全文获取类型
收费全文 | 70488篇 |
免费 | 10844篇 |
国内免费 | 15654篇 |
专业分类
测绘学 | 7544篇 |
大气科学 | 9115篇 |
地球物理 | 10926篇 |
地质学 | 32756篇 |
海洋学 | 12356篇 |
天文学 | 7779篇 |
综合类 | 4647篇 |
自然地理 | 11863篇 |
出版年
2024年 | 172篇 |
2023年 | 801篇 |
2022年 | 2404篇 |
2021年 | 2644篇 |
2020年 | 2651篇 |
2019年 | 2959篇 |
2018年 | 2478篇 |
2017年 | 2852篇 |
2016年 | 2921篇 |
2015年 | 3183篇 |
2014年 | 4143篇 |
2013年 | 4383篇 |
2012年 | 4210篇 |
2011年 | 4639篇 |
2010年 | 4024篇 |
2009年 | 5183篇 |
2008年 | 5128篇 |
2007年 | 5052篇 |
2006年 | 4828篇 |
2005年 | 4441篇 |
2004年 | 3925篇 |
2003年 | 3527篇 |
2002年 | 3048篇 |
2001年 | 2618篇 |
2000年 | 2573篇 |
1999年 | 2275篇 |
1998年 | 1888篇 |
1997年 | 1458篇 |
1996年 | 1191篇 |
1995年 | 1000篇 |
1994年 | 962篇 |
1993年 | 804篇 |
1992年 | 604篇 |
1991年 | 502篇 |
1990年 | 355篇 |
1989年 | 288篇 |
1988年 | 223篇 |
1987年 | 129篇 |
1986年 | 88篇 |
1985年 | 96篇 |
1984年 | 59篇 |
1983年 | 55篇 |
1982年 | 51篇 |
1981年 | 39篇 |
1980年 | 24篇 |
1979年 | 14篇 |
1978年 | 29篇 |
1977年 | 19篇 |
1976年 | 6篇 |
1954年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
昆仑山8.1级地震前中国大陆的构造应变背景 总被引:10,自引:4,他引:6
利用“网络工程”1998~2001年累积的1181个测站的GPS重复观测资料,采用双三次样条函数模型建立中国大陆水平运动模型速度场,用大地坐标在椭球面上计算各类应变场,详细分析了2001年昆仑山8.1级地震前中国大陆水平构造应变场空间分布特征。各类构造应变场的最高值都出现在喜马拉雅构造带与昆仑山地块内(地震断裂带南侧),鲜水河—安宁河断裂带次之。分析表明,昆仑山8.1级地震正好发生在张性面膨胀应变率的高值区,第一、第二和最大剪应变率高值区边缘的突变区和最大、最小主应变率的高值区。 相似文献
102.
E.A. Evstigneeva R.R. de Carvalho A.L. Ribeiro H.V. Capelato 《Astrophysics and Space Science》2003,284(2):487-490
We present the preliminary results of a study of how small stellar systems merge to form larger ones. As we display the families
of galaxies in the μe - Re plane (effective surface brightness versus effective radius) we realize that different morphological types occupy different
loci, evidencing the different physical mechanisms operating in each family. As proposed by Capaccioli et al. (1992) this
diagram is the logical equivalent of the HR diagram for stars. Here we take some initial steps in understanding of how we
can establish the evolutionary tracks, solely due to dynamical processes, in the μe - Re plane, ultimately making a dwarf elliptical to turn into a normal elliptical galaxy.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
103.
104.
105.
106.
V. J. Mclntyre A. C. Gilmore J. B. Hearnshaw 《Journal of Astrophysics and Astronomy》1990,11(1):81-123
Photographic spectra of SN1987A in the LMC have been obtained from 1987 February 25 to 1988 June 30. Microdensitometer tracings
of these have been reduced to intensity and corrections for instrumental response have been applied to the spectra. This paper
presents these data in an atlas format, discusses the reduction procedures in detail, and presents radial velocity measurements
of selected lines in the spectra 相似文献
107.
Himmerfjärd is a Swedish estuary bordering on the Baltic. The estuary lacks astronomical tides and its circulation is driven by winds and freshwater runoff. Because of a tertiary sewage treatment plant located at its inner end, the estuary is becoming increasingly eutrophic. A field study was carried out for a 78-day period in late summer and early fall of 1977 to determine rates of nutrient transport and to construct nutrient budgets. Since physical parameters (current velocity, temperature, salinity, winds and water level changes) were measured more frequently than nutrients (phosphate, nitrate, nitrite and ammonium) it was necessary to develop a suitable method to calculate nutrient flux time series and net nutrient fluxes. Over the study period, Himmerfjärd imported phosphorus and exported nitrogen. Direction of nutrient fluxes and changes in flux direction were consistent with the structure of the baroclinic currents. 相似文献
108.
Richard J. Pike 《The Professional geographer》1987,39(2):131-145
Extraterrestrial geography has become a reality, as we move from Earth's moon to the planets. A broad-scale regional physiography is being established on twenty planets and satellites through remote sensing techniques. Spacecraft images yield most of the information on Solar System landscapes. Topographic measurements are extracted by monoscopic image-processing, stereophotogrammetry, and radar analysis. Invisible parts of the spectrum furnish non-topographic data. 相似文献
109.
Reconnaissance seismic shot in 1971/72 showed a number of well defined seismic anomalies within the East Sengkang Basin which were interpreted as buried reefs. Subsequent fieldwork revealed that Upper Miocene reefs outcropped along the southern margin of the basin. A drilling programme in 1975 and 1976 proved the presence of shallow, gas-bearing, Upper Miocene reefs in the northern part of the basin. Seismic acquisition and drilling during 1981 confirmed the economic significance of these discoveries, with four separate accumulations containing about 750 × 109 cubic feet of dry gas in place at an average depth of 700 m. Kampung Baru is the largest field and contains over half the total, both reservoir quality and gas deliverability are excellent. Deposition in the East Sengkang Basin probably started during the Early Miocene. A sequence of Lower Miocene mudstones and limestones unconformably overlies acoustic basement which consists of Eocene volcanics. During the tectonically active Middle Miocene, deposition was interrupted by two periods of deformation and erosion. Carbonate deposition became established in the Late Miocene with widespread development of platform limestones throughout the East Sengkang Basin. Thick pinnacle reef complexes developed in the areas where reef growth could keep pace with the relative rise in sea level. Most reef growth ceased at the end of the Miocene and subsequent renewed clastic sedimentation covered the irregular limestone surface. Late Pliocene regression culminated in the Holocene with erosion. The Walanae fault zone, part of a major regional sinistral strike-slip system, separates the East and West Sengkang Basins. Both normal and reverse faulting are inferred from seismic data and post Late Pliocene reverse faulting is seen in outcrop. 相似文献
110.
R. Surendiranath N. Kameswara Rao Ram Sagar J. S. Nathan K. K. Ghosh 《Journal of Astrophysics and Astronomy》1990,11(2):151-166
bdAbstract The open cluster NGC 2818 containing a planetary nebula has been observed inVRI bands using the CCD system at prime focus of the 2.3-metre Vainu Bappu Telescope. The study extending to starsV ∼ 21 magnitude establishes the distance modulus as(m-M)
0 = 12.9 ±0.1 for the cluster. Based on the fitting of theoretical isochrones computed for solar metallicity, an age of 5(±1)
× 108 years has been assigned to the cluster. Association of the planetary nebula with the cluster indicates that the progenitor
mass of the planetary nebula on the main sequence is ≥2.5M⊙
Based on observations obtained with the Vainu Bappu Telescope. 相似文献