全文获取类型
收费全文 | 58046篇 |
免费 | 562篇 |
国内免费 | 1149篇 |
专业分类
测绘学 | 1997篇 |
大气科学 | 3957篇 |
地球物理 | 10893篇 |
地质学 | 24807篇 |
海洋学 | 4265篇 |
天文学 | 9034篇 |
综合类 | 2284篇 |
自然地理 | 2520篇 |
出版年
2022年 | 388篇 |
2021年 | 591篇 |
2020年 | 573篇 |
2019年 | 659篇 |
2018年 | 6038篇 |
2017年 | 5205篇 |
2016年 | 3864篇 |
2015年 | 808篇 |
2014年 | 1302篇 |
2013年 | 1944篇 |
2012年 | 2380篇 |
2011年 | 4328篇 |
2010年 | 3575篇 |
2009年 | 4111篇 |
2008年 | 3461篇 |
2007年 | 4089篇 |
2006年 | 1596篇 |
2005年 | 1071篇 |
2004年 | 1213篇 |
2003年 | 1190篇 |
2002年 | 1058篇 |
2001年 | 772篇 |
2000年 | 688篇 |
1999年 | 505篇 |
1998年 | 522篇 |
1997年 | 489篇 |
1996年 | 362篇 |
1995年 | 377篇 |
1994年 | 343篇 |
1993年 | 273篇 |
1992年 | 276篇 |
1991年 | 264篇 |
1990年 | 286篇 |
1989年 | 255篇 |
1988年 | 234篇 |
1987年 | 273篇 |
1986年 | 245篇 |
1985年 | 309篇 |
1984年 | 288篇 |
1983年 | 296篇 |
1982年 | 268篇 |
1981年 | 268篇 |
1980年 | 270篇 |
1979年 | 261篇 |
1978年 | 238篇 |
1977年 | 216篇 |
1976年 | 194篇 |
1975年 | 193篇 |
1974年 | 193篇 |
1973年 | 224篇 |
排序方式: 共有10000条查询结果,搜索用时 483 毫秒
171.
North-South asymmetry of the daily interplanetary magnetic field spiral during the period: 1965–1990
I. Sabbah 《Earth, Moon, and Planets》1995,70(1-3):173-178
We have extended our earlier study of the dependance of interplanetary magnetic field (IMF) spiral on the magnetic polarity to cover the 26-year period 1965–1990. Our analysis reveals that: 1. The spiral angle north of the current sheet is higher than south of it. 2. During both of negative solar polarity epochs the IMF spiral is stable; it shows more variation during positive polarity epoch. 3. The included angle is lower than 180° during negative polarity epochs and higher than 180° during positive polarity epoch. 4. The Earth spent more time north of the current sheet during our period of analysis. 相似文献
172.
INTRODUCTIONTheSubeiShoalandtheChangjiangRiverestuarineareainthewestoftheHuanghaiandEastChinaSeasisoneofthemarginalseasintheworld ,wheresuspendedmatterisextremelyhigh .Here ,notonlyistheretheTaiwanWarmCurrentoneoftheKuroshio’sbranchesintheEastChinaSea,butalsotheHuanghaiCoastalCurrent,andChangjiangDilutedWater.Sothestrongmixingbetweenthecoastalandoffshorewaterscomplicatessuspendedmatterdistributioninthisarea.HowthesuspendedmatterdischargedfromtheChangjiangRiverandtheabandonedHuan… 相似文献
173.
FUZZY COMPREHENSIVE EVALUATION OF CONTAINER TRANSPORTATION MODES ALONG THE CHANGJIANG RIVER MAIN LINE AND ITS DELTA AREA 总被引:1,自引:0,他引:1
ZHANGShi-yu XIAOHan-liang 《中国地理科学(英文版)》2003,13(3):259-261
The Changjiang River (Yangtze) is one of the fastest growth areas of container transportation in Chi-na. Rail, road and water transportation have competed against each other for container transportation in the Chang-jiang River main line and its delta area. It is of significance to assess these different transportation modes scientifi-cally in order to organize container transportation efficiently in this area and make decision for integral plan and construction of transportation system in this area. This paper outlines application of fuzzy comprehensive evaluation to appraise different modes of typical direction of containers. Twelve assessment indexes were decided. Membership functions were formulated. Evaluation results indicated that road transportation was optimal mode in the Changjiang River delta area, however water transportation was the primary way in the Changjiang River main line. 相似文献
174.
M. Fiore L. O. Silva C. Ren M. A. Tzoufras W. B. Mori 《Monthly notices of the Royal Astronomical Society》2006,372(4):1851-1855
The dynamics of two counter-streaming electron–positron–ion unmagnetized plasma shells with zero net charge is analysed in the context of magnetic field generation in gamma-ray burst internal shocks due to the Weibel instability. The effects of large thermal motion of plasma particles, arbitrary mixture of plasma species and space charge effects are taken into account. We show that, although thermal effects slow down the instability, baryon loading leads to a non-negligible growth rate even for large temperatures and different shell velocities, thus guaranteeing the robustness and the occurrence of the Weibel instability for a wide range of scenarios. 相似文献
175.
M.L. Litvak I.G. Mitrofanov A.B. Sanin W.V. Boynton D. Hamara R.S. Saunders 《Icarus》2006,180(1):23-37
In this paper, we have analyzed neutron spectroscopy data gathered by the High Energy Neutron Detector (HEND) instrument onboard Mars Odyssey for comparison of polar regions. It is known that observation of the neutron albedo of Mars provides important information about the distribution of water-ice in subsurface layers and about peculiarities of the CO2 seasonal cycle. It was found that there are large water-rich permafrost areas with contents of up to ∼50% water by mass fraction at both the north and south Mars polar regions. The water-ice layers at high northern latitudes are placed close to the surface, but in the south they are covered by a dry and relatively thick (10-20 cm) layer of soil. Analysis of temporal variations of neutron flux between summer and winter seasons allowed the estimation of the masses of the CO2 deposits which seasonally condense at the polar regions. The total mass of the southern seasonal deposition was estimated as 6.3×1015 kg, which is larger than the total mass of the seasonal deposition at the north by 40-50%. These results are in good agreement with predictions from the NASA Ames Research Center General Circulation Model (GCM). But, the dynamics of the condensation and sublimation processes are not quite as consistent with these models: the peak accumulation of the condensed mass of CO2 occurred 10-15 degrees of Ls later than is predicted by the GCM. 相似文献
176.
Based on a topological magnetic field model for active region (AR) 8086 observed on September 15–21, 1997, we calculate the evolution of the magnetic flux imbalance during its disk passage. We have established possible causes of the observed imbalance. Using model ARs produced by perfectly balanced magnetic field sources as examples, we show that even in this case, the observed imbalance can reach a significant value, depending on the AR size and location. The peculiar properties of the magnetic field imbalance in ARs predicted by the topological model must be taken into account when present-day magnetographic observations of the Sun are interpreted. 相似文献
177.
A. D. Biggs D. Rusin I. W. A. Browne A. G. de Bruyn N. J. Jackson L. V. E. Koopmans J. P. McKean S. T. Myers R. D. Blandford K.-H. Chae C. D. Fassnacht M. A. Norbury T. J. Pearson P. M. Phillips A. C. S. Readhead P. N. Wilkinson 《Monthly notices of the Royal Astronomical Society》2003,338(4):1084-1088
178.
Rodger I. Thompson 《Astrophysics and Space Science》2003,284(2):353-356
Tests and constraints on current theories of galaxy formation and evolution are presented. They are derived from observations
of the Northern Hubble Deep Field with WFPC2 and NICMOS. Photometric redshifts, extinctions and spectral energy distributions
are calculated for all objects in the field. The tests and constraints are derived from the output of this analysis. The tests
of the predictions from hierarchical and pure luminosity evolution galaxy evolution calculations favor the hierarchical model.
Constraints are provided by the current luminosity function and its evolution to a redshift of 6.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
179.