全文获取类型
收费全文 | 319371篇 |
免费 | 3953篇 |
国内免费 | 1118篇 |
专业分类
化学 | 174245篇 |
晶体学 | 4518篇 |
力学 | 13173篇 |
综合类 | 7篇 |
数学 | 36680篇 |
物理学 | 95819篇 |
出版年
2020年 | 2083篇 |
2019年 | 2055篇 |
2018年 | 2044篇 |
2017年 | 1964篇 |
2016年 | 3995篇 |
2015年 | 3397篇 |
2014年 | 4630篇 |
2013年 | 14328篇 |
2012年 | 11101篇 |
2011年 | 13768篇 |
2010年 | 8537篇 |
2009年 | 8473篇 |
2008年 | 12702篇 |
2007年 | 12870篇 |
2006年 | 12516篇 |
2005年 | 11384篇 |
2004年 | 10256篇 |
2003年 | 9039篇 |
2002年 | 8891篇 |
2001年 | 10214篇 |
2000年 | 7787篇 |
1999年 | 6183篇 |
1998年 | 4940篇 |
1997年 | 4758篇 |
1996年 | 4814篇 |
1995年 | 4406篇 |
1994年 | 4144篇 |
1993年 | 3975篇 |
1992年 | 4459篇 |
1991年 | 4306篇 |
1990年 | 4039篇 |
1989年 | 3855篇 |
1988年 | 4133篇 |
1987年 | 3796篇 |
1986年 | 3678篇 |
1985年 | 5333篇 |
1984年 | 5404篇 |
1983年 | 4386篇 |
1982年 | 4764篇 |
1981年 | 4804篇 |
1980年 | 4553篇 |
1979年 | 4664篇 |
1978年 | 4668篇 |
1977年 | 4647篇 |
1976年 | 4597篇 |
1975年 | 4510篇 |
1974年 | 4359篇 |
1973年 | 4526篇 |
1972年 | 2569篇 |
1971年 | 1880篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Dilek Yildiz JeronimusP.A.J. vanBeeck MichelL. Riethmuller 《Particle & Particle Systems Characterization》2004,21(5):390-402
Two‐phase flows hold an interest in many areas of science and engineering. In the safety field, one such topic is the accidental release of flammable and toxic pressure‐liquefied gases. In case of such a release, a flashing vapor explosion takes place resulting in a very dense two‐phase cloud. If the released substance is flammable, this cloud can be combustible and can lead to deflagration or detonation. For understanding the source processes of flashing and risk assessment, data related to cloud characteristics (i.e. droplet size, velocity etc.) is needed especially in the near region of the release. Due to the non‐equilibrium nature of the near field regions accurate data measurement is not possible with intrusive techniques. Therefore, laser‐based optical techniques (like Particle Image Velocimetry (PIV), Particle Tracking Velocimetry and Sizing (PTVS), Phase Doppler Anemometry (PDA) etc.) present the only possibility to obtain information for particle diameter and velocity evolution in this harsh environment. 相似文献
972.
Marie‐France Llauro Julien Loiseau Fernande Boisson Frdric Delolme Catherine Ladavire J. Claverie 《Journal of polymer science. Part A, Polymer chemistry》2004,42(21):5439-5462
Low‐molecular‐weight poly(acrylic acid) (PAA) was synthesized by reversible addition fragmentation chain transfer polymerization with a trithiocarbonate as chain‐transfer agent (CTA). With a combination of NMR spectroscopy and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry, the PAA end‐groups of the polymer were analyzed before and after neutralization by sodium hydroxide. The polymer prior to neutralization is made up of the expected trithiocarbonate chain‐ends and of the H‐terminated chains issued from a reaction of transfer to solvent. After neutralization, the trithiocarbonates are transformed into thiols, disulfides, thiolactones, and additional H‐terminated chains. By quantifying the different end‐groups, it was possible to demonstrate that fragmentation is the rate limiting step in the transfer reaction. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5439–5462, 2004 相似文献
973.
R. López-Martens J. Mauritsson P. Johnsson K. Varjú A. L’Huillier W. Kornelis J. Biegert U. Keller M. Gaarde K. Schafer 《Applied physics. B, Lasers and optics》2004,78(7-8):835-840
We characterize the temporal structure of high-order harmonic radiation on both the femtosecond and attosecond time scales. The harmonic emission is characterized by mixed-color two-photon ionization with an infrared femtosecond laser using a Mach–Zehnder interferometer where both pump and probe arms travel completely separate paths. In a first experiment, we measure the duration and chirp of individual harmonics. In a second experiment, we resolve, for the first time with this type of setup, the attosecond beating of several harmonics generated under conditions similar to the first experiment. We suggest that the results of both measurements can be combined to determine the full attosecond time structure of the harmonic emission. PACS 32.80.Rm; 42.65.Ky 相似文献
974.
Auvergne R. Saint‐Loup R. Joly‐Duhamel C. Robin J. J. Boutevin B. 《Journal of polymer science. Part A, Polymer chemistry》2007,45(7):1324-1335
The synthesis and characterization of photopolymerizable unsaturated polyester resins based on PET waste are described. The resins came from a depolymerization process based on the glycolysis of PET by diethylene glycol (DEG). Different molecular weights of glycolysates were synthesized. Then, the latter was functionalized by a methyl hemiester of maleic acid to obtain unsatured α,ω‐bismaleate PET oligomers. In the presence of an electron donor monomer, such as triethylene glycol divinyl ether, these electron acceptor oligomers were copolymerized by way of charge‐transfer complexes under UV irradiation. The reaction was monitored in situ by real‐time IR spectroscopy to study the kinetics of photopolymerization. This one was studied in relation with the physical and chemical characteristics of oligoesters and the composition of mixtures containing divinyl ethers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1324–1335, 2007 相似文献
975.
Lightly cross-linked anisotropic networks with uniaxial and π/2 twisted orientations were produced by photopolymerization of monotropic mixtures containing liquid crystal mono and diacrylates. In this way the polymer backbone was immobilized and became decoupled from the motion of the mesogenic side groups. The networks showed very good reversibility and even after becoming isotropic, upon cooling, the initial orientation was recovered. In the same way, in the presence of electric fields the mesogenic groups could be reoriented in the direction of the electric field, reverting back to the initial orientation on removal of the field at a rate comparable with those observed in the monomeric state. Combining viscoelastic measurements with the dielectric behaviour of the monomeric liquid crystal and the anisotropic network, a comparison between the internal and bulk rotational viscosities was also made. 相似文献
976.
977.
The linear relaxation of a one-dimensional bonded fluid model is studied in the dynamical mean field approximation at the pair level. The results are compared with simulation data. Relaxation at low temperatures shows a cooperative character that can be understood in terms of a simple diffusion picture. 相似文献
978.
Summary Two polyampholyte copolymers based on sodium-2-acrylamido-2-methylsulfonate (NaAMPS) and methacryloyloxyethyltrimethylammonium
chloride (MADQUAT) have been prepared either in homogeneous solution or by an inverse microemulsion polymerization technique.
The copolymer microstructure was shown to depend on the method of preparation. The microemulsion polymerization yields copolymers
with a monomer sequence distribution not far from random while those obtained by polymerization in solution have a strong
tendency to alternation. The aqueous-solution properties of the two samples have been investigated by viscometry. The results
show that the charge distribution along the copolymer chain affects considerably its conformation, in good agreement with
recent theoretical studies.
Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994 相似文献
979.
980.
VICENTE LUIS N.; JUDICE JOAQUIM J.; PARDALOS PANOS M. 《IMA Journal of Management Mathematics》1992,4(4):343-349
In this paper, we discuss a multiparametric technique for findinga global minimum for an indefinite quadratic programming problembased on the spectral decomposition of the matrix of the quadraticform. Special attention is given to the case where this matrixhas only rank 1, where the multiparametric linear program turnsout to be a single-parameter linear program. An extension ofthe traditional linear parametric procedure is introduced whichin general solves this problem efficiently. However, an exampleis presented showing that this technique may take an exponentialnumber of steps. 相似文献