全文获取类型
收费全文 | 69876篇 |
免费 | 11698篇 |
国内免费 | 16561篇 |
专业分类
测绘学 | 7101篇 |
大气科学 | 8883篇 |
地球物理 | 13587篇 |
地质学 | 38204篇 |
海洋学 | 9771篇 |
天文学 | 3886篇 |
综合类 | 5269篇 |
自然地理 | 11434篇 |
出版年
2024年 | 245篇 |
2023年 | 674篇 |
2022年 | 1929篇 |
2021年 | 2281篇 |
2020年 | 2514篇 |
2019年 | 3097篇 |
2018年 | 2388篇 |
2017年 | 2740篇 |
2016年 | 2881篇 |
2015年 | 3249篇 |
2014年 | 3789篇 |
2013年 | 3927篇 |
2012年 | 4211篇 |
2011年 | 4442篇 |
2010年 | 3765篇 |
2009年 | 4493篇 |
2008年 | 4498篇 |
2007年 | 5058篇 |
2006年 | 4950篇 |
2005年 | 4375篇 |
2004年 | 4053篇 |
2003年 | 3773篇 |
2002年 | 3343篇 |
2001年 | 2820篇 |
2000年 | 2765篇 |
1999年 | 2539篇 |
1998年 | 2149篇 |
1997年 | 1832篇 |
1996年 | 1658篇 |
1995年 | 1392篇 |
1994年 | 1347篇 |
1993年 | 1182篇 |
1992年 | 937篇 |
1991年 | 664篇 |
1990年 | 545篇 |
1989年 | 502篇 |
1988年 | 329篇 |
1987年 | 217篇 |
1986年 | 154篇 |
1985年 | 106篇 |
1984年 | 48篇 |
1983年 | 38篇 |
1982年 | 39篇 |
1981年 | 24篇 |
1980年 | 27篇 |
1979年 | 35篇 |
1978年 | 43篇 |
1977年 | 25篇 |
1975年 | 5篇 |
1954年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
61.
APPLICATION OF ANALYTIC HIERARCHY PROCESS TO ASSESSING THE ECOLOGICAL VULNERABILITY OF WETLANDS IN THE JIANGHAN PLAIN 总被引:5,自引:1,他引:4
WANGXue-lei NINGLong-mei HUWang-bin 《中国地理科学(英文版)》2003,13(3):272-276
Wetlands in the Jianghan Plain are important components of wetland types in lake area in the middle and lower reaches the Changjiang (Yangtze) River and they fulfill many uses and functions related to hydrology,waste assimilation, ecosystem productivity and biodiversity. Owing to natural factors and human activities, especially excessive reclamation from lakes, the shrinking process of the lakes has been accelerated. Wetland ecosystem has shown the characteristics of vulnerability. According to the analysis of wetland ecological function in the Jianghan Plain, this paper presented an index system related to productivity, stability and environmental capacity. By using the method of Analytic Hierarchy Process, we computed the values of the relative weights of the indexes, and evaluated the vulnerability level of the wetland ecosystem by the method of multi-indexes. The case study showed that the fragile extent of wetland ecosystem in the Jianghan Plain is 5.6. This means that the wetland ecosystem in the Jiang-han Plain is laid to the state of middle vulnerability. Therefore, the wetland conservation and eco-rehabilitation in the JiangJaan Plain should be paid attention to. 相似文献
62.
63.
64.
N. Ivanova K. Belczynski J. M. Fregeau F. A. Rasio 《Monthly notices of the Royal Astronomical Society》2005,358(2):572-584
We study the evolution of binary stars in globular clusters using a new Monte Carlo approach combining a population synthesis code ( startrack ) and a simple treatment of dynamical interactions in the dense cluster core using a new tool for computing three- and four-body interactions ( fewbody ). We find that the combination of stellar evolution and dynamical interactions (binary–single and binary–binary) leads to a rapid depletion of the binary population in the cluster core. The maximum binary fraction today in the core of a typical dense cluster such as 47 Tuc, assuming an initial binary fraction of 100 per cent, is only ∼ 5–10 per cent. We show that this is in good agreement with recent Hubble Space Telescope observations of close binaries in the core of 47 Tuc, provided that a realistic distribution of binary periods is used to interpret the results. Our findings also have important consequences for the dynamical modelling of globular clusters, suggesting that 'realistic models' should incorporate much larger initial binary fractions than has usually been the case in the past. 相似文献
65.
66.
We present new 1.45-1.75 μm spectra of Europa's dark non-ice material with a spectral resolution (λ/δλ) of 1200, obtained by using adaptive optics on the Keck telescope to spatially separate the spectrum of the non-ice material from that of the surrounding ice-rich regions. Despite the great increase in spectral resolution over the previous best spectra of the non-ice material, taken with Galileo's near-infrared mapping spectrometer (NIMS) with λ/δλ=66, no new fine-scale spectral structure is revealed. The smoothness of the spectra is inconsistent with available laboratory spectra of crystalline hydrated salts at Europa temperatures, but is more consistent with various combinations of non-crystalline hydrated salts and/or hydrated sulfuric acid, as have been matched to the lower-resolution NIMS spectra. 相似文献
67.
Yunfei Bao Shengbo Chen 《东北亚地学研究》2006,9(1):100-108
IntroductionThe radiance leaving the earth-atmosphere sys-tem which can be sensed by a satellite borne ra-diometer is the sum of radiation emission fromtheearth surface and each atmospheric level that aretransmittedtothe top of the atmosphere.The radia-tion emissionfromthe earthsurface andthe radianceof each atmospheric level can be separated fromtheradiance at the top the atmospheric level a satellitemeasured.Thus,the earth surface parameters willbe retrieved from the surface radiance after a… 相似文献
68.
利用 12年的Lageos 1卫星激光测距资料 (1990 - 2 0 0 1)解算得到了地球定向参数 (EOP) ,将该序列的结果与同期的EOP(IERS)C0 4进行比较 ,其外符精度为 :极移XP— 0 .4 0mas,YP— 0 .4 2mas ,日长变化Dr— 0 .0 35ms。 相似文献
69.
The time evolution behaviour of the superhumps of the dwarf nova1RXS J232953.9+ 062814 is investigated with the wavelet analysis
method. On the basis of two nights CCD photometry performed during its first superoutburst as well as other published brightness
data, we reveal the superhump's time-dependence as a function of periods and time. Our light curves, which phased in the rapid
decay ending portion of the superoutburst and in the dawn of a following normal outburst, are important to help trace the
superhump evolution for the star. Both the superhump period and the orbital period of the binary system are detected in the
present data. We obtain P
sh=0.0458±0.0002d and P
orb=0.0450±0.0002d. They agree with those existing values. The two periods exchanged their roles during the superhump evolution.
The general profile of brightness fading over the outbursts roughly followed an exponential decay law or a form of a five-order
polynomial.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
70.
JINFeng-jun 《中国地理科学(英文版)》2003,13(2):97-103
It is very important to establish cooperative mechanism to guarantee all members to develop their e-conomies in the Yellow Sea Rim. In this paper, the development strategies ofshipplng centers and transportation networkare discussed based on economic giobalization tendency. The results argue that a united transportation network should bebuilt in order to promote the economic competition of Northeast Asia in the world. As a key component of the economiccooperation, a hierarchical shipping centers network should be established with Hong Kong, Shanghai, Pusan, Koho,and Tokyo as cores. The authorities of China, Japan, R. O. Korea and D. P. B. Korea should make more efforts tobuild a set of cooperation institutions based on raising the transportation efficiency. 相似文献