全文获取类型
收费全文 | 154639篇 |
免费 | 17193篇 |
国内免费 | 9504篇 |
专业分类
化学 | 90959篇 |
晶体学 | 1951篇 |
力学 | 9441篇 |
综合类 | 523篇 |
数学 | 15648篇 |
物理学 | 62814篇 |
出版年
2023年 | 2171篇 |
2022年 | 3833篇 |
2021年 | 4013篇 |
2020年 | 4379篇 |
2019年 | 3959篇 |
2018年 | 3821篇 |
2017年 | 3396篇 |
2016年 | 5539篇 |
2015年 | 5047篇 |
2014年 | 6378篇 |
2013年 | 9496篇 |
2012年 | 10700篇 |
2011年 | 11603篇 |
2010年 | 7839篇 |
2009年 | 7670篇 |
2008年 | 8718篇 |
2007年 | 7890篇 |
2006年 | 7569篇 |
2005年 | 6245篇 |
2004年 | 5165篇 |
2003年 | 4260篇 |
2002年 | 3975篇 |
2001年 | 5192篇 |
2000年 | 3974篇 |
1999年 | 3581篇 |
1998年 | 2796篇 |
1997年 | 2770篇 |
1996年 | 2572篇 |
1995年 | 2220篇 |
1994年 | 1977篇 |
1993年 | 1710篇 |
1992年 | 1896篇 |
1991年 | 1815篇 |
1990年 | 1579篇 |
1989年 | 1317篇 |
1988年 | 1156篇 |
1987年 | 1157篇 |
1986年 | 1038篇 |
1985年 | 1211篇 |
1984年 | 1023篇 |
1983年 | 718篇 |
1982年 | 680篇 |
1981年 | 613篇 |
1980年 | 554篇 |
1979年 | 651篇 |
1978年 | 667篇 |
1977年 | 676篇 |
1976年 | 597篇 |
1975年 | 507篇 |
1974年 | 542篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Solid state nuclear track detectors are commonly used for measurements of concentrations of radon gas and/or radon progeny. All these measurements depend critically on the thickness of the removed layer during etching. However, the thickness of removed layer calculated using the etching period does not necessarily provide a sufficiently accurate measure of the thickness. For example, the bulk etch rate depends on the strength of stirring during etching for the LR 115 detector. We propose here to measure the thickness of the removed layer by using energy-dispersive X-ray fluorescence spectrometry. In the present work, a reference silver nitrate pellet is placed beneath the LR 115 detector, and the fluorescence X-ray intensity for silver is then measured. We have found a linear relationship between the X-ray intensity and the thickness of the removed layer for LR 115 detector. This provides a fast method to measure the thickness of removed layer from etching of LR 115 detector. However, this method was found to be inapplicable for the CR-39 detector. Therefore, alternative methods have yet to be explored for the CR-39 detector. 相似文献
62.
63.
Nickel complexes 1–4 ligated with 2,9-disubstituted-1,10-phenanthroline were synthesized and characterized by FT-IR spectra and elemental analysis.
The molecular structure of complex 2 was confirmed by X-ray crystal diffraction analysis. Activated with methylaluminoxane (MAO), those complexes showed moderate
activities for ethylene oligomerization.
Published in Kinetika i Kataliz, 2007, Vol. 48, No. 5, pp. 710–714.
This article was submitted by the authors in English. 相似文献
64.
J. Song H. Jiang Z.J. Liu D.Y. Khang Y. Huang J.A. Rogers C. Lu C.G. Koh 《International Journal of Solids and Structures》2008,45(10):3107-3121
A finite-deformation theory is developed to study the mechanics of thin buckled films on compliant substrates. Perturbation analysis is performed for this highly nonlinear system to obtain the analytical solution. The results agree well with experiments and finite element analysis in wavelength and amplitude. In particular, it is found that the wavelength depends on the strain. Based on the accurate wavelength and amplitude, the membrane and peak strains in thin films, and stretchability and compressibility of the system are also obtained analytically. 相似文献
65.
Current methodologies used for the inference of thin film stress through curvature measurement are strictly restricted to stress and curvature states that are assumed to remain uniform over the entire film/substrate system. These methodologies have recently been extended to a single layer of thin film deposited on a substrate subjected to the non-uniform misfit strain in the thin film. Such methodologies are further extended to multi-layer thin films deposited on a substrate in the present study. Each thin film may have its own non-uniform misfit strain. We derive relations between the stresses in each thin film and the change of system curvatures due to the deposition of each thin film. The interface shear stresses between the adjacent films and between the thin film and the substrate are also obtained from the system curvatures. This provides the basis for the experimental determination of thin film stresses in multi-layer thin films on a substrate. 相似文献
66.
67.
Guobao Zhang Jianming Zhang Shenguo Wang Deyan Shen 《Journal of Polymer Science.Polymer Physics》2003,41(1):23-30
Blends of amorphous poly(DL‐lactide) (DL‐PLA) and crystalline poly(L‐lactide) (PLLA) with poly(methyl methacrylate) (PMMA) were prepared by both solution/precipitation and solution‐casting film methods. The miscibility, crystallization behavior, and component interaction of these blends were examined by differential scanning calorimetry. Only one glass‐transition temperature (Tg) was found in the DL‐PLA/PMMA solution/precipitation blends, indicating miscibility in this system. Two isolated Tg's appeared in the DL‐PLA/PMMA solution‐casting film blends, suggesting two segregated phases in the blend system, but evidence showed that two components were partially miscible. In the PLLA/PMMA blend, the crystallization of PLLA was greatly restricted by amorphous PMMA. Once the thermal history of the blend was destroyed, PLLA and PMMA were miscible. The Tg composition relationship for both DL‐PLA/PMMA and PLLA/PMMA miscible systems obeyed the Gordon–Taylor equation. Experiment results indicated that there is no more favorable trend of DL‐PLA to form miscible blends with PMMA than PLLA when PLLA is in the amorphous state. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 23–30, 2003 相似文献
68.
本文提出的MMD算法用于提高模型区别错误信息和正确信息的能力.利用该算法在对模型的参数进行重估计时.涉及到复杂的目标函数的梯度运算.击运用矩阵运算使得梯度运算变得简单明了,因此本文给出了MMD算法下的HMM参数重估计的矩阵表示形式并给出了证明. 相似文献
69.
Zhang Meirong 《数学年刊B辑(英文版)》1989,10(3):416-425
This paper considers the following question: Given an Anosov endomorphism f on T~m, whether f is topologically conjugate to some hyperbolic total endomorphism? It is well known that the answer for Anosov diffeomorphisms and expanding endomorphisms is affirmative. Hwever for the remainder Anosov endomorphisms, a quite different answer is obtained in this paper, i. e., for generic Anosov endomorphisms, they are not topologically conjugate to any hyperbolic toral endomorphism. 相似文献
70.
本文提出从高分辨电子显微像中,利用光学、全息和部分相干等方法,提取传递函数,制作相位和振幅滤波器,实现解卷,提高高分辨电子显微像的分辨率. 相似文献