全文获取类型
收费全文 | 7861篇 |
免费 | 184篇 |
国内免费 | 244篇 |
专业分类
测绘学 | 214篇 |
大气科学 | 608篇 |
地球物理 | 1615篇 |
地质学 | 2888篇 |
海洋学 | 639篇 |
天文学 | 1868篇 |
综合类 | 31篇 |
自然地理 | 426篇 |
出版年
2023年 | 60篇 |
2022年 | 53篇 |
2021年 | 61篇 |
2020年 | 72篇 |
2019年 | 89篇 |
2018年 | 235篇 |
2017年 | 190篇 |
2016年 | 276篇 |
2015年 | 161篇 |
2014年 | 263篇 |
2013年 | 412篇 |
2012年 | 238篇 |
2011年 | 404篇 |
2010年 | 287篇 |
2009年 | 456篇 |
2008年 | 357篇 |
2007年 | 323篇 |
2006年 | 335篇 |
2005年 | 305篇 |
2004年 | 289篇 |
2003年 | 272篇 |
2002年 | 250篇 |
2001年 | 218篇 |
2000年 | 205篇 |
1999年 | 178篇 |
1998年 | 168篇 |
1997年 | 161篇 |
1996年 | 154篇 |
1995年 | 137篇 |
1994年 | 114篇 |
1993年 | 92篇 |
1992年 | 78篇 |
1991年 | 87篇 |
1990年 | 78篇 |
1989年 | 86篇 |
1988年 | 59篇 |
1987年 | 101篇 |
1986年 | 64篇 |
1985年 | 64篇 |
1984年 | 69篇 |
1983年 | 71篇 |
1982年 | 72篇 |
1981年 | 68篇 |
1980年 | 54篇 |
1979年 | 51篇 |
1977年 | 48篇 |
1976年 | 47篇 |
1975年 | 35篇 |
1974年 | 30篇 |
1973年 | 41篇 |
排序方式: 共有8289条查询结果,搜索用时 15 毫秒
21.
The sway, heave and roll added masses of three uniform cylinders with semi-circular, rectangular and triangular cross-sectional shapes in shallow and narrow water are numerically analysed. The method is based on simulation of the potential flow induced by the cylinder's mode of motion. The effects of shallow and narrow water on added mass are analysed and presented. It is concluded that the shallow and narrow water effects on added mass depend on the different cross-section shapes of the cylinders. In particular, the water depth effect on sway added mass is stronger than that on heave added mass while the narrow water effect on sway is weaker than that on heave. The shallow water effect on added mass tends to weaken the narrow water effect. Lastly the effect of shallow and narrow water on added mass on a rectangular cylinder is the strongest while that on a triangular cylinder is the weakest. 相似文献
22.
A series of batch tests have been presented to investigate the effects of solid-solution contact time, solid:solution ratio, and pH of solution on sorption of Cd2+ and Pb2+ on Ariake clay from Kyushu region of Japan. The results show that, among the three investigated factors, solid:solution ratio (SD/SN) seems to be the crucial controlling factor. The Freundlich sorption parameters determined from the batch tests were applied to a typical field landfill in which the Ariake clay was used as soil barrier. The impacts of the landfill were assessed by numerical analysis. Based on the analysis result, the significance of selecting proper solid:solution ratio for determining sorption parameters from batch test has been discussed. 相似文献
23.
Y. M. Wang 《Journal of Geodesy》1990,64(3):231-246
The method of analytical downward continuation has been used for solving Molodensky’s problem. This method can also be used
to reduce the surface free air anomaly to the ellipsoid for the determination of the coefficients of the spherical harmonic
expansion of the geopotential. In the reduction of airborne or satellite gradiometry data, if the sea level is chosen as reference
surface, we will encounter the problem of the analytical downward continuation of the disturbing potential into the earth,
too. The goal of this paper is to find out the topographic effect of solving Stoke’sboundary value problem (determination
of the geoid) by using the method of analytical downward continuation.
It is shown that the disturbing potential obtained by using the analytical downward continuation is different from the true
disturbing potential on the sea level mostly by a −2πGρh 2/p. This correction is important and it is very easy to compute
and add to the final results. A terrain effect (effect of the topography from the Bouguer plate) is found to be much smaller
than the correction of the Bouguer plate and can be neglected in most cases.
It is also shown that the geoid determined by using the Helmert’s second condensation (including the indirect effect) and
using the analytical downward continuation procedure (including the topographic effect) are identical. They are different
procedures and may be used in different environments, e.g., the analytical downward continuation procedure is also more convenient
for processing the aerial gravity gradient data.
A numerical test was completed in a rough mountain area, 35°<ϕ<38°, 240°<λ<243°. A digital height model in 30″×30″ point value
was used. The test indicated that the terrain effect in the test area has theRMS value ±0.2−0.3 cm for geoid. The topographic effect on the deflections of the vertical is around1 arc second. 相似文献
24.
Four groups of thermal springs with temperatures from 50 to 80 °C are located on the S–SW–W slopes of El Chichón volcano, a composite dome-tephra edifice, which exploded in 1982 with a 1 km wide, 160 m deep crater left. Very dynamic thermal activity inside the crater (variations in chemistry and migration of pools and fumaroles, drastic changes in the crater lake volume and chemistry) contrasts with the stable behavior of the flank hot springs during the time of observations (1974–2005). All known groups of hot springs are located on the contact of the basement and volcanic edifice, and only on the W–SW–S slopes of the volcano at almost same elevations 600–650 m asl and less than 3 km of direct distance from the crater. Three groups of near-neutral (pH ≈ 6) springs at SW–S slopes have the total thermal water outflow rate higher than 300 l/s and are similar in composition. The fourth and farthest group on the western slope discharges acidic (pH ≈ 2) saline (10 g/kg of Cl) water with a much lower outflow rate (< 10 l/s). 相似文献
25.
26.
Marcela Laštovičková Y. V. Ramana B. S. Gogte Reviewer A. Janáčková 《Studia Geophysica et Geodaetica》1987,31(1):60-72
Summary Results on electrical conductivity, chemical analysis and age of the rock samples from the Indian Subcontinent are presented. The old Precambrian Indian rocks tend to be less conductive than characteristic rocks of crustal and upper mantle structures.
nuam mam uu mnm¶rt;mu, uu aaua u n¶rt;u u uu n¶rt; u ¶rt;uu. ma nauu n¶rt; u ¶rt;uu naam mn¶rt;m aamumuu n¶rt; u amuu.相似文献
27.
2021年1月20日,民主党人拜登宣誓就任美国第46届总统,上任第一天就签署行政指令重新加入《巴黎协定》.根据《巴黎协定》要求,美国于递交国家批准函30天后,也就是2021年2月19日正式重新加入《巴黎协定》,实现美国气候政治转向.拜登政府的气候政策尚未完全清晰,但其发布的"国内国际应对气候危机行政指令"[1]可以为分... 相似文献
28.
O. Ozutsumi S. Sawada S. Iai Y. Takeshima W. Sugiyama T. Shimazu 《Soil Dynamics and Earthquake Engineering》2002,22(9-12):1075-1082
A series of effective stress analyses is carried out on the seismic performance of river dikes based on the case histories during the 1993 Hokkaido-Nansei-oki and 1995 Hyogoken-Nambu earthquakes in Japan. Seven case histories selected for the analyses involve a crest settlement ranging from none to 2.7 m in the dikes 3–6 m high with evidence of liquefaction at foundation soil. The effective stress model used is based on a multiple shear mechanism and was developed by one of the authors. The soil parameters are evaluated based on the site investigation and laboratory test results. The results of the analyses are basically consistent with the observed performance of the river dikes. In particular, the effective stress model shows a reasonable capability to reproduce the varying degree of settlements depending on the geotechnical conditions of foundation soils beneath the dikes. The analyses also indicate that the effect of a cohesive soil layer mixed with the liquefiable sand layers beneath the dikes can be a primary factor for reducing the liquefaction-induced deformation of dikes. 相似文献
29.
Ole B. Andersen Gary D. Egbert Svetlana Y. Erofeeva Richard D. Ray 《Ocean Dynamics》2006,56(5-6):416-429
Overtides and compound tides are generated by nonlinear mechanisms operative primarily in shallow waters. Their presence complicates
tidal analysis owing to the multitude of new constituents and their possible frequency overlap with astronomical tides. The
science of nonlinear tides was greatly advanced by the pioneering researches of Christian Le Provost who employed analytical
theory, physical modeling, and numerical modeling in many extensive studies, especially of the tides of the English Channel.
Le Provost’s complementary work with satellite altimetry motivates our attempts to merge these two interests. After a brief
review, we describe initial steps toward the assimilation of altimetry into models of nonlinear tides via generalized inverse
methods. A series of barotropic inverse solutions is computed for the M tide over the northwest European Shelf. Future applications of altimetry to regions with fewer in situ measurements will
require improved understanding of error covariance models because these control the tradeoffs between fitting hydrodynamics
and data, a delicate issue in coastal regions. While M can now be robustly determined along the Topex/Poseidon satellite ground tracks, many other compound tides face serious aliasing
problems.
In memory of Christian Le Provost 相似文献
30.
Abstract The Taiwan orogen has been the focus of a number of models of mountain building processes, but little attention has been paid to high‐pressure (HP) metamorphic rocks that are found as exotic blocks intermingled within the deepest units of the mountain belt. In this study, we re‐appraise from updated petrological and thermodynamic databases the physical conditions of HP metamorphism in Taiwan, and we combine our findings with available geochronological data to estimate the thermal history of these rocks. Our results indicate that peak metamorphic conditions of ~550 °C and 10–12 kbar have been followed by a rapid isothermal decompression, with exhumation possibly as rapid as burial. These units have subsequently been stored at a pressure of ~3 kbar for ~4–5 Myr, before their final exhumation, probably facilitated by the accretion of passive margin sequences during the Late Cenozoic collision. Therefore, HP units in Taiwan maintain a record of processes at depth from the early stages of oceanic subduction to the present arc‐continent collision. 相似文献