全文获取类型
收费全文 | 20268篇 |
免费 | 2035篇 |
国内免费 | 843篇 |
专业分类
化学 | 14795篇 |
晶体学 | 145篇 |
力学 | 663篇 |
综合类 | 47篇 |
数学 | 2547篇 |
物理学 | 4949篇 |
出版年
2023年 | 257篇 |
2022年 | 296篇 |
2021年 | 371篇 |
2020年 | 498篇 |
2019年 | 509篇 |
2018年 | 392篇 |
2017年 | 373篇 |
2016年 | 769篇 |
2015年 | 804篇 |
2014年 | 910篇 |
2013年 | 1489篇 |
2012年 | 1729篇 |
2011年 | 1643篇 |
2010年 | 1060篇 |
2009年 | 896篇 |
2008年 | 1392篇 |
2007年 | 1250篇 |
2006年 | 1262篇 |
2005年 | 1113篇 |
2004年 | 926篇 |
2003年 | 757篇 |
2002年 | 677篇 |
2001年 | 378篇 |
2000年 | 321篇 |
1999年 | 252篇 |
1998年 | 211篇 |
1997年 | 229篇 |
1996年 | 257篇 |
1995年 | 188篇 |
1994年 | 176篇 |
1993年 | 171篇 |
1992年 | 123篇 |
1991年 | 103篇 |
1990年 | 105篇 |
1989年 | 79篇 |
1988年 | 65篇 |
1987年 | 58篇 |
1986年 | 88篇 |
1985年 | 109篇 |
1984年 | 86篇 |
1983年 | 53篇 |
1982年 | 68篇 |
1981年 | 66篇 |
1980年 | 69篇 |
1979年 | 59篇 |
1978年 | 55篇 |
1977年 | 44篇 |
1976年 | 60篇 |
1975年 | 32篇 |
1973年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
32.
The present paper determines the form of automorphisms of $\[{E_2}(R)\]$ and $\[G{E_2}(R)\]$ over commutative rings provided 2, 3 and 5 are units. 相似文献
33.
ZHU Yabin ZHOU Yueliang LIU Zhen WANG Shufang CHEN Zhenghao U Huibin YANG Guozhen XlAO Ling Ren Hongtao JIAO Yulei Zheng Minghui 《中国科学G辑(英文版)》2004,47(2):165-172
The irreversibility field (Hirr) of Y-based superconductor is much higher than that of Bi-based superconductor. Y-based superconductor is capable of maintaining stable electrical currents in high magnetic field and electric field, so it is a better suited mate-rial for electric-current applications. Commonly, the Y-based tapes comprise a YBCO thick film deposited on a flexible substrate, typically with an intermediate buffer layer, and an overcoat of noble metal. In this process, the interm… 相似文献
34.
This paper is devoted to a detailed theoretical study of an ion pair SN2 reaction LiNCO+CH3F in the gas phase and in solution at the level of MP2(full)/6-31+G**//HF/6-31+G**. Two possible reaction mechanisms, inversion and retention, are discussed. There are eight possible reaction pathways. The inversion mechanism is more favorable no matter in the gas phase or in solution based on analyses of the transition structures. Methyl isocyanate should form preferentially in the gas phase and more stable methyl cyanate is the main product in solution. The retardation of the reaction in solvents was attributed to the difference in solvation in the separated reactants and in the transition state. 相似文献
35.
Catalytic properties of silica-supported heteropolyacids (HPA) in a mechanical mixture with reduced Me-Ce oxides (Me = Ni,
Pd) in n-hexane isomerization are studied. The role of each component of the mixed oxides (Ce and, typically, Ni and Pd) and their
optimum content has been illuminated: cerium is not only beneficial for eliminating or preventing coke deposition but is also
effective for maintaining the Keggin structure of the highly-organized HPA during the reaction and probably allows a better
dispersion of the second metal species. Nickel and palladium, present as Ni0 and Pd0, reinforce the activation of the alkane, which is difficult to obtain by means of a direct attack by an acid, and, thus,
enhance noticeably the activity of the catalyst. The best mechanical mixtures are obtained with 30–70 wt % NiCeO-HPW/SiO2 and 50–50 wt % Pd0.1CeO-HPW/SiO2. These mixtures have the highest efficiency for a Ni/(Ni + W) atomic ratio of 0.66 and a Pd/(Pd + W) ratio of 0.40, respectively.
Finally, the conversion of n-hexane is in the order HPW > HSiW > HBW, which seems to be consistent with the order of their acid strength as per the literature,
but the isomerization selectivity appears to be slightly higher on HSiW.
Published in Russian in Kinetika i Kataliz, 2006, Vol. 47, No. 1, pp. 24–28.
The text was submitted by the authors in English. 相似文献
36.
The concept of super hamiltonian semigroup is introduced. As a result, the structure theorems obtained by A. Cherubini and A. Varisco on quasi commutative semi-groups and quasi hamiltonian semigroups respectively are extended to super hamiltonian semigroups. 相似文献
37.
Abstract. We propose a general approach to deal with nonlinear, nonconvex variational problems based on a reformulation of the problem
resulting in an optimization problem with linear cost functional and convex constraints. As a first step we explicitly explore
these ideas to some one-dimensional variational problems and obtain specific conclusions of an analytical and numerical nature. 相似文献
38.
Ana Luísa Daniel‐da‐Silva João Carlos Moura Bordado José Miguel Martín‐Martínez 《Journal of Polymer Science.Polymer Physics》2007,45(22):3034-3045
The degree of phase separation in several moisture‐cured poly(urethane urea)s (PUUs) was studied by FTIR spectroscopy, wide angle X‐ray diffraction (WAXD), and temperature‐modulated differential scanning calorimetry (TMDSC). This latter technique was shown to be particularly useful in analysing the degree of phase separation in PUU polymers. Both phase mixing and phase segregation coexisted in the PUUs and the degree of phase separation increased as the urea hard segment (HS) content in the PUU increased. The maximum solubility of urea HSs into the polyol soft segments (SSs) was achieved for 50 wt % urea HS content in diol‐based PUUs, whereas for triol‐based PUUs the highest solubility between HS and SS was reached for lower urea HS amount. Finally, the higher the urea HS content the higher the extent of phase separation in the PUU. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3034–3045, 2007 相似文献
39.
André Markoff 《Mathematische Annalen》1886,27(2):177-182
Sans résumé 相似文献
40.
Monika Goikoetxea María J. Barandiaran José M. Asua 《Journal of polymer science. Part A, Polymer chemistry》2007,45(24):5838-5846
The mechanisms involved in the formation of n‐butanol during the synthesis of butyl acrylate containing latices were investigated. The experimental results showed that neither the hydrolysis of butyl acrylate nor of the ester bond in the butyl acrylate segments of the polymer played a major role in the formation of n‐butanol, which was mainly generated from the polymer backbone, by transfer reactions to polymer chain followed by cyclization. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5838–5846, 2007 相似文献