全文获取类型
收费全文 | 19934篇 |
免费 | 3413篇 |
国内免费 | 5562篇 |
专业分类
测绘学 | 2780篇 |
大气科学 | 3051篇 |
地球物理 | 3986篇 |
地质学 | 9698篇 |
海洋学 | 3285篇 |
天文学 | 2349篇 |
综合类 | 1595篇 |
自然地理 | 2165篇 |
出版年
2024年 | 87篇 |
2023年 | 217篇 |
2022年 | 762篇 |
2021年 | 815篇 |
2020年 | 1020篇 |
2019年 | 1159篇 |
2018年 | 790篇 |
2017年 | 890篇 |
2016年 | 873篇 |
2015年 | 1099篇 |
2014年 | 1129篇 |
2013年 | 1259篇 |
2012年 | 1261篇 |
2011年 | 1240篇 |
2010年 | 1064篇 |
2009年 | 1246篇 |
2008年 | 1326篇 |
2007年 | 1563篇 |
2006年 | 1582篇 |
2005年 | 1381篇 |
2004年 | 1176篇 |
2003年 | 992篇 |
2002年 | 885篇 |
2001年 | 724篇 |
2000年 | 822篇 |
1999年 | 760篇 |
1998年 | 660篇 |
1997年 | 417篇 |
1996年 | 342篇 |
1995年 | 256篇 |
1994年 | 230篇 |
1993年 | 227篇 |
1992年 | 177篇 |
1991年 | 115篇 |
1990年 | 69篇 |
1989年 | 89篇 |
1988年 | 52篇 |
1987年 | 42篇 |
1986年 | 37篇 |
1985年 | 22篇 |
1984年 | 15篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1973年 | 2篇 |
1954年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
EFFECT OF SULPHATE-REDUCING BACTERIA ON ELECTRO-CHEMICAL CORROSION BEHAVIOR OF 16Mn STEEL IN SEA MUD
INTRODUCTIONItwasgenerallyconsideredpreviouslythatthecorrosionofsteelinseamudwasnotserious.However,itwaslaterfoundthatthecorrosionrateofsteelinsomeseamudwashigherthanthatinseawater(King,1980;Sehmide,1982;Guoetal.,1997;Hou,1998).Therearesomereportsthatthecorrosionr… 相似文献
83.
Fabio Fontanot Pierluigi Monaco Stefano Borgani 《Monthly notices of the Royal Astronomical Society》2003,341(2):692-706
We apply the ztrace algorithm to the optical NOG and infrared PSC z galaxy catalogues to reconstruct the pattern of primordial fluctuations that have generated our local Universe. We check that the density fields traced by the two catalogues are well correlated, and consistent with a linear relation [either in δ or in log (1 +δ) ] with relative bias (of NOG with respect to PSC z ) b rel = 1.1 ± 0.1 . The relative bias relation is used to fill the optical zone of avoidance at | b | < 20° using the PSC z galaxy density field.
We perform extensive testing on simulated galaxy catalogues to optimize the reconstruction. The quality of the reconstruction is predicted to be good at large scales, up to a limiting wavenumber klim ≃ 0.4 h Mpc−1 beyond which all information is lost. We find that the improvement arising from the denser sampling of the optical catalogue is compensated by the uncertainties connected to the larger zone of avoidance.
The initial conditions reconstructed from the NOG catalogue are found (analogously to those from the PSC z ) to be consistent with a Gaussian paradigm. We use the reconstructions to produce sets of initial conditions ready to be used for constrained simulations of our local Universe. 相似文献
We perform extensive testing on simulated galaxy catalogues to optimize the reconstruction. The quality of the reconstruction is predicted to be good at large scales, up to a limiting wavenumber k
The initial conditions reconstructed from the NOG catalogue are found (analogously to those from the PSC z ) to be consistent with a Gaussian paradigm. We use the reconstructions to produce sets of initial conditions ready to be used for constrained simulations of our local Universe. 相似文献
84.
85.
86.
87.
88.
S.W. Allen 《Astrophysics and Space Science》2003,285(1):247-256
Chandra X-ray observations of rich, dynamically relaxed galaxy clusters allow the properties of the X-ray gas and the total
gravitating mass to be determined precisely. Here, we discuss how Chandra observations may be used as a powerful tool for
cosmological studies. By combining Chandra X-ray results on the X-ray gas mass fractions in clusters with independent measurements
of the Hubble constant and the mean baryonic matter density of the universe, we obtain a tight constraint on the mean total
matter density of the universe, Οm, and an interesting constraint on the cosmological constant, ΟΛ. Using these results, together with the observed local X-ray luminosity function of the most X-ray luminous galaxy clusters,
a mass-luminosity relation determined from Chandra and ROSAT X-ray data and weak gravitational lensing observations, and the
mass function predicted by numerical simulations, we obtain a precise constraint on the normalization of the power spectrum
of density fluctuations in the nearby universe,σ8. We compare our results with those obtained from other, independent methods.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
89.
90.
In view of rapid developments in iterative solvers, it is timely to re‐examine the merits of using mixed formulation for incompressible problems. This paper presents extensive numerical studies to compare the accuracy of undrained solutions resulting from the standard displacement formulation with a penalty term and the two‐field mixed formulation. The standard displacement and two‐field mixed formulations are solved using both direct and iterative approaches to assess if it is cost‐effective to achieve more accurate solutions. Numerical studies of a simple footing problem show that the mixed formulation is able to solve the incompressible problem ‘exactly’, does not create pressure and stress instabilities, and obviate the need for an ad hoc penalty number. In addition, for large‐scale problems where it is not possible to perform direct solutions entirely within available random access memory, it turns out that the larger system of equations from mixed formulation also can be solved much more efficiently than the smaller system of equations arising from standard formulation by using the symmetric quasi‐minimal residual (SQMR) method with the generalized Jacobi (GJ) preconditioner. Iterative solution by SQMR with GJ preconditioning also is more elegant, faster, and more accurate than the popular Uzawa method. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献