全文获取类型
收费全文 | 77412篇 |
免费 | 1081篇 |
国内免费 | 1430篇 |
专业分类
测绘学 | 2582篇 |
大气科学 | 5640篇 |
地球物理 | 14616篇 |
地质学 | 31213篇 |
海洋学 | 6064篇 |
天文学 | 13616篇 |
综合类 | 2272篇 |
自然地理 | 3920篇 |
出版年
2022年 | 408篇 |
2021年 | 668篇 |
2020年 | 742篇 |
2019年 | 773篇 |
2018年 | 6185篇 |
2017年 | 5415篇 |
2016年 | 4279篇 |
2015年 | 1147篇 |
2014年 | 1777篇 |
2013年 | 3015篇 |
2012年 | 2818篇 |
2011年 | 4970篇 |
2010年 | 4052篇 |
2009年 | 4811篇 |
2008年 | 4073篇 |
2007年 | 4577篇 |
2006年 | 2286篇 |
2005年 | 1678篇 |
2004年 | 1820篇 |
2003年 | 1735篇 |
2002年 | 1591篇 |
2001年 | 1286篇 |
2000年 | 1233篇 |
1999年 | 961篇 |
1998年 | 941篇 |
1997年 | 982篇 |
1996年 | 805篇 |
1995年 | 768篇 |
1994年 | 787篇 |
1993年 | 633篇 |
1992年 | 629篇 |
1991年 | 599篇 |
1990年 | 648篇 |
1989年 | 540篇 |
1988年 | 545篇 |
1987年 | 612篇 |
1986年 | 499篇 |
1985年 | 707篇 |
1984年 | 661篇 |
1983年 | 671篇 |
1982年 | 650篇 |
1981年 | 555篇 |
1980年 | 618篇 |
1979年 | 486篇 |
1978年 | 487篇 |
1977年 | 436篇 |
1976年 | 416篇 |
1975年 | 416篇 |
1974年 | 419篇 |
1973年 | 393篇 |
排序方式: 共有10000条查询结果,搜索用时 468 毫秒
931.
Qualitative and quantitative composition of meiobenthos was studied in Amursky Bay (Peter the Great Bay, the East Sea). Ten
taxonomic groups were found, where nematodes were dominant. Density of meiobenthos in ground sediments of the Bay were not
uniform, and the average density was measured at 126.4±62.3 ind. m-2. 56 species of nematodes were detected, and dominant species wereSabatieria palmaris, Paracanthonchus macrodon, Sphaerolaimus limosus, S. gracilis andOncholaimium ramosum. Five taxocenes of nematodes were allocated based on the results of cluster analysis and species domination according to density.
Low diversity in species composition of nematodes was noted in the northwestern part of the Bay, which is a zone of desalination,
and in the eastern part, which is exposed to household drains. 相似文献
932.
We have sampled particles of native aluminium (Al°) in two sediment cores from the Central Indian Basin (CIB). The cores are geographically separated but are located at the base of two seamounts. The native Al° particles occurring as grains and spherules, have an average Al content of 95% and are associated with volcanogenic–hydrothermal material. Morphologically and compositionally, the specimens are similar to those reported from the East Pacific Rise. After ruling out several processes for the presence of the native Al°, we hypothesize that during progressive melting of magma, a basaltic magma is produced which has high contents of reductants such as methane and hydrogen, and a low oxygen fugacity. During the upward migration of such magma, reduction to metallic aluminium and the formation of native Al° particles takes place. 相似文献
933.
An unsteady wave driver for narrowbanded waves: modeling nearshore circulation driven by wave groups
In this paper, we derive an unsteady refraction–diffraction model for narrowbanded water waves for use in computing coupled wave–current motion in the nearshore. The end result is a variable coefficient, nonlinear Schrödinger-type wave driver (describing the envelope of narrow-banded incident waves) coupled to forced nonlinear shallow water equations (describing steady or unsteady mean flows driven by the short-wave field). Comparisons with experimental data show that good accuracy can be obtained for cases of nonbreaking wave transformation. Numerical simulations show that the interaction of wave groups with longshore topographic nonuniformities generates strong edge wave resonances, providing a generating mechanism for low-order edge waves. 相似文献
934.
935.
936.
V. N. Kudryavtsev 《Physical Oceanography》1996,7(2):99-125
This paper discusses a simplified model for the evolution of the atmospheric planetary boundary layer overlying a thermal
front in the sea. The model provides local values of the friction/heat transfer geostrophic coefficients and the direction
of surface wind stress, as well as the wind/temperature profiles at any point on the front. With the running over a warm front,
the baroclinicity of the internal boundary layer leads to the generation of a near-surface current of air directed down the
front. The model can be used to interpret radar imagery of the sea surface with the purpose of determining its mesoscale variability.
Translated by Vladimir A. Puchkin. 相似文献
937.
The distribution and geochemical composition of suspended-particulate matter (SPM) in the East China Sea (ECS) were investigated
during the summer period of high continental runoff to elucidate SPM sources, distribution and cross-shelf transport. The
spatial variability of SPM distribution (0.3–6.5 mg l−1) and geochemical composition (POC, Al, Si, Fe, Mn, Ca, Mg and K) in the ECS was pronounced during summer when the continental
fluxes of freshwater and terrestrial materials were highest during the year. Under the influences of Changjiang runoff, Kuroshio
intrusion, surface production and bottom resuspension, the distribution generally showed strong gradients decreasing seaward
for both biogenic and lithogenic materials. Particulate organic carbon was enriched in surface water (mean ∼18%) due to the
influence of biological productivity, and was diluted by resuspended and/or laterally-transported materials in bottom water
(mean 9.4%). The abundance of lithogenic elements (Al, Si, Fe, Mn) increased toward the bottom, and the distribution correlations
were highly significant. Particulate CaCO3 distribution provided evidence that the SPM of the bottom water in the northern part of the study area was likely mixed with
sediments originally derived from Huanghe. A distinct benthic nepheloid layer (BNL) was present in all seaward transects of
the ECS shelf. Sediment resuspension may be caused by tidal fluctuation and other forcing and be regarded as the principal
agent in the formation of BNL. This BNL was likely responsible for the transport of biogenic and lithogenic particles across
or along the ECS shelf. Total inventories of SPM, POC and PN are 46, 2.8 and 0.4 Tg, respectively, measured over the total
area of 0.45 × 106 km2 of the ECS shelf. Their mean residence times are about 27, 13 and 11 days, respectively. The inventory of SPM in the water
column was higher in the northernmost and southernmost transects and lower in the middle transects, reflecting the influences
of terrestrial inputs from Changjiang and/or resuspended materials from Huanghe deposits in the north and perhaps from Minjiang
and/or Taiwan’s rivers in the south. The distribution and transport patterns of SPM and geochemical elements strongly indicate
that continental sources and cross-shelf transport modulate ECS particulate matter in summer. 相似文献
938.
939.
The organic carbon of 280–320 m deep Laurentian Trough sediments at landward and seaward sites (13–24 mgN/g) consisted of carbohydrates (15–22%), hydrolysable amino acids (7–13%), lipids (1–5%), labile proteins (0.3–1%) and a non-characterized fraction (62–74%). Amino acids, proteins and uncharacterized compounds accounted for 21–43, 0.9–4 and 51–78%, respectively, of total nitrogen (1.2–2.2 mgN/g). A clear reactivity trend (pheopigments ? lipids > proteins > amino acids ≈ nitrogen > carbon > carbohydrates) was deduced from the concentration decreases between settling particles and surficial sediments. This was confirmed by one-year inventories in the top cm, burial rates at 35 cm depth, and one-G model calculations. Lipids were a dominant substrate near the sediment-water interface whereas carbohydrates and amino acids constituted the principal energy sources deeper in the sediment. In the porewaters, DOC levels were low (2–6 mg/l) in the top 4 cm, indicating rapid removal (i.e. consumption, irrigation, diffusion), and increased with depth (8–12 mg/l), reflecting the buildup of refractory products. There were also clear compositional changes of DOC with depth. Geographical differences in water column fluxes were recorded in the sediments. The organic contents and ratios were higher at the landward site due to higher rates of sedimentation, bioturbation and terrestrial and total organic inputs. At the seaward station, the lower rates of these processes and stronger marine influence resulted in lower ratios and a more complete decay of organic matter within the top 35 cm sediments. 相似文献
940.
V. A. Dulov S. I. Klyushnikov V. N. Kudryavtsev O. V. Shulgin O. G. Shcherbak 《Physical Oceanography》1991,2(4):269-282
An overview of experiments is given on the observation of the dependence of the intensity of wind wave breaking on large-scale
currents' inhomogeneities and atmospheric boundary layer stratification. The data were interpreted using a model in which
the variance of the wind wave breaking intensity reflects fluctuations in the influx of energy to wind waves due to various
factors.
Translated by V. Puchkin. 相似文献