全文获取类型
收费全文 | 73634篇 |
免费 | 883篇 |
国内免费 | 622篇 |
专业分类
测绘学 | 1869篇 |
大气科学 | 5646篇 |
地球物理 | 15007篇 |
地质学 | 25954篇 |
海洋学 | 5901篇 |
天文学 | 16611篇 |
综合类 | 253篇 |
自然地理 | 3898篇 |
出版年
2021年 | 609篇 |
2020年 | 708篇 |
2019年 | 722篇 |
2018年 | 1578篇 |
2017年 | 1476篇 |
2016年 | 1909篇 |
2015年 | 1129篇 |
2014年 | 1865篇 |
2013年 | 3540篇 |
2012年 | 2045篇 |
2011年 | 2695篇 |
2010年 | 2421篇 |
2009年 | 3309篇 |
2008年 | 2768篇 |
2007年 | 2664篇 |
2006年 | 2580篇 |
2005年 | 2050篇 |
2004年 | 2027篇 |
2003年 | 1944篇 |
2002年 | 1875篇 |
2001年 | 1697篇 |
2000年 | 1657篇 |
1999年 | 1415篇 |
1998年 | 1422篇 |
1997年 | 1372篇 |
1996年 | 1219篇 |
1995年 | 1185篇 |
1994年 | 1071篇 |
1993年 | 924篇 |
1992年 | 880篇 |
1991年 | 883篇 |
1990年 | 960篇 |
1989年 | 866篇 |
1988年 | 804篇 |
1987年 | 1008篇 |
1986年 | 878篇 |
1985年 | 1024篇 |
1984年 | 1207篇 |
1983年 | 1179篇 |
1982年 | 1035篇 |
1981年 | 1062篇 |
1980年 | 926篇 |
1979年 | 871篇 |
1978年 | 906篇 |
1977年 | 815篇 |
1976年 | 753篇 |
1975年 | 747篇 |
1974年 | 767篇 |
1973年 | 789篇 |
1972年 | 495篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
261.
262.
Reinforced concrete columns with insufficient transverse reinforcement and non‐seismic reinforcement details are vulnerable to brittle shear failure and to loss of axial load carrying capacity in the event of a strong earthquake. In this paper, a procedure is presented after examining the application of two macro models for displacement‐based analysis of reinforced concrete columns subjected to lateral loads. In the proposed model, lateral load‐deformation response of the column is simulated by estimating flexural and shear deformation components separately while considering their interaction and then combining these together according to a set of rules depending upon column's yield, flexural and shear strengths. In addition, lateral deformation caused by reinforcement slip in beam–column joint regions and buckling of compression bars are taken into account and considered in the analysis. Implementation of the proposed procedure produces satisfactory lateral load–displacement relationships, which are comparable with experimental data. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
263.
Age of amphibolites associated with alpine peridotites in the Dinaride ophiolite zone,Yugoslavia 总被引:1,自引:0,他引:1
Marvin A. Lanphere Robert G. Coleman Steven Karamata Jakob Pamić 《Earth and Planetary Science Letters》1975,26(3):271-276
Amphibolites associated with alpine peridotites in the Central Ophiolite zone in Yugoslavia have K-Ar ages of 160–170 m.y. These amphibolites and associated peridotites underwent deep-seated metamorphism prior to tectonic emplacement into the sedimentary-volcanic assemblage of the Dinarides. The alpine peridotites and associated local rocks of the ophiolite suite are interpreted as Jurassic oceanic crust and upper mantle. 相似文献
264.
Our intent has been to develop rapid and sensitive bioassay procedures for laboratory and field applications based on hemolymph factors in animals such as the bay mussel, Mytilus edulis. We found that mussel hemolymph could be easily and repeatedly sampled from individual animals in sufficient amounts to allow analyses for lysozyme, proteolytic activity, total protein and hemocyte counts. In static tests there seemed to be graded responses indicating release of increasing amounts of the above factors into the hemolymph in roughly direct proportion to Cu2+ concentration at lethal and sublethal levels. We interpreted this to be evidence for increased lysosomal and cellular disruption as cupric ion exposure was increased or prolonged. At the same time, Cu2+ concentrations in the mussel hemolymph increased up to an order of magnitude above ambient in the range of 26 to 267 ppb. We felt that this was evidence for the release of Cu-binding proteins into the mussel hemolymph. Simultaneously with the above events the serum granulocytes increased in numbers above control values by factors of 3 or 4 in response to copper challenge while macrophage (terminology of Moore & Lowe, 1977) counts, including controls, declined precipitously. 相似文献
265.
266.
Milton Blander H.N. Planner K. Keil L.S. Nelson N.L. Richardson 《Geochimica et cosmochimica acta》1976,40(8):889-896
Laser-melted magnesium silicate droplets, supercooled 400–750°C below their equilibrium liquidus temperatures before crystallization, were examined to provide a comparison with meteoritic and lunar chondrules and to examine physicochemical parameters that may indicate the conditions of their formation. Internal textures of the spherules strikingly resemble textures observed in some chondrules. Definite trends in crystal morphology, crystal width and texture were established with respect to nucleation temperature and bulk composition. Such trends provide a framework for determining the nucleation temperature of chondrules. The only phase to nucleate from the supercooled forsterite-enstatite normative melts was forsterite, which was present in more-than-normative amounts. Highly siliceous glass (~65wt. % SiO2) was identified interstitially to the forsterite crystals in seven of the spherules and is thought to be present in all. The presence of enstatite and the large proportion of crystals in some meteoritic chondrules implies that they were maintained at temperatures considerably in excess of 600°C at some point in their history. 相似文献
267.
268.
269.
270.
S.I. Recca E.R.D. Scott K. Keil R.N. Clayton T.K. Mayeda G.I Huss E. Jarosewich K.S. Weeks F.A. Hasan D.W.G. Sears R. Wieler P. Signer 《Meteoritics & planetary science》1986,21(2):217-229
The Ragland, New Mexico chondrite was found in 1978, and consists of a single stone of 12.16 kg that broke into three pieces. The stone is moderately weathered and has a pronounced chondritic texture. Bulk composition favors an LL classification, and modal analysis and oxygen isotopic composition are consistent with this. The thermoluminescence sensitivity of 0.056 ± 0.020 normalized to Dhajala, compositional variability of olivine (mean Fa 18.3, σ = 10.1) and low-Ca pyroxene (mean Fs 14.6, σ = 6.7), and Ca concentrations in olivine indicate metamorphic subtype 3.4 ± 0.1. The isotopically heavy oxygen composition, which is characteristic of subtypes 3.0–3.1, may be a primary characteristic and not a result of weathering. Low concentrations of radiogenic 40Ar and planetary 36Ar suggest noble gas loss. 相似文献