全文获取类型
收费全文 | 117822篇 |
免费 | 19117篇 |
国内免费 | 42972篇 |
专业分类
测绘学 | 4624篇 |
大气科学 | 27730篇 |
地球物理 | 29863篇 |
地质学 | 61265篇 |
海洋学 | 23350篇 |
天文学 | 20784篇 |
综合类 | 4177篇 |
自然地理 | 8118篇 |
出版年
2021年 | 1006篇 |
2020年 | 2400篇 |
2019年 | 5872篇 |
2018年 | 6749篇 |
2017年 | 6458篇 |
2016年 | 7136篇 |
2015年 | 5982篇 |
2014年 | 5958篇 |
2013年 | 9021篇 |
2012年 | 6411篇 |
2011年 | 7179篇 |
2010年 | 6694篇 |
2009年 | 7315篇 |
2008年 | 6260篇 |
2007年 | 5975篇 |
2006年 | 5602篇 |
2005年 | 5141篇 |
2004年 | 5569篇 |
2003年 | 5108篇 |
2002年 | 4713篇 |
2001年 | 4193篇 |
2000年 | 3793篇 |
1999年 | 3554篇 |
1998年 | 3591篇 |
1997年 | 3636篇 |
1996年 | 3033篇 |
1995年 | 2808篇 |
1994年 | 2581篇 |
1993年 | 2412篇 |
1992年 | 2166篇 |
1991年 | 1823篇 |
1990年 | 1923篇 |
1989年 | 1673篇 |
1988年 | 1485篇 |
1987年 | 1597篇 |
1986年 | 1407篇 |
1985年 | 1603篇 |
1984年 | 1811篇 |
1983年 | 1661篇 |
1982年 | 1570篇 |
1981年 | 1430篇 |
1980年 | 1236篇 |
1979年 | 1179篇 |
1978年 | 1182篇 |
1977年 | 1059篇 |
1976年 | 1000篇 |
1975年 | 932篇 |
1974年 | 953篇 |
1973年 | 965篇 |
1972年 | 610篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
601.
602.
603.
On October 3 and 4, 1986, DSRVAlvin dives encountered a strong current at 2,300 m in South Wilmington Canyon. The current, estimated at 1 knot, transported surficial
sediment and constructed and modified bedforms. It appears to have been constant in its direction of flow from 30 to 40°.
The observed current was probably a burst of fast flow in a region of slow average currents in the Deep Western Boundary Undercurrent.
Such episodic events may have a greater influence on the stratigraphic record than the temporally longer more tranquil flow
conditions. 相似文献
604.
605.
The motion and the drift force of a floating OWC (oscillating water column) wave energy device in regular waves are studied taking account of the oscillating surface-pressure due to the pressure drop across the duct of the air chamber. The potential problem inside the chamber is formulated by making use of the Green integral equation associated with the Rankine-type Green function while the outer problem with the Kelvin-type Green function. The added mass, wave damping and excitation coefficients as well as the motion and drift force of the OWC device are calculated for various values of parameter related to the pressure drop. 相似文献
606.
The ecology of hydrocarbon-degrading bacteria were investigated during five cruises in Xiamen Harbor. The results demonstrated that number of hydrocarbon-degrading bacteria were 2.1×102-7.5×106 cell/1 and 1.7×102-1.5×106 ceil/g dry and hetcrotrophic bacteria were 3.0× 104-5.9× 109 cell/1 and 2.53× 103-5.0× 103 cell/g dry in seawater and sediment respectively. The isolated strains which can degrade the petroleum belong to fifteen genera. Most, strains can only degsade one kind of hydro- carbon or petroleum. The results showed that the population and the species-composition of hydro carbon-degrading microorganisms were positively correlated with existing level of oil pollution and with water temperature, but independent of total microbtat count. 相似文献
607.
It has for many years been controversial whether there was a Pleistocene high sea level on the Shandong Peninsula. Our investigations in recent years suggest that the red sandy sediments distributed around the Yuanyaodun village, Weihai County, the "Liukuang Red Bed" and the loess-like deposits near Penglai County should be terrestrial deposits, and there is will not a convincing evidence to confirm that abrasion landforms found above the 10m elevation oa the coast are of marine origin. From these, it is still not safe to say that a high sea level had occurred in the Shandong Peninsula during the Pleistocene. 相似文献
608.
Numerical simulation of undersea cable dynamics 总被引:7,自引:0,他引:7
A fully three-dimensional code has been written to compute the motion of a towed cable. The code is based on a robust and stable finite difference approximation to the differential equations derived from basic dynamics. A 3500-ft (1.07 km) cable pulled at 18.5 knots (34.3 km hr−1) through a circular turn of 700 yd (0.64 km) radius has been computed in about half of the real time of the maneuver. The computed displacements are close to the measured ones; the changes in depth are within 2%. 相似文献
609.
The Lagrangian diffusion equation appropriate for the dispersion of current followers (e. g., floats, drogues, drifters) is proposed. The analytical solution to the equation is obtained for a uniform deformation field, characterized by Lagrangian deformations and anisotropic eddy diffusivities both varying with time. Expressions are derived for the patch area and its elongation and rotation. For small values of elapsed time after the initial release the patch area can be accounted for by the exponential of the cumulative value of the horizontal divergence; the relative rate of change of the patch area can be accounted for by the horizontal divergence. 相似文献
610.
从统计分析看控制东海重矿物分布的因素 总被引:1,自引:0,他引:1
任何地质作用过程都是复杂的,东海也不例外,其沉积过程具有长期性、继承性和叠加性的特点.因而反映在矿物组合及其分布变化上较为复杂,影响因素颇多.然而,运用数学地质方法却可帮助我们寻找和确定其主要的影响因素,查明它们的相互关系,甚至建立定量描述的模式.而这正是传统地质学研究中的难题之一. 相似文献