全文获取类型
收费全文 | 98094篇 |
免费 | 1604篇 |
国内免费 | 840篇 |
专业分类
测绘学 | 2296篇 |
大气科学 | 6857篇 |
地球物理 | 19600篇 |
地质学 | 35079篇 |
海洋学 | 8601篇 |
天文学 | 21917篇 |
综合类 | 282篇 |
自然地理 | 5906篇 |
出版年
2022年 | 559篇 |
2021年 | 982篇 |
2020年 | 1097篇 |
2019年 | 1193篇 |
2018年 | 2502篇 |
2017年 | 2392篇 |
2016年 | 2910篇 |
2015年 | 1699篇 |
2014年 | 2867篇 |
2013年 | 5054篇 |
2012年 | 3031篇 |
2011年 | 4154篇 |
2010年 | 3561篇 |
2009年 | 4664篇 |
2008年 | 4252篇 |
2007年 | 4130篇 |
2006年 | 3873篇 |
2005年 | 3016篇 |
2004年 | 2950篇 |
2003年 | 2871篇 |
2002年 | 2613篇 |
2001年 | 2373篇 |
2000年 | 2246篇 |
1999年 | 1851篇 |
1998年 | 1943篇 |
1997年 | 1872篇 |
1996年 | 1550篇 |
1995年 | 1542篇 |
1994年 | 1339篇 |
1993年 | 1214篇 |
1992年 | 1137篇 |
1991年 | 1094篇 |
1990年 | 1187篇 |
1989年 | 1029篇 |
1988年 | 934篇 |
1987年 | 1104篇 |
1986年 | 988篇 |
1985年 | 1240篇 |
1984年 | 1348篇 |
1983年 | 1279篇 |
1982年 | 1229篇 |
1981年 | 1072篇 |
1980年 | 1007篇 |
1979年 | 937篇 |
1978年 | 906篇 |
1977年 | 861篇 |
1976年 | 818篇 |
1975年 | 787篇 |
1974年 | 784篇 |
1973年 | 772篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
Photometric observations of the over-contact binary ER ORI were performed during November 2007 and February to April 2008
with the 51 cm telescope of Biruni Observatory of Shiraz University in U, B and V filters (Johnson system) and an RCA 4509
photomultiplier. We used these data to obtain the light curves and calculate the newtimes of minimum light in each filter
and plot the O-C diagram of ER ORI. Using theWilson’s computer code with the help of an auxiliary computer program to improve
the optimizations, the light curve analyses were carried out to find out the photometric elements of the system. 相似文献
912.
913.
914.
The first results of U–Pb isotopic dating (LA–ICP–MS) of detrital zircons from metasedimentary rocks of the pre-Devonian basement of the SW part of western Spitsbergen (from Upper Mezoproterozoic Gulliksenfellet quartzite) showed ages ranging from 1700 ± 25 to 2948 ± 27 Ma. 相似文献
915.
A scored lithological map including 10 radiometric units is established through applying factor analysis approach to aerial spectrometric data of Area-1, Syrian desert, which includes Ur, eU, eTh, K%, eU/eTh, eU/K%, and eTh/K%. A model of four rotated factors F1, F2, F3, and F4 is adapted for representing 234,829 data measured points in Area-1, where 86% of total data variance is interpreted. A geological scored pseudo-section derived from the lithological scored map is established and analyzed in order to show the possible stratigraphic and structural traps for uranium occurrences associated with phosphate deposits in the studied Area-1. These identified traps presented in this paper need detailed investigation and must be necessarily followed and checked by ground validations and subsurface well logging, in order to locate the anomalous uranium occurrences and explore with more confidence and certitude their characteristics as a function of depth. 相似文献
916.
The paper presents the experimental investigation and analysis of the non-linear elasto-plastic stress–strain behaviour of
normally consolidated lacustrine clay. Drained triaxial stress path tests were performed on natural block samples of Swiss
lacustrine clay. Data were analysed using plasticity theory and the shape and extent of kinematic yield and bounding surfaces
were determined and found to be elliptical but not congruent. Cross-anisotropic elasticity was used to quantify elastic strains
to permit plastic strain increment vectors and hence a plastic potential surface to be defined. 相似文献
917.
An unusual jaw found in a calcite nodule from Collishaw Point, Hornby Island, British Columbia (off the east coast of Vancouver Island) represents the first definitive pterosaur found in British Columbia, and the first istiodactylid from Canada. 相似文献
918.
Zooplankton are an essential component of the marine and estuarine food chains. The ecotoxicological risk to zooplanktonic communities, estimated through the use of the biomarkers, can be used as an early warning signal of a potential alteration of the ecosystem health. The aim of this project was to evaluate the potential use of several biomarkers (esterases, mixed function oxidases, porphyrins) in zooplanktonic organisms. The acetylcholinesterase activity (AChE) was determined in homogenates of whole organisms of 10 different zooplanktonic crustaceans. Mean activity of AChE was 10.05 micromol/min/g for Acartia margalefi; 3.30 for Acartia latisetosa; 79.70 for Siriella clausi; 49.97 for Diamysis bahirensis; 7.48 for Siriella armata; 14.20 for Mysidopsis gibbosa; 4.49 for Euphausia crystallorophias; 1.66 for Euphausia superba; 2.74 for Streetsia challengeri; 13.26 for Meganycthiphanes norvegica. The species moreover showed a linear increase in enzyme activity in relation to the increase in sample concentration. The key result of this study concerns the different AChE activity basal values of the crustaceans' different species. 相似文献
919.
C12 stars in the range 1.04–1.55M
are evolved to simulate the core evolution of the possible precursors of planetary nebulae. The nuclear shell burning in stars above 1.2M
advances to within about 0.2M
of the surface, where the intense radiation interacts with the surface matter and causes mass loss. Comparison between our theoretical results and observations suggests that this may be a mechanism by which planetary nebulae are formed.Presented at the Trieste Colloquium on Mass Loss from Stars, September 12–16, 1968. 相似文献
920.
H. M. Bibby 《Geophysical Journal International》1981,66(3):513-533
Summary. A method of simultaneous reduction is presented for determining strain rates from multiple triangulation surveys where common triangulation stations have been used, but the angles of the old survey have not necessarily been reobserved. This method is applied to triangulation in the northern South Island, at the southern end of the Tonga-Kermadec-Hikurangi subduction zone. From a profile of shear strain across the Indian-Pacific plate boundary, the displacement of the Indian plate relative to the Pacific is calculated to be 54 ± 9 mm yr−1 at an azimuth of 84°± 10°, in remarkable agreement with the motion predicted by global plate tectonic models. Most of this motion occurs within a 150 km wide zone bounded on the east by the Hikurangi Trough. Within this zone the motion is partitioned: near the Hikurangi Trough no slip is occurring at the upper surface of the subducting Pacific plate (the subduction thrust) and motion is predominantly thrusting normal to the trough axis: to the west is a region of predominantly dextral strike slip faulting. This pattern is consistent with Fitch's model of oblique subduction. To the south of the profile, a change is observed in the azimuth of the faulting along a line which marks the southern extent of the subduction slab, indicating the end of the partitioned motion. 相似文献