全文获取类型
收费全文 | 378895篇 |
免费 | 4121篇 |
国内免费 | 1050篇 |
专业分类
化学 | 200350篇 |
晶体学 | 6450篇 |
力学 | 16508篇 |
综合类 | 15篇 |
数学 | 40539篇 |
物理学 | 120204篇 |
出版年
2021年 | 2896篇 |
2020年 | 3338篇 |
2019年 | 3704篇 |
2018年 | 4649篇 |
2017年 | 4607篇 |
2016年 | 6809篇 |
2015年 | 4288篇 |
2014年 | 6767篇 |
2013年 | 17125篇 |
2012年 | 12969篇 |
2011年 | 15686篇 |
2010年 | 10969篇 |
2009年 | 10857篇 |
2008年 | 14047篇 |
2007年 | 14050篇 |
2006年 | 13274篇 |
2005年 | 11998篇 |
2004年 | 11059篇 |
2003年 | 9943篇 |
2002年 | 9616篇 |
2001年 | 11404篇 |
2000年 | 8754篇 |
1999年 | 6769篇 |
1998年 | 5338篇 |
1997年 | 5365篇 |
1996年 | 5034篇 |
1995年 | 4680篇 |
1994年 | 4502篇 |
1993年 | 4239篇 |
1992年 | 5163篇 |
1991年 | 5005篇 |
1990年 | 4929篇 |
1989年 | 4747篇 |
1988年 | 4805篇 |
1987年 | 4830篇 |
1986年 | 4528篇 |
1985年 | 5902篇 |
1984年 | 6123篇 |
1983年 | 4919篇 |
1982年 | 5125篇 |
1981年 | 5187篇 |
1980年 | 4876篇 |
1979年 | 5221篇 |
1978年 | 5333篇 |
1977年 | 5448篇 |
1976年 | 5307篇 |
1975年 | 4896篇 |
1974年 | 4844篇 |
1973年 | 4944篇 |
1972年 | 3266篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
Highly sensitive optical reflectivity measurements are used to investigate the layer-by-layer transition in extremely thin
and thick N-(4-n-hexyloxybenzylidene)-4-n-hexylaniline (6O.6) films. The simple power-law form, N=N
0
t
−1/3, for the penetration of the crystal-B order is found to describe the transitions only near the surface. A deviation from
the power law is observed for the interior layers.
Pis’ma Zh. éksp. Teor. Fiz. 63, No. 4, 266–269 (25 February 1996)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
192.
Open circuit voltage (OCV) measurements in H2O/air concentration cells at T<580 K using Yb-doped SrCeO3 electrolyte indicate that under these conditions, protons are transported through the electrolyte as -ve ions, possibly as
hydroxyl (OH−) ions. The H+ ionic transport, which is generally reported, becomes the dominant mode for H2O/air concentration cells at temperatures greater than 750 K or when H2O/air electrodes are replaced by H2/Ar, and the anomalous OCV sign disappears. The combination of low temperature and the presence of hydrogen and oxygen as
provided by the H2O/air system appears to be necessary for the postulated hydroxyl ion electrode reactions to take place.
In addition to OCV measurements, results from impedance spectroscopy are used to provide evidence in support of the suggested
hydroxyl ion mode of protonic transport under the specified conditions. These findings are directly relevant in the development
of novel humidity sensors in the temperature range 450–580K and is reported in a separate paper in this conference.
Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996 相似文献
193.
In this Note we give a necessary and sufficient condition for the spectral controllability from one simple node of a general network of strings that undergoes transversal vibrations in a sufficiently large time. This condition asserts that no eigenfunction vanishes identically on the string that contains the controlled node. The proof combines the Beurling–Malliavin's theorem and an asymptotic formula for the eigenvalues of the network. The optimal control time may be characterized as twice the sum of the lengths of all the strings of the network. To cite this article: R. Dáger, E. Zuazua, C. R. Acad. Sci. Paris, Ser. I 334 (2002) 545–550. 相似文献
194.
An M/G/1 retrial queueing system with additional phase of service and possible preemptive resume service discipline is considered. For an arbitrarily distributed retrial time distribution, the necessary and sufficient condition for the system stability is obtained, assuming that only the customer at the head of the orbit has priority access to the server. The steady-state distributions of the server state and the number of customers in the orbit are obtained along with other performance measures. The effects of various parameters on the system performance are analysed numerically. A general decomposition law for this retrial queueing system is established. 相似文献
195.
The three-band two-dimensional repulsive Hubbard model in the formalism of the temperature Green function is investigated.
The applicability of the weak coupling approach at the values of the dimensionless coupling constant U/t≈10–11 is justified.
The normal state, the antiferromagnetic state with Neel magnetic ordering on the “copper” sublattice, and the superconducting
state with nontrivial Cooper pairing in channels with odd angular momenta are studied. The possibility of other magnetic states
in the model is discussed. Bibliography: 20 titles.
Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 209, 1994, pp. 194–228.
Translated by K. Malyshev. 相似文献
196.
A. K. Lopatin 《Ukrainian Mathematical Journal》1997,49(1):51-74
We consider the method of normal forms, the Bogolyubov averaging method, and the method of asymptotic decomposition proposed by Yu. A. Mitropol’skii and the author of this paper. Under certain assumptions about group-theoretic properties of a system of zero approximation, the results obtained by the method of asymptotic decomposition coincide with the results obtained by the method of normal forms or the Bogolyubov averaging method. We develop a new algorithm of asymptotic decomposition by a part of the variables and its partial case — the algorithm of averaging on a compact Lie group. For the first time, it became possible to consider asymptotic expansions of solutions of differential equations on noncommutative compact groups. 相似文献
197.
This paper deals mainly with generalizations of results in finitary combinatorics to infinite ordinals. It is well-known that for finite ordinals ∑bT<αβ is the number of 2-element subsets of an α-element set. It is shown here that for any well-ordered set of arbitrary infinite order type α, ∑bT<αβ is the ordinal of the set M of 2-element subsets, where M is ordered in some natural way. The result is then extended to evaluating the ordinal of the set of all n-element subsets for each natural number n ≥ 2. Moreover, series ∑β<αf(β) are investigated and evaluated, where α is a limit ordinal and the function f belongs to a certain class of functions containing polynomials with natural number coefficients. The tools developed for this result can be extended to cover all infinite α, but the case of finite α appears to be quite problematic. 相似文献
198.
199.
200.
A. J. Parsons S. D. J. Inglethorpe D. J. Morgan A. C. Dunham 《Journal of Thermal Analysis and Calorimetry》1997,48(1):49-62
Using a system based on non-dispersive infrared (NDIR) detectors, evolved gas analysis (EGA) was able to identify and quantify the principal volatiles produced by heating powdered samples of UK brick clays. From these results, atmospheric emissions likely to result from brick production can be predicted. In addition, EGA results for extruded brick clay test pieces are significantly different from those of powdered samples. Within an extruded brick clay body, evolved gases are contained within a pore system and evolved gas-solid phase reactions also occur. This EGA study provides further evidence on the nature of firing reactions within brick clay bodies. The qualitative and quantitative influence of heating rate — a key process condition in brick manufacture — on gas release is also outlined.Dedicated to Dr. Robert Mackenzie on the occasion of his 75th birthday 相似文献