全文获取类型
收费全文 | 1508篇 |
免费 | 29篇 |
国内免费 | 4篇 |
专业分类
化学 | 713篇 |
晶体学 | 13篇 |
力学 | 58篇 |
数学 | 140篇 |
物理学 | 617篇 |
出版年
2022年 | 21篇 |
2021年 | 20篇 |
2020年 | 22篇 |
2019年 | 19篇 |
2018年 | 23篇 |
2017年 | 28篇 |
2016年 | 38篇 |
2015年 | 26篇 |
2014年 | 39篇 |
2013年 | 94篇 |
2012年 | 80篇 |
2011年 | 91篇 |
2010年 | 56篇 |
2009年 | 54篇 |
2008年 | 80篇 |
2007年 | 66篇 |
2006年 | 45篇 |
2005年 | 62篇 |
2004年 | 50篇 |
2003年 | 41篇 |
2002年 | 43篇 |
2001年 | 27篇 |
2000年 | 29篇 |
1999年 | 31篇 |
1998年 | 17篇 |
1997年 | 19篇 |
1996年 | 20篇 |
1995年 | 12篇 |
1994年 | 22篇 |
1993年 | 30篇 |
1992年 | 26篇 |
1991年 | 22篇 |
1990年 | 14篇 |
1989年 | 23篇 |
1988年 | 15篇 |
1987年 | 15篇 |
1986年 | 12篇 |
1985年 | 16篇 |
1984年 | 13篇 |
1983年 | 12篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1980年 | 10篇 |
1979年 | 12篇 |
1978年 | 19篇 |
1977年 | 10篇 |
1976年 | 11篇 |
1975年 | 12篇 |
1974年 | 13篇 |
1973年 | 9篇 |
排序方式: 共有1541条查询结果,搜索用时 8 毫秒
101.
Braunisch H Habashy TM Sinha BK Pabon J Kong JA 《The Journal of the Acoustical Society of America》2004,115(1):269-279
The problem of inferring unknown geometry and material parameters of a waveguide model from noisy samples of the associated modal dispersion curves is considered. In a significant reduction of the complexity of a common inversion methodology, the inner of two nested iterations is eliminated: The approach described does not employ explicit fitting of the data to computed dispersion curves. Instead, the unknown parameters are adjusted to minimize a cost function derived directly from the determinant of the boundary condition system matrix. This results in an efficient inversion scheme that, in the case of noise-free data, yields exact results. Multimode data can be simultaneously processed without extra complications. Furthermore, the inversion scheme can accommodate an arbitrary number of unknown parameters, provided that the data have sufficient sensitivity to these parameters. As an important application, we consider the sonic guidance condition for a fluid-filled borehole in an elastic, homogeneous, and isotropic rock formation for numerical forward and inverse dispersion analysis. We investigate numerically the parametric inversion with errors in the model parameters and the influence of bandwidth and noise, and examine the cases of multifrequency and multimode data, using simulated flexural and Stoneley dispersion data. 相似文献
102.
Gutt C Ghaderi T Chamard V Madsen A Seydel T Tolan M Sprung M Grübel G Sinha SK 《Physical review letters》2003,91(7):076104
We report measurements of propagating capillary waves on a liquid water surface at T=5 degrees C with x-ray photon correlation spectroscopy. The experiment has been performed under grazing incidence conditions with an incoming x-ray beam below the critical angle of total external reflection. In the q region investigated the measured intensity-intensity autocorrelation functions of the liquid water surface were found to be heterodyne signals, i.e., a combination of first- and second-order correlation functions g(1)(tau) and g(2)(tau). 相似文献
103.
We present a method for solving the wormlike-chain (WLC) model for twisting semiflexible polymers to any desired accuracy. We show that the WLC free energy is a periodic function of the applied twist with period 4pi. We develop an analogy between WLC elasticity and the geometric phase of a spin-1 / 2 system. These analogies are used to predict elastic properties of twist-storing polymers. We graphically display the elastic response of a single molecule to an applied torque. This study is relevant to mechanical properties of biopolymers such as DNA. 相似文献
104.
In this article, we first investigate the bending of light rays in 4D line elements representing spherically symmetric, static on–brane geometries. The amount of bending in these four dimensional, strong and weak field solutions is derived. Signatures, which appear in the bending formulae, due to the presence of extra dimensions are discussed. Subsequently, as a separate exercise, we calculate the bending of null geodesic trajectories in a bulk five dimensional spacetime with a Schwarzschild line element on the 3-brane section. We interpret the deviation of null trajectories as that of gravitational signals or five dimensional photons, which are, unlike light rays confined to four dimensions, allowed to propagate along the fifth (extra) dimension. Features of the presence of extra dimensions in the effective potentials and the bending formula are analysed in this context. 相似文献
105.
Phytochemical investigation of the leaves of Bidens pilosa lead to the isolation and characterization of a new disubstituted acetylacetone (1) named as 3-Propyl-3-(2,4,5-trimethoxy)benzyloxy-pentan-2,4-dione. 相似文献
106.
Yb:YAG and Nd:YAG edge-pumped slab lasers 总被引:9,自引:0,他引:9
Experimental demonstrations of two edge-pumped zigzag slab lasers are presented. The Nd:YAG slab laser generated 127 W of multimode output power with 300W of pump power. Preliminary results with a Yb:YAG slab produced 46 W of output power with 315W of pump power. The edge-pumped slab design permits symmetric conduction cooling and efficient pump absorption and accepts large-numerical-aperture pump sources. 相似文献
107.
Defibrillation via the elimination of spiral turbulence in a model for ventricular fibrillation 总被引:6,自引:0,他引:6
Ventricular fibrillation, the major reason behind sudden cardiac death, is turbulent cardiac electrical activity in which rapid, irregular disturbances in the spatiotemporal electrical activation of the heart make it incapable of any concerted pumping action. Methods of controlling ventricular fibrillation include electrical defibrillation as well as injected medication. Electrical defibrillation, though widely used, involves subjecting the whole heart to massive, and often counterproductive, electrical shocks. We propose a defibrillation method that uses a very low-amplitude shock (of order mV) applied for a brief duration (of order 100 ms) and over a coarse mesh of lines on our model ventricle. 相似文献
108.
N. Pathak G. K. Mahanti T. K. Sinha Mahapatra 《International Journal of Infrared and Millimeter Waves》2007,28(11):953-960
In this paper, we present a new method based on real-coded Genetic Algorithm (GA) with elitist model for optimal design of
a reconfigurable symmetrical dual-beam uniformly spaced linear isotropic antenna array with phase-only control of quantized
phase shifters. The problem is to find a common amplitude distribution that will generate a pencil beam with zero phases and
a flat-top beam with discrete phases of a six-bit discrete phase shifter, without or with pre-fixing the value of dynamic
range ratio (|I
max/I
min|) of excitation current amplitude distribution equal to or less than five. 相似文献
109.
Hiten J. Shah Mohan L. Kundlik Nitesh K. Patel Gunta Subbaiah Dasharath M. Patel Bhanubhai N. Suhagia Chhagan N. Patel 《Journal of separation science》2009,32(20):3388-3394
A rapid LC–MS/MS method has been developed and validated for the determination of losartan (LOS) and its metabolite losartan acid (LA) (EXP‐3174) in human plasma using multiplexing technique (two HPLC units connected to one MS/MS). LOS and LA were extracted from human plasma by SPE technique using Oasis HLB® cartridge without evaporation and reconstitution steps. Hydroflumethiazide (HFTZ) was used as an internal standard (IS). The analytes were separated on Zorbax SB C‐18 column. The mass transition [M–H] ions used for detection were m/z 421.0 → 127.0 for LOS, m/z 435.0 → 157.0 for LA, and m/z 330.0 → 239.0 for HFTZ. The proposed method was validated over the concentration range of 2.5–2000 ng/mL for LOS and 5.0–3000 ng/mL for LA with correlation coefficient ?0.9993. The overall recoveries for LOS, LA, and IS were 96.53, 99.86, and 94.16%, respectively. Total MS run time was 2.0 min/sample. The validated method has been successfully used to analyze human plasma samples for applications in 100 mg fasted and fed pharmacokinetic studies. 相似文献
110.
Mrinal Kanti Paira Tapan Kumar Mondal Elena López-Torres Joan Ribas Chittaranjan Sinha 《Polyhedron》2010
Copper(II) complexes of 3-((2-(alkylthio)phenylazo)-2,4-pentanedione, tridentate O, N, S donor ligands, are described in this work. Chloride bridged copper(II) polymers (1) and thiocyanato bridged copper(II) dimmers (2) are characterized by a single crystal X-ray diffraction study. The complexes show antiferromagnetic interactions, with J = −0.5 ± 0.1 cm−1 (1a) and −25.8 ± 0.5 cm−1 (2b), which implies stronger coupling in the –SCN-bridging compound. The spectra, redox and magnetism are explained by DFT studies. 相似文献