全文获取类型
收费全文 | 21892篇 |
免费 | 888篇 |
国内免费 | 182篇 |
专业分类
化学 | 14469篇 |
晶体学 | 146篇 |
力学 | 480篇 |
综合类 | 1篇 |
数学 | 4008篇 |
物理学 | 3858篇 |
出版年
2023年 | 154篇 |
2022年 | 181篇 |
2021年 | 405篇 |
2020年 | 471篇 |
2019年 | 583篇 |
2018年 | 448篇 |
2017年 | 347篇 |
2016年 | 729篇 |
2015年 | 699篇 |
2014年 | 684篇 |
2013年 | 1279篇 |
2012年 | 1381篇 |
2011年 | 1664篇 |
2010年 | 857篇 |
2009年 | 740篇 |
2008年 | 1244篇 |
2007年 | 1180篇 |
2006年 | 1146篇 |
2005年 | 1116篇 |
2004年 | 884篇 |
2003年 | 771篇 |
2002年 | 707篇 |
2001年 | 363篇 |
2000年 | 280篇 |
1999年 | 276篇 |
1998年 | 227篇 |
1997年 | 257篇 |
1996年 | 269篇 |
1995年 | 249篇 |
1994年 | 208篇 |
1993年 | 176篇 |
1992年 | 147篇 |
1991年 | 149篇 |
1990年 | 119篇 |
1989年 | 108篇 |
1988年 | 124篇 |
1987年 | 106篇 |
1986年 | 107篇 |
1985年 | 154篇 |
1984年 | 169篇 |
1983年 | 110篇 |
1982年 | 155篇 |
1981年 | 150篇 |
1980年 | 140篇 |
1979年 | 122篇 |
1978年 | 129篇 |
1977年 | 120篇 |
1976年 | 119篇 |
1975年 | 91篇 |
1974年 | 88篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
31.
Vijaya Gracias Alan F. Gasiecki Joel D. Moore Irini Akritopoulou-Zanze Stevan W. Djuric 《Tetrahedron letters》2006,47(50):8977-8980
A general method for the preparation of diaza-spirocycles is reported. This method used an olefin metathesis in order to construct the desired spirocyclic framework. Beginning with commercially available protected amino ketones, this strategy ultimately produced pharmacologically relevant diaza-scaffolds in an efficient and high-yielding process. 相似文献
32.
Alexander Katsevich 《Journal of Fourier Analysis and Applications》2002,8(5):407-426
In this article we propose an FBP-type algorithm for inversion of spiral cone beam data, study its theoretical properties, and illustrate performance of the algorithm by numerical examples. In particular, it is shown that the algorithm does not reconstruct f exactly, but computes the result of applying a pseudo-differential operator (PDO) with singular symbol to f. Away from critical directions the amplitude of this PDO is homogeneous of order zero in the dual variable, bounded, and approaches one as the pitch of the spiral goes to zero. Numerical experiments presented in the article show that even when the pitch is relatively large, the accuracy of reconstruction is quite high. On the other hand, under certain circumstances, the algorithm produces artifacts typical of all FBP-type algorithms. 相似文献
33.
The MPEG-1 Layer 3 compression schema of audio signal, commonly known as mp3, has caused a great impact in recent years as it has reached high compression rates while conserving a high sound quality. Music and speech samples compressed at high bitrates are perceptually indistinguishable from the original samples, but very little was known about how compression acoustically affects the voice signal. A previous work with normal voices showed a high fidelity at high-bitrate compressions both in voice parameters and the amplitude-frequency spectrum. In the present work, dysphonic voices were tested through two studies. In the first study, spectrograms, long-term average spectra (LTAS), and fast Fourier transform (FFT) spectra of compressed and original samples of running speech were compared. In the second study, intensities, formant frequencies, formant bandwidths, and a multidimensional set of voice parameters were tested in a set of sustained phonations. Results showed that compression at high bitrates (96 and 128 kbps) preserved the relevant acoustic properties of the pathological voices. With compressions at lower bitrates, fidelity decreases, introducing some important alterations. Results from both works, Gonzalez and Cervera and this paper, open up the possibility of using MPEG-compression at high bitrates to store or transmit high-quality speech recordings, without altering their acoustic properties. 相似文献
34.
Jeroen J. L. M. Cornelissen W. Sander Graswinckel Alan E. Rowan Nico A. J. M. Sommerdijk Roeland J. M. Nolte 《Journal of polymer science. Part A, Polymer chemistry》2003,41(11):1725-1736
The conformational properties of polymers derived from isocyanodipeptides have been investigated with a combination of model calculations, X‐ray diffraction, and circular dichroism spectroscopy. Depending on the configuration of the side chains, defined arrays of hydrogen bonds along the polymeric backbone are formed. This leads to a well‐defined conformation as, for example, expressed in the formation of lyotropic liquid‐crystalline phases and increased helical stability. Upon the disruption of the hydrogen bonds by a strong acid, a less well‐defined macromolecular conformation is observed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1725–1736, 2003 相似文献
35.
Statistical Inference with Fractional Brownian Motion 总被引:3,自引:1,他引:2
Kukush Alexander Mishura Yulia Valkeila Esko 《Statistical Inference for Stochastic Processes》2005,8(1):71-93
We give a test between two complex hypothesis; namely we test whether a fractional Brownian motion (fBm) has a linear trend against a certain non-linear trend. We study some related questions, like goodness-of-fit test and volatility estimation in these models. 相似文献
36.
We discuss when a generic subspace of some fixed proportional dimension of a finite-dimensional normed space can be isomorphic to a generic quotient of some proportional dimension of another space. We show (in Theorem 4.1) that if this happens (for some natural random structures) then for any proportion arbitrarily close to 1, the first space has a lot of Euclidean subspaces and the second space has a lot of Euclidean quotients. 相似文献
37.
Admissible slopes for monotone and convex interpolation 总被引:1,自引:0,他引:1
Summary In many applications, interpolation of experimental data exhibiting some geometric property such as nonnegativity, monotonicity or convexity is unacceptable unless the interpolant reflects these characteristics. This paper identifies admissible slopes at data points of variousC
1 interpolants which ensure a desirable shape. We discuss this question, in turn for the following function classes commonly used for shape preserving interpolations: monotone polynomials,C
1 monotone piecewise polynomials, convex polynomials, parametric cubic curves and rational functions. 相似文献
38.
39.
40.
Nonlinear Dynamics, Psychology, and Life Sciences - 相似文献