全文获取类型
收费全文 | 37467篇 |
免费 | 18510篇 |
国内免费 | 43296篇 |
专业分类
测绘学 | 3133篇 |
大气科学 | 21748篇 |
地球物理 | 13155篇 |
地质学 | 36451篇 |
海洋学 | 16198篇 |
天文学 | 1192篇 |
综合类 | 4595篇 |
自然地理 | 2801篇 |
出版年
2024年 | 169篇 |
2023年 | 357篇 |
2022年 | 660篇 |
2021年 | 1011篇 |
2020年 | 2143篇 |
2019年 | 5540篇 |
2018年 | 5785篇 |
2017年 | 5538篇 |
2016年 | 5551篇 |
2015年 | 4932篇 |
2014年 | 4424篇 |
2013年 | 5006篇 |
2012年 | 4741篇 |
2011年 | 4524篇 |
2010年 | 4458篇 |
2009年 | 3803篇 |
2008年 | 3118篇 |
2007年 | 3129篇 |
2006年 | 2656篇 |
2005年 | 2618篇 |
2004年 | 2917篇 |
2003年 | 2608篇 |
2002年 | 2346篇 |
2001年 | 2173篇 |
2000年 | 1760篇 |
1999年 | 1781篇 |
1998年 | 1864篇 |
1997年 | 1923篇 |
1996年 | 1475篇 |
1995年 | 1438篇 |
1994年 | 1267篇 |
1993年 | 1239篇 |
1992年 | 1041篇 |
1991年 | 774篇 |
1990年 | 743篇 |
1989年 | 620篇 |
1988年 | 528篇 |
1987年 | 410篇 |
1986年 | 338篇 |
1985年 | 258篇 |
1984年 | 291篇 |
1983年 | 168篇 |
1982年 | 208篇 |
1981年 | 148篇 |
1980年 | 116篇 |
1979年 | 112篇 |
1978年 | 55篇 |
1977年 | 52篇 |
1971年 | 53篇 |
1970年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
本文对徐州地震台JB—72水平摆倾斜仪1988年11月至1989年5月间所记录到的24次同震阶变进行了深入分析,认为:a.造成同震阶变的原因是多方面的,而反应了地球应变场准静态调整的同震阶变才是有价值的价变异常;b.多观测手段的地震台站,同震阶变应该在不止一台仪器上得到响应。 相似文献
102.
本文作者利用IOS近似模型,计算了星际分子云条件下A型CH3CN-H2含超精细能级的碰撞跃迁速率系数。温度范围是20K-140K。为研究分子云与恒星形成区的物理、化学性质提供了有用的基础分子数据。 相似文献
103.
104.
105.
利用三维有限元模拟两层地球模型(包括弹性层和粘弹性层)介质的横向不均匀和断层错动的复杂性对震后地表位移场的影响,其数值结果包括弹性解和粘弹性解。结果表明,震后位移场的分布特征不仅与粘弹性层的流变特性有关,还与弹性层介质的剪切模量以及断层的同震错动有关。 相似文献
106.
Dong-Mei Qin Ping Guo Zhan-Yi Hu Yong-Heng ZhaoNational Laboratory of Pattern Recognition Laboratory Institute of Automation Chinese Academy of Sciences Beijing dmqin@nlpr.ia.ac.cnDepartment of Computer Sciences Beijing Normal University Beijing National Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2003,3(3)
For LAMOST, the largest sky survey program in China, the solution of the problem of automatic discrimination of stars from galaxies by spectra has shown that the results of the PSF test can be significantly refined. However, the problem is made worse when the redshifts of galaxies are not available. We present a new automatic method of star/(normal) galaxy separation, which is based on Statistical Mixture Modeling with Radial Basis Function Neural Networks (SMM-RBFNN). This work is a continuation of our previous one, where active and non-active celestial objects were successfully segregated. By combining the method in this paper and the previous one, stars can now be effectively separated from galaxies and AGNs by their spectra-a major goal of LAMOST, and an indispensable step in any automatic spectrum classification system. In our work, the training set includes standard stellar spectra from Jacoby's spectrum library and simulated galaxy spectra of EO, SO, Sa, Sb types with redshift ranging from 0 to 1 相似文献
107.
Lance B. Morrissey Philippe Janvier Simon J. Braddy John P. Bennett Susan B. Marriott Peter R. Tarrant 《Geology Today》2006,22(2):66-67
Armoured jawless fish, or 'ostracoderms', lived 450–360 million years ago, and display unusual morphologies, unlike any modern fish group. Since they left no living descendants, their mode of swimming has, until recently, remained speculative, although this is a crucial question as the first true pectoral fins evolved within the 'ostracoderms'. The discovery of the oldest-known fish trails, from the Early Devonian (400 million year old) 'Lower Old Red Sandstone' of south-east Wales offers new insights into the swimming behaviour of these early fish, notably the osteostracan 'ostracoderms' (or cephalaspids), whose horseshoe-shaped head and paddle-shaped pectoral fins have remained a functional riddle. 相似文献
108.
The new polyenzyme method for making gravy fromHarengula zunasi offal involves protein enzymolysis with flavorase after proper alkaline and neutral protease levels were established by orthogonal
trials to select the best hydrolytic conditions for processing offal with alkaline and neutral protease. The conditions for
the polyenzyme method were pH of 7.0, temperature of 50°C, alkaline and neutral protease concentration of 1.5% respectively,
hydrolysis time of 120 min, and flavorase concentration of 2.0%, for 60 min. The new gravy-making technology yields a nutritious
and delicious gravy containing 40.3% of total essential amino acids, with delicious amino acids Glu, Asp, Gly, Ala, Pro and
Ser comprising 49.5%, total and amino nitrogen being respectively 1.9 and 1.1 g/100 g (amino acid nitrogen being 61.0% of
total nitrogen), The polyenzyme method was used to make 14.8% protein gravy fromHarengula zunasi offal. In addition, inorganic elements, the phosphorus content is the highest.
This project was aided financially by the Guangdong Science and Technology Office (No. 2KM06002S). 相似文献
109.
1IntroductionOne of the key factors related to basin geody-namics is deep process controlling formation and evolution of sedimentary basin. Depth and tempera-ture of asthenosphere,existence of mantle plume,occurrence of mantle melting,and amounts of melts under depressurization during thinning of lithosphere are controlling factors influenced formation and characteristics of extensional basin directly (Li,1994). Rifting is probably governed by frictional forces exerted on the base of litho… 相似文献
110.