全文获取类型
收费全文 | 74010篇 |
免费 | 1230篇 |
国内免费 | 730篇 |
专业分类
测绘学 | 1886篇 |
大气科学 | 5375篇 |
地球物理 | 14152篇 |
地质学 | 26481篇 |
海洋学 | 6537篇 |
天文学 | 17318篇 |
综合类 | 224篇 |
自然地理 | 3997篇 |
出版年
2022年 | 429篇 |
2021年 | 736篇 |
2020年 | 804篇 |
2019年 | 864篇 |
2018年 | 1923篇 |
2017年 | 1840篇 |
2016年 | 2288篇 |
2015年 | 1310篇 |
2014年 | 2219篇 |
2013年 | 3820篇 |
2012年 | 2387篇 |
2011年 | 3134篇 |
2010年 | 2716篇 |
2009年 | 3598篇 |
2008年 | 3072篇 |
2007年 | 3137篇 |
2006年 | 2935篇 |
2005年 | 2249篇 |
2004年 | 2271篇 |
2003年 | 2148篇 |
2002年 | 2034篇 |
2001年 | 1830篇 |
2000年 | 1726篇 |
1999年 | 1440篇 |
1998年 | 1492篇 |
1997年 | 1404篇 |
1996年 | 1181篇 |
1995年 | 1130篇 |
1994年 | 1006篇 |
1993年 | 886篇 |
1992年 | 862篇 |
1991年 | 820篇 |
1990年 | 873篇 |
1989年 | 725篇 |
1988年 | 700篇 |
1987年 | 790篇 |
1986年 | 702篇 |
1985年 | 891篇 |
1984年 | 1003篇 |
1983年 | 923篇 |
1982年 | 851篇 |
1981年 | 782篇 |
1980年 | 752篇 |
1979年 | 727篇 |
1978年 | 739篇 |
1977年 | 605篇 |
1976年 | 583篇 |
1975年 | 607篇 |
1974年 | 528篇 |
1973年 | 559篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
F. Molenkamp 《国际地质力学数值与分析法杂志》1991,15(3):147-168
To increase the insight into the phenomenon of liquefaction a theoretical study has been performed of material instability for undrained behaviour. Material instability concerns the instability of an equilibrium state of an infinite homogeneous solid for both uniform deformation and shear-band generation. In this paper shear-band generation is considered. In a companion paper the case of uniform deformation is elaborated and combined with the current results. In this paper it is shown that, for a contractant material, shear-band generation is accelerated by decreasing the drainage. 相似文献
92.
The axisymmetric elastic response of circular footings and anchor plates in a linearly non-homogeneous elastic soil is analysed. It is assumed that footings/anchors are flexible and subjected to axisymmetric vertical loads. The response of the footing/anchor is modelled by using the classical Poisson–Kirchhoff thin plate theory. A variational technique is used to analyse the interaction problem. A representation for the contact stress is established by using a fundamental solution corresponding to a unit vertical pressure acting over an annular region in the interior of the non-homogeneous soil. The fundamental solution can be derived by using rigorous analytical procedures. The influence of the footing flexibility and the degree of soil non-homogeneity on the displacements, bending moments and contact stresses of a surface footing is examined over a wide range of governing parameters. In the case of anchor plates the influence of depth of embedment, degree of soil non-homogeneity and anchor flexibility on the anchor displacement is investigated. 相似文献
93.
I.A. Bond F. Abe R.J. Dodd J.B. Hearnshaw M. Honda J. Jugaku P.M. Kilmartin A. Marles K. Masuda Y. Matsubara Y. Muraki T. Nakamura G. Nankivell S. Noda C. Noguchi K. Ohnishi N.J. Rattenbury M. Reid To. Saito H. Sato M. Sekiguchi J. Skuljan D.J. Sullivan T. Sumi M. Takeuti Y. Watase S. Wilkinson R. Yamada T. Yanagisawa P.C.M. Yock 《Monthly notices of the Royal Astronomical Society》2001,327(3):868-880
We describe observations carried out by the MOA group of the Galactic bulge during 2000 that were designed to detect efficiently gravitational microlensing of faint stars in which the magnification is high and/or of short duration. These events are particularly useful for studies of extrasolar planets and faint stars. Approximately 17 deg2 were monitored at a sampling rate of up to six times per night. The images were analysed in real time using a difference imaging technique. 20 microlensing candidates were detected, of which eight were alerted to the microlensing community whilst in progress. Approximately half of the candidates had high magnifications (≳10), at least one had very high magnification (≳50), and one exhibited a clear parallax effect. The details of these events are reported here, together with details of the on-line difference imaging technique. Some nova-like events were also observed and these are described, together with one asteroid. 相似文献
94.
Richard T. Jones Jim D. Marshall Stephen F. Crowley Alan Bedford Nigel Richardson Jan Bloemendal Frank Oldfield 《第四纪科学杂志》2002,17(4):329-340
A lacustrine carbonate sequence from Hawes Water, Lancashire, UK, has been studied using stable isotopic, lithological, pollen and mineral magnetic analysis. The data reveal four abrupt climatic oscillations in the Late‐glacial Interstadial leading up to the onset of the Loch Lomond Stadial. The data also point to climatic warming relatively early within the stadial, ca. 12 500 GRIP yr, prior to the onset of the Holocene. The oxygen isotope record is taken as a signature of climate forcing against which the response of the lake‐system can be monitored. By adopting this approach it is revealed that the response of the biological system to the rapid climatic oscillations is non‐linear and primarily a function of the antecedent conditions. A significant end‐Devensian isotopic excursion (A) is matched by only minor changes in the cold‐adapted floras and faunas. During the warmer interstadial, the response of the biological ecosystem (events B–D) is clearly influenced by thresholds: major changes in the catchment vegetation associated with relatively minor oscillations in the isotopic signature. The stratigraphical patterns reveal significant lag effects between the onset of climate deterioration and resulting changes in vegetation. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
95.
96.
Jonathan S. Price 《水文研究》1994,8(2):167-177
Over an oceanic peatland, the concentration of Na in fog averaged 38.1 mgl?1 compared with 1.8 mgl?1 in rain, resulting in a significant flux of mineral elements to the surface. Between 16 May and 20 June 1990 the average mass flux of Na to the bog surface by fog, rain, and dry deposition was 21.9, 10.4 and 7.0 mg m?2 d?1. There was little long-term storage of Na within the peatland system, where Na losses measured in stream runoff averaged 34.8 mg m2 d?1, and deep groundwater losses 4 mg m?2 d?1. Calcium and Mg were preferentially retained in the organic soil, whereas K was relatively mobile. Potassium tended to become concentrated in the unsaturated zone. Stream runoff had a consistently higher pH than groundwater, corresponding to higher Ca and Mg concentrations, which may have been from mineral sources in the headwater ponds. Otherwise, the stream water chemistry was closely related to groundwater in the upper layers of the peat deposit. 相似文献
97.
We report on SWS and LWS observations of the circumstellar disks of young stars of a few solar masses. The ISO spectra of
these objects present a diversity of emission features of carbon-rich and oxygen-rich grains. The similarity of the forsterite
spectra observed for Comet Hale-Bopp and the Haebe star HD100546 is particularly striking and provides a new argument that
huge comet swarms are formed in the disks surrounding young stars. While the data suggest that the formation of crystalline
silicates in the dust disks essentially occurs when a Haebe star has already reached the main sequence, no clear correlation
with stellar age only is apparent.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
98.
Generally speaking, variable stars are monitored through observing campaigns which coordinate multi-site telescopes at various
longitudes. A new practice is in progress: devoted networks involving robotic telescopes. We will review these two technologies
and will emphasize the NORT (Network of Oriental Robotic Telescopes) project which we are promoting in North Africa, Middle-Eastern
countries and Asia.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
99.
G. S. Sahakian 《Astrophysics》1997,40(1):77-82
The problem of the equation of state of cosmic matter is discussed and the constants of integration in the Friedmann solutions
are determined.
Translated from Astrofizika, Vol. 40, No. 1, pp. 117–124, January–March, 1997. 相似文献
100.
Published in Astrofizika, Vol. 38, No. 4, pp. 677–680, October–December, 1995. 相似文献