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81.
An attempt is made to study the planetary boundary layer (PBL) characteristics during the winter period at Anand (22.4°N, 72.6°E), a semi-arid region, which is located in the western part of India. A one-dimensional turbulent kinetic energy (TKE) closure model is used for the study. The structure of the PBL,which consists of profiles of zonal and meridional components of wind,potential temperature and specific humidity, is simulated. A one-dimensional soil heat and moisture transport parameterization scheme is incorporated for the accurate representation of the energy exchange processes at the soil-atmosphere interface. The diurnal variation of fluxes of sensible heat, latent heat, shortwave radiation, net radiation and soil flux, soil temperature at different depths, Richardson number and TKE at the height of the constant flux layer is studied. The model predictions are compared with the available observations obtained from a special Land Surface Processes (LSP) experiment. 相似文献
82.
本文分析了中国科学院大气物理研究所大气环流模式(IAP GCM)模式大气波谱结构(沿纬圈的谐波波谱和时域上的频率谱)及其在厄尔尼诺年的异常。结果表明,超长波是低纬波动的主要空间形式,准40天振荡在一定地理区域内显著存在,并与观测结果有一定联系,它们在厄尔尼诺年均发生明显异常。本工作对鉴定GCM性能及开发GCM的研究领域可能是一种有益的尝试。 相似文献
83.
N. U. Ain M. Latif K. Ullah S. Adnan R. Ahmed M. Umar M. Azam 《Theoretical and Applied Climatology》2020,140(1):69-89
As a result of climate change and unsustainable land use management in the recent past, droughts have become one of the most devastating climatic hazards whose impacts may prolong from months to years. This study presents analysis of droughts for two major cropping seasons, i.e., Kharif (May–September) and Rabi (October–April), over the Potwar Plateau of Pakistan. The analysis is performed using various datasets viz. observational, reanalysis, and Regional Climate Models (RCMs), for the past (1981–2010) and future (2011–2100) time periods. The following two methods for the identification of dry and wet years, also referred to as drought and wetness, are applied: (1) the percentile rank approach and (2) the drought indices, Standardized Precipitation Index (SPI) and Reconnaissance Drought Index (RDI). Future projections of droughts are investigated using RCM (RegCM4.4 and RCA4) outputs from CORDEX South Asia domain under two Representative Concentration Pathway (RCP) scenarios, RCP4.5 and RCP8.5. Generally, the indices show non-significant decreasing trends of drought severity in the recent past for all cases; however, significant increasing trends are observed for annual (0.006) and Kharif (0.007) cases under RCP4.5 scenario. The analysis of large-scale atmospheric dynamics suggests the significant role of low-level geopotential height anomalies over Tibetan Plateau (northwest of Pakistan) during Kharif (Rabi) season in controlling drought occurrence by transporting moisture from the Bay of Bengal (Arabian Sea). Moreover, composites of vertically integrated moisture transport, moisture flux convergence/divergence, and precipitable water anomalies show their marked contribution in maintaining the drought/wetness conditions over the Potwar region. 相似文献
84.
A comprehensive model inter-comparison study investigating the water budget during the BALTEX-PIDCAP period 总被引:2,自引:0,他引:2
D. Jacob B. J. J. M. Van den Hurk U. Andræ G. Elgered C. Fortelius L. P. Graham S. D. Jackson U. Karstens Chr. Köpken R. Lindau R. Podzun B. Rockel F. Rubel B. H. Sass R. N. B. Smith X. Yang 《Meteorology and Atmospheric Physics》2001,77(1-4):19-43
Summary A comparison of 8 regional atmospheric model systems was carried out for a three-month late summer/early autumn period in
1995 over the Baltic Sea and its catchment area. All models were configured on a common grid using similar surface and lateral
boundary conditions, and ran in either data assimilation mode (short term forecasts plus data assimilation), forecast mode
(short term forecasts initialised daily with analyses) or climate mode (no re-initialisation of model interior during entire
simulation period). Model results presented in this paper were generally post processed as daily averaged quantities, separate
for land and sea areas when relevant. Post processed output was compared against available analyses or observations of cloud
cover, precipitation, vertically integrated atmospheric specific humidity, runoff, surface radiation and near surface synoptic
observations.
The definition of a common grid and lateral forcing resulted in a high degree of agreement among the participating model results
for most cases. Models operated in climate mode generally displayed slightly larger deviations from the observations than
the data assimilation or forecast mode integration, but in all cases synoptic events were well captured. Correspondence to
near surface synoptic quantities was good. Significant disagreement between model results was shown in particular for cloud
cover and the radiative properties, average precipitation and runoff. Problems with choosing appropriate initial soil moisture
conditions from a common initial soil moisture field resulted in a wide range of evaporation and sensible heat flux values
during the first few weeks of the simulations, but better agreement was shown at later times.
Received September 8, 2000 Revised April 3, 2001 相似文献
85.
Simulation of the influence of solar radiation variations on the global climate with an ocean-atmosphere general circulation model 总被引:9,自引:4,他引:9
Two simulations with a global coupled ocean-atmosphere circulation model have been carried out to study the potential impact
of solar variability on climate. The Hoyt and Schatten estimate of solar variability from 1700 to 1992 has been used to force
the model. Results indicate that the near-surface temperature simulated by the model is dominated by the long periodic solar
fluctuations (Gleissberg cycle), with global mean temperatures varying by about 0.5 K. Further results indicate that solar
variability and an increase in greenhouse gases both induce to a first approximation a comparable pattern of surface temperature
change, i.e., an increase of the land-sea contrast. However, the solar-induced warming pattern in annual means and summer
is more centered over the subtropics, compared to a more uniform warming associated with the increase in greenhouse gases.
The observed temperature rise over the most recent 30 and 100 years is larger than the trend in the solar forcing simulation
during the same period, indicating a strong likelihood that, if the model forcing and response is realistic, other factors
have contributed to the observed warming. Since the pattern of the recent observed warming agrees better with the greenhouse
warming pattern than with the solar variability response, it is likely that one of these factors is the increase of the atmospheric
greenhouse gas concentration.
Received: 14 October 1996 / Accepted: 9 May 1997 相似文献
86.
J. Steppeler R. Hess U. Schättler L. Bonaventura 《Meteorology and Atmospheric Physics》2003,82(1-4):287-301
Summary ?Currently available computer power allows to run operational numerical weather prediction models at resolutions higher than
10 km. The aim of such high resolution modeling is the prediction of local weather, including orographically induced winds
and local precipitation patterns. In this range the hydrostatic approximation is no longer valid and nonhydrostatic models
have to be used instead. For several decades these models have been developed for research purposes only, but operational
application is now reality. In this paper, the numerical methods used in current nonhydrostatic forecast models will be reviewed
and some promising techniques in this field will be discussed. Special attention is given to aspects such as the choice of
the vertical coordinate, the efficiency of algebraic solvers for semi-implicit time discretizations, and accurate and non-oscillatory
advection schemes.
Received July 6, 2001; revision October 12, 2001 相似文献
87.
黑河流域大气资料尺度转换的对比分析 总被引:6,自引:2,他引:6
尺度转换是解决尺度差异问题的有效方法之一。尺度转换统计模式的可靠性和正确性如何,在很大程度上取决于建立统计模式时所用的实际气象资料的处理,尤其在下垫面分布极不均匀地区。本文研究了黑河流域这一复杂下垫面条件下的大气资料的尺度转换问题,对比分析了由NCEP再分析资料直接内插到较小尺度而得到的局地气候变化与由尺度转换统计模式,经过客观分析所得到的局地气候变化。结果表明,直接插值所得的细网格值只能用于对平坦地区的温、湿状况的描述,而对较高山区的区域特征描述不够;进行观测资料的客观分析可以更准确地反映黑河流域复杂下垫面背景下近地层大气要素场的变化。研究表明,客观分析过程是尺度转换过程的重要环节。 相似文献
88.
Summary The summer monsoon circulation shows various spatial and temporal oscillations and often a combination of systems produces
an integrated effect. In this study phases of the southwest (SW) monsoon have been identified in an objective manner with
the help of T-mode principal component analysis (PCA) of weekly rainfall anomalies. Mean composite charts have been prepared
utilising all available upper air data (1977–1986) for each category of the SW monsoon epochs identified by the PCA. These
sets of charts have been constructed for both the strong and weak phases associated with the first four significant principal
components (PCs).
A well defined east-west oriented trough system, extending from about 28° N Latitude/65° E Longitude to 20° N Latitude/90° E
Longitude, in the lower levels, has been the main feature associated with the strong phase of the monsoon corresponding to
PC I. The trough in the lower levels is more marked in the eastern half compared to the western half in both the sets of charts
associated with strong phases of the monsoon related to the PC II and PC III. With PC II, the position of the troughs in the
lower levels is further north of its location in PC III. The east-west trough system associated with the strong phase of PC
IV has a large southward tilt with height. The charts corresponding to the weak phases of these PCs have synoptic features,
such as the position of the trough close to the foothills of the Himalayas, and the shifting of middle and upper tropospheric
anticyclones to the south.
The study suggests an objective method of interpretation of principal components by utilising synoptic data. In addition,
synoptic models and data sets corresponding to different phases of the monsoon can also be prepared in an objective manner
by such PCA.
Received July 18, 1997 Revised April 30, 1999 相似文献
89.
由中国石油学会石油地质专业委员会、中国地质学会石油地质专业委员会、北京石油学会、国家自然科学基金委地学部、国土资源部油气资源战略研究中心和中国石油大学共同主办的“第四届油气成藏机理与油气资源评价国际学术研讨会”,于2006年10月14日-16日在中国北京顺利召开。共有260余位代表参加了这次大会,他们分别来自俄罗斯、加拿大、澳大利亚、英国、挪威、德国、韩国以及国内的18个科研院所和34个油田公司。这次大会提交的会议论文和摘要116篇,其中大会主题报告28篇,分会交流34篇。[第一段] 相似文献
90.
U. von Grafenstein H. Erlenkeuser A. Kleinmann J. Müller P. Trimborn 《Journal of Paleolimnology》1994,11(3):349-357
High-resolution oxygen-isotope records of benthic ostracods and molluscs from Ammersee, southern Germany, show high-frequency climatic changes during the last deglaciation and parallel in great detail published faunal and floral variations reconstructed from Norwegian Sea sediments and isotope variations in Greenland ice cores. The marine and the terrestrial records give evidence of a synchronous late glacial climatic development in Greenland, NW- and Mid-Europe. However,14C-ages of the supraregional climatic events and of two tephra layers in the marine sediments of the northeastern Atlantic Ocean are significantly older than the14C-ages of the corresponding horizons on land. These differences strongly suggest that major short-term events have affected the exchangeable carbon on earth during the dramatic environmental changes related to the deglaciation and in particular have affected the CO2-distribution within the ocean and between ocean and atmosphere. Dating methods independent of climatic variations and of the global carbon budget should be given priority to refine the timescales of the marine and atmospheric processes during the last deglaciation.This is the fourth paper in a series of papers published in this issue on high-resolution paleolimnology. These papers were presented at the Sixth International Palaeolimnology Symposium held 19–21 April, 1993 at the Australian National University, Canberra, Australia. Dr. A. F. Lotter and Dr. M. Sturm served as guest editors for these papers. 相似文献