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排序方式: 共有419条查询结果,搜索用时 250 毫秒
81.
J. Kesselmeier 《Journal of Atmospheric Chemistry》2001,39(3):219-233
Field and laboratory investigations of the exchange of the short-chain organic acids – formic acid and acetic acid – as well as their homologous aldehydes are discussed. Both acids are substantially released from several plant species. Emission measurements under field conditions are compiled to give an overview of three years of measurements. Emission rates from several tree species were found in the range between zero and 60 nmoles m–2 min–1 for acetic acid and between zero and 90 nmoles m–2 min–1 for formic acid though also a deposition has been observed to orange trees. Investigations under laboratory conditions showed an order of magnitude lower emission rates with significant differences under light and dark conditions, and a deposition was observed under certain conditions. Hence, low emission rates or even a bi-directional exchange, emission as well as deposition have to be taken into account. Further differences between field and laboratory studies are discussed considering age of trees, stress effects and a potential production of acids by photochemical conversion of precursors inside enclosures during sampling. Field data on the exchange of form- and acetaldehyde show a complex behavior. We found emission as well as uptake. The bi-directional exchange is significantly triggered by the ambient mixing ratios of both aldehyde species and exhibits a compensation point. Further studies are needed for generalization of the exchange of these and potentially also for other compounds. 相似文献
82.
氢化物发生—原子荧光法直接测定锑及其化合物中的铅 总被引:1,自引:0,他引:1
通过在样品处理阶段用HBr除去大量锑基体,实现了不需再通过其他化学分离直接运用氢化物发生-原子荧光法测定锑及其相关产品中的微量铅,并用于实际样品的分析.该方法对样品检测下限小于10-6,在实际样品分析中,分析结果与原子吸收法测定结果之间无显著性差异,RSD<2.0%(n=4),对样品分析的加标回收率在95%~105%. 相似文献
83.
胜利油田孤岛原油中有机硅化合物的发现及其石油地质意义 总被引:7,自引:0,他引:7
采用溶剂萃取法从胜利油田孤岛原油中分离得到浓缩的含氧化合物,再用柱色谱分离得到有机硅及其它组分。用红外、电子能谱、气相色谱-质谱法分离鉴定了有机硅组分。鉴定出的有机硅化合物有硅Si3-Si7的甲基硅氧烷和Si3-Si5的环甲基硅氧烷以及三甲基硅的衍生物。资料表明:在高等和低等生物体中还不能肯定含有Si-C键的有机化合物。因此,原油中有机硅化合物的发现是原油无机成因的一个证据。本文还简要讨论了位于勃海湾盆地孤岛原油的无机成因的地质环境及其石油地质意义。 相似文献
84.
S. Derenne C. Largeau E. Casadevall J.S. Sinninghe Damst E.W. Tegelaar J.W. de Leeuw 《Organic Geochemistry》1990,16(4-6)
The kerogen of a sample of Estonian Kukersite (Ordovician) was examined by spectroscopic (solid state 13C NMR, FTIR) and pyrolytic (“off-line”, flash) methods. This revealed an important contribution of long, linear alkyl chains in Kukersite kerogen. The hydrocarbons formed upon pyrolysis are dominated by n-alkanes and n-alk-1-enes and probably reflect a major contribution of selectivity preserved, highly aliphatic, resistant biomacromolecules from the outer cell walls of Gloeocapsomorpha prisca. This is consistent with the abundant presence of this fossilized organism in Kukersite kerogen. In addition high amounts of phenolic compounds were identified in the pyrolysates. Series of non-methylated, mono-, di- and trimethylated 3-n-alkylphenols, 5-n-alkyl-1,3-benzenediols and n-alkylhydroxybenzofurans were identified. All series of phenolic compounds contain long (up to C19), linear alkyl side-chains. Kukersite kerogen is, therefore, an aliphatic type II/I kerogen, despite the abundance of free phenolic moieties. This study shows that phenol-derived moieties are not necessarily associated with higher plant-derived organic matter.The flash pyrolysate of Kukersite kerogen was also compared with that of the kerogen of the Guttenberg Oil Rock (Ordovician) which is also composed of accumulations of fossilized G. prisca. Similarities in the distributions of hydrocarbons and sulphur compounds were noted, especially for the C1–C6 alkylbenzene and alkylthiophene distributions. However, no phenolic compounds were detected in the flash pyrolysate of the Guttenberg kerogen. Possible explanations for the observed similarities and differences are discussed. 相似文献
85.
从松节藻中分离的含卤素化合物表现出显著PTP1B抑制活性。其中BPN效果最佳。为研究BPN侧链基团极性对其抑制活性的影响,本文以香兰素(1)为起始原料,经过溴代、氧化、还原、傅克烷基化以及酯化等反应,成功合成了新化合物2,3-二溴-1-(2-溴-3,4-二甲氧基-6-((4-硝基苯氧基)甲基)苯甲基)-4,5-二甲氧基苯(10)、4-((3-溴-2-(2,3-二溴-4,5-二甲氧基苄基)-4,5-二甲氧基苄基)醚)苯胺(11)、4-((3-溴-2-(2,3-二溴-4,5-二甲氧基苄基)-4,5-二甲氧基苄基)醚)-4-乙酰乙酸(12)和3-溴-2-(2,3-二溴-4,5-二甲氧基苄基)-4,5-二甲氧基苯甲醛肟(14)。通过1 H-NMR,13C-NMR等方法对目标产物进行了结构表征。并对化合物进行了PTP1B酶抑制活性的测定,结果表明化合物侧链极性对PTP1B酶抑制活性有显著影响。 相似文献
86.
87.
Permeability characteristics of lime treated marine clay 总被引:1,自引:0,他引:1
An attempt has been made to investigate the lime induced permeability changes in the permeability and engineering behavior of different lime column treated soil systems. Lime columns treated marine clay shows an increase in permeability up to a maximum value of 15–18 times that of untreated soil with time. The shear strength of the treated soil systems show an increment up to 8–10 that of untreated soil within a period of 30–45 days curing. In the case of lime injection systems, the permeability has been increased up to 10–15 times that of untreated soil, whereas the strength of the soil has been higher by 8–10 times that of untreated soil. Further, consolidation tests show a reduction in the compressibility up to 1/2–1/3 of original values. The test results revealed that both lime column and injection techniques could be used to improve the behaviour of underwater marine clay deposits. 相似文献
88.
裙带菜(Undaria pinnitifida)色素蛋白复合物的分离及光谱特性的初步研究 总被引:5,自引:2,他引:5
以褐藻裙带菜(Undaria pinnatifida)为实验材料,采用蔗糖密度梯度超速离心的方法纯化类囊体膜;以去污剂sDs为增溶剂(SDS:Chl=20:1,4℃增溶20min),再用蔗糖密度为60%、50%、40%、30%、20%、15%和10%的梯度离心法,从裙带菜中成功地分离出5条含色素的蛋白质复合物带。离心结果显示在离心管顶部没有任何颜色,表明经过SDS增溶没有产生游离色素,纯化的类囊体膜和5条色素条带进行吸收光谱分析,显示了属于叶绿素n(Chl-a)的吸收峰:418、436和667到672nm。叶绿素c(Chl-c)的吸收峰:615和620nm。荧光发射最高峰位于682到690nm的区域。荧光激发光谱显示有Chl-a和Chl-c的激发峰,40%层带所含有的色素复合物只有属于Chl.n的吸收峰。分析结果表明:10%、15%层带所含有的色素复合物是褐藻的捕光色素复合物;20%、30%层带所含有的色素复合物是浅绿色的PSⅡ复合体(仍然含有捕光色素),40%层带所含有的色素复合物是深绿色PSⅠ复合体,50%层带所含有的色素复合物是没有被增溶的类囊体膜。 相似文献
89.
Richard A. Feely Gary J. Massoth Anthony J. Paulson James F. Gendron 《Estuarine, Coastal and Shelf Science》1983,17(6):693-708
Total and weak-acid-soluble trace elements in suspended matter from the Duwamish River and Elliott Bay were determined from samples collected in February and September 1980. The results indicate that Mn scavenging in the water column is coincident with enrichments of Cr, Ni, Cu, Zn, and Pb in the suspended matter, suggesting a possible enrichment of these trace elements in a hydrous Mn oxide phase. This process occurs primarily in the sub-surface waters of Elliott Bay. Since mass balance calculations show a net export of Mn out of the bay, this mechanism may be an important means of transporting toxic trace metals from polluted estuaries and embayments to cleaner coastal environments. 相似文献
90.
Geographical and temporal variation in levels of organochlorine contaminants in marine mammals 总被引:1,自引:0,他引:1
The interpretation of the spatial and temporal patterns of variation in organochlorine concentrations in marine mammal populations is complex because of the lack of wide-scale, long-term surveys. Therefore the results from several surveys must be combined and this causes undesired heterogeneity due to differences in the sampling and analytical techniques used and in the biological characteristics of the individuals sampled. Moreover, information is not homogeneously distributed in either space or in time. Most research is concentrated in western Europe, northern America and certain areas of Asia, while it is extremely limited or non-existent in Africa and most regions of the southern hemisphere. Marine mammals from the temperate fringe of the northern hemisphere, particularly fish-eating species which inhabit the mid-latitudes of Europe and North America, show the greatest organochlorine loads; noteworthy are the extremely high levels found in the Mediterranean Sea and certain locations on the western coasts of the United States. Concentrations in the tropical and equatorial fringe of the northern hemisphere and throughout the southern hemisphere are low or extremely low. The polar regions of both hemispheres showed the lowest concentrations of DDTs and PCBs, although levels of HCHs, chlordanes and HCB were moderate to high in the cold waters of the North Pacific. During recent decades, concentrations have tended to decrease in the regions where pollution was initially high but they have increased in regions located far from the pollution source as a consequence of atmospheric transport and redistribution. It is expected that the Arctic and, to a lesser extent, the Antarctic, will become major sinks for organochlorines in the future; this process may already be significant for some compounds such as HCB and HCHs. Effort should be devoted to both assessment of organochlorine trends in the now highly polluted populations of the temperate fringe of the northern hemisphere and to the implementation of long-term monitoring of marine mammal populations inhabiting polar regions. 相似文献