全文获取类型
收费全文 | 29364篇 |
免费 | 466篇 |
国内免费 | 320篇 |
专业分类
测绘学 | 619篇 |
大气科学 | 1834篇 |
地球物理 | 5273篇 |
地质学 | 11319篇 |
海洋学 | 2971篇 |
天文学 | 6862篇 |
综合类 | 72篇 |
自然地理 | 1200篇 |
出版年
2022年 | 299篇 |
2021年 | 463篇 |
2020年 | 515篇 |
2019年 | 556篇 |
2018年 | 1098篇 |
2017年 | 1042篇 |
2016年 | 1154篇 |
2015年 | 548篇 |
2014年 | 1042篇 |
2013年 | 1694篇 |
2012年 | 1156篇 |
2011年 | 1443篇 |
2010年 | 1296篇 |
2009年 | 1566篇 |
2008年 | 1332篇 |
2007年 | 1397篇 |
2006年 | 1306篇 |
2005年 | 767篇 |
2004年 | 707篇 |
2003年 | 659篇 |
2002年 | 689篇 |
2001年 | 622篇 |
2000年 | 568篇 |
1999年 | 462篇 |
1998年 | 481篇 |
1997年 | 454篇 |
1996年 | 391篇 |
1995年 | 350篇 |
1994年 | 378篇 |
1993年 | 294篇 |
1992年 | 297篇 |
1991年 | 286篇 |
1990年 | 322篇 |
1989年 | 220篇 |
1988年 | 225篇 |
1987年 | 268篇 |
1986年 | 209篇 |
1985年 | 314篇 |
1984年 | 277篇 |
1983年 | 258篇 |
1982年 | 275篇 |
1981年 | 203篇 |
1980年 | 243篇 |
1979年 | 195篇 |
1978年 | 211篇 |
1977年 | 165篇 |
1976年 | 163篇 |
1975年 | 172篇 |
1974年 | 167篇 |
1973年 | 167篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
261.
This paper discusses the results obtained through numerical modelling of the annual course of circulation and thermohaline field evolution in the tropical Atlantic under the impact of real wind forcing (from March 1982 to March 1983) and compares them with the calculation of seasonal variability induced by the climatic wind. Changes in the pattern of the equatorial currents and related temperature fields induced by the specific peculiarities in the wind field are analysed.Translated by Vladimir A. Puchkin. 相似文献
262.
Lysosomal sequestration of polynuclear aromatic hydrocarbons (PNAHs), a major class of environmental contaminant, is a well-established phenomenon;1 considerably less is known about their pathological effects on lysosomes. Marine molluscs contain a number of lysosome-rich tissues and PNAHs are known to induce deleterious alterations in lysosomal structure and latency of lysosomal enzymes.2 The latter are presumed to involve destabilisation of the lysosomal membrane, resulting in increased permeability and reduced enzyme latency. If lysosomal injury involves derangement of membrane-lipid structure due to the interaction of PNAHs then it would be expected that membrane damage would be closely linked to the structural characteristics of the intruding molecule. Our results show that the effects of the isomeric PNAHs phenanthrene and anthracene on digestive cell lysosomal stability were markedly different in the marine mussel (Mytilus edulis) over the same range of tissue concentrations. Lysosomal membrane stability was determined using a cytochemical test for enzyme latency.3 相似文献
263.
G. Pagano M. Cipollaro G. Corsale A. Esposito E. Ragucci G.G. Giordano N.M. Trieff 《Marine environmental research》1985,17(2-4)
The aim of this study was to compare the biological actions of selected chlorinated biphenyls (CB's) (with different degrees of chlorine substitution), using the sea urchin test system, for their ability to affect fertilisation, embryogenesis and mitotic activity. Sea urchin embryos were exposed to the test agents throughout larval development or for shorter intervals (e.g. before or after hatching). Sperm or eggs were exposed before fertilisation, thereafter the contaminants were removed from embryo cultures. The results showed maximal activities from medium-chlorinated (tetra- and hexachloro-substituted) compounds, as compared to low- and high-chlorinated biphenyls (mono-, di- and octachloro-substituted), at nominal levels ranging from 10−6m to 10−5m. This held true for the different parameters and treatment schedules. Developmental defects were only detected following post hatching exposure of embryos to CB's, whereas pre-hatching exposure failed to reveal any embryological or cytogenetic abnormalities. 相似文献
264.
Abstract. Boonea (= Odostomia) impressa is a common ectoparasite of oysters. In the laboratory, small oysters (Crassostrea virginica) parasitized by natural densities of B. impressa produced 75 % less new shell than unparasitized oysters. Shell deposition rates of previously parasitized oysters increased significantly after all B. impressa were removed. Thus, the decrease in growth rate, although significant, apparently was not permanent. B. impressa preferentially parasitized small, living oysters (≤2.5cm) in the field, even though a higher percentage of large, living oysters (>2.5cm) was available. The snails maintained an aggregated distribution on the oyster reef. The number of B. impressa per oyster clump was positively correlated with the number of living oysters per clump, however some clumps with few or no living oysters had many B. impressa. Thus, food availability only partially explained the pattern of distribution. B. impressa was very mobile. About 50 % of the population moved in one week. Reproduction occurred throughout the year with a peak period in May. Recruitment was greatest in July, however new recruits were observed throughout the year. The reduction in growth rate of parasitized oysters, the snaiľs propensity towards parasitizing small oysters and the snail's tendency to be contagiously distributed suggests that B. impressa potentially exerts a significant influence on the population structure and health of oyster populations. 相似文献
265.
Forces induced by regular waves on submarine pipelines resting on as well as near a plane boundary and aligned parallel to wave fronts of the oncoming waves are investigated experimentally. The inline hydrodynamic coefficients of drag and inertia are evaluated through the use of Morison equation and the least squares method. The transverse force is analysed in terms of maximum transverse force and transverse root mean square (r.m.s.) coefficients. The resulting inline and transverse hydrodynamic coefficients are correlated with the period parameter or Keulegan-Carpenter number and relative clearance of the pipeline from the plane boundary. The effect of depth parameter on these coefficients and the correlation between maximum transverse force and transverse r.m.s. coefficients are also reported. 相似文献
266.
Partial equivalent conductances and partial equivalent volumes of the major constituents in seawater were used to evaluate the specific gravity-conductivity-chlorinity-salinity relationships in the marine environment. For example, in the open ocean, the relationships between Cl‰ and both S‰ and specific gravity are valid to within 0.014‰ and 0.014 σt, respectively. The relationships between conductivity and S‰ and specific gravity are valid to within 0.006‰ and 0.007 σt. In river diluted nearshore areas specific gravity anomalies inferred from Cl‰, can be as great as 0.06 σt and 0.04 σt when inferred from a conductivity ratio measurement. 相似文献
267.
The original prognostic equations for the JONSWAP-spectrum contained inconsistencies. A subsequent paper (Hasselmann et al., 1976, J. phys. Oceanogr.6, 200–208) attempted to regularise the situation. This paper shows that there were still inconsistencies in the prognostic equations giving overestimations of the first moment of the spectrum and consequently the significant wave height. The prognostic equations are reworked systematically and results presented. It is shown that variable σa, σb and γ must be used to achieve consistent results 相似文献
268.
The radioelement and heavy mineral distribution in river, beach and innershelf areas of the southern Kerala coast is related
to placer mineral concentration on the beaches at Chavara. Southern Kerala rivers—Neyyar, Karamana and Vamanapuram—transport
higher amounts of radioactive elements than the larger Kallada River due to higher radioactive minerals in the hinterland
rocks. Coastal configurations and the seasonal longshore current pattern seems to control along-shore distribution of minerals.
The proposed model for placer concentration suggests that the energy difference and seasonal current direction along this
coast is important. 相似文献
269.
The influence of inhomogeneities of surface currents on the intensity of breaking wind waves is considered and a model for the relation between whitecap contrasts and the tensor of current gradients is developed. The imagery of typical patterns of ocean currents is discussed. The results of field observations supporting this model are given.Translated by Mikhail M. Trufanov. 相似文献
270.
The relationship between the RMS amplitudes of the wind wave spectral components and the wind speed has been studied at ten frequencies in the band of 0.65–23 Hz. To measure the parameters of the high-frequenci waves, a resistance elevation wave gauge was operated, which was deployed in the Black See on an oceanographic platform near Katsively. The correlation between the wave amplitudes and the wind velocity at high frequencies of 5–23 Hz, corresponding to gravitation-capillary ripples, was found to reach a value of 0.8. At lower frequencies of 0.65–4.3 Hz, corresponding to short gravity waves, it dropped to 0.5–0.7. The response of spectral components to the wind speed variations in the gravity-capillary range is higher than in the range of short gravity waves. The results obtained differ from Phillips' idea about a saturated range for the frequency form of the spectrum of high-frequency gravity waves, since a linear dependence of the spectral amplitudes on the wind speed is established at a wind of force 1–8.Translated by Mikhail M. Trufanov. 相似文献