全文获取类型
收费全文 | 47651篇 |
免费 | 8631篇 |
国内免费 | 10968篇 |
专业分类
测绘学 | 4125篇 |
大气科学 | 5106篇 |
地球物理 | 7427篇 |
地质学 | 32370篇 |
海洋学 | 5278篇 |
天文学 | 3452篇 |
综合类 | 3329篇 |
自然地理 | 6163篇 |
出版年
2024年 | 236篇 |
2023年 | 634篇 |
2022年 | 1622篇 |
2021年 | 1911篇 |
2020年 | 1762篇 |
2019年 | 2250篇 |
2018年 | 1610篇 |
2017年 | 1938篇 |
2016年 | 2142篇 |
2015年 | 2271篇 |
2014年 | 2965篇 |
2013年 | 2750篇 |
2012年 | 2996篇 |
2011年 | 3177篇 |
2010年 | 2786篇 |
2009年 | 3328篇 |
2008年 | 3228篇 |
2007年 | 3378篇 |
2006年 | 3306篇 |
2005年 | 3021篇 |
2004年 | 2654篇 |
2003年 | 2479篇 |
2002年 | 2161篇 |
2001年 | 1923篇 |
2000年 | 1892篇 |
1999年 | 1661篇 |
1998年 | 1444篇 |
1997年 | 1095篇 |
1996年 | 879篇 |
1995年 | 733篇 |
1994年 | 668篇 |
1993年 | 577篇 |
1992年 | 425篇 |
1991年 | 354篇 |
1990年 | 248篇 |
1989年 | 194篇 |
1988年 | 160篇 |
1987年 | 88篇 |
1986年 | 65篇 |
1985年 | 54篇 |
1984年 | 37篇 |
1983年 | 24篇 |
1982年 | 25篇 |
1981年 | 14篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1978年 | 21篇 |
1977年 | 7篇 |
1976年 | 4篇 |
1954年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
本文扼要介绍了山东省金矿地质勘查、开发现状及存在的环境问题 ,为确保山东省黄金资源可持续开发利用 ,提出要保证黄金资源的可持续供给 ,要在资源开发过程中保护好环境 ,以及要高度重视地勘单位和矿山企业自身的可持续发展等建议。 相似文献
72.
Boli basin, between Yishu fracture belt and Dunmi fracture belt, is the biggest Mesozoic coal basin in the east of Heilongjiang Province. Now it is a fault - fold remnant basin. The basin' s shape is generally consistent with the whole distribution of the cover folds, an arc protruding southwards. The basement of the basin can be divided into three fault blocks or structural units. The formation and evoluation of the basin in Mesozoic was determined by the basement fault blocks' displacement features rusulted from by the movement of the edge faults and the main basement faults. 相似文献
73.
成都及附近地区旅游气候资源研究 总被引:9,自引:0,他引:9
通过对成都及附近等7个地区多年气候资源及人体舒适指数进行分级比较,得出了7个地区的人体舒适指数的时间分布特征及对当地旅游的影响。 相似文献
74.
The dust shell around the evolved star HD 179821 has been detected in scattered light in near-IR imaging polarimetry observations. Here, we subtract the contribution of the unpolarized stellar light to obtain an intrinsic linear polarization of between 30 and 40 per cent in the shell that seems to increase with radial offset from the star. The J - and K -band data are modelled using a scattering code to determine the shell parameters and dust properties. We find that the observations are well described by a spherically-symmetric distribution of dust with an r −2 density law, indicating that when mass-loss was occurring, the mass-loss rate was constant. The models predict that the detached nature of a spherically-symmetric, optically-thin dust shell, with a distinct inner boundary, will only be apparent in polarized flux. This is in accordance with the observations of this and other optically-thin circumstellar shells, such as IRAS 17436+5003. By fitting the shell brightness we derive an optical depth to the star that is consistent with V -band observations and that, assuming a distance of 6 kpc, gives an inner-shell radius of , a dust number density of at r in and a dust mass of . We have explored axisymmetric shell models but conclude that any deviations from spherical symmetry in the shell must be slight, with an equator-to-pole density contrast of less than 2:1. We have not been able to fit simultaneously the high linear polarizations and the small colour excess of the shell and we attribute this to the unusual scattering properties of the dust. We suggest that the dust grains around HD 179821 either are highly elongated or consist of aggregates of smaller particles. 相似文献
75.
矿床谱系是对成矿多样性的理论概括,而成矿多样性又是由不同级别、不同性质的致矿地质异常决定的.本文论述了山东省内生金矿矿床谱系及其致矿地质异常. 相似文献
76.
M. A. P. Torres J. Casares I. G. Martínez-Pais P. A. Charles 《Monthly notices of the Royal Astronomical Society》2002,334(1):233-240
We present a library of 47 open-cluster integrated spectra, mostly obtained at CASLEO (San Juan, Argentina) in the range 3600 < λ < 7400 Å , which are made available at CDS. The data are combined with previous spectra to obtain 10 high signal-to-noise ratio basic templates in the young and intermediate-age domains, which are also provided in the library. These Galactic disc templates represent the increased time resolution spectral evolution of a stellar population unit around the Solar metallicity level. The improved signal-to-noise ratio of the present templates with respect to previous template lists, together with their increased time resolution, allowed us to improve the fundamental parameters of some open clusters. The present spectral library will be useful for several astrophysical applications, particularly for population syntheses of star-forming giant galaxies. 相似文献
77.
In recent years,scholars at home and abroad have method,and that vanous disasters would be analyzed assynthetically studied natural dlsaste‘theoretically and an Integral.SHI Peilun(1991)putforwad a scientificmethodologlcally,as well as its cases analys。s(CND,term—regional disaster system,which Indicates that1987; MA et al,1990; MARBLE,1990; NE et al,the situation of a disaster(calamity loss)results from1999; PATAK et al,1982; SHI,1991;VAN et al,h… 相似文献
78.
79.
C.J. Mooney W.R.J. Rolleston F.P. Keenan P.L. Dufton D.L. Pollacco H.R. Magee 《Monthly notices of the Royal Astronomical Society》2001,326(3):1101-1109
We present a model-atmosphere analysis for the bright ( V ∼13) star ZNG-1, in the globular cluster M10. From high-resolution ( R ∼40 000) optical spectra we confirm ZNG-1 to be a post-asymptotic giant branch (post-AGB) star. The derived atmospheric parameters are T eff =26 500±1000 K and log g =3.6±0.2 dex . A differential abundance analysis reveals a chemical composition typical of hot post-AGB objects, with ZNG-1 being generally metal poor, although helium is approximately solar. The most interesting feature is the large carbon underabundance of more than 1.3 dex. This carbon deficiency, along with an observed nitrogen enhancement relative to other elements, may suggest that ZNG-1 evolved off the AGB before the third dredge-up occurred. Also, iron depletions observed in other similar stars suggest that gas–dust fractionation in the AGB progenitor could be responsible for the observed composition of these objects. However, we need not invoke either scenario since the chemical composition of ZNG-1 is in good agreement with abundances found for a Population II star of the same metallicity. 相似文献
80.
R. A.Street KeithHorne T. A.Lister A.Penny Y.Tsapras A.Quirrenbach N.Safizadeh J.Cooke D.Mitchell A.Collier Cameron 《Monthly notices of the Royal Astronomical Society》2002,330(3):737-754
We report on the discovery of 25 variable stars plus 13 suspected variables found in the field of the open cluster NGC 6819. The stars were identified from time-series photometric data obtained on the Isaac Newton Telescope, La Palma, during two observing runs covering the 19 nights between 1999 June 22–30 and 1999 July 22–31 . The variables found include 12 eclipsing binaries with an additional three suspected, nine BY Draconis systems, plus four variables of other types, including one star believed to be a Cepheid. Three of the 15 eclipsing binaries are believed to be cluster members. Details of a further 10 suspected variable stars are also included. 相似文献