全文获取类型
收费全文 | 4942篇 |
免费 | 108篇 |
国内免费 | 13篇 |
专业分类
化学 | 2547篇 |
晶体学 | 97篇 |
力学 | 227篇 |
数学 | 666篇 |
物理学 | 1526篇 |
出版年
2022年 | 40篇 |
2021年 | 76篇 |
2020年 | 84篇 |
2019年 | 99篇 |
2018年 | 71篇 |
2017年 | 92篇 |
2016年 | 131篇 |
2015年 | 110篇 |
2014年 | 134篇 |
2013年 | 357篇 |
2012年 | 244篇 |
2011年 | 272篇 |
2010年 | 170篇 |
2009年 | 168篇 |
2008年 | 210篇 |
2007年 | 220篇 |
2006年 | 167篇 |
2005年 | 174篇 |
2004年 | 139篇 |
2003年 | 97篇 |
2002年 | 91篇 |
2001年 | 64篇 |
2000年 | 51篇 |
1999年 | 54篇 |
1998年 | 50篇 |
1996年 | 50篇 |
1995年 | 41篇 |
1994年 | 52篇 |
1993年 | 64篇 |
1992年 | 62篇 |
1991年 | 47篇 |
1990年 | 58篇 |
1989年 | 49篇 |
1988年 | 57篇 |
1987年 | 46篇 |
1986年 | 29篇 |
1985年 | 72篇 |
1984年 | 96篇 |
1983年 | 60篇 |
1982年 | 64篇 |
1981年 | 69篇 |
1980年 | 70篇 |
1979年 | 74篇 |
1978年 | 67篇 |
1977年 | 62篇 |
1976年 | 57篇 |
1975年 | 44篇 |
1974年 | 47篇 |
1973年 | 55篇 |
1972年 | 33篇 |
排序方式: 共有5063条查询结果,搜索用时 15 毫秒
991.
A short‐range force constant model has been applied to investigate the Raman and the infrared wavenumbers in R2BaNiO5 (R = Y, Gd) in their orthorhombic phase of space group Immm. Calculations of zone‐center phonons are made with seven stretching and four bending force constants. The force constants are evaluated by fitting nine Raman and two infrared modes. Two Raman modes are reassigned on the basis of group theoretical calculations. The calculated Raman and infrared modes show good agreement with the observed values. The infrared values are assigned for the first time in these oxides. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
992.
Guohua Chen Malancha Gupta Kelvin Chan Karen K. Gleason 《Macromolecular rapid communications》2007,28(23):2205-2209
Furan ring‐functionalized solid surfaces are achieved by the initiated chemical vapor deposition (iCVD) method, a solvent‐free process to form films under mild conditions. The polymerization of furfuryl methacrylate monomer is initiated by a resistively heated filament wire. The functionality of the furan group in the iCVD film enabled Diels–Alder chemistry with 4‐phenyl‐1,2,3‐triazolin‐3,5‐dione (N‐PTD).
993.
A. K. Gupta Bowling Green State University USA D. G. Kabe Sf. Mary''''s University USA 《数学物理学报(B辑英文版)》2001,21(2):221-223
1 IntroductionWe are given k independent Wishart densities of the p x p random symmetric positivedefinite matrices G1, G2,' t Gkwhere Ri denotes the population correlation matrir, and K as a generic letter denotes thenormalizing constants of density functions in this paper. The squared multiple correlationcoefficient of the i-th population is pf = r:Riz1.)ri, whereand a likelihood ratio test for testing the hypothesisis desired.Now Wilks (l932, l946) provides certain procedures and guidel… 相似文献
994.
The crystal and molecular structures of the alkaloid Royline {(1α,6β,14α, 16β)-20-ethyl-4-hydroxymethyl)-1,6,14,16-tetramethoxyaconitane-7,8-diol} with a water molecule has been determined by X-ray diffraction analysis. The compound crystallizes in the space group P21 with the unit cell parameters a = 10.985(1) Å, b = 7.898(1) Å, c = 14.956(1) Å, β = 102.96(1)°, V = 1264.52 Å3, Z = 2, λMoK α = 0.71073 Å, and R = 0.033 for 2067 observed reflections. Rings A, B, and C adopt a chair conformation, ring D is a half-boat, ring E is a half-chair, and ring F is in an envelope conformation with C(14) at the flap. Molecules are linked together in the crystal by hydrogen bonds. 相似文献
995.
Rajnikant V. K. Gupta E. H. Khan S. Shafi S. Hashmi Shafiullah B. Varghese Dinesh 《Crystallography Reports》2001,46(6):963-966
The crystal structure of cholest-4-ene-3,6-dione (C27H44O2) has been determined by X-ray diffraction methods. The compound crystallizes in the monoclinic crystal system (space group P21) with the unit cell parameters a = 10.503(4) Å, b = 8.059(1) Å, c = 14.649(1) Å, β = 105.4(2)°, and Z = 2. The structure has been refined to an R value of 0.035 for 2252 observed reflections. Ring A of the steroid nucleus exists in a sofa conformation, while rings B and C adopt a chair conformation. The five-membered ring D exhibits a half-chair conformation. The molecules in the unit cell are linked together by the C-H?O hydrogen bonds. 相似文献
996.
When a laser source is used to illuminate a transmission hologram, the zero order beam is not utilised and is just wasted. The paper describes a new technique for economical utilisation of laser light by recycling the transmitted light to reconstruct a number of holograms simultaneously for viewing by a large number of observers. There is no danger to viewer who is exposed to the undiffracted laser beams transmitted through the hologram. The paper also discusses the diffraction efficiency requirement of successive hologram and the limit of number of holograms in the scheme. 相似文献
997.
Monisha Singhal Sreemoyee Chatterjee Ajeet Kumar Asad Syed Ali H. Bahkali Nidhi Gupta Surendra Nimesh 《Molecules (Basel, Switzerland)》2021,26(19)
The current research work illustrates an economical and rapid approach towards the biogenic synthesis of silver nanoparticles using aqueous Punica granatum leaves extract (PGL-AgNPs). The optimization of major parameters involved in the biosynthesis process was done using Box-Behnken Design (BBD). The effects of different independent variables (parameters), namely concentration of AgNO3, temperature and ratio of extract to AgNO3, on response viz. particle size and polydispersity index were analyzed. As a result of experiment designing, 17 reactions were generated, which were further validated experimentally. The statistical and mathematical approaches were employed on these reactions in order to interpret the relationship between the factors and responses. The biosynthesized nanoparticles were initially characterized by UV-vis spectrophotometry followed by physicochemical analysis for determination of particle size, polydispersity index and zeta potential via dynamic light scattering (DLS), SEM and EDX studies. Moreover, the determination of the functional group present in the leaves extract and PGL-AgNPs was done by FTIR. Antibacterial and antibiofilm efficacies of PGL-AgNPs against Gram-positive and Gram-negative bacteria were further determined. The physicochemical studies suggested that PGL-AgNPs were round in shape and of ~37.5 nm in size with uniform distribution. Our studies suggested that PGL-AgNPs exhibit potent antibacterial and antibiofilm properties. 相似文献
998.
999.
Analysis of thermal expansion coefficients under the effect of high temperature for minerals 总被引:1,自引:0,他引:1
A simple and straightforward method for the determination of thermal expansion is investigated and applied for four minerals of geophysical importance. The results obtained for four minerals such as Mg2SiO3, Al2O3, Grossular garnet and Pyrope garnet at different temperatures are found to be in excellent agreement with the experimental data. The simplicity of the method is discussed in the light of another method in high temperature research on minerals. 相似文献
1000.
Fiber optic evanescent field absorption sensor: Effect of fiber parameters and geometry of the probe 总被引:5,自引:0,他引:5
A comparative experimental study of the fiber-optic evanescent field absorption sensor based on straight and U-shaped probes is presented. The effects of numerical aperture and the core radius of the fiber on the sensitivity of the sensor are experimentally investigated. Increase in the numerical aperture of the fiber increases the sensitivity of the sensor in the case of both the probes. The effect of core radius on the sensitivity depends on the bending radius of the probe. In the case of straight probe (i.e. infinite bending radius) the fiber with smaller core radius has high sensitivity while in the case of U-shaped probe with 0.17 cm bending radius, the fiber with larger core radius has high sensitivity. Thus, which fiber (with small or large core radius) has maximum sensitivity depends on the bending radius of the probe. For a given fiber, decrease in the bending radius increases the sensitivity of the U-shaped probe. An inverse power law relationship between the bending radius and the evanescent absorbance and hence the sensitivity is established. 相似文献