全文获取类型
收费全文 | 85165篇 |
免费 | 1580篇 |
国内免费 | 597篇 |
专业分类
测绘学 | 1906篇 |
大气科学 | 6201篇 |
地球物理 | 17437篇 |
地质学 | 29322篇 |
海洋学 | 7653篇 |
天文学 | 19303篇 |
综合类 | 168篇 |
自然地理 | 5352篇 |
出版年
2021年 | 744篇 |
2020年 | 847篇 |
2019年 | 936篇 |
2018年 | 1815篇 |
2017年 | 1724篇 |
2016年 | 2157篇 |
2015年 | 1311篇 |
2014年 | 2103篇 |
2013年 | 4360篇 |
2012年 | 2279篇 |
2011年 | 3232篇 |
2010年 | 2871篇 |
2009年 | 3958篇 |
2008年 | 3534篇 |
2007年 | 3435篇 |
2006年 | 3355篇 |
2005年 | 2520篇 |
2004年 | 2620篇 |
2003年 | 2448篇 |
2002年 | 2391篇 |
2001年 | 2165篇 |
2000年 | 2054篇 |
1999年 | 1749篇 |
1998年 | 1722篇 |
1997年 | 1710篇 |
1996年 | 1464篇 |
1995年 | 1408篇 |
1994年 | 1268篇 |
1993年 | 1124篇 |
1992年 | 1105篇 |
1991年 | 945篇 |
1990年 | 1163篇 |
1989年 | 1007篇 |
1988年 | 873篇 |
1987年 | 1069篇 |
1986年 | 954篇 |
1985年 | 1184篇 |
1984年 | 1349篇 |
1983年 | 1282篇 |
1982年 | 1165篇 |
1981年 | 1118篇 |
1980年 | 963篇 |
1979年 | 963篇 |
1978年 | 990篇 |
1977年 | 901篇 |
1976年 | 867篇 |
1975年 | 798篇 |
1974年 | 802篇 |
1973年 | 826篇 |
1972年 | 519篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
Three data sets of suspensate concentrations, collected under different sampling plans, were analyzed to develop a minimal sampling period, consistent with a predetermined precision. Individual samples collected during any part of a given day were within ±50% of the daily average. In the main channel of the estuary, a monthly sampling scheme closely approximated a weekly pattern; however, seasonal sampling was unsatisfactory. Outside the main channel, weekly, monthly, and seasonal sampling patterns did not differ greatly. Variability in suspensate concentrations must be considered when calculating sediment flux in estuarine and coastal waters. 相似文献
992.
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
993.
In this study male largemouth bass (LMB) were exposed to the naturally occurring androgens, dihydrotestosterone (DHT) or 11-ketotestosterone (11-KT) in order to identify genes that are differentially regulated by these steroid hormones. Using subtractive hybridization on livers of fish treated with DHT against vehicle control, many novel LMB genes were cloned. These genes were added to our gene library and arrayed. Six genes were up-regulated and five were down-regulated by both androgens. But, each androgen also regulated specific genes. One gene that was identified as a potential androgen marker was spermidine-spermine-N(1)-acetyltransferase that was up-regulated by both androgens. Determining which genes are responsive to natural androgens will help to identify biochemical pathways that are impacted. 相似文献
994.
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
995.
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
996.
A non-hydrostatic algorithm for the Regional Oceanic Modeling System (ROMS) is proposed. It is based on a decomposition technique for hydrostatic and non-hydrostatic pressure. The algorithm has a pressure-correction scheme with split-explicit time-stepping for baroclinic and barotropic vertical modes with a free surface. The algorithm implementation requires solving a Poisson equation for a non-hydrostatic pressure that has a non-symmetric matrix in discrete form. The efficiency of a different class of solvers and preconditioners were tested. The algorithm is successfully implemented with several examples where non-hydrostatic effects are important. These include standing external gravity waves; strongly nonlinear internal wave generation and transformation; stratified shear instability and its associated mixing; and nonlinear internal tidal generation over a ridge. The corresponding changes in the pre-processing and post-processing infrastructure in the existing hydrostatic ROMS code were performed to implement parallel elliptic solvers and a new set of dynamical equations. 相似文献
997.
M. I. Yaroshevich 《Izvestiya Atmospheric and Oceanic Physics》2006,42(1):40-45
The dynamics of some characteristics of a cyclonic situation (cyclonic regime) of the northwestern Pacific cyclonic zone is studied. The characteristics that are considered are the density of cyclonic energy at a point (intensity) and the power over a given area. In the model, the intensity at a point is defined as the sum of all intensities of preceding cyclones, with consideration for their spatial and temporal separation from the given point. Power for a given moment and a given area is defined as the sum of intensities over this area. Cyclonically active seasons are considered. The dynamics of the power was estimated for areas of different size. It is shown that the point values of cyclonic intensity, at the times of their maximum, are statistically related to one another by a negative power-law dependence. Periodicity is observed in the time evolution of the power in different areas. 相似文献
998.
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
999.
Sedimentary facies of cores from the eastern side of the Rockall Bank and the Feni Drift (55°–58°N) have been studied. They confirm the existence of slumping which contributes only in small part to drift build-up.
These slumps occurred at different episodes during last Glacial and early Post-Glacial periods. They are sandwiched in between more important turbidites, and are found in places where the drift lies against the slope and so is acted upon by continental-rise sedimentary processes. The sea level rise periods with ice melting seems to favour gravity flow release. 相似文献
1000.