全文获取类型
收费全文 | 71979篇 |
免费 | 5886篇 |
国内免费 | 7191篇 |
专业分类
测绘学 | 2310篇 |
大气科学 | 9405篇 |
地球物理 | 16157篇 |
地质学 | 29309篇 |
海洋学 | 7047篇 |
天文学 | 12014篇 |
综合类 | 3354篇 |
自然地理 | 5460篇 |
出版年
2023年 | 451篇 |
2022年 | 1375篇 |
2021年 | 1725篇 |
2020年 | 1619篇 |
2019年 | 1719篇 |
2018年 | 2569篇 |
2017年 | 2362篇 |
2016年 | 2794篇 |
2015年 | 1914篇 |
2014年 | 2819篇 |
2013年 | 3695篇 |
2012年 | 2751篇 |
2011年 | 3224篇 |
2010年 | 3177篇 |
2009年 | 3820篇 |
2008年 | 3214篇 |
2007年 | 3185篇 |
2006年 | 2833篇 |
2005年 | 2312篇 |
2004年 | 2089篇 |
2003年 | 2013篇 |
2002年 | 1940篇 |
2001年 | 1803篇 |
2000年 | 1952篇 |
1999年 | 2269篇 |
1998年 | 2052篇 |
1997年 | 2101篇 |
1996年 | 1766篇 |
1995年 | 1689篇 |
1994年 | 1507篇 |
1993年 | 1310篇 |
1992年 | 1126篇 |
1991年 | 957篇 |
1990年 | 889篇 |
1989年 | 840篇 |
1988年 | 745篇 |
1987年 | 782篇 |
1986年 | 639篇 |
1985年 | 709篇 |
1984年 | 773篇 |
1983年 | 713篇 |
1982年 | 639篇 |
1981年 | 644篇 |
1980年 | 535篇 |
1979年 | 492篇 |
1978年 | 481篇 |
1977年 | 430篇 |
1976年 | 411篇 |
1975年 | 410篇 |
1973年 | 426篇 |
排序方式: 共有10000条查询结果,搜索用时 18 毫秒
121.
JIANGDong WANGNai-bin YANGXIao-huan WANGJi-hua 《中国地理科学(英文版)》2003,13(1):62-65
Daily and ten-day Normalized Difference Vegetation Index(NDVI) of crops were retrieved from meteorological statellite NOAA AVHRR images ,The temporal variations of the NDVI were analyzed during the whole growing season,and thus the principle of the interaction between NDIV profile and the growing status of crops was discussed,As a case in point,the relationship between integral NDVI and winter wheat yield of Henan Province in 1999 had been analyzed.By putting integral NDVI values of 60 sample counties into the winter wheat yield-integral NDVI coordination,scattering map was plotted. It demonstrated that integral NDVI had a close relation with winter wheat yield.These relation could be described with linear,cubic polynomial ,and exponential regression,and the cubic polynomial regression was the best way,In general ,NDVI reflects growing status of green vegetation ,so crop monitoring and crop yield estimation could be realized by using remote sensing technique on the basis of time serial NDVI data together with agriculture calendars. 相似文献
122.
In this paper general solutions are found for domain walls in Lyra geometry in the plane symmetric spacetime metric given
by Taub. Expressions for the energy density and pressure of domain walls are derived in both cases of uniform and time varying
displacement field β. It is also shown that the results obtained by Rahaman et al [IJMPD, 10, 735 (2001)] are particular case
of our solutions. Finally, the geodesic equations and acceleration of the test particle are discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
123.
C.S. Botzler J. Snigula R. Bender N. Drory G. Feulner G.J. Hill U. Hopp C. Maraston C. Mendes de Oliveira 《Astrophysics and Space Science》2003,284(2):393-396
The Munich Near-IR Cluster Survey (MUNICS) is a wide-area, medium-deep, photometric survey selected in the K' band. The project's
main scientific aims are the identification of galaxy clusters up to redshifts of unity and the selection of a large sample
of field early-type galaxies up to z < 1.5 for evolutionary studies. We created a Large Scale Structure catalog, using a new structure finding technique specialized
for photometric datasets, that we developed on the basis of a friends-of-friends algorithm. We tested the plausibility of
the resulting galaxy group and cluster catalog with the help of Color-Magnitude Diagrams (CMD), as well as a likelihood- and
Voronoi-approach.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
124.
We explore the possibility of searching for groups of radio sources from the FIRST catalog on angular scales 1′–5′. We developed an efficient method of searching for such groups that takes into account the need for combining the components of extended sources represented in the catalog by separate objects. We found 31 groups of radio sources with angular sizes <5′ that contain no fewer than five sources with flux densities ≥3 mJy. This number is at least triple the expected number of such groups for a random Poisson distribution of radio sources in the sky. The prospects for using groups of radio sources to detect and study distant systems of galaxies are discussed. 相似文献
125.
126.
127.
茅排金矿床属中-低温硫化物金矿床,矿体的分布严格受断裂构造控制.通过应用不同的物探方法来寻找控矿断裂,从而达到间接地寻找矿体分布的目的,取得了较好的效果。 相似文献
128.
We present two spectra of the supernova SN1988A in M58 (NGC4579) over the wavelength range 4000–9700 Å, as recorded by the Faint Object Spectrograph on the 4.2 m William Herschel Telescope at the Observatorio del Roque de los Muchachos. We conclude that SN1988A was a type II supernova. 相似文献
129.
G. A. GRAHAM P. G. GRANT R. J. CHATER A. J. WESTPHAL A. T. KEARSLEY C. SNEAD G. DOMÍNGUEZ A. L. BUTTERWORTH D. S. McPHAIL G. BENCH J. P. BRADLEY 《Meteoritics & planetary science》2004,39(9):1461-1473
Abstract— In 2006, the Stardust spacecraft will return to Earth with cometary and perhaps interstellar dust particles embedded in silica aerogel collectors for analysis in terrestrial laboratories. These particles will be the first sample return from a solid planetary body since the Apollo missions. In preparation for the return, analogue particles were implanted into a keystone of silica aerogel that had been extracted from bulk silica aerogel using the optical technique described in Westphal et al. (2004). These particles were subsequently analyzed using analytical techniques associated with the use of a nuclear microprobe. The particles have been analyzed using: a) scanning transmission ion microscopy (STIM) that enables quantitative density imaging; b) proton elastic scattering analysis (PESA) and proton backscattering (PBS) for the detection of light elements including hydrogen; and c) proton‐induced X‐ray emission (PIXE) for elements with Z > 11. These analytical techniques have enabled us to quantify the composition of the encapsulated particles. A significant observation from the study is the variable column density of the silica aerogel. We also observed organic contamination within the silica aerogel. The implanted particles were then subjected to focused ion beam (FIB) milling using a 30 keV gallium ion beam to ablate silica aerogel in site‐specific areas to expose embedded particles. An ion polished flat surface of one of the particles was also prepared using the FIB. Here, we show that ion beam techniques have great potential in assisting with the analysis and exposure of Stardust particles. 相似文献
130.
Kunde Yang Yuanliang Ma Chao Sun Miller J.H. Potty G.R. 《Oceanic Engineering, IEEE Journal of》2004,29(4):964-972
This paper discusses the results of geoacoustic inversion carried out using explosive charge data from the Asian Seas International Acoustic Experiment (ASIAEX) East China Sea (ECS) Experiment. A multifrequency incoherent matched-field inversion processor and a genetic algorithm (GA) are used for the inversion. A multistep matched field inversion approach is presented, which makes use of the varying sensitivities of wave fields at various frequencies to reduce the inversion problem into a sequence of smaller inversions with fewer unknowns to estimate at each stage. Different parameters are estimated using data at different frequencies according to their sensitivities. Inversion results for different areas in the ECS region are summarized and compared with core data. 相似文献