全文获取类型
收费全文 | 84440篇 |
免费 | 1413篇 |
国内免费 | 840篇 |
专业分类
测绘学 | 2390篇 |
大气科学 | 6084篇 |
地球物理 | 16618篇 |
地质学 | 29350篇 |
海洋学 | 7590篇 |
天文学 | 20043篇 |
综合类 | 280篇 |
自然地理 | 4338篇 |
出版年
2022年 | 479篇 |
2021年 | 832篇 |
2020年 | 910篇 |
2019年 | 1014篇 |
2018年 | 2212篇 |
2017年 | 2084篇 |
2016年 | 2653篇 |
2015年 | 1453篇 |
2014年 | 2502篇 |
2013年 | 4321篇 |
2012年 | 2671篇 |
2011年 | 3481篇 |
2010年 | 3100篇 |
2009年 | 4102篇 |
2008年 | 3530篇 |
2007年 | 3609篇 |
2006年 | 3374篇 |
2005年 | 2509篇 |
2004年 | 2562篇 |
2003年 | 2401篇 |
2002年 | 2360篇 |
2001年 | 2079篇 |
2000年 | 1976篇 |
1999年 | 1680篇 |
1998年 | 1716篇 |
1997年 | 1637篇 |
1996年 | 1369篇 |
1995年 | 1316篇 |
1994年 | 1164篇 |
1993年 | 1047篇 |
1992年 | 977篇 |
1991年 | 980篇 |
1990年 | 996篇 |
1989年 | 891篇 |
1988年 | 853篇 |
1987年 | 945篇 |
1986年 | 869篇 |
1985年 | 1046篇 |
1984年 | 1236篇 |
1983年 | 1061篇 |
1982年 | 1038篇 |
1981年 | 935篇 |
1980年 | 846篇 |
1979年 | 825篇 |
1978年 | 839篇 |
1977年 | 695篇 |
1976年 | 648篇 |
1975年 | 656篇 |
1974年 | 596篇 |
1973年 | 663篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
The biogeochemistry of organic matter in a macrotidal estuary, the Loire, France, has been studied for two years during different seasons. Both particulate matter and sediment have been sampled in the riverine zone, in the maximum turbidity zone and in the ocean near the river mouth. Two techniques have been used: carbon isotopic ratio determination and analysis of lipid-marker signatures in the n-alkane, n-alkene and fatty acid series. For the period corresponding to the output of the maximum turbidity zone in the ocean, the complete change of organic matter, continental in nature in the inner estuary, pure marine in the outer estuary is well illustrated by the decrease of δ13C values and of carbon preference index of n-alkanes. Input sources of organic matter by continental plants, plankton and micro-organisms are discussed from biogeochemical-marker analyses data along with the processes of accumulation of particles and their evolution with the season. Some criteria for evidencing the nature of various organic-matter pools are assessed and compared in different chemical-marker series as follows: high molecular weight n-alkanes and fatty acids, perylene for continental imprints, polyunsaturated 18-, 20- and 22-carbon fatty acids, n-C17, n-alkenes and squalene for algae imprints, branched iso and anteiso fatty acids, Δ11-C18:1 for microbial imprints. 相似文献
962.
K. N. Visheratin N. E. Kamenogradskii F. V. Kashin V. K. Semenov V. P. Sinyakov L. I. Sorokina 《Izvestiya Atmospheric and Oceanic Physics》2006,42(2):184-202
The results of long-term (1980–2003) systematic measurements of the total ozone content at the Issyk Kul station (42.6° N, 77.0° E; 1650 m above sea level) are presented. The statistical characteristics and spectral structure of variations in the total ozone and the main tendencies of its temporal variability are determined. It is found that the total ozone content decreased in 1980–2003 at an average rate of (?1.29±0.08) DU/yr. The results of Fourier and wavelet analyses have shown that only oscillations with periods of 12, 27–29, and 102–105 months are rather stable and can be represented as harmonic oscillations. Oscillations with periods shorter than six months have the character of periodically arising pulsations. Among these, oscillations with periods of 27–29 and 34–37 days can be distinguished. It is noted that the spectral-temporal structure of variations in the total ozone content obtained from ground-based measurements at the Issyk Kul station is in good agreement with the corresponding structure obtained from TOMS satellite measurements. 相似文献
963.
A detailed marine survey made to the South West of Mount Eratosthenes is described. The results show the existence of a narrow zone of WNW trending deformed sediment west of the mount surrounded by an evaporite sequence in different stages of deformation.This work was intended to settle the conflict between the results of three previous interpretations of the tectonic structure of this area. We see the area being characterised by five areas with different degrees of tectonic deformation yet showing little causal relationship to overburden of Nile Cone sediments. A fault controlled cliff coincides with the previously described salt wall and strike slip fault yet we see no evidence for its diapiric origin nor positive evidence for strike slip motion along it. We concur with the previously observed area of higher free-air gravity anomalies termed the Eratosthenes tectonic zone, although it is traversed by several boundaries between areas of different deformation. Our results thus show some agreements and some re-interpretations of the observations. This complicated region is not yet fully understood however. 相似文献
964.
965.
966.
We study the processes of global self-regulation of Earth’s biota (GAIA-theory) by applying the method of adaptive balance of causes proposed by the authors. By using, as an example, the Daisy World model constructed by this method, we reveal the phenomenon of preservation of the mean temperature of Earth’s surface due
to the presence of the vegetation cover. We develop an integral model of global natural, social, and economic processes in
which the World Ocean is one of the factors regulating the amount of greenhouse gases in the atmosphere. The decrease in the
amount of greenhouse gases in the atmosphere caused by the GAIA-effects increases the number of hurricanes and floods on the Earth. As a result, the levels of ecological and social hazards
for the mankind become much higher. To eliminate these threats, it is necessary to intensify the processes of self-organization
of the society realized via the improvement of education, development of science, and global regulation of the competition
for natural resources. We present the results of numerical experiments performed by using the model demonstrating possible
scenarios of global development with regard for the processes of self-organization of the society.
__________
Translated From Morskoi Gidrofizicheskii Zhurnal, No. 3, Pp. 62–80, May–June, 2007. 相似文献
967.
968.
Eurgain H. John Sonia D. Batten Roger P. Harris Graeme C. Hays 《Journal of Sea Research》2001,46(3-4)
Zooplankton sampling has been carried out by the Continuous Plankton Recorder (CPR) survey since the 1930s enabling the study of long-term changes in plankton populations, the elucidation of seasonal patterns of abundance, and more recently providing zooplankton biomass estimates for ecosystem models. Data for zooplankton abundance collected by CPR tows in the Western English Channel (between 1988 and 1998) were compared to vertically integrated samples collected from station L4 off Plymouth, UK. Comparisons were made for locally abundant copepods (including Acartia, Calanus, Para/Pseudocalanus, Centropages, Oithona and Temora) collected by CPR and WP-2 nets. All dominant species recorded at L4 were also common to the CPR data. However, the position of the taxa in the two datasets was not equivalent. Seasonal cycles revealed by CPR data were significantly similar to those recorded throughout the water column at L4 for most taxa. However, absolute levels of abundance differed for the two datasets: abundances were underestimated by CPR samples when compared to those of vertically integrated samples by a factor of between 2 and 35, with the exception of Centropages. The differing mesh sizes (200 and 270 μm) of the WP-2 net and CPR mesh could only partially explain these differences in abundance, implying that the behaviour of individual taxa and their depth in the water column also influenced the abundance recorded. 相似文献
969.
The wadic project: A comprehensive field evaluation of directional wave instrumentation 总被引:1,自引:0,他引:1
J. Allender T. Audunson S. F. Barstow S. Bjerken H. E. Krogstad P. Steinbakke L. Vartdal L. E. Borgman C. Graham 《Ocean Engineering》1989,16(5-6)
The results of a comprehensive field trial of nearly all commercially available directional wave measurement systems at the Edda field in the North Sea during winter 1985-86 are presented. The results summarize the accuracy of the principal engineering wave parameters from each system and the dependence on sea state. Limiting factors on system performance and operational problems are also included in the assessment. Overall experience has been good with systems utilizing widely different measurement principles returning consistent results. 相似文献
970.