全文获取类型
收费全文 | 214篇 |
免费 | 66篇 |
国内免费 | 116篇 |
专业分类
测绘学 | 1篇 |
大气科学 | 1篇 |
地球物理 | 61篇 |
地质学 | 274篇 |
海洋学 | 38篇 |
天文学 | 5篇 |
综合类 | 6篇 |
自然地理 | 10篇 |
出版年
2023年 | 3篇 |
2022年 | 6篇 |
2021年 | 13篇 |
2020年 | 8篇 |
2019年 | 11篇 |
2018年 | 10篇 |
2017年 | 8篇 |
2016年 | 11篇 |
2015年 | 6篇 |
2014年 | 18篇 |
2013年 | 11篇 |
2012年 | 15篇 |
2011年 | 22篇 |
2010年 | 21篇 |
2009年 | 16篇 |
2008年 | 26篇 |
2007年 | 20篇 |
2006年 | 19篇 |
2005年 | 22篇 |
2004年 | 18篇 |
2003年 | 14篇 |
2002年 | 23篇 |
2001年 | 14篇 |
2000年 | 11篇 |
1999年 | 13篇 |
1998年 | 10篇 |
1997年 | 5篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1987年 | 1篇 |
排序方式: 共有396条查询结果,搜索用时 31 毫秒
41.
Abdul Hameed Shahida Hasnain 《中国海洋湖沼学报》2005,23(4):433-441
Many unicellular cyanobacteria were isolated from different places: fields, ponds, polluted water, and soils from Muredkey and Kasur tannery areas, near Lahore, Pakistan. Different media like BG 11 medium, Bold Basal medium, Chu's # 10 medium and Gotham's medium, in standard forms and with slight variations of ingredients, and different pH, temperature and light regimes were checked for the optimum growth of the isolates. The isolation pro- cedure was repeated with different concentrations of chromium to select the resistant strains. These selected strains grew on chromium of the range 100-200 μg/ml in BG 11 medium. Cyanobacteria were maintained in solid and liquid media with/without shaking. Cyanobacterial strains were collected from natural habitats that were accompanied by a diversified group of organisms including bacteria, protozoan, and rotifers etc. In order to eliminate these agents termed as contaminants, we used several methods including phenol treatment, use of antibiotic and careful manual picking of unicellular cyanobacteria. Resistance of these strains against different heavy metals (ZnSO4, MnSO4, NiSO4, COCl2, Pb(NO3)3, CuSO4, HgCl2, AgNO3 and CdCl2) and antibiotics (erythromycin, streptomycin, kanamycin, chloramphenicol, neomycin) was evaluated. Optimum temperature was 30℃ with variable pH for the reduction of Cr^6+ in to Cr^3+ in majority of strains. 相似文献
42.
The >1800 km long Coast Mountains–North Cascades orogen of the Canadian Cordillera and north-western US developed as a continental magmatic arc. Metamorphic rocks in the orogen contain widespread evidence for burial of supracrustal rocks to depths of c. 40 km, followed by nearly isothermal decompression to depths of <10 km. Near many shallowly-emplaced, mid-Cretaceous plutons, low-pressure contact metamorphic effects were overprinted by high-pressure regional metamorphic minerals and textures, as evidenced by kyanite±staurolite pseudomorphs after andalusite in metapelitic rocks. Therefore, near-pluton rocks record the loading history of the orogen. Metapelitic rocks not associated with plutons only preserve evidence for high-pressure conditions and/or high-temperature decompression, as indicated, for example, by sillimanite and cordierite after kyanite and garnet, respectively. Petrological evidence for burial and decompression is therefore recorded in different rocks. Various regions of the orogen differ in timing of metamorphism, the overall shape of P–T paths and the relative timing and regional extent of the high-pressure event, but most of these data and observations are consistent with thrusting and/or pure shear thickening as primary loading mechanisms throughout the orogen, as opposed to magma-dominated loading. This interpretation is further supported by comparison with thermal models, which demonstrate that the P–T paths are consistent with simultaneous thrusting and folding at a high initial geothermal gradient (35–40 °C km?1) in much of the orogen. A high geothermal gradient supports tectonic models invoking intra-arc contraction and suggests that magmatism played an important role in regional temperature-time paths. This tectonic-thermal history may be typical of other contractional orogens and illustrates the importance of large vertical displacement of crust in magmatic arcs. 相似文献
43.
Transformation of ammonium nitrogen and response characteristics of nitrifying functional genes in tannery sludge contaminated soil
下载免费PDF全文
![点击此处可从《地下水科学与工程》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Kong Xiang-ke Zhang Zi-xuan Wang Ping Wang Yan-yan Zhang Zhao-ji Han Zhan-tao Ma Li-sha 《地下水科学与工程》2022,10(3):223-232
High concentrations of ammonium nitrogen released from tannery sludge during storage in open air may cause nitrogen pollution to soil and groundwater. To study the transformation mechanism of NH4+-N by nitrifying functional bacteria in tannery sludge contaminated soils, a series of contaminated soil culture experiments were conducted in this study. The contents of ammonium nitrogen (as NH4+-N), nitrite nitrogen (as NO2?-N) and nitrate nitrogen (as NO3?-N) were analyzed during the culture period under different conditions of pollution load, soil particle and redox environment. Sigmodial equation was used to interpret the change of NO3?-N with time in contaminated soils. The abundance variations of nitrifying functional genes (amoA and nxrA) were also detected using the real-time quantitative fluorescence PCR method. The results show that the nitrification of NH4+-N was aggravated in the contaminated silt soil and fine sand under the condition of lower pollution load, finer particle size and more oxidizing environment. The sigmodial equation well fitted the dynamic accumulation curve of the NO3?-N content in the tannery sludge contaminated soils. The Cr(III) content increased with increasing pollution load, which inhibited the reproduction and activity of nitrifying bacteria in the soils, especially in coarse-grained soil. The accumulation of NO2?-N contents became more obvious with the increase of pollution load in the fine sand, and only 41.5% of the NH4+-N was transformed to NO3?-N. The redox environment was the main factor affecting nitrification process in the soil. Compared to the aerobic soil environment, the transformation of NH4+-N was significantly inhibited under anaerobic incubation condition, and the NO3?-N contents decreased by 37.2%, 61.9% and 91.9% under low, medium and high pollution loads, respectively. Nitrification was stronger in the silt soil since its copy number of amoA and nxrA genes was two times larger than that of fine sand. Moreover, the copy numbers of amoA and nxrA genes in the silt soil under the aerobic environment were 2.7 times and 2.2 times larger than those in the anaerobic environment. The abundance changes of the amoA and nxrA functional genes have a positive correlation with the nitrification intensity in the tannery sludge-contaminated soil. 相似文献
44.
介绍了国内外铝合金钻杆的研制现状,分析了绳索取心铝合金钻杆在地质钻探中的优势。对φ71 mm×5.5 mm绳索取心铝合金钻杆体与钢接头连接结构进行了详细设计。通过对试验钻杆进行静拉力、扭矩试验,得出了铝合金钻杆体与钢接头主要技术参数。 相似文献
45.
46.
Takeshi Naganuma Masanori Kyo Tatsuhiko Ueki Kazuhiko Takeda Jun-ichiro Ishibashi 《Journal of Oceanography》1998,54(3):241-246
A new hydrothermal fluid sampler has been developed to provide more maneuverability in underwater operation. The sampler characteristically
employs a shape-memory alloy, which senses high temperature and actuates the suction mechanism. A shape-memory alloy is also
used to switch the intake valve of the sampler, the intention being to avoid missampling when the inlet is in low temperature
water. Prototype samplers were designed to collect the fluids hotter than 80°C. Test sampling was performed at hydrothermal
vents (1372–1374 m deep) in the submarine volcano, Suiyo Seamount, Izu-Bonin Arc, northwestern Pacific. Observed fluid temperature
was between 138 and 298°C, while the ambient seawater temperature was 3.1°C. Each prototype collected about 100 ml fluid as
designed. The magnesium concentration in the samples indicated a seawater content of 47.5–90.8%, which indicates the entrainment
of ambient seawater. Microscopic observatinn revealed the occurrence of microorganisms in the sample fluids at a population
density of 105 to 106 cells ml−1, which is 2–3 orders of magnitude higher than those in seawater at that depth. The use of the newly developed fluid sampler
will greatly facilitate the collection of vent-associated microorganisms, which are of potential biological and biotechnological
interest. 相似文献
47.
考虑到多维地震输入对网架结构的不利影响,基于形状记忆合金超弹性,研制出一种兼具自复位、高耗能及放大功能于一体的形状记忆合金复合黏滞阻尼器(Hybrid Shape Memory Alloy Viscous Dampers,简称HSMAVD),并通过试验研究该阻尼器在循环荷载作用下的力学性能;然后以平面四角锥网架模型为基础,将该阻尼器替换部分网架结构杆件,并分析该阻尼器减震控制效果。结果表明形状记忆合金与黏滞阻尼器复合后具有良好的协同工作能力,可有效发挥形状记忆合金的超弹性和黏滞阻尼器的速度相关特性,使其具有稳定的滞回性能和良好的耗能能力;采用阻尼杆件替换原杆件的方法既能对结构进行有效的减震控制,又不改变原有的结构形式,是一种优越的减震控制方法,并为HSMAVD被动控制系统在结构抗震中的实际应用提供新思路。 相似文献
48.
Computational study of self‐centering buckling‐restrained braced frame seismic performance
下载免费PDF全文
![点击此处可从《地震工程与结构动力学》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Recent research developed and experimentally validated a self‐centering buckling‐restrained brace (SC‐BRB) that employs a restoring mechanism created using concentric tubes held flush with pretensioned shape memory alloy rods, in conjunction with a buckling‐restrained brace (BRB) that dissipates seismic energy. The present computational study investigated how the SC‐BRB can be implemented in real buildings to improve seismic performance. First, a computational brace model was developed and calibrated against experimental data, including the definition of a new cyclic material model for superelastic NiTi shape memory alloy. A parametric study were then conducted to explore the design space for SC‐BRBs. Finally, a set of prototype buildings was designed and computationally subjected to a suite of ground motions. The effect of the lateral resistance of gravity framing on self‐centering was also examined. From the component study, the SC‐BRB was found to dissipate sufficient energy even with large self‐centering ratios (as large as 4) based on criteria found in the literature for limiting peak drifts. From the prototype building study, a SC‐BRB self‐centering ratio of 0.5 was capable of reliably limiting residual drifts to negligible values, which is consistent with a dynamic form of self‐centering discussed in the literature. Because large self‐centering ratios can create significant overstrength, the most efficient SC‐BRB frame designs had a self‐centering ratio in the range of 0.5–1.5. Ambient building resistance (e.g., gravity framing) was found to reduce peak drifts, but had a negligible effect on residual drifts. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
49.
During the manufacturing of chromate salts (1972–1992) large quantities of Chromite Ore Processing Residue (COPR) were released
into a decantation pond east of the former chemical plant of Porto-Romano (Durres, Albania), giving rise to yellow colored
pond sediments. These Cr(VI) bearing sediments were deposited upon Quaternary silty-clay lagoonal sediments rich in iron oxides
and organic matter. The pH values in these lagoonal sediments vary around 6.6, while in the pond sediments, it is mainly acidic
(due to the presence of the sulfur stock piles in the area and the release of the H2SO4 from the activity of the former chemical plant), varying between 1.4 and 3.8. Continuous leaching of the COPR waste resulted
in yellow-colored surface water runoff. The prediction of pH changes in the different types of sediments based upon acid/base
neutralizing capacity (ANC/BNC) jointly with the quantitative data on release of heavy metals and especially Cr is considered
an important advantage of the pHstat leaching test if compared to conventional leaching procedures. Thus, factors controlling the leaching of Cr(VI), Cr(III),
Ca, Al, Fe, Mg from the COPR were investigated by means of pHstat batch leaching tests and mineralogical analysis. Moreover, mathematical and geochemical modeling complemented the study.
The COPR in the area contain very high concentrations of chromium 24,409 mg/kg, which mainly occurs as Cr(III) (75–90%) as
well as Cr(VI) (25–10%). The leaching of Cr(VI) occurs in all the range (2–10) of the tested pH values, however, it decreases
under acidic conditions. Beside some reduction of Cr(VI) to Cr(III), the Cr(VI) content of the leachtes remains relatively
high in the acidic environment, while the limning of Cr(VI) pond sediments will increase the release of the latter specie.
The leaching of the Cr(III) occurs strictly under acidic conditions, whereby limning of these sediments will give rise to
the lower solubility of Cr(III). The key mineral phases responsible for the fast release of the Cr(VI) are: the chromate salts
(i.e. sodium chromate and sodium dichromate), while sparingly soluble chromatite (CaCrO4) and hashemite (BaCrO4) release Cr(VI) very slowly. Thus, pH and mineral solubility have been identified as key factors in the retention and the
release of the hexavalent CrO4
2− and Cr2O7
− from the COPR-rich pond sediments. 相似文献
50.
This paper presents an experimental study to investigate the performance of shape memory alloy(SMA) restrainers for mitigating the pounding and unseating of highway bridges when subjected to seismic excitations.Mechanical property tests of the SMA wire used in the restrainers are conducted first to understand the pseudo-elastic characteristics of the material.Then,a series of shaking table tests are carried out on a highway bridge model.The structural responses of the highway bridge model equipped with SMA restrainers,installed in the form of deck-deck and deck-pile connections,are analyzed and compared with the uncontrolled structures.The test results of this study indicate that the SMA restrainers are not only effective in preventing unseating but also in suppressing the seismic-induced pounding of the highway bridge model used in this study. 相似文献