全文获取类型
收费全文 | 2643篇 |
免费 | 78篇 |
国内免费 | 10篇 |
专业分类
化学 | 1913篇 |
晶体学 | 7篇 |
力学 | 28篇 |
数学 | 444篇 |
物理学 | 339篇 |
出版年
2021年 | 20篇 |
2020年 | 41篇 |
2019年 | 44篇 |
2018年 | 21篇 |
2016年 | 62篇 |
2015年 | 63篇 |
2014年 | 76篇 |
2013年 | 92篇 |
2012年 | 123篇 |
2011年 | 137篇 |
2010年 | 89篇 |
2009年 | 61篇 |
2008年 | 100篇 |
2007年 | 127篇 |
2006年 | 133篇 |
2005年 | 119篇 |
2004年 | 82篇 |
2003年 | 75篇 |
2002年 | 84篇 |
2001年 | 56篇 |
2000年 | 37篇 |
1999年 | 43篇 |
1998年 | 40篇 |
1997年 | 28篇 |
1996年 | 25篇 |
1995年 | 32篇 |
1994年 | 34篇 |
1993年 | 30篇 |
1992年 | 45篇 |
1991年 | 26篇 |
1990年 | 27篇 |
1989年 | 30篇 |
1988年 | 36篇 |
1987年 | 39篇 |
1986年 | 31篇 |
1985年 | 43篇 |
1984年 | 33篇 |
1983年 | 22篇 |
1982年 | 24篇 |
1981年 | 31篇 |
1980年 | 33篇 |
1979年 | 23篇 |
1978年 | 30篇 |
1977年 | 25篇 |
1976年 | 28篇 |
1975年 | 32篇 |
1974年 | 34篇 |
1973年 | 32篇 |
1972年 | 17篇 |
1971年 | 20篇 |
排序方式: 共有2731条查询结果,搜索用时 0 毫秒
101.
Dr. Jindong Ren Dr. Henning Klaasen Melanie C. Witteler Lena Viergutz Prof. Dr. Johannes Neugebauer Dr. Hong-Ying Gao Prof. Dr. Armido Studer Prof. Dr. Harald Fuchs 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(70):16727-16732
The reactivity of aryl triflates in on-surface C−C coupling is reported. It is shown that the triflate group in aryl triflates enables regioselective homo coupling with preceding or concomitant hydrodetriflation on Cu(111). Three different symmetrical π-systems with two and three triflate functionalities were used as monomers leading to oligomeric conjugated π-systems. The cascade, comprising different intermediates at different reaction temperatures as observed for one of the molecules, proceeds via initial removal of the trifluoromethyl sulfonyl group to give an aryloxy radical which in turn is deoxygenated to the corresponding aryl radical. Thermodynamically driven regioselective 1,2-hydrogen atom transfer leads to a translocated aryl radical which in turn undergoes coupling. For a sterically more hindered bistriflate, where one ortho position was blocked, dehydrogenative coupling occurred at remote position with good regioselectivity. Starting materials, intermediates as well as products were analyzed by scanning tunneling microscopy. Structures and suggested mechanism were further supported by DFT calculations. 相似文献
102.
The lattice profile analyzes the intrinsic structure of pseudorandom number sequences with applications in Monte Carlo methods and cryptology. In this paper, using the discrete Fourier transform for periodic sequences and the relation between the lattice profile and the linear complexity, we give general formulas for the expected value, variance, and counting function of the lattice profile of periodic sequences with fixed period. Moreover, we determine in a more explicit form the expected value, variance, and counting function of the lattice profile of periodic sequences for special values of the period. 相似文献
103.
Harald Biller 《Transactions of the American Mathematical Society》2003,355(1):407-432
Essential results about actions of compact Lie groups on connected manifolds are generalized to proper actions of arbitrary groups on connected cohomology manifolds. Slices are replaced by certain fiber bundle structures on orbit neighborhoods. The group dimension is shown to be effectively finite. The orbits of maximal dimension form a dense open connected subset. If some orbit has codimension at most , then the group is effectively a Lie group.
104.
Grigory Bordyugov Nils Fischer Harald Engel Oliver Steinbock 《Physica D: Nonlinear Phenomena》2010,239(11):766-4694
We report results on dispersion relations and instabilities of traveling waves in excitable systems. Experiments employ solutions of the 1,4-cyclohexanedione Belousov-Zhabotinsky reaction confined to thin capillary tubes which create a pseudo-one-dimensional system. Theoretical analyses focus on a three-variable reaction-diffusion model that is known to reproduce qualitatively many of the experimentally observed dynamics. Using continuation methods, we show that the transition from normal, monotonic to anomalous, single-overshoot dispersion curves is due to an orbit flip bifurcation of the solitary pulse homoclinics. In the case of “wave stacking”, this anomaly induces attractive pulse interaction, slow solitary pulses, and faster wave trains. For “wave merging”, wave trains break up in the wake of the slow solitary pulse due to an instability of wave trains at small wavelength. A third case, “wave tracking” is characterized by the non-existence of solitary waves but existence of periodic wave trains. The corresponding dispersion curve is a closed curve covering a finite band of wavelengths. 相似文献
105.
Let Σn be the symmetric group on n letters. For l ≤ n identify Σl with a subgroup of Σn in the natural way. Let k be an algebraically closed field of characteristic p. This article begins to develop a theory for modules over the centralizer algebras kΣnΣl that is analogous to James's theory of permutation modules, Specht modules, and simple modules over kΣn. We make a conjecture about how to construct all simple kΣnΣl-modules, we develop tools to test the conjecture, and we prove that it is correct for all n when l < p. 相似文献
106.
George Hohlneicher Harald Pulm Hans-Joachim Freund 《Journal of Electron Spectroscopy and Related Phenomena》1985,37(2):209-224
First, we show that the quantity Δβ(i) = ΔEA(kii) + 2ΔEB(i) — ΔEB(k) is directly related to the final state relaxation contribution ΔER(i) of the binding energy shift ΔEB(i). ΔEA(kii) is the kinetic energy shift of the Auger transition which corresponds to the decay of a hole state with a hole in level k into a final state with two holes in level i. The shift parameter Δβ(i), which is based on information on two binding energies, is conceptually similar to Wagner's Auger parameter. To establish the relation between Δβ(i) and ΔR(i) one needs, however, less drastic approximations than in the case of Auger parameter shifts. The only approximation necessary is the assumption that ΔR(i) is determined by coulomb contributions.Secondly, we use Δβ (i) to analyse the experimental data of eighteen gaseous phosphorus-containing compounds obtained by Sodhi and Cavell1. It is shown that ΔR(P2p) is strongly related to changes in the polarizability of the ligands. The initial state effects derived from our study deviate from those expected on the basis of simple electronegativity considerations. 相似文献
107.
We study quartic matrix models with partition function \({\mathcal{Z}[E, J] = \int dM}\) exp(trace \({(JM - EM^{2} - \frac{\lambda}{4} M^4)}\) ). The integral is over the space of Hermitean \({\mathcal{N} \times \mathcal{N}}\) -matrices, the external matrix E encodes the dynamics, \({\lambda > 0}\) is a scalar coupling constant and the matrix J is used to generate correlation functions. For E not a multiple of the identity matrix, we prove a universal algebraic recursion formula which gives all higher correlation functions in terms of the 2-point function and the distinct eigenvalues of E. The 2-point function itself satisfies a closed non-linear equation which must be solved case by case for given E. These results imply that if the 2-point function of a quartic matrix model is renormalisable by mass and wavefunction renormalisation, then the entire model is renormalisable and has vanishing β-function. As the main application we prove that Euclidean \({\phi^4}\) -quantum field theory on four-dimensional Moyal space with harmonic propagation, taken at its self-duality point and in the infinite volume limit, is exactly solvable and non-trivial. This model is a quartic matrix model, where E has for \({\mathcal{N} \to \infty}\) the same spectrum as the Laplace operator in four dimensions. Using the theory of singular integral equations of Carleman type we compute (for \({\mathcal{N} \to \infty}\) and after renormalisation of \({E, \lambda}\) ) the free energy density (1/volume) log \({(\mathcal{Z}[E, J]/\mathcal{Z}[E, 0])}\) exactly in terms of the solution of a non-linear integral equation. Existence of a solution is proved via the Schauder fixed point theorem. The derivation of the non-linear integral equation relies on an assumption which in subsequent work is verified for coupling constants \({\lambda \leq 0}\) . 相似文献
108.
In Baak et al. (J Math Anal Appl 314(1):150–161, 2006) the authors considered the functional equation where \(d,\ell \in \mathbb {N}\), \(1<\ell <d/2\) and \(r\in \mathbb {Q}{\setminus }\{0\}\). The authors determined all odd solutions \(f:X\rightarrow Y\) for vector spaces X, Y over \(\mathbb {Q}\). In Oubbi (Can Math Bull 60:173–183, 2017) the author considered the same equation but now for arbitrary real \(r\not =0\) and real vector spaces X, Y. Generalizing similar results from (J Math Anal Appl 314(1):150–161, 2006) he additionally investigates certain stability questions for the equation above, but as for that equation itself for odd approximate solutions only. The present paper deals with the general solution of the equation and the corresponding stability inequality. In particular it is shown that under certain circumstances non-odd solutions of the equation exist.
相似文献
$$\begin{aligned} r f\left( \frac{1}{r}\,\sum _{j=1}^{d}x_j\right)+ & {} \sum _{i(j)\in \{0,1\} \atop \sum _{1\le j\le d} i(j)=\ell }r f\left( \frac{1}{r}\,\sum _{j=1}^d (-1)^{i(j)}x_j\right) \\= & {} \left( {d-1\atopwithdelims ()\ell }-{d-1\atopwithdelims ()\ell -1} +1\right) \sum _{j=1}^{d} f(x_j) \end{aligned}$$
109.
Illarion Dorofeyev Harald Fuchs Katja Sobakinskaya 《Central European Journal of Physics》2005,3(3):351-375
Spectral characteristics of stochastic fields and their spatial derivatives in various planar structures composed by lossy
materials described by realistic dielectric functions are numerically calculated based on solutions to the problems of multipolar
electromagnetic fields in a plane layered geometry. A displacement of the maximum of the spectral power densities for spatial
derivatives of fluctuating fields to the high-frequency domain, a resonant increase in the density of states of the fluctuating
fields at the frequencies of interface excitations and interference modes for the radiative part of the spectra, the influence
of geometry on the density of states, and other peculiarities are found by numerical calculations and graphically demonstrated.
Interpretations of the above effects are provided. 相似文献
110.
For any prime power q and any dimension s≥1, a new construction of (t, s)-sequences in base q using global function fields is presented. The construction yields an analog of Halton sequences for global function fields. It is the first general construction of (t, s)-sequences that is not directly based on the digital method. The construction can also be put into the framework of the theory of (u, e, s)-sequences that was recently introduced by Tezuka and leads in this way to better discrepancy bounds for the constructed sequences. 相似文献