全文获取类型
收费全文 | 131765篇 |
免费 | 2391篇 |
国内免费 | 940篇 |
专业分类
测绘学 | 3043篇 |
大气科学 | 9223篇 |
地球物理 | 26284篇 |
地质学 | 46450篇 |
海洋学 | 11910篇 |
天文学 | 29586篇 |
综合类 | 329篇 |
自然地理 | 8271篇 |
出版年
2021年 | 1284篇 |
2020年 | 1470篇 |
2019年 | 1606篇 |
2018年 | 3191篇 |
2017年 | 2993篇 |
2016年 | 3669篇 |
2015年 | 2075篇 |
2014年 | 3569篇 |
2013年 | 6813篇 |
2012年 | 3839篇 |
2011年 | 5207篇 |
2010年 | 4682篇 |
2009年 | 6153篇 |
2008年 | 5422篇 |
2007年 | 5329篇 |
2006年 | 5130篇 |
2005年 | 3928篇 |
2004年 | 3899篇 |
2003年 | 3671篇 |
2002年 | 3578篇 |
2001年 | 3136篇 |
2000年 | 3086篇 |
1999年 | 2563篇 |
1998年 | 2588篇 |
1997年 | 2438篇 |
1996年 | 2158篇 |
1995年 | 2104篇 |
1994年 | 1841篇 |
1993年 | 1741篇 |
1992年 | 1636篇 |
1991年 | 1559篇 |
1990年 | 1682篇 |
1989年 | 1483篇 |
1988年 | 1327篇 |
1987年 | 1603篇 |
1986年 | 1414篇 |
1985年 | 1728篇 |
1984年 | 2002篇 |
1983年 | 1906篇 |
1982年 | 1743篇 |
1981年 | 1648篇 |
1980年 | 1438篇 |
1979年 | 1400篇 |
1978年 | 1409篇 |
1977年 | 1263篇 |
1976年 | 1215篇 |
1975年 | 1183篇 |
1974年 | 1166篇 |
1973年 | 1217篇 |
1972年 | 747篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
P. J. Wingham 《Ocean Engineering》1977,4(2):57-74
The relationship between the depth and trail attained by a towed submerged vehicle and the magnitude and direction of the forces on it has been examined theoretically, for cases involving faired cables.It is shown that when the body force is varied the body in equilibrium moves on an almost circular path as if the cable were straight, and that depth changes depend primarily upon the change in the component of the body force that acts at right angles to the line joining the top and bottom of the cable.Examples are given which demonstrate that for bodies towed at large depression angles the use of water brakes is more effective in changing depth than the use of lifting wings.The data is presented so that a rapid preliminary assessment can be made of any proposed system to obtain the best combination of speed and scope for achieving a given depth with a body having known lift and drag coefficients. 相似文献
982.
983.
We describe the methodology and software developed for the numerical analysis of the characteristics of the horizontal and vertical structure of geostrophic currents. We present the results of computation of these characteristics according to the data of the summer survey of the Black Sea carried out as a part of the ComSBlack-92 program. The distinctive features of the space structure of geostrophic currents discovered as a result and the established parameters of their variability may supplement the existing data on the current field in the Black Sea. 相似文献
984.
Ya. A. Virolainen Yu. M. Timofeev A. V. Polyakov H. Steele M. Newchurch 《Izvestiya Atmospheric and Oceanic Physics》2006,42(6):752-764
A statistical ensemble of microphysical parameters of the background stratospheric aerosol at altitudes of 15 to 30 km is modeled on the basis of experimental data. The aerosol attenuation coefficients (AACs) in the wavelength range 0.38–16.3 μm are calculated for all realizations of the ensemble by algorithms of the Mie theory. Analysis of correlations between the AACs and the microphysical parameters indicate that the AAC correlates most strongly with the total volume V and area S of all particles. The errors of determining the microphysical parameters from AAC measurements are analyzed via the method of linear regression. It is shown that, if the AAC is measured with an error of 5%, the errors of determining both the particle size distribution (PSD) for particles with sizes of 0.4 to 4 μm and the parameter S are an order of magnitude smaller than the prior uncertainty, whereas the error of determining V is two orders of magnitude smaller than the prior uncertainty. Schemes of AAC measurements with the SAGE III, ISAMS, CLAES, HALOE instruments and an IR interferometer in the visible and IR regions are discussed. It is shown that combining the schemes makes it possible to extend the range of particle sizes for which the PSD is retrieved with a satisfactory accuracy and to increase the accuracy of determining S and V substantially and the accuracy of determining the total number of particles N opt to a lesser extent. Examples of interpreting AAC measurements carried out simultaneously with the SAGE III and HALOE instruments within the same spatial region are presented. A systematic discrepancy between vertical profiles of S and V obtained from SAGE III and HALOE measurements is revealed. 相似文献
985.
986.
987.
988.
Fertilisation and larval metamorphosis of reef-building corals are important life history events leading to recruitment of juvenile corals to reef populations. Little is known of the sensitivity of these early life phases to pollution, or their relative susceptibility to certain toxicants compared with established coral colonies. Inhibition of fertilisation and larval metamorphosis of the coral Acropora millepora (Ehrenberg, 1834) was assessed in response to solutions of the antifoulants tributyltin (TBT) and copper (Cu) using laboratory-based bioassays. Nominal concentrations that inhibited 50% fertilisation and metamorphosis (IC50) were calculated from 4 h fertilisation and 24 h metamorphosis assays and were based on introduced dose. Cu was most potent towards fertilisation with an IC50 of 17.4 micrograms/l. TBT however, proved more toxic to larval metamorphosis having an IC50 of 2.0 micrograms/l. Inert surfaces coated with either Cu- or TBT-based antifouling paint also inhibited fertilisation and metamorphosis. The degree of inhibition was correlated with surface area of the paint coating. These results indicate fertilisation and metamorphosis of coral can be sensitive to active components of antifouling paints. 相似文献
989.
cDNA's coding for cytochrome P4501A1 (CYP1A1), phenol UDP-glucuronosyltransferase (UDPGT) and glutathione S-transferase (GST-A) were cloned and sequenced from an expression library prepared from the liver of a 3-methylcholanthrene (3-MC) induced plaice. Plaice CYP1A1 and Phenol UDPGT display a high degree of structural conservation with homologous mammalian isoforms and their mRNAs were shown to be highly induced in liver after 3-MC treatment of fish. Expression of plaice GST-A, which displays closer homology to GSTs from plants and invertebrates than those of mammals, is repressed after 3-MC treatment. 相似文献
990.
The currents and surface level oscillations in the Sea of Azov ensuing from contraction of the mouth of Taganrog Bay are computed using the grid technique on the basis of a numerical solution to the system of quasi-linear, degenerate, parabolic, partial derivative equations (shallow-water equations). It is demonstrated what changes are to be expected in the dynamics of the Sea of Azov should this project be realized. The computations were carried out for typical wind directions.Translated by Vladimir A. Puchkin. 相似文献