全文获取类型
收费全文 | 52413篇 |
免费 | 8714篇 |
国内免费 | 11063篇 |
专业分类
测绘学 | 6119篇 |
大气科学 | 7099篇 |
地球物理 | 8540篇 |
地质学 | 26142篇 |
海洋学 | 5945篇 |
天文学 | 3450篇 |
综合类 | 3979篇 |
自然地理 | 10916篇 |
出版年
2024年 | 246篇 |
2023年 | 715篇 |
2022年 | 1982篇 |
2021年 | 2299篇 |
2020年 | 2199篇 |
2019年 | 2801篇 |
2018年 | 2009篇 |
2017年 | 2344篇 |
2016年 | 2381篇 |
2015年 | 2614篇 |
2014年 | 3228篇 |
2013年 | 3321篇 |
2012年 | 3348篇 |
2011年 | 3436篇 |
2010年 | 2843篇 |
2009年 | 3404篇 |
2008年 | 3342篇 |
2007年 | 3515篇 |
2006年 | 3422篇 |
2005年 | 3147篇 |
2004年 | 2774篇 |
2003年 | 2496篇 |
2002年 | 2143篇 |
2001年 | 1842篇 |
2000年 | 1830篇 |
1999年 | 1576篇 |
1998年 | 1366篇 |
1997年 | 1012篇 |
1996年 | 827篇 |
1995年 | 718篇 |
1994年 | 687篇 |
1993年 | 572篇 |
1992年 | 444篇 |
1991年 | 348篇 |
1990年 | 250篇 |
1989年 | 183篇 |
1988年 | 147篇 |
1987年 | 97篇 |
1986年 | 59篇 |
1985年 | 51篇 |
1984年 | 30篇 |
1983年 | 23篇 |
1982年 | 16篇 |
1981年 | 14篇 |
1980年 | 13篇 |
1979年 | 10篇 |
1978年 | 17篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1954年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
182.
Tony T. Gregg Amanda Dewees Drema Gross Bill Hoffman Dan Strub Matt Watson 《中国海洋大学学报(英文版)》2006,5(4):375-380
1Water LossInitiativesUnaccounted-for water(or unbilled water)has beenreceiving newscrutiny at both the state and nationallevels.For years,water conservationeffortsin Europehave emphasized reduction in water loss to a muchgreater extent thaninthe United S… 相似文献
183.
Aharon Kellerman 《The Professional geographer》1985,37(2):133-143
Of the several classifications of services, each emphasizes different characteristics. The International Standard Industrial Classification (ISIC) is used for a comparative study on the transformation into service economies of the U.S., Canada, Great Britain, France, West Germany, Italy and Japan. Service economies are defined as national economies in which employment in services surpassed that in manufacturing. The pace of the evolution of service economies has been rapid with North America leading, followed in order by Great Britain, France, Italy, Japan and West Germany. Service economies have important implications for urban growth, intercity competition, and international trade. 相似文献
184.
Variables related to urban park awareness are identified and methods for relaxing assumptions of perfect information in park use models are discussed. Park awareness is related to park characteristics (age and degree of development of the park), population characteristics (race, age, length of residence, recreation participation), and distance. Park attributes are stronger predictors of both park awareness and use than is distance. These findings parallel similar research on the cognitive aspects of shopping decisions. 相似文献
185.
Natalia Babkovskaia Juri Poutanen Anita M. S. Richards Ryszard Szczerba 《Monthly notices of the Royal Astronomical Society》2006,370(4):1921-1927
The silicate carbon star V778 Cyg is a source of 22-GHz water maser emission which was recently resolved by MERLIN. Observations revealed an elongated -like structure along which the velocities of the maser features show a linear dependence on the impact parameter. This is consistent with a doubly warped m = 2 disc observed edge-on. Water masers and silicate dust emission (detected by the Infrared Astronomical Satellite and Infrared Space Observatory ) have a common origin in O-rich material and are likely to be co-located in the disc. We propose a detailed self-consistent model of a masing gas–dust disc around a companion to the carbon star in a binary system, which allows us to estimate the companion mass of 1.7 ± 0.1 M⊙ , the disc radius of 40 ± 3 au and the distance between companions of ∼80 au. Using a dust–gas coupling model for water masing, we calculate the maser power self-consistently, accounting for both the gas and the dust energy balances. Comparing the simulation results with the observational data, we deduce the main physical parameters of the masing disc, such as the gas and dust temperatures and their densities. We also present an analysis of the stability of the disc. 相似文献
186.
187.
《The Professional geographer》1987,39(1):85-94
Reviews of geographic software in this article: DEMO-GRAPHICS: WORLD POPULATIONS AND PROJECTIONS. ESP GAUSS. CEMODEL S. Damus LIMDEP. William H. Greene MICROSTAT 4.1 OTIS PCIPS. (Personal Computer Image Processing System) . H.J. Meyers and R. Bernstein. REGRESSION ANALYSIS OF TIME SERIES (RATS) SPSS/PC+ URBAN DATA MANAGEMENT SOFTWARE (UDMS) 相似文献
188.
Stable oxygen isotope analysis and measurement of several dissolved cations and anions of bulk meltwater samples have provided information about the hydrochemical environment of the glacial hydrological system at Imersuaq Glacier, an outlet tongue from the Greenland ice‐sheet, West Greenland. The samples were collected at frequent intervals during the period 20–28 July 2000 in a small (<20 L s?1) englacial meltwater outlet at the glacier margin. The results document the following findings: (i) a marked diurnal variation of δ18O is related to the composition of oxygen isotope provenances, mainly near‐marginal local superimposed ice and basal up‐sheared ice further up‐glacier; (ii) a relationship is seen between all base cations (Na+, K+, Ca2+, Mg2+), SO42? and δ18O, indicating that solute acquisition is provided by solid–solution contact with the up‐sheared ice—as the relationship with Cl? is weak the influence of seasalt‐derived solutes is small in the area; (iii) when the melt rate is high, two diurnal maxima of δ18O values and solute concentrations are measured, and it is suggested that a snow meltwater component is responsible for the second maximum of δ18O—a short residence time leads to a delayed decrease in ion concentrations. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
189.
190.