全文获取类型
收费全文 | 2519篇 |
免费 | 107篇 |
国内免费 | 194篇 |
专业分类
化学 | 1323篇 |
晶体学 | 35篇 |
力学 | 239篇 |
综合类 | 46篇 |
数学 | 565篇 |
物理学 | 612篇 |
出版年
2024年 | 4篇 |
2023年 | 35篇 |
2022年 | 113篇 |
2021年 | 90篇 |
2020年 | 61篇 |
2019年 | 62篇 |
2018年 | 55篇 |
2017年 | 61篇 |
2016年 | 95篇 |
2015年 | 71篇 |
2014年 | 95篇 |
2013年 | 161篇 |
2012年 | 86篇 |
2011年 | 134篇 |
2010年 | 142篇 |
2009年 | 140篇 |
2008年 | 113篇 |
2007年 | 132篇 |
2006年 | 116篇 |
2005年 | 130篇 |
2004年 | 115篇 |
2003年 | 104篇 |
2002年 | 95篇 |
2001年 | 60篇 |
2000年 | 61篇 |
1999年 | 56篇 |
1998年 | 51篇 |
1997年 | 58篇 |
1996年 | 52篇 |
1995年 | 31篇 |
1994年 | 41篇 |
1993年 | 35篇 |
1992年 | 18篇 |
1991年 | 18篇 |
1990年 | 12篇 |
1989年 | 13篇 |
1988年 | 14篇 |
1987年 | 16篇 |
1986年 | 8篇 |
1985年 | 18篇 |
1984年 | 14篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 10篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1977年 | 1篇 |
1968年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有2820条查询结果,搜索用时 0 毫秒
101.
Let H(B) denote the space of all holomorphic functions on the unit ball B of Cn. Let φ be a holomorphic self-map of B and g ∈ H(B) such that g(0) = 0. In this paper, we investigate the boundedness and compactness of the generalized composition operator
102.
Design of a Rectangular to Circular Groove Waveguide Transition by Finite Element Method 总被引:1,自引:0,他引:1
Yaozhong Xu Zhifang Qian Hongsheng Yang 《International Journal of Infrared and Millimeter Waves》2001,22(9):1381-1391
A rectangular to circular groove waveguide transition is described in millimeter-wave band. The transition maintains a constant cutoff wavelength. Using the Finite Element Method, the size of the variable cross-section throughout the transition are calculated and the transition is designed. 相似文献
103.
The composition operators with closed rangc on H2(B
n) are characterized, and the Fredholmness of products of Toeplitz and composition operators discussed. Moreover, using composition
operators, the spectra of Toeplitz operators are studied.
Project supported by the National Natural Sciencc Foundation of China and the Postdoctoral Science Foundation of China. 相似文献
104.
The multiplicities a of simple modules L in the composition series of Kac modules V lambda for the Lie superalgebra
(m/n ) were described by Serganova, leading to her solution of the character problem for
(m/n ). In Serganova's algorithm all with nonzero a are determined for a given this algorithm, turns out to be rather complicated. In this Letter, a simple rule is conjectured to find all nonzero a for any given weight . In particular, we claim that for an r-fold atypical weight there are 2r distinct weights such that a = 1, and a = 0 for all other weights . Some related properties on the multiplicities a are proved, and arguments in favour of our main conjecture are given. Finally, an extension of the conjecture describing the inverse of the matrix of Kazhdan–Lusztig polynomials is discussed. 相似文献
105.
用边界单元法计算离心风机噪声辐射 总被引:1,自引:0,他引:1
1概述在工业生产中,噪声已成为考查风机性能的重要指标之一。然而,为了准确测出风机的噪声量值,需要一个适宜的声学环境,否则往往无法测出其真实的噪声量值。其次在噪声测量中,从机壳辐射的噪声同通过进、出口管道面辐射的噪声相互影响,因而把这两种能量途径分开几乎是不可能的。本文提出了一种评估风机机壳单独的噪声辐射的方法。这种方法运用边界元法在测量风机机壳表面振动速度的基础上计算蜗壳表面的声压分布及其辐射的声功率.当然它也可以用来计算入口管、出口管(不包括蜗壳)所辐射的声功率。2等参单元法计算三维辐射声场声… 相似文献
106.
提出了一种无须进行电离积分的用于高压结终端模拟的边界元素法,分析了界面电荷对FP-JTE终端结构击穿电压的影响,结果表明击穿电压几乎与界面电荷浓度呈线性关系,场板可减弱界面电荷对击穿电压的影响。 相似文献
107.
108.
基于近红外光谱技术的石油组分定量分析新方法 总被引:12,自引:1,他引:12
针对石油化工产品生产控制和质量检查的需要,为提高测定产品组成的效率,将近红外光谱法作为基础测定方法,以直馏柴油、加氢精制柴油和催化裂化柴油为校正模型的训练样本,测定其中饱和烃、胶质、单环芳烃、双环芳烃、三环芳烃和环烷烃的组成,论述了采用模糊神经网络建立校正模型测定石油化工产品组成的可行性。基于dSPACE硬件平台,用验证样本对模糊神经网络校正模型进行了检验,实验结果表明,该方法响应快、误差小、鲁棒性强,在近红外长波区内,校正样品和验证样品的均方误差小于10-6。该方法可用于石油化工产品的生产工艺研究中。 相似文献
109.
Elisa Musella Dr. Isacco Gualandi Dr. Erika Scavetta Dr. Massimo Gazzano Arianna Rivalta Dr. Elisabetta Venuti Dr. Meganne Christian Dr. Vittorio Morandi Prof. Dr. Domenica Tonelli 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(71):16301-16310
Layered double hydroxides (LDHs) have been widely studied for their plethora of fascinating features and applications. The potentiostatic electrodeposition of LDHs has been extensively applied in the literature as a fast and direct method to substitute classical chemical routes. However, the electrochemical approach does not usually allow for a fine control of the MII/MIII ratio in the synthesized material. By employing a recently proposed potentiodynamic method, LDH films of controlled composition are herein prepared with good reproducibility, using different ratios of the trivalent (Fe or Al) to bivalent (Co) cations in the electrolytic solution. All the obtained materials are shown to be effective oxygen evolution reaction (OER) catalysts, and are thoroughly characterized by a multi-technique approach, including FE-SEM, XRD, Raman, AES and a wide range of electrochemical procedures. 相似文献
110.
In the paper an important issue of vibrations of the transmission line in real conditions was analyzed. Such research was carried out by the authors of this paper taking into account the cross-section of the cable being in use on thetransmission line. Analysis was performed for the modern ACSR high voltage transmission line with span of 213.0 m. The purpose of the investigation was to analyze the vibrations of the power transmission line in the natural environmentand compare with the results obtained in the numerical simulations. Analysis was performed for natural and wind excited vibrations. The numerical model was made using the Spectral Element Method. In the spectral model, for variousparameters of stiffness, damping and tension force, the system response was checked and compared with the results of the accelerations obtained in the situ measurements. A frequency response functions (FRF) were calculated. Thecredibility of the model was assessed through a validation process carried out by comparing graphical plots of FRF functions and numerical values expressing differences in acceleration amplitude (MSG), phase angle differences (PSG) and differences in acceleration and phase angle total (CSG) values. Particular attention was paid to the hysteretic damping analysis. Sensitivity of the wave number was performed for changing of the tension force and section area of thecable. The next aspect constituting the purpose of this paper was to present the wide possibilities of modelling and simulation of slender conductors using the Spectral Element Method. The obtained results show very good accuracy in the range of both experimental measurements as well as simulation analysis. The paper emphasizes the ease with which the sensitivity of the conductor and its response to changes in density of spectral mesh division, cable cross-section,tensile strength or material damping can be studied. 相似文献