全文获取类型
收费全文 | 95501篇 |
免费 | 20768篇 |
国内免费 | 44627篇 |
专业分类
测绘学 | 5349篇 |
大气科学 | 26387篇 |
地球物理 | 24830篇 |
地质学 | 57524篇 |
海洋学 | 21213篇 |
天文学 | 13804篇 |
综合类 | 5558篇 |
自然地理 | 6231篇 |
出版年
2023年 | 555篇 |
2022年 | 1362篇 |
2021年 | 1925篇 |
2020年 | 2999篇 |
2019年 | 6445篇 |
2018年 | 7474篇 |
2017年 | 7067篇 |
2016年 | 7504篇 |
2015年 | 6100篇 |
2014年 | 6371篇 |
2013年 | 8144篇 |
2012年 | 6733篇 |
2011年 | 6952篇 |
2010年 | 6655篇 |
2009年 | 6510篇 |
2008年 | 5462篇 |
2007年 | 5349篇 |
2006年 | 4910篇 |
2005年 | 4391篇 |
2004年 | 4527篇 |
2003年 | 4163篇 |
2002年 | 3799篇 |
2001年 | 3478篇 |
2000年 | 3100篇 |
1999年 | 3145篇 |
1998年 | 3090篇 |
1997年 | 3071篇 |
1996年 | 2561篇 |
1995年 | 2361篇 |
1994年 | 2251篇 |
1993年 | 2003篇 |
1992年 | 1770篇 |
1991年 | 1465篇 |
1990年 | 1458篇 |
1989年 | 1277篇 |
1988年 | 1128篇 |
1987年 | 1110篇 |
1986年 | 907篇 |
1985年 | 1001篇 |
1984年 | 1053篇 |
1983年 | 919篇 |
1982年 | 930篇 |
1981年 | 717篇 |
1980年 | 708篇 |
1979年 | 614篇 |
1978年 | 545篇 |
1977年 | 525篇 |
1976年 | 457篇 |
1974年 | 452篇 |
1973年 | 473篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
701.
-In order to avoid prescribing open boundary condition on the upstream side of the Hangzhou Bay, in numerical simulation of the tides and residual currents of the Bay, a 1-D model for the Qiantang River is connected to the 2-D model for the Hangzhou Bay. The harmonic constants of diurnal constituent [ (K1 O1)/2],semidiurnal constituent (M2) and shallow water constituent (M4) are obtained. The results produced by the combined model are in better agreement with the observed ones than those produced solely by the original 2-D model. The combined model gives much more reliable results for tide-induced residual water level and current. 相似文献
702.
Effect of Cyclic Loading Frequency on Undrained Behaviors of Undisturbed Marine Clay 总被引:2,自引:0,他引:2
Based on a series of cyclic triaxial tests, the effect of cyclic frequency on the undrained behaviors of undisturbed marine clay is investigated. For a given dynamic stress ratio, the accumulated pore water pressure and dynamic strain increase with the number of cycles. There exists a threshold value for beth the accumulated pore water pressure and dynamic strain, below which the effect of cyclic frequency is very small, but above which the accumulated pore water pressure and dynamic strain increase intensely with the decrease of cyclic frequency for a given number of cycles. The dynamic strength increases with the increase of cyclic frequency, whereas the effect of cyclic frequency on it gradually diminishes to zero when the number of cycles is large enough, and the dynamic strengths at different frequencies tend to the same limiting minimum dynamic strength. The test results demonstrate that the reasons for the frequency effect on the undrained soil behaviors are beth the creep effect induced by the loading rate and the decrease of sample effective confining pressure caused by the accumulated pore water pressure. 相似文献
703.
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
704.
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
705.
A basalt outcrop was discovered on Alderdice Bank on the outer Louisiana continental shelf. The basalt shows an age of 76.8 ± 3.3 × 106 years. Textural, mineralogical, and chemical characteristics indicate that it is an alkali basalt of shallow intrusive origin. It was probably brought to the seafloor by salt tectonics and exposed due to salt dissolution.An accurate account of the Mesozoic geologic history of the Gulf of Mexico must consider the apparent consanguinity of all magmatic rocks of the region, including the Alderdice Bank basalt, and the apparent basinward decrease in age of magmatic activities. 相似文献
706.
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
707.
708.
Parthenogenesis in Laminaria and Alaria has been observed by Yabu, Nakaharaet al. and Fang et al. After we had made some preliminary progress in the study ofthe haploid phases of Laminaria japonica, similar study was started in 1974 on anotherspecies of brown algae, i. e., Undaria pinnatifida Sur. Some interesting results of such astudy on Undaria are summarized here. I. MATERIAL AND METHODS The material used in the experiments was mature sporophyte of Undaria collectedfrom the lower tide regions at Qingdao. The methods used in collecting Undaria zoo- 相似文献
709.
黄海鲱鱼的人工孵化及胚胎发育的初步观察 总被引:1,自引:0,他引:1
对鲱科鱼类个体发育及早期形态特征的研究,国外早已进行过,尤以苏联和日本的资料最多。 相似文献
710.
A new and inexpensive pop-up ocean-bottom hydrophone recorder has been developed for use in seismic refraction experiments. It is capable of operating in water depths of up to 4000 m and in very rugged topography, and uses an acoustic command system built by the U.K. Institute of Oceanographic Sciences for recovery. The instrument is mounted in an inexpensive cylindrical pressure case based on commercially available extruded aluminium alloy tubing, and uses glass spheres and syntactic foam for buoyancy. Hydrophone and clock signals are frequency modulated and recorded on tape cassettes, with a recording duration of three hours allowing up to 18 programmed shot windows. The prototype has made seven free descents on the Mid-Atlantic ridge and in the Gulf of Oman, and successfully recorded shots under operational conditions for the first time in September 1979. The total component cost of the prototype was £2740 (1979 prices).(Department of Earth Sciences, University of Cambridge Contribution No. ES135). 相似文献