全文获取类型
收费全文 | 5671篇 |
免费 | 14篇 |
国内免费 | 9篇 |
专业分类
测绘学 | 38篇 |
大气科学 | 1030篇 |
地球物理 | 1300篇 |
地质学 | 3187篇 |
海洋学 | 39篇 |
天文学 | 50篇 |
综合类 | 3篇 |
自然地理 | 47篇 |
出版年
2013年 | 71篇 |
2006年 | 35篇 |
1997年 | 38篇 |
1996年 | 80篇 |
1995年 | 49篇 |
1994年 | 48篇 |
1993年 | 63篇 |
1992年 | 151篇 |
1991年 | 158篇 |
1990年 | 141篇 |
1989年 | 140篇 |
1988年 | 139篇 |
1987年 | 175篇 |
1986年 | 133篇 |
1985年 | 119篇 |
1984年 | 154篇 |
1983年 | 171篇 |
1982年 | 188篇 |
1981年 | 186篇 |
1980年 | 155篇 |
1979年 | 187篇 |
1978年 | 160篇 |
1977年 | 150篇 |
1976年 | 120篇 |
1975年 | 139篇 |
1974年 | 128篇 |
1973年 | 145篇 |
1972年 | 129篇 |
1971年 | 140篇 |
1970年 | 147篇 |
1969年 | 100篇 |
1968年 | 132篇 |
1967年 | 125篇 |
1966年 | 87篇 |
1965年 | 97篇 |
1964年 | 101篇 |
1963年 | 47篇 |
1962年 | 93篇 |
1960年 | 107篇 |
1959年 | 35篇 |
1957年 | 41篇 |
1956年 | 37篇 |
1955年 | 40篇 |
1954年 | 67篇 |
1953年 | 38篇 |
1952年 | 49篇 |
1951年 | 39篇 |
1950年 | 62篇 |
1949年 | 44篇 |
1948年 | 35篇 |
排序方式: 共有5694条查询结果,搜索用时 9 毫秒
61.
The Bulgarian food distribution system, like those of its Central and East European neighbours, lags behind the West in critical performance areas. Previous research quantified Central and East European food distribution deficiencies on the basis of a five factor model. This study investigates the attitudes of 250 Bulgarian consumers using these same five factors: food processing, quality, cost, availability and retailing. The findings show that the Bulgarian food distribution system does not satisfy consumer wants as well as do systems in other former communist countries in four of the five factors. At the same time, Bulgarian consumers are more satisfied than UK and US consumers in the system's ability to make some foods available. The study also shows that Bulgarian consumers who use privatised shops perceive the system more positively than those who use state and cooperative outlets. The implications of these and other findings are discussed in terms of critical policy concerns for government and industry stakeholders. 相似文献
62.
Prof. Dr. I. D. Ryabchikov Dr. Ch. Miller Prof. Dr. P. W. Mirwald 《Mineralogy and Petrology》1996,58(1-2):101-110
Summary Compositions of the hydrous melts in equilibrium with garnet, omphacitic clinopyroxene and quartz have been investigated experimentally at 28.5 and 35 kbar. They are represented by silica-rich liquids (> 70% SiO2) with low MgO, FeO and CaO contents. The removal of ca 10–15% of the magma of this composition may be sufficient to convert quartz eclogite formed after subduction of altered MORB into a quartz-free bimineralic eclogite assemblage, which is a common type of xenoliths in kimberlites.At 28.5 kbar the solidus temperature is between 700 and 750° C in the system quartz eclogite—water, and the high pressure amphibole-out boundary lies at ca 25 kbar in accord with the previous studies.
With 1 Figures 相似文献
Die Zusammensetzung wasserhältiger Schmelzen im Gleichgewicht mit Quarz-Eklogiten
Zusammenfassung Um Prozesse zu simulieren, die bei der Subduktion von Ozeanbodenbasalten durch partielle Anatexis im Stabilitätsfeld von Eklogiten ablaufen, wurde die Zusammensetzung wasserhältiger Schmelzen in Gleichgewicht mit Granat, Omphacit und Quarz bei 28.5 und 35 Kbar experimentell untersucht. Diese Schmelzen sind reich an SiO2 (> 70 Gew%) und arm an Mg0, Fe0 and CaO. Die Extraktion von ca. 10–15% derartiger Schmelzen würde genügen, um quarzführende Eklogite, die durch die Subduktion von alteriertem MORB Material entstanden sind, in quarzfreie bimineralische Eklogite umzuwandeln wie sie häufig als Xenolithe in Kimberliten beobachtet werden.Im System Quarz-Eklogit-Wasser liegt die Solidustemperatur bei 28.5 Kbar zwischen 700 und 750°C. Die obere Stabilitätsgrenze von Amphibol liegt in diesem Temperaturbereich bei ca. 25 Kbar.
With 1 Figures 相似文献
63.
The squeezing potential of rock around tunnels: Theory and prediction with examples taken from Japan 总被引:5,自引:2,他引:5
Summary Large deformations of surrounding media around tunnels are often encountered during excavations in rocks with squeezing characteristics. These deformations may sometimes continue for a long period of time. Predictions of deformations of tunnels in such grounds are urgently needed, not because of stability concerns, but also of their sevicability. In the present study, the squeezing phenomenon of rock around tunnels and its mechanism and associated factors are first clarified by carefully studying failures of tunnels, and a survey of tunnels in squeezing rocks in Japan is presented and its results are summarised. Then, a practical method is proposed to predic the squeezing potential and deformation of tunnels in squeezing rock and this method has beeen applied to actual tunnelling projects, where squeezing problems were encountered, to check its applicability and validity. Finally, an extension of this method to the time-dependent behaviour of squeezing rocks is given and an application of this method to an actual tunnel is presented. 相似文献
64.
利用断裂活动过程中留下的各种地质标记研究断裂发育史是比较困难的 ,已有的研究方法主要可归纳出七种 ,都存在局限性。岩层离距图法是以地震剖面为基础 ,将穿过断裂的各剖面上的标志层投影到沿断裂走向的铅垂面上 ,得到多组标志层的垂向断距数据 ,然后用下部各标志层的断距减去最上部标志层的断距 ,并作多轮次计算 ,直到最后的断距差近似为零或仅剩一个非零标志层。每一轮次计算代表一个活动期次 ,如果出现负值 ,则表示有构造反转。对松辽盆地敖古拉断裂作了实例计算 ,结果为该断裂发育经历了三个正断活动期和一个逆断活动期 ,与盆地区域性活动有些差别。岩层离距图法比起其他已有方法 ,可靠程度大大提高 相似文献
65.
René Rutten, Director of the Isaac Newton Group of Telescopes, sets the scene for future developments in international astronomy on La Palma. 相似文献
66.
Helmut Kerndorff Stephan Kühn Thomas Minden Dagmar Orlikowski Thomas Struppe 《Environmental Geology》2008,55(2):291-301
The aim of this research project is to identify, characterize and quantify natural attenuation (NA) processes in groundwater
affected by emissions of abandoned waste disposal sites in Berlin-Kladow/Gatow, Germany. It is part of the funding priority
called KORA established by the Federal Ministry for Education and Research (BMBF) to explore the extent to which NA can be
used for remedial purposes for varied forms of soil and groundwater contamination. Information on the emission behaviour of
individual parameters is generated on the basis of hydrogeochemical comparison of 20 years old and new data. Using groundwater-modelling
and CFC-analysis, information on the transport and retention of pollutants in groundwater is compiled. The microbial colonization
of contaminated aquifers is characterized by molecular biological methods [polymerase chain reaction (PCR) and denaturing
gradient gel electrophoresis (DGGE)] to differentiate between contaminated and not contaminated zones. 相似文献
67.
68.
Prof. Dr T. N. Krishnamurti Wei Han D. Oosterhof 《Meteorology and Atmospheric Physics》1998,65(3-4):171-181
Summary Intensity forecasts of a hurricane are shown to be quite sensitive to the initial meso-convective scale precipitation distributions. These are included within the data assimilation using a physical initialization that was developed at Florida State University. We show a case study of a hurricane forecast where the inclusion of the observed precipitation did provide reasonable intensity forecasts. Further experimentation with the inclusion or exclusion of individual meso-convective rainfall elements, around and over the storm, shows that the intensity forecasts were quite sensitive to these initial rainfall distributions. The exclusion of initial rain in the inner rain area of a hurricane leads to a much reduced intensity forecast, whereas that impact is less if the rainfall of an outer rain band was initially excluded.Intensity forecasts of hurricanes may be sensitive to a number of factors such as sea surface temperature anomalies, presence or absence of concentric eye walls, potential vorticity interactions in the upper troposphere and other environmental factors.This paper is a sequel to a recent study, Krishnamurti et al., 1997, on the prediction of hurricane OPAL of 1995 that was a category III storm over the Gulf of Mexico. In that study we showed successful forecasts of the storm intensity from the inclusion of observed rainfall distributions within physical initialization. In that paper we examined the issues of diabatic potential vorticity and the angular momentum in order to diagnose the storm intensity. All of the terms of the complete Ertel potential vorticity equation were evaluated and it was concluded that the diabatic contributions to the potential vorticity were quite important for the diagnosis of the storm's intensity. The present paper addresses some sensitivity issues related to the individual mesoconvective precipitating elements.With 4 Figures 相似文献
69.
The formation of tropical cyclones 总被引:16,自引:1,他引:16
Prof. Dr. W. M. Gray 《Meteorology and Atmospheric Physics》1998,67(1-4):37-69
Summary This paper attempts a synthesis of new observations and new concepts on how tropical cyclone formation occurs. Despite many worthy observational and numerical modeling studies in recent decades, our understanding of the detailed physical processes associated with the early stages of tropical cyclone formation is still inadequate; operational forecast skill is not very high. Although theoretical ideas cover a wide range of possibilities, results of new observations are helping us to narrow our search into more specific and relevant topic areas.With 33 FiguresPrologueThis paper is dedicated to Professor Herbert Riehl under whom I studied tropical meteorology at the University of Chicago from 1957–1961 and was later associated with at Colorado State University (CSU). Professor Riehl arranged my first aircraft flights into hurricanes in the late 1950s and gave great encouragment to me to explore the secrets of what causes a tropical disturbance to be transformed into a tropical storm.Herbert would persist in asking me nearly every week or so what causes a hurricane to form? I and my graduate students and research colleagues at CSU have been working to uncover the secrets of tropical cyclone formation ever since. The following article gives my current best estimate of the primary physical processes involved with this topic. 相似文献
70.