全文获取类型
收费全文 | 51126篇 |
免费 | 499篇 |
国内免费 | 312篇 |
专业分类
测绘学 | 995篇 |
大气科学 | 2573篇 |
地球物理 | 9809篇 |
地质学 | 19552篇 |
海洋学 | 4855篇 |
天文学 | 12258篇 |
综合类 | 129篇 |
自然地理 | 1766篇 |
出版年
2022年 | 577篇 |
2021年 | 854篇 |
2020年 | 896篇 |
2019年 | 1007篇 |
2018年 | 2104篇 |
2017年 | 1915篇 |
2016年 | 2044篇 |
2015年 | 836篇 |
2014年 | 1828篇 |
2013年 | 2797篇 |
2012年 | 2079篇 |
2011年 | 2470篇 |
2010年 | 2323篇 |
2009年 | 2688篇 |
2008年 | 2360篇 |
2007年 | 2623篇 |
2006年 | 2304篇 |
2005年 | 1299篇 |
2004年 | 1217篇 |
2003年 | 1194篇 |
2002年 | 1157篇 |
2001年 | 1130篇 |
2000年 | 937篇 |
1999年 | 692篇 |
1998年 | 704篇 |
1997年 | 735篇 |
1996年 | 548篇 |
1995年 | 572篇 |
1994年 | 535篇 |
1993年 | 433篇 |
1992年 | 448篇 |
1991年 | 428篇 |
1990年 | 477篇 |
1989年 | 422篇 |
1988年 | 389篇 |
1987年 | 409篇 |
1986年 | 336篇 |
1985年 | 463篇 |
1984年 | 468篇 |
1983年 | 453篇 |
1982年 | 432篇 |
1981年 | 387篇 |
1980年 | 395篇 |
1979年 | 347篇 |
1978年 | 378篇 |
1977年 | 320篇 |
1976年 | 287篇 |
1975年 | 293篇 |
1974年 | 274篇 |
1973年 | 344篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
131.
JiřÍ Polcar Martin Topinka Graziella Pizzichini Eliana Palazzi Nicola Masetti RenÉ Hudec Věra HudcovÁ 《Astrophysics and Space Science》2005,296(1-4):485-488
We report on our statistical research of space–time correlated supernovae and CGRO-BATSE gamma-ray bursts (GRBs). There exists
a significantly higher abundance of core-collapse supernovae among the correlated supernovae, but the subset of all correlated
objects does not seem to be physically different from the whole set. 相似文献
132.
E. I. Timoshkova 《Celestial Mechanics and Dynamical Astronomy》1985,36(2):105-121
The first integrals of motion of the restricted planar circular problem of three bodies are constructed as the formal power series in r1/2, r being the distance of a moving particle from the primary. It is shown that the coefficients of these series are trigonometric polynomials of an angular variable. Some particular solutions have been found in a closed form. The proposed method for constructing the formal integrals can be generalized to a spatial problem of three bodies. 相似文献
133.
V. Maupin 《Geophysical Journal International》1985,83(2):379-398
Summary. Surface wave behaviour in flat anisotropic structures is first illustrated by performing an exact computation on a simple two-layer model. The variational procedure of Smith & Dahlen is then used to compute the partial derivatives of surface wave phase velocities with respect to the elastic parameters in more realistic earth models. Linear relationships between the partial derivatives for a general anisotropic structure and those for a transversely isotropic structure are derived. When considering waves propagating in a fixed direction, there are only four independent derivatives for Rayleigh waves, and two for Love waves. To avoid the lack of resolution in an inverse method, we propose to use physically constrained models. These results are illustrated by using a model with hexagonal symmetry and a symmetry axis oriented either vertically or horizontally. Quasi-Love- and quasi-Rayleigh-wave partial derivatives are computed for both axis orientations. Modes up to the second overtone and periods ranging between 45 and 130 s have been considered. Finally, anomalies of phase velocity are computed in an oceanic model made of 1/6 oriented olivine crystals with horizontal or vertical preferred orientations of the a -axis. 相似文献
134.
Nucleosynthetic yields and production rates of helium and heavy elements are derived using new initial mass functions which
take into account the recent revisions in O star counts and the stellar models of Maeder (1981a, b) which incorporate the
effects of massloss on evolution. The current production rates are significantly higher than the earlier results due to Chiosi
& Caimmi (1979) and Chiosi (1979), and a near-uniform birthrate operating over the history of the galactic disc explains the
currently observed abundances. However, the yields are incompatibly high, and to obtain agreement it is necessary to assume
that stars above a certain mass do not explode but proceed to total collapse. Further confirmation of this idea comes from
the consideration of the specific yields and production rates of oxygen, carbon and iron and the constraints imposed by the
observational enrichment history in the disc as discussed by Twarog & Wheeler (1982). Substantial amounts of4He and14C, amongst the primary synthesis species, are contributed by the intermediate mass stars in their wind phases. If substantial
numbers of them exploded as Type I SN, their contribution to the yields of12C and56Fe would be far in excess of the requirements of galactic nucleosynthesis. Either efficient massloss precludes such catastrophic
ends for these stars, or the current stellar models are sufficiently in error to leave room for substantial revisions in the
specific yields. The proposed upward revision of the12C (α,γ)16O rate may produce the necessary changes in stellar yields to provide a solution to this problem. Stars that produce most
of the metals in the Galaxy are the same ones that contribute most to the observed supernova rate. 相似文献
135.
136.
Data from the Pulkovo spectrophotometric data base on the absolute quasimonochromatic fluxes from oCet in the 320–1080 nm range are used to determine the physical parameters of this star in different phases of its light curve. The continuum emission layer is found to expand between the phases of the cycle corresponding to the rising and falling branches of the light curve. The average expansion velocity is 32 km/s. By the time the star’s brightness has fallen by roughly three magnitudes, its radius has increased by almost a factor of three. Over this same time the temperature of the layer has fallen from 3000 K to 2200 K. For this expansion velocity, the calculated mass rate loss is ⊙ M /year.__________Translated from Astrofizika, Vol. 48, No. 2, pp. 175–189 (May 2005). 相似文献
137.
138.
139.
Surface waters of Alsea Bay, an unpolluted estuary on the Oregon coast, were analysed for nitrous oxide, nitrate and nitrite on a weekly or biweekly basis during the summer of 1979. The estuary was found to be a variable source of N2O to the atmosphere. Large and rapid increases in the concentrations of N2O, NO3?, and NO2? occurred at the beginning of the sampling period and are attributed to the influx of nutrient-rich upwelling water into the estuary with the tide. The subsequent decline in concentrations of nitrate, nitrite and nitrous oxide over the remainder of the summer is attributed to a decrease in upwelling intensity, a decline in nitrification rates and to assimilatory nitrate reduction. Measurements of nitrous oxide at six stations along the Alsea River were also made in September and October before and after the onset of the rainy season. Samples taken after flood conditions were established were systematically 50% higher than pre-flood samples. The data suggest that soil runoff results in elevated concentrations of N2O in rivers. 相似文献
140.