全文获取类型
收费全文 | 13118篇 |
免费 | 2396篇 |
国内免费 | 2191篇 |
专业分类
测绘学 | 2320篇 |
大气科学 | 1262篇 |
地球物理 | 3737篇 |
地质学 | 6251篇 |
海洋学 | 1437篇 |
天文学 | 391篇 |
综合类 | 732篇 |
自然地理 | 1575篇 |
出版年
2024年 | 36篇 |
2023年 | 129篇 |
2022年 | 380篇 |
2021年 | 521篇 |
2020年 | 566篇 |
2019年 | 486篇 |
2018年 | 479篇 |
2017年 | 647篇 |
2016年 | 608篇 |
2015年 | 607篇 |
2014年 | 831篇 |
2013年 | 1023篇 |
2012年 | 797篇 |
2011年 | 859篇 |
2010年 | 725篇 |
2009年 | 862篇 |
2008年 | 984篇 |
2007年 | 834篇 |
2006年 | 906篇 |
2005年 | 749篇 |
2004年 | 647篇 |
2003年 | 524篇 |
2002年 | 519篇 |
2001年 | 408篇 |
2000年 | 360篇 |
1999年 | 350篇 |
1998年 | 315篇 |
1997年 | 257篇 |
1996年 | 208篇 |
1995年 | 182篇 |
1994年 | 171篇 |
1993年 | 164篇 |
1992年 | 134篇 |
1991年 | 100篇 |
1990年 | 93篇 |
1989年 | 55篇 |
1988年 | 58篇 |
1987年 | 25篇 |
1986年 | 21篇 |
1985年 | 12篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 3篇 |
1978年 | 18篇 |
1977年 | 6篇 |
1972年 | 1篇 |
1954年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
21.
概略地叙述了西宁地区的泥石流形成条件和形成机理,并将西宁地区泥石流划分为稀性泥石流类及泥石质泥石流种类。在此基础上提出防治泥石流灾害的意见。 相似文献
22.
Virtual Huanghe River System: Framework and Technology 总被引:2,自引:0,他引:2
LU Heli LIU Guifang SUN Jiulin 《中国地理科学(英文版)》2006,16(3):255-259
1 Introduction Huanghe (Yellow) River basin is located in 32°–42°N, 96°–119°E. The area of the catchment is more than 752,000km2. The river is 5464km long with a drop in elevation of 4830m. Among the whole area, the moun- tainous and stone area accounts for 29%, loess and hills area 46%, sandy area 11% and plain area 14%, respec- tively. Different natural landscapes exist in this area. The Huanghe River flows through the Loess Plateau, where the soil is eroded seriously (Wang, 2002;… 相似文献
23.
通过将车流量的增大或减小转化为路长权重的变化。将交通流量的动态问题转化为静态问题,用解决最短路问题的Dijkstra方法,给出交通流量实时最优控制的可行性模型及其有效算法。 相似文献
24.
WANGXie-kang HUANGEr CUIPeng 《中国地理科学(英文版)》2003,13(3):262-266
Debris flow is one of the most destructive phenomena of natural hazards. Recently, major natural haz-ard, claiming human lives and assets, is due to debris flow in the world. Several practical methods for forecasting de-bris flow have been proposed, however, the accuracy of these methods is not high enough for practical use because of the stochastic and non-linear characteristics of debris flow. Artificial neural network has proven to be feasible and use-fill in developing models for nonlinear systems. On the other hand, predicting the future behavior based on a time se-ries of collected historical data is also an important tool in many scientific applications. In this study we present a three-layer feed-forward neural network model to forecast surge of debris flow according to the time series data collect-ed in the Jiangjia Ravine, situated in north part of Yunnan Province of China. The simulation and prediction of debris flow using the proposed approach shows this model is feasible, however, further studies are needed. 相似文献
25.
We report the first detection, with Chandra , of X-ray emission from the jet of the powerful narrow-line radio galaxy 3C 346. X-rays are detected from the bright radio and optical knot at which the jet apparently bends by approximately 70°. The Chandra observation also reveals a bright galaxy-scale atmosphere within the previously known cluster and provides a good X-ray spectrum for the bright core of 3C 346. The X-ray emission from the knot is synchrotron radiation, as seen in lower-power sources. In common with these sources, there is evidence of morphological differences between the radio/optical and X-ray structures, and the spectrum is inconsistent with a one-component continuous-injection model. We suggest that the X-ray-bright knot is associated with a strong oblique shock in a moderately relativistic, light jet, at ∼ 20° to the line of sight, and that this shock is caused by the jet interacting with the wake in the cluster medium behind the companion galaxy of 3C 346. The general jet curvature can result from pressure gradients in the cluster atmosphere. 相似文献
26.
王大新 《地球信息科学学报》2001,3(2):25-28
计算机制图(CAC)和电子出版系统的普及和推广,从根本上改变了传统的地图生产工艺。本文结合制图实践,讨论了应用Coreldraw图形软件编辑出版专题地图的适应性、系统条件和工艺流程,并总结了一些制图经验和应该注意的若干问题。 相似文献
27.
28.
M. J. Hardcastle M. Birkinshaw D. M. Worrall 《Monthly notices of the Royal Astronomical Society》2001,323(2):L17-L22
Chandra X-ray Observatory observations of the powerful, peculiar radio galaxy 3C 123 have resulted in an X-ray detection of the bright eastern hotspot, with a 1-keV flux density of ∼5 nJy. The X-ray flux and spectrum of the hotspot are consistent with the X-rays being inverse-Compton scattering of radio synchrotron photons by the population of electrons responsible for the radio emission ('synchrotron self-Compton emission') if the magnetic fields in the hotspot are close to their equipartition values. 3C 123 is thus the third radio galaxy to show X-ray emission from a hotspot which is consistent with being in equipartition. Chandra also detects emission from a moderately rich cluster surrounding 3C 123, with L X (2–10 keV)=2×1044 erg s−1 and kT ∼5 keV, and absorbed emission from the active nucleus, with an inferred intrinsic column density of 1.7×1022 cm−2 and an intrinsic 2–10 keV luminosity of 1044 erg s−1 . 相似文献
29.
This paper presents a method that incorporates a non‐associated flow rule into the limit analysis to investigate the influence of the dilatancy angle on the factor of safety for the slope stability analysis. The proposed method retain's the advantage of the upper bound method, which is simple and has no stress involvement in the calculation of the energy dissipation and the factor of safety. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
30.
LUO Kai-li LI Bao-sheng ZHU Yi-zhi JIN He-ling ZHANG David Dian YAN Man-cun LI Hou-xin YAO Chun-xia ZHANG Yu-hongf . Department of Geography South China Normal University Guangzhou P. R. China . State Key Labor 《中国地理科学(英文版)》2001,11(4):336-342
About 70years ago,Frenc卜卜alaeohdoglst回LL sc卜dars al卜ome and a卜road卜ave successively con-HARD de Chardin P.et al.Initiated the Quaternary ducted large amount ofwork on the Later Quaternarygeologlcal research In the >alawusu River Basin of strata(TEILHARD,1924; YUAN,1978; LI,1987;desert region of Northern China and established th,ZHENG,1989; SUN et al,1996; LI et al,1993),Salawusu Formation门EILHARD,1924).Sine,then,palaeobiology… 相似文献