全文获取类型
收费全文 | 37437篇 |
免费 | 18984篇 |
国内免费 | 43320篇 |
专业分类
测绘学 | 3311篇 |
大气科学 | 21754篇 |
地球物理 | 13108篇 |
地质学 | 36293篇 |
海洋学 | 16359篇 |
天文学 | 1058篇 |
综合类 | 4893篇 |
自然地理 | 2965篇 |
出版年
2024年 | 165篇 |
2023年 | 366篇 |
2022年 | 708篇 |
2021年 | 1067篇 |
2020年 | 2192篇 |
2019年 | 5557篇 |
2018年 | 5821篇 |
2017年 | 5513篇 |
2016年 | 5607篇 |
2015年 | 4928篇 |
2014年 | 4505篇 |
2013年 | 5070篇 |
2012年 | 4779篇 |
2011年 | 4539篇 |
2010年 | 4513篇 |
2009年 | 3835篇 |
2008年 | 3092篇 |
2007年 | 3139篇 |
2006年 | 2720篇 |
2005年 | 2575篇 |
2004年 | 2850篇 |
2003年 | 2570篇 |
2002年 | 2347篇 |
2001年 | 2150篇 |
2000年 | 1794篇 |
1999年 | 1857篇 |
1998年 | 1849篇 |
1997年 | 1902篇 |
1996年 | 1490篇 |
1995年 | 1426篇 |
1994年 | 1318篇 |
1993年 | 1236篇 |
1992年 | 1042篇 |
1991年 | 793篇 |
1990年 | 738篇 |
1989年 | 600篇 |
1988年 | 521篇 |
1987年 | 408篇 |
1986年 | 334篇 |
1985年 | 263篇 |
1984年 | 283篇 |
1983年 | 162篇 |
1982年 | 210篇 |
1981年 | 145篇 |
1980年 | 108篇 |
1979年 | 109篇 |
1978年 | 47篇 |
1977年 | 43篇 |
1971年 | 54篇 |
1970年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
1 INTRODUCTIONCompact Symmetric Objects (CSOs) are powerful and compact sources (overall size <1 bpc) with lobe emission on both sides of the central engine. The small size of these sourcesis almost certainly to be attributed to the youth of the sources themselves (ages < 104 yr) andnot due to a dense coallning medium (Readhead 1996). The unification scenario assumes thatCSOs evolve into compact steep spectrum (CSS) sotirces and then into Fanaroff-Riley type 11objects (Fanti 1995). … 相似文献
72.
Yanjun ZHANG Fenglong ZHANG Full QI Fuquan NI 《东北亚地学研究》2006,9(2):199-203
In view of the situation of excavation of open coal mine for the underground water disaster,we should carry out simulation studies for the numerical value of the water lowering project and improve the accuracy and the level of the water lowering project.On the basis of the hydrological geological conditions of certain open mine digging,a more reasonable seepage numerical model was built according to MODFLOW.It was simulated in advance that the process of the confined water level descending with the time,and combining with the actual observations to test the correctness of the model.The calculation showed that the results coincided well with the results of actual measurement.Based on this,different water lowering numerical simulations were built for the open coal mine digging.It could be simulated and forecast that the changes of the groundwater level in drainage process within and outside the mine pit,and it was quantitatively assessed that the possible water lowering result of the opencast water drainage process,which provide an important basis for the actual water lowering project and the possible project disposal. 相似文献
73.
1995年7月11日—12日,广西地矿厅和河池地区行署首次联合举办矿产资源勘查成果展销会,会址设在河池市,与会代表130余人。展销会提交大会展销的矿产资源勘查成果38项,引资勘查项目38项。经买卖双方三天的洽谈,涉及到的项目25项,会议期间签订矿产资源勘查成果合同协议4项,愈千万元,取得较好的社会经济效益。为地勘资金多渠道来源开辟了新路子,对促进地勘单位地质找矿工作及勘查成果有偿使用发挥了重要作用 相似文献
74.
75.
Axial surveys were performed in the two river tributaries of the Cochin estuary, SW India during November 1988. Surficial sediments were subjected to sequential chemical extractions to delineate five metal fractions, namely, exchangeable, carbonate bound, easily reducible, organic/sulfide bound, and residual. The results indicated selective accumulation of Mn and Ni in carbonate bound and organic/sulfide forms, along with marginal amounts of Co in the exchangeable fraction. Large portions of Fe and Cr occurred in the residual fraction, whereas composite fractionation of Zn species was noticed. The exchangeable fractions of Fe and Cr as well as of easily reducible cobalt were below detection limits. The levels of Cr and Zn indicate anthropogenic inputs in this estuary, whereas Co and Ni show regional contamination exceeding natural levels. The analytical speciation procedure helps to deduce the sedimental diagenetic processes in the estuarine environment. 相似文献
76.
77.
Universal cokriging is used to obtain predictions when dealing with multivariate random functions. An important type of nonstationarity is defined in terms of multivariate random functions with increments which are stationary of orderk. The covariance between increments of different variables is modeled by means of the pseudo-cross-covariance function. Criteria are formulated to which the parameters of pseudo-cross-covariance functions must comply so as to ensure positive-definiteness. Cokriging equations and the induced cokriging equations are given. The study is illustrated by an example from soil science. 相似文献
78.
79.
80.
Three continuous marine fish cell lines of FG (i. e., Hounder Gill) from flounder (Paralichthys olivaceus) gill, SPH (i. e. , Sea Perch Heart) from sea perch (Lateolabrax japonicus) heart and RSBF (i.e., Red Sea Bream Fin) from red sea bream (Pagrosomus major) fin, were characterized by lactate dehydrogenase (LDH) isozyme and morphological analysis. The LDH isozyme patterns of these three cell lines and their corresponding tissues of origin were investigated and compared. The results showed: (1) No difference was found in the LDH isozyme patterns of FG and flounder gill tissue. However, the LDH isozyme patterns of SPH and RSBF were significantly different from their corresponding tissues of origin; (2) LDH isozyme patterns of FG, SPH and RSBF were markedly different from each other and could serve as genetic markers for species identification and detection of cross contamination. Morphological change analysis of these three cell lines in comparison to their original tissues indicated that FG cells still appeared epithelioid without morphological transformation. However, morphological changes were found in SPH and RSBF compared to their original tissues. Therefore, the cellular morphology was still plastic in the relatively stable culture conditions, and it was possible that change of LDH patterns wasrelated to morphological changes of fish cells in vitro. 相似文献