全文获取类型
收费全文 | 18186篇 |
免费 | 5252篇 |
国内免费 | 1160篇 |
学科分类
地球科学 | 24598篇 |
出版年
2025年 | 178篇 |
2024年 | 475篇 |
2023年 | 584篇 |
2022年 | 863篇 |
2021年 | 1087篇 |
2020年 | 1004篇 |
2019年 | 970篇 |
2018年 | 1188篇 |
2017年 | 1092篇 |
2016年 | 1103篇 |
2015年 | 860篇 |
2014年 | 1068篇 |
2013年 | 1116篇 |
2012年 | 1083篇 |
2011年 | 1186篇 |
2010年 | 1081篇 |
2009年 | 1014篇 |
2008年 | 937篇 |
2007年 | 980篇 |
2006年 | 880篇 |
2005年 | 485篇 |
2004年 | 420篇 |
2003年 | 455篇 |
2002年 | 545篇 |
2001年 | 482篇 |
2000年 | 365篇 |
1999年 | 375篇 |
1998年 | 297篇 |
1997年 | 317篇 |
1996年 | 265篇 |
1995年 | 264篇 |
1994年 | 237篇 |
1993年 | 187篇 |
1992年 | 167篇 |
1991年 | 118篇 |
1990年 | 97篇 |
1989年 | 114篇 |
1988年 | 86篇 |
1987年 | 65篇 |
1986年 | 64篇 |
1985年 | 48篇 |
1984年 | 45篇 |
1983年 | 47篇 |
1982年 | 41篇 |
1981年 | 28篇 |
1980年 | 24篇 |
1979年 | 30篇 |
1978年 | 19篇 |
1977年 | 19篇 |
1975年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 5 毫秒
61.
Check dams are commonly constructed around the world for alleviating soil erosion and preventing sedimentation of downstream rivers and reservoirs.Check dams are more vulnerable to failure due to their less stringent flood control standards compared to other dams.Determining the critical precipitation that will result in overtopping of a dam is a useful approach to assessing the risk of failure on a probabilistic basis and for providing early warning in case of an emergency.However,many check dams are built in groups,spreading in several tributaries in cascade forms,comprising a complex network.Determining the critical precipitation for dam overtopping requires a knowledge of its upstream dams on whether they survived or were overtopped during the same storm,while these upstream dams in turn need the information for their upstream dams.The current paper presents an approach of decomposing the dam cluster into(1)the heading dam,(2)border dams,and(3)intermediate dams.The algorithm begins with the border dams that have no upstream dams and proceeds with upgraded maps without the previous border dams until all the dams have been checked.It is believed that this approach is applicable for small-scale check dam systems where the time lag of flood routing can be neglected.As a pilot study,the current paper presents the analytical results for the Wangmaogou Check Dam System that has 22 dams connected in series and parallel.The algorithm clearly identified 7 surviving dams,with the remaining ones being overtopped for a storm of 179.6 mm in 12 h,which is associated with a return period of one in 200 years. 相似文献
62.
Smirnov S. E. Mikhailov Yu. M. Mikhailova G. A. Kapustina O. V. 《Geomagnetism and Aeronomy》2019,59(6):696-703
Geomagnetism and Aeronomy - Winter thunderstorms in Kamchatka are a rare meteorological phenomenon. Temporal variations of the quasi-static electric field and meteorological values at the Paratunka... 相似文献
63.
Interaction between water flow and ridge bedforms has been studied. The results of experimental studies of velocity distribution over ridge bedforms in a hydraulic laboratory flume are given. The distribution of pressure along the contour of a rigid model ridge, determined in an aerodynamic canal, is also given. 相似文献
64.
Solar energy is clean and renewable energy that plays an important role in mitigating impacts of environmental problems and climate change. Solar radiation received on the earth’s surface determines the efficiency of power generation and the location and layout of photovoltaic arrays. In this paper, the average daily solar radiation of 77 stations in China from 1957 to 2016 was analyzed in terms of spatial and temporal characteristics. The results indicate that Xinjiang, the Qinghai-Tibet Platea... 相似文献
65.
G. M. Tovmasyan R. Kh. Oganesyan R. A. Epremyan S. E. Nersesyan M. A. Mkrtchyan Yu. M. Khodzhayants M. N. Krmoyan A. L. Kashin D. Huguenin S. I. Serova Yu. V. Romanenko A. P. Aleksandrov V. G. Titov M. Kh. Manarov 《Astrophysics》1990,32(1):1-5
Byurakan Astrophysical Observatory; SKB Granit; Geneva Observatory; Flight Control Center. Translated from Astrofizika, Vol. 32, No. 1, p. 5–13, January–February, 1990. 相似文献
66.
D. V. Ionov M. A. Kshevetskaya Yu. M. Timofeev A. V. Poberovskii 《Izvestiya Atmospheric and Oceanic Physics》2013,49(5):519-529
Atmospheric NO2 content data obtained from regular ground-based measurements of solar IR radiation in the St. Petersburg region using a spectrometer with a high spectral resolution are analyzed. The absorption spectra of the NO2 multiplet in the vicinity of ~2915 cm?1 allow one to obtain data on variations in the stratospheric total content of NO2 in 2009–2011. The accuracy of these data is estimated from their comparison with data obtained from independent ground-based and satellite measurements. The parameters of the seasonal cycle of the stratospheric content of NO2 are estimated. The body of data accumulated during these measurements in the IR region made it possible to isolate the component of a daytime photochemical increase in the stratospheric content of NO2 and estimate its rate. 相似文献
67.
Ya. A. Virolainen Yu. M. Timofeev A. V. Polyakov H. Steele M. Newchurch 《Izvestiya Atmospheric and Oceanic Physics》2006,42(6):752-764
A statistical ensemble of microphysical parameters of the background stratospheric aerosol at altitudes of 15 to 30 km is modeled on the basis of experimental data. The aerosol attenuation coefficients (AACs) in the wavelength range 0.38–16.3 μm are calculated for all realizations of the ensemble by algorithms of the Mie theory. Analysis of correlations between the AACs and the microphysical parameters indicate that the AAC correlates most strongly with the total volume V and area S of all particles. The errors of determining the microphysical parameters from AAC measurements are analyzed via the method of linear regression. It is shown that, if the AAC is measured with an error of 5%, the errors of determining both the particle size distribution (PSD) for particles with sizes of 0.4 to 4 μm and the parameter S are an order of magnitude smaller than the prior uncertainty, whereas the error of determining V is two orders of magnitude smaller than the prior uncertainty. Schemes of AAC measurements with the SAGE III, ISAMS, CLAES, HALOE instruments and an IR interferometer in the visible and IR regions are discussed. It is shown that combining the schemes makes it possible to extend the range of particle sizes for which the PSD is retrieved with a satisfactory accuracy and to increase the accuracy of determining S and V substantially and the accuracy of determining the total number of particles N opt to a lesser extent. Examples of interpreting AAC measurements carried out simultaneously with the SAGE III and HALOE instruments within the same spatial region are presented. A systematic discrepancy between vertical profiles of S and V obtained from SAGE III and HALOE measurements is revealed. 相似文献
68.
69.
本文介绍了便携式人卫光电望远镜的主要性能特点,探讨了将其应用于狮子座流星暴观测的可能性。 相似文献
70.
Kaminsky F. V. Shilobreeva S. N. Ber B. Ya. Kazantsev D. Yu. 《Doklady Earth Sciences》2020,494(1):699-703
Doklady Earth Sciences - The volumetric concentration of hydrogen in two Brazilian diamonds is determined using secondary ion mass spectrometry and implantation of hydrogen into an external... 相似文献