全文获取类型
收费全文 | 101767篇 |
免费 | 1361篇 |
国内免费 | 859篇 |
专业分类
测绘学 | 2720篇 |
大气科学 | 7059篇 |
地球物理 | 19261篇 |
地质学 | 38074篇 |
海洋学 | 8610篇 |
天文学 | 23055篇 |
综合类 | 378篇 |
自然地理 | 4830篇 |
出版年
2022年 | 513篇 |
2021年 | 887篇 |
2020年 | 968篇 |
2019年 | 1005篇 |
2018年 | 4252篇 |
2017年 | 3928篇 |
2016年 | 3692篇 |
2015年 | 1531篇 |
2014年 | 2567篇 |
2013年 | 4504篇 |
2012年 | 3464篇 |
2011年 | 5439篇 |
2010年 | 4803篇 |
2009年 | 5891篇 |
2008年 | 4933篇 |
2007年 | 5437篇 |
2006年 | 3409篇 |
2005年 | 2866篇 |
2004年 | 2834篇 |
2003年 | 2710篇 |
2002年 | 2529篇 |
2001年 | 2082篇 |
2000年 | 1963篇 |
1999年 | 1628篇 |
1998年 | 1696篇 |
1997年 | 1571篇 |
1996年 | 1369篇 |
1995年 | 1330篇 |
1994年 | 1175篇 |
1993年 | 1043篇 |
1992年 | 999篇 |
1991年 | 1019篇 |
1990年 | 1102篇 |
1989年 | 908篇 |
1988年 | 883篇 |
1987年 | 1020篇 |
1986年 | 891篇 |
1985年 | 1129篇 |
1984年 | 1253篇 |
1983年 | 1145篇 |
1982年 | 1064篇 |
1981年 | 1036篇 |
1980年 | 927篇 |
1979年 | 877篇 |
1978年 | 860篇 |
1977年 | 737篇 |
1976年 | 706篇 |
1975年 | 709篇 |
1974年 | 663篇 |
1973年 | 714篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
Two spectrophotometric scans of comet Levy (1990c) have been analysed to estimate Haser model column densities and production rates of CN andC
2 molecules. 相似文献
102.
103.
104.
Several physical and observational effects may contribute to the significant imbalances of magnetic flux that are often observed in active regions. We consider an effect not previously treated: the influence of electric currents in the photosphere. Electric currents can cause a line-of-sight flux imbalance because of the directionality of the magnetic field they produce. Currents associated with magnetic flux tubes produce larger imbalances than do smoothly-varying distributions of flux and current. We estimate the magnitude of this effect for current densities, total currents, and magnetic geometry consistent with observations. The expected imbalances lie approximately in the range 0–15%, depending on the character of the current-carrying fields and the angle from which they are viewed. Observationally, current-induced flux imbalances could be indicated by a statistical dependence of the imbalance on angular distance from disk center. A general study of magnetic flux balance in active regions is needed to determine the relative importance of other - probably larger -effects such as dilute flux (too weak to measure or rendered invisible by radiative transfer effects), merging with weak background fields, and long-range connections between active regions.Operated for the National Science Foundation by the Association of Universities for Research in Astronomy. 相似文献
105.
S. K. El-Labany 《Astrophysics and Space Science》1992,191(2):185-194
The propagation of an ion-acoustic soliton in a collisionless plasma with adiabatic positive and negative ions (with equal ion temperature) and hot non-isothermal electrons is studied by use of the renormalization method introduced by Kodama and Taniuti in the reductive perturbation method. The basic set of fluid equations describing the system is reduced to a Korteweg-de Vries (K-dV)-type equation for the first-order perturbed potential and to a linear inhomogeneous differential equation to the second-order of the perturbed potential. A stationary solution of the coupled equations is obtained. 相似文献
106.
107.
The problem of the interaction between magnetic fields and differential rotation in the radiative zone of the Sun is investigated. It is demonstrated that effects of magnetic buoyancy can be neglected in the analysis of this interaction. It is shown that hydromagnetic torsional waves propagating from the solar core cannot be responsible for the 22-year solar cycle. A possible geometry of the magnetic field that conforms with stationary differential rotation is considered. A verifying method for hypotheses on the structure of the magnetic field and torsional oscillations in the radiative zone of the Sun is proposed based on helioseismic data. 相似文献
108.
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
109.
Several temperature-depth profiles measured in Kasai and in Shaba provinces of Zaire using mining exploration boreholes exhibit a significant negative temperature gradient near the surface. This anomalous curvature which extends to 100–200 m depth could reflect the effect of variations in surface conditions. Applying the theory of heat conduction in a semi-infinite homogeneous medium, these profiles indicate a surface warming by 3–4°C. This warming is related to the effect of the environmental changes associated with the mining exploitation and the urbanization during the last 40–90 years. 相似文献
110.
Gösta Gahm 《Astrophysics and Space Science》2006,304(1-4):149-152
The number of confirmed and suspected close T Tauri binaries (period days) is increasing. We discuss some systems with enhanced emission line activity and periodic line profile changes. Non-axisymmetric flows of plasma in the region between the circumbinary disk and the stars can be generated through the influence of the secondary component. Such enhanced activity is found around binaries with eccentric as well as circular orbits. We discuss our observations of the T Tauri stars RW Aurigae A and RU Lupi, which may host very close brown dwarf companions. Model simulations indicate that non-axisymmetric flows are generated around close binaries with circumbinary disks, also in systems with circular orbits. 相似文献