全文获取类型
收费全文 | 82859篇 |
免费 | 18428篇 |
国内免费 | 43548篇 |
专业分类
测绘学 | 3515篇 |
大气科学 | 23709篇 |
地球物理 | 22243篇 |
地质学 | 53502篇 |
海洋学 | 20682篇 |
天文学 | 13089篇 |
综合类 | 4423篇 |
自然地理 | 3672篇 |
出版年
2022年 | 864篇 |
2021年 | 1403篇 |
2020年 | 2686篇 |
2019年 | 6226篇 |
2018年 | 7540篇 |
2017年 | 7080篇 |
2016年 | 7268篇 |
2015年 | 5440篇 |
2014年 | 5862篇 |
2013年 | 7380篇 |
2012年 | 6391篇 |
2011年 | 6777篇 |
2010年 | 6647篇 |
2009年 | 6508篇 |
2008年 | 5106篇 |
2007年 | 5148篇 |
2006年 | 4617篇 |
2005年 | 3826篇 |
2004年 | 4349篇 |
2003年 | 3890篇 |
2002年 | 3493篇 |
2001年 | 3198篇 |
2000年 | 2559篇 |
1999年 | 2316篇 |
1998年 | 2496篇 |
1997年 | 2593篇 |
1996年 | 1965篇 |
1995年 | 1904篇 |
1994年 | 1751篇 |
1993年 | 1794篇 |
1992年 | 1615篇 |
1991年 | 1229篇 |
1990年 | 1174篇 |
1989年 | 1026篇 |
1988年 | 879篇 |
1987年 | 825篇 |
1986年 | 664篇 |
1985年 | 702篇 |
1984年 | 738篇 |
1983年 | 618篇 |
1982年 | 636篇 |
1981年 | 529篇 |
1980年 | 500篇 |
1979年 | 457篇 |
1978年 | 432篇 |
1977年 | 375篇 |
1976年 | 326篇 |
1975年 | 302篇 |
1974年 | 289篇 |
1973年 | 361篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Takuya Matsumoto Masahiko Honda Ian McDougall Igor Yatsevich Suzanne Y. O'Reilly 《地学学报》2004,16(1):23-26
Using a Rayleigh distillation fractionation model, we calculate that the maximum isotope fractionation potentially achievable is less than 5% during the early stages of gas release from a sample. Our calculation corrects the erroneous conclusions of Gautheron and Moreira (2003), who re‐interpreted the plume‐like neon isotopic compositions found in metasomatic apatite from a south‐eastern Australian xenolith (Matsumoto et al., 1997) to be the result of Rayleigh‐type isotope fractionation of originally MORB‐type neon during stepheating gas extraction. We stress that the modelling of neon isotopic fractionation by Gautheron and Moreira (2003) is incorrect, and that the finding of a plume‐like neon isotopic composition in the apatite by Matsumoto et al. (1997) remains a quite valid and robust conclusion. 相似文献
52.
V. G. Gorbatskii 《Astrophysics》1990,32(2):149-154
Leningrad State University. Translated from Astrofizika, Vol. 32, No. 2, pp. 267–275, March–April, 1990. 相似文献
53.
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
54.
55.
同时采用4个台站的国际超导重力仪长期连续重力观测资料和国际地球自转服务中心提供的同步地球自转参数,研究了极移引起的地球重力场变化特征。利用自回归模型估计了各序列的功率谱密度和积谱密度,结果表明极移导致的重力效应的主要能量集中在Chandler摆动和周年项附近,叠积后实际重力观测与极移重力信号理论值之间的差异分别为0.4%和3.9%,说明超导重力仪可有效监测极移导致的重力变化。 相似文献
56.
地震前后垂直形变场动态演化的量化指标 总被引:3,自引:2,他引:1
提出一种表达垂直形变场动态演化过程的量化指标——区域应变率、应变集中度。在此基础上,对南北地震带各水准监测区近30年的垂直形变资料进行了实际计算.并结合具体震例进行了对比研究。结果表明:量化指标在一定程度上能够反映地震前后形变场的动态演化过程和地壳运动状态,对地震的中长期预报有一定的积极意义。 相似文献
57.
In this paper we analyse error-removing techniques used without sufficient theoretical support in a previous paper, where Chandrasekhar's higher-order perturbation theories were developed for either uniformly or differentially-rotating polytropic stars. 相似文献
58.
J. Zhang D. B. Williams J. I. Goldstein R. S. Clarke 《Meteoritics & planetary science》1990,25(3):167-175
Abstract— Characterization of the microstructural features of the metal of the Santa Catharina meteorite was performed using a variety of electron optical techniques. Sample USNM#6293 is chemically homogeneous on the micron scale and has a Ni content of 28.2 wt.%. Its microstructure is similar to that of the Twin City ataxite and contains clear taenite II, i.e., fcc taenite with domains of tetrataenite, < 10 nm in size. Sample USNM#3043 is a more typical Santa Catharina specimen with dark and light regions as observed with the light optical microscope. The dark regions are inhomogeneous and contain 45–50 wt.% Ni and 7–12 wt.% O. The light regions are homogeneous and contain 35 wt.% Ni and no detectable oxygen. The microstructure is that of cloudy zone, i.e., islands of tetrataenite, ~20 nm in size, in a honeycomb matrix. The honeycomb phase contains Ni rich oxide in the dark regions and contains metal, fcc taenite, in the light regions. The original metal structure of USNM#3043 is cloudy zone which formed during cooling into the low temperature miscibility gap of the Fe-Ni phase diagram. The dark regions were developed from the metal by selective corrosion of the honeycomb structure, transforming it into Ni containing oxides, possibly non-stoichiometric Fe2NiO4 while retaining the tetrataenite islands. Using the results of this study, many of the existing discrepancies concerning the microstructure of Santa Catharina can be explained. 相似文献
59.
Solutions of field equations of the generalized theory of gravitation for neutral and charged point masses are found. The problem is formulated so that the solution may be expressed in harmonic, isotropic, Schwarzschild and, if necessary, any other coordinates. A method for the solution of the static axisymmetric problem (an analogue of a well-known Weyl's solution) is also proposed. 相似文献
60.