全文获取类型
收费全文 | 4127篇 |
免费 | 88篇 |
国内免费 | 24篇 |
专业分类
化学 | 2577篇 |
晶体学 | 32篇 |
力学 | 128篇 |
数学 | 554篇 |
物理学 | 948篇 |
出版年
2022年 | 31篇 |
2021年 | 52篇 |
2020年 | 49篇 |
2019年 | 39篇 |
2017年 | 34篇 |
2016年 | 63篇 |
2015年 | 61篇 |
2014年 | 64篇 |
2013年 | 169篇 |
2012年 | 145篇 |
2011年 | 193篇 |
2010年 | 98篇 |
2009年 | 114篇 |
2008年 | 174篇 |
2007年 | 191篇 |
2006年 | 186篇 |
2005年 | 162篇 |
2004年 | 153篇 |
2003年 | 140篇 |
2002年 | 135篇 |
2001年 | 105篇 |
2000年 | 104篇 |
1999年 | 73篇 |
1998年 | 52篇 |
1997年 | 50篇 |
1996年 | 59篇 |
1995年 | 72篇 |
1994年 | 63篇 |
1993年 | 67篇 |
1992年 | 66篇 |
1991年 | 52篇 |
1990年 | 54篇 |
1989年 | 61篇 |
1988年 | 60篇 |
1987年 | 46篇 |
1986年 | 39篇 |
1985年 | 65篇 |
1984年 | 53篇 |
1983年 | 53篇 |
1982年 | 76篇 |
1981年 | 51篇 |
1980年 | 57篇 |
1979年 | 44篇 |
1978年 | 52篇 |
1977年 | 38篇 |
1976年 | 50篇 |
1975年 | 61篇 |
1974年 | 38篇 |
1973年 | 47篇 |
1972年 | 36篇 |
排序方式: 共有4239条查询结果,搜索用时 875 毫秒
21.
Using the time differential perturbed angular correlation technique, the hyperfine interactions as titanium sites in ZnTiF6·6H2O and its decomposition products were determined between room temperature (300 K) and 1273 K. The different steps in the decomposition pattern were identified and a simple model is given for it. 相似文献
22.
Rü diger W. Braun Reinhold Meise B. A. Taylor 《Proceedings of the American Mathematical Society》2003,131(8):2423-2433
We give a sufficient condition for a local radial Phragmén-Lindelöf principle on analytic varieties. This condition is expressed in terms of existence of hyperbolic directions.
23.
This paper reports the results of a survey intended to discover the extent to which Checkland's Soft Systems Methodology (SSM) is used in practice. Some 300 questionnaires were sent to people who had had some exposure to SSM and, surprisingly, nearly half were returned. The majority described in detail their uses of SSM and most felt that it had been successful. This paper describes the overall quantitative results from the survey as well as presenting a qualitative analysis of the experiences of using SSM. 相似文献
24.
We have demonstrated a temperature switch based on an optically bistable device integrated with an optical fibre. The principle demonstrated here might lead to the development of new types of all-optical temperature sensors. 相似文献
25.
D. W. Taylor V. Villas-Boas Q. Lu M. F. Rossignol F. P. Missell D. Givord S. Hirosawa 《Journal of magnetism and magnetic materials》1994,130(1-3):225-236
We studied the coercivity in magnets of composition R17Fe83−χBχ (R = Nd, Pr and χ = 8, 30), using measurements of the coercive field Hc, its angular dependence, and the magnetic viscosity coefficient Sv, for temperatures between 4.2 and 500 K. The results are discussed in relation to a model which does not specifically consider the detailed mechanisms involved in magnetization reversal, but which provides information about the magnetic properties in the activation volume v where magnetization reversal is initiated. It is concluded that the ordering temperature in v tends to be slightly smaller than in the bulk and that the room temperature anisotropy in v is not strongly reduced with respect to the bulk value. Finally, a direct evaluation of the dipolar interactions is in good agreement with results obtained from Hc(T). 相似文献
26.
27.
R. A. Taylor S. Haacke B. Deveaud I. Bar Joseph R. Zimmermann 《Physica E: Low-dimensional Systems and Nanostructures》1998,2(1-4)
The time-resolved secondary emission of resonantly created excitons in GaAs quantum wells is studied using femtosecond up-conversion spectroscopy. The behaviour of the rise and decay of the secondary emission and reflectivity in quantum wells is strongly dependent upon the disorder at the interfaces, the exciton density and the temperature. In the case of low densities and temperatures the emission is independent of the exciton density and rises quadratically in time, in excellent agreement with recent theory for Rayleigh scattering from two-dimensional excitons subjected to disorder. These rise times are compared directly with
times measured by time-integrated four-wave mixing (FWM). The comparison of the dynamics displayed in time-resolved secondary radiation and time-integrated FWM provide a clear understanding of the coherence properties of QW excitons in the first few picoseconds after excitation. High-contrast oscillations that are due to quantum beats between the heavy- and light-hole 1s-states are seen. The visibility decay at very low densities is long
ps and is related to the action of potential fluctuations on the scattering of heavy-hole and light-hole excitons. 相似文献
28.
D. A. Johnson A. G. Maddock M. Taylor 《Journal of Radioanalytical and Nuclear Chemistry》1987,119(1):43-50
When anhydrous EuCl3, GdCl3, DyCl3 or Eu2O3 are irradiated with fast neutrons and then dissolved in dilute hydrochloric acid, small amounts of reducing species, believed to be divalent lanthanide cations, are revealed. The amount produced increases with the thermodynamic stability of the Ln2+ species /Eu>Dy>Gd>/. 相似文献
29.
E. Todd Brown Karen Karp Joseph M. Petrosko Jane Jones Gloria Beswick Carrie Howe Kathy Zwanzig 《School science and mathematics》2007,107(3):102-116
This study investigated K‐12 teachers' beliefs and reported teaching practices regarding calculator use in their mathematics instruction. A survey was administered to more than 800 elementary, middle and high school teachers in a large metropolitan area to address the following questions: (a) what are the beliefs and practices of mathematics teachers regarding calculator use? and (b) how do these beliefs and practices differ among teachers in three grade bands? Factor analysis of 20 Likert scale items revealed four factors that accounted for 54% of the variance in the ratings. These factors were named Catalyst Beliefs, Teacher Knowledge, Crutch Beliefs, and Teacher Practices. Compared to elementary teachers, high school teachers were significantly higher in their perception of calculator use as a catalyst in mathematics instruction. However, the higher the grade level of the teacher, the higher the mean score on the perception that calculator use may be a way of getting answers without understanding mathematical processes. The mean scores for teachers in all three grade bands indicated agreement that students can learn mathematics through calculator use and using calculators in instruction will lead to better student understanding and make mathematics more interesting. The survey results shed light on teachers' self reported beliefs, knowledge, and practices in regard to consistency with elements of the National Council of Teachers of Mathematics Principles and Standards for School Mathematics (2000) technology principle and the NCTM use of technology position paper (2003). This study extended previous research on teachers' beliefs regarding calculator use in classrooms by examining and comparing the results of teacher surveys across three grade bands. 相似文献
30.
Suzanne J. Dilly Steven J. Carlisle Andrew J. Clark Andrew R. Shepherd Stephen C. Smith Paul C. Taylor Andrew Marsh 《Journal of polymer science. Part A, Polymer chemistry》2006,44(7):2248-2259
A practical and divergent synthesis of supported [1,3,5]‐triazine dendritic molecules on Wang resin, PEGA resin, SynPhase? Lanterns, and silica gel is described. The alkylamine linkers used allow derivatization with functionality for both synthetic (e.g., supported reagent and scavenger activity) and chemical biology applications. The use of supported intermediates allows differentiation of symmetric linkers without the need for protecting group chemistry. The synthetic route uses inexpensive, readily available starting materials in a straightforward and scaleable strategy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2248–2259, 2006 相似文献