全文获取类型
收费全文 | 96822篇 |
免费 | 1393篇 |
国内免费 | 612篇 |
专业分类
测绘学 | 1995篇 |
大气科学 | 6220篇 |
地球物理 | 18618篇 |
地质学 | 34946篇 |
海洋学 | 8923篇 |
天文学 | 22619篇 |
综合类 | 249篇 |
自然地理 | 5257篇 |
出版年
2022年 | 710篇 |
2021年 | 1182篇 |
2020年 | 1235篇 |
2019年 | 1396篇 |
2018年 | 2873篇 |
2017年 | 2638篇 |
2016年 | 3049篇 |
2015年 | 1517篇 |
2014年 | 2953篇 |
2013年 | 5109篇 |
2012年 | 3246篇 |
2011年 | 4172篇 |
2010年 | 3811篇 |
2009年 | 4808篇 |
2008年 | 4195篇 |
2007年 | 4388篇 |
2006年 | 4011篇 |
2005年 | 2815篇 |
2004年 | 2745篇 |
2003年 | 2580篇 |
2002年 | 2597篇 |
2001年 | 2263篇 |
2000年 | 2172篇 |
1999年 | 1735篇 |
1998年 | 1776篇 |
1997年 | 1659篇 |
1996年 | 1420篇 |
1995年 | 1401篇 |
1994年 | 1214篇 |
1993年 | 1129篇 |
1992年 | 1073篇 |
1991年 | 1080篇 |
1990年 | 1061篇 |
1989年 | 943篇 |
1988年 | 855篇 |
1987年 | 1026篇 |
1986年 | 896篇 |
1985年 | 1092篇 |
1984年 | 1212篇 |
1983年 | 1177篇 |
1982年 | 1083篇 |
1981年 | 1006篇 |
1980年 | 909篇 |
1979年 | 886篇 |
1978年 | 845篇 |
1977年 | 728篇 |
1976年 | 713篇 |
1975年 | 717篇 |
1974年 | 686篇 |
1973年 | 774篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
S. A. Lamzin 《Astrophysics and Space Science》1995,224(1-2):211-214
I argue that temperatures of spots, responsible for observed periodical light variations of T Tauri stars (TTS), are not known with reliable accuracy to discriminate between chromospheric and accretion theories of TTS 's phenomenon. The hypothesis is set up that spots on classical TTS (CTTS) are due to heating of stellar surface by radiation from a collisional accretion shock, whereas spots on weak line TTS (WTTS), at least in some cases, are connected with a collisionless accretion shock rather than chromospheric activity. Possible scenarios of WTTS interaction with circumstellar matter are discussed. 相似文献
42.
43.
Gavin L. England Birger Rasmussen Neal J. McNaughton Ian R. Fletcher David I. Groves & Bryan Krapez 《地学学报》2001,13(5):360-367
SHRIMP dating of xenotime overgrowths on detrital zircon grains can constrain maximum durations since diagenesis and therefore provide minimum dates of sediment deposition. Thus, xenotime dating has significant economic application to Precambrian sediment-hosted ore deposits, such as Witwatersrand Au–U, for which there are no precise depositional ages. The growth history of xenotime in the Witwatersrand Supergroup is texturally complex, with several phases evident. The oldest authigenic xenotime 207 Pb/206 Pb age obtained in sandstone underlying the Vaal Reef is 2764 ± 5 Myr (1 σ), and most likely represents a mixture of diagenetic and hydrothermal growth. Nevertheless, this represents the oldest authigenic mineral age yet recorded in the sequence and provides a minimum age of deposition. Other xenotime data record a spread of ages that correspond to numerous post-diagenetic thermotectonic events (including a Ventersdorp event at ≈ 2720 Ma) up to the ≈2020 Ma Vredefort event. 相似文献
44.
We report intermediate resolution H spectroscopy of the black hole candidate Nova Muscae 1991 during quiescence. We classify the companion star as a K3-K4V which contributes 85±6 percent to the total flux from the binary. The photospheric absorption lines are broadened by 106±13 kms−1 with respect to template field stars, leading to a system mass ratio of q =M1/M2 = 7.8−2.0+3.4. Doppler imaging of the H line shows strong emission coming from the secondary star (EW=3.1±0.6Å) which we associate with chromospheric activity. However, the hot-spot is not detected and this may indicate a lower mass transfer rate than in other X-ray transients of comparable orbital periods. The surface brightness distribution of the accretion disk in H follows a relation I∝R−1.1, less steep than typically observed in cataclysmic variables. Updated system parameters are also presented. 相似文献
45.
R. Sarmiento M. Gallardo A. Laquidara J. Reyna Almandos 《Astrophysics and Space Science》1997,256(1-2):359-363
This work presents preliminaries spectroscopic results about ionized xenon and xenon-helium mixture using a capillary pulsed discharge under several experimental results. 相似文献
46.
Harker David E. Woodward Charles E. McMURTRY Craig W. Goetz J. A. Pipher J. L. Forrest W. J. 《Earth, Moon, and Planets》1997,78(1-3):259-264
We present 1- to 5-μm broadband and CVF images of comet Hale-Bopp taken 1997 February 10.5 UT, 50 days before perihelion.
All the images exhibit a nonspherical coma with a bright “ridge” in the direction of the dust tail approximately 10″ from
the coma. Synthetic aperture spectrophotometry implies that the optically important grains are of a radius ≤0.4 μm; smallest
radius for any comet seen to date. The variation of the integrated surface brightness with radial distance from the coma (ρ)
in all the images closely follows the “steady state” ρ−1 model for comet dust ablation (Gehrz and Ney, 1992). The near-infrared colors taken along the dust tail are not constant
implying the dust grain properties vary with coma distance.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
47.
The problem of clock synchronization: A relativistic approach 总被引:2,自引:0,他引:2
Sergei A Klioner 《Celestial Mechanics and Dynamical Astronomy》1992,53(1):81-109
The problem of synchronization of the Earth-based clocks has been discussed in the framework of General Relativity Theory. The synchronization is considered as the transformation of the observers' proper time scales to the coordinate time scale of local inertial geocentric reference system, which is single for all the observers. The formulas for the relativistic corrections occurring in some methods of Earth-based clock synchronization (transported clock, duplex communication via geostationary satellite and meteor-burst link, LASSO experiments) have been derived enabling one to attain the accuracy of 0.1 ns. 相似文献
48.
49.
T. H. BELL S. E. JOHNSON B. DAVIS A. FORDE N. HAYWARD C. WILKINS 《Journal of Metamorphic Geology》1992,10(3):295-307
Extensive examination of large numbers of spatially orientated thin sections of orientated samples from orogens of all ages around the world has demonstrated that porphyroblasts do not rotate relative to geographical coordinates during highly non-coaxial ductile deformation of the matrix subsequent to their growth. This has been demonstrated for all tectonic environments so far investigated. The work also has provided new insights and data on metamorphic, structural and tectonic processes including: (1) the intimate control of deformation partitioning on metamorphic reactions; (2) solutions to the lack of correlation between lineations that indicate the direction of movement within thrusts and shear zones, and relative plate motion; and (3) a possible technique for determining the direction of relative plate motion that caused orogenesis in ancient orogens. 相似文献
50.
I. Malakpour 《Astrophysics and Space Science》1992,193(1):47-50
The4He abundance of the Nova Delphini 1967 is determined, using their nebular stage spectra, which is of the order 0.18 by number and 0.39 by mass. Our results and similar measurements on other novae show that the4He abundance in novae is about twice the amount predicted by the Big-Bang theory. The binary structure is the main cause of4He overabundance in novae. 相似文献