全文获取类型
收费全文 | 7525篇 |
免费 | 1250篇 |
国内免费 | 1591篇 |
专业分类
测绘学 | 304篇 |
大气科学 | 1453篇 |
地球物理 | 1897篇 |
地质学 | 3530篇 |
海洋学 | 1020篇 |
天文学 | 490篇 |
综合类 | 837篇 |
自然地理 | 835篇 |
出版年
2024年 | 10篇 |
2023年 | 89篇 |
2022年 | 297篇 |
2021年 | 331篇 |
2020年 | 318篇 |
2019年 | 289篇 |
2018年 | 388篇 |
2017年 | 366篇 |
2016年 | 446篇 |
2015年 | 319篇 |
2014年 | 415篇 |
2013年 | 427篇 |
2012年 | 383篇 |
2011年 | 422篇 |
2010年 | 436篇 |
2009年 | 433篇 |
2008年 | 348篇 |
2007年 | 359篇 |
2006年 | 330篇 |
2005年 | 242篇 |
2004年 | 217篇 |
2003年 | 242篇 |
2002年 | 225篇 |
2001年 | 209篇 |
2000年 | 225篇 |
1999年 | 330篇 |
1998年 | 315篇 |
1997年 | 294篇 |
1996年 | 252篇 |
1995年 | 258篇 |
1994年 | 225篇 |
1993年 | 178篇 |
1992年 | 156篇 |
1991年 | 97篇 |
1990年 | 101篇 |
1989年 | 72篇 |
1988年 | 57篇 |
1987年 | 48篇 |
1986年 | 25篇 |
1985年 | 26篇 |
1984年 | 29篇 |
1983年 | 23篇 |
1982年 | 25篇 |
1981年 | 21篇 |
1980年 | 12篇 |
1979年 | 15篇 |
1975年 | 5篇 |
1974年 | 7篇 |
1973年 | 7篇 |
1958年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
The anodic stripping voltammetry with physically-coating mercury film electrode was used to investigate the complexing action
of trace heavy metals in seawater with organic ligands. The apparent copper complexing capacity of seawater was determined
by titrating the organic ligands in natural seawater with standard ionic copper solution. The complexing actions of copper
in seawater with humic acid (HA) or fulvic acid (FA) were investigated by titrating copper in seawater with HA or FA solution.
The equilibrium time, electrodeposition potential, and effect of pH etc. were investigated respectively. The results show
that the interaction of copper in seawater with organic matter is a fast process. At natural pH, HA or FA tend to act with
copper in seawater to form nonlabile complexes. During experimental electrode process, these complexes did not significantly
dissociate. The experimental results were calculated according to 1∶1 complex formation. 相似文献
23.
The accuracy of the AE index as a measure of the joule heat production rate is examined for a typical substorm event on 18 March 1978 by estimating the global joule heat production rate, as a function of time, using data obtained from the IMS six meridian chains. In spite of the fact that the AE index had had an initial slow growth which was followed by a rapid growth, the joule heat production rate attained a high level during the slow growth and thus their variations were considerably different from those of the AE index. Therefore, although the AE index is statistically linearly related to the global joule heat production rate, one should be cautious in assuming that details of time variations of the AE index during individual events represent those of the joule heat production rate. 相似文献
24.
严格论证了在对空间或地面目标的定位中,利用伪距测量观测模型的几何因子大于用台站间一次差分观测模型的几何因子.此外,台站间完全差分测量观测的定位精度优于不完全测量情形的定位精度.这些结果给人们在实际工作中采取何种定位方式提供了可靠的理论依据. 相似文献
25.
26.
THECONSTRUCTIONANDITSDEVELOPMENTOFTHEOVERSEASTRANSPORTSYSTEMINNORTHEASTCHINAGaoShali(高莎丽)(DepartmentofGeography,NortheastNorm... 相似文献
27.
Dr M. J. Wooller D. L. Swain K. J. Ficken A. D. Q. Agnew F. A. Street-Perrott G. Eglinton 《第四纪科学杂志》2003,18(1):3-15
Woody, subalpine shrubs and grasses currently surround Lake Rutundu, Mount Kenya. Multiple proxies, including carbon isotopes, pollen and grass cuticles, from a 755‐cm‐long core were used to reconstruct the vegetation over the past 38 300 calendar years. Stable carbon‐isotope ratios of total organic carbon and terrestrial biomarkers from the lake sediments imply that the proportion of terrestrial plants using the C4 photosynthetic pathway was greater during the Late Pleistocene than in the Holocene. Pollen data show that grasses were a major constituent of the vegetation throughout the Late Pleistocene and Holocene. The proportion of grass pollen relative to the pollen from other plants was greatest at the last glacial maximum (LGM). Grass cuticles confirm evidence that C4 grass taxa were present at the LGM and that the majority followed the cold‐tolerant NADP‐MEC4 subpathway. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
28.
D. H. Morgan Q. A. Parker Martin Cohen 《Monthly notices of the Royal Astronomical Society》2003,346(3):719-730
We report the discovery of the first probable Galactic [WN] central star of a planetary nebula (CSPN). The planetary nebula candidate was found during our systematic scans of the AAO/UKST Hα Survey of the Milky Way. Subsequent confirmatory spectroscopy of the nebula and central star reveals the remarkable nature of this object. The nebular spectrum shows emission lines with large expansion velocities exceeding 150 km s−1 , suggesting that perhaps the object is not a conventional planetary nebula. The central star itself is very red and is identified as being of the [WN] class, which makes it unique in the Galaxy. A large body of supplementary observational data supports the hypothesis that this object is indeed a planetary nebula and not a Population I Wolf–Rayet star with a ring nebula. 相似文献
29.
The IRAS and 2MASS associations for 193 T Tauri stars are identified in this paper. From the color–color diagrams and spectral index, it is found that the IR excesses for most samples are due to thermal emission from the circumstellar material, as suggested previously. It is also found that the IR excesses at IRAS region for few T Tauri stars and the near-IR excesses for some T Tauri stars are likely attributed to free-free emission or free-bound emission from the circumstellar ionized gas. Moreover, It is found in deredened J–H versus H–K color–color diagram that there is a slight separation in different spectral groups. The T Tauri stars locus equation in J–H versus H–K color–color diagram for our sample is also presented. 相似文献
30.
EFFECT OF SULPHATE-REDUCING BACTERIA ON ELECTRO-CHEMICAL CORROSION BEHAVIOR OF 16Mn STEEL IN SEA MUD
INTRODUCTIONItwasgenerallyconsideredpreviouslythatthecorrosionofsteelinseamudwasnotserious.However,itwaslaterfoundthatthecorrosionrateofsteelinsomeseamudwashigherthanthatinseawater(King,1980;Sehmide,1982;Guoetal.,1997;Hou,1998).Therearesomereportsthatthecorrosionr… 相似文献