全文获取类型
收费全文 | 20400篇 |
免费 | 3420篇 |
国内免费 | 5382篇 |
专业分类
测绘学 | 557篇 |
大气科学 | 2992篇 |
地球物理 | 4842篇 |
地质学 | 9100篇 |
海洋学 | 7281篇 |
天文学 | 851篇 |
综合类 | 1025篇 |
自然地理 | 2554篇 |
出版年
2024年 | 76篇 |
2023年 | 245篇 |
2022年 | 605篇 |
2021年 | 638篇 |
2020年 | 684篇 |
2019年 | 853篇 |
2018年 | 726篇 |
2017年 | 863篇 |
2016年 | 842篇 |
2015年 | 936篇 |
2014年 | 1271篇 |
2013年 | 1291篇 |
2012年 | 1018篇 |
2011年 | 1262篇 |
2010年 | 995篇 |
2009年 | 1525篇 |
2008年 | 1533篇 |
2007年 | 1515篇 |
2006年 | 1436篇 |
2005年 | 1321篇 |
2004年 | 1140篇 |
2003年 | 1071篇 |
2002年 | 1000篇 |
2001年 | 833篇 |
2000年 | 789篇 |
1999年 | 732篇 |
1998年 | 645篇 |
1997年 | 559篇 |
1996年 | 488篇 |
1995年 | 405篇 |
1994年 | 392篇 |
1993年 | 341篇 |
1992年 | 261篇 |
1991年 | 196篇 |
1990年 | 147篇 |
1989年 | 159篇 |
1988年 | 101篇 |
1987年 | 65篇 |
1986年 | 45篇 |
1985年 | 47篇 |
1984年 | 38篇 |
1983年 | 23篇 |
1982年 | 24篇 |
1981年 | 25篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 12篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1954年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
1.
《Astroparticle Physics》2002,16(4):183-386
Frequency distributions of local muon densities in high-energy extensive air showers (EAS) are presented as signature of the primary cosmic ray energy spectrum in the knee region. Together with the gross shower variables like shower core position, angle of incidence, and the shower sizes, the KASCADE experiment is able to measure local muon densities for two different muon energy thresholds. The spectra have been reconstructed for various core distances, as well as for particular subsamples, classified on the basis of the shower size ratio Nμ/Ne. The measured density spectra of the total sample exhibit clear kinks reflecting the knee of the primary energy spectrum. While relatively sharp changes of the slopes are observed in the spectrum of EAS with small values of the shower size ratio, no such feature is detected at EAS of large Nμ/Ne ratio in the energy range of 1–10 PeV. Comparing the spectra for various thresholds and core distances with detailed Monte Carlo simulations the validity of EAS simulations is discussed. 相似文献
2.
唐森铭 《中国海洋湖沼学报》2002,(1)
INTRODUCTIONThemainpurposeofthisstudywastodeterminethemagnitudeandfrequencyofharmfuldiatomanddinoflagellateoutbreaksinHongKong’swesternandeasternwaters (e .g.LammaStraitsandPortShelterrespectively)fortheperiodJanuary 1 997toDecember1 999.Thiswasdoneinordertod… 相似文献
3.
高速滑坡问题是当前工程地质和环境地质学界极为关注的问题。本文对诸如滑体高速滑动所对应的时空界限、滑体滑动过程所产生的热效应以及空气浮托力等高速滑坡产生机制问题进行了初步探讨。 相似文献
4.
Durgesh Tripathi 《Journal of Astrophysics and Astronomy》2006,27(2-3):193-200
The Large Angle Spectrometric Coronagraph (LASCO) and Extreme-ultraviolet Imaging Telescope (EIT) onboard Solar and Heliospheric
Observatory (SOHO) provide us with unprecedented multi-wavelength observations helping us to understand different dynamic
phenomena on the Sun and in the corona. In this paper we discuss the association between post-eruptive arcades (PEAs) detected
by EIT and white-light coronal mass ejections (CMEs) detected by LASCO/C2 telescope. 相似文献
5.
6.
Himmerfjärd is a Swedish estuary bordering on the Baltic. The estuary lacks astronomical tides and its circulation is driven by winds and freshwater runoff. Because of a tertiary sewage treatment plant located at its inner end, the estuary is becoming increasingly eutrophic. A field study was carried out for a 78-day period in late summer and early fall of 1977 to determine rates of nutrient transport and to construct nutrient budgets. Since physical parameters (current velocity, temperature, salinity, winds and water level changes) were measured more frequently than nutrients (phosphate, nitrate, nitrite and ammonium) it was necessary to develop a suitable method to calculate nutrient flux time series and net nutrient fluxes. Over the study period, Himmerfjärd imported phosphorus and exported nitrogen. Direction of nutrient fluxes and changes in flux direction were consistent with the structure of the baroclinic currents. 相似文献
7.
JINFeng-jun 《中国地理科学(英文版)》2003,13(2):97-103
It is very important to establish cooperative mechanism to guarantee all members to develop their e-conomies in the Yellow Sea Rim. In this paper, the development strategies ofshipplng centers and transportation networkare discussed based on economic giobalization tendency. The results argue that a united transportation network should bebuilt in order to promote the economic competition of Northeast Asia in the world. As a key component of the economiccooperation, a hierarchical shipping centers network should be established with Hong Kong, Shanghai, Pusan, Koho,and Tokyo as cores. The authorities of China, Japan, R. O. Korea and D. P. B. Korea should make more efforts tobuild a set of cooperation institutions based on raising the transportation efficiency. 相似文献
8.
9.
MEN Wu ) WEI Hao ) and LIU Guangshan ) * ) College of Oceanography Environmental Science Xiamen University State Key Laboratory of Marine Environmental Science 《中国海洋大学学报(英文版)》2006,5(3):228-234
1Introduction Therearefourradiumisotopesinnature,ofwhich224Ra,226Raand228Rahavebeenwidelyinvestigated inmarineresearch,butthespecificactivityof223Rais toolowtobemeasured,therefore,itsapplicationsarelimited(Moore,1969;Broeckeretal.,1976;KuandLin,1976;Nozak… 相似文献
10.
I. P. Williams 《Celestial Mechanics and Dynamical Astronomy》2003,87(1-2):13-25
The role of tides in deforming and possibly disrupting a secondary body orbiting about a primary body has been known for a considerable time. This was first inspired by the observations of ocean tides on Earth and then seen as playing an important role in the formation and evolution of the Earth–Moon system. Finally, in the beginning of the 20th century it was generally thought to have a significant role in the formation of the solar system through the tidal disruption of the Sun. Here, an overview of the historical developments of the ideas concerned with tidal disruption of a secondary body that can lead to mass loss is given. Some discussion of possible extensions to consider more realistic situations where the secondary body may not be moving on a circular orbit and may not rotate so as to maintain the phase-on configuration to the primary body is also given. 相似文献