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191.
192.
193.
真实性检验是评价遥感反演产品质量和验证遥感应用产品是否准确、真实地反映实际情况的重要途径。叶面积指数(LAI)是表征陆地植被结构和长势的关键参数,全面准确评价和验证LAI产品是产品用于陆面过程模型的前提。本文以MODIS LAI与GLASS LAI产品为研究对象,在尺度效应和尺度转换的基础上,建立了针对非均匀像元的低分辨率LAI产品真实性检验方法。在考虑空间异质性和植被长势差异的情况下,借助中分辨率的遥感影像,分别利用1 km像元平均叶面积指数和反演表观叶面积指数实现了对LAI算法和产品的真实性检验。为了比较作物长势差异和地表非均匀度对产品的影响,本文选择有代表性的河南鹤壁和甘肃张掖两个地区进行两种LAI产品真实性检验研究。研究结果表明,GLASS LAI和MODIS LAI产品均存在明显的低估现象。这并不是产品算法的问题,而是由于地表异质性和非均匀度的影响。在异质性更显著的张掖盈科灌区,低估现象更明显。GLASS LAI产品是多种LAI产品的融合,它的平均LAI比MODIS更接近真实情况,但是LAI的动态范围比MODIS窄。 相似文献
194.
Analysis of a simple reinforced concrete (RC) structure damaged by the Bhuj, India, earthquake was carried out to estimate the level of shaking in the epicentral region. For this, an attempt was made to estimate the level of input motion to cause inelastic behavior to the extent observed during the field visit. To consider the inelastic effects, both yielding of steel bars as well as crushing of the concrete cover has been investigated employing the hysteretic model known as the Fiber model. The only available record at Ahmedabad of the Bhuj earthquake and four additional earthquake records from Japan and California were used in the analysis. Considering simple scaling of input motion, the level of input motion to cause crushing and spall‐off of the concrete cover as observed in the field was estimated to be of the order of 6 times the original instrumental record obtained at 240 km away from the epicenter. The methodology proposed was promising in providing a useful quantitative indication of the level of shaking when instrumental records are not available. It was also noted that the design response spectrum specified in Indian seismic code IS1893: 1984 appears inadequate compared to the extent of shaking estimated. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
195.
196.
本文扼要介绍了中国科学院东川泥石流观测研究站对外开放三年来,在泥石流观测试验研究和防灾减灾工作中的新进展,同时也简述了站设基金课题、国家基金课题和中外合作交流项目的进展情况,并对今后的观测研究工作提出了展望和建议。 相似文献
197.
198.
Valentina?MontaldoEmail author Ezio?Faccioli Gaetano?Zonno Aybige?Akinci Luca?Malagnini 《Journal of Seismology》2005,9(3):295-316
In the framework of the 2004 reference seismic hazard map of Italy the amplitude of the strong-motion (expressed in terms
of Peak Horizontal Acceleration with 10% probability of non-exceedence in 50 years, referred to average hard ground conditions)
was computed using different predictive relationships. Equations derived in Italy and in Europe from strong-motion data, as
well as a set of weak and strong-motion based empirical predictive relationships were employed in a logic tree procedure,
in order to capture the epistemic uncertainty affecting ground-motion attenuation. This article describes the adjustments
and conversions required to eliminate the incompatibilities amongst the relations. Particularly significant are distance conversions
and style-of-faulting adjustments, as well as the problems related to the use of regional relations, such as the selection
of a reference depth, the quantification of random variability and the strong-motion prediction. Moreover, a regional attenuation
relationship specific for volcanic areas was also employed, allowing a more realistic evaluation of seismic hazard, as confirmed
by the attenuation of macroseismic intensities. 相似文献
199.
Aftershock Statistics 总被引:2,自引:0,他引:2
Robert Shcherbakov Donald L. Turcotte John B. Rundle 《Pure and Applied Geophysics》2005,162(6-7):1051-1076
The statistical properties of aftershock sequences are associated with three empirical scaling relations: (1) Gutenberg-Richter frequency-magnitude scaling, (2) Båths law for the magnitude of the largest aftershock, and (3) the modified Omoris law for the temporal decay of aftershocks. In this paper these three laws are combined to give a relation for the aftershock decay rate that depends on only a few parameters. This result is used to study the temporal properties of aftershock sequences of several large California earthquakes. A review of different mechanisms and models of aftershocks are also given. The scale invariance of the process of stress transfer caused by a main shock and the heterogeneous medium in which aftershocks occur are responsible for the occurrence of scaling laws. We suggest that the observed partitioning of energy could play a crucial role in explaining the physical origin of Båths law. We also study the stress relaxation process in a simple model of damage mechanics and find that the rate of energy release in this model is identical to the rate of aftershock occurrence described by the modified Omoris law. 相似文献
200.
A space-time envelope of minor seismicity related to major shallow earthquakes is identified from observations of the long-term Precursory Scale Increase () phenomenon, which quantifies the three-stage faulting model of seismogenesis. The envelope, which includes the source area of the major earthquake, is here demarcated for 47 earthquakes from four regions, with tectonic regimes ranging from subduction to continental collision and continental transform. The earthquakes range in magnitude from 5.8 to 8.2, and include the 24 most recent mainshocks of magnitude 6.4 and larger in the San Andreas system of California, the Hellenic Arc region of Greece, and the New Zealand region, together with the six most recent mainshocks of magnitude 7.4 and larger in the Pacific Arc region of Japan. Also included are the destructive earthquakes that occurred at Kobe, Japan (1995, magnitude 7.2), Izmit, Turkey (1999, magnitude 7.4), and W.Tottori, Japan (2000, magnitude 7.3). The space (A
P
) in the space-time envelope is optimised with respect to the scale increase, while the time (T
P
) is the interval between the onset of the scale increase and the occurrence of the earthquake. A strong correlation is found between the envelope A
P
T
P
and the magnitude of the earthquake; hence the conclusion that the set of precursory earthquakes contained in the envelope is intrinsic to the seismogenic process. Yet A
P
and T
P
are correlated only weakly with each other, suggesting that A
P
is affected by differences in statical conditions, such as geological structure and lithology, and T
P
by differences in dynamical conditions, such as plate velocity. Among other scaling relations, predictive regressions are found between, on the one hand, the magnitude level of the precursory seismicity, and on the other hand, both T
P
and the major earthquake magnitude. Hence the method, as here applied to retrospective analysis, is potentially adaptable to long-range forecasting of the place, time and magnitude of major earthquakes. 相似文献