全文获取类型
收费全文 | 35961篇 |
免费 | 278篇 |
国内免费 | 984篇 |
专业分类
测绘学 | 1644篇 |
大气科学 | 2706篇 |
地球物理 | 6679篇 |
地质学 | 16060篇 |
海洋学 | 2179篇 |
天文学 | 4079篇 |
综合类 | 2207篇 |
自然地理 | 1669篇 |
出版年
2022年 | 144篇 |
2021年 | 207篇 |
2020年 | 191篇 |
2019年 | 227篇 |
2018年 | 5249篇 |
2017年 | 4431篇 |
2016年 | 3032篇 |
2015年 | 419篇 |
2014年 | 497篇 |
2013年 | 629篇 |
2012年 | 1438篇 |
2011年 | 3261篇 |
2010年 | 2551篇 |
2009年 | 2928篇 |
2008年 | 2445篇 |
2007年 | 2905篇 |
2006年 | 544篇 |
2005年 | 519篇 |
2004年 | 711篇 |
2003年 | 688篇 |
2002年 | 523篇 |
2001年 | 291篇 |
2000年 | 305篇 |
1999年 | 182篇 |
1998年 | 205篇 |
1997年 | 171篇 |
1996年 | 115篇 |
1995年 | 131篇 |
1994年 | 115篇 |
1993年 | 97篇 |
1992年 | 71篇 |
1991年 | 98篇 |
1990年 | 97篇 |
1989年 | 68篇 |
1988年 | 79篇 |
1987年 | 99篇 |
1986年 | 80篇 |
1985年 | 107篇 |
1984年 | 95篇 |
1983年 | 104篇 |
1982年 | 86篇 |
1981年 | 102篇 |
1980年 | 116篇 |
1979年 | 88篇 |
1978年 | 87篇 |
1977年 | 77篇 |
1976年 | 65篇 |
1975年 | 63篇 |
1974年 | 71篇 |
1973年 | 64篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
Ahmad Rami El-Nabulsi 《Astrophysics and Space Science》2011,332(1):37-42
We investigate the late-time dynamics of a four-dimensional universe based on the effective action of a Brans-Dicke scalar
field in the presence of the matter source term, conformal coupling of the scalar curvature to the scalar field, a dynamical
cosmological constant and Gauss-Bonnet higher-order terms in the scalar curvature. Many new interesting features are revealed
and discussed in some details. 相似文献
93.
The evolutionary status of a sample of 31 W UMa-type systems (20 of W, 9 of A, and 2 of A/W sub-class) is examined and discussed on the basis of their positions in the H-R, mass-radius and mass-luminosity diagrams. The absolute elements of these systems have been evaluated by use of their spectroscopic and photometric data as they were found in the literature. Since different analysis methods have been used by the various investigators this gives the opportunity to make different H-R, mass-radius and mass-luminosity diagrams, according to the method used, and compare the results.Moreover, from the spectral type-period diagram of those systems that have spectral types from O to G2 it was found that all of them lie in the evolved region. Finally, the log (L
l/L
s) log (M
l/M
s) diagrams are presented and discussed. 相似文献
94.
95.
A. Savaş Arapoğlu Ezgi Yalçınkaya A. Emrah Yükselci 《Astrophysics and Space Science》2018,363(10):215
A five-dimensional cosmological model including a single perfect fluid is studied in the framework of dynamical system analysis. All the critical points of the system are listed with their stability properties and some representative phase diagrams are explicitly shown. It is found that the stabilization of extra dimension is possible and the observed flatness of the three-dimensional space is provided for certain ranges of the equation of state parameter of the fluid. The model suggested here can be considered as a simplified model for examining the possible effects of the extra dimensions in the early universe. 相似文献
96.
HUXue-lian CHENGCheng-qi WUDe-wen MAAi-nai 《中国地理科学(英文版)》2003,13(1):84-90
Based on the analysis of the development of GIS technology and application,this paper brought forward the concept of GoGIS,namely Cooperative GIS ,CoGIS is GIS facing group-users and supporting human-human interaction,which makes it differ from the former GISs,Then,the characteristics of general Computer Spport Cooperative Work (CSCW)applications and the complexity of Geographic Information Science were analyzed,and the conclusion the CoGIS was not a simple GIS layer on CSCW was reached,Further,this paper gaver the hierarchical architecture of CoGIS,and analyzed the coperative platform in detail from the following:1)basic elements;2) collaboration patterns;3) cooperation control mechanism;4) synchronization mechanism;5) security and 6) group communication and so on.With those,the problems about GIS applications are discussed,such as 1)distributed multi-source GIS information and knowledge sharing platform;2)the fusion and visualization of GIS information;3)virtual reality cooperative modeling;4) dymamic simulation;5)expert system and 6) decision-making.Finally,this paper analyzed CoGIS application mode in brief. 相似文献
97.
YANGYong-liang SHITong-guang JLANGLU-guang LIYue 《中国地理科学(英文版)》2003,13(2):130-133
In recent years, many coal-producing countries have paid great attention to the land subsidence causedby coal cutting. In China, because of the dense population in coalfield areas, the land subsidence hazard is more seri-ous. After a brief analysis on the mechanism of land subsidence, this paper gives a comprehensive and systematical ac-count on all kinds of hazards caused by the land subsidence in China. The study shows that land subsidence has endan-gered land, buildings, traffic and communication lines, dykes and dams. It also causes damage to ecological and socialenvironment. In order to lessen the hazard of land subsidence, preventive measures should be taken to reduce the col-lapse amount, such as extraction with stowing, banded mining system, succession and coordination mining system, orhigh-pressure mudflow between rock strata. Measures of reinforcing or moving certain buildings should also be taken toreduce the destructive degree. In order to harness the subsidence land and bring them under control for fanning, mea-sures should be taken such as filling with spoil or fine breeze, excavating the deeper and covering the shallower land. 相似文献
98.
AGGLOMERATION AND RADIATION EFFECT OF THE PULL OF URBANIZATION 总被引:1,自引:1,他引:1
QIJin-li 《中国地理科学(英文版)》2003,13(3):224-227
In order to explore the train of thought for China‘s urbanizing development and coordinated rural eco-nomic development, and to find good ways of solving rural problems through urbanization, this paper absorbs the push-and-pull forces theory and the systematic dynamic theory in the traditional population migration theories, views urbanization as a dynamic system, makes research on the push-and-pull mechanism of urbanization. The pulling power of urbanization is analyzed according to two aspects, the agglomeration effect and the radiation effect of cities. The agglomeration effect provides continuous propelling force for urbanization, and the radiation effect further accelerates the urbanization process by pushing forward the development of rural economy. Of course, the slow de-velopment of urbanization can result in the hindrance to rural economic development. 相似文献
99.
The spectacular prominence eruption and CME of 31 August 2007 are analyzed stereoscopically using data from NASA??s twin Solar Terrestrial Relations Observatory (STEREO) spacecraft. The technique of tie pointing and triangulation (T&T) is used to reconstruct the prominence (or filament when seen on the disk) before and during the eruption. For the first time, a filament barb is reconstructed in three-dimensions, confirming that the barb connects the filament spine to the solar surface. The chirality of the filament system is determined from the barb and magnetogram and confirmed by the skew of the loops of the post-eruptive arcade relative to the polarity reversal boundary below. The T&T analysis shows that the filament rotates as it erupts in the direction expected for a filament system of the given chirality. While the prominence begins to rotate in the slow-rise phase, most of the rotation occurs during the fast-rise phase, after formation of the CME begins. The stereoscopic analysis also allows us to analyze the spatial relationships among various features of the eruption including the pre-eruptive filament, the flare ribbons, the erupting prominence, and the cavity of the coronal mass ejection (CME). We find that erupting prominence strands and the CME have different (non-radial) trajectories; we relate the trajectories to the structure of the coronal magnetic fields. The possible cause of the eruption is also discussed. 相似文献
100.
We study the steady-state structure of an accretion disc with a corona surrounding a central, rotating, magnetized star. We
assume that the magneto-rotational instability is the dominant mechanism of angular momentum transport inside the disc and
is responsible for producing magnetic tubes above the disc. In our model, a fraction of the dissipated energy inside the disc
is transported to the corona via these magnetic tubes. This energy exchange from the disc to the corona which depends on the
disc physical properties is modified because of the magnetic interaction between the stellar magnetic field and the accretion
disc. According to our fully analytical solutions for such a system, the existence of a corona not only increases the surface
density but reduces the temperature of the accretion disc. Also, the presence of a corona enhances the ratio of gas pressure
to the total pressure. Our solutions show that when the strength of the magnetic field of the central neutron star is large
or the star is rotating fast enough, profiles of the physical variables of the disc significantly modify due to the existence
of a corona. 相似文献