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921.
The vertical temperature profiles of snow and sea ice have been measured in the Arctic during the 2nd Chinese National Arctic Research Expedition in 2003(CHINARE2003).The high-resolution temperature profile in snow is solved by one-dimensional heat transfer equation.The effective heat diffusivity,internal heat sources are identified.The internal heat source refers to the penetrated solar radiation which usually warms the lower part of the snow layer in summer.By temperature gradient analysis,the zero level can be clarified quantitatively as the boundary of the dry and wet snow.According to the in situ time series of vertical temperature profile,the time series of water content in snow is obtained based on an evaluation method of snow water content associated with the snow and ice physical parameters.The relationship of snow water content and snow temperature and temporal-spatial distribution of snow water content are presented 相似文献
922.
This study considers a 35‐year record of streamwater nitrate concentration in a small agricultural catchment in south west England (Slapton Wood). The study revisits earlier work to assess whether upward trends have been maintained and how the controls upon streamwater concentration have been altered. The study has shown that (1) the catchment has reached a new position of equilibrium and increases in nitrate concentration have lessened; (2) the occurrence of severe drought in the record means that records of less than a decade are misleading and only long‐term records can illustrate changes of state; (3) the change of state observed in the catchment is illustrated in the switching of long‐term memory effects from a negative to a positive annual memory and (4) several significant long‐term impulsivity relationships with rainfall that become insignificant over the course of the study period. The study shows the importance of long‐term records in understanding changes in state in catchments and understanding the time constants of a range of driving processes. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
923.
Short‐term prediction of environmental variables such as stream flow rate is useful to members of the general public and environmental scientists alike, providing the ability to predict environmental disasters or scientifically interesting events. Here, a neural‐network based method is presented, which is capable of providing advance flood warnings or the prediction of high stream flow events for research purposes in a small upland headwater in NE Scotland. This method relies on training from past time series data acquired in the field, and provides the ability to predict a range of hydrological and meteorological variables up to 24 h ahead using feedback of predicted values at time t as new inputs for the next time step t + 1. The system is rapid and effective, relies on standard neural network training methods, and has the potential to be implemented in a web‐based monitoring and prediction package. The model design could be implemented at any study site where time series data has been gathered, and is sufficiently flexible to accept whatever data is available. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
924.
初论中亚黑色岩系型金矿床的基本特征——兼论新疆黑色岩系型金矿找矿方向 总被引:2,自引:0,他引:2
黑色岩系型金矿床实质上是一种早期形成于富含碳质细碎屑岩建造的滨浅海还原环境,后期经强烈区域低温强动力挤压作用改造形成于韧性剪切带中的低温变质热液金矿床,属韧剪型金矿的1个亚型.在20世纪80年代后引起重视,在世界各地,特别是中亚地区和我国新疆及西南地区取得许多重大找矿突破.中亚地区黑色岩型金矿床十分发育,形成了以穆龙套、库姆托尔、巴克尔奇克为代表的诸多特大型、超大型和大型金矿床.这类矿床具低温蚀变、韧剪性显著、富含碳质和含金石英脉等特点.新疆黑色岩系型金矿成矿地质背景和成矿地质构造条件优越,找矿前景广阔.主要成矿时代为前二叠纪,其次是二叠—三叠纪(昆仑),找矿有利成矿区带主要是北准噶尔、中天山、南天山、东昆仑和北天山,其次有阿尔泰和东准噶尔等地. 相似文献
925.
926.
Mireille Polve Rene C. Maury Sebastien Jego Herve Bellon Ahmed Margoum Graciano P. Yumul Jr Betchaida D. Payot Rodolfo A. Tamayo Jr Joseph Cotten 《Resource Geology》2007,57(2):197-218
Baguio, in the Central Cordillera of Northern Luzon, is a district that displays porphyry copper and epithermal gold mineralization, associated with Early Miocene–Pliocene–Quaternary calc‐alkaline and adakitic intrusions. Systematic sampling, K‐Ar dating, major and trace elements, and Sr, Nd, Pb isotopic analyses of fresh magmatic rocks indicate three magmatic pulses: an Early Miocene phase (21.2–18.7 Ma), a Middle–Late Miocene phase (15.3–8 Ma) and finally a Pliocene–Quaternary event (3–1 Ma). The first phase emplaced evolved calc‐alkaline magmas, essentially within the Agno Batholith complex, and is thought to be related to the westward‐dipping subduction of the West Philippine Basin. After a quiescence period during which the Kennon limestone was deposited, magmatic activity resumed at 15.3 Ma, in connection with the start of the subduction of the South China Sea along the Manila Trench. It emplaced first petrogenetically related and relatively unradiogenic low‐K calc‐alkaline lavas and intermediate adakites. Temporal geochemical patterns observed from 15.3 to 1 Ma include progressive enrichment in K and other large ion lithophile elements, increase in radiogenic Sr and Pb and corresponding decrease in radiogenic Nd. These features are thought to reflect the progressive addition to the Luzon arc mantle wedge of incompatible elements largely inherited from South China Sea sediments. The origin of the long quiescence period, from 8 to 3 Ma, remains problematic. It might represent a local consequence of the docking of the Zambales ophiolitic terrane to Northern Luzon. Then, magmatic activity resumed at 3 Ma, emplacing chemically diversified rocks ranging from low K to high K and including a large proportion of adakites, especially during the Quaternary (dacitic plugs). The authors tentatively relate this diversity to the development of a slab tear linked with the subduction of the fossil South China Sea ridge beneath the Baguio area. 相似文献
927.
928.
ZHANG Jingxiong David Roy Sadashiva Devadiga ZHENG Min 《地球空间信息科学学报》2007,10(1):44-50
With remote sensing information products becoming increasingly varied and arguably improved, scientific applications of such products rely on their quality assessment. In an operational context such as the NASA (National Aeronautics and Space Administration) information production based on the MODIS (Moderate Resolution Imaging Spectroradiometer) instrument on board Earth Observing System (EOS) Terra and Aqua satellites, efficient ways of detecting product anomaly, i.e., to discriminate between product artifacts and real changes in Earth processes being monitored, are extremely important to assist and inform the user communities about potential unreliability in the products. A technique for anomaly detection, known as MAD (the median of absolute deviate from the median), in MODIS land products via time series analysis is described, which can handle intra- and in-ter-annual variation in the data by using MAD statistics of the original data and their first-order difference. This method is shown to be robust and work across major land products, including NDVI, active fire, snow cover, and surface reflectance, and its applicabil-ity to multi-disciplinary products is anticipated. 相似文献
929.
The quadrant technique, a conditional sampling approach that allocates Reynolds stresses into four different types of events
(ejections or bursts, sweeps, inward interactions and outward interactions), is applied to stable marine atmospheric boundary-layer
data, collected in the framework of the Coupled Boundary Layer Air—Sea Transfer, Low wind component experiment at Nantucket
Island, Massachusetts, USA. The general properties of both scalar and momentum transport are analyzed under the scope of quadrant
analysis experimentally and theoretically. It is shown that the third-order Gram–Charlier series is necessary and even sufficient
in most of the cases, in describing the experimental time and flux contributions of each quadrant to the total transfer, for
both scalar and momentum transport, while the ability of the Gaussian distribution is limited to outlining the general pattern
of these quantities. Moreover, a threshold value is applied to the conditional analysis, separating the most important events
from the less significant ones and the sensitivity of the flux and especially the time fraction of each quadrant on the choice
of this value is presented and discussed. Also, a set of numerically extracted equations, completing the analytical relations,
is derived, enabling the prediction of the time and flux fractions of each quadrant, for a wide range of correlation coefficient
and threshold values. Finally, the sensitivity of the analysis to the atmospheric stability and the Reynolds averaging scales
showed that correlated and uncorrelated motions tend to balance for increasingly stable conditions and/or for large time scales. 相似文献
930.
研究关于重级数型Hardy-Hilbert不等式改进的问题。通过给出如下形式的权系数的估计式∞研究关于重级数型Hardy-Hilbert不等式改进的问题。通过给出如下形式的权系数的估计式ω(q,n)=∑∞m=11m nnm1q<πsinπp-12np1 2en-q1,q>1,1p q1=1,n∈N,从而得到Hardy-Hilbert不等式的一个新的改进形式∑∞m=1∑∞n=1ambnm n<∑∞n=1πsinπp-12n1p 2en-1qanp1p∑∞n=1πsinπp-12n1q 2en-1pbnq1q。 相似文献