全文获取类型
收费全文 | 1978篇 |
免费 | 65篇 |
国内免费 | 11篇 |
专业分类
化学 | 1212篇 |
晶体学 | 15篇 |
力学 | 45篇 |
数学 | 439篇 |
物理学 | 343篇 |
出版年
2020年 | 20篇 |
2019年 | 22篇 |
2018年 | 15篇 |
2017年 | 16篇 |
2016年 | 38篇 |
2015年 | 40篇 |
2014年 | 39篇 |
2013年 | 102篇 |
2012年 | 87篇 |
2011年 | 107篇 |
2010年 | 57篇 |
2009年 | 47篇 |
2008年 | 91篇 |
2007年 | 84篇 |
2006年 | 102篇 |
2005年 | 98篇 |
2004年 | 75篇 |
2003年 | 76篇 |
2002年 | 92篇 |
2001年 | 27篇 |
2000年 | 37篇 |
1999年 | 30篇 |
1998年 | 31篇 |
1997年 | 33篇 |
1996年 | 28篇 |
1995年 | 15篇 |
1994年 | 32篇 |
1993年 | 28篇 |
1992年 | 25篇 |
1991年 | 23篇 |
1990年 | 20篇 |
1989年 | 18篇 |
1988年 | 14篇 |
1987年 | 19篇 |
1986年 | 21篇 |
1985年 | 22篇 |
1984年 | 30篇 |
1983年 | 22篇 |
1982年 | 31篇 |
1981年 | 35篇 |
1980年 | 29篇 |
1979年 | 27篇 |
1978年 | 31篇 |
1977年 | 26篇 |
1976年 | 20篇 |
1975年 | 17篇 |
1974年 | 21篇 |
1973年 | 19篇 |
1972年 | 14篇 |
1971年 | 13篇 |
排序方式: 共有2054条查询结果,搜索用时 46 毫秒
941.
Abbas‐Ali Shaik Martin Richter Hans R. Kricheldorf Ralph‐P. Krüger 《Journal of polymer science. Part A, Polymer chemistry》2001,39(19):3371-3382
Copolyesters with an alternating sequence of terephthalic acid and aliphatic dicarboxylic acids were prepared with three different methods. First, dicarboxylic acid dichlorides were reacted with bis(2‐hydroxyethyl)terephthalate (BHET) in refluxing 1,2‐dichlorobenzene. Second, the same monomers were polycondensed at 0–20 °C in the presence of pyridine. Third, dicarboxylic acid dichlorides and silylated BHET were polycondensed in bulk. Only this third method gave satisfactory molecular weights. Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry revealed that the copolyesters prepared by the pyridine and silyl methods might have contained considerable fractions of cyclic oligoesters and polyesters despite the absence of transesterification and backbiting processes. The alternating sequences and thermal properties were characterized with 1H NMR spectroscopy and differential scanning calorimetry measurements, respectively. In agreement with the alternating sequence, all copolyesters proved to be crystalline, but the crystallization was extremely slow [slower than that of poly(ethylene terephthalate)]. A second series of alternating copolyesters was prepared by the polycondensation of silylated bis(4‐hydroxybut‐ yl)terephthalate with various aliphatic dicarboxylic acid dichlorides. The resulting copolyesters showed significantly higher rates of crystallization, and the melting temperatures were higher than those of the BHET‐based copolyesters. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3371–3382, 2001 相似文献
942.
Using inequality techniques and coincidence degree theory, new results are provided concerning the existence and uniqueness of T-periodic solutions for a Liénard equations with delay. An illustrative example is provided to demonstrate that the results in this paper hold under weaker conditions than existing results, and are more effective. 相似文献
943.
Christian Hecht Nadine van der Schoot Helmut Kronemayer Irenaeus Wlokas Ralph Lindken Christof Schulz 《Experiments in fluids》2012,52(3):743-748
Main components of proton exchange membrane fuel cells are bipolar plates that electrically connect the electrodes and provide
a gas flow to the membrane. We investigate the flow in the channel structures of bipolar plates. Flow seeding is used to visualize
the propagating and mixing gas stream. It is shown that a part of the gas is transported perpendicularly to the channel structure.
An analysis of the diffusion compared with the convection shows different transport behavior for both flow directions. Additionally,
the convective flow field is investigated in detail near the channel wall using Micro-PIV in a Reynolds-number-scaled liquid
fluid system. For a more exact comparison of the experimental setups, flow seeding in both gas and liquid systems is performed. 相似文献
944.
David G. Costa Hossein Tehrani Ralph Thomas 《Journal of Mathematical Analysis and Applications》2012,391(1):170-182
In this paper we consider a class of logistic-type problems for the p-Laplacian in the whole space. Using minimization we prove existence of a positive solution and its behavior at infinity. We also consider questions of uniqueness and sharp estimates at infinity. 相似文献
945.
946.
We report an electrochemical impedance spectroscopy (EIS) based method to measure the doping level of conducting polymers. Using EIS the Faradaic current and the capacitive charging current can be separated without relying on any unverifiable assumptions. We demonstrate the method for three types of conducting polymer thin films that are the basis for many commercial applications (poly(3,4-ethylenedioxythiophene), poly-3-hexylthiophene and polypyrrole). 相似文献
947.
Berta Holló Zoran D. Tomić Péter Pogány Attila Kovács Vukadin M. Leovac Katalin Mészáros Szécsényi 《Polyhedron》2009,28(17):3881-3889
The complex formation of 3,5-dimethylpyrazole-1-carboxamidinium nitrate, HL·HNO3 with ammine complexes of cadmium(II) halides (Cl, Br, I) and zinc(II) chloride has been investigated under self-controlled reaction conditions. The complexes have been characterized by X-ray diffraction, FT-IR spectroscopy, thermal analysis and quantum chemical calculations. In the case of cadmium bromide and iodide salts, isostructural complexes with composition of [CdX2(HL)2] were formed. With CdCl2 a binuclear octahedral [Cd2(HL)4(μ-Cl)2](NO3)2 complex is obtained. Zinc(II) chloride with HL·HNO3 gives [Zn(HL)2Cl]NO3, the zinc center exhibiting severely distorted five-coordinate stereochemistry, intermediate between an ideal trigonal bipyramid and a square pyramid. The course of complex formation as well as the thermal properties of the compounds has been explained using the HSAB principle. The assignment of the FT-IR spectra was supported by DFT computations. 相似文献
948.
949.
950.
Forest fire is a burn model for reactive hydro simulations that is widely used to describe both initiation and propagation of detonation waves in solid high explosives. Here we thoroughly review the assumptions of the model. In analogy with Whitham–Chisnell shock dynamics, we derive the Forest fire rate based on a characteristic analysis of a shock-to-detonation transition. Code issues with implementing the Forest fire model are also discussed. The analysis leading to the Forest fire rate is more general than the simplifying assumptions used by the model. The Forest fire analysis provides important constraints needed for any burn model to fit shock initiation data. This data is fundamental to ignition sensitivity of high explosives. 相似文献