全文获取类型
收费全文 | 4912篇 |
免费 | 192篇 |
国内免费 | 32篇 |
专业分类
化学 | 3556篇 |
晶体学 | 28篇 |
力学 | 140篇 |
数学 | 620篇 |
物理学 | 792篇 |
出版年
2023年 | 43篇 |
2022年 | 57篇 |
2021年 | 84篇 |
2020年 | 110篇 |
2019年 | 111篇 |
2018年 | 74篇 |
2017年 | 62篇 |
2016年 | 147篇 |
2015年 | 129篇 |
2014年 | 168篇 |
2013年 | 249篇 |
2012年 | 318篇 |
2011年 | 389篇 |
2010年 | 176篇 |
2009年 | 133篇 |
2008年 | 339篇 |
2007年 | 350篇 |
2006年 | 325篇 |
2005年 | 278篇 |
2004年 | 236篇 |
2003年 | 218篇 |
2002年 | 170篇 |
2001年 | 48篇 |
2000年 | 48篇 |
1999年 | 40篇 |
1998年 | 40篇 |
1997年 | 54篇 |
1996年 | 61篇 |
1995年 | 39篇 |
1994年 | 36篇 |
1993年 | 32篇 |
1992年 | 25篇 |
1991年 | 42篇 |
1990年 | 42篇 |
1989年 | 28篇 |
1988年 | 22篇 |
1987年 | 21篇 |
1986年 | 13篇 |
1985年 | 38篇 |
1984年 | 42篇 |
1983年 | 17篇 |
1982年 | 19篇 |
1981年 | 30篇 |
1980年 | 28篇 |
1979年 | 19篇 |
1978年 | 28篇 |
1977年 | 21篇 |
1976年 | 17篇 |
1975年 | 13篇 |
1974年 | 16篇 |
排序方式: 共有5136条查询结果,搜索用时 15 毫秒
71.
Kevin Prince 《Synchrotron Radiation News》2015,28(3)
Anew initiative to facilitate interdisciplinary research on advanced materials, biomaterials, and nanotechnology has begun operation in Europe. CERIC, the Central European Research Infrastructure Consortium, is a partnership between two synchrotrons and seven other advanced, user-based research centers, each in a different country participating in the consortium (see Figure 1). 相似文献
72.
Duygu Avci Lon J. Mathias Kevin Thigpen 《Journal of polymer science. Part A, Polymer chemistry》1996,34(15):3191-3201
Several new benzoate ester derivatives of ethyl α-hydroxymethylacrylate were synthesized using phase transfer catalysis and found to display unexpectedly rapid photopolymerization; i.e., from 2 to 8 times faster than MMA. New derivatives described here include the 4-fluoro-, 4-trifluoromethyl-, 4-methyl-, 2-hydroxy-, 4-nitro-, 4-methoxy-, 4-cyano-, and 3,4,5-trimethoxybenzoate esters along with the parent benzoate ester. Relative reactivities of these monomers in photopolymerizations were compared with those of the nonaromatic formate, acetate, hexanoate, and stearate derivatives. Reactivities of the nonaromatic ester derivatives increased with the length of the side chain while for the more reactive aromatic esters, rates increased in the order 4-methyl-, 4-fluoro- and benzoate < 4-trifluoromethyl- and 2-hydroxy- < 4-cyano- < 4-methoxy- < 3,4,5-trimethoxybenzoate. Tgs of the benzoate polymers ranged from 125°C for the 4-fluoro to 163°C for the 4-cyanobenzoate while those of the alkyl ester derivatives ranged from 15 to 78°C. Number average molecular weights of photoinitiated polymers (ca 10,000–20,000) were lower than those found for bulk and solution polymers (20,000—708,000) consistent with higher radical concentrations from photoinitiation. These materials greatly expand the number of candidates available for rapid photocure in thin film and coating applications, especially because their physical properties are those of linear rather than highly crosslinked structures formed from multifunctional systems. © 1996 John Wiley & Sons, Inc. 相似文献
73.
If G is a graph on n vertices and r ≥ 2, we let mr(G) denote the minimum number of complete multipartite subgraphs, with r or fewer parts, needed to partition the edge set, E(G). In determining mr(G), we may assume that no two vertices of G have the same neighbor set. For such reducedgraphs G, we prove that mr(G) ≥ log2 (n + r − 1)/r. Furthermore, for each k ≥ 0 and r ≥ 2, there is a unique reduced graph G = G(r, k) with mr(G) = k for which equality holds. We conclude with a short proof of the known eigenvalue bound mr(G) ≥ max{n+ (G, n−(G)/(r − 1)}, and show that equality holds if G = G(r, k). © 1996 John Wiley & Sons, Inc. 相似文献
74.
75.
Friction force microscopy of alkylphosphonic acid and carboxylic acids adsorbed on the native oxide of aluminum 总被引:1,自引:0,他引:1
Foster TT Alexander MR Leggett GJ McAlpine E 《Langmuir : the ACS journal of surfaces and colloids》2006,22(22):9254-9259
Monolayers of alkylphosphonic acids (APA) and alkylcarboxylic acids (ACA) on magnetron-sputtered aluminum films have been investigated by friction force microscopy (FFM), contact angle measurement, and polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS). Clear evidence has been provided from PM-IRRAS that friction coefficients, determined from FFM data, may be correlated directly with variations in adsorbate molecular structure. The friction coefficient increased with the length of the adsorbate molecule, but reached a limiting value when the alkyl chain of the adsorbate contained eight carbons in the case of APA or 12 carbons in the case of ACA. For a given alkyl chain length, APA monolayers yielded coefficients of friction that were similar to those of monolayers of alkylthiols of the same length, but smaller than those of ACA. These data indicate that APA monolayers are better ordered than ACA monolayers. These inferences were supported by PM-IRRAS data, which enabled the density of gauche defects to be estimated and correlated with variations in the coefficient of friction. 相似文献
76.
Ana Isabel González Flórez Eike Mucha Dr. Doo‐Sik Ahn Sandy Gewinner Dr. Wieland Schöllkopf Prof. Dr. Kevin Pagel Dr. Gert von Helden 《Angewandte Chemie (International ed. in English)》2016,55(10):3295-3299
Here we present a combined experimental and theoretical study on the secondary structure of isolated proteins as a function of charge state. In infrared spectra of the proteins ubiquitin and cytochrome c, amide I (C=O stretch) and amide II (N–H bend) bands can be found at positions that are typical for condensed‐phase proteins. For high charge states a new band appears, substantially red‐shifted from the amide II band observed at lower charge states. The observations are interpreted in terms of Coulomb‐driven transitions in secondary structures from mostly helical to extended C5‐type hydrogen‐bonded structures. Support for this interpretation comes from simple energy considerations as well as from quantum chemical calculations on model peptides. This transition in secondary structure is most likely universal for isolated proteins that occur in mass spectrometric experiments. 相似文献
77.
78.
We present experimental evidence for the spontaneous formation of a macroscopic spin polarization in overlapping regions of two independent Bose-Einstein condensates produced in different hyperfine states of 87Rb. The condensates are independent in the sense that we do not explicitly introduce a relative phase between them. A single "spin-tip" pulse maps the transverse spin polarization into longitudinal spin polarization, and the atomic density distributions are measured with a Stern-Gerlach imaging method. The resulting matter-wave interference patterns are anticorrelated. 相似文献
79.
Dilute gas Bose-Einstein condensates (BEC's), currently used to cool fermionic atoms in atom traps, can also probe the superfluidity of these fermions. The damping rate of BEC-acoustic excitations (phonon modes), measured in the middle of the trap as a function of the phonon momentum, yields an unambiguous signature of BCS-like superfluidity, provides a measurement of the superfluid gap parameter, and gives an estimate of the size of the Cooper pairs in the BEC-BCS crossover regime. We also predict kinks in the momentum dependence of the damping rate which can reveal detailed information about the fermion quasiparticle dispersion relation. 相似文献
80.
We report the observation of enhanced near-infrared transmission through arrays of subwavelength coaxial metallic structures compared with that through comparable diameter hole arrays as a result of localized electromagnetic modes supported by the complex coaxial unit cell. Polarization and angle-dependent transmission measurements clearly demonstrate the coupling between this localized mode and delocalized surface plasmon modes. A generalized, multiple discrete states Fano line shape provides a good fit to the experimental results. 相似文献