全文获取类型
收费全文 | 8674篇 |
免费 | 748篇 |
国内免费 | 170篇 |
专业分类
系统科学 | 1183篇 |
丛书文集 | 95篇 |
教育与普及 | 70篇 |
理论与方法论 | 288篇 |
现状及发展 | 876篇 |
研究方法 | 13篇 |
综合类 | 7067篇 |
出版年
2024年 | 18篇 |
2023年 | 45篇 |
2022年 | 59篇 |
2021年 | 56篇 |
2020年 | 42篇 |
2019年 | 21篇 |
2018年 | 743篇 |
2017年 | 751篇 |
2016年 | 453篇 |
2015年 | 100篇 |
2014年 | 102篇 |
2013年 | 78篇 |
2012年 | 354篇 |
2011年 | 1028篇 |
2010年 | 931篇 |
2009年 | 560篇 |
2008年 | 640篇 |
2007年 | 901篇 |
2006年 | 120篇 |
2005年 | 151篇 |
2004年 | 227篇 |
2003年 | 255篇 |
2002年 | 175篇 |
2001年 | 127篇 |
2000年 | 109篇 |
1999年 | 174篇 |
1998年 | 176篇 |
1997年 | 182篇 |
1996年 | 169篇 |
1995年 | 153篇 |
1994年 | 132篇 |
1993年 | 96篇 |
1992年 | 86篇 |
1991年 | 118篇 |
1990年 | 68篇 |
1989年 | 67篇 |
1988年 | 48篇 |
1987年 | 41篇 |
1986年 | 19篇 |
1985年 | 11篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有9592条查询结果,搜索用时 31 毫秒
961.
It has been found that high-order deformation (e.g.β6) can have important effects on the structures of superheavy nuclei. In the present work, we investigate octupole deformation effects on superheavy nuclei with an improved potential-energy-surface (PES) calculation by including reflection-asymmetric deformations in a space of (β2 ,β3 ,β4 , β5). The calculations give various deformations including highly deformed (β2 ≈ 0.4) and superdeformed (β2 ≈ 0.7) shapes. The octupole-deformation degree of freedom mainly affects the fission barrier beyond the second minimum of PES. 相似文献
962.
<正> In this paper,a two-scale finite element approach is proposed and analyzed for approximationsof Green's function in three-dimensions.This approach is based on a two-scale finite elementspace defined,respectively,on the whole domain with size H and on some subdomain containing singularpoints with size h (h H).It is shown that this two-scale discretization approach is very efficient.In particular,the two-scale discretization approach is applied to solve Poisson-Boltzmann equationssuccessfully. 相似文献
963.
针对Seminar模式实施中学生在课外阅读存在的问题,有针对性的提出相应的解决方案,并从理论高度指导学生的课外阅读。 相似文献
964.
In order to develop an efficient identification method for Fallopia plants and drugs, molecular analysis of the partial matK gene sequences was performed on 6 Fallopia species. Based on the matK sequences, a phylogenetic tree was constructed, which showed that different populations of inter- and intra-species could
be specified and distinguished. The matK gene sequences of the 6 Fallopia species were all found to be of 1 271 bp in length, with some nucleotide variations throughout the entire sequences. The
nucleotide difference at position 1 041 could distinguish F. denticulata from others, while specific nucleotide at position 1 154 became identification markers for F. aubertii. Moreover, four specific marker sites for F. multiflora var. ciliinerve at positions 216, 224, 1 060 and 1 179, seven for F. convolvulus at 318, 765, 772, 874, 936, 952 and 1 036, and seven for F. dentate alata at 111, 192, 366, 450, 457, 1 032 and 1 074 were also observed. By detecting the marker nucleotides and analyzing the phylogenetic
relationship, the botanical origins of five inspected drugs were determined, suggesting that matK sequences can be used for authenticating Fallopia plants and drugs. 相似文献
965.
A new watermarking algorithm resisting to geometric transformation based on singular value decomposition(SVD) in logarithm polar coordinate is proposed.The log-polar mapping(LPM) is used to resist rotation and scaling attacks,and the odd-even quantization algorithm is used to embed watermark so it can be extracted without the original host image.The experiments show that the proposed algorithm not only resists various geometric attacks but also is robust enough to the common signal processing. 相似文献
966.
The process of 180° domain switching in PbTiO3 single crystal under an antiparallel electric field was investigated by the three-dimensional phase field simulation, especially
the effect of electric field on the type and duration of domain switching. It is found that the polarization reversal of domains
takes place under an antiparallel electric field in PbTiO3 single crystal. The results of the phase field simulation indicate that there is only 90° domain switching under a weak electric
field. With the rise of the electric field, 180° domain switching appears. If the electric field is strengthened further,
90° domain switching disappears and the duration of domain switching is shortened. 相似文献
967.
It is important to reduce data redundancy of stereo video in practical applications. In this paper,first,a data embedding method for stereo video(DEMSV) is investigated by embedding the encoding data into the reference frame to encode stereo video. It can use only one channel to transfer all the video data and the receiver can choose a monocular video decoder or stereo video decoder adaptively. Then,introducing the joint prediction scheme in the coding process of DEMSV,we propose a novel data embedding meth... 相似文献
968.
An efficient method for the synthesis of tetrahydroquinoline derivatives via lanthanide halides catalyzed domino reactions
of arylamines with dihydropyran is described. Either the cis or the trans isomer can be obtained as the major product in good yield by changing the catalyst and reaction conditions. 相似文献
969.
970.
曾文平 《华侨大学学报(自然科学版)》2001,22(3):237-241
首先把具耗散项的二阶双曲型方程分解为两个一阶方程,然后利用不对称公式提出解此类二阶双曲型方程的分组显式方法,进而,证明交替分组显式方法是无条件稳定的,数值试验表明,这些新方法是令人满意的。 相似文献