全文获取类型
收费全文 | 386篇 |
免费 | 53篇 |
国内免费 | 102篇 |
专业分类
测绘学 | 4篇 |
大气科学 | 104篇 |
地球物理 | 144篇 |
地质学 | 200篇 |
海洋学 | 54篇 |
天文学 | 4篇 |
综合类 | 8篇 |
自然地理 | 23篇 |
出版年
2023年 | 2篇 |
2022年 | 13篇 |
2021年 | 10篇 |
2020年 | 9篇 |
2019年 | 11篇 |
2018年 | 9篇 |
2017年 | 15篇 |
2016年 | 15篇 |
2015年 | 10篇 |
2014年 | 22篇 |
2013年 | 24篇 |
2012年 | 12篇 |
2011年 | 20篇 |
2010年 | 25篇 |
2009年 | 29篇 |
2008年 | 35篇 |
2007年 | 39篇 |
2006年 | 27篇 |
2005年 | 26篇 |
2004年 | 22篇 |
2003年 | 18篇 |
2002年 | 19篇 |
2001年 | 14篇 |
2000年 | 13篇 |
1999年 | 14篇 |
1998年 | 14篇 |
1997年 | 8篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 10篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 7篇 |
1990年 | 9篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1986年 | 4篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 2篇 |
排序方式: 共有541条查询结果,搜索用时 437 毫秒
111.
底栖生物生产力现场测试系统(BCSPM)的建立及其初步实验结果 总被引:1,自引:1,他引:1
为对生态系统的健康评估及底栖生物资源的开发利用提供技术支撑,在胶州湾筏式养殖水域,建立了底栖生物生产力现场测试系统(BCSPM),并在光照和黑暗条件下测定了沉积物海水界面溶解氧随时间的变化、计算了氧通量、估算了底栖总初级生产力和群落呼吸。在光照较强的中午时刻测定的群落总生产力为20.76mgCm^-2h^-1;养殖水域沉积物中的群落呼吸要高于邻近水域。BCSPM整体运转良好,初步结果为系统的改进和进一步实验提供了依据。 相似文献
112.
Rate coefficients have been measured for the reactions of hydroxyl radicals with five aliphatic ethers over the temperature range 242–328 K. Competitive studies were carried out in an atmospheric flow reactor in which the hydroxyl radicals were generated by the photolysis of methyl nitrite in the presence of air containing nitric oxide. The reaction of OH with 2,3-dimethyl-butane was used as the reference reaction and the following Arrhenius parameters have been obtained for the reactions: OH+RORproducts:
相似文献
ROR | E/kJ mol–1 | 1012 A/cm3 molecule–1 s–1 |
---|---|---|
dethyl ether | –2.8±0.4 | 3.5±0.6 |
di-n-propyl ether | –1.2±0.6 | 11.5±2.7 |
methylt-butyl ether | 0.85±0.59 | 4.0±1.3 |
ethyln-butyl ether | –1.3±0.5 | 8.7±1.7 |
ethylt-butyl ether | –1.2±0.6 | 3.0±0.8 |
113.
We describe texture, mineralogy and whole-rock composition of cognate monzonite sub-volcanic clasts within debris flow deposits
related to the 5000 years catastrophic phreatomagmatic eruption probably linked to the Sciara del Fuoco sector collapse. The
debris flows are at the top of accretionary lapilli-rich ash deposits overlying potassic (KS, shoshonites) lavas of the Neostromboli
period. The monzonites are inferred to be crystallized in situ, at low P, at the side walls and/or roof margins of a shallow magma chamber and to be cogenetic with the KS Neostromboli
extrusives. They can be considered "ideal orthocumulates" since they approximately retain a bulk liquid composition and possibly
represent "slowly cooled equivalents" of their KS shoshonite host rock. The "closure temperature" of final solidification
of the monzonite lithic suite was estimated through ternary-feldspar geothermobarometry, plagioclase–K-feldspar and K-feldspar–biotite
equilibria and is in the range of 750–790 °C with a maximum –logfO2 around 15.1–15.3. The estimated pressure of crystallization is <0.5 kbar. Potassic lavas and dikes, previously emplaced during
the Neostromboli period, also resemble the monzonites in both major trace elements and mineral chemistry. The cogenetic relationship
between KS Neostromboli extrusives and the monzonite host-rock magma from which the sub-volcanic clasts were derived is clear
evidence that a shallow magma chamber existed between the caldera collapse of the Vancori period and the Sciara del Fuoco
sector collapse (i.e. between 13 000 and 5000 years). The monzonite clasts were derived from crystallization at very shallow
depth (ca. 1 km) and strongly support the hypothesis of violent decompression of the shallow magmatic plumbing system during
the Sciara del Fuoco sector collapse. Climax of the regressive landslide event, with maximum disruption of the chamber walls,
took place during emplacement of the debris flows, i.e. during the late stage of the Neostromboli phreatomagmatic eruption.
Received: 15 September 1996 / Accepted: 5 May 1997 相似文献
114.
Mitrovica, northern Kosovo, is the site of some of the highest Pb concentrations reported in human populations; exemplified by Pb concentrations in scalp hair of up to 130 μg g−1 and widely-publicized of Pb-related ill-health and mortality amongst internally displaced populations. High human Pb burdens are accompanied by elevated concentrations of potentially harmful elements (PHEs) in soils and house dust within the city, which has a long history of mining and metallurgy. In this study enrichment-levels for PHEs in soils are quantified and compared to environmental quality guidelines and a statistically-derived estimation of background concentration. In addition, Pb isotopes (207Pb/206Pb, 208Pb/206Pb) are used to characterise the isotopic signatures of potential point sources of Pb and a mixing model employed to quantify the contribution of sources to Pb present in soils, house dust, and the scalp hair of children and young people. Pb isotopic evidence suggests that Pb in surface soils and house-dust is predominantly sourced from historical deposition of Pb-containing aerosols from metal smelting, with lower contributions from wind-blown dispersal of metalliferous waste. Pb present in scalp hair is interpreted as the result of non-occupational exposure and the ingestion and/or inhalation of Pb-enriched surface soil and house dust. This study represents one of the very few instances where this type of geochemical tracing technique has been successfully applied to definitively identify the source of Pb present within biological samples. The results of this study are of particular relevance to environmental management and highlight the human health risk posed by the legacy of now inactive mining and metallurgy in addition to the challenge posed in mitigating the risk posed by diffuse soil pollution. 相似文献
115.
针对城镇地下管线信息化建设中对大批量井室高效建模的要求,提出了地下管线井室的分类方法,在此基础上设计实现了真三维井室三维数据模型和自动化建模方法,并将该方法与传统3DMax建模方法在效率与效果上做了对比实验。实验表明,真三维井室自动化建模方法能极大提高井室三维建模的效率和精度。 相似文献
116.
Laboratory Studies on Property Changes in Surrounding Clays Due to Installation of Deep Mixing Columns 总被引:6,自引:0,他引:6
Shui-Long Shen Xing-Chun Huang Shou-Ji Du Jie Han 《Marine Georesources & Geotechnology》2003,21(1):15-35
This paper has identified six major factors causing property changes in surrounding soils during and after installation of deep mixing columns: soil thixotropy, soil fracturing, cement penetration and diffusion, cementation, consolidation, and heating. Laboratory tests were performed to investigate the effects of soil thixotropy, soil fracturing, and cementation in a soft marine clay, Ariake clay. Laboratory tests were conducted to evaluate property changes in surrounding clays due to installation of deep mixing columns. Test results showed that an influential zone of property changes existed in surrounding clay ranging from the edge of the columns to the distance of about twice the radius of the columns. Within this influential zone, water content decreased as samples neared the columns, while pH values and electric conductivity increased. Test results also showed that undrained shear strengths of the surrounding clays decreased during mixing but regained after a 7-day curing period and continued increasing during 28 days in this study. 相似文献
117.
Elena Roget Iossif Lozovatsky Xavier Sanchez Manuel Figueroa 《Progress in Oceanography》2006,70(2-4):126
Modern approaches to microstructure data processing, including wavelet denoising, are discussed. The wavelet procedure is applied to small-scale shear signals before estimating the dissipation rate ε and to the temperature/density profiles used to calculate Thorpe scales. Microstructure data obtained on the Mediterranean shelf of Catalonia are used to illustrate various approaches to the Thorpe displacement calculations. It is suggested that the Weibull probability function is an appropriate model for the Thorpe scale distribution. Microstructure measurements from the upper layer of the Boadella reservoir (Catalonia, Spain) support this finding.A new analytical approximation for the 1D Panchev–Kesich spectrum is deduced and the results of ε computation are compared with spectral fitting by the widely used Nasmyth spectrum. Applying the Kraichnan spectral model to compute ε from temperature spectra in the convective-viscous sub-range is examined as an alternative to the Batchelor spectrum. Microstructure measurements taken in Lake Banyoles (Catalonia, Spain) and in the North Atlantic were used for spectral calculations.Statistical analysis of eddy Kb and thermal Kθ diffusivities measured on a shallow shelf of the Black Sea shows the importance of process-orientated domain averaging of the diffusivities in obtaining good correspondence between Kb and Kθ in active turbulent regions. In weakly turbulent, stratified interior layers, the averaged Kb and Kθ differ significantly, which may point to the inapplicability of isotropic formulae used for ε and temperature dissipation χθ estimates, as well as to a dependence of the mixing efficiency γ on the Richardson number or in some cases on regions of fossil turbulence. 相似文献
118.
222Rn was measured in the near-bottom waters of the continental slope of the Mid-Atlantic Bight. Separate measurements of the 222Rn supported by dissolved 226Ra allowed the excess 222Rn that is derived from the underlying sediments to be distinguished. Measurements of production of 222Rn by the sediments were used to calculate fluxes of 222Rn from sediments that would be expected as a result of molecular diffusion. On the upper slope and on the lower slope excess 222Rn standing crops were, respectively, greater than and consistent with fluxes of radon from sediments by molecular diffusion as are typical of most ocean environments. On the middle slope, however, observed excess 222Rn concentrations and standing crops were significantly lower than what would be expected from the calculated fluxes from the underlying sediments. This unusual feature of low radon concentrations on the middle slope is referred to as the low-radon zone (LRZ). This LRZ was always present over several years and seasons, but was variable in intensity (excess-radon concentration and standing crop) and in location on the slope. Low concentrations of suspended particulate matter and low current velocities observed by others in the same region are consistent with low mixing as a possible cause of the LRZ. Radon profile shapes and recent work by others on near bottom mixing due to interactions between topography and internal waves, however, suggest that high mixing due to internal waves is a more likely cause of the LRZ. 相似文献
119.
潮间带大弹涂鱼产卵习性和自然受精卵孵化研究 总被引:5,自引:0,他引:5
从环氧树脂模型揭示了福建省福宁湾潮间带滩涂大弹涂鱼Boleophthalmus pectinirostris洞穴的整体结构。多数洞穴略呈Y字形,每个洞穴有主洞口和次洞口之分。春季5—6月大弹涂鱼洞穴的中下部出现1个产卵室,产卵室横切面的上方呈拱形,底部平坦。潮间带滩涂产卵习性实验表明,产卵前性成熟雄鱼建造产卵室,并引诱性成熟雌鱼进入产卵室内交配产卵,受精卵依靠粘着丝粘在产卵室的顶部和周壁。产卵后雄鱼留洞护卵。每个产卵室的受精卵总数为3 595—4 314粒,平均为3 957粒,平均受精率高达99.67%,受精卵密度为58—114粒.cm-2,平均为87粒.cm-2。产卵室顶部和周壁受精卵的粘着丝位于上端,胚体位于下端,呈倒立状态,大多数受精卵的胚体头部朝下,为反向卵(平均占98.07%),易于孵化出仔鱼。将潮间带洞穴内产卵室受精卵取回实验室,模拟洞穴的小生境进行孵化实验。2次模拟孵化实验结果表明,受精卵始终全淹没于海水的平均孵化率(81.19%—82.90%)高于受精卵湿露24h后才全淹没于海水的平均孵化率(76.38%—79.19%)。湿露而不淹没于海水的受精卵不能孵化出仔鱼。 相似文献
120.