全文获取类型
收费全文 | 1540篇 |
免费 | 267篇 |
国内免费 | 369篇 |
专业分类
测绘学 | 65篇 |
大气科学 | 17篇 |
地球物理 | 518篇 |
地质学 | 995篇 |
海洋学 | 240篇 |
天文学 | 79篇 |
综合类 | 86篇 |
自然地理 | 176篇 |
出版年
2024年 | 3篇 |
2023年 | 12篇 |
2022年 | 57篇 |
2021年 | 54篇 |
2020年 | 63篇 |
2019年 | 68篇 |
2018年 | 52篇 |
2017年 | 54篇 |
2016年 | 70篇 |
2015年 | 72篇 |
2014年 | 88篇 |
2013年 | 92篇 |
2012年 | 84篇 |
2011年 | 71篇 |
2010年 | 61篇 |
2009年 | 76篇 |
2008年 | 84篇 |
2007年 | 102篇 |
2006年 | 97篇 |
2005年 | 73篇 |
2004年 | 91篇 |
2003年 | 97篇 |
2002年 | 79篇 |
2001年 | 55篇 |
2000年 | 68篇 |
1999年 | 47篇 |
1998年 | 49篇 |
1997年 | 52篇 |
1996年 | 51篇 |
1995年 | 45篇 |
1994年 | 46篇 |
1993年 | 41篇 |
1992年 | 31篇 |
1991年 | 23篇 |
1990年 | 14篇 |
1989年 | 18篇 |
1988年 | 10篇 |
1987年 | 12篇 |
1986年 | 8篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有2176条查询结果,搜索用时 31 毫秒
941.
I. D. Karachentsev Yu. N. Kudrya V. E. Karachentseva S. N. Mitronova 《Astrophysics》2006,49(4):450-461
The 2MFGC catalog we have used contains 18020 galaxies selected from the extended objects in the 2MASS infrared sky survey
as having apparent ratios of the axes b/a<0.3. Most of them are spiral galaxies of later morphological types whose disks are
seen almost edge-on. The individual distances to the 2724 2MFGC galaxies with known rotation velocities and radial velocities
are determined using a multiparameter infrared Tully-Fisher relation. A list of the distances and peculiar velocities of these
galaxies is presented. The collective motion of the 2MFGC galaxies relative to the cosmic microwave background is characterized
by a velocity V = 199 ± 37 km/s in the direction l = 304° ±11°, b = −8°±8°. Our list is currently the most representative
and uniform sample for analyzing non-Hubble motions of galaxies on a scale of ∼100 Mpc.
__________
Translated from Astrofizika, Vol. 49, No. 4, pp. 527–540 (November 2006). 相似文献
942.
空间大地测量测定板块运动的新进展及其与地质学成果的比较 总被引:2,自引:0,他引:2
阐述利用空间大地测量测定和研究板块运动的基本方法、研究成果及最新进展 ,并和地质学方法进行了比较。结果表明 ,用地质学方法与用大地测量方法建立的板块运动模型参数在整体上具有很好的一致性 ,但对某些板块而言两者相差甚大 ,超出了模型误差的范围 ,其中 ,所有大地测量得到的太平洋板块速率都大于地质模型 ,极位置经度都偏小。不同作者利用空间大地测量建立的板块运动模型参数也存在着一定的差异 ,这种差异与所利用的数据类型、板块及其边界划分方案、测站的数量与分布状态及测站取舍的原则有关 ,尤其是与测站的分布及强变形 (非刚性板块运动 )测站的取舍有关。在研究区域性地壳运动时 ,采用不同的板块运动模型将会得到不同的背景场 ,从而会得到不同的区域运动图像 ,因此选择合适的背景场模型是至关重要的。 相似文献
943.
敦化盆地是由白垩—古近纪的新开岭盆地、大山嘴子—镜泊湖盆地和新近—第四纪敦化火山盆地的组合总称。它的形成严格受敦密断裂带地堑式两条平行断裂所控制。敦密断裂带在侏罗—白垩纪时期受伊佐奈歧板块的向西俯冲、挤压形成的火山造山带的地堑式断裂带,而新近—第四纪则主要受长白山火山地幔热柱和太平洋板块向西俯冲带而形成的不完整复式裂谷... 相似文献
944.
The wave transmission characteristics and wave induced pressures on twin plate breakwater are investigated experimentally in regular and random waves.A total of twenty pressure transducers are fixed on four surfaces of twin plate to measure the wave induced dynamic pressures.The spatial distribution of dynamic wave pressure is given along the surface of the twin plate.The uplift wave force obtained by integrating the hydrodynamic pressure along the structure is presented.Discussed are the influence of different incident wave parameters including the relative plate width B /L,relative wave height /i H a and relative submergence depth s /a on the non-dimensional dynamic wave pressures and total wave forces.From the investigation,it is found that the optimum transmission coefficient,t K occurs around B /L 0.41 ~ 0.43,and the twin plate breakwater is more effective in different water depths.The maximum of pressure ratio decreases from 1.8 to 1.1 when the relative submergence depth of top plate is increased from 0.8to +0.8. 相似文献
945.
E.V. Koutandos 《Ocean Engineering》2011,38(1):34-48
In the present study, wave interaction with a fixed, partially immersed breakwater of box type with a plate attached (impermeable-permeable) at the front part of the structure is investigated numerically and experimentally. The large scale laboratory experiments on the interaction of regular waves with the special breakwater were conducted in the wave flume of Laboratori d’Enginyeria Marνtima (LIM) at Universitat Politecnica de Catalunya (UPC) in Barcelona. Experimental results are compared with numerical results obtained with the use of the Cornell breaking Wave and Structures (COBRAS) wave model. The effects of an impermeable as well as a permeable plate attached to the bottom of the breakwater on its hydrodynamic characteristics (wave transmission, reflection, dissipation, velocity and turbulence kinetic energy) are investigated. Computed velocities and turbulence kinetic energy in the vicinity of the structure indicate the effects of the breakwater with the attached (impermeable/permeable) plate on the flow pattern and the turbulence structure. The attached impermeable plate at the front part of the breakwater enhances significantly the efficiency of the structure in attenuating the incident waves. The permeable plate reduces the efficiency of the structure since wave energy is transmitted through the porous body of the plate. Based on the hydrodynamic characteristics it is inferred that the breakwater with an impermeable plate attached to its bottom is more efficient. The comparison of horizontal and vertical forces acting on the breakwater for all cases examined reveals that plate porosity influences slightly vertical force and severely horizontal force acting on the structure, reducing maximum values in both cases. 相似文献
946.
JONATHAN LEIB 《Geographical review》2011,101(1):37-52
In the early 1900s, U.S. state and Canadian provincial governments began to register automobiles and issue license plates to their owners. Within several decades of the first issuance of license plates, state and provincial governments began to use these plates for advertising purposes, such as promoting local economies and tourism. In recent decades, however, governments have used license plates to promote national identities and nationalist ideals. Using examples from the United States and Canada, I examine how governments have used such banal signifiers of place as license plates to craft and promote these identities and how drivers have contested that usage. 相似文献
947.
Winston L. Sweatman 《Celestial Mechanics and Dynamical Astronomy》2006,94(1):37-65
We locate members of an important category of periodic orbits in the Newtonian four-body problem. These systems perform an interplay motion similar to that of the periodic three-body orbit discovered by Schubart. Such orbits, when stable, have been shown to be a key feature and influence on the dynamics of few-body systems. We consider the restricted case where the masses are collinear and are distributed symmetrically about their centre of mass. A family of orbits is generated from the known (three-dimensionally) unstable equal masses case by varying the mass ratio, whilst maintaining the symmetry. The stability of these orbits to perturbation is studied using linear stability analysis, analytical approximation of limiting cases and nonlinear simulation. We answer the natural question: are there any stable periodic orbits of this kind? Three ranges of the mass ratio are found to have stable orbits and three ranges have unstable orbits for three-dimensional motion. The systems closely resemble their three-body counterparts. Here the family of interplay orbits is simpler requiring just one parameter to characterise the mass ratio. Our results provide a further insight into three-body orbits studied previously. 相似文献
948.
Using modern astronomical databases, particularly 2MASS All - Sky Data Release Point Source Catalog and USNO-B1.0 catalog, we investigate the properties of about 840 FBS red stars in order to clarifiy their nature. We use and analyse their JHK 2MASS photometry, together with the R-band magnitudes and the proper motions provided by USNO - B1.0. Approximately 70% of all objects appear to be Asymptotic Giant Branch stars, 18% are giants, and close to 12% are objects with detectable proper motions, allowing to consider them as dwarf M-type stars. When plotted in a J - K versus R - K colour-colour diagram, one finds that objects with proper motions are well separated into a narrow belt.__________Published in Astrofizika, Vol. 48, No. 3, pp. 383–392 (August 2005). 相似文献
949.
O. A. Titov 《Astronomy Letters》2007,33(7):481-487
According to the most recent geodetic VLBI data, some of the radio sources that define the fundamental celestial reference frame are astrometrically unstable. In contrast to the stellar proper motions described by a linear function, the apparent proper motions of quasars are more complex. Therefore, they are difficult to approximate by a particular model. Being disregarded, the positional instability of the defining quasars can lead to a bias in the estimates of other parameters from observations, for example, the nutation angle corrections. 相似文献
950.