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991.
利用庐山气象站逐月观测资料,对1956—2005年庐山气温和降水的变化趋势进行了分析。结果表明,近50 a庐山年平均气温上升了0.8℃,其中冬季上升最明显,为1.5℃;夏季呈下降趋势,为0.2℃。20世纪60年代庐山年平均气温、夏季最高气温下降最为明显,1996年以后上升最为明显。年降水量自1996年起明显下降。庐山的年最高气温、年最低气温、秋季平均气温、秋季最高气温、春季最高气温、春季最低气温在1998年发生了均值突变,冬季最低气温则在1992年前后出现了均值突变;夏季降水在1995年出现均值突变。 相似文献
992.
数值天气预报的创新之路--从初值问题到反问题 总被引:2,自引:2,他引:2
基于大气并非是一个确定论的系统,从信息论的视角考察了数值天气预报问题。认为表征初值和边值的数据可以视为输入信息(信息源),而数值模式则不过是一个信息变换机构,它把输入信息变换成预报结论而输出来,输出的预报结论则是未来天气状况的信息。于是预报的准确性受制于:一是输入信息所包含的输出信息的信息量,另一是信息在变换过程中丢失的信息量。从初值的形成过程揭示出了当前观测系统在一个时刻提供的数据没有包含初值所要求的全部信息,而缺失的部分或多或少的隐藏在过去的观测数据中。提为初值问题意味着只依据一个时刻的状态导致输入的信息量缺失,应考虑过去的历史数据以增加输入数据中所包含的预报量的信息。文中指出由于输出信息比输入还多的数值模式是不存在的,这样的改进带有根本性。进一步论证了数值模式的误差信息,也或多或少的隐藏在过去的历史数据中,为了充分使用过去的观测数据,本文建议改变问题的提法,不提成初值问题,提成反问题。资料同化本质上是反问题,其欠定性不应人为夸大。提成反问题的数值天气预报能充分应用过去的历史资料,将天气方法、统计方法、动力方法有机地结合在一起。对于这个反问题如何具体求解方面,在分析了业务和研究的区别,模式的普适性和针对性的统一的基础上,给出了反问题的具体解决途径。强调无需构建新模式(这是非常困难的工作),只需运行现成的模式,借助所关心的预报对象的历史数据来改造现成模式,因而是完全可行的。 相似文献
993.
994.
Summary. We attempted to gain some insight into the mechanical properties of poorly consolidated granular rock by preparing and testing synthetic rock specimens in which different cement content and bimodal grain-size distributions were used. We mixed various proportions of fine and coarse sand, Portland cement, and water. The mixture was cast in a mold and left pressure-free during curing, thus ensuring that the final material was poorly consolidated. The specimens were tested in a uniaxial press. During these tests, the static Youngs modulus was measured by performing small stress excursions at discrete intervals along the stress-strain curve. We observed significant non-linear elasticity (i.e., Youngs modulus increased with stress) in all the specimens. As expected, the uniaxial compressive strength increased with increasing cement content. Furthermore, we observed a transition from grain-size sensitivity of strength at cement contents less than 20–30% to grain-size independence above this value. At high cement content, the measured values of Youngs modulus are relatively well explained by a model based on rigid inclusions embedded in a soft matrix. At low cement content, we suggest that modelling the individual cemented grain-to-grain contacts becomes necessary. But this could not be done here for lack of microstructural information. 相似文献
995.
YU Jinhai & ZHANG Chuanding . Institute of Geodesy Geophysics of Chinese Academy of Sciences Wuhan China . Zhengzhou Information Engineering University Zhengzhou China 《中国科学D辑(英文版)》2005,48(3):398-405
Boundary value problem (BVP) plays a funda-mental role in physical geodesy that aims at determin-ing the earth’s shape and its external gravity field. TheMolodensky BVP and the Stokes BVP are typical inphysical geodesy, and the gravity anomaly is a kind ofbasic data. With the wide use of GPS, measurementaccuracy of the earth’s surface can reach one centime-ter, while that of the gravity measurement can reachμgals. Hence, it is necessary to establish a new kind ofBVP which can satisfy… 相似文献
996.
Bruno Cordani 《Celestial Mechanics and Dynamical Astronomy》2004,89(2):165-179
A method for the expansion of the perturbative Hamiltonian in the planetary problem is presented, which allows one to immediately
detect the terms vanishing under the averaging process. The method bases itself on a geometrical analysis, through the groups
SO(3) and SU(2), of the Poincaré canonical variables or of the similar Laplace variables. As an outcome, one obtains a MAPLE
program, which calculates the first averaged terms of the perturbative Hamiltonian.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
997.
The problem of three bodies when one of them is a gyrostat is considered. Using the symmetries of the system we carry out two reductions. Global considerations about the conditions for relative equilibria are made. Finally, we restrict to an approximated model of the dynamics and a complete study of the relative equilibria is made. 相似文献
998.
天然气水合物(gas hydrates)作为一种新的潜在能源 是目前世界范围内研究的热点和难点之一。目前 普遍认为拟海底反射(简称BSR)是天然气水合物存 在的重要标志之一,但有关水合物的识别仍有很 多问题需要解决。例如世界各地已发现水合物的 例证表明在没有BSR的情况下仍然存在水合物,在 没有BSR的情况下如何识别水合物仍是没有解决 的研究课题。本文以天然气水合物的识别为研究 目的,以AVO属性交汇图为研究手段,通过双相介 质正演理论模型研究了当地层含有天然气水合物 或游离气时的AVO属性特征,并与由双相介质的 交错网格有限差分法得到的合成地震记录所反演 得出的AVO交汇图进行了对比,得到高度一致的 对比结果,表明利用AVO属性交汇图是识别天然 气水合物和游离气并能估测其含量的有效技术。 相似文献
999.
Alexey?V.?BorisovEmail author Ivan?S.?Mamaev 《Celestial Mechanics and Dynamical Astronomy》2005,92(4):371-380
We consider integrable spherical analog of the Darboux potential, which appear in the problem (and its generalizations) of
the planar motion of a particle in the field of two and four fixed Newtonian centers. The obtained results can be useful when
constructing a theory of motion of satellites in the field of an oblate spheroid in constant curvature spaces. 相似文献
1000.
George Voyatzis John D. Hadjidemetriou 《Celestial Mechanics and Dynamical Astronomy》2005,93(1-4):263-294
Families of asymmetric periodic orbits at the 2/1 resonance are computed for different mass ratios. The existence of the asymmetric
families depends on the ratio of the planetary (or satellite) masses. As models we used the Io-Europa system of the satellites
of Jupiter for the case m1>m2, the system HD82943 for the new masses, for the case m1=m2 and the same system HD82943 for the values of the masses m1<m2 given in previous work. In the case m1≥ m2 there is a family of asymmetric orbits that bifurcates from a family of symmetric periodic orbits, but there exist also an
asymmetric family that is independent of the symmetric families. In the case m1<m2 all the asymmetric families are independent from the symmetric families. In many cases the asymmetry, as measured by
and by the mean anomaly M of the outer planet when the inner planet is at perihelion, is very large. The stability of these asymmetric families has
been studied and it is found that there exist large regions in phase space where we have stable asymmetric librations. It
is also shown that the asymmetry is a stabilizing factor. A shift from asymmetry to symmetry, other elements being the same,
may destabilize the system. 相似文献