全文获取类型
收费全文 | 345442篇 |
免费 | 4231篇 |
国内免费 | 1192篇 |
专业分类
化学 | 165122篇 |
晶体学 | 4869篇 |
力学 | 18498篇 |
综合类 | 1篇 |
数学 | 62282篇 |
物理学 | 100093篇 |
出版年
2021年 | 2010篇 |
2020年 | 2369篇 |
2019年 | 2604篇 |
2018年 | 13363篇 |
2017年 | 12989篇 |
2016年 | 10901篇 |
2015年 | 4356篇 |
2014年 | 5403篇 |
2013年 | 12789篇 |
2012年 | 13918篇 |
2011年 | 22041篇 |
2010年 | 13690篇 |
2009年 | 13698篇 |
2008年 | 17277篇 |
2007年 | 19336篇 |
2006年 | 10647篇 |
2005年 | 10812篇 |
2004年 | 10139篇 |
2003年 | 9416篇 |
2002年 | 8245篇 |
2001年 | 7920篇 |
2000年 | 6149篇 |
1999年 | 4749篇 |
1998年 | 4039篇 |
1997年 | 3874篇 |
1996年 | 3867篇 |
1995年 | 3363篇 |
1994年 | 3317篇 |
1993年 | 3418篇 |
1992年 | 3520篇 |
1991年 | 3647篇 |
1990年 | 3387篇 |
1989年 | 3350篇 |
1988年 | 3331篇 |
1987年 | 3218篇 |
1986年 | 3027篇 |
1985年 | 4154篇 |
1984年 | 4321篇 |
1983年 | 3419篇 |
1982年 | 3715篇 |
1981年 | 3617篇 |
1980年 | 3500篇 |
1979年 | 3589篇 |
1978年 | 3666篇 |
1977年 | 3545篇 |
1976年 | 3677篇 |
1975年 | 3339篇 |
1974年 | 3357篇 |
1973年 | 3375篇 |
1972年 | 2316篇 |
排序方式: 共有10000条查询结果,搜索用时 437 毫秒
991.
Combining layered positional order as smectic order and chirality can generate complex architectures since twist parallel
to the layers is not allowed. This paper will review some new experimental results on different phases resulting from the
competition between smectic positional order and twist orientational order. It concerns the TGBA and the NL*, that is the liquid line phase as well as the SmQ phase. Chiral effects in the isotropic phase will also be discussed. 相似文献
992.
CuPc molecules adsorbed on Au(1 1 0)-(1 × 2): growth morphology and evolution of valence band states
Fabrizio Evangelista A. RuoccoValdis Corradini M.P. DonzelloCarlo Mariani Maria Grazia Betti 《Surface science》2003,531(2):123-130
We present the growth morphology, the long-range ordering, and the evolution of the valence band electronic states of ultrathin films of copper phthalocyanine (CuPc) deposited on the Au(1 1 0)-(1 × 2) reconstructed surface, as a function of the organic molecule coverage. The low energy electron diffraction patterns present a (5 × 3) reconstruction from the early adsorption stages. High-resolution UV photoelectron spectroscopy data show the disappearance of the Au surface states related to the (1 × 2) reconstruction, and the presence of new electronic features related to the molecule-substrate interaction and to the CuPc molecular states. The CuPc highest occupied molecular orbital gradually emerges in the valence band, while the interface electronic states are quenched, upon increasing the coverage. 相似文献
993.
I. Antoniou M. Gadella J. Mateo G.P. Pronko 《International Journal of Theoretical Physics》2003,42(10):2389-2402
Through two examples: the Friedrichs model and a particular case of central potential scattering, we illustrate the way of constructing Gamow vectors. 相似文献
994.
Z. A. Samoilenko V. D. Okunev E. I. Pushenko T. A. D’yachenko A. Cherenkov P. Gierlowski S. J. Lewandowski A. Abal’oshev A. Klimov A. Szewczyk 《Technical Physics》2003,48(2):250-256
Crystallographic phase transitions in perovskite-like LaSrMnO metallic oxides are studied. The transitions are induced when
internal stresses generated during film synthesis (at temperatures between 450 and 730°C) vary (decrease or increase) upon
subsequent irradiation by a KrF laser emitting in the UV range. As the synthesis temperature T
s grows, the rhombohedral-to-orthorhombic phase transition occurs at 650–670°C. The resistivity is shown to be either temperature-independent,
ρ(T)=const, at T<T
crit, or varies and reaches a maximum, ρ(T)=ρmax, at the Curie temperature T
c. Optical transmission spectra taken at photon energies ℏω=0.5–2.5 eV exhibit both a high (0.8–0.9) and low (0.1–0.3) transmission
coefficient t, depending on the synthesis temperature. As follows from X-ray diffraction data, the laser irradiation causes a phase transition
only in LaSrMnO films grown at T
s<650°C. Phases of different size scales appear: the long-range-order orthorhombic matrix and mesoscopic-range-order rhombohedral
clusters are observed in the films grown at T
s=450–550°C and the rhombohedral matrix with orthorhombic clusters, in the films grown at T
s=550–650°C. 相似文献
995.
P. Mun F. C. Fonseca R. Muccillo R. F. Jardim 《Physica C: Superconductivity and its Applications》2003,390(4):363-373
A systematic study of the magnetic hysteresis in transport properties of polycrystalline YBa2Cu3O7−δ–Ag compounds has been made based on two kinds of measurements at 77 K and under applied magnetic fields up to 30 mT: critical current density Jc(Ba) and magnetoresistance R(Ba). The R(Ba) curves show a minimum in their decreasing branch occurring at B=Bmin which was found to be both the excitation current Iex and the maximum applied magnetic field Bam dependent. In addition, for a certain value of Bam>5 mT, we have observed that Bmin increases with increasing Iex and reaches a saturation value. The Jc(Ba) curves show a maximum in decreasing applied magnetic fields occurring at B=Bmax. We have also found that Bmax increases with increasing Bam and reaches a saturation value. The minimum in the R(Ba) and the maximum in Jc(Ba) curves were found to be related to the trapped flux within the grains. All the experimental results are discussed within the context of the flux dynamics and transport mechanisms in these high-Tc materials. 相似文献
996.
Komarov A. V. Yakovlev I. P. Novikov D. V. Semakova T. L. Zakhs V. E. 《Russian Journal of General Chemistry》2003,73(11):1806-1809
Methylmalonyl dichloride reacts with (2E)-3-phenylacrylamides and (2E)-3-(2-furyl)acrylamide to give the corresponding E-isomeric 2-substituted 4-hydroxy-5-methyl-6H-1,3-oxazin-6-ones. The reaction of methylmalonyl dichloride with acrylamide afforded N-(3-chloropropionyl)-2-methylmalonamic acid. The structure of the products was confirmed by the 1H and 13C NMR, IR, and UV spectra. 相似文献
997.
Given a map f: X→Y and a Nielsen root class, there is a number associated to this root class, which is the minimal number of points among all
root classes which are H-related to the given one for all homotopies H of the map f. We show that for maps between closed surfaces it is possible to deform f such that all the Nielsen root classes have cardinality equal to the minimal number if and only if either N R[f]≤1, or N R[f]>1 and f satisfies the Wecken property. Here N R[f] denotes the Nielsen root number. The condition “f satisfies the Wecken property is known to be equivalent to |deg(f)|≤N R[f]/(1−χ(M
2)−χ(M
10/(1−χ(M
2)) for maps between closed orientable surfaces. In the case of nonorientable surfaces the condition is A(f)≤N R[f]/(1−χ(M
2)−χ(M
2)/(1−χ(M
2)). Also we construct, for each integer n≥3, an example of a map f: K
n
→N from an n-dimensionally connected complex of dimension n to an n-dimensional manifold such that we cannot deform f in a way that all the Nielsen root classes reach the minimal number of points at the same time. 相似文献
998.
999.
L. Villa P. D' Agati C. Mansueto C. Pellerito M. Scopelliti T. Fiore L. Nagy L. Pellerito 《应用有机金属化学》2003,17(2):106-112
Ascidia malaca gametes before fertilization incubated in 10?5 or 10?7 M solutions of tributyltin(IV) chloride, TBTCl, for 3 h appear highly damaged under transmission electron microscopy observation. Also, the fertilization process is affected by the compound: the damaged spermatozoa are present in the vitelline coat and the egg does not cleave. An increase of microbodies, structurally similar to peroxisomes, have been detected in the egg peripheral cytoplasm, probably in relation to their role in alleviating damage to some cellular components. The results have shown that the reproduction of ascidians under unfavourable environmental conditions is prevented. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
1000.
A short and efficient RCM route is reported for the construction of the key nine-membered B ring of eleutherobin starting from the readily available 1,2,5,6-diisopropylidene-d-glucose. 相似文献