全文获取类型
收费全文 | 23435篇 |
免费 | 4250篇 |
国内免费 | 7339篇 |
专业分类
测绘学 | 904篇 |
大气科学 | 7274篇 |
地球物理 | 3712篇 |
地质学 | 9950篇 |
海洋学 | 4009篇 |
天文学 | 6148篇 |
综合类 | 1110篇 |
自然地理 | 1917篇 |
出版年
2024年 | 112篇 |
2023年 | 313篇 |
2022年 | 720篇 |
2021年 | 773篇 |
2020年 | 894篇 |
2019年 | 1056篇 |
2018年 | 910篇 |
2017年 | 809篇 |
2016年 | 885篇 |
2015年 | 1016篇 |
2014年 | 1548篇 |
2013年 | 1641篇 |
2012年 | 1624篇 |
2011年 | 1741篇 |
2010年 | 1603篇 |
2009年 | 2140篇 |
2008年 | 2071篇 |
2007年 | 2142篇 |
2006年 | 1994篇 |
2005年 | 1657篇 |
2004年 | 1512篇 |
2003年 | 1273篇 |
2002年 | 1023篇 |
2001年 | 908篇 |
2000年 | 813篇 |
1999年 | 751篇 |
1998年 | 630篇 |
1997年 | 428篇 |
1996年 | 408篇 |
1995年 | 332篇 |
1994年 | 301篇 |
1993年 | 226篇 |
1992年 | 155篇 |
1991年 | 131篇 |
1990年 | 77篇 |
1989年 | 59篇 |
1988年 | 71篇 |
1987年 | 37篇 |
1986年 | 29篇 |
1985年 | 40篇 |
1984年 | 31篇 |
1983年 | 21篇 |
1982年 | 20篇 |
1981年 | 22篇 |
1980年 | 13篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1977年 | 20篇 |
1976年 | 10篇 |
1971年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
101.
102.
K. Nagamine † M. Fukugita R. Cen J.P. Ostriker 《Monthly notices of the Royal Astronomical Society》2001,327(1):L10-L14
The luminosity function of galaxies is derived from a cosmological hydrodynamic simulation of a Λ cold dark matter universe with the aid of a stellar population synthesis model. At , the resulting B -band luminosity function has a flat faint-end slope of with the characteristic luminosity and the normalization in fair agreement with observations, while the dark matter halo mass function is steep with a slope of . The colour distribution of galaxies also agrees well with local observations. We also discuss the evolution of the luminosity function, and the colour distribution of galaxies from to 5. A large evolution of the characteristic mass in the stellar mass function as a result of number evolution is compensated by luminosity evolution; the characteristic luminosity increases only by 0.8 mag from to 2, and then declines towards higher redshift, while the B -band luminosity density continues to increase from to 5 (but only slowly at . 相似文献
103.
The analyses of X-ray emission from classical novae during the outburst stage have shown that the soft X-ray emission below 1 keV, which is thought to originate from the photosphere of the white dwarf, is inconsistent with the simple blackbody model of emission. Thus, ROSAT Position Sensitive Proportional Counter (PSPC) archival data of the classical Nova Mus 1983 (GQ Mus) have been re-analysed in order to understand the spectral development in the X-ray wavelengths during the outburst stage. The X-ray spectra are fitted with the hot white dwarf (WD) atmosphere emission models developed for the remnants of classical novae near the Eddington luminosity. The post-outburst X-ray spectra of the remnant white dwarf are examined in the context of evolution on the Hertzsprung–Russell diagram using C–O enhanced atmosphere models. The data obtained in 1991 August (during the ROSAT All Sky Survey) indicate that the effective temperature is . The 1992 February data show that the white dwarf had reached an effective temperature in the range with an unabsorbed X-ray flux (i.e. ∼ bolometric flux) between and . We show that the H burning at the surface of the WD had most likely ceased at the time of the X-ray observations. Only the 1991 August data show evidence for ongoing H burning. 相似文献
104.
基于拖带坐标法建立了岩层大变形的一维非线性微分方程,然后用解析与数值方法研究了变刚度、可伸缩岩层在侧向压力及自重作用下的分叉特性,初步揭示了褶皱岩层初始挠曲的形成机理。 相似文献
105.
THE SIMULATED STORAGE CAPACITY OF FLOOD AND WATERLOGGING IN THE TYPICAL AGRICULTURAL REGION IN JIANGHAN PLAIN 总被引:2,自引:0,他引:2
1INTRODUCTIONJianghanPlainisoneoftheimportantbasesofChina′sagriculturalproductivitylocatedinthemiddleChangjiangRivervalleyofcentralChina.TheJianghanplainapproximately6.6×104km2inareaandover30millioninpopulationistherenowned“countryoffishandrice"in… 相似文献
106.
向文 《大地测量与地球动力学》1997,(2)
为了根据离散观测数据构制连续空间重力变化图像,分析和讨论了3种数值插值方法,计算结果表明多面函数方法插值精度最高。由于逐步回归分析筛选核函数中心点的计算繁琐,文中提出根据分形理论和Shannon取样定理来确定核函数中心点。对滇西试验场进行模拟试算,插值精度可达到4~5(10-8ms-2)。 相似文献
107.
108.
Northern Hemispheric“polar lows”,i.e.maritime,small,but fairly intense cyclonic systems have been studied formore than two decades.Recently researchers have turned their attention towards the occurrence of polar lows and othersmall-scale cyclonic disturbances on the Southern Hemisphere.In this paper a short account of our present knowledgeof Northern Hemispheric polar lows will be given,followed by some preliminary results of an investigation of the natureand occurrence of polar lows on the Southern Hemisphere. 相似文献
109.
Based on the Intensive Field Campaign(IFC-1)data of Boreal Ecosystem-Atmosphere Study(BOREAS).a three-dimensional meso-β scale model is used to simulate the effect of boreal forests onthe lower atmosphere.A fine horizontal resolution of 2 km×2 km is used in order to distinguish thevegetative heterogeneity in the boreal region.A total of 20×25 grid points cover the entire sub-modeling area in BOREAS' South Study Area(SSA).The ecosystem types and their coverage ineach grid square are extracted from the North American Land Cover Characteristics Data Base(NALCCD)generated by the U.S.Geographical Survey(USGS)and the University of Nebraska-Lincoln(UNL).The topography of the study area is taken from the Digital Elevation Map(DEM)of USGS.The model outputs include the components of the energy balance budget within the canopyand at the ground.the turbulence parameters in the atmospheric boundary layer and the wind.temperature and humidity profiles extending up to a height of 1500 m.In addition to the fine timeand spatial step,the unique feature of the present model is the incorporation of both dynamic andbiological effects of the Boreal forest into the model parameterization scheme.The model resultscompare favorably with BOREAS' IFC-1 data in 1994 when the forest was in the luxuriant growingperiod. 相似文献
110.
T.D. Thoroughgood V.S. Dhillon S.P. Littlefair T.R. Marsh D.A. Smith 《Monthly notices of the Royal Astronomical Society》2001,327(4):1323-1333
We present spectroscopy of the eclipsing recurrent nova U Sco. The radial velocity semi-amplitude of the primary star was found to be from the motion of the wings of the He ii λ 4686-Å emission line. By detecting weak absorption features from the secondary star, we find its radial velocity semi-amplitude to be . From these parameters, we obtain a mass of for the white dwarf primary star and a mass of for the secondary star. The radius of the secondary is calculated to be , confirming that it is evolved. The inclination of the system is calculated to be , consistent with the deep eclipse seen in the light-curves. The helium emission lines are double-peaked, with the blueshifted regions of the disc being eclipsed prior to the redshifted regions, clearly indicating the presence of an accretion disc. The high mass of the white dwarf is consistent with the thermonuclear runaway model of recurrent nova outbursts, and confirms that U Sco is the best Type Ia supernova progenitor currently known. We predict that U Sco is likely to explode within ∼700 000 yr. 相似文献