全文获取类型
收费全文 | 11648篇 |
免费 | 1792篇 |
国内免费 | 1797篇 |
专业分类
化学 | 4650篇 |
晶体学 | 219篇 |
力学 | 338篇 |
综合类 | 104篇 |
数学 | 1340篇 |
物理学 | 8586篇 |
出版年
2024年 | 19篇 |
2023年 | 91篇 |
2022年 | 276篇 |
2021年 | 308篇 |
2020年 | 239篇 |
2019年 | 298篇 |
2018年 | 288篇 |
2017年 | 433篇 |
2016年 | 458篇 |
2015年 | 444篇 |
2014年 | 693篇 |
2013年 | 1025篇 |
2012年 | 785篇 |
2011年 | 713篇 |
2010年 | 653篇 |
2009年 | 781篇 |
2008年 | 862篇 |
2007年 | 880篇 |
2006年 | 786篇 |
2005年 | 680篇 |
2004年 | 559篇 |
2003年 | 510篇 |
2002年 | 445篇 |
2001年 | 403篇 |
2000年 | 377篇 |
1999年 | 334篇 |
1998年 | 280篇 |
1997年 | 285篇 |
1996年 | 218篇 |
1995年 | 180篇 |
1994年 | 142篇 |
1993年 | 132篇 |
1992年 | 125篇 |
1991年 | 75篇 |
1990年 | 60篇 |
1989年 | 76篇 |
1988年 | 108篇 |
1987年 | 42篇 |
1986年 | 24篇 |
1985年 | 26篇 |
1984年 | 26篇 |
1983年 | 7篇 |
1982年 | 18篇 |
1981年 | 21篇 |
1980年 | 12篇 |
1979年 | 12篇 |
1977年 | 5篇 |
1974年 | 5篇 |
1973年 | 5篇 |
1971年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
《Laser \u0026amp; Photonics Reviews》2017,11(5)
Mid‐infrared ultrafast lasers have emerged as a promising platform for both science and industry because of their inherent high raw power and eye‐safe spectrum. 2D nanostructures such as graphene have emerged as promising photonic materials for laser mode‐locking to generate ultrashort pulses. However, there are still many unanswered questions about graphene's key advantages to be practical devices, especially over the matured semiconductor saturable absorber mirror (SESAM). In this work, we conducted systematic comparisons on the nonlinear optical properties of graphene and that of a commercial SESAM at 2 μm wavelength. Our results showed that graphene has significant advantages over the commercial SESAM, exhibiting ∼28% less absorptive cross‐section ratio of excited‐state to ground‐state and ∼50 times faster relaxation time. This implies that graphene can be exploited as a better mode‐locker than the current commercial SESAM for high power, high repetition rate and ultrafast mid‐infrared laser sources. 相似文献
942.
用等离子体粒子能谱拟合温度的新方法 总被引:1,自引:1,他引:0
秦运文 《核聚变与等离子体物理》2001,21(1):49-52
用最小二乘法拟合等离子体粒子能谱实验数据时,通常使拟合函数与实验能谱数据之间的误差平方和极小化。如果将能谱实验数据的对数拟合成直线以求得粒子温度,则最好对温度误差的平方和极小化。给出了这种拟合方法的计算公式,并对两种不同方法得到的结果进行了比较。 相似文献
944.
Maria BURGOS ;E Amin KAIDI ;Antonio Morales CAMPOY ;Antonio M. PERALTA ;Maribel RAMIREZ 《数学学报(英文版)》2008,24(2):185-200
We revise the notion of von Neumann regularity in JB^*-triples by finding a new characterisation in terms of the range of the quadratic operator Q(a). We introduce the quadratic conorm of an element a in a JB^*-triple as the minimum reduced modulus of the mapping Q(a). It is shown that the quadratic conorm of a coincides with the infimum of the squares of the points in the triple spectrum of a. It is established that a contractive bijection between JBW^*-triples is a triple isomorphism if, and only if, it preserves quadratic conorms. The continuity of the quadratic conorm and the generalized inverse are discussed. Some applications to C^*-algebras and von Neumann algebras are also studied. 相似文献
945.
Mathematical Notes - 相似文献
946.
Liyan Yu 《Microchemical Journal》2008,90(1):63-66
The aim of this study was to assess the feasibility of near infrared spectroscopy (NIRS) for analysis of acyclovir in plasma. This methodology was based on the direct measurement of the transmission spectra of liquid samples and a multivariate calibration model (partial least squares, PLS) to determine the acyclovir concentration in plasma sample. The PLS calibration set was built on using the spiked samples by mixing different amounts of acyclovir. Concentration of acyclovir in the plasma samples was calculated employing a 6-factors PLS calibration using the spectral information in the range of 6102-5450 cm− 1. The root mean square errors of prediction (RMSEP) found was 1.21 for acyclovir. The developed PLS-NIRS procedure allows the determination of 120 samples/h does not require any sample pretreatment and avoids waste generation. 相似文献
947.
Xichang Wang Zhen hua Yanjun Gong 《International Journal of Infrared and Millimeter Waves》2005,26(8):1195-1205
Infrared ray (IR) has great potential in medical diagnosis and therapy. In order to detect tumor in skin, we set up the steady-state and time domain IR diffusion model of an n-layered matched medium with an infinitely thick. We utilize the diffuse equation to solve a five-layered infinite matched medium and obtain the accurate solution of a matched medium of the steady state and time domain in tissue. We compare the steady-state spatially resolved reflectance calculated with Monte-Carlo simulations. The Monte-Carlo simulation shows that the solution is valid. Our equation can be used to obtain the tumor information in medical diagnosis and therapy. 相似文献
948.
The time dependence of the concentration of CO2 in an electrochemical thin layer cavity is studied with Fourier transform infrared spectroscopy (FTIR) in order to evaluate
the extent to which the thin layer cavity is diffusionally decoupled from the surrounding bulk electrolyte. For the model
system of CO on Pt(111) in 0.1 M HClO4, it is found that the concentration of CO2, formed by electro-oxidation of CO, equilibrates rapidly with the surrounding bulk electrolyte. This rapid equilibration
indicates that there is diffusion out of the thin layer, even on the short time scales of typical infrared experiments (1–3 min).
However, since the measured CO2 absorbance intensity as a function of time is reproducible to within 10%, a new time-dependent method for surface coverage
calibration using solution-phase species is proposed.
Dedicated to Prof. Dr. Teresa Iwasita on the occasion of her 65th birthday in recognition of her numerous contributions to
interfacial electrochemistry. 相似文献
949.
A. Andres Leal Joseph M. Deitzel Steven H. McKnight John W. Gillespie Jr. 《Journal of Polymer Science.Polymer Physics》2009,47(18):1809-1824
Poly‐pyridobisimiazole (M5) single filaments subjected to varying degrees of heat treatment have been analyzed using Fourier Transform Infrared (FTIR) microspectroscopy in transmission mode to detect changes in the state of intermolecular hydrogen bonding as a function of fiber annealing conditions. The FTIR absorbance bands associated with hydrogen bonding in M5 fiber have been identified, and the integrated molar absorption coefficients for the bands of interest have been determined experimentally, which allows to quantify the concentration of N? H vibration groups hydrogen‐bonded (H‐bonded) to water molecules, and the concentration of N? H vibration groups H‐bonded to adjacent polymer chains in the fiber. A dual mechanism kinetic rate expression is used to describe intermolecular H‐bond formation in M5 fiber as a function of annealing conditions, from which an activation energy for H‐bond formation of 14.8 kJ/mol is obtained. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1809–1824, 2009 相似文献
950.
Venkat R. Donuru Giri K. Vegesna Singaravelu Velayudham Ge Meng Haiying Liu 《Journal of polymer science. Part A, Polymer chemistry》2009,47(20):5354-5366
Novel deep‐red emissive poly(2,6‐BODIPY‐ethynylene)s bearing dodecyl side chains (polymers A , B , and C ) have been prepared by palladium‐catalyzed Sonogashira polymerization of 2,6‐diiodo‐functionalized BODIPY monomers with 2,6‐diethynyl‐functionalized BODIPY monomers. These polymers emit in the deep‐red region with emission maxima at up to 690 nm, and exhibit significant red shifts (up to 166 and 179 nm) of both absorption and emission maxima compared with their parent BODIPY dyes due to significant extension of π‐conjugation. These polymers possess good thermal stability with decomposition temperature between 270 and 360 °C. The polymers exhibit a little larger Stokes shifts and shorter lifetime than their corresponding BODIPY dyes. The solid state thin films of polymers A , B , and C emit in near‐infrared region between 723 and 743 nm, and show significantly red shifts (up to 57 nm) in absorption and emission maxima relative to their polymer solution. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5354–5366, 2009 相似文献