全文获取类型
收费全文 | 86474篇 |
免费 | 27705篇 |
国内免费 | 54601篇 |
专业分类
测绘学 | 12957篇 |
大气科学 | 25896篇 |
地球物理 | 21409篇 |
地质学 | 64540篇 |
海洋学 | 23799篇 |
天文学 | 1568篇 |
综合类 | 8135篇 |
自然地理 | 10476篇 |
出版年
2024年 | 823篇 |
2023年 | 2112篇 |
2022年 | 4179篇 |
2021年 | 5171篇 |
2020年 | 5126篇 |
2019年 | 8030篇 |
2018年 | 7754篇 |
2017年 | 7350篇 |
2016年 | 7537篇 |
2015年 | 7776篇 |
2014年 | 7131篇 |
2013年 | 8419篇 |
2012年 | 8784篇 |
2011年 | 8621篇 |
2010年 | 8635篇 |
2009年 | 7686篇 |
2008年 | 7080篇 |
2007年 | 6914篇 |
2006年 | 6347篇 |
2005年 | 5529篇 |
2004年 | 4966篇 |
2003年 | 4025篇 |
2002年 | 3928篇 |
2001年 | 3516篇 |
2000年 | 2949篇 |
1999年 | 2207篇 |
1998年 | 1953篇 |
1997年 | 1989篇 |
1996年 | 1555篇 |
1995年 | 1432篇 |
1994年 | 1300篇 |
1993年 | 1258篇 |
1992年 | 1075篇 |
1991年 | 805篇 |
1990年 | 769篇 |
1989年 | 624篇 |
1988年 | 545篇 |
1987年 | 439篇 |
1986年 | 364篇 |
1985年 | 288篇 |
1984年 | 312篇 |
1983年 | 186篇 |
1982年 | 235篇 |
1981年 | 169篇 |
1980年 | 115篇 |
1979年 | 134篇 |
1978年 | 60篇 |
1977年 | 49篇 |
1971年 | 53篇 |
1954年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
311.
A comparison of methods for the calculation of the hydrodynamic characteristics of arrays of wave power devices is presented. In particular, the plane-wave approximation and an exact multiple scattering formulation have been used to compute exciting wave forces, hydrodynamic coefficients and q factors for arrays of interacting wave power devices. The results obtained are compared with each other, and accuracy aspects of the computations are stressed and critically assessed. 相似文献
312.
Based on the analysis of cyclic triaxial test for the South-Sea sand, a comprehensive normalized model of soil stress-strain relationship is presented herein, which includes effects of not only initial stress states but also loading cycles. Consequently, a pseudo-static procedure to analyse the deformation behavior of foundations is suggested. Example of calculations shows that the suggested procedure is convenient in application. 相似文献
313.
In this paper, the numerical modelling of the tidal level and current in the Bohai Sea was carried out with ADI method, by taking the sum of four main tidal components M2,S2K2,O1 as the open boundary condition. The calculated values were consistent with the predicted ones (the observed values in the case of calm) in the Tidal Table. On the basis of the modelling of the tide, the sea level and current fields under the effects of strong wind were simulated. The calculated results were also quite satisfactory. 相似文献
314.
Genetic diversity of cultivated populations was investigated using assay of vertical slabpolyacrylamide gel electrophoresis in 4 species of shrimps, which were Penaeus japonicus, Penaeus monodon , Penaeus vannamei and Metapenaeus ensis, The results showed that the mean number of alle-les per locus (A) is 1.3±0.2, 1.3±0.1, 1.3±0.1 and 1.3 ±0.1 respectively; the percentage of polymorphic loci (P0.95) is 12.5, 6.7, 20 and 23.5 respectively; the expected heterozygosity (He) is 0.042±0.034,0.042±0.031, 0.094±0.042 and 0.097±0.047 respectively; and the observed heterozygosity (H0)is 0.029±0.024, 0.028±0.023,0.154±0.082 and 0.150±0.084 respectively. The difference of genetic diversity is obvious in 4 species of shrimps. The degree of genetic diversity is M. ensis > P. vannamei > P. japonicus > P. monodon. In short, the lower level of genetic diversity is estimated in 4 species of shrimps. 相似文献
315.
316.
东海浮游动物量的分布特征 总被引:7,自引:5,他引:7
浮游动物生物量属于海洋次级生产力的范畴,在海洋食物链中是极其重要的环节。对其生产力大小的探讨,可以评价海洋渔业资源的潜力和开发远景,由此可以看出浮游动物生物量,是渔场调查中必要的基础资料。东海是我国海洋渔业十分重要的开发区域。这里有鲐鲹等中上层鱼类;有带鱼、大黄鱼、小黄鱼等底层鱼类。这些鱼类都有比较广泛的食性[2,3],在它们发育早期或者直到成年阶段,必须有依赖浮游动物为食的时期。因此浮游动物的数量分布与经济鱼类的幼鱼或成鱼的数量分布都有密切的关系。本文根据为1971年7月至1974年6月,共历时4年,在北纬27°—32°、东经127°以西海区所进行的35个航次,1577个测站的调查资料。采集系用大型浮游动物网(口径80厘米,网目每厘米15个)由底到表垂直拖网。 相似文献
317.
In this paper, the irregular wave force on a cylindrical pier group is calculated by the method of spectrum analysis, and the coefficients of the group effect of piers in the pier group are given here. The calculated results, using P-M and Bretshneider's. (B's) spectra, are obtained for the cases of 2 piers, 3 piers and 4 piers. To compare these results with those obtained for regular waves, we can come to some significant conclusions. Under the action of the irregular wave, when the distance between the piers in the pier group increases, the coefficient of the group effect decreases and tends rapidly to the case of a single pier. In general, when the ratio of the distance between the piers to the diameter of the pier is greater than 4, the group effect can be neglected. 相似文献
318.
作者1987年于四川省乐山市大渡河尾段发现椎实螺属一新种,现命名为乐山椎实螺(Lymnaea leshanensis sp.nov.)。该种与日本琵琶湖产的 Lymnaea onychia 相似,但贝壳的形态、齿式、齿形、两性生殖系统的诸器官、外套膜的色带、个体大小、生活环境和动物区系均有所不同。前者属东洋区系,后者属古北区系。 相似文献
319.
ComparativeresearchonkaryotypeinthreespeciesofArcidaeZhengJiasheng;WangMeilin;GuoDanhong;XuXimindandGaoQinglanAbstract:Byair-... 相似文献
320.
Population structure of Haliotis rubra from South Australia inferred from nuclear and mtDNA analyses 总被引:1,自引:0,他引:1
1Introduction ThemajorityofAustralia’sabalonefisheryex ports(5.135kt,worth$216millionin2002~2003,ABARE2004)consistofblacklipabalone(HaliotisrubraLeach,1814).AssuchH.rubrais consideredasanimportantmarineresourcewithin Australia.Likemanyabalonespecieswor… 相似文献