全文获取类型
收费全文 | 62451篇 |
免费 | 1124篇 |
国内免费 | 876篇 |
专业分类
测绘学 | 1472篇 |
大气科学 | 4593篇 |
地球物理 | 12041篇 |
地质学 | 22429篇 |
海洋学 | 6014篇 |
天文学 | 14281篇 |
综合类 | 181篇 |
自然地理 | 3440篇 |
出版年
2022年 | 378篇 |
2021年 | 637篇 |
2020年 | 737篇 |
2019年 | 786篇 |
2018年 | 1635篇 |
2017年 | 1534篇 |
2016年 | 1930篇 |
2015年 | 1101篇 |
2014年 | 1803篇 |
2013年 | 3407篇 |
2012年 | 2058篇 |
2011年 | 2708篇 |
2010年 | 2348篇 |
2009年 | 3107篇 |
2008年 | 2724篇 |
2007年 | 2727篇 |
2006年 | 2540篇 |
2005年 | 1895篇 |
2004年 | 1781篇 |
2003年 | 1710篇 |
2002年 | 1678篇 |
2001年 | 1494篇 |
2000年 | 1458篇 |
1999年 | 1248篇 |
1998年 | 1218篇 |
1997年 | 1205篇 |
1996年 | 1044篇 |
1995年 | 932篇 |
1994年 | 881篇 |
1993年 | 750篇 |
1992年 | 746篇 |
1991年 | 720篇 |
1990年 | 751篇 |
1989年 | 607篇 |
1988年 | 589篇 |
1987年 | 684篇 |
1986年 | 614篇 |
1985年 | 794篇 |
1984年 | 819篇 |
1983年 | 783篇 |
1982年 | 752篇 |
1981年 | 646篇 |
1980年 | 647篇 |
1979年 | 575篇 |
1978年 | 600篇 |
1977年 | 501篇 |
1976年 | 461篇 |
1975年 | 481篇 |
1974年 | 484篇 |
1973年 | 491篇 |
排序方式: 共有10000条查询结果,搜索用时 273 毫秒
311.
312.
Pavlova viridis sp. nov. is described on the basis of light and electron microscope observations. The material was collected from the coast
of haiyang county of Shandong, China. It is characterized by 1) yellowish green to green chloroplast, 2) rudimentary short
flagellum 0.3 μm long and hook-shaped, 3) long flagellum with small spherical knob-scales, 4) absence of pyrenoid and stigma,
and 5) marine habitat. This new species andP. salina seem to be most closely related to each other but their colour, the insertion of their three appendages, the shape of their
knob scales, and their cell periplasts are quite different from one another.
Contribution No. 1879 from the Institute of Oceanology, Academia Sinica 相似文献
313.
314.
B. R. Johnson M. E. Abroe P. Ade J. Bock J. Borrill J. S. Collins P. Ferreira S. Hanany A. H. Jaffe T. Jones A. T. Lee L. Levinson T. Matsumura B. Rabii T. Renbarger P. L. Richards G. F. Smoot R. Stompor H. T. Tran C. D. Winant 《New Astronomy Reviews》2003,47(11-12):1067
We discuss MAXIPOL, a bolometric balloon-borne experiment designed to measure the E-mode polarization anisotropy of the cosmic microwave background radiation (CMB) on angular scales of 10′ to 2°. MAXIPOL is the first CMB experiment to collect data with a polarimeter that utilizes a rotating half-wave plate and fixed wire-grid polarizer. We present the instrument design, elaborate on the polarimeter strategy and show the instrument performance during flight with some time domain data. Our primary dataset was collected during a 26 h turnaround flight that was launched from the National Scientific Ballooning Facility in Ft. Sumner, New Mexico in May 2003. During this flight five regions of the sky were mapped. Data analysis is in progress. 相似文献
315.
The internal structure of stellar jets arising from young stellar objects is characterized by a series of `knots' or condensations which have highly supersonic proper motions. These structures, we believe, are the result of a variable ejection from the source, which leads to the formation of internal working surfaces or small bowshock within the jet beam. In this paper we present a long-slit spectrum of Herbig-Haro object HH 111 obtained with STIS and an interpretation of this observation in terms of an ejection velocity variability model. 相似文献
316.
317.
A high-velocity ionized outflow and XUV photosphere in the narrow emission line quasar PG1211+143 总被引:1,自引:0,他引:1
K. A. Pounds J. N. Reeves A. R. King K. L. Page P. T. O'Brien M. J. L. Turner 《Monthly notices of the Royal Astronomical Society》2003,345(3):705-713
We report on the analysis of a ∼60-ks XMM–Newton observation of the bright, narrow emission line quasar PG1211+143. Absorption lines are seen in both European Photon Imaging Camera and Reflection Grating Spectrometer spectra corresponding to H- and He-like ions of Fe, S, Mg, Ne, O, N and C. The observed line energies indicate an ionized outflow velocity of ∼24 000 km s−1 . The highest energy lines require a column density of N H ∼ 5 × 1023 cm−2 , at an ionization parameter of log ξ∼ 3.4 . If the origin of this high-velocity outflow lies in matter being driven from the inner disc, then the flow is likely to be optically thick within a radius of ∼130 Schwarzschild radii, providing a natural explanation for the big blue bump (and strong soft X-ray) emission in PG1211+143. 相似文献
318.
319.
M. Fiore L. O. Silva C. Ren M. A. Tzoufras W. B. Mori 《Monthly notices of the Royal Astronomical Society》2006,372(4):1851-1855
The dynamics of two counter-streaming electron–positron–ion unmagnetized plasma shells with zero net charge is analysed in the context of magnetic field generation in gamma-ray burst internal shocks due to the Weibel instability. The effects of large thermal motion of plasma particles, arbitrary mixture of plasma species and space charge effects are taken into account. We show that, although thermal effects slow down the instability, baryon loading leads to a non-negligible growth rate even for large temperatures and different shell velocities, thus guaranteeing the robustness and the occurrence of the Weibel instability for a wide range of scenarios. 相似文献
320.
A. D. Biggs D. Rusin I. W. A. Browne A. G. de Bruyn N. J. Jackson L. V. E. Koopmans J. P. McKean S. T. Myers R. D. Blandford K.-H. Chae C. D. Fassnacht M. A. Norbury T. J. Pearson P. M. Phillips A. C. S. Readhead P. N. Wilkinson 《Monthly notices of the Royal Astronomical Society》2003,338(4):1084-1088