全文获取类型
收费全文 | 4826篇 |
免费 | 826篇 |
国内免费 | 656篇 |
专业分类
测绘学 | 756篇 |
大气科学 | 589篇 |
地球物理 | 1650篇 |
地质学 | 1154篇 |
海洋学 | 583篇 |
天文学 | 414篇 |
综合类 | 428篇 |
自然地理 | 734篇 |
出版年
2024年 | 13篇 |
2023年 | 57篇 |
2022年 | 119篇 |
2021年 | 151篇 |
2020年 | 158篇 |
2019年 | 212篇 |
2018年 | 153篇 |
2017年 | 191篇 |
2016年 | 195篇 |
2015年 | 201篇 |
2014年 | 238篇 |
2013年 | 265篇 |
2012年 | 281篇 |
2011年 | 287篇 |
2010年 | 231篇 |
2009年 | 310篇 |
2008年 | 265篇 |
2007年 | 338篇 |
2006年 | 331篇 |
2005年 | 264篇 |
2004年 | 240篇 |
2003年 | 228篇 |
2002年 | 180篇 |
2001年 | 183篇 |
2000年 | 148篇 |
1999年 | 146篇 |
1998年 | 176篇 |
1997年 | 97篇 |
1996年 | 95篇 |
1995年 | 102篇 |
1994年 | 101篇 |
1993年 | 85篇 |
1992年 | 57篇 |
1991年 | 42篇 |
1990年 | 29篇 |
1989年 | 51篇 |
1988年 | 23篇 |
1987年 | 22篇 |
1986年 | 12篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有6308条查询结果,搜索用时 0 毫秒
371.
从横向均匀介质满足的基本方程出发,得到视电阻率核函数的一阶非线性微分方程,通过方程求解,并利用滤波系数法容易得到电阻率随深度任意变化的视电阻率问题。当各层介质电性结构随深度呈指数变化时,还可得到各层之间核函数的递推关系,这对实际介质的正反演问题都有重要意义和应用价值。 相似文献
372.
本文用样条函数法实现了二维位场的向上延拓和向下延拓,向上延拓用样条函数法计算泊松积分,向下延拓用样条函数法求解第一类Fredholm积分方程。模型和实例计算表明,本文方法正确可行且精度高。 相似文献
373.
Neil Trentham 《Monthly notices of the Royal Astronomical Society》1998,293(1):71-88
We present the luminosity function and measurements of the scalelengths, colours and radial distribution of dwarf galaxies in the Coma cluster down to R =24. Our survey area is 674 arcmin2 ; this is the deepest and most detailed survey covering such a large area.
Our measurements agree with those of most previous authors at bright and intermediate magnitudes. The new results are as follows.
(1) Galaxies in the Coma cluster have a luminosity function φ( L )∝ Lα that is steep (α∼−1.7) for −15< MR <−11, and is shallower brighter than this. The curvature in the luminosity function at MR ∼−15 is statistically significant.
(2) The galaxies that contribute most strongly to the luminosity function at −14< MR <−12 have colours and scalelengths that are consistent with those of local dwarf spheroidal galaxies placed at the distance of Coma.
(3) These galaxies with −14< MR <−12 have a colour distribution that is very strongly peaked at B − R =1.3. This is suggestive of a substantial degree of homogeneity in their star formation histories and metallicities.
(4) These galaxies with −14< MR <−12 also appear to be more confined to the cluster core ( r ∼200 kpc) than the brighter galaxies. Alternatively, this observation may be explained in part or whole by the presence of an anomalously high number of background galaxies behind the cluster core. Velocity measurements of these galaxies would distinguish between these two possibilities. 相似文献
Our measurements agree with those of most previous authors at bright and intermediate magnitudes. The new results are as follows.
(1) Galaxies in the Coma cluster have a luminosity function φ( L )∝ L
(2) The galaxies that contribute most strongly to the luminosity function at −14< M
(3) These galaxies with −14< M
(4) These galaxies with −14< M
374.
Neil Trentham 《Monthly notices of the Royal Astronomical Society》1998,294(2):193-200
We present the results from a CCD survey of the B -band luminosity function of nine clusters of galaxies, and compare them to published photographic luminosity functions of nearby poor clusters like Virgo and Fornax, and also to the field luminosity function. We derive a composite luminosity function by taking the weighted mean of all the individual cluster luminosity functions; this composite luminosity function is steep at bright and faint magnitudes and is shallow in-between.
All clusters have luminosity functions consistent with this single composite function. This is true both for rich clusters like Coma and for poor clusters like Virgo.
This same composite function is also individually consistent with the deep field luminosity functions found by Cowie et al. and Ellis et al., and also with the faint end of the Las Campanas Redshift Survey R -band luminosity function, shifted by 1.5 mag. A comparison with the Loveday et al. field luminosity function, which is well determined at the bright end, shows that the composite function, which fits the field data well fainter than MB =−19, drops too steeply between M B =−19 and −22 to fit the field data there. 相似文献
All clusters have luminosity functions consistent with this single composite function. This is true both for rich clusters like Coma and for poor clusters like Virgo.
This same composite function is also individually consistent with the deep field luminosity functions found by Cowie et al. and Ellis et al., and also with the faint end of the Las Campanas Redshift Survey R -band luminosity function, shifted by 1.5 mag. A comparison with the Loveday et al. field luminosity function, which is well determined at the bright end, shows that the composite function, which fits the field data well fainter than M
375.
Pippa Goldschmidt & Lance Miller 《Monthly notices of the Royal Astronomical Society》1998,293(1):107-112
The recently finished Edinburgh UVX quasar survey at B <18 is used together with other complete samples to estimate the shape and evolution of the optical luminosity function in the redshift range 0.3< z <2.2. There is a significantly higher space density of quasars at high luminosity and low redshift than previously found in the PG sample of Schmidt & Green, with the result that the shape of the luminosity function at low redshifts ( z <1) is seen to be consistent with a single power law. At higher redshifts the slope of the power law at high luminosities appears to steepen significantly. There does not appear to be any consistent break feature which could be used as a tracer of luminosity evolution in the population. 相似文献
376.
运用伏特拉核函数基本理论,建立了南桐矿区红岩煤矿矿井涌水量的线性、非线性核函数模型,介绍了计算核孙数模型所用的递归算法,同时对模拟结果的残差进行了分析,并用AR模型进行了改进。 相似文献
377.
Volker Springel & Simon D. M. White 《Monthly notices of the Royal Astronomical Society》1998,298(1):143-152
A new method is presented to obtain a non-parametric maximum likelihood estimate of the luminosity function and the selection function of a flux-limited redshift survey. The method parametrizes the selection function as a series of stepwise power laws and allows possible evolution of the luminosity function. We also propose a new technique to estimate the rate of evolution of the luminosity function. This is based on a minimization of the observed large-scale power with respect to the evolutionary model. We use an ensemble of mock surveys extracted from an N -body simulation to verify the power of this method. We apply our estimators to the 1.2-Jy survey of IRAS galaxies. We find a far-infrared luminosity function in good agreement with previously published results and evidence for rather strong evolution. If the comoving number density of IRAS galaxies is assumed to scale ∝ (1 + z ) P , we estimate P = 4.3 ± 1.4. 相似文献
378.
Neil Trentham & Bahram Mobasher 《Monthly notices of the Royal Astronomical Society》1998,299(2):488-498
We present the K -band (2.2 μm) luminosity functions (LFs) of the X-ray-luminous clusters MS1054–0321 ( z = 0.823), MS0451–0305 ( z = 0.55), Abell 963 ( z = 0.206), Abell 665 ( z = 0.182) and Abell 1795 ( z = 0.063) down to absolute magnitudes M K = −20. Our measurements probe fainter absolute magnitudes than do any previous studies of the near-infrared LFs of clusters. All the clusters are found to have similar LFs within the errors, when the galaxy populations are evolved to redshift z = 0. It is known that the most massive bound systems in the Universe at all redshifts are X-ray-luminous clusters. Therefore, assuming that the clusters in our sample correspond to a single population seen at different redshifts, the results here imply that not only had the stars in present-day ellipticals in rich clusters formed by z = 0.8, but that they existed in as luminous galaxies then as they do today. Additionally, the clusters have K -band LFs which appear to be consistent with the K -band field LF in the range −24 < M K < −22, although the uncertainties in both the field and cluster samples are large. 相似文献
379.
W. J. Maciel & H. J. Rocha-Pinto 《Monthly notices of the Royal Astronomical Society》1998,299(3):889-894
The initial mass function (IMF) in the solar neighbourhood is determined on the basis of a recently derived history of the star formation rate (SFR) which shows the presence of a star formation burst about 8 Gyr ago. The observed present-day mass function (PDMF) is considered, and the average past distribution of stars of a given mass is estimated. Two cases are considered, namely (i) constant SFR, and (ii) variable SFR as derived from the new metallicity distribution of G dwarfs. The resulting IMF is compared with previous determinations by Scalo and Kroupa et al., and the variation with stellar mass of the slope of the IMF is compared with reference determinations in the literature. 相似文献
380.
The regional dynamical model of the atmospheric ozonosphere 总被引:1,自引:0,他引:1
TheRegionalDynamicalModeloftheAtmosphericOzonosphereWangWeiguo(王卫国),XieYingqi(谢应齐)DepartmentofEarthscience.YunnanUniversity,K... 相似文献