全文获取类型
收费全文 | 8532篇 |
免费 | 1981篇 |
国内免费 | 2205篇 |
专业分类
测绘学 | 327篇 |
大气科学 | 212篇 |
地球物理 | 888篇 |
地质学 | 9237篇 |
海洋学 | 427篇 |
天文学 | 331篇 |
综合类 | 776篇 |
自然地理 | 520篇 |
出版年
2024年 | 56篇 |
2023年 | 137篇 |
2022年 | 353篇 |
2021年 | 416篇 |
2020年 | 389篇 |
2019年 | 428篇 |
2018年 | 308篇 |
2017年 | 343篇 |
2016年 | 447篇 |
2015年 | 470篇 |
2014年 | 682篇 |
2013年 | 584篇 |
2012年 | 601篇 |
2011年 | 591篇 |
2010年 | 571篇 |
2009年 | 641篇 |
2008年 | 536篇 |
2007年 | 638篇 |
2006年 | 639篇 |
2005年 | 556篇 |
2004年 | 470篇 |
2003年 | 398篇 |
2002年 | 365篇 |
2001年 | 328篇 |
2000年 | 289篇 |
1999年 | 288篇 |
1998年 | 254篇 |
1997年 | 189篇 |
1996年 | 144篇 |
1995年 | 128篇 |
1994年 | 116篇 |
1993年 | 82篇 |
1992年 | 70篇 |
1991年 | 62篇 |
1990年 | 35篇 |
1989年 | 40篇 |
1988年 | 12篇 |
1987年 | 12篇 |
1986年 | 16篇 |
1985年 | 14篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1963年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
791.
Bagla 《Monthly notices of the Royal Astronomical Society》1998,297(1):251-254
Recent observations show a large concentration of galaxies at high redshift. At first sight, strong clustering of galaxies at high redshifts seems to be in contradiction with the models of structure formation. In this paper we show that such structures are a manifestation of the strong clustering of rare peaks in the density field. We compute the frequency of occurrence of such large concentrations of galaxies in some models of structure formation. 相似文献
792.
The pattern and style of mantle convection govern the thermal evolution, internal dynamics, and large-scale surface deformation of the terrestrial planets. In order to characterize the nature of heat transport and convective behaviour at Rayleigh numbers, Ra, appropriate for planetary mantles (between 104 and 108), we perform a set of laboratory experiments. Convection is driven by a temperature gradient imposed between two rigid surfaces, and there is no internal heating. As the Rayleigh number is increased, two transitions in convective behaviour occur. First we observe a change from steady to time-dependent convection at Ra≈105. A second transition occurs at higher Rayleigh numbers, Ra≈5×106, with large-scale time-dependent flow being replaced by isolated rising and sinking plumes. Corresponding to the latter transition, the exponent β in the power law relating the Nusselt number Nu to the Rayleigh number (NuRaβ) is reduced. Both rising and sinking plumes always consist of plume heads followed by tails. There is no characteristic frequency for the formation of plumes. 相似文献
793.
Though entropy production is forbidden in standard FRW Cosmology, Berman and Som presented a simple inflationary model where
entropy production by bulk viscosity, during standard inflation without ad hoc pressure terms can be accommodated with Robertson–Walker’s
metric, so the requirement that the early Universe be anisotropic is not essential in order to have entropy growth during
inflationary phase, as we show. Entropy also grows due to shear viscosity, for the anisotropic case. The intrinsically inflationary
metric that we propose can be thought of as defining a polarized vacuum, and leads directly to the desired effects without
the need of introducing extra pressure terms. 相似文献
794.
Ralph Fyfe 《第四纪科学杂志》2007,22(6):571-578
New and existing pollen data from Wales, UK, are used to assess the level of landscape openness at the regional and local scale. At the regional scale, the existing pollen data support the high‐forest model of vegetation structure by 6000 cal. yr. BC prior to any palynological signal for anthropogenic impact in the region. New data from two sites in southwest Wales follow the general regional pattern of early to middle Holocene vegetation succession, but are striking owing to maintenance of high non‐arboreal pollen percentages (NAPs) throughout the mid‐Holocene. It is argued that these NAPs indicate that a significant degree of openness can be found at the local level (and beyond the confines of the peat‐forming site) within regions characterised by closed woodland. It is possible that woodland development in these areas may have been suppressed by reduced drainage, although the role of grazing animals in maintenance of clearings cannot be assessed. Implications for this local degree of openness are discussed, in particular the significance of vegetation heterogeneity at the local scale for the construction of place or locale for prehistoric communities. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
795.
S. I. Grachev 《Astrophysics》2007,50(4):515-524
A new method is proposed to account for multiple scattering by electrons in calculations of the correlation functions describing
the angular fluctuations in the cosmic microwave background radiation (CMBR). The apparatus of the theory of radiative transport
with Rayleigh scattering is used. The problem is reduced to solving an integral equation for the vector source function (dependent
only on time), along with differential equations for the other quantities (scalar potentials, baryon velocities, etc.) which
show up in the problem. The quantities which describe the angular fluctuations in the CMBR (in the temperature and in the
polarization) are then calculated by integrating the vector source function along the line of sight. As an illustration, the
correlation functions and power spectra are calculated for the case where the fluctuations are produced by some initial gaussian
perturbations of the CMBR.
__________
Translated from Astrofizika, Vol. 50, No. 4, pp. 621–631 (November 2007). 相似文献
796.
797.
高密度电法在老山隧道勘察中的应用 总被引:2,自引:0,他引:2
应用高密度电阻率法勘察宁淮高速公路南京老山隧道工程,查明了隧道YK5 280~ZK5 540段的地层分布和构造特征,并推断出鹰嘴山断层的位置和产状,结合勘察资料证明该断层为高角度逆断层。预测出隧道和断层破碎带相交处为浅部裂隙岩溶含水带中的优良导水带,该处涌水的可能性很大,其推断结果在施工中得到证实。说明高密度电法是进行隧道勘察和构造裂隙岩溶富水带探测的一种可靠手段。 相似文献
798.
799.
800.
“干支回推法”是针对中国历史时期所特有的干支材料而设计的新天文年代学方法.以一组假设的材料为例,系统地给出了该方法的完整求解过程.指出该方法的优势在于准确高效,能有效地处理某些年代学难题.此外,除材料的公历日期外还能将当时的历法细节一同迭代解出. 相似文献