全文获取类型
收费全文 | 67260篇 |
免费 | 17973篇 |
国内免费 | 42408篇 |
专业分类
测绘学 | 3132篇 |
大气科学 | 23280篇 |
地球物理 | 19019篇 |
地质学 | 45754篇 |
海洋学 | 19075篇 |
天文学 | 9312篇 |
综合类 | 4020篇 |
自然地理 | 4049篇 |
出版年
2022年 | 534篇 |
2021年 | 966篇 |
2020年 | 2265篇 |
2019年 | 5779篇 |
2018年 | 6421篇 |
2017年 | 6161篇 |
2016年 | 6251篇 |
2015年 | 5145篇 |
2014年 | 5027篇 |
2013年 | 6391篇 |
2012年 | 5461篇 |
2011年 | 5569篇 |
2010年 | 5441篇 |
2009年 | 5129篇 |
2008年 | 4261篇 |
2007年 | 4263篇 |
2006年 | 3796篇 |
2005年 | 3304篇 |
2004年 | 3692篇 |
2003年 | 3476篇 |
2002年 | 3075篇 |
2001年 | 2738篇 |
2000年 | 2297篇 |
1999年 | 2239篇 |
1998年 | 2339篇 |
1997年 | 2439篇 |
1996年 | 1905篇 |
1995年 | 1828篇 |
1994年 | 1652篇 |
1993年 | 1576篇 |
1992年 | 1354篇 |
1991年 | 1127篇 |
1990年 | 1097篇 |
1989年 | 946篇 |
1988年 | 838篇 |
1987年 | 775篇 |
1986年 | 711篇 |
1985年 | 740篇 |
1984年 | 804篇 |
1983年 | 702篇 |
1982年 | 687篇 |
1981年 | 589篇 |
1980年 | 533篇 |
1979年 | 509篇 |
1978年 | 416篇 |
1977年 | 422篇 |
1976年 | 376篇 |
1975年 | 362篇 |
1974年 | 355篇 |
1973年 | 384篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
The Speckle camera of the 3.5 m Telescopio Nazionale Galileo (TNG) has been used to measure apparent sizes and shapes of a number of main belt asteroids. The average size measurements are in a generally good agreement with the results of indirect IRAS-based radiometric techniques. The measured shapes are compared with predictions based on previously derived spin axis directions and lightcurve photometry of some of the observed objects. Also in this case the agreement is reasonable and the speckle observations allow us to discriminate in some cases between the two pole solutions usually found for each object. No clear evidence of binaries was found. The results show that the TNG speckle camera can be a powerful tool to resolve relatively large main belt asteroids and to calibrate the results of the IRAS survey. 相似文献
82.
83.
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
84.
Chiang E. I. Lovering J. R. Millis R. L. Buie M. W. Wasserman L. H. Meech K. J. 《Earth, Moon, and Planets》2003,92(1-4):49-62
We review ongoing efforts to identify occupants of mean-motion resonances(MMRs) and collisional families in the Edgeworth–Kuiper belt. Directintegrations of trajectories of Kuiper belt objects (KBOs) reveal the 1:1(Trojan), 5:4, 4:3, 3:2 (Plutino), 5:3, 7:4, 9:5, 2:1 (Twotino), and 5:2 MMRsto be inhabited. Apart from the Trojan, resonant KBOs typically have largeorbital eccentricities and inclinations. The observed pattern of resonanceoccupation is consistent with resonant capture and adiabatic excitation bya migratory Neptune; however, the dynamically cold initial conditions priorto resonance sweeping that are typically assumed by migration simulationsare probably inadequate. Given the dynamically hot residents of the 5:2 MMRand the substantial inclinations observed in all exterior MMRs, a fraction ofthe primordial belt was likely dynamically pre-heated prior to resonancesweeping. A pre-heated population may have arisen as Neptune gravitationallyscattered objects into trans-Neptunian space. The spatial distribution of Twotinosoffers a unique diagnostic of Neptune's migration history. The Neptunian Trojanpopulation may rival the Jovian Trojan population, and the former's existence isargued to rule out violent orbital histories for Neptune. Finally, lowest-order seculartheory is applied to several hundred non-resonant KBOs with well-measured orbitsto update proposals of collisional families. No convincing family is detected. 相似文献
85.
超基性岩中含铜、钴块状硫化物矿床——德尔尼铜矿成因新认识 总被引:1,自引:0,他引:1
长期以来对德尔尼铜矿的成因存在着不同认识。从矿石组成和结构、构造来看,应属典型的块状硫化物矿石,矿床亦应属于含铜黄铁矿型矿床。但从其地质产状来看又与一般的黄铁矿型矿床大不相同,与一般的岩浆熔离铜镍硫化物矿床也有较多差异。这就是本矿床类型独特之处。近年来通过工作又取得一些新资料,特别是超基性岩和矿石的同位素年龄数据。本文在综合新老资料基础上,提出新看法,认为该矿床形成于上地幔,再就位于地壳浅部。其成因类型暂定为:“深部熔离—构造侵位矿床”。鉴于本矿床与一般块状硫化物矿床相比有其独特性,建议命名为“德尔尼型”。 相似文献
86.
We present two spectra of the supernova SN1988A in M58 (NGC4579) over the wavelength range 4000–9700 Å, as recorded by the Faint Object Spectrograph on the 4.2 m William Herschel Telescope at the Observatorio del Roque de los Muchachos. We conclude that SN1988A was a type II supernova. 相似文献
87.
88.
The occultation of Io by Ganymede as observed on 10 June 1985 is reported. The middle of the occultation minimum was found to occur at 14h 14m 5.7s UT. In the plane perpendicular to the line of sight the centres of the two satellite disks passed to within ~ 2530 km of each other, at a relative velocity, in this plane, of about 11 kms–1. The values of these last two quantities, however, depend on what assumptions are made about the light distribution over io's disk. 相似文献
89.
90.
This paper presents an on-line trained neural net work controller for ship track-keeping problems. Following a brief review of the ship track-keeping control development since the 1980's, an analysis of various existing backpropagation-based neural controllers is provided. We then propose a single-input multioutput (SIMO) neural control strategy for situations where the exact mathematical dynamics of the ship are not available. The aim of this study is to build an autonomous neural controller which uses rudder to regulate both the tracking error and heading error. During the whole control process, the proposed SIMO neural controller adapts itself on-line from a direct evaluation of the control accuracy, and hence the need for a “teacher” or an off-line training process can be removed. With a relatively modest amount of quantitative knowledge of the ship behavior, the design philosophy enables real time control of a nonlinear ship model under random wind disturbances and measurement noise. Three different track-keeping tasks have been simulated to demonstrate the effectiveness of the training method and the robust performance of the proposed neural control strategy 相似文献