (SIR-C) data acquired over Gujarat, India in 1994 were processed and analysed using differnet techniques
applicable to polarimetric SAR data such as polarization signatures, polarization index, decomposition of the signal and polarization
phase difference and limited groundtruth data. It has been observed that multi-frequency polarimetric data enhances the potential
of retrieving geo-physical parameters. The polarization signatures are found to vary with the nature of the target. Target
decomposition of the returned signal will be useful for the classification of various features. Polarization Phase Difference
(PPD) gives good information about the vegetation parameters. 相似文献
45.
Mudanyal O. Yldz S. Semerci O. Yapar A. Akduman I. 《Geoscience and Remote Sensing Letters, IEEE》2008,5(2):180-184
A microwave imaging method for nondestructive testing of perfectly conducting surfaces beyond a layered media is presented. The method is an adaptation of the surface reconstruction approach by Yapar et al. to the present problem. It is based on the analytical continuation of the measured data to the surface under test through a special representation of the scattered field in terms of Fourier transform and Taylor expansion. Then the problem is reduced to the solution of a nonlinear equation which is solved iteratively via the Newton method and regularization in the least squares sense. Numerical simulations show that defects as small as lambda/500 can be recovered through the presented algorithm. 相似文献
46.
47.
48.
49.
50.