全文获取类型
收费全文 | 2949篇 |
免费 | 110篇 |
国内免费 | 18篇 |
专业分类
化学 | 1674篇 |
晶体学 | 47篇 |
力学 | 106篇 |
数学 | 632篇 |
物理学 | 618篇 |
出版年
2023年 | 22篇 |
2022年 | 36篇 |
2021年 | 54篇 |
2020年 | 71篇 |
2019年 | 84篇 |
2018年 | 120篇 |
2017年 | 124篇 |
2016年 | 137篇 |
2015年 | 102篇 |
2014年 | 148篇 |
2013年 | 372篇 |
2012年 | 165篇 |
2011年 | 188篇 |
2010年 | 176篇 |
2009年 | 124篇 |
2008年 | 157篇 |
2007年 | 140篇 |
2006年 | 101篇 |
2005年 | 85篇 |
2004年 | 80篇 |
2003年 | 62篇 |
2002年 | 61篇 |
2001年 | 34篇 |
2000年 | 24篇 |
1999年 | 25篇 |
1998年 | 27篇 |
1997年 | 28篇 |
1996年 | 20篇 |
1995年 | 13篇 |
1994年 | 9篇 |
1990年 | 6篇 |
1989年 | 10篇 |
1988年 | 8篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 27篇 |
1984年 | 16篇 |
1983年 | 11篇 |
1982年 | 14篇 |
1981年 | 19篇 |
1980年 | 8篇 |
1979年 | 14篇 |
1978年 | 9篇 |
1977年 | 13篇 |
1976年 | 21篇 |
1975年 | 11篇 |
1974年 | 16篇 |
1973年 | 12篇 |
1968年 | 9篇 |
1967年 | 6篇 |
排序方式: 共有3077条查询结果,搜索用时 31 毫秒
71.
The experimental results obtained with the chalcogenide glass Ge15Te81S2As2 with imposed overall pressure up to 700 MPa are presented. The material exhibits the switching effect and the memory effect. It is shown that the overall pressure changes remarkably d.c. electrical conductivity of the amorphous semiconductor. It is assumed that the changes in conductivity are caused by changes in activation energy. The changes in activation energy within the range of considered pressures are, as follows from our measurements, E/p–10·95×10–5 eV/MPa +p × 10·41 W 10–7 eV/MPa2. The assumption of the activation energy dependence on pressurep are confirmed also by measurements of dependence In vs. 1/T at various pressures. 相似文献
72.
73.
Laura Pop Pierrik Lassalas László Csaba Bencze Monica Ioana Toşa Botond Nagy Florin Dan Irimie Christophe Hoarau 《Tetrahedron: Asymmetry》2012,23(6-7):474-481
Stereoselective preparative enzymatic acylation and hydrolysis/methanolysis of various C-substituted rac-thiazol-2-yl-methanols were achieved for the preparation of enantiopure or enantiomerically enriched, naturally occurring 2-hydroxymethylthiazoles. The absolute configurations of the resulting secondary alcohols were determined by a detailed 1H NMR study of Mosher’s derivatives. 相似文献
74.
The semicontinuous emulsion polymerization of vinyl acetate has been studied. Poly(vinyl alcohol) as a protective colloid and ethoxylated cetyl alcohol as a coemulsifier were used. The conversion and particle diameter were affected by the stirring speed and the coemulsifier distribution between initial reactor charge and continuously introduced monomer. The amount of unreacted monomer oscillates with time. 相似文献
75.
Correlations between single qubit and classical environment are studied by means of the stochastic Liouville equation, where a dephasing coupling between them is assumed. When the dephasing of the qubit is characterized by the two-state-jump Markov process, the properties of the total, classical and quantum correlations are examined. 相似文献
76.
Masoud Behzad Karel Samec Sang-In Bak Yacine Kadi Claudio Tenreiro Seung-Woo Hong Jong-Seo Chai 《Journal of Radioanalytical and Nuclear Chemistry》2014,299(2):1001-1006
A worldwide challenge in the near future will be to find a way of producing radioisotopes in sufficient quantity without relying on research reactors. The motivation for this innovative work on targets lies in the accelerator-based production of radioisotopes using a neutron converter target as in the transmutation by adiabatic resonance crossing concept. Thermal analysis of a multi-channel helium cooled device is performed with the computational fluid dynamics code CFX. Different boundary conditions are taken into account in the simulation process and many important parameters such as maximum allowable solid target temperature as well as uniform inlet velocity and outlet pressure changes in the channels are investigated. The results confirm that the cooling configuration works well; hence such a solid target could be operated safely and may be considered for a prototype target. 相似文献
77.
78.
79.
There has been a considerable interest in recent years in developing polymer gel matrices for many important applications such as 2DE for quantization and separation of a variety of proteins and drug delivery system to control the release of active agents. However, a well‐defined knowledge of the ultrastructures of the gels has been elusive. In this study, we report the characterization of two different polymers used in 2DE: Gelatin, a naturally occurring polymer derived from collagen (protein) and agar, a polymer of polysaccharide (sugar) origin. Low‐temperature SEM is used to examine the internal structure of these gels in their frozen natural hydrated states. Results of this study show that both polymers have an array of hollow cells that resembles honeycomb structures. While agar pores are almost circular, the corresponding Gaussian curve is very broad exhibiting a range of radii from nearly 370 to 700 nm. Gelatin pores are smaller and more homogeneous reflecting a narrower distribution from nearly 320 to 650 nm. Overall, these ultrastructural findings could be used to correlate with functions of the polymers. 相似文献
80.
Nader Mansoori Oghaz Behzad Haghighi Mohammad Mehdi Alavianmehr Ebrahim Ghiamati 《Journal of solution chemistry》2013,42(3):544-554
A robust and efficient procedure is presented for calculating the solubility parameter. An analytical equation for internal pressure is proposed. Through a simple relation reported by Verdier and Andersen (fluid phase equilibrium 231: 125–137, 2005), one can easily find the solubility parameter via our analytical equation for the internal pressure. Also, the radial distribution function (RDF) of a Lennard–Jones LJ (12, 6) fluid, proposed by Xu and Hu (fluid phase equilibrium 30: 221–228, 1986), has been employed to calculate the internal pressure of normal alkanes from methane to decane. Their solubility parameters were evaluated according to the calculated values of the internal pressure. A comparison between the experimental and the estimated values demonstrated a very good agreement between them. 相似文献