全文获取类型
收费全文 | 37246篇 |
免费 | 6012篇 |
国内免费 | 8085篇 |
专业分类
测绘学 | 3412篇 |
大气科学 | 5121篇 |
地球物理 | 6581篇 |
地质学 | 20093篇 |
海洋学 | 4215篇 |
天文学 | 4182篇 |
综合类 | 2279篇 |
自然地理 | 5460篇 |
出版年
2024年 | 274篇 |
2023年 | 672篇 |
2022年 | 1312篇 |
2021年 | 1528篇 |
2020年 | 1403篇 |
2019年 | 1722篇 |
2018年 | 1221篇 |
2017年 | 1441篇 |
2016年 | 1470篇 |
2015年 | 1657篇 |
2014年 | 2039篇 |
2013年 | 2001篇 |
2012年 | 2135篇 |
2011年 | 2274篇 |
2010年 | 1983篇 |
2009年 | 2564篇 |
2008年 | 2456篇 |
2007年 | 2548篇 |
2006年 | 2518篇 |
2005年 | 2346篇 |
2004年 | 2084篇 |
2003年 | 1959篇 |
2002年 | 1706篇 |
2001年 | 1500篇 |
2000年 | 1528篇 |
1999年 | 1333篇 |
1998年 | 1157篇 |
1997年 | 807篇 |
1996年 | 678篇 |
1995年 | 577篇 |
1994年 | 555篇 |
1993年 | 466篇 |
1992年 | 328篇 |
1991年 | 284篇 |
1990年 | 205篇 |
1989年 | 158篇 |
1988年 | 133篇 |
1987年 | 80篇 |
1986年 | 44篇 |
1985年 | 41篇 |
1984年 | 26篇 |
1983年 | 17篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1980年 | 16篇 |
1979年 | 8篇 |
1978年 | 17篇 |
1977年 | 10篇 |
1976年 | 4篇 |
1954年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 25 毫秒
991.
“六五”和“七五”期间,新疆地矿局强化了地质找矿的科学管理,充分发挥了地质科技在找矿中的先导作用,争取到了一个好的外部环境,取得了地质找矿的重大突破。他们既找矿又开矿,以找矿促开发,走找矿与开矿结合的道路,实行探、采、工、贸一体化,创造了搞活地勘单位,振兴地方经济的成功经验。 相似文献
992.
Lower Pleistocene sediments recovered in boreholes from the Aberdeen Ground Formation in the central North Sea indicate that the unit was deposited in a delta front to prodelta/shallow, open shelf marine setting. Possible estuarine and clastic nearshore marine deposits have been identified on the western margin of the basin. The delta front sediments consist of interbedded, structureless to laminated sands and muds with organic debris, ferruginous nodules and common soft sediment deformation structures. Sporadic rippled and graded beds, basal scours to beds and starved ripples suggest periodic wave–current reworking. Prodelta/shelf marine sediments are predominantly argillaceous with only occasional thin sand beds and rare phosphatic bands. One exceptionally thick sand body or submarine channel-fill although this remains uncertain. The estuarine/clastic nearshore marine sediments include coarse channel-lag deposits and rippled and laminated subtidal sands. A rich microfossil assemblage recovered from the prodelta/shelf marine sequence indicates that deposition occurred under fluctuating climatic conditions. 相似文献
993.
Michael Ed. Hohn Edward B. Nuhfer Robert J. Vinopal David S. Klanderman 《Mathematical Geology》1980,12(6):589-606
Classifying very fine-grained rocks through fabric elements provides information about depositional environments, but is subject to the biases of visual taxonomy. To evaluate the statistical significance of an empirical classification of very fine-grained rocks, samples from Devonian shales in four cored wells in West Virginia and Virginia were measured for 15 variables: quartz, illite, pyrite and expandable clays determined by X-ray diffraction; total sulfur, organic content, inorganic carbon, matrix density, bulk density, porosity, silt, as well as density, sonic travel time, resistivity, and -ray response measured from well logs. The four lithologic types comprised: (1) sharply banded shale, (2) thinly laminated shale, (3) lenticularly laminated shale, and (4) nonbanded shale. Univariate and multivariate analyses of variance showed that the lithologic classification reflects significant differences for the variables measured, difference that can be detected independently of stratigraphic effects. Little-known statistical methods found useful in this work included: the multivariate analysis of variance with more than one effect, simultaneous plotting of samples and variables on canonical variates, and the use of parametric ANOVA and MANOVA on ranked data. 相似文献
994.
新疆棉花"矮密早"栽培技术的气候条件 总被引:2,自引:0,他引:2
李星华 《沙漠与绿洲气象(新疆气象)》2002,25(6):19-21
简要论述了新疆棉花“矮密早”栽培技术形成的气候条件和依据。 相似文献
995.
《中国科学D辑(英文版)》2006,(Z2)
Long-term measurement of carbon metabolism of old-growth forests is critical to predict their behaviors and to reduce the uncertainties of carbon accounting under changing climate. Eddy covariance technology was applied to investigate the long-term carbon exchange over a 200 year-old Chinese broad-leaved Korean pine mixed forest in the Changbai Mountains (128°28'E and 42°24'N, Jilin Province, P. R. China) since August 2002. On the data obtained with open-path eddy covariance system and CO2 profile measurement system from Jan. 2003 to Dec. 2004, this paper reports (i) annual and seasonal variation of FNEE, FGPP and Re; (ii) regulation of environmental factors on phase and amplitude of ecosystem CO2 uptake and release Corrections due to storage and friction velocity were applied to the eddy carbon flux. Lal and soil temperature determined the seasonal and annual dynamics of FGPP and RE separately. VPD and air temperature regulated ecosystem photosynthesis at finer scales in growing seasons. Water condition at the root zone exerted a significant influence on ecosystem maintenance carbon metabolism of this forest in winter. The forest was a net sink of atmospheric CO2 and sequestered -449 g C·m-2 during the study period; -278 and -171 gC·m-2 for 2003 and 2004 respectively. FGPP and FRE over 2003 and 2004 were -1332, -1294 g C·m-2. and 1054, 1124 g C·m-2 respectively. This study shows that old-growth forest can be a strong net carbon sink of atmospheric CO2. There was significant seasonal and annual variation in carbon metabolism. In winter, there was weak photosynthesis while the ecosystem emitted CO2. Carbon exchanges were active in spring and fall but contributed little to carbon sequestration on an annual scale. The summer is the most significant season as far as ecosystem carbon balance is concerned. The 90 days of summer contributed 66.9, 68.9% of FGPp, and 60.4, 62.1% of RE of the entire year. 相似文献
996.
《中国科学D辑(英文版)》2006,(Z2)
The study by the eddy covariance technique in the alpine shrub meadow of the Qing-hai-Tibet Plateau in 2003 and 2004 showed that the net ecosystem carbon dioxide exchange (NEE) exhibited noticeable diurnal and annual variations, with more distinct daily changes during the warmer seasons. The CO2 emission of the shrub ecosystem culminated in April and September while the CO2 absorption capacity reached a maximum in July and August. The absorbed carbon dioxide during the two consecutive years was 231.4 and 274.8 g CO2·m-2 respectively, yielding an average of 253.1 gCO2·m-2 per year: that accounts for a large proportion of absorbed CO2 in the region. Obviously, the diurnal carbon flux was negatively related to temperature, radiation and other atmospheric factors. Still, minute discrepancies in kurtosis and duration of carbon emission/absorption were detected between 2003 and 2004. It was found that the CO2 flux in the daytime was similarly affected by photosynthetic photon flux density in both years. Temperature appears to be the most important determinant of CO2 flux: specifically, the high temperature during the plant growing season inhibits the carbon absorption capacity. One potential explanation is that soil respiration is enhanced under such condition. Analysis of biomass revealed that the annual net carbon fixed capacity of aboveground and belowground biomass was 544.0 in 2003 and 559.4 g Cm"2 in 2004, which coincided with the NEE absorption capacity (63.1 g C·m-2 in 2003 and 74.9 g C·m-2 in 2004) in the corresponding plant growing season. 相似文献
997.
《测绘工程》2006,(3)
,CATV of Lingfen Iron and Steel Company,Lingfen Shanxi 041000,China)This article introduces the design idea and experiences in innovating process of bi-directional HFC network,the design ideas of light pitch point,the optical cable skeleton line and the assignment network.Also the 相似文献
998.
鞍山某基坑支护工程事故分析 总被引:3,自引:0,他引:3
论述了鞍山某基坑支护工程设计参数的选取与加固措施,分析了出现事故及险情的原因,总结了鞍山地区基坑支护设计与施工的经验和教训。 相似文献
999.
对我国2000-2004年发表的“RS”论文的统计分析 总被引:2,自引:0,他引:2
本文对近年来国内主要科技期刊上有关“RS”论文进行统计与分析,叙述了近年来我国RS科学研究的现状和水平,揭示了这一学科的应用范围、研究者现状、分布的特点和规律,明确了RS在国民经济建设中的重要地位。对RS的发展阶段给予了评价。 相似文献
1000.
概述辽、金、元三代有关测绘的管理和机构,职官设置,各类测绘状况及成果,着重介绍了元代的测绘技术,发明创造及著述。 相似文献