首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   79969篇
  免费   898篇
  国内免费   1335篇
测绘学   2545篇
大气科学   5021篇
地球物理   15134篇
地质学   32218篇
海洋学   6327篇
天文学   15349篇
综合类   2315篇
自然地理   3293篇
  2022年   604篇
  2021年   909篇
  2020年   1040篇
  2019年   1079篇
  2018年   6745篇
  2017年   5859篇
  2016年   4759篇
  2015年   1203篇
  2014年   2097篇
  2013年   3156篇
  2012年   3179篇
  2011年   5334篇
  2010年   4442篇
  2009年   5169篇
  2008年   4421篇
  2007年   5042篇
  2006年   2591篇
  2005年   1657篇
  2004年   1754篇
  2003年   1671篇
  2002年   1504篇
  2001年   1256篇
  2000年   1120篇
  1999年   816篇
  1998年   868篇
  1997年   836篇
  1996年   668篇
  1995年   654篇
  1994年   656篇
  1993年   528篇
  1992年   525篇
  1991年   530篇
  1990年   602篇
  1989年   455篇
  1988年   443篇
  1987年   497篇
  1986年   374篇
  1985年   570篇
  1984年   547篇
  1983年   506篇
  1982年   519篇
  1981年   444篇
  1980年   480篇
  1979年   375篇
  1978年   425篇
  1977年   341篇
  1976年   329篇
  1975年   336篇
  1974年   314篇
  1973年   341篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
In this work, the history of the development of the Turali area (the Dagestan coast of the Caspian Sea) in the Late Holocene is under consideration. The analysis of the geological structure of the bay bar that separates the Bolshoy Turali lagoon from the sea, the granulometric analysis of the coastal deposits, and the data of geo-radar profiles make it possible to assert that the large eolian relief forms were formed during the New Caspian (Novokaspiyskoe) transgression of the Caspian Sea.  相似文献   
32.
Detailed photometrical monitoring of the cataclysmic variable SDSS J080434.20+510349.2 began at the Crimean Astrophysical Observatory (Ukraine) and the Apache Point Observatory (United States) before the 2006 outburst, continued during the outburst, as well as the following two years. We established the unique nature of the primary and secondary components of the binary. We performed a comprehensive study of the white dwarf’s pulsations over the course of five months, two years after the 2006 outburst. It is shown that the most stable pulsations are equal to or double a period of 12.6 min. On the basis of all the available observations, more precise values for the orbital and the superhump periods were found to be 0.0590048(3) days and 0.059729(4) days, respectively. Our estimation of the mass of the secondary component lies in the range of solar mass from 0.037 to 0.087. This confirms the previous suggestion that the secondary component is most probably a brown dwarf.  相似文献   
33.
We present thermal mass loss calculations over evolutionary time scales for the investigation if the smallest transiting rocky exoplanets CoRoT-7b (∼1.68REarth) and Kepler-10b (∼1.416REarth) could be remnants of an initially more massive hydrogen-rich gas giant or a hot Neptune-class exoplanet. We apply a thermal mass loss formula which yields results that are comparable to hydrodynamic loss models. Our approach considers the effect of the Roche lobe, realistic heating efficiencies and a radius scaling law derived from observations of hot Jupiters. We study the influence of the mean planetary density on the thermal mass loss by placing hypothetical exoplanets with the characteristics of Jupiter, Saturn, Neptune, and Uranus to the orbital location of CoRoT-7b at 0.017 AU and Kepler-10b at 0.01684 AU and assuming that these planets orbit a K- or G-type host star. Our findings indicate that hydrogen-rich gas giants within the mass domain of Saturn or Jupiter cannot thermally lose such an amount of mass that CoRoT-7b and Kepler-10b would result in a rocky residue. Moreover, our calculations show that the present time mass of both rocky exoplanets can be neither a result of evaporation of a hydrogen envelope of a “Hot Neptune” nor a “Hot Uranus”-class object. Depending on the initial density and mass, these planets most likely were always rocky planets which could lose a thin hydrogen envelope, but not cores of thermally evaporated initially much more massive and larger objects.  相似文献   
34.
Zakharov's equation is applied to study numerically the evolution of wave amplitudes. It is demonstrated that, owing to Krasitskii's new kernel functions, the system of surface waves remains Hamiltonian, in contrast to the former approaches used by Yuen, Lake, and Zakharov. If surface waves are wind-generated, they grow and become stochastic. If the effect of the waves on the wind is considered, then the wave amplitude evolution, similar to the no-wind case, continues to be recurrent. Translated by Vladimir A. Puchkin.  相似文献   
35.
Water vapor plays a key role in weather and climate forming, which leads to the need for continuous monitoring of its content in different parts of the Earth. Intercomparison and validation of different methods for integrated water vapor (IWV) measurements are essential for determining the real accuracies of these methods. CIMEL photometers measure IWV at hundreds of ground-based stations of the AERONET network. We analyze simultaneous IWV measurements performed by a CIMEL photometer, an RPG-HATPRO MW radiometer, and a FTIR Bruker 125-HR spectrometer at the Peterhof station of St. Petersburg State University. We show that the CIMEL photometer calibrated by the manufacturer significantly underestimates the IWV obtained by other devices. We may conclude from this intercomparison that it is necessary to perform an additional calibration of the CIMEL photometer, as well as a possible correction of the interpretation technique for CIMEL measurements at the Peterhof site.  相似文献   
36.
37.
We have identified 20 of the 75 unidentified Equatorial Infrared Catalogue Number-1 sources with stars in the BD Catalogue. Two of these are also found in the HD Catalogue.  相似文献   
38.
39.
Since their discovery 20 year ago, transition region bright points have never been observed spectroscopically. Bright point properties have not been compared with similar transition region and coronal structures. In this work we have investigated three transient quiet Sun brightenings including a transition region bright point (TR BP), a coronal bright point (CBP) and a blinker. We use time-series observations of the extreme-ultraviolet emission lines of a wide range of temperature T (logT=5.3?–?6.4) from the EUV Imaging Spectrometer (EIS) onboard the Hinode satellite. We present the EIS temperature maps and Doppler maps, which are compared with magnetograms from the Michelson Doppler Imager (MDI) onboard the SOHO satellite. Doppler velocities of the TR BP and blinker are ≤?25 km?s?1, which is typical of transient TR phenomena. The Doppler velocities of the CBP were found to be ≤?20 km?s?1 with exception of those measured at logT=6.2 where a distinct bi-directional jet is observed. From an EM loci analysis we find evidence of single and double isothermal components in the TR BP and CBP, respectively. TR BP and CBP loci curves are characterized by broad distributions suggesting the existence of unresolved structure. By comparing and contrasting the physical characteristics of the events we find that the BP phenomena are an indication of multi-scaled self-similarity, given the similarities in both their underlying magnetic field configuration and evolution in relation to EUV flux changes. In contrast, the blinker phenomena and the TR BP are sufficiently dissimilar in their observed properties as to constitute different event classes. Our work is an indication that the measurement of similar characteristics across multiple event types holds class-predictive power, and is a significant step towards automated solar atmospheric multi-class classification of unresolved transient EUV sources. Finally, the analysis performed here establishes a connection between solar quiet region CBPs and jets.  相似文献   
40.
Two-station pairing approaches are routinely used to infill missing information in incomplete rainfall databases. We evaluated the performance of three simple methodologies to reconstruct incomplete time series in presence of variable nonlinear correlation between data pairs. Nonlinearity stems from the statistics describing the marginal peak-over-threshold (POT) values of rainfall events. A Monte Carlo analysis was developed to quantitatively assess expected errors from the use of chronological pairing (CP) with linear and nonlinear regression and frequency pairing (FP). CP is based on a priori selection of regression functions, while FP is based on matching the probability of non-exceedance of an event from one time series with the probability of non-exceedance of a similar event from another time series. We adopted a generalized Pareto (GP) model to describe POT events, and a t-copula algorithm to generate reference nonlinearly correlated pairs of random temporal distributions distributed according with the GP model. The results suggest that the optimal methodology strongly depends on GP statistics. In general, CP seems to provide the lowest errors when GP statistics were similar and correlation became linear; we found that a power-2 function performs well for the selected statistics when the number of missing points is limited. FP outperforms the other methods when POT statistics are different and variables are markedly nonlinearly correlated. Ensemble-based results seem to be supported by the analysis of observed precipitation at two real-world gauge stations.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号