全文获取类型
收费全文 | 14116篇 |
免费 | 2847篇 |
国内免费 | 4109篇 |
专业分类
测绘学 | 1367篇 |
大气科学 | 3110篇 |
地球物理 | 3289篇 |
地质学 | 7748篇 |
海洋学 | 1845篇 |
天文学 | 568篇 |
综合类 | 1409篇 |
自然地理 | 1736篇 |
出版年
2024年 | 85篇 |
2023年 | 298篇 |
2022年 | 842篇 |
2021年 | 952篇 |
2020年 | 707篇 |
2019年 | 897篇 |
2018年 | 923篇 |
2017年 | 883篇 |
2016年 | 947篇 |
2015年 | 874篇 |
2014年 | 952篇 |
2013年 | 989篇 |
2012年 | 989篇 |
2011年 | 947篇 |
2010年 | 958篇 |
2009年 | 877篇 |
2008年 | 814篇 |
2007年 | 740篇 |
2006年 | 623篇 |
2005年 | 518篇 |
2004年 | 363篇 |
2003年 | 359篇 |
2002年 | 330篇 |
2001年 | 319篇 |
2000年 | 373篇 |
1999年 | 498篇 |
1998年 | 433篇 |
1997年 | 437篇 |
1996年 | 375篇 |
1995年 | 327篇 |
1994年 | 288篇 |
1993年 | 221篇 |
1992年 | 202篇 |
1991年 | 148篇 |
1990年 | 100篇 |
1989年 | 105篇 |
1988年 | 98篇 |
1987年 | 64篇 |
1986年 | 44篇 |
1985年 | 37篇 |
1984年 | 24篇 |
1983年 | 27篇 |
1982年 | 11篇 |
1981年 | 16篇 |
1980年 | 19篇 |
1979年 | 11篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1958年 | 14篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
981.
本文对川滇地区自有地方台,网建立以来的21年间记录到的239次小震群进行了研究,发现Ms≥6.7级的强震绝大多数都发生在小震群年频度增高的背景上。并引用了归一化熵值K作为衡量震群序列中能量分布均匀度的特征量,分析了不同K值的震群与中强震发生的对应关系,发现K≥0.8的震群发生与Ms≥5.5的中强震发生的对应率为59.3%;虚报率为40.7%;漏报率约占14%。K<0.8的震群发生满足无震条件的约占56%。以上结果表明,用归一化熵值K≥0.8来区别前兆震群与一般震群,结果没有华北地区的那样显著。在川滇地区,要将所对应的强震震级提高到6.5级,结果才比较好。 相似文献
982.
Li Zongkai Pan Yunxian Zhou Chaofu Jiang Weimei Tang Shibao Zhu Zengwang 《Acta Meteorologica Sinica》1988,2(2):196-204
The fumigation during the mountain-valley wind shift has been first identified as a special type of pol-lutant diffusion using the monitoring measurements of Dukou,Southwest Sichuan,China.Such a pheno-menon occurs frequently all year around but summer,particularly in winter months.A new model for thefumigation during the mountain-valley wind shift period is developed that allows satisfactory explanation ofthe fact.Analyses indicate that the model can more accurately predict not only the high concentration ofPollutants but the time and locality of the occurrence as well.The ground concentration of SO_2 during fumigation is several times up to over a decade higher thanthe daily mean for the whole region,one of the main contamination processes that affect the air quality ofthe city.The medel analyses provide a basis for more effective prediction of the quality and precautionstudy against the disaster. 相似文献
983.
A new method is presented for the prediction of a torrential rain (TR) area, where some atmo-physical parameters are used with their given values as criteria most favorable for the occurrence ofTR; an over-all examination is done of the relative favorabilities of these factors for the TR productionin other regions which are then composited and numeralized by means of the theory of nonlinearmapping with the results plotted (‘reflected') on a weather chart, allowing to make an objectiveforecast of the TR area. The preliminary results indicate that the technique is able to objectivelycomposite and clearly exhibit principal distribution features of the parameters on the map, thus show-ing a certain amount of effectiveness for the diagnosis and prediction of a TR area. Regression analysis is used for factor selection to automatically discriminate and locate the jet-stream axis with the aid of a computer. In the calculation of the mapping the gradient method isadopted, in the light of the functional properties of the optimized index K, in place of the simplerelaxational iteration now in general use, thus getting rid of the non-convergence by the iterationmethod because of the increased number of the samples used. The square of the gradient mod-ulus <10~(-4) is set to be the criterion for the iteration convergence. The improved method canmeet the requirements of operational forecasts generally with 50 or less iterations. 相似文献
984.
Zhou Binbin 《Acta Meteorologica Sinica》1988,2(2):223-233
The formation and development of radiation fog are studied by using a one-dimensional model.Theresults are as follows:(1)The fog can change the ambient wind and temperature fields,on the contrary,theambient fields may also influence the fog;(2)The modeling fog forms initially at a certain level above thesurface,which is detailedly explained in the paper;(3)Turbulence delays the formation of fog but promotesits development;(4)Whether fog liquid water content exchange coefficient equals momentum exchangecoefficient has no influence on the numerical results.In addition,wind,temperature,exchange coefficient,and net radiative flux before and after the formation of radiation fog,are also studied. 相似文献
985.
THE RELATIONSHIP BETWEEN INDIAN MONSOON SYSTEMS IN SUMMER AND THE CONTINUOUS HEAVY RAIN OVER THE UPPER REACHES OF CHANGJIANG RIVER 下载免费PDF全文
In this paper,the continuous heavy rains over the upper reaches of Changjiang River during June—Augustare analyzed.They are closely related to the Indian monsoon systems.The average synoptic situationsand the average distributions of some meteorological elements over the Bay of Bengal during the period ofheavy rains are presented.The correlation coefficients between meteorological elements and rainfall arecalculated and the main monsoon influence systems and the key regions are denoted.Results can be usedas a reference in the 24 h forecast of rainfall. 相似文献
986.
987.
在急倾斜构造部位大力使用硬合金回转钻进时,常常会产生弯曲度很大的走向偏斜情况。这是因为不同岩层的阻力差异使钻头受到一种平行于岩层走向的偏斜力,迫使钻头向侧方研磨井壁;在不同井径变换部位所产生的偏斜效果是不同的。这样造成钻孔沿地层走向发生有规律的定向偏斜。 相似文献
988.
989.
Based on the statistical outcomes relevant to elliptical isoseisms given in ref. [1], the average focal depth and rupture length of fault for earthquakes with different magnitudes or epicentral intensities occurring in East and West China are discussed. A set of intensity attenuation functions appropriated to point source (regarding focal distance as the distance parameter in the attenuation law) and the line source (regarding the shortest distance from the site to rupture line or the average distance from the site to both ends of the rupture line as the distance parameter) are proposed. 相似文献
990.
Rui Feng Jun Wang Shuzhen Zheng Guifang Huang Huifen Yan Hainan Zhou Ruoshui Zhang 《地震学报(英文版)》1988,1(4):73-84
Following Airy and Pratt principles, five kinds of local-compensation models are analysed and a rapid 3-D gravity formula
is utilized to calculate isostatic anomalies for 66 models with different parameters. It is noted that isostatic gravity maps
appear nearly identical in their main patterns and features. The optimum compensation model in North China is one of modified
Airy models in which the different density distribution in the surface, upper crust and lower crust is taken into account
and the standard crustal thickness is about 50km. The position of the complete compensation interface is located in the upper
mantle. The North China platform as a whole is under sub-isostatic equilibrium status with an isostatic anomaly of about 18·10−5 m/s2 on an average. The distribution of isostatic gravity anomaly shows an obvious blockwise pattern. Most positive anomaly areas
occur over the eastern part, the Jiao-Liao Block, Mt. Yan block and northern margin of the Hebei-Shandong block, whereas a
negative area occurs in the Shanxi graben. The comparison of models indicates that the Moho discontinuity is not suitable
to be taken as a compensation interface, and the compensation effects in Airy model are better than that in Pratt model, which
is consistent with the feature of dominant layered structure and less lateral inhomogeneity in crust. Some results about composite
compensation, the basic characteristics of isostatic anomaly and deep stucture will be published later in the second part
of this paper.
Wang Bowen took part in some work in this paper. 相似文献