全文获取类型
收费全文 | 76419篇 |
免费 | 864篇 |
国内免费 | 1471篇 |
专业分类
测绘学 | 2741篇 |
大气科学 | 5659篇 |
地球物理 | 14231篇 |
地质学 | 29864篇 |
海洋学 | 5889篇 |
天文学 | 14343篇 |
综合类 | 2315篇 |
自然地理 | 3712篇 |
出版年
2022年 | 366篇 |
2021年 | 630篇 |
2020年 | 659篇 |
2019年 | 708篇 |
2018年 | 6069篇 |
2017年 | 5270篇 |
2016年 | 4323篇 |
2015年 | 1204篇 |
2014年 | 1815篇 |
2013年 | 2883篇 |
2012年 | 2757篇 |
2011年 | 4902篇 |
2010年 | 3954篇 |
2009年 | 4820篇 |
2008年 | 4068篇 |
2007年 | 4572篇 |
2006年 | 2245篇 |
2005年 | 1810篇 |
2004年 | 2023篇 |
2003年 | 1928篇 |
2002年 | 1708篇 |
2001年 | 1341篇 |
2000年 | 1268篇 |
1999年 | 1007篇 |
1998年 | 1061篇 |
1997年 | 947篇 |
1996年 | 816篇 |
1995年 | 782篇 |
1994年 | 686篇 |
1993年 | 605篇 |
1992年 | 592篇 |
1991年 | 593篇 |
1990年 | 622篇 |
1989年 | 493篇 |
1988年 | 504篇 |
1987年 | 528篇 |
1986年 | 487篇 |
1985年 | 610篇 |
1984年 | 673篇 |
1983年 | 590篇 |
1982年 | 561篇 |
1981年 | 518篇 |
1980年 | 486篇 |
1979年 | 477篇 |
1978年 | 458篇 |
1977年 | 368篇 |
1976年 | 351篇 |
1975年 | 357篇 |
1974年 | 308篇 |
1973年 | 342篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
291.
N. V. Makarova V. M. Makeev T. V. Sukhanova P. S. Miklyaev A. L. Dorozhko I. V. Korobova 《Moscow University Geology Bulletin》2012,67(4):209-217
The neotectonic structures of the Lower Oka (Nizhneokskii) Region formed under different geodynamic conditions. This is attested by the morphology, orientation, internal structure, and jointing of the structures. The Oka-Tsna arc formed under the effect of tension from an inner source on the one hand and stress from the Alpian belt on the other hand. The latitudinally-oriented structures of the northwestern slope of the Tokmovo arc emerged as a result of uplift and widening. Both types of structure are combined within the limits of the Oka-Murom trough, which is a geodynamically active zone. 相似文献
292.
G. Ajeagah Aghaindum S. Foto Menbohan 《International Journal of Environmental Science and Technology》2012,9(4):655-660
The optimum period for ciliated protozoa colonizing of an artificial substrate, the polyurethane foams have been assessed in a tropical aquatic ecosystem, the Ekozoa stream of the Mfoundi River Basin in Yaounde (Cameroon). 5?days were calculated as the highest period for the biological indicators of pollution to optimally colonize the artificial substrate. This time interval is the same for all the sampling stations assessed from upstream to downstream and the various microhabitats along the water course. The statistical method applied is that of the completely randomized blocks. The colonization of the substrate increases from the first day to the fifth day, before decreasing to the tenth day. The statistical analysis of variance between the maximum day and the other sampling period was significant at 5?% while the calculation of the value between different points of the same station was not significant. The average number of ciliated protozoan ranges from 20 to 23, from upstream to downstream. 相似文献
293.
The recent geodynamics of Sakhalin are determined by the convergence between the Eurasian and North American lithospheric plates, which is reflected in the high seismicity of the island. The method of inversion of the horizontal velocities of the island surface with account for the geological features of the region is used to analyze the different models of the convergence between the plates. This made it possible to estimate the depth of the mechanical contact between the plates and the velocities of their convergence for the southern, central, and northern segments of the island. 相似文献
294.
Stress Responses to Rapid Temperature Changes of the Juvenile Sea Cucumber (Apostichopusjaponicus Selenka) 总被引:2,自引:0,他引:2
DONG Yunwei JI Tingting DONG Shuanglin 《中国海洋大学学报(英文版)》2007,6(3):275-280
Activities of hexokinase (HK), pyruvate kinase (PK), superoxide dismutase (SOD) and catalase (CAT) and Hsp70 level were measured to evaluate the response of the commercially important sea cucumber (Apostichopus japonicus Selenka) to rapid temperature changes in laboratory. Animals were subjected to a higher temperature (from 10 to 20℃) (Tinc treatment) or to a lower temperature (from 20 to 10℃) (Tddec treatment) for 72 h. At 1, 3, 12, 24, 72 h of exposure, animals were removed and prepared for further analysis. Results showed that the effect of acute temperature changes on enzyme activities was significant. In Tinc treatment, activities of SOD and CAT increased immediately. The significant enhancement of SOD and CAT activities suggested that oxidative stress increases significantly when ambient temperature increasing from 10 to 20℃. The up-regulation of Flsp70 in Tinc and Tdec treatments indicated that Hsp70 was a bioindicator of thermal stress in the sea cucumber, and the expression pattern depended on the thermal treatment. 相似文献
295.
296.
L. Hjalmarsdotter A. A. Zdziarski S. Larsson V. Beckmann M. McCollough D. C. Hannikainen O. Vilhu 《Monthly notices of the Royal Astronomical Society》2008,384(1):278-290
The X-ray binary Cygnus X-3 (Cyg X-3) is a highly variable X-ray source that displays a wide range of observed spectral states. One of the main states is significantly harder than the others, peaking at ∼20 keV, with only a weak low-energy component. Due to the enigmatic nature of this object, hidden inside the strong stellar wind of its Wolf–Rayet companion, it has remained unclear whether this state represents an intrinsic hard state, with truncation of the inner disc, or whether it is just a result of increased local absorption. We study the X-ray light curves from RXTE /ASM and CGRO /BATSE in terms of distributions and correlations of flux and hardness and find several signs of a bimodal behaviour of the accretion flow that are not likely to be the result of increased absorption in a surrounding medium. Using INTEGRAL observations, we model the broad-band spectrum of Cyg X-3 in its apparent hard state. We find that it can be well described by a model of a hard state with a truncated disc, despite the low cut-off energy, provided the accreted power is supplied to the electrons in the inner flow in the form of acceleration rather than thermal heating, resulting in a hybrid electron distribution and a spectrum with a significant contribution from non-thermal Comptonization, usually observed only in soft states. The high luminosity of this non-thermal hard state implies that either the transition takes place at significantly higher L / L E than in the usual advection models, or the mass of the compact object is ≳20 M⊙ , possibly making it the most-massive black hole observed in an X-ray binary in our Galaxy so far. We find that an absorption model as well as a model of almost pure Compton reflection also fit the data well, but both have difficulties explaining other results, in particular the radio/X-ray correlation. 相似文献
297.
CCD photometry data of the T Tauri star H 187 are presented. They show that a new eclipse of this star began at the end of
2004. Since only one eclipse of this star has been observed previously with a duration of 3.5 years, our data indicate that
the eclipses of this object are periodic with a period P=4.9 years between eclipses. Thus, in terms of the absolute duration
of the eclipses and in terms of their relative length as a fraction of the period, H 187 is one of the most exotic objects
in the sky.
__________
Translated from Astrofizika, Vol. 48, No. 4, pp. 529–534 (November 2005). 相似文献
298.
Janice Brahney John J. Clague Brian Menounos Thomas W. D. Edwards 《Journal of Paleolimnology》2008,40(1):489-505
The level of Kluane Lake in southwest Yukon Territory, Canada, has fluctuated tens of metres during the late Holocene. Contributions
of sediment from different watersheds in the basin over the past 5,000 years were inferred from the elemental geochemistry
of Kluane Lake sediment cores. Elements associated with organic material and oxyhydroxides were used to reconstruct redox
fluctuations in the hypolimnion of the lake. The data reveal complex relationships between climate and river discharge during
the late Holocene. A period of influx of Duke River sediment coincides with a relatively warm climate around 1,300 years BP.
Discharge of Slims River into Kluane Lake occurred when Kaskawulsh Glacier advanced to the present drainage divide separating
flow to the Pacific Ocean via Kaskawulsh and Alsek rivers from flow to Bering Sea via tributaries of Yukon River. During periods
when neither Duke nor Slims river discharged into Kluane Lake, the level of the lake was low and stable thermal stratification
developed, with anoxic and eventually euxinic conditions in the hypolimnion. 相似文献
299.
S. A. Gasanov 《Astronomy Letters》2007,33(12):827-843
The problem of the motion of a star inside a layered inhomogeneous rotating elliptical galaxy with a variable mass is considered. We have found an analogue of the Jacobi integral and determined the possible regions of motion. A solution to the equations of perturbed motion has been obtained. 相似文献
300.
WANGHai-xia WANZhong-juan YUShao-peng LUOXin-zheng SUNGuang-you 《中国地理科学(英文版)》2004,14(2):179-185
Although the Songnen Plain in the northeastern China was developed relatively late in the temperate zone of the world, its eco-environment has changed greatly. This paper analyzes the changes of land cover and the rates and trends ofdesertification during the past 100 years in the Songnen Plain. According to the macroscopic analysis, we find that the eco-environment in the plain has reached to the threshold of catastrophic change since the 1950s. The Thorn Needle Catastrophic Model was used to determine and validate this conclusion. Human activities, including large-scale construction projects, such as huge dams and dikes, and excessive grazing were the primary factors contributing to regional eco-environmental catastrophe. And irrational reclamation of the wilderness also affected the eco-environmental change. The results reveal the complex human-land interactions. 相似文献