全文获取类型
收费全文 | 92739篇 |
免费 | 1257篇 |
国内免费 | 882篇 |
专业分类
测绘学 | 2645篇 |
大气科学 | 6746篇 |
地球物理 | 17325篇 |
地质学 | 35125篇 |
海洋学 | 7755篇 |
天文学 | 20715篇 |
综合类 | 396篇 |
自然地理 | 4171篇 |
出版年
2022年 | 477篇 |
2021年 | 821篇 |
2020年 | 851篇 |
2019年 | 949篇 |
2018年 | 4195篇 |
2017年 | 3866篇 |
2016年 | 3613篇 |
2015年 | 1492篇 |
2014年 | 2460篇 |
2013年 | 4091篇 |
2012年 | 3282篇 |
2011年 | 5222篇 |
2010年 | 4579篇 |
2009年 | 5470篇 |
2008年 | 4595篇 |
2007年 | 5149篇 |
2006年 | 3052篇 |
2005年 | 2623篇 |
2004年 | 2506篇 |
2003年 | 2475篇 |
2002年 | 2283篇 |
2001年 | 1861篇 |
2000年 | 1766篇 |
1999年 | 1468篇 |
1998年 | 1485篇 |
1997年 | 1395篇 |
1996年 | 1238篇 |
1995年 | 1202篇 |
1994年 | 1073篇 |
1993年 | 924篇 |
1992年 | 878篇 |
1991年 | 890篇 |
1990年 | 939篇 |
1989年 | 790篇 |
1988年 | 774篇 |
1987年 | 892篇 |
1986年 | 764篇 |
1985年 | 956篇 |
1984年 | 1045篇 |
1983年 | 962篇 |
1982年 | 917篇 |
1981年 | 802篇 |
1980年 | 778篇 |
1979年 | 712篇 |
1978年 | 706篇 |
1977年 | 623篇 |
1976年 | 564篇 |
1975年 | 553篇 |
1974年 | 550篇 |
1973年 | 601篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
291.
We investigate the evolution of rotation period and spindown age of a pulsar whose surface magnetic field undergoes a phase
of growth. Application of these results to the Crab pulsar strongly indicates that its parameters cannot be accounted for
by the field growth theories. 相似文献
292.
N. S. Chauhan 《Astrophysics and Space Science》1985,112(1):185-192
The treatment followed by Coxet al. (1973) for the estimation of the effects of thermal imbalance on the pulsational stability of stars is applied to Roche and point source (Chandrika Prashad) model. The calculations suggest that the eigenvalues obtained for the above model are correct to 0(t
ff/ts). The expressions for stability coefficients and corresponding eigenfunctions for the stars in thermal imbalance for the above models have also been derived. 相似文献
293.
P.S. Rainbow 《Estuarine, Coastal and Shelf Science》1985,21(5):669-686
The crab Carcinus maenas (L.) and the barnacle Elminius modestus Darwin were exposed to a range of dissolved concentrations of Zn, Cu and Cd for 21 days in artificial seawater. Accumulation of Zn and Cu by crabs has been interpreted in terms of the presence of a regulation mechanism to maintain constant body concentrations (83·2 ± 19·4 μg Zn g?1 dry wt.; 39·8 ± 9·8 μg Cu g?1 dry wt.) under varying external dissolved metal levels, until a threshold dissolved metal concentration (c. 400 μg Zn l?1; c. 170 μg Cu l?1) beyond which net accumulation of metal begins. Cadium appears to be accumulated by C. maenas at all exposures with no evidence for regulation of body cadmium concentrations. Exposure of E. modestus to Zn, Cu or Cd caused net accumulation of the respective metal in the bodies of the barnacles, with no evidence for regulation of body metal concentrations. 相似文献
294.
The Ivrea-Verbano Zone in northern Italy represents a section through the lower continental crust which has been tilted and emplaced into its present position during the Alpine orogeny. Recent and on-going structurally-oriented geological mapping in this region is providing new information about the geometry of the complex. The central part of the zone is dominated by a large basic complex (the 'mafic formation') which is intrusive into the surrounding gneisses. The foliation within the envelope of gneisses is deflected around the intrusive complex as if by ballooning, but in the region south-west of Monte Capio both units are folded together into a tight to isoclinal steeply plunging fold with an amplitude of c. 10 km. This fold locally inverts the stratigraphy of the layered basic group of the complex, and is thought to be the result of gravitational collapse following intrusion and inflation of a large magma body into the lower crust.
Several high-temperature shear zones have now been traced within the country rock for distances up to 20 km. The geometry of these, and their relationship to the basic complex suggests that at least some of the extensional collapse of the mafic body is related to uplift caused by intrusion of this body.
Close parallels can be drawn between the observed structure in the Ivrea-Verbano Zone (after removing the effects of late, low-temperature faulting and folding related to emplacement of the rocks into their present position), and those inferred from deep seismic reflection profiling in areas of current extension such as parts of the US Basin and Range province. 相似文献
Several high-temperature shear zones have now been traced within the country rock for distances up to 20 km. The geometry of these, and their relationship to the basic complex suggests that at least some of the extensional collapse of the mafic body is related to uplift caused by intrusion of this body.
Close parallels can be drawn between the observed structure in the Ivrea-Verbano Zone (after removing the effects of late, low-temperature faulting and folding related to emplacement of the rocks into their present position), and those inferred from deep seismic reflection profiling in areas of current extension such as parts of the US Basin and Range province. 相似文献
295.
S. Casertano M. G. Lattanzi M. A. C. Perryman A. Spagna 《Astrophysics and Space Science》1996,241(1):89-104
The proposed baseline GAIA mission will be able to detect the astrometric signature of Jupiter-size planets around of the order of a million stars, using either global or narrow-angle astrometry. If the mission can realize the higher astrometric accuracy that photon statistics allows for bright stars, lower-mass planets (from Earth size to ten times larger) can be found around ten to a few hundred stars. 相似文献
296.
The main analytical properties of the generalized Shkarofsky function and a numerical code for its computation are discussed. The results of a numerical analysis are compared with the results of an asymptotic analysis for parameter values relevant to the problem of whistler-mode propagation in the Earth's magnetosphere. This comparison allows us to specify the range of applicability of different approximations to the generalized Shkarofsky function, which have been used for the analysis of relativistic effects on whistler-mode propagation and instability. 相似文献
297.
Wrinkle ridge systems within and around Martian highland craters were studied in order to find their basin-induced and regional aspects. Most prominent ridge directions indicate regional tectonic patterns. Radial ridges near large craters are often slightly deflected along regional or global ridge systems. Crater floor ridges have simpler local distributions. Smaller or older craters are less resistant against the effects of global or regional stress systems. In craters concentric ridge rings locate at 0.8 crater radius with additional minor rings at 0.66, 0.44 and 0.94 crater radius. This pattern illustrates compression of lava fill over buried topography. 相似文献
298.
Axial surveys were performed in the two river tributaries of the Cochin estuary, SW India during November 1988. Surficial sediments were subjected to sequential chemical extractions to delineate five metal fractions, namely, exchangeable, carbonate bound, easily reducible, organic/sulfide bound, and residual. The results indicated selective accumulation of Mn and Ni in carbonate bound and organic/sulfide forms, along with marginal amounts of Co in the exchangeable fraction. Large portions of Fe and Cr occurred in the residual fraction, whereas composite fractionation of Zn species was noticed. The exchangeable fractions of Fe and Cr as well as of easily reducible cobalt were below detection limits. The levels of Cr and Zn indicate anthropogenic inputs in this estuary, whereas Co and Ni show regional contamination exceeding natural levels. The analytical speciation procedure helps to deduce the sedimental diagenetic processes in the estuarine environment. 相似文献
299.
300.
The effect of finite conductivity on the Rayleigh-Taylor instability of an incompressible, viscous rotating fluid through a porous medium has been studied in the presence of a two-dimensional horizontal magnetic field. It has been shown that the solution is characterized by a variational principle. By making use of the existence of the variational principle, proper solutions have been obtained for a semi-infinite fluid in which density has a one-dimensional (exponential) vertical stratification. The dispersion relation has been derived and solved numerically. It is found that finite resistivity and porosity have a destabilizing effect on the Rayleigh-Taylor instability while rotation has a stabilizing effect. 相似文献