全文获取类型
收费全文 | 14507篇 |
免费 | 496篇 |
国内免费 | 29篇 |
专业分类
化学 | 8377篇 |
晶体学 | 171篇 |
力学 | 295篇 |
综合类 | 3篇 |
数学 | 2525篇 |
物理学 | 3661篇 |
出版年
2022年 | 138篇 |
2021年 | 205篇 |
2020年 | 217篇 |
2019年 | 199篇 |
2018年 | 280篇 |
2017年 | 314篇 |
2016年 | 581篇 |
2015年 | 425篇 |
2014年 | 469篇 |
2013年 | 1069篇 |
2012年 | 725篇 |
2011年 | 899篇 |
2010年 | 627篇 |
2009年 | 519篇 |
2008年 | 518篇 |
2007年 | 458篇 |
2006年 | 388篇 |
2005年 | 311篇 |
2004年 | 287篇 |
2003年 | 300篇 |
2002年 | 315篇 |
2001年 | 217篇 |
2000年 | 200篇 |
1999年 | 202篇 |
1998年 | 187篇 |
1997年 | 181篇 |
1996年 | 178篇 |
1995年 | 157篇 |
1994年 | 150篇 |
1993年 | 156篇 |
1992年 | 149篇 |
1991年 | 141篇 |
1990年 | 122篇 |
1989年 | 125篇 |
1988年 | 123篇 |
1987年 | 144篇 |
1986年 | 109篇 |
1985年 | 149篇 |
1984年 | 143篇 |
1983年 | 137篇 |
1982年 | 148篇 |
1981年 | 137篇 |
1980年 | 142篇 |
1979年 | 140篇 |
1978年 | 144篇 |
1977年 | 134篇 |
1976年 | 134篇 |
1975年 | 121篇 |
1974年 | 129篇 |
1973年 | 117篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Roberto Martínez Corte C. Eduardo Salazar E. Olivia Linzaga E. Irma 《Journal of heterocyclic chemistry》1994,31(4):1061-1063
Catalytic hydrogenation of o-nitrophenylbenz[a], benz[c], dibenz[a,h] and dibenz[a,g]acridinones using Pd/C as catalyst, at 60 psi of pressure, gave the hiterto unknown benzoquinoacridine N-oxides and benzo-pyranonaphthyridine N-oxides. The structure of all products was corroborated by ir, 1H- and 13C-nmr and mass spectra data. 相似文献
72.
73.
G. Michałek B.R. Bułka 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(1):121-128
The currents and their fluctuations in two capacitively coupled single electron transistors are determined in the limit of
sequential tunnelling. Our considerations are restricted to the case when the islands (dots) of the transistors are atomic-sized,
which means each of them has only one single electronic level available for the tunnelling processes. The Coulomb interactions
of accumulated charges on the both single electron transistors lead to the effect of the negative differential resistance.
An enhancement of the current shot-noise was also found. Spectral decomposition analysis indicated the two main contributions
to the shot-noise: low- and high-frequency fluctuations. It was found that the low frequency fluctuations (polarization noise)
are responsible for a strong enhancement of the current noise.
Received 9 October 2001 / Received in final form 8 March 2002 Published online 9 July 2002 相似文献
74.
The validity of local parton-hadron duality within the framework of HERWIG and JETSET event generators is investigated. We concentrate one
+
e
– annihilations in LEP 2 energy range as these interactions provide theoretically the cleanest condition for the discussion of this concept. We conclude that the concept of local parton-hadron duality is not valid in either of the two generators considered. 相似文献
75.
Š. Jakševičius 《Lithuanian Mathematical Journal》1992,32(2):174-180
Kaunas Academy of Agriculture, 4324 Noreikiškés, Lithuania. Translated from Lietuvos Matematikos Rinkinys, Vol. 32, No. 2,
pp. 221–228, April–June, 1992. 相似文献
76.
Principles and recent developments in ultrasound contrast agents 总被引:6,自引:1,他引:5
The behaviour of gas bubbles and gas encapsulated spheres as echographic contrast agents is reviewed. Compared with rigid spheres, gas bubbles are superior scattering agents and they offer a number of useful properties which can be exploited in a variety of ways. The analysis of their velocity of sound, back-scatter intensity, second harmonic emission and resonant frequency opens up new perspectives in the development of contrast agents for echocardiographic research with potential clinical applications. 相似文献
77.
On the numerical solution of axisymmetric domain optimization problems by dual finite element method
Shape optimization of an axisymmetric three-dimensional domain with an elliptic boundary value state problem is solved. Since the cost functional is given in terms of the cogradient of the solution, a dual finite element method based on the minimum of complementary energy principle is used. © 1994 John Wiley & Sons, Inc. 相似文献
78.
Adducts of the conjugate addition of benzylamine to enantiopure amides of aroylacrylic acid possess high enantiomeric and diastereomeric purity. A high degree of stereoselectivity has been achieved by means of crystallization-induced asymmetric transformation. A practical synthesis leading to dipeptides containing homophenylalanine is depicted. 相似文献
79.
František Toman Ludvík Beneš 《Journal of inclusion phenomena and macrocyclic chemistry》2007,59(3-4):231-236
Differential molar adsorption enthalpies (DMAE) were determined by gas chromatographic measurements of specific retention
volume of vapors on the surface of two forms of Mg–Al hydrotalcite. A linear dependence of the DMAE on the number of the carbon
atoms in hydrocarbons was observed for both form of hydrotalcite. The dependence of the differential molar adsorption enthalpies
on the number of chlorine atoms in organic molecules is discussed. A linear dependence of DMAE on the molecular weight of
chloroderivatives of methane and ethylene on the basic form in an order monochloromethane < dichloromethane < trichloromethane
or vinylidene chloride < 1,1-dichloroethylene < trichloroethylene was found. 相似文献
80.
The paper is devoted to the research of large deviation probabilities in the approximation by compound Poisson law. 相似文献