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   52581篇
  免费   1237篇
  国内免费   880篇
测绘学   1679篇
大气科学   4048篇
地球物理   10476篇
地质学   19154篇
海洋学   4419篇
天文学   11696篇
综合类   309篇
自然地理   2917篇
  2022年   368篇
  2021年   618篇
  2020年   600篇
  2019年   661篇
  2018年   1316篇
  2017年   1222篇
  2016年   1552篇
  2015年   1020篇
  2014年   1499篇
  2013年   2730篇
  2012年   1791篇
  2011年   2341篇
  2010年   1967篇
  2009年   2534篇
  2008年   2170篇
  2007年   2180篇
  2006年   2144篇
  2005年   1615篇
  2004年   1508篇
  2003年   1445篇
  2002年   1364篇
  2001年   1200篇
  2000年   1178篇
  1999年   997篇
  1998年   998篇
  1997年   966篇
  1996年   865篇
  1995年   822篇
  1994年   720篇
  1993年   646篇
  1992年   590篇
  1991年   621篇
  1990年   656篇
  1989年   571篇
  1988年   535篇
  1987年   665篇
  1986年   553篇
  1985年   638篇
  1984年   768篇
  1983年   692篇
  1982年   692篇
  1981年   588篇
  1980年   599篇
  1979年   516篇
  1978年   494篇
  1977年   488篇
  1976年   429篇
  1975年   423篇
  1974年   449篇
  1973年   484篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
We estimated wet-bulb globe temperature (WBGT) using measured meteorological data to understand the bioclimates of human living spaces during the summer season. Our research focused on commercial and residential areas of Okayama City, Japan (population ~700,000). The commercial spaces (CO) mainly consisted of multi-story office buildings, whereas the residential spaces (RE) consisted of one- or two-story residential buildings. On a fine day with southeast winds, the spatially averaged WBGT measured in the CO was higher than that in the RE. The difference was statistically significant and would have caused noticeable discomfort and a high risk of heat disorder for occupants of the CO over the long term. For instance, at 1900 Japan Standard Time (JST), the maximum difference in the WBGT between the CO and RE sites was 2.0°C (23.5°C for the CO and 21.5°C for the RE). From 1800 to 1900 JST, the wet-bulb temperature in the CO was still 1.5–2.0°C higher than that in the RE, even though both areas had the same dry-bulb temperature. This indicates that the CO retained greater amounts of water vapor for longer periods compared to the RE. The wet-bulb temperature in the CO increased rapidly at most observation points when the southeast sea breeze arrived. In contrast, in the RE, the wet-bulb temperature decreased until evening. This difference was caused by moist air transported from a river about 1 km upwind from the CO. The moist air forced an increase in the WBGT and elevated the risk of heat disorder in the CO. The spatially averaged globe temperature of the CO at 1500 JST was 6.2°C lower than that at the RE, causing the WBGT of the CO to decrease. The results suggest that the higher WBGT in the CO was caused by higher wet-bulb temperatures. On a day with southwest winds, the CO and RE showed no difference in WBGT because the river was not included in the upwind source area.  相似文献   
132.
The theory of heat and mass transfer in turbulent pipe flow is applied to a semi-infinite moist-walled cylindrical pipe to determine the longitudinal distributions of both temperature and moisture content as functions of external conditions, pipe radius and wall temperature, and flow velocity. Since many cave and mine passages approximate this model, the results are directly applicable to cave microclimate studies and mine ventilation problems. The results are found to agree well with previously published microclimate observations. The theory is also applicable to water flow in free-flow karst aquifers; specifically to the study of temperature variations and of solution kinetics under turbulent flow conditions.  相似文献   
133.
134.
The results of the Cosmos-900 satellite observ ations of plasma density inhomogeneities in the geomagnetic equator region and the longitudinal distributions of the equatorial spread-F, according to the Intercosmos-19 satellite data are presented. It is show n that the dependence of radiosignal propagation in the ionosphere on geophysical parameters is related to development of the electrostatic instability of the inhomo-geneous ionospheric plasma. The longitudinal dependence of the spread-F, can reflect the influence of the energetic sources, located outside the ionospheric layer that scatters a radio pulse, on the ionosphere. The manifestation of the longitudinal effect in the equatorial spread-F, in the Atlantic region can be explained by the influence of the cone instability on the plasma electrodynamics in the South Atlantic geomagnetic anomaly.  相似文献   
135.
This review describes developments major and in trace element determination using atomic absorption spectroscopy (AAS), inductively coupled plasma-atomic emission spectrometry (ICP-AES), instrumental neutron activation analysis (INAA), and X-ray fluorescence (XRF) spectrometry that were reported in 2008 and 2009. Publication levels were comparable to those of previous years, except for XRF which showed an increase in the number of articles published in the past 2 years. In terms of number of publications and impact, the most active field was AAS, while INAA was the least active. As expected for well-established and mature methods, novel developments for all four analytical techniques were relatively sparse. For AAS, the most notable publications concerned developments in sample introduction, particularly focussing on solid samples, increasing analyte sensitivity, and higher sample throughput. For ICP-AES, publication of developments in sample introduction, remediation of matrix effects and calibration continues. Compared with past years, there was a clear focus on sample preconcentration methods, but very few publications reporting new hyphenated speciation methods. For INAA, there were several publications exploring the accuracy and robustness of the method, as well as the requirements for INAA to meet criteria for a primary method of measurement. Two other related techniques, delayed neutron activation analysis, and prompt gamma activation analysis, were also described. Hyphenated XRF techniques showed interesting developments in enabling XRF and XRD analysis on the same spot, and further work characterising and calibrating three-dimensional micro-XRF shows promising results for investigating sample heterogeneity.  相似文献   
136.
A series of high temperature experiments was undertaken to study partitioning of several highly siderophile elements (HSE; Ru, Rh, Pd, Re, Os, Ir, Pt and Au) between Cr-rich spinel, olivine, pyroxene and silicate melt. Runs were carried out on a Hawaiian ankaramite, a synthetic eucrite basalt, and a DiAn eutectic melt, at one bar, 19 kbar, and 20 kbar, respectively, in the temperature range of 1200 to 1300°C, at oxygen fugacities between the nickel-nickel oxide (NNO) and hematite-magnetite (HM) oxygen buffers. High oxygen fugacities were used to suppress the formation of HSE-rich “nuggets” in the silicate melts. The resulting oxide and silicate crystals (<100 μm) were analyzed using both SIMS and LA-ICP-MS, with a spatial resolution of 15 to 50 μm. Rhenium, Au and Pd were all found to be incompatible in Cr-rich spinel (DResp/melt = 0.0012-0.21, DAusp/melt = 0.076, DPdsp/melt = 0.14), whereas Rh, Ru and Ir were all found to be highly compatible (DRhsp/melt = 41-530, DRusp/melt = 76-1143, DIrsp/melt = 5-22000). Rhenium, Pd, Au and Ru were all found to be incompatible in olivine (DReoliv/melt = 0.017-0.073, DPdoliv/melt = 0.12, DAuoliv/melt = 0.12, DRuoliv/melt = 0.23), Re is incompatible in orthopyroxene and clinopyroxene (DReopx/melt = 0.013, DRecpx/melt = 0.18-0.21), and Pt is compatible in clinopyroxene (DPtcpx/melt = 1.5). The results are compared to and combined with previous work on HSE partitioning among spinel-structured oxides, and applied to some natural magmatic suites to demonstrate consistency.  相似文献   
137.
We have developed the planning documents for model territories of a different dimension: the landscape program of Adzharia (Georgia), the landscape structure plan for the Lake Sevan watershed basin (Armenia), and the landscape plan for the Shirvan National Park (Azerbaijan). Variants of the solution of regional natural-ecological problems are proposed, and the measures for implementation of the target concepts are substantiated.  相似文献   
138.
139.
A comparative analysis is made of the landscape-forming factors, and their role in the formation of the spatial structure of landscapes in the Kuril and Hawaiian Islands is determined. The research has been done on the basis of landscape mapping at a scale of 1:200 000. A correlative study was made of the different genetic varieties of geosystems: classical landscapes, catenary and nuclear. In spite of the dissimilar character of manifestation of landscape-forming processes, there occur largely identical formation principles for the spatial structure of landscapes.  相似文献   
140.
Transformation of an Arctic aquatic ecosystem (a case study of Lake Imandra) under the impact of a mining industrial complex is considered. Water chemical composition and the ecosystem’s structural components (phyto- and zooplankton, zoobenthos, and ichthiofauna) are analyzed for the following periods: the preindustrial background (reference) conditions, industrial development of mineral resources and strong anthropogenic impact, industrial recession and decreased anthropogenic impact, and stabilization. The main regularities of the aquatic ecosystem successions under the conditions of anthropogenic loads and their decrease are established.  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