全文获取类型
收费全文 | 99953篇 |
免费 | 1926篇 |
国内免费 | 952篇 |
专业分类
测绘学 | 2697篇 |
大气科学 | 7108篇 |
地球物理 | 20475篇 |
地质学 | 34940篇 |
海洋学 | 8636篇 |
天文学 | 22912篇 |
综合类 | 297篇 |
自然地理 | 5766篇 |
出版年
2021年 | 926篇 |
2020年 | 1036篇 |
2019年 | 1127篇 |
2018年 | 2542篇 |
2017年 | 2371篇 |
2016年 | 3017篇 |
2015年 | 1751篇 |
2014年 | 2887篇 |
2013年 | 5201篇 |
2012年 | 3064篇 |
2011年 | 4161篇 |
2010年 | 3576篇 |
2009年 | 4816篇 |
2008年 | 4352篇 |
2007年 | 4220篇 |
2006年 | 3966篇 |
2005年 | 3145篇 |
2004年 | 3082篇 |
2003年 | 2865篇 |
2002年 | 2754篇 |
2001年 | 2521篇 |
2000年 | 2399篇 |
1999年 | 1973篇 |
1998年 | 2070篇 |
1997年 | 2005篇 |
1996年 | 1610篇 |
1995年 | 1610篇 |
1994年 | 1396篇 |
1993年 | 1288篇 |
1992年 | 1188篇 |
1991年 | 1141篇 |
1990年 | 1205篇 |
1989年 | 1099篇 |
1988年 | 983篇 |
1987年 | 1181篇 |
1986年 | 1017篇 |
1985年 | 1262篇 |
1984年 | 1417篇 |
1983年 | 1312篇 |
1982年 | 1269篇 |
1981年 | 1123篇 |
1980年 | 1020篇 |
1979年 | 963篇 |
1978年 | 971篇 |
1977年 | 855篇 |
1976年 | 820篇 |
1975年 | 798篇 |
1974年 | 771篇 |
1973年 | 782篇 |
1972年 | 537篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
811.
Nicholas H. Vrolijk Nancy M. Targett Bruce R. Woodin John J. Stegeman 《Marine environmental research》1995,39(1-4)
The relationship between cytochrome P450 and feeding on terpenoid-rich gorgonian corals was investigated in a species of tropical butterflyfish and compared with two other sympatric congeners that do not feed on gorgonians. Fish were collected from non-polluted waters in Belize and the levels of two cytochrome P450 isozymes (CYP2B and CYP3A) were immunoquantitated in addition to quantification of total P450. Chaetodon capistratus regularly feeds on gorgonian corals and has higher levels of total hepatic microsomal cytochrome P450 than C. ocellatus or C. striatus. The content of hepatic P450 (0.588–0.794 nmol mg−1) in C. capistratus is among the highest ever reported in teleosts from non-polluted waters and is significantly greater than detected in C. ocellatus or C. striatus. Chaetodon capistratus also had a larger hepatic index (g liver per g fish) and more microsomal protein (mg protein per g liver), factors that translate into 3.3- to 8-fold more total P450 per g fish. Sexual differences in total P450 were observed between male and female C. capistratus, but not among the other species. The contents of proteins detected by immunoassay with polyclonal anti-scup P450B (CYP2B) and anti-human P4503A (CYP3A) were 2- to 10-fold and 2- to 20-fold greater, respectively, in C. capistratus than in the congeneric species. CYP2 and CYP3 gene families in mammals are thought to have evolved partially in response to dietary allelochemicals. These results suggest that these P450 isozymes may also be important in marine teleosts that feed on terpenoid-rich prey. 相似文献
812.
M. M. F. Yuen 《Ocean Engineering》1987,14(1)
The wave diffraction problem on axisymmetric structures are solved by treating the fluid field as two separate domains. The velocity potential in the inner domain is represented by a 1/r type Green's function whilst that of the outer domain is represented by an eigenfunction expansion. The simple form of the Green's function in the inner domain reduces significantly the computational effort whilst the eigenfunction expansion in the outer domain is able to satisfy the radiation boundary condition completely. The method requires to have elements cover the entire containing boundary. Results for a number of typical structural geometries are presented and discussions are made on the effect of various parameters. 相似文献
813.
Cabell S. Davis Scott M. Gallager Martin Marra W. Kenneth Stewart 《Deep Sea Research Part II: Topical Studies in Oceanography》1996,43(7-8)
Traditional methods for determining spatial distributions of planktonic taxa involve net, pump, and bottle collections followed by the tedious and time-consuming task of plankton sample analysis. Thus, plankton ecologists often require months or even years to process samples from a single study. In this paper, we present a method that allows rapid visualization of the distribution of planktonic taxa while at sea. Rapid characterization of plankton distributions is essential in the dynamic physical environment, where biological and physical patterns can change quickly. Such a “sample-and-observe” capability is necessary for mapping ephemeral features (such as patches, eddies, jets, plumes) and determining appropriate locations to conduct more localized sampling, including in situ observational studies. We describe the techniques used in imaging the plankton, analyzing the video, and visualizing the data. We present an example of at-sea data analysis conducted aboard R.V. Columbus Iselin on Georges Bank in May 1994 and visualizations of the 3-dimensional distribution of selected planktonic taxa in a 2 × 2 km × 90 m volume of seawater. A video of the image processing and visualization is included on the CD-ROM accompanying this volume and is an essential part of this paper. 相似文献
814.
Observations from a surface mooring, in a weak-flow regime over the southeastern Bering Sea shelf, were used to derive surface heat fluxes for the period May–July 1996. Changes in heat content of the water column also were determined from subsurface temperature measurements. Agreement of net surface heat flux and change in heat content was within 2%. This result provides additional evidence that heat advection and diffusion are small in this region. 相似文献
815.
The basic relations of the classical dyamic method have been complemented with the condition allowing for the non-monotonicity
of the vertical kinematic structure. The elements of the multi-layered system of geostrophic currents have been found to correlate
over depth with seawater density and hydrostatic pressure distribution. An example of the analysis of the vertical structure
of currents, involving specific hydrological data, is given.
Translated by Vladimir A. Puchkin. 相似文献
816.
817.
The potential of heterotrophs to degrade aromatic hydrocarbons derived from oil in water and sediments in the northern North Sea around the Brent, Beryl, Forties and Murchison oilfields and at a number of stations, from the Forties field to the Firth of Forth, was estimated using 1-14C naphthalene and 7, 10-14C benzo(a)pyrene. The degradation of uniformly labelled 14C mixed 1-amino acids was used as a measure of total heterotrophic activity. Results showed that microorganisms have the potential to degrade the smaller aromatic hydrocarbon molecules rapidly in the water column and in surface sediments. Close to the Beryl platform, where diesel-washed drill cuttings have been continuously dumped, the rate of input of hydrocarbons to the sediment has exceeded the rate of degradation. Mineralization of benzo(a)pyrene, estimated in the sediments only, was minimal. Close to production platforms the biodegradation rate of mixed 1-amino acids showed no increase comparable with that found for naphthalene, suggesting that existing microbial populations had not increased but adapted to degrade oil in water and sediments. 相似文献
818.
The sway, heave and roll added masses of three uniform cylinders with semi-circular, rectangular and triangular cross-sectional shapes in shallow and narrow water are numerically analysed. The method is based on simulation of the potential flow induced by the cylinder's mode of motion. The effects of shallow and narrow water on added mass are analysed and presented. It is concluded that the shallow and narrow water effects on added mass depend on the different cross-section shapes of the cylinders. In particular, the water depth effect on sway added mass is stronger than that on heave added mass while the narrow water effect on sway is weaker than that on heave. The shallow water effect on added mass tends to weaken the narrow water effect. Lastly the effect of shallow and narrow water on added mass on a rectangular cylinder is the strongest while that on a triangular cylinder is the weakest. 相似文献
819.
A. G. Matul T. A. Khusid V. V. Mukhina M. P. Chekhovskaya S. A. Safarova 《Oceanology》2007,47(1):80-90
The study of diatoms and benthic foraminifers from the southeastern shelf of the Laptev Sea shows that their most diverse and abundant recent assemblages populate the peripheral underwater part of the Lena River delta representing the marginal filter of the sea. This area is characterized by an intense interaction between the fresh waters of the Siberian rivers and the basin seawater, the Atlantic one included. Local Late Holocene (~last 2300 years) environments reflect the main regional and global paleoclimatic changes, the Medieval Warm Period (~600–1100 years B.P.) and the Little Ice Age (~100–600 years B.P.) inclusive. In addition, the composition and distribution of planktonic foraminifers implies a strong influence of the Atlantic water during the Holocene optimum ~5100–6200 years B.P. 相似文献
820.