全文获取类型
收费全文 | 129391篇 |
免费 | 17782篇 |
国内免费 | 11148篇 |
专业分类
化学 | 61694篇 |
晶体学 | 944篇 |
力学 | 5782篇 |
综合类 | 530篇 |
数学 | 10321篇 |
物理学 | 36227篇 |
综合类 | 42823篇 |
出版年
2024年 | 457篇 |
2023年 | 2624篇 |
2022年 | 3560篇 |
2021年 | 4105篇 |
2020年 | 4423篇 |
2019年 | 3705篇 |
2018年 | 3449篇 |
2017年 | 3195篇 |
2016年 | 4943篇 |
2015年 | 5040篇 |
2014年 | 6505篇 |
2013年 | 7853篇 |
2012年 | 9357篇 |
2011年 | 9755篇 |
2010年 | 6900篇 |
2009年 | 6949篇 |
2008年 | 7552篇 |
2007年 | 6855篇 |
2006年 | 6190篇 |
2005年 | 5319篇 |
2004年 | 4102篇 |
2003年 | 3263篇 |
2002年 | 3139篇 |
2001年 | 2906篇 |
2000年 | 2839篇 |
1999年 | 4117篇 |
1998年 | 3739篇 |
1997年 | 3713篇 |
1996年 | 3568篇 |
1995年 | 3115篇 |
1994年 | 2702篇 |
1993年 | 2334篇 |
1992年 | 2049篇 |
1991年 | 1857篇 |
1990年 | 1568篇 |
1989年 | 1336篇 |
1988年 | 1055篇 |
1987年 | 741篇 |
1986年 | 548篇 |
1985年 | 348篇 |
1984年 | 168篇 |
1983年 | 125篇 |
1982年 | 102篇 |
1981年 | 60篇 |
1980年 | 42篇 |
1979年 | 11篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1957年 | 31篇 |
1922年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 781 毫秒
231.
232.
233.
We study the structure of invertible substitutions on three-letter alphabet. We show that there exists a finite set
of invertible substitutions such that any invertible substitution can be written as Iwσ1σ2σk, where Iw is the inner automorphism associated with w, and
for 1jk. As a consequence, M is the matrix of an invertible substitution if and only if it is a finite product of non-negative elementary matrices. 相似文献
234.
本文对一类具有对称轴的图A_n(n≥0),得到了它的特征多项式及匹配多项式的精确表达式;同时还得到A_(?)的完美匹配数。 相似文献
235.
We investigate the origin of ultraviolet (UV) emission from Mg0.12 Zn0.88 O alloy thin films with a wurtzite structure fabricated on c-plane Al2O3 substrates by plasma assisted molecular beam epitaxy. At room temperature, the absorption edge and UV emission band of the Mg0.12Zn0.88O film shift to high-energy side compared with ZnO films. Temperature dependence of the photoluminescence spectra shows that the UV emission is composed of free exciton and neutral donor bound exciton emissions. Two-step dissociation processes of the UV emission are observed with the increasing temperature. The thermal quenching mechanism is attributed to the dissociation of the free exciton from the neutral donor bound exciton in the low temperature region and the dissociation of free electron and hole from the free exciton in the high temperature region. 相似文献
236.
The first α‐diimine nickel(I) complex having a chloro bridge is reported. The centrosymmetric dinuclear structure of {[ArN?C(Me)C(Me)?NAr]NiCl}2[Ar?2,6?C6H3(i‐Pr)2] features two chelating α‐diimine ligands and two bridged chlorine atoms, so that a distorted tetrahedral N2Cl2 coordination geometry for nickel results. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
237.
Static extracting method of software intended behavior based on API functions invoking 总被引:1,自引:0,他引:1
The method of extracting and describing the intended behavior of software precisely has become one of the key points in the fields of software behavior's dynamic and trusted authentication. In this paper, the author proposes a specified measure of extracting SIBDS (software intended behaviors describing sets) statically from the binary executable using the software's API functions invoking, and also introduces the definition of the structure used to store the SIBDS in detail. Experimental results demonstrate that the extracting method and the storage structure definition offers three strong properties: (i) it can describe the software's intended behavior accurately; (ii) it demands a small storage expense; (iii) it provides strong capability to defend against mimicry attack. 相似文献
238.
239.
Jihua Zhang Xi WangWeidong Yu Tao FengFumin Zhang Zhihong ZhengQiong Li Xianghuai Liu 《Solid State Communications》2003,127(4):289-293
Effects of ion impinging on the microstructure and field electron emission properties of screen-printed carbon nanotube films were investigated. We observed that the plasma treatment modified the microstructure of CNTs along with the remarkable increase of emission site density. With the prolongation of ion impinging time, the emission current falls down first, and then rises up to higher than that of the untreated films. It is proposed that the change of emission characteristics is due to the different emission mechanisms. After the treatment, electrons are emitted predominantly from the nano-nodes on the tube wall instead from the nanotube tips. 相似文献
240.
High-density event-related potentials (ERPs) were measured when participants were required to evaluate oneself, significant others (father and mother) and the most familiar public figures (Lei Feng and Jiang Qing) based on trait adjectives. There were three referential conditions and a non-referential control condition including self-evaluation (SE), significant other-evaluation (SOE), general other-evaluation (GOE), and semantic positivity-evaluation (SPE). The behavioral data showed that RTs to GOE condition were longer than the other three conditions. Scalp ERP analysis revealed that (1) SPE condition elicited a more negative N2 than SE condition, which was associated with inhibition of responses; (2) SE condition elicited a more positive P300 than SPE condition, which was an index of attention to self-relevant stimuli; (3) there was no difference on the amplitude and latency of P300 between SE and SOE conditions, which reflected that the concept of “self” included intimate others (e.g., father and mother) in Chinese culture. 相似文献