全文获取类型
收费全文 | 11702篇 |
免费 | 3041篇 |
国内免费 | 3779篇 |
专业分类
测绘学 | 2049篇 |
大气科学 | 1576篇 |
地球物理 | 2337篇 |
地质学 | 7427篇 |
海洋学 | 2072篇 |
天文学 | 196篇 |
综合类 | 933篇 |
自然地理 | 1932篇 |
出版年
2024年 | 89篇 |
2023年 | 317篇 |
2022年 | 755篇 |
2021年 | 938篇 |
2020年 | 720篇 |
2019年 | 865篇 |
2018年 | 772篇 |
2017年 | 687篇 |
2016年 | 721篇 |
2015年 | 813篇 |
2014年 | 825篇 |
2013年 | 976篇 |
2012年 | 1000篇 |
2011年 | 1034篇 |
2010年 | 988篇 |
2009年 | 900篇 |
2008年 | 939篇 |
2007年 | 869篇 |
2006年 | 822篇 |
2005年 | 697篇 |
2004年 | 489篇 |
2003年 | 413篇 |
2002年 | 568篇 |
2001年 | 440篇 |
2000年 | 314篇 |
1999年 | 180篇 |
1998年 | 60篇 |
1997年 | 59篇 |
1996年 | 56篇 |
1995年 | 29篇 |
1994年 | 24篇 |
1993年 | 23篇 |
1992年 | 29篇 |
1991年 | 16篇 |
1990年 | 12篇 |
1989年 | 14篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1965年 | 4篇 |
1964年 | 2篇 |
1954年 | 8篇 |
1934年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
991.
Both the level 2.5 Mellor-Yamada turbulence closure scheme(MY) and K-profile parameterization(KPP) are popularly used by the ocean modeling community.The MY and the KPP are improved through including the non-breaking surface wave-induced vertical mixing(Bv),and the improved schemes were tested by using continuous data at the Papa ocean weather station(OWS) during 1961–1965.The numerical results showed that the Bv can make the temperature simulations fit much better with the continuous data from Papa Station.The two improved schemes overcame the shortcomings of predicting too shallow upper mixed layer depth and consequently overheated sea surface temperature during summertime,which are in fact common problems for all turbulence closure models.Statistical analysis showed that the Bv effectively reduced the mean absolute error and root mean square error of the upper layer temperature and increased the correlation coefficient between simulation and the observation.Furthermore,the performance of vertical mixing induced by shear instability and the Bv is also compared.Both the temperature structure and its seasonal cycle significantly improved by including the Bv,regardless of whether shear instability was included or not,especially for the KPP mixing scheme,which suggested that Bv played a dominant role in the upper ocean where the mean current was relatively weak,such as at Papa Station.These results may provide a clue to improve ocean circulation models. 相似文献
992.
Rainfall effects on wind waves and turbulence are investigated through the laboratory experiments in a large wind-wave tank. It is found that the wind waves are damped as a whole at low wind speeds, but are enhanced at high wind speeds. This dual effect of rain on the wind waves increases with the increase of rain rate, while the influence of rainfall-area length is not observable. At the low wind speed, the corresponding turbulence in terms of the turbulent kinetic energy (TKE) dissipation rate is significantly enhanced by rain- fall as the waves are damped severely. At the high wind speed, the augment of the TKE dissipation rate is suppressed while the wind waves are enhanced simultaneously. In the field, however, rainfall usually hin- ders the development of waves. In order to explain this contradiction of rainfall effect on waves, a possibility about energy transfer from turbulence to waves in case of the spectral peak of waves overlapping the inertial subrange of turbulence is assumed. It can be applied to interpret the damping phenomenon of gas trans- fer velocity in the laboratory experiments, and the variation of the TKE dissipation rates near sea surface compared with the law of wall. 相似文献
993.
The vertical structure of the atmospheric boundary layer over the central Arctic Ocean 总被引:2,自引:1,他引:1
The tropopause height and the atmospheric boundarylayer (PBL) height as well as the variation of inversion layer above the floating ice surface are presented using GPS (global position system ) radiosonde sounding data and relevant data obtained by Chinas fourth arctic scientific expedition team over the central Arctic Ocean (86°-88°N, 144°-170°W) during the summer of 2010. The tropopause height is from 9.8 to 10.5 km, with a temperature range between -52.2 and -54.10C in the central Arctic Ocean. Two zones of maximum wind (over 12 m/s) are found in the wind profile, namely, low- and upper-level jets, located in the middle troposphere and the tropopause, respectively. The wind direction has a marked variation point in the two jets from the southeast to the southwest. The average PBL height determined by two methods is 341 and 453 m respectively. These two methods can both be used when the inversion layer is very low, but the results vary significantly when the inversion layer is very high. A significant logarithmic relationship exists between the PBL height and the inversion intensity, with a correlation coefficient of 0.66, indicating that the more intense the temperature inversion is, the lower the boundary layer will be. The observation results obviously differ from those of the third arctic expedition zone (800-85° N). The PBL height and the inversion layer thickness are much lower than those at 870-88° N, but the inversion temperature is more intense, meaning a strong ice- atmosphere interaction in the sea near the North Pole. The PBL structure is related to the weather system and the sea ice concentration, which affects the observation station. 相似文献
994.
The Tarim Basin is the only petroliferous basin enriched with marine oil and gas in China. It is presently also the deepest basin for petroleum exploration and development in the world. There are two main sets of marine Source Rocks (SRs) in the Tarim Basin, namely the high over-mature Cambrian–Lower Ordovician (∈–O1) and the moderately mature Middle–Upper Ordovician (O2–3). The characteristic biomarkers of SRs and oils indicate that the main origin of the marine petroleum is a mixed source of ∈–O1 and O2–3 SRs. With increasing burial, the hydrocarbon contribution of the ∈–O1 SRs gradually increases. Accompanied by the superposition of multi-stage hydrocarbon-generation of the SRs and various secondary alteration processes, the emergence and abnormal enrichment of terpenoids, thiophene and trimethylaryl isoprenoid in deep reservoirs indicate a complex genesis of various deep oils and gases. Through the analysis of the biofacies and sedimentary environments of the ∈–O1 and O2–3 SRs, it is shown that the lower Paleozoic high-quality SRs in the Tarim Basin were mainly deposited in a passive continental margin and the gentle slope of the platform, deep-water shelf and slope facies, which has exhibited a good response to the local tectonic-sedimentary environment. The slope of the paleo-uplift is the mutual area for the development of carbonate reservoirs and the deposition of marine SRs, which would be favorable for the accumulation of petroleum. Due to the characteristics of low ground temperature, the latest rapid and deep burial does not cause massive oil-cracking in the paleo-uplift and slope area. Therefore, it is speculated that the marine reservoirs in the slope of the Tabei Uplift are likely to be a favorable area for deep petroleum exploration, while the oil-cracking gas would be a potential reserve around the west margin of the Manjiaer Depression. Hydrocarbons were generated from various unit SRs, mainly migrating along the lateral unconformities or reservoirs and the vertical faults. They eventually brought up three major types of exploration fields: middle and lower Cambrian salt-related assemblages, dolomite inner reservoirs and Middle and Lower Ordovician oil-bearing karst, which would become the most favorable target of marine ultra-deep exploration in the Tarim Basin. 相似文献
995.
玉树地震地表破裂调查与灾后重建避让选址研究 总被引:13,自引:0,他引:13
2010年4月14日07时49分40.7秒,青海省玉树县发生Ms7.1级地震。通过现场调查和分析,玉树地震的发震断裂是甘孜—玉树活动断裂的玉树段,地震产生的地表破裂长度为23km,走向北西西—北西,总体表现为左旋走滑特征,可进一步分为3段:西段呈连续延伸的左旋走滑破裂,在隆宝镇的"郭央烟宋多"附近(坐标:北纬33°03′11″、东经96°51′26″)最大水平位移达1.75m,可定为宏观震中;中段主要位于县城南侧,由多条右阶斜列的破裂组成;东段表现为逆冲兼左旋走滑。玉树地震除了造成大量房屋破坏外,次生地质灾害主要包括:地震砂土液化及其引起的公路变形、地震滑坡、地震诱发水渠破坏及其链生土质滑坡和泥石流等。通过对内外动力地质灾害的综合分析,初步提出了玉树地震灾区灾后重建避让选址的建议。 相似文献
996.
西太平洋深海沉积物古菌多样性垂直分布 总被引:3,自引:2,他引:1
以提取并纯化的西太平洋深海沉积物DNA为模板,利用古菌PCR特异性引物扩增出样品中古菌的16S rDNA片段,构建其克隆文库,建立阳性克隆子RFLP(Restriction Fragment Length Polymor-phism)酶切图谱。据酶切图谱对所获得的120个克隆进行测序,并与数据库中的序列进行比对,从而进行古菌的多样性和系统发育分析。结果表明,沉积物中扩增的16S rDNA古菌序列分别来自泉古生菌(Crenarchaeota)和广古生菌(Euryarchaeota),以Marine Benthic Group B(11.8%)、Marine Benthic Group D(13.6%)、Marine Crenarchaeotic Group(68.69%)为主。少量序列为South African Gold Mine Euryarchaeotic Group(1.07%)、Deep-Sea Hydrothermal Vent Euryarchaeotic Group(1.61%)、UIIB(1.25%)、VALIII(1.79%)、Marine Benthic Group E(0.18%)。以上结果表明西太平洋深海沉积物中有丰富多样的古菌群落。 相似文献
997.
998.
999.
通过地表观察和钻孔资料,对洞庭盆地安乡凹陷及其西缘第四纪构造沉积特征和环境演化进行了研究,为江汉—洞庭盆地第四纪地质研究补充了新的资料。凹陷总体呈南北向,周边为正断裂。凹陷内第四系厚一般为100-220 m,最厚达300 m,自下而上依次为早更新世华田组、汨罗组,中更新世洞庭湖组,晚更新世坡头组和全新世湖冲积。第四系以砾石层、砂层为主,次为(含)粉砂质黏土、黏土,岩性、岩相横向变化大。安乡凹陷西缘(即太阳山隆起东缘),呈自西向东缓倾的丘岗地貌。区内主要发育中更新世白沙井组,其中南部下部以砂、砾石层为主,上部为黏土;北部以粉砂质黏土沉积为主,下部可发育砂层。根据地貌、沉积及控凹断裂特征,重塑安乡凹陷及其西缘第四纪构造活动与环境演化过程:早更新世—中更新世早期,凹陷西边的北北东向周家店断裂伸展活动,安乡凹陷不均匀沉降,总体具河流和过流性湖泊环境并接受沅水沉积;同期凹陷西缘构造抬升,处于剥蚀的山地环境。中更新世中期断陷活动向西扩展,凹陷区为过流性湖泊环境;凹陷西缘地区转为河流(南部)和湖泊(北部)环境并接受沉积。中更新世晚期安乡凹陷及其西缘整体抬升并遭受剥蚀,凹陷西缘同时具有自西向东的掀斜。晚更新世安乡凹陷拗陷沉降,具河流和湖泊环境;同期凹陷西缘遭受剥蚀。晚更新世末受区域海平面下降影响,安乡凹陷遭受剥蚀。全新世安乡凹陷拗陷沉降,具泛滥平原之河流、湖泊环境。 相似文献
1000.