全文获取类型
收费全文 | 33532篇 |
免费 | 4957篇 |
国内免费 | 6688篇 |
专业分类
测绘学 | 1833篇 |
大气科学 | 5868篇 |
地球物理 | 8068篇 |
地质学 | 16141篇 |
海洋学 | 4578篇 |
天文学 | 2553篇 |
综合类 | 2626篇 |
自然地理 | 3510篇 |
出版年
2024年 | 120篇 |
2023年 | 482篇 |
2022年 | 1358篇 |
2021年 | 1637篇 |
2020年 | 1431篇 |
2019年 | 1512篇 |
2018年 | 1900篇 |
2017年 | 1794篇 |
2016年 | 1877篇 |
2015年 | 1491篇 |
2014年 | 1851篇 |
2013年 | 2049篇 |
2012年 | 1888篇 |
2011年 | 2004篇 |
2010年 | 1963篇 |
2009年 | 1873篇 |
2008年 | 1662篇 |
2007年 | 1752篇 |
2006年 | 1444篇 |
2005年 | 1045篇 |
2004年 | 813篇 |
2003年 | 918篇 |
2002年 | 959篇 |
2001年 | 929篇 |
2000年 | 937篇 |
1999年 | 1231篇 |
1998年 | 1016篇 |
1997年 | 1041篇 |
1996年 | 955篇 |
1995年 | 880篇 |
1994年 | 775篇 |
1993年 | 656篇 |
1992年 | 559篇 |
1991年 | 385篇 |
1990年 | 309篇 |
1989年 | 293篇 |
1988年 | 253篇 |
1987年 | 160篇 |
1986年 | 163篇 |
1985年 | 105篇 |
1984年 | 96篇 |
1983年 | 95篇 |
1982年 | 93篇 |
1981年 | 63篇 |
1980年 | 60篇 |
1979年 | 60篇 |
1978年 | 31篇 |
1977年 | 26篇 |
1976年 | 22篇 |
1975年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 64 毫秒
121.
The abundances of light elements (deuterium, helium and lithium) are calculated in unconventional cosmologies in which these elements are produced by interaction of fast -particles ejected by massive pregalactic stars with a purely hydrogenous cosmological substrate. The number density and energetics of such stars needed for suitable production of light elements are estimated. It is shown that the models always lead to overproduction of lithium. The intensity of ultraviolet, X-ray, and -ray emission caused by explosions of pregalactic massive stars is calculated. The distortions of cosmic background radiation by Compton losses of electrons heated by explosive stars are also calculated. 相似文献
122.
《徐霞客游记》的科学性和时代性——怒江、腾冲地区的实地验证 总被引:2,自引:0,他引:2
作者选取本人身历其境作过工作的怒江、腾冲地区来验证《徐霞客游记》,从徐氏进步的地理概念、游记严谨的逻辑结构、游记作者观察的细致深入等方面论述了徐霞客的献身精神和不朽贡献。 相似文献
123.
Trace and RE element geochemistry and genesis have been studied with respect to ferromanganese nodules from the sediments of the Pacific, Atlantic and Indian oceans. 相似文献
124.
Ni Xiang-bin Jiang Yao-tiao Chen Zai-zhang Fang Cheng 《Chinese Astronomy and Astrophysics》1985,9(4):273-277
We propose a new heating mechanism of faculae. We think that the formation of faculae is a result of the Joule dissipation of the Hall current generated by the interaction of the convection field of granules in an active region and the inter-granular magnetic field. For a region to generate effectively Hall current, its characteristic length must be such that the magnetic Reynolds number is less than 1. The equation of energy balance in the facula region is .For five observational models of faculae, we calculated the corresponding velocity fields, and the results are in basic agreement with the observed fields. The present mechanism explains the dependence of the facula brightness on the magnetic and velocity fields, the apparent distribution of the faculae on the solar disk and suggest a possible interpretation of the five structures of faculae. 相似文献
125.
A series of hydrodynamical models of type-II supernova outbursts (SNII) has been calculated. Approximate relations connecting the total outburst energy ε, the mass of envelope ejectedM, the presupernova radiusR, and the amount of ionizing quanta radiated by the supernovaeN H with such values as the duration of the light curve plateau Δt, and absolute magnitude in the wavelength bandV and photospheric velocityU PH observed near the middle of the plateau have been established. Advantage has been taken of the relations to obtain a preliminary evaluation for the characteristics of the average SN II: ε=7×1050 erg,M=6M ⊙,R=500R ⊙,N H=2×1058. The SNIIs with plateau-like light curves seem to be accounted for by thermonuclear explosions of degenerate cores of red giant stars and result in a total disruption of the star without any stellar remnant. To the contrary, SNIIs with linear light curves have substantially different properties (in particular, they throw considerably less massive envelopes off). These SNII must signify the birth of collapsed objects—neutron stars (pulsars) or black holes. 相似文献
126.
Xie-Yan Song Hua-Wen Qi Paul T. Robinson Mei-Fu Zhou Zhi-Min Cao Lie-Meng Chen 《Lithos》2008,100(1-4):93-111
The Emeishan continental flood basalt (ECFB) sequence in Dongchuan, SW China comprises a basal tephrite unit overlain by an upper tholeiitic basalt unit. The upper basalts have high TiO2 contents (3.2–5.2 wt.%), relatively high rare-earth element (REE) concentrations (40 to 60 ppm La, 12.5 to 16.5 ppm Sm, and 3 to 4 ppm Yb), moderate Zr/Nb and Nb/La ratios (9.3–10.2 and 0.6–0.9, respectively) and relatively high Nd (t) values, ranging from − 0.94 to 2.3, and are comparable to the high-Ti ECFB elsewhere. The tephrites have relatively high P2O5 (1.3–2.0 wt.%), low REE concentrations (e.g., 17 to 23 ppm La, 4 to 5.3 ppm Sm, and 2 to 3 ppm Yb), high Nb/La (2.0–3.9) ratios, low Zr/Nb ratios (2.3–4.2), and extremely low Nd (t) values (mostly ranging from − 10.6 to − 11.1). The distinct compositional differences between the tephrites and the overlying tholeiitic basalts cannot be explained by either fractional crystallization or crustal contamination of a common parental magma. The tholeiitic basalts formed by partial melting of the Emeishan plume head at a depth where garnet was stable, perhaps > 80 km. We propose that the tephrites were derived from magmas formed when the base of the previously metasomatized, volatile-mineral bearing subcontinental lithospheric mantle was heated by the upwelling mantle plume. 相似文献
127.
128.
Evolution of melt composition during intrusion of basalts into a silicic magma chamber 总被引:3,自引:0,他引:3
P. Yu. Plechov I. S. Fomin O. E. Mel’nik N. V. Gorokhova 《Moscow University Geology Bulletin》2008,63(4):247-257
The article describes heat exchange between basaltic and rhyolite melts accompanied by fractional crystallization of phases in a basaltic melt. A numerical model has been developed for the homogenization mechanism of magma composition during intrusion of basaltic magma batches into felsic magma chambers. The results of numerical modeling demonstrate that the time needed for cooling the basalts and their fractionation to rhyolite melts is much shorter than the time required for chemical interaction based on diffusive mechanisms. 相似文献
129.
G. A. Golodkovskaya I. V. Kalinichenko Yu. L. Filimonov V. G. Khloptsov 《Moscow University Geology Bulletin》2008,63(3):162-170
This paper discusses issues of the decline of the reservoir properties of arenaceous-argillaceous rocks as a result of declining porosity due to long-term operation of underground gas storage facilities. An analysis of the many-year operation of storage facilities, as well as calculation, has revealed that the active capacity of a storage reservoir gradually decreases under certain conditions of underground storage operations. We performed a series of experiments with model specimens in order to support the hypothesis of decreasing reservoir (capacity-filtration) properties because of changes in the value and structure of the pore space. These experiments showed that the cyclic loading and unloading of arenaceous-silty rocks during long-term operation of underground gas storage facilities can significantly decrease the reservoir parameters of reservoirs created within worked out gas-and-gas condensate fields. Laboratory studies of model specimens corresponding to feldspar sandstone in their composition, porosity, and strength proved that porosity considerably decreases in such reservoirs at actually existing values of formation pressure. Tests of sand performed under conditions close to those existing during the development of hydrocarbon fields also showed that their permeability gradually decreases in the process of cyclic changes of effective pressure. 相似文献
130.
The joint evolution of organic matter and silica in petroliferous sequences is considered in the terms of the laws of transformation of dispersion systems. The dispersion systems are transformed under conditions of low-temperature solid-phase processes accompanied by the silica phase transition and dehydration that favors the evolution of organic matter. 相似文献