全文获取类型
收费全文 | 34673篇 |
免费 | 117篇 |
国内免费 | 137篇 |
专业分类
测绘学 | 940篇 |
大气科学 | 2378篇 |
地球物理 | 5778篇 |
地质学 | 15899篇 |
海洋学 | 2598篇 |
天文学 | 6043篇 |
综合类 | 201篇 |
自然地理 | 1090篇 |
出版年
2022年 | 144篇 |
2021年 | 206篇 |
2020年 | 191篇 |
2019年 | 228篇 |
2018年 | 3534篇 |
2017年 | 3249篇 |
2016年 | 2083篇 |
2015年 | 313篇 |
2014年 | 445篇 |
2013年 | 607篇 |
2012年 | 1564篇 |
2011年 | 3294篇 |
2010年 | 3065篇 |
2009年 | 3238篇 |
2008年 | 2584篇 |
2007年 | 3249篇 |
2006年 | 539篇 |
2005年 | 793篇 |
2004年 | 688篇 |
2003年 | 748篇 |
2002年 | 547篇 |
2001年 | 275篇 |
2000年 | 292篇 |
1999年 | 170篇 |
1998年 | 184篇 |
1997年 | 171篇 |
1996年 | 115篇 |
1995年 | 131篇 |
1994年 | 115篇 |
1993年 | 97篇 |
1992年 | 71篇 |
1991年 | 98篇 |
1990年 | 98篇 |
1989年 | 68篇 |
1988年 | 79篇 |
1987年 | 99篇 |
1986年 | 80篇 |
1985年 | 107篇 |
1984年 | 95篇 |
1983年 | 105篇 |
1982年 | 86篇 |
1981年 | 95篇 |
1980年 | 118篇 |
1979年 | 88篇 |
1978年 | 87篇 |
1977年 | 77篇 |
1976年 | 63篇 |
1975年 | 63篇 |
1974年 | 71篇 |
1973年 | 64篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
Presented are the technique and results of studying the landscape structure of the north-west of Western Siberia on the basis of the Hansen mosaic dataset consisting of elements covering the entire territory of the Earth. To study this area used a synthesis of classical methods of thematic system mapping as described in the doctrine of geosystems of V. B. Sochava, and automated interpretation of remote sensing data and mapping using GIS technologies. The method of geoinformational mapping of the landscape structure with the use of MultiSpec and Quantum GIS software programs for the purpose of drawing up real-time raster landscape maps is shown. In drawing up the map and the legend, the principle of geomic system-hierarchical representation of the territory as a complex multi-level “bottom-up” structure from topological-level geosystems (groups and classes of landscape facies) to regional-level geosystems (geoms, groups and classes of geoms) was used. Compilation of operational raster landscape maps of the north-west of Western Siberia involved multilevel automated interpretation of the Hansen mosaic dataset and mapping of areas (clusters) on images with different brightness characteristics, with the landscape structure of key areas and stationary physical and geographical profiles. A characteristic of this approach also implies using a dynamic classification of geosystems based on the study of their variable states. Such an approach permits a monitoring of changes in landscape structure and its areas and the intensity of anthropogenic impacts on forest and marsh landscapes, and determination of permissible pressure on geosystems in areas with high technogenic pressure of the oil and gas complex represented by the north-west of Siberia. An automated processing of data based on a supervised classification of territorial objects allows for the elimination of inaccuracies arising in visual image interpretation. Raster landscape maps can be used both for a further generation of vector maps and as a real-time information base for purposes of environmental management and protection. 相似文献
132.
133.
A. E. Volvach A. A. Berezhnoi L. N. Volvach I. D. Strepka E. A. Volvach 《Bulletin of the Crimean Astrophysical Observatory》2011,107(1):122-124
Investigations on OH maser lines in comets have been performed with the RT-22 at CrAO. The results of observations of 9P/Temper1
and Lulin C/2007 N3 comets in the OH molecule line at a wavelength of 18 cm are presented. An original technique for observation
data analysis has been developed. The gas production rate of OH molecules in these comets is estimated. 相似文献
134.
Manasi Buzar Baruah Samiran Chatterjee Madhurjya P. Bora 《Astrophysics and Space Science》2010,325(2):217-225
In this work, we consider radiation (thermal) instability in a weakly ionized plasma with continuous ionization and recombination.
The situation can be visualized in the case of envelopes of planetary nebulae, which are envelopes of ionized plasmas surrounding
red giant stars. Various observations report continuous photoionization of these plasmas by the highly energetic streams of
photons emanating from the parent star. Recently, it has been shown that thermal instability can be a probable candidate in
such plasmas for the existence of small scale structures (viz., striations) whose kinematic age is much smaller than that
of the parent nebula. We therefore report a systematic study of these plasmas with photoionization and determine the instability
domain. We have shown that the continuous ionization and recombination may lead to modification of the underlying instability,
which may limit the size of the small structures that are believed to form from these instabilities, and may thus provide
an explanation of the physical processes responsible for the existence of these structures. We further show that in many cases
the system bifurcates to an ovserstable (growing wave) state from a condensation instability (monotonic) and vice versa. 相似文献
135.
Yu Liu Hiroki Kurokawa Chang Liu David H. Brooks Jingping Dun Takako T. Ishii Hongqi Zhang 《Solar physics》2007,240(2):253-262
Vector magnetograms taken at Huairou Solar Observing Station (HSOS) and Mees Solar Observatory (MSO) reveal that the super
active region (AR) NOAA 10486 was a complex region containing current helicity flux of opposite signs. The main positive sunspots
were dominated by negative helicity fields, while positive helicity patches persisted both inside and around the main positive
sunspots. Based on a comparison of two days of deduced current helicity density, pronounced changes associated with the occurrence
of an X10 flare that peaked at 20:49 UT on 29 October 2003 were noticed. The average current helicity density (negative) of
the main sunspots decreased significantly by about 50%. Accordingly, the helicity densities of counter-helical patches (positive)
were also found to decay by the same proportion or more. In addition, two hard X-ray (HXR) “footpoints” were observed by the
Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) during the flare in the 50 – 100 keV energy range. The cores
of these two HXR footpoints were adjacent to the positions of two patches with positive current helicity that disappeared
after the flare. This strongly suggested that the X10 flare on 29 October 2003 resulted from reconnection between magnetic
flux tubes having opposite current helicity. Finally, the global decrease of current helicity in AR 10486 by ∼50% can be understood
as the helicity launched away by the halo coronal mass ejection (CME) associated with the X10 flare.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
136.
A. F. Morozov B. N. Khakhaev O. V. Petrov V. I. Gorbachev G. V. Tarkhanov L. D. Tsvetkov Yu. M. Erinchek A. M. Akhmedov V. A. Krupenik K. Yu. Sveshnikova 《Doklady Earth Sciences》2010,435(1):1483-1486
A thick (200 m) rock salt mass covering Late Archean granitoids was exposed for the first time in the Early Proterozoic volcanogenic-sedimentary
formations in the Onega trough of the east Baltic Shield by the Onega parametric well. The mineral composition of salts, their
geochemical features, and the isotopic composition of carbonate carbon and oxygen have been studied. After fluid inclusions
present in salts, their metamorphism temperature and isotopic composition of helium and argon were determined. The obtained
results give evidence of the fact that rock salts and magnesites associated with them were formed in an evaporate basin with
participation of deep crustal processes. The age of the underlying granitoids (2.716 ± 9 Ma) is determined using the Pb—Pb
method. 相似文献
137.
138.
Coefficients of atmospheric extinction in the Johnson-Cousins system are determined for the astronomical point at Mount Koshka
(Simeiz, Crimea). The astronomical point is characterized by high transparency and frequent periods of low quality of the
image, which is explained by its position between the Crimean Range and the Black Sea. 相似文献
139.
The effect of particle-particle interaction on the adiabatic index γ for an electron-positron plasma is considered. An improved method for numerically calculating the Hartree-Fock exchange integral is presented and its relativistic asymptotics is determined. An approximation formula is derived for the correlation part of the interaction in the low-density limit. This formula includes degeneracy and the positron component. 相似文献
140.
Natural Resources Research - Sand failure and production occurs when the formation stress exceeds the strength of the formation, which is derived majorly from the natural material that cements the... 相似文献