首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1143篇
  免费   67篇
  国内免费   14篇
测绘学   49篇
大气科学   87篇
地球物理   299篇
地质学   364篇
海洋学   50篇
天文学   266篇
综合类   7篇
自然地理   102篇
  2023年   9篇
  2022年   12篇
  2021年   27篇
  2020年   25篇
  2019年   37篇
  2018年   62篇
  2017年   50篇
  2016年   75篇
  2015年   63篇
  2014年   58篇
  2013年   61篇
  2012年   57篇
  2011年   47篇
  2010年   52篇
  2009年   77篇
  2008年   58篇
  2007年   58篇
  2006年   36篇
  2005年   37篇
  2004年   27篇
  2003年   30篇
  2002年   29篇
  2001年   11篇
  2000年   22篇
  1999年   11篇
  1998年   13篇
  1997年   6篇
  1996年   12篇
  1995年   5篇
  1994年   9篇
  1993年   7篇
  1992年   12篇
  1991年   10篇
  1990年   8篇
  1989年   7篇
  1988年   4篇
  1987年   4篇
  1986年   11篇
  1985年   7篇
  1984年   4篇
  1983年   7篇
  1982年   5篇
  1981年   4篇
  1979年   4篇
  1978年   6篇
  1977年   10篇
  1976年   9篇
  1975年   6篇
  1973年   4篇
  1968年   3篇
排序方式: 共有1224条查询结果,搜索用时 15 毫秒
961.
Mineralogy and Petrology - The results of the new Electron Microprobe Analysis of apatite, hornblende and biotite crystals of the hornblende-biotite variety of the Strzegom-Sobótka granite...  相似文献   
962.
963.
Georadar methodology has a considerable potential as a tool for verification of archeological hypotheses. I applied it in the present study to resolve a discussion on the importance of a Proto-Romanesque structure located on Lasota Hill. It is one of the oldest structures on the right bank of Vistula River in Kraków in Poland and some archeologists believe that it was the first seat of the rulers of Lesser Poland in the 9th century. After few decades, the prince’s castle was built on Wawel Hill, where subsequently the royal castle was constructed. On the place of the abandoned Proto-Romanesque edifice, a small St. Benedict’s Church was raised, but the importance of its predecessor was discussed. Archeological excavations suggested that it served as the prince’s residence, but this view would be much strengthened if traces of a prince’s building — palatium — could be found. With this in mind, I undertook a search for traces of palatium, employing georadar methodology. I carried out the measurements using Georadar PROEX produced by MALA Geoscience with a set of shielded antennas of frequencies 500 and 800 MHz. They permitted to construct echogram profiles, whose interpretation suggested the existence of palatium. Thus, the georadar data supported the archeological hypothesis about the important role of the Proto-Romanesque structures on Lasota Hill in the early medieval era in Poland, and at the same time demonstrated the usefulness of introducing geophysical methods to archaeology.  相似文献   
964.
Methods of computing the deflections of flexible vegetation elements under the dynamic pressure of water were presented in the paper. Two methods, based on Euler-Bernoulli beam theory, were discussed, one designed for small deflections and the other, generalized one, also for larger deflections. The choice of the method for computations of deflections was discussed from the perspective of the computation of flow velocities above flexible vegetation. Computational results were compared with laboratory experiments and it was found that the simplified, computationally less expensive method may be used in many practical situations without deterioration of the results.  相似文献   
965.
Consumption of marine organisms represents one of the main exposure sources of contaminants for human populations. To obtain a global view of the contamination in commercial fish in the NW Mediterranean Sea, we analysed four types of priority contaminants (PCBs, PBDEs, Hg and (137)Cs) in the European hake, Merluccius merluccius, from the Gulf of Lions in relation with organism's trophic level (δ(15)N). All contaminants presented a significant increase in concentration in hake muscle with trophic level. However, obvious differences between contaminants were evidenced. Biomagnification factors (BMF and FWMF) along the hake food web were higher for Hg and CB-153 than for BDE-47 and (137)Cs, and increase in contaminant concentration with trophic level occurred at different rates depending on contaminants. Such differences of biomagnification patterns can be related to physico-chemical properties of the different contaminants.  相似文献   
966.
This study reports systematic analysis of air pollution concentration by particulate matter (PM) in relation to annual changes of metrological conditions. The concentration of PM collected on filters was evaluated by magnetic properties. Long series of filters collected during 1977, 1980, 1981 and 1985 in Warsaw have been used for measurement. Such long time series allowed a better determination of correlation between seasonal susceptibility changes and meteorological conditions and to verify the repeatability of annual behavior. The magnetic susceptibility normalized by mass (??) has been used as a proxy of pollution. Monthly variations of ?? (??m) demonstrated slow and small seasonal changes disturbed by quick, high peaks. The filters with high susceptibilities contain a mixture of magnetic single and multidomain grains which is characteristic for anthropogenic pollution, with the frequency-dependent susceptibility ??fd being less than 4%. The low susceptibility samples are characterized by admixture of small amount of pseudo-single domain (PSD) and possible small amount of superparamagnetic (SP) grains. Detailed analysis of reduced mean monthly susceptibility ??R revealed that temperature and absolute humidity correlate positively in cold period of year and negatively in warm months. The linear correlation coefficients range from 0.7 to 0.9 and from 0.3 to 0.4 for negative and positive linear correlation, respectively. The dispersion of pollutants in a city depends on the way of ventilation. The big cities like Warsaw are urban heat islands which act the most effective way for the warm period and for the cold time. The correlation of ??R with absolute humidity is similar to that for temperature but for different reasons. The presence of big amount of water vapor particles in the atmosphere can favor the adhesion of smaller ferromagnetic grains to their surface which can accelerate the process of falling down of such agglomerates. Such a process can take place during wintertime. We do not observe clear correlation between ??R and precipitation.  相似文献   
967.
Mount Morning is a Cenozoic, alkaline eruptive center in the south-west Ross Sea, Antarctica. New ages on 17 Mount Morning volcanic rocks (combined with 34 existing ages) allows division of Mount Morning volcanism into two phases, erupted between at least 18.7 Ma and 11.4 Ma, and 6.13 and 0.02 Ma. The position of Mount Morning on the active West Antarctic Rift System within the stationary Antarctic plate is a key factor in the eruptive center’s longevity. The earliest, mildly alkaline, Phase I volcanism comprises predominantly trachytic rocks produced by combined assimilation and fractional crystallization processes over 7.3 m.y. Strongly alkaline Phase II volcanism is dominated by a basanite – phonolite lineage, with the youngest (post last glacial maximum) activity dominated by small volume primitive basanite eruptions. The evolution from mildly to strongly alkaline chemistry between phases reflects magma residence time in the crust, the degree of mantle melting, or the degree of magma—country-rock interaction. Phase I magmatism occurred over a comparable area to the present-day, Phase II shield. The 5.2 m.y. volcanic hiatus separating Phase I and II coincides with a cycle of eruption and glacial erosion at the nearby Minna Bluff eruptive center. Mount Morning is the likely source of volcanic detritus in Cape Roberts drill-core (about 24.1 to 18.4 Ma) and in ANDRILL drill-hole 1B (about 13.6 Ma), located 170 km north and 105 km north-east respectively, of Mount Morning. Based upon the timing of eruptions and high heat-flow, Mount Morning should be considered a dormant volcano.  相似文献   
968.
Quantifying hyporheic solute dynamics has been limited by our ability to assess the magnitude and extent of stream interactions with multiple domains: mobile subsurface storage (MSS, e.g., freely flowing pore water) and immobile subsurface storage (ISS, e.g., poorly connected pore water). Stream-tracer experiments coupled with solute transport modeling are frequently used to characterize lumped MSS and ISS dynamics, but are limited by the ability to sample only “mobile” water and by window of detection issues. Here, we couple simulations of near-surface electrical resistivity (ER) methods with conservative solute transport to directly compare solute transport with ER interpretations, and to determine the ability of ER to predict spatial and temporal trends of solute distribution and transport in stream–hyporheic systems. Results show that temporal moments from both ER and solute transport data are well correlated for locations where advection is not the dominant solute transport process. Mean arrival time and variance are especially well-predicted by ER interpretation, providing the potential to estimate rate-limited mass transport (i.e. diffusive) parameters from these data in a distributed domain, substantially increasing our knowledge of the fate and transport of subsurface solutes.  相似文献   
969.
The effects of low counts on assemblage inferences in paleolimnological investigations have been examined for many biological proxies, but not yet for Cladocera. Established guidelines leading to the determination of an adequate, minimum count are absent with respect to sampling cladoceran remains from lake sediments. Using simulated subsamples derived from observed assemblages of considerably higher counts, we investigated the effect of counting effort on three principal characteristics of an assemblage: richness, number of new taxa encountered, and the absolute differences in relative abundances of dominant taxa. Results from six lakes located within diverse ecological regions (i.e. Subarctic, Canadian Shield, Acadian Forest) suggest that a minimum of between 70 and 100 individuals is satisfactory to characterize most assemblages. Doubling counting effort from 100 to 200 individuals leads to only modest gains in subsample relatedness to the observed assemblage. Greater counting effort may be necessary when the primary interest is in presence-absence or distributional data, or when abundances of ecologically relevant taxa are exceptionally low.  相似文献   
970.
The paper summarizes the findings about a seismic event on January 22, 2010, near Bełchatów, Poland, in terms of data, event location, magnitude and source parameters.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号