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   3916篇
  免费   35篇
  国内免费   41篇
测绘学   42篇
大气科学   320篇
地球物理   655篇
地质学   1978篇
海洋学   334篇
天文学   474篇
综合类   64篇
自然地理   125篇
  2023年   4篇
  2022年   49篇
  2021年   66篇
  2020年   84篇
  2019年   99篇
  2018年   222篇
  2017年   217篇
  2016年   252篇
  2015年   110篇
  2014年   244篇
  2013年   318篇
  2012年   319篇
  2011年   313篇
  2010年   334篇
  2009年   269篇
  2008年   253篇
  2007年   280篇
  2006年   218篇
  2005年   102篇
  2004年   39篇
  2003年   28篇
  2002年   30篇
  2001年   28篇
  2000年   27篇
  1999年   9篇
  1998年   9篇
  1997年   18篇
  1996年   8篇
  1995年   3篇
  1994年   2篇
  1993年   1篇
  1992年   3篇
  1991年   4篇
  1990年   1篇
  1989年   1篇
  1988年   2篇
  1987年   3篇
  1986年   3篇
  1985年   3篇
  1984年   5篇
  1982年   2篇
  1980年   2篇
  1979年   1篇
  1976年   1篇
  1975年   1篇
  1972年   1篇
  1968年   1篇
  1958年   2篇
  1955年   1篇
排序方式: 共有3992条查询结果,搜索用时 359 毫秒
811.
The composition of volatile components in picroilmenites from Yakutian kimberlitic pipes of various ages (the Olivinovaya, Malokuonapskaya, and Udachnaya–East pipes) was studied for the first time by means of gas chromatography–mass spectrometry (GC-MS). It was shown that picroilmenites and olivines from same kimberlitic pipes contained volatile components of close composition, whereas these components were quite different in these minerals from different pipes. These features point to a common source and represent the specificity of the magma chamber formed under the pronounced influence of hydrocarbons with their derivates, as well as nitrogen-, chlorine-, and sulfur-containing compounds. The fraction of hydrocarbons and derivates in the composition of volatile matter is as high as 99%, including 9.7% of chlorine- and fluorinecontaining compounds.  相似文献   
812.
The properties of the relative abundances of rapid and slow neutron-capture elements are studied using a catalog containing spectroscopic abundance determinations for 14 elements produced in various nuclear-synthesis processes for 90 open clusters. The catalog also contains the positions, ages, velocities, and elements of the Galactic orbits of the clusters. The relative abundances of both r-elements (Eu) and s-elements (Y, Ba, La, and Ce) in clusters with high, elongated orbits and in field stars of the Galactic thin disk display different dependences on metallicity, age, Galactocentric distance, and the elements of the Galactic orbits, supporting the view that these objects have different natures. In young clusters, not only barium, but also the three other studied s-elements display significantly higher relative abundances than field stars of the same metallicity. The relative abundances of Eu are lower in highmetallicity clusters ([Fe/H] > -0.1) with high, elongated orbits than in field giants, on average, while the [Eu/Fe] ratios in lower-metallicity clusters are the same as those in field stars, on average, although with a large scatter. The metallicity dependence of the [O, Mg/Eu] ratios in clusters with high, elongated orbits and in field stars are substantially different. These and other described properties of the Eu abundances, together with the properties of the abundances of primary a-elements, can be understood in a natural way if clusters with high, elongated orbits with different metallicities formed as a result of interactions of two types of high-velocity clouds with the interstellar medium of the Galactic disk: low-metallicity highvelocity clouds that formed from “primordial” gas, and high-metallicity clouds with intermediate velocities that formed in “Galactic fountains.”  相似文献   
813.
Five regions of massive-star formation have been observed in various molecular lines in the frequency range~85?89 GHz. The studied regions comprise dense cores, which host young stellar objects. The physical parameters of the cores are estimated, including the kinetic temperatures (~20?40 K), the sizes of the emitting regions (~0.1?0.6 pc), and the virial masses (~40?500 M). The column densities and abundances of various molecules are calculated assuming Local Thermodynamical Equilibrium(LTE). The core in 99.982+4.17, which is associated with the weakest IRAS source, is characterized by reduced molecular abundances. The molecular line widths decrease with increasing distance from the core centers (b). For b ? 0.1 pc, the dependences ΔV (b) are close to power laws (∝b?p), where p varies from ~0.2 to ~0.5, depending on the object. In four cores, the asymmetries of the optically thick HCN(1–0) and HCO+(1–0) lines indicates systematicmotions along the line of sight: collapse in two cores and expansion in two others. Approximate estimates of the accretion rates in the collapsing cores indicate that the forming stars have masses exceeding the solar mass.  相似文献   
814.
The variability of upwelling events in the coastal zone of Primorye in the northwestern part of the Sea of Japan is studied using the SeaWinds/QuikSCAT scatterometer wind data for the period of 1999-2009. The intensity of upwelling is defined by the wind-induced offshore Ekman transport (the upwelling index). It was found that along the southern coast of Primorye upwelling events occur from September to March (April). The winter monsoon period is the most favorable for the upwelling development. In the eastern part of the coastal zone of Primorye upwelling is observed in transitional seasons between winter and summer monsoon (February-April and September-October). On the northeastern coast of Primorye, the upwelling season is from August to October (November). The common feature of the coastal zone of Primorye is a wind-driven upwelling in autumn (September-October). The interannual variability of winter upwelling along the southern coast of Primorye is related to the East Asia high pressure center (the Siberian High). The upwelling intensifies in the years with positive air pressure anomalies in the Siberian High and weakens in the years with negative anomalies.  相似文献   
815.
A statistical model is proposed which describes the texture of the images of 25 types of clouds from the MODIS satellite data with the spatial resolution of 250 m. A technique is presented which compiles the sets of image segments with typical textures for different cloud types. To describe the texture, the following statistical methods are applied: Gray-Level Co-occurrences Matrix, Gray-Level Difference Vector, and Sum and Difference Histogram. The correlation analysis is used to form the sets of informative textural features for the images of different cloud types. Two-parameter distribution laws and the estimates of their parameters are presented which describe fluctuations in the efficient set of textural features of different cloud types.  相似文献   
816.
Ash clouds resulting from explosive volcanic eruptions pose a real threat to human life (for aircraft flights, airport operations, etc.); therefore, the detection, monitoring, and forecast of their movement is an urgent and important issue. The features and examples of application of the new tool developed on the basis of "Monitoring of Active Volcanoes of Kamchatka and the Kurile Islands" information system (VolSatView) are described. It allows the integrated monitoring and forecasting of ash cloud transport using the data of remote sensing and mathematical modeling as well as the assessment of the parameters of explosive events.  相似文献   
817.
Based on the NCEP/NCAR and ERA-Interim reanalysis archives, we investigated different methods to detect atmospheric blocking events in Western Siberia. Two criteria were studied that are based on calculating meridional gradients of the 500 hPa height and potential temperature at the dynamic tropopause. A situation is considered blocking, when it features a gradient inversion of the investigated characteristics. Additionally, we performed a synoptic analysis of individual blocking events.  相似文献   
818.
The results of numerical experiments with the data assimilation system including the WRF-ARW mesoscale atmospheric model and WRFDA analysis package in the 3D-Var mode are considered. The focus is on the impact of Doppler weather radar data on the quality of short-range weather forecasting. The maps of weather events and cloud top constructed from the modeling by GIMET-2010 software package are analyzed using the web-GIS METEORAD. The experiments in the Moscow region demonstrated that if only radial wind is assimilated, the intensity of simulated cloud and precipitation formation is the closest to the observed one; however, the spatial mismatches of simulated and observed cloud systems are possible. If Doppler radar data on radial wind and reflectivity are assimilated, the general pattern and location of clouds and precipitation are simulated more accurately, but there is a certain overestimation of convection intensity which leads to the overestimation of the number of thunderstorms and rainfall rate.  相似文献   
819.
Physical regularities of free oscillations of the Azov Sea level induced after the cessation of long-lasting action of wind are analyzed. Spatial characteristics of seiche oscillations, the position of nodal lines, and the velocity of induced currents are simulated with the three-dimensional nonlinear barotropic hydrodynamic model. It was found that in the coastal zone the maximum amplitude of these oscillations is comparable with the value of storm surges. It is demonstrated that seiches make essential contribution to the variability of velocity of currents.  相似文献   
820.
The distributions of kinetic energy (KE) and available potential energy (APE) in the lower and middle atmosphere of the Northern and Southern hemispheres over the period 1992–2003 are investigated. Annual mean values of the amplitude and phase of annual and semiannual oscillations in the zonal and eddy forms of KE and APE are calculated in the height range 0–55 km (1000–0.316 hPa) for the 21st layer. A clearly pronounced annual cycle of the zonal and eddy components of KE and APE with maxima in the winter season are observed in the troposphere of both hemispheres. In the lower stratosphere, the annual-cycle maximum is shifted toward the summer season because of the meridional gradient of the zonal mean temperature. In the stratosphere of both hemispheres, along with annual oscillations, semiannual oscillations are present in all forms of energy. The intensity of these oscillations for the zonal KE and APE at the upper-stratosphere heights is comparable to the intensity of annual oscillations. A local structure of the energy regime of the upper mesosphere-lower thermosphere is investigated against the background of the global energy regime from the data of meteor sounding in Kazan. It is shown that, for both the global and regional regimes, specific features of the phase profiles of energy characteristics can be explained by the presence of barriers during the propagation of wave disturbances along the vertical.  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