全文获取类型
收费全文 | 1098篇 |
免费 | 84篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 14篇 |
大气科学 | 116篇 |
地球物理 | 348篇 |
地质学 | 410篇 |
海洋学 | 76篇 |
天文学 | 148篇 |
综合类 | 10篇 |
自然地理 | 61篇 |
出版年
2024年 | 2篇 |
2023年 | 3篇 |
2022年 | 9篇 |
2021年 | 34篇 |
2020年 | 31篇 |
2019年 | 13篇 |
2018年 | 60篇 |
2017年 | 55篇 |
2016年 | 106篇 |
2015年 | 67篇 |
2014年 | 86篇 |
2013年 | 79篇 |
2012年 | 44篇 |
2011年 | 60篇 |
2010年 | 62篇 |
2009年 | 66篇 |
2008年 | 49篇 |
2007年 | 29篇 |
2006年 | 32篇 |
2005年 | 24篇 |
2004年 | 25篇 |
2003年 | 24篇 |
2002年 | 30篇 |
2001年 | 15篇 |
2000年 | 17篇 |
1999年 | 15篇 |
1998年 | 15篇 |
1997年 | 13篇 |
1996年 | 6篇 |
1995年 | 11篇 |
1994年 | 12篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 11篇 |
1990年 | 14篇 |
1989年 | 8篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1984年 | 3篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1975年 | 1篇 |
1974年 | 4篇 |
1973年 | 6篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 2篇 |
1960年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有1183条查询结果,搜索用时 468 毫秒
101.
J. Martí D. Pérez-Ramírez P. Luque-Escamilla J. L. Garrido J. M. Paredes A. Muñoz-Arjonilla J. R. Sánchez-Sutil 《Astrophysics and Space Science》2007,309(1-4):309-313
We report and shortly discuss here the observational work carried out in order to test the possibility that two previously
detected radio sources, in the vicinity of the well known microquasar Cygnus X-3, could be hot spot tracers of interaction
between its relativistic jet and the interstellar medium (ISM). The motivation behind this search is in part justified considering
recent theoretical models of high energy γ-ray emission which strongly rely on the interaction sites of galactic relativistic jets with nearby ISM clouds.
The results presented in this paper include an improved radio exploration of the several arc-minute field around Cygnus X-3
using the Very Large Array (VLA), as well as deep near infrared (NIR) imaging with the Calar Alto 3.5 m telescope. We anticipate
here that our observations do not appear to support the initial hot spot hypothesis. Instead, the resulting images suggest
that the two radio sources, originally believed to be hot spot candidates, are most likely background or foreground objects. 相似文献
102.
A multifractal analysis was carried out in order to validate the simulation of hourly rainfall records of a local climate model for the Iberian Peninsula. Observed and simulated hourly rainfall data from four locations in Andalusia (southern Spain) were used to carry out the study. In order to detect the influence of the length of the data series on the results, two different sizes were used for the real data: 4 years, and 20 years. The results show that algebraic tails are required to fit the probability distribution of extreme rain event sizes, and rain and dry event durations for both kinds of rainfall data. Similar results are found for the extreme rain event sizes and dry event durations fits when the real and synthetic data are considered. Nevertheless, some differences appear in the cases of rain event durations. The detection of the presence of a first‐order multifractal phase transition associated with a critical moment in the empirical moment scaling exponent function and the results of the extreme rain event sizes fits, reveal that real rainfall is a self‐organized criticality (SOC) process. That behaviour is less evident in the simulated rainfall series. The same ‘synoptic maximum’ value was found for each place with both types of rainfall data. A time clustering analysis was carried out applying the count‐based periodogram and the Fano factor methods. Some periodicities have been detected in the periodograms, especially for the longest real rainfall data series. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
103.
Spijker Jeroen Recaño Joaquín Martínez Sandra Carioli Alessandra 《Journal of Geographical Systems》2021,23(2):161-207
Journal of Geographical Systems - Colombia is undergoing major changes in mortality patterns. National- and department-level cause-specific analyses have previously been carried out, but very... 相似文献
104.
105.
106.
J. A. Combi J. F. Albacete Colombo L. Pellizza J. López-Santiago G. E. Romero J. Martí A. J. Muñoz-Arjonilla E. Sánchez-Ayaso P. L. Luque-Escamilla J. R. Sánchez-Sutil 《Astrophysics and Space Science》2011,331(1):53-61
We present a catalog of cross-correlated radio, infrared and X-ray sources using a very restrictive selection criteria with
an IDL-based code developed by us. The significance of the observed coincidences was evaluated through Monte Carlo simulations
of synthetic sources following a well-tested protocol. We found 3320 coincident radio/X-ray sources with a high statistical
significance characterized by the sum of error-weighted coordinate differences. For 997 of them, 2MASS counterparts were found.
The percentage of chance coincidences is less than 1%. X-ray hardness ratios of well-known populations of objects were used
to provide a crude representation of their X-ray spectrum and to make a preliminary diagnosis of the possible nature of unidentified
X-ray sources. The results support the fact that the X-ray sky is largely dominated by Active Galactic Nuclei at high galactic
latitudes (|b|≥10°). At low galactic latitudes (|b|≤10°) most of unidentified X-ray sources (∼94%) lie at |b|≤2°. This result suggests that most of the unidentified sources found toward the Milky Way plane are galactic objects. Well-known
and unidentified sources were classified in different tables with their corresponding radio/infrared and X-ray properties.
These tables are intended as a useful tool for researchers interested in particular identifications. 相似文献
107.
Essential macroscopic internal properties of compact objects can be related to each other with the help of General Relativity.
A somewhat familiar example is the relationship between the compactness M/R and the gravitational redshift for nonrotating bodies. Rotation poses new challenges when trying to relate observed or potentially
observed quantities such as the graviational redshift, mass, radius, and angular velocity. Using a perturbative approach,
we present an analytical approximation whose purpose is to relate these quantities. Two main results are highlighted: Derivation
of a new maximal angular velocity depending only on the mass of the object and a possible estimate of the radius from a measurement
of the gravitational redshift. 相似文献
108.
109.
The southeast area of the Argentine Pampas is characterized by the presence of an unconfined aquifer in a wide plain. A methodology is proposed that deals with the aquifer vulnerability where the homogeneity of the hydrogeological variables used by traditional methods (in this case, DRASTIC-P) causes vulnerability maps to show more than 80% of the territory under the same class. This absence of discrimination renders vulnerability maps of little use to decision-makers. In addition, the proposed methodology avoids the traditional vague classification (high, low, and moderate vulnerability) which is highly dependent on subjectivity in its association of each class with hydrogeological considerations. That traditional vulnerability assessment methodology was adapted using a geographic information system to reclassify classes, based on the Natural Breaks (Jenks) method. The pixel-to-pixel comparison between the result obtained by the DRASTIC-P and the reclassified classes generates the so-called operational vulnerability index (OVI), which shows four classes, associating each with different hydrogeological requirements to make decisions. 相似文献
110.
Gabriel Auvinet-Guichard Juan F. Rodríguez-Rebolledo José L. Rangel-Núñez 《Acta Geotechnica》2010,5(1):63-68
The drainage system of Mexico City, one of the largest metropolitan areas in the world, is formed by a large network of interceptors
and collectors leading to the main outlet: a 49.3-km-long tunnel with a 6.5 m diameter. To build the access shafts to the
tunnels of the system and the deep sumps of the pumping stations in the very soft clays of the lacustrine area of Mexico valley,
a technique known as “flotation method” has been commonly used since 1969. The paper presents the main construction steps
followed and some aspects of the analysis and design of shafts constructed by this technique. The experience gained obtained
after more than 30 shafts have been constructed by this method, and the actual trends in its application are also discussed. 相似文献