全文获取类型
收费全文 | 110608篇 |
免费 | 1580篇 |
国内免费 | 907篇 |
专业分类
测绘学 | 2719篇 |
大气科学 | 8398篇 |
地球物理 | 22187篇 |
地质学 | 39578篇 |
海洋学 | 9065篇 |
天文学 | 24211篇 |
综合类 | 289篇 |
自然地理 | 6648篇 |
出版年
2021年 | 905篇 |
2020年 | 1014篇 |
2019年 | 1051篇 |
2018年 | 2418篇 |
2017年 | 2287篇 |
2016年 | 2915篇 |
2015年 | 1761篇 |
2014年 | 2939篇 |
2013年 | 5558篇 |
2012年 | 2985篇 |
2011年 | 4101篇 |
2010年 | 3550篇 |
2009年 | 4728篇 |
2008年 | 4355篇 |
2007年 | 4194篇 |
2006年 | 3974篇 |
2005年 | 3336篇 |
2004年 | 3246篇 |
2003年 | 3009篇 |
2002年 | 2822篇 |
2001年 | 2625篇 |
2000年 | 2467篇 |
1999年 | 2146篇 |
1998年 | 2196篇 |
1997年 | 2135篇 |
1996年 | 1776篇 |
1995年 | 1751篇 |
1994年 | 1559篇 |
1993年 | 1453篇 |
1992年 | 1472篇 |
1991年 | 1410篇 |
1990年 | 1550篇 |
1989年 | 1367篇 |
1988年 | 1276篇 |
1987年 | 1496篇 |
1986年 | 1270篇 |
1985年 | 1583篇 |
1984年 | 1792篇 |
1983年 | 1724篇 |
1982年 | 1668篇 |
1981年 | 1528篇 |
1980年 | 1367篇 |
1979年 | 1328篇 |
1978年 | 1302篇 |
1977年 | 1191篇 |
1976年 | 1146篇 |
1975年 | 1049篇 |
1974年 | 1106篇 |
1973年 | 1082篇 |
1972年 | 731篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
801.
Yu. M. Smirnov 《Astronomy Reports》2003,47(3):240-247
We have experimentally studied the excitation of the rhenium atom by collisions with slow monoenergetic electrons and measured 47 excitational cross sections for lines of ReI at an electron energy of 50 eV. Previously published information about the probabilities of radiative transitions of ReI is analyzed. The data for two experimental studies of the ratios Iλ/gA for transitions with a common upper level differ by three orders of magnitude. 相似文献
802.
Beach seines are widely used to estimate the density and species richness of fishes in estuaries. We evaluated the causes
and extent of bias in estimates from seines using a series of field experiments in small estuaries in southern California,
USA. Seining in spatially paired areas that were either enclosed by block nets or not, revealed that seines used without block
nets und erestimated density by more than 4-fold and species richness by more than 2-fold relative to blocked areas. Seining
in paired blocked areas with seines of two lengths revealed that net length affected estimates of density, but not species
richness; a 7.6-m long seine produced 1.6-fold higher estimates of total density than did a 15.2-m long seine due to increased
catches of demersal fishes, but not midwater species. Paired sampling in blocked areas also revealed that many fishes initially
evaded capture by the seine. Estimates of density but not species richness were significantly higher in areas through which
a seine was swept 5 times compared to once. This was due to higher catches of demersal fishes but not midwater fishes in areas
seined 5 times. Repeated seining through blocked areas revealed that the vast majority (90% or more) of species and individuals
of midwater fishes were captured within the first 5 sweeps, compared to only about 50% of the individuals of demersal species.
A mark-recapture study in blocked areas revealed lower probabilities of capture for demersal species relative to midwater
species. 相似文献
803.
M. Burša 《Studia Geophysica et Geodaetica》1991,35(2):61-74
Summary It has been shown that dynamically, on the basis of the distribution of angular momenta, the Jovian system cannot be considered an analogue within the Solar system. The total tidal decrease in the angular momentum of Jupiter and in its angular velocity of rotation have been estimated, as well as the loss of mechanical energy due to tidal dissipation. It has been concluded that there are no dynamical contradictions with the hypothesis of the common cosmogonic origin of Jupiter and of its eight close satellites.
aam, m ¶rt;uauu, n an¶rt;u m uma ¶rt;uu, um numa umam aayu um. a a y au ma uma ¶rt;uu numa u z mu z au u—a nuuz mu, ma a nmu au yuu um u—a ¶rt;uunauu. a au, m m ¶rt;uauu azau zunm m zuu aaa numa u z uau u nmu.相似文献
804.
A. Eff-Darwich J. Coello R. Viñas V. Soler M. C. Martin-Luis I. Farrujia M. L. Quesada J. de la Nuez 《Pure and Applied Geophysics》2008,165(1):135-145
The spatial distribution of groundwater temperatures in the volcanic island of Tenerife, Canary Islands, has been inferred
through measurements of water temperatures collected in the vast network of wells and subhorizontal tunnels, locally called
“galleries,” which constitutes the main water supply of the island. The spatial coverage of the network of galleries allows
us to reach from depth almost any geological feature of the island. The complex spatial distribution of temperatures in the
interior of Tenerife is the result of the complex geological evolution of the island. Groundwater temperatures are greatly
affected by groundwater flow and are considerably warmer in those galleries located in areas where water circulation is reduced
due to the low permeability of materials and/or to the low infiltration rate of cooling meteoric water. In this sense, groundwater
temperature should be characterized in quiescent conditions (background level), in order to facilitate monitoring changes
in heat flow, such as those induced by ascending gases expected with an increase in volcanic activity. 相似文献
805.
The giant gas planets have hot convective interiors, and therefore a common assumption is that these deep atmospheres are close to a barotropic state. Here we show using a new anelastic general circulation model that baroclinic vorticity contributions are not negligible, and drive the system away from an isentropic and therefore barotropic state. The motion is still aligned with the direction of the axis of rotation as in a barotropic rotating fluid, but the wind structure has a vertical shear with stronger winds in the atmosphere than in the interior. This shear is associated with baroclinic compressibility effects. Most previous convection models of giant planets have used the Boussinesq approximation, which assumes the density is constant in depth; however, Jupiter's actual density varies by four orders of magnitude through its deep molecular envelope. We therefore developed a new general circulation model (based on the MITgcm) that is anelastic and thereby incorporates this density variation. The model's geometry is a full 3D sphere down to a small inner core. It is nonhydrostatic, uses an equation of state suitable for hydrogen-helium mixtures (SCVH), and is driven by an internal heating profile. We demonstrate the effect of compressibility by comparing anelastic and Boussinesq cases. The simulations develop a mean state that is geostrophic and hydrostatic including the often neglected, but significant, vertical Coriolis contribution. This leads to modification of the standard thermal wind relation for a deep compressible atmosphere. The interior flow organizes in large cyclonically rotating columnar eddies parallel to the rotation axis, which drive upgradient angular momentum eddy fluxes, generating the observed equatorial superrotation. Heat fluxes align with the axis of rotation, and provide a mechanism for the transport of heat poleward, which can cause the observed flat meridional emission. We address the issue of over-forcing which is common in such convection models and analyze the dependence of our results on this; showing that the vertical wind structure is not very sensitive to the Rayleigh number. We also study the effect of rotation, showing how the transition from a rapidly to a slowly rotating system affects the dynamics. 相似文献
806.
Biraja Kumar Sahu Mehmuna Begum M.K. Khadanga Dilip Kr Jha N.V. Vinithkumar R. Kirubagaran 《Marine pollution bulletin》2013,66(1-2):246-251
Port Blair is the capital city of Andaman & Nicobar Islands, the union territory of India. More than 50% of the population of these islands lives around Port Blair Bay. Therefore the anthropogenic effects in the bay water were studied for monitoring purpose from seven stations. Physico-chemical parameters of seawater were analyzed in samples collected once in every 3 months for 2 years from seven sampling stations located in Port Blair Bay, South Andaman Island to evaluate the spatial and tidal variation. Cluster analysis and factor analysis were applied to the experimental data in an attempt to understand the sources of variation of physico-chemical parameters. In cluster analysis, the stations Junglighat Bay and Phoenix Bay having high anthropogenic influence formed a separate group. The factors obtained from factor analysis indicated that the parameters responsible for physico-chemical variations are mainly related to land run-off, sewage outfall and tidal flow. 相似文献
807.
Application of Hilbert‐like transforms for enhanced processing of full tensor magnetic gradient data 下载免费PDF全文
M. Schiffler M. Queitsch R. Stolz H.‐G. Meyer N. Kukowski 《Geophysical Prospecting》2017,65(Z1):68-81
Commonly, geomagnetic prospection is performed via scalar magnetometers that measure values of the total magnetic intensity. Recent developments of superconducting quantum interference devices have led to their integration in full tensor magnetic gradiometry systems consisting of planar‐type first‐order gradiometers and magnetometers fabricated in thin‐film technology. With these systems measuring directly the magnetic gradient tensor and field vector, a significantly higher magnetic and spatial resolution of the magnetic maps is yield than those produced via conventional magnetometers. In order to preserve the high data quality in this work, we develop a workflow containing all the necessary steps for generating the gradient tensor and field vector quantities from the raw measurement data up to their integration into highresolution, lownoise, and artefactless two‐dimensional maps of the magnetic field vector. The gradient tensor components are processed by superposition of the balanced gradiometer signals and rotation into an Earth‐centred Earth‐fixed coordinate frame. As the magnetometers have sensitivity lower than that of gradiometers and the total magnetic intensity is not directly recorded, we employ Hilbert‐like transforms, e.g., integration of the gradient tensor components or the conversion of the total magnetic intensity derived by calibrated magnetometer readings to obtain these values. This can lead to a better interpretation of the measured magnetic anomalies of the Earth's magnetic field that is possible from scalar total magnetic intensity measurements. Our conclusions are drawn from the application of these algorithms on a survey acquired in South Africa containing full tensor magnetic gradiometry data. 相似文献
808.
The time varying conditions in the near-Earth space environment that may affect space-borne or ground-based technological
systems and may endanger human health or life are referred to as space weather. Space weather effects arise from the dynamic
and highly variable conditions in the geospace environment starting from explosive events on the Sun (solar flares), Coronal
Mass Ejections near the Sun in the interplanetary medium, and various energetic effects in the magnetosphere–ionosphere–atmosphere
system. As the utilization of space has become part of our everyday lives, and as our lives have become increasingly dependent
on technological systems vulnerable to the space weather influences, the understanding and prediction of hazards posed by
these active solar events have grown in importance. In this paper, we review the processes of the Sun–Earth interactions,
the dynamic conditions within the magnetosphere, and the predictability of space weather effects on radio waves, satellites
and ground-based technological systems today. 相似文献
809.
810.
G. A. Avanesov R. V. Gordeev V. A. Grishin B. S. Zhukov S. B. Zhukov E. V. Kolomeets E. B. Krasnopevtseva M. I. Kudelin A. A. Krupin V. M. Murav’ev A. A. Forsh 《Solar System Research》2010,44(5):444-450
A TV system for navigation and guidance (TVSNG) has been designed for solving the navigation and scientific tasks of the Phobos-Grunt mission. It consists of two narrow-angle and two wide-angle television cameras. Each camera has a built-in processor for the real-time processing of received images. The program of TVSNG observations includes three modes: Imaging of Stars, Sequential Imaging, and Landing. The first two modes will be used to calibrate the TVSNG against the stars, to take images of Phobos and Mars, and to detect the dust rings of Mars. In the Landing mode, the height and velocity components of the spacecraft during the landing on Phobos will be measured, and an autonomous selection of the landing site will be made. 相似文献