全文获取类型
收费全文 | 44810篇 |
免费 | 10570篇 |
国内免费 | 14734篇 |
专业分类
测绘学 | 7558篇 |
大气科学 | 5332篇 |
地球物理 | 8379篇 |
地质学 | 29731篇 |
海洋学 | 8185篇 |
天文学 | 1063篇 |
综合类 | 3552篇 |
自然地理 | 6314篇 |
出版年
2024年 | 253篇 |
2023年 | 956篇 |
2022年 | 2573篇 |
2021年 | 3214篇 |
2020年 | 2544篇 |
2019年 | 2908篇 |
2018年 | 2817篇 |
2017年 | 2673篇 |
2016年 | 2662篇 |
2015年 | 3105篇 |
2014年 | 3168篇 |
2013年 | 3878篇 |
2012年 | 4152篇 |
2011年 | 4173篇 |
2010年 | 4050篇 |
2009年 | 3763篇 |
2008年 | 3782篇 |
2007年 | 3603篇 |
2006年 | 3448篇 |
2005年 | 2825篇 |
2004年 | 2091篇 |
2003年 | 1443篇 |
2002年 | 1586篇 |
2001年 | 1388篇 |
2000年 | 1129篇 |
1999年 | 501篇 |
1998年 | 226篇 |
1997年 | 185篇 |
1996年 | 137篇 |
1995年 | 81篇 |
1994年 | 80篇 |
1993年 | 67篇 |
1992年 | 78篇 |
1991年 | 50篇 |
1990年 | 56篇 |
1989年 | 38篇 |
1988年 | 32篇 |
1987年 | 34篇 |
1986年 | 33篇 |
1985年 | 30篇 |
1984年 | 27篇 |
1983年 | 17篇 |
1982年 | 19篇 |
1981年 | 11篇 |
1979年 | 30篇 |
1977年 | 11篇 |
1976年 | 10篇 |
1958年 | 11篇 |
1957年 | 16篇 |
1954年 | 31篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
刘崇蓉 《地球信息科学学报》1996,(2):54-54
以往的南水北调工程局限在长江流域内,没有谈到从藏东调水。西线调水的方案很多,原有的规划是在本流域内.现在是跨流域调水。到底如何选取调水目标?那些地区是真缺水?调水顺序如何?应做全面和系统的规划,规划中要有西部需水的总体规划。 对于雅鲁藏布江的调水工程也要有全面的综合规划。供水和调水区可调多少水.要从总的经济效益来评价。这应是多学科、多方面专家共同讨论的问题。 相似文献
102.
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
103.
104.
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
105.
低频扩频中伪随机序列产生方法的研究 总被引:2,自引:0,他引:2
伪随机序列的产生是实现BPC低频时码发播台扩展频谱技术升级的一个重要环节。针对BPC低频时码发播台的现有系统,提出了伪随机序列的产生方案,并对其性能作了分析。 相似文献
106.
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
107.
Xiang Shouping 《Astrophysics and Space Science》1985,112(1):83-91
In a two-component Universe which consists of fluid (visible matter) plus collisinless massive neutrino gas (dark matter), the remarkable difference between the developed inhomogeneities in two components could be formed after the decoupling time. Whether the initial perturbation was in which of the two components, the inhomogeneities developed in visible matter are larger than that in neutrinos, especially on smaller scales. The necessary condition for such a situation to arise is only that the density of neutrinos in the Universe is dominant. That means the non-dominant visible component in the Universe is strongly clustered especially on smaller scales, while the distribution of the dominant dark matter (neutrinos) is fairly uniform. 相似文献
108.
109.
S. Maaløe 《Mineralogy and Petrology》2003,77(1-2):1-24
Summary ?Partial melting of the mantle is polybaric which implies that the phase relations change during partial melting. In addition
to the pressure the composition of the melt depends on the melting mode. Various melting models have been suggested. Here
the basic phase relations of polybaric batch, percolative, and critical melting are considered, using a simple ternary system.
The percolative melts are in equilibrium with their residua, but differ somewhat in composition from those of batch melting.
Critical melting is a fractional type of melting where the residuum contain interstitial melt. The critical melts differ in
composition from batch melts. The linear trends of peridotites from ophiolites show that the extracted melts had nearly constant
compositions, and therefore were extracted within a small pressure interval. A comparison between the trends of mantle peridotite
and experimental batch melts suggests strongly that the melt extracted from the peridotites are in equilibrium with their
residua. This could suggest that either batch or percolative melting are relevant melting modes for the mantle. However, isotopic
disequilibria favor instead a critical mode of melting. This inconsistency can be avoided if the ascending melts are accumulated
within a source region and equilibrate with the residuum before the melt is extracted from the source region. The evidence
for equilibrium suggests that multisaturation of tholeiitic compositions in PT-diagrams is relevant for estimating pressure
and temperature of generation of primary tholeiitic magmas.
Received September 2, 2001; revised version accepted March 20, 2002 相似文献
110.