全文获取类型
收费全文 | 85014篇 |
免费 | 998篇 |
国内免费 | 572篇 |
专业分类
测绘学 | 2298篇 |
大气科学 | 5532篇 |
地球物理 | 16393篇 |
地质学 | 32299篇 |
海洋学 | 7112篇 |
天文学 | 19108篇 |
综合类 | 317篇 |
自然地理 | 3525篇 |
出版年
2022年 | 573篇 |
2021年 | 878篇 |
2020年 | 976篇 |
2019年 | 1094篇 |
2018年 | 4274篇 |
2017年 | 3814篇 |
2016年 | 3469篇 |
2015年 | 1258篇 |
2014年 | 2265篇 |
2013年 | 3664篇 |
2012年 | 3148篇 |
2011年 | 4862篇 |
2010年 | 4307篇 |
2009年 | 5175篇 |
2008年 | 4417篇 |
2007年 | 4930篇 |
2006年 | 3058篇 |
2005年 | 2231篇 |
2004年 | 2173篇 |
2003年 | 2086篇 |
2002年 | 2015篇 |
2001年 | 1706篇 |
2000年 | 1547篇 |
1999年 | 1210篇 |
1998年 | 1237篇 |
1997年 | 1259篇 |
1996年 | 984篇 |
1995年 | 954篇 |
1994年 | 887篇 |
1993年 | 769篇 |
1992年 | 685篇 |
1991年 | 709篇 |
1990年 | 729篇 |
1989年 | 688篇 |
1988年 | 635篇 |
1987年 | 701篇 |
1986年 | 600篇 |
1985年 | 779篇 |
1984年 | 885篇 |
1983年 | 790篇 |
1982年 | 777篇 |
1981年 | 711篇 |
1980年 | 667篇 |
1979年 | 581篇 |
1978年 | 638篇 |
1977年 | 548篇 |
1976年 | 489篇 |
1975年 | 499篇 |
1974年 | 464篇 |
1973年 | 542篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
971.
The dissolution of opaline silica of diatom tests in sea water 总被引:3,自引:0,他引:3
Two different series of measurements have been made of the solubilities and rates of solution in sea water of acid-washed siliceous tests of the diatomsThalassiosira decipiens andRhizosolenia hebetata. The kinetic approach was carried out on the assumption that the tests behave as identical solid spheres. If the tests were present in considerable excess over that required for saturation of the water with respect to silica, the dissolution obeyed first order reaction kinetics and its rate was proportional to the surface area of the exposed tests. When the tests were not in excess the kinetics of dissolution appeared to be more complex. This was considered to be due to a decrease in specific surface area as dissolution proceeded. An expression developed to allow for the change of surface area as a sphere dissolves offers a partial explanation of the kinetics when the tests are not present in excess. 相似文献
972.
V. A. Frol’kis I. L. Karol’ A. A. Kiselev Yu. E. Ozolin V. A. Zubov 《Izvestiya Atmospheric and Oceanic Physics》2007,43(4):413-422
This is a study of the sensitivity of model results (atmospheric content of main gas constituents and radiative characteristics of the atmosphere) to errors in emissions of a number of atmospheric gaseous pollutants. Groups of the model variables most dependent on these errors are selected. Two variants of emissions are considered: one without their evolution and the other with their variation according to the IPCC scenario. The estimates are made on the basis of standard statistical methods for the results obtained with the detailed onedimensional radiative—photochemical model of the Main Geophysical Observatory (MGO). Some approaches to such estimations with models of higher complexity and to the solution of the inverse problem (i.e., the estimation of the necessary accuracy of external model parameters for obtaining the given accuracy of model results) are outlined. 相似文献
973.
Hydrodynamic and sediment transport measurements from instrumentation deployed during a 54-day winter period at two sites on the Louisiana inner shelf are presented. Strong extratropical storms, with wind speeds of 7.8 to 15.1 m s-1, were the dominant forcing mechanism during the study. These typically caused mean oscillatory flows and shear velocities about 33% higher than fair weather (averaging 12.3 and 3.2 cm s-1 at the landward site, and 11.4 and 2.7 cm s-1 at the seaward site, respectively). These responses were coupled with mean near-bottom currents more than twice as strong as during fair weather (10.3 and 7.5 cm s-1 at the landward and seaward sites, respectively). These flowed in approximately the same direction as the veering wind, causing a net offshore transport of fine sand. Weak storms were responsible for little sediment transport whereas during fair weather, onshore sand transport of approximately 25-75% of the storm values appears to have occurred. This contradicts previous predictions of negligible fair-weather sediment movement on this inner shelf. 相似文献
974.
V. M. Kushnir 《Physical Oceanography》1997,8(1):29-38
Experimentally-derived data are used to scrutinize structural peculiarities of the upper boundary of deep near-bottom layer
in the Black Sea. Thermal fluxes through the layer’s upper boundary have been evaluated and compared with the geothermal fluxes.
Although there is significant divergence between the individual evaluations, the quantities at issue generally agree with
one another. It is shown that in evaluating thermal fluxes, it is necessary to consider fine structure of the differential-diffusive
type. Stability of the upper boundary of the deep near-bottom layer has been examined, and diagrams of stability/instability
resulting from the development of convection have been plotted.
Translated by Vladimir A. Puchkin. 相似文献
975.
M.E. vinogradov E.A. Shushkina V.I. Vedernikov N.P. Nezlin V.I. Gagarin 《Deep Sea Research Part II: Topical Studies in Oceanography》1997,44(9-10)
Data collected from 20 years of observations by the P. P. Shirshov Institute of Oceanology (about 250 comprehensive ecosystem stations) are summarized to evaluate the primary production and biomass of the principal groups of plankton in the Pacific Ocean. The stations were classified into geographical regions according to satellite determined criteria. The areas of these regions were evaluated according to CZCS data from 1978 to 1986. The total value of primary production was evaluated as 26·9 Gt C year−1. Taking the “bottle effect” correction into account, this value may be as high as 45.6 Gt C year−1. Total biomass values of phytoplankton (134 Mt C), bacteria (86 Mt C), protozoa (26 Mt C) and mesoplankton (184 Mt C) were also calculated. Seasonal variabilities of all these values were remarkably insignificant. 相似文献
976.
Water velocity and density profiles were obtained in late-spring and late-winter to document reversing mean circulation patterns at the entrance to a semiarid coastal lagoon, the Bay of Guaymas, in the Gulf of California, Mexico. The lagoon is shallow but the bathymetry at its entrance is similar to that of temperate estuaries with an asymmetrically positioned channel flanked by shoals. In late-spring the mean circulation at the entrance to the lagoon was driven by horizontal density gradients that arose from excess evaporation over precipitation in the area as evidenced by water density profiles. The lagoon exported relatively warm (25·8 °C) and salty (36·2) water to the Gulf of California through the channel. This export was consistent with inverse estuarine circulation influenced by bathymetry. In late-winter, the circulation at the entrance of the lagoon was mostly driven by wind stress that blew from the northwest, roughly along the main axis of the lagoon. Relatively cool (16·0) °C) and less salty (35·1) water from the Gulf of California was driven into the lagoon within the channel. Density gradients inside the lagoon seem to have played a secondary role in driving the circulation. The late-winter circulation was then estuarine-like, with outflow in the direction of the wind over the shallow areas and a compensatory inflow appearing in the channel as expected from theory of wind-driven flow over bathymetry. This estuarine-like circulation developed despite the lack of measurable freshwater input to the lagoon and was the opposite to that observed in late-spring. These observations then document a reversal in water exchange patterns from season to season in a semiarid coastal lagoon. The observations also constitute one of the few reported examples of flow over shoals driven in the same direction as the wind stress with a compensatory flow in the channel. 相似文献
977.
Analysis of microbiological and chitinase activities relative to the white shrimpPenaeus setiferus, and its chitinoclastic endosymbionts, have demonstrated the relevance of total chitinolytic processes in penaeid biology. Microorganisms may serve as a direct source of nutrients for the animal as well as in the elaboration of extracellularin situ chitinase enzymes. The enzyme produced by the predominant gut bacteria,Beneckea neptuna, is a moderately actively inducible chitinase while the shrimp has an indigenous constitutive chitinase and chitobiase system. Factors of temperature, pH, ion inhibition and reducing sugar ratios have been compared for the bacterial and animal enzymes. This dual enzyme system suggests that metabolic chitin transformation may play a vital role in crustacean metabolism. 相似文献
978.
Freezing as a method of sample preservation for the analysis of dissolved inorganic nutrients in seawater 总被引:1,自引:0,他引:1
John E. Dore Terrence Houlihan Dale V. Hebel Georgia Tien Luis Tupas David M. Karl 《Marine Chemistry》1996,53(3-4)
It is often desirable or necessary to store collected seawater samples prior to analysis for dissolved inorganic nutrients. It is therefore important to establish preservation and storage techniques that will ensure sample integrity and will not alter the precision or accuracy of analysis. We have performed a series of experiments on the storage of nutrient samples collected at the oligotrophic North Pacific benchmark Station ALOHA, using both standard autoanalyses and low-level techniques. Our results reveal that for oligotrophic oceanic waters, the immediate freezing of an unfiltered water sample in a clean polyethylene bottle is a suitable preservation method. This procedure is simple, it avoids potentially contaminating sample manipulations and chemical additions, and it adequately preserves the concentrations of nitrate + nitrite, soluble reactive phosphate, and soluble reactive silicate within a single water sample. 相似文献
979.
980.
Cluster analysis is discussed in the context of its application to map various test areas in the sea. By analysing the correspondence of the identified categories to areas with specific hydrological conditions, an attempt is made to relate the types of fine structure to diverse background conditions. With two test areas mapped, a conclusion is made as to the possible application of cluster analysis to this end.Translated by Vladimir A. Puchkin. 相似文献