全文获取类型
收费全文 | 88119篇 |
免费 | 1424篇 |
国内免费 | 696篇 |
专业分类
测绘学 | 2245篇 |
大气科学 | 6281篇 |
地球物理 | 16924篇 |
地质学 | 33500篇 |
海洋学 | 7333篇 |
天文学 | 18999篇 |
综合类 | 331篇 |
自然地理 | 4626篇 |
出版年
2022年 | 396篇 |
2021年 | 684篇 |
2020年 | 776篇 |
2019年 | 823篇 |
2018年 | 4099篇 |
2017年 | 3868篇 |
2016年 | 3407篇 |
2015年 | 1414篇 |
2014年 | 2198篇 |
2013年 | 3766篇 |
2012年 | 3132篇 |
2011年 | 5311篇 |
2010年 | 4630篇 |
2009年 | 5567篇 |
2008年 | 4801篇 |
2007年 | 5162篇 |
2006年 | 2909篇 |
2005年 | 2718篇 |
2004年 | 2545篇 |
2003年 | 2459篇 |
2002年 | 2125篇 |
2001年 | 1824篇 |
2000年 | 1750篇 |
1999年 | 1376篇 |
1998年 | 1471篇 |
1997年 | 1371篇 |
1996年 | 993篇 |
1995年 | 1125篇 |
1994年 | 948篇 |
1993年 | 855篇 |
1992年 | 830篇 |
1991年 | 753篇 |
1990年 | 833篇 |
1989年 | 693篇 |
1988年 | 631篇 |
1987年 | 790篇 |
1986年 | 646篇 |
1985年 | 841篇 |
1984年 | 905篇 |
1983年 | 846篇 |
1982年 | 812篇 |
1981年 | 708篇 |
1980年 | 665篇 |
1979年 | 597篇 |
1978年 | 597篇 |
1977年 | 547篇 |
1976年 | 533篇 |
1975年 | 498篇 |
1974年 | 503篇 |
1973年 | 465篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
51.
52.
In this paper the steady lateral growth of three-dimensional turbulent inclined turbidity current is investigated. To simulate the current, an experimental setup is developed to analyze the turbidity current for different regimes in the particle laden density currents environment. The Buckingham's π theorem together with a dimensional analysis is implemented to derive the appropriate non-dimensional variables. The experimental results were normalized and plotted in the form of non-dimensional graphs from which a theoretical model is developed and analyzed. Based on the results obtained for the steady lateral growth, three different regimes, namely, inertia-viscous one as the first regime, buoyancy-viscous and gravity-viscous as the second and third regimes are distinguished within the current.In these regimes, the force balance is between the driving and resisting forces. Namely, in the first regime, the force balance is between the inertia and viscous forces, in the second regime, the buoyancy and viscous forces, and in the third regime, gravity and viscous forces are balanced. The experimental results indicate that the lateral growth rate in the first regime is smaller than that in the second and third regimes due to the magnitude and type of the forces involved in those regimes. According to the graphical results, the three different lateral growth rates appear when the normalized current length is smaller than about 3, between about 3 and 10, and larger than about 10. In those regions,the slopes of the data are different with respect to one another. 相似文献
53.
Fully nonlinear features of heavy ion-acoustic solitary waves (HIASWs) have been investigated in an astrophysical degenerate relativistic quantum plasma (ADRQP) containing relativistically degenerate electrons and non-relativistically degenerate light ion species, and non-degenerate heavy ion species. The pseudo-energy balance equation is derived from the fluid dynamical equations by adopting the well-known Sagdeev-potential approach, and the properties of arbitrary amplitude HIASWs are examined. The small amplitude limit for the propagation of HIASWs is also recovered. The basic features (width, amplitude, polarity, critical Mach number, speed, etc.) of HIASWs are found to be significantly modified by the relativistic effect of the electron species, and also by the variation of the number density of electron, light ion, and heavy ion species. The basic properties of HIASWs, that may propagated in some realistic astrophysical plasma systems (e.g., in white dwarfs), are briefly discussed. 相似文献
54.
Izvestiya, Atmospheric and Oceanic Physics - The problem of atmospheric correction for shortwave channels of a multispectral low-resolution scanning radiometer onboard the Meteor-M No. 2 satellite... 相似文献
55.
Korzhenkov A. M. Gadzhiev M. S. Ovsyuchenko A. N. Lar’kov A. S. Rogozhin E. A. 《Izvestiya Atmospheric and Oceanic Physics》2020,56(7):633-656
Izvestiya, Atmospheric and Oceanic Physics - As a result of studies conducted in the city of Derbent, it is established that its monumental fortification structures erected at the end of the 560s... 相似文献
56.
Yu Xinran Ahmadinia Masoud Shariatipour Seyed M. Lawton Don Osadetz Kirk Saeedfar Amin 《Natural Resources Research》2020,29(4):2735-2752
Natural Resources Research - Carbon capture and storage is part of Canada’s climate change action plan to reduce greenhouse gas emissions. The Containment and Monitoring Institute Field... 相似文献
57.
Abstract— Active capture is a new process for the incorporation of large quantities of heavy noble gases into growing surfaces. Adsorption in the conventional sense involves surface bonding by polarization (Van der Waals forces). What is referred to as “anomalous adsorption” of heavy noble gases involves chemical bonds and can occur when other (more chemically active) species are not available to preempt sites with unfilled bonds. Anomalous adsorption has been observed under conditions of fracture, vacuum deposition and ionizing radiation. Active capture depends upon anomalous adsorption to retain noble gases on a surface long enough to be captured in a growing surface film as it is deposited. The fundamental principle may be the impingement onto the growing film with sufficient energy to liberate surface electrons (work function energy of a few electronvolts) so that they are retained by anomalous adsorption long enough to be entrapped in the growing surface. Trapping efficiencies of ?1% have been observed for Kr and Xe in laboratory experiments, implying a fundamentally new mechanism for the incorporation of heavy noble gases onto surfaces. It may play a role in explaining the large concentrations of planetary noble gases contained in phase‐Q. 相似文献
58.
Abstract— The possibility of volcanism on Mercury has been a topic of discussion since Mariner 10 returned images of half the planet's surface showing widespread plains material. These plains could be volcanic or lobate crater ejecta. An assessment of the mechanics of the ascent and eruption of magma shows that it is possible to have widespread volcanism, no volcanism on the surface whatsoever, or some range in between. It is difficult to distinguish between a lava flow and lobate crater ejecta based on morphology and morphometry. No definite volcanic features have been identified on Mercury. However, known lunar volcanic features cannot be identified in images with similar resolutions and viewing geometries as the Mariner 10 dataset. Examination of high‐resolution, low Sun angle Mariner 10 images reveals several features which are interpreted to be flow fronts; it is unclear if these are volcanic flows or ejecta flows. This analysis implies that a clear assessment of volcanism on Mercury must wait for better data. MESSENGER (MErcury: Surface, Space ENvironment, GEochemistry, Ranging) will take images with viewing geometries and resolutions appropriate for the identification of such features. 相似文献
59.
60.
We present our spectroscopic observations of the novae V1425, V1493, and V1494 Aql carried out with the 125-cm telescope at the Crimean Station of the Sternberg Astronomical Institute in the wavelength range 4000–11000 Å. We measured the emission-line intensities, determined the nova shell expansion velocities from the line profile FWHMs and components, and estimated the interstellar reddening from the first members of the Balmer series. The chemical composition of the nova shells is analyzed. Nitrogen and oxygen were found to be overabundant in V1425 and V1494 Aql; the helium abundance turned out to be normal in the two stars. 相似文献