全文获取类型
收费全文 | 57603篇 |
免费 | 1100篇 |
国内免费 | 784篇 |
专业分类
测绘学 | 1475篇 |
大气科学 | 4620篇 |
地球物理 | 11950篇 |
地质学 | 19640篇 |
海洋学 | 5036篇 |
天文学 | 12778篇 |
综合类 | 150篇 |
自然地理 | 3838篇 |
出版年
2020年 | 374篇 |
2019年 | 361篇 |
2018年 | 846篇 |
2017年 | 776篇 |
2016年 | 1215篇 |
2015年 | 860篇 |
2014年 | 1183篇 |
2013年 | 2848篇 |
2012年 | 1423篇 |
2011年 | 2067篇 |
2010年 | 1703篇 |
2009年 | 2459篇 |
2008年 | 2199篇 |
2007年 | 2102篇 |
2006年 | 2053篇 |
2005年 | 1845篇 |
2004年 | 1795篇 |
2003年 | 1725篇 |
2002年 | 1646篇 |
2001年 | 1435篇 |
2000年 | 1452篇 |
1999年 | 1376篇 |
1998年 | 1267篇 |
1997年 | 1286篇 |
1996年 | 1099篇 |
1995年 | 1018篇 |
1994年 | 931篇 |
1993年 | 851篇 |
1992年 | 822篇 |
1991年 | 752篇 |
1990年 | 797篇 |
1989年 | 665篇 |
1988年 | 691篇 |
1987年 | 765篇 |
1986年 | 717篇 |
1985年 | 941篇 |
1984年 | 1041篇 |
1983年 | 1013篇 |
1982年 | 874篇 |
1981年 | 837篇 |
1980年 | 816篇 |
1979年 | 732篇 |
1978年 | 765篇 |
1977年 | 661篇 |
1976年 | 662篇 |
1975年 | 642篇 |
1974年 | 670篇 |
1973年 | 671篇 |
1972年 | 405篇 |
1971年 | 341篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
781.
C.Guedes Soares 《Ocean Engineering》1986,13(6)
Visual observations of wave properties are an important source of statistical information needed for the prediction of design and operational conditions of ocean structures. In particular, mean wave periods are important parameters for predicting the response of ocean structures. The existing calibration studies were based on data sets with a poor correlation between observations and measurements. The data set analysed here show a good correlation indicating the feasibility of collecting further good data sets to provide an adequate calibration to the existing statistical compilations of wave data. 相似文献
782.
Wen Shengchang 《海洋学报(英文版)》1988,7(1):1-16
In this part ot the paper theoretical wind-wave spectra nave been derived oy (I) expressing the spectrum in series composed of exponential terms; (2) assuming that the spectrum satisfies a high order linear ordinary differential equation; (3) introducing proper parameters in the spectrum; and (4) making use of some known charateristics of wind-wave spectrum, for instance, the law governing the equilibrium range. The spectrum obtained contains the zero order moment of the spectrum m0, the peak frequency ω0 and the ratio R =ω/ω0 (ω being the mean zero-crossing frequency) as parameters. The shape of the nondimensional spectrum S(ω) = ω0S(ω)/m0(ω=ω/ω0) changes with R and theoretically reduces to a Dirac delta function δ(ω-1) when R = 1. A spectrum of simplified form is given for practical uses, in which R is replaced by a peakness factor P=S(1). 相似文献
783.
Core 7710, recovered on the George Bligh/Rockall Channel, is composed of fine grained ocher-colored sediments rich in ferriferous smectite (montmorillonite, beidellite). These sediments were deposited during early Eocene in a shallow marine environment. Their mineralogic, chemical and isotopic constituents indicate subaerial weathering of lower Eocene intermediate igneous rocks (ferrodiorite, marscoiite) eroded from the still-emergent George Bligh and Rockall Banks. Lack of any post Eocene Sediments may be due to major morphologic and hydrologic changes forming sedimentation gaps. 相似文献
784.
Brent L. Lewis Pamela D. Holt Steven W. Taylor Steven W. Wilhelm Charles G. Trick Alison Butler George W. Luther III 《Marine Chemistry》1995,50(1-4)
Thermodynamic stability constants have been estimated for the complexation of iron(III) with catecholate-type siderophores isolated from the marine bacterium Alteromonas luteoviolacea and from the marine cyanobacterium Synechococcus sp. PCC 7002. Stability constants were determined utilizing the “chelate scale” of Taylor et al. (1994). The scale is based upon a linear relationship between the reduction potentials and the pH-independent thermodynamic stability constants for known iron(III) complexes. Log K values for the alterobactin B ferric iron complex are 43.6 ± 1.5 at pH 8.2 and 37.6 ± 1.2 at pH 6, consistent with a shift from bis-catecholate to monosalicylate/monocatecholate iron coordination with decreasing pH. Synechococcus isolates PCC 7002 Nos. 1 and 3 formed iron(III) complexes with stability constants of approximately 38.1 ± 1.2 and 42.3 ± 1.5, respectively. The binding strengths of the iron(III) complexes examined in this study are quite high, suggesting that catecholate siderophores may play a role in the solubilization and biological uptake of iron in the marine environment. 相似文献
785.
Don Maurer Richard T Keck Jeff C Tinsman Wayne A Leathem 《Marine environmental research》1982,6(1):49-68
The survival of benthic invertebrates from dredging and disposal activities is a major environmental concern in such projects. The purpose of the research described in this paper was to determine the ability of benthos (polychaetes, Scoloplos fragilis and Nereis succinea) to migrate vertically in natural and exotic sediments and to determine the survival of benthos when exposed to particular amounts of simulated dredged material.Mortalities generally increased with increased sediment depth, exotic sediment and burial time. Temperature also affected vertical migration and mortalities. These experiments, together with other experiments conducted by us and other workers, indicate that polychaetes in particular, and benthos in general, can survive dredging and disposal projects. Under certain conditions several major taxa (polychaetes, molluscs, crustaceans) can be expected to successfully recolonise disposal sites by vertical migration. 相似文献
786.
Abstract. The distribution of Ibla cumingi DARWIN on different types of hard substrata along 30 km of coast in the Gulf of Elat was studied. I. cumingi was found among and underneath Tetraclita squamosa rufotincta , in oyster beds, underneath slabs of beachrock, and in fissures in igneous rocks. In the Tetraclita belt, I. cumingi is most frequent in empty shells of dead Tetraclita while in the oyster bed it is common inside the meshwork made by the oysters. The distribution is regarded as clustered distribution. The density and size of the clusters of I. cumingi is determined by the available sheltered space within the midlittoral zone. The form of the habitat determines the shape of the animals. Those found in the oyster bed and fissures are usually longer than those found in the Tetraclita belt due to the depth of the fissures or to the bigger spaces within the oyster bed. I. cumingi is orientated so that the capitulum with the cirri is projecting towards the open water, and the water current. It is concluded that I. cumingi can withstand the physical stress encountered in a tropical intertidal zone, but that the distribution pattern is caused by predation. 相似文献
787.
A survey of the aerobic heterotrophic bacteria present in sediments at Sawyers Bay, New Zealand, receiving tannery effluent high in Cr, and a control site, indicates that the populations present are different and show seasonal variation. The bacterial population present at the polluted site appears more able to tolerate CrIII at concentrations less than 0·2 μmol ml?1. 相似文献
788.
C. Graham 《Coastal Engineering》1982,6(4)
This study sets out to define the basic forms in which wind speed and wave height persistence statistics may be defined for offshore engineering applications, and describes the development of a mathematical persistence model.The model incorporates some of the principles laid down by other workers, but it is fundamentally based on a new concept for parameterising persistence statistics, linking wind speed and sea state percentage probability of exceedance with the persistence average duration.North Sea measured wind and wave data have been used to calibrate and test the model. During the course of these test runs it proved necessary to fine tune the basic Weibull equation of the model, but following these adjustments the model runs were found to correlate well with the measured data.It is concluded that the model may be used to predict wind speed and wave height persistence statistics with acceptable accuracy for preliminary stage oil industry planning purposes and that the calibrated model has particular application for those areas where little measured data are currently available. 相似文献
789.
790.