全文获取类型
收费全文 | 1345篇 |
免费 | 142篇 |
国内免费 | 102篇 |
专业分类
化学 | 650篇 |
晶体学 | 4篇 |
力学 | 85篇 |
综合类 | 22篇 |
数学 | 569篇 |
物理学 | 259篇 |
出版年
2024年 | 2篇 |
2023年 | 11篇 |
2022年 | 31篇 |
2021年 | 23篇 |
2020年 | 28篇 |
2019年 | 43篇 |
2018年 | 26篇 |
2017年 | 36篇 |
2016年 | 61篇 |
2015年 | 50篇 |
2014年 | 65篇 |
2013年 | 96篇 |
2012年 | 58篇 |
2011年 | 82篇 |
2010年 | 74篇 |
2009年 | 83篇 |
2008年 | 85篇 |
2007年 | 78篇 |
2006年 | 78篇 |
2005年 | 83篇 |
2004年 | 77篇 |
2003年 | 88篇 |
2002年 | 61篇 |
2001年 | 53篇 |
2000年 | 38篇 |
1999年 | 32篇 |
1998年 | 27篇 |
1997年 | 16篇 |
1996年 | 20篇 |
1995年 | 10篇 |
1994年 | 12篇 |
1993年 | 10篇 |
1992年 | 9篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有1589条查询结果,搜索用时 15 毫秒
11.
YAN Zi-Feng 《天然气化学杂志》1996,5(3):261-271
Introduction0ncofthcintriguingpr0blcmsinhctcrogcncouscatal}'sisisthcactit'ationanddircctconversionofmcthancintoliquidfucIanduscful.h..i..l,lllMcthancactivationisvcry'difficultbccauscn1cthancisathcrmod}'namicalI}'stablccompoundt`ithanoblcgas-likcconfigurati0nThcvcry'strongtctrahcdralC-Hbonds(435kJ/mol)offcrnofiJnctionalgroups,magncticm0mcnts'orpolardistortionstofacilitatcchcmicalattackThismakcsmcthanelcssrcactivcthanncarl}'allitsconvcrsionproducts.Rccentl}'oxidativccouplinghasbecnconsidcrcda… 相似文献
12.
A. I. Bostan Yu. I. Pyatnitskii L. N. Raevskaya V. G. Pryanikova S. A. Nedil’ko A. G. Dzyaz’ko E. G. Zen’kovich 《Theoretical and Experimental Chemistry》2005,41(1):32-36
The oxidative coupling of methane (OCM) in a periodic regime over the SrMnO3 and its derivatives has been investigated. It has been established that partial replacement of the strontium ion by alkali metal ions leads to an increase in both catalytic activity and in selectivity with respect to higher hydrocarbons. Comparison of the results obtained in the present work with those obtained earlier for catalysts based on SrCoO3 led to the conclusion that the Co-containing catalysts were preferable to the Mn-containing catalysts for carrying out oxidative coupling of methane in a periodic regime.__________Translated from Teoreticheskaya i Éksperimentalnaya Khimiya, Vol. 41, No. 1, pp. 30–34, January–February, 2005. 相似文献
13.
Stefan Müller-Stach 《K-Theory》1995,9(4):395-406
LetX be a smooth projective variety over an algebraically closed fieldk. We repeat Bloch's construction of aG
m
-biextension (torseur)E over CH
hom
p
(X)×CH
hom
q
(X) forp+q=dim(X)+1. First we show that in characteristic zeroE comes via pullback from the Poincaré biextension over the corresponding product of intermediate Jacobians which has been conjectured by Bloch and Murre. Then the relations betweenE and various equivalence relations for algebraic cycles are studied. In particular we reprove Murre's theorem stating that Griffiths' conjecture holds for codimension 2 cycles, i.e. every 2-codimensional cycle which is algebraically and incidence equivalent to zero has torsion Abel-Jacobi invariant. 相似文献
14.
Michael Sturgeon 《Annals of the Institute of Statistical Mathematics》1996,48(4):675-686
f(x) is a univariate density in C
4 with bounded support. For any n and sufficiently small kernel bandwidths, the symmetric appendage of any negative mass, –U, to any smooth unimodal symmetric kernel of order p=2 shifts expected estimator mass from regions where f(x)>0 to regions where f(x)<0. For large n, the mean automatic kernel adaptation induced by –U is analyzed in the simplest MISE reduction scenario: The symmetric appendage of –U to the uniform kernel K(x, X) over MISE-optimal bandwidths reduces MISE by shifting K(x, X) mass asymmetrically across the observation X in the direction of decreasing |f(x)|. 相似文献
15.
The progress of high temperature processes is generally described in terms of variation of the degree of conversion () with time (t). The present paper outlines a procedure for making use of-t plots for comparative assessment of productivity and energy requirements for a test system with respect to a reference, on the basis of some simplifying assumptions. It is assumed that the throughput is inversely proportional to reaction time as in the case of batch reactors and plug flow reactors. It is also assumed that the energy requirement is a simple function of process temperature. The principles outlined is illustrated with reference to some laboratory data for reduction of iron oxide by coal.The authors wish to thank Prof. P. R. Rao, Director National Metallurgical Laboratory, Jamshedpur, India, for providing facilities for experimental work and for according permission to publish this work. 相似文献
16.
Aude Fayol 《Tetrahedron》2005,61(48):11511-11519
Three-component reaction of an α-isocyanoacetamide 7, an homoallylamine 8 and an aldehyde 9 in methanol at room temperature provides oxa-bridged tricycle 4 in good to excellent yield as a mixture of two separable diastereoisomers. In this one-pot multicomponent process, one C-N, one C-O and three C-C bonds are formed with concomitant creation of five asymmetric centers and three rings. Fragmentation of epoxy-tetrahydronaphthyridine 4 affords differentially substituted 5,6,7,8-tetrahydro-1,7-naphthyridine (5, 6) depending on the reaction conditions, providing thus additional structural diversity. A one-pot three-component synthesis of 5,6,7,8-tetrahydro-1,7-naphthyridine (6) from 7, 8 and 9 is also documented. 相似文献
17.
Hyosuk Son Young Jun Jung Seong-Cheol Park Il Ryong Kim Joung Hun Park Mi-Kyeong Jang Jung Ro Lee 《Molecules (Basel, Switzerland)》2022,27(18)
Profilins (PFNs) are actin monomer-binding proteins that function as antimicrobial agents in plant phloem sap. Although the roles of Arabidopsis thaliana profilin protein isoforms (AtPFNs) in regulating actin polymerization have already been described, their biochemical and molecular functions remain to be elucidated. Interestingly, a previous study indicated that AtPFN2 with high molecular weight (HMW) complexes showed lower antifungal activity than AtPFN1 with low molecular weight (LMW). These were bacterially expressed and purified to characterize the unknown functions of AtPFNs with different structures. In this study, we found that AtPFN1 and AtPFN2 proteins have LMW and HMW structures, respectively, but only AtPFN2 has a potential function as a molecular chaperone, which has never been reported elsewhere. AtPFN2 has better protein stability than AtPFN1 due to its higher molecular weight under heat shock conditions. The function of AtPFN2 as a holdase chaperone predominated in the HMW complexes, whereas the chaperone function of AtPFN1 was not observed in the LMW forms. These results suggest that AtPFN2 plays a critical role in plant tolerance by increasing hydrophobicity due to external heat stress. 相似文献
18.
Wan-Li He Yong-Feng Cui Shi-Guang Luo Wen-Tuo Hu Kai-Nan Wang Zhou Yang Hui Cao Dong Wang 《Molecules (Basel, Switzerland)》2022,27(20)
Blue-phase liquid crystal (BPLC) is considered as the next-generation liquid crystal display material, but its practical application is seriously affected by a narrow temperature range and a long research period. In this paper, we used inkjet printing technology to prepare BPLC materials with high throughput, and try to use machine vision technology to test BPLC with high throughput. The “standard curve method” for establishing each printing channel and the “vector matching method” for searching the chromaticity value of the minimum distance were proposed to improve the accuracy of inkjet printing BPLC materials. For a large number of sample-phase images, we propose a machine learning method to identify the liquid crystal phase. In this paper, for the first time, the high-throughput preparation and high-throughput detection of 1080 BPLC samples with five common components by a comprehensive experimental method has been successfully realized. The results are helpful to improve the research efficiency of blue-phase materials and provide a theoretical basis and practical guidance for rapid screening of multi-component BPLC materials. 相似文献
19.
20.
A volume of fluid (VOF) method is developed combining a first‐order limited downwind scheme with higher order accurate schemes. The method is characterized by retaining a sharp fluid interface and a reduction in numerical diffusion near the interface, but avoids complicated geometrical reconstruction as occurs in most volume tracing algorithms. To demonstrate the accuracy and robustness of the method, a selection of numerical experiments are presented involving a pure advection problem, a water wave impact caused by a dam breaking and liquid sloshing in a partially filled tank. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献