全文获取类型
收费全文 | 28914篇 |
免费 | 119篇 |
国内免费 | 270篇 |
专业分类
化学 | 10522篇 |
晶体学 | 266篇 |
力学 | 1380篇 |
综合类 | 13篇 |
数学 | 9015篇 |
物理学 | 8107篇 |
出版年
2021年 | 28篇 |
2018年 | 1193篇 |
2017年 | 1451篇 |
2016年 | 712篇 |
2015年 | 563篇 |
2014年 | 474篇 |
2013年 | 664篇 |
2012年 | 3118篇 |
2011年 | 2303篇 |
2010年 | 1804篇 |
2009年 | 1550篇 |
2008年 | 554篇 |
2007年 | 602篇 |
2006年 | 595篇 |
2005年 | 4422篇 |
2004年 | 3910篇 |
2003年 | 2295篇 |
2002年 | 492篇 |
2001年 | 294篇 |
2000年 | 99篇 |
1999年 | 172篇 |
1998年 | 109篇 |
1997年 | 70篇 |
1996年 | 46篇 |
1995年 | 42篇 |
1994年 | 44篇 |
1992年 | 172篇 |
1991年 | 156篇 |
1990年 | 139篇 |
1989年 | 109篇 |
1988年 | 102篇 |
1987年 | 60篇 |
1986年 | 45篇 |
1985年 | 39篇 |
1984年 | 31篇 |
1983年 | 30篇 |
1979年 | 34篇 |
1978年 | 25篇 |
1976年 | 80篇 |
1975年 | 38篇 |
1974年 | 43篇 |
1973年 | 52篇 |
1972年 | 39篇 |
1971年 | 25篇 |
1970年 | 38篇 |
1969年 | 37篇 |
1968年 | 36篇 |
1967年 | 31篇 |
1966年 | 38篇 |
1923年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
991.
Linfeng?YangEmail author Jiangwei?Chen Huatong?Yang Jinming?Dong 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,43(3):399-403
We have calculated the quantum conductance of single-walled
carbon nanotube (SWNT) waveguide by using a tight binding-based
Greens function approach. Our calculations show that the slow
conductance oscillations as well as the fast conductance
oscillations are manifestations of the intrinsic quantum
interference properties of the conducting SWNTs, being independent
of the defect and disorder of the SWNTs. And zigzag type tubes do
not show the slow oscillations. The SWNT electron waveguide is
also found to have distinctly different transport behavior
depending on whether or not the length of the tube is commensurate
with a (3N+1) rule, with N the number of basic carbon repeat
units along the nanotube length. 相似文献
992.
Bo?Feng Sarada?Bulchand Emre?Yaksi Rainer?W?Friedrich Suresh?JesuthasanEmail author 《BMC neuroscience》2005,6(1):46
Background
Rag1 (Recombination activation gene-1) mediates genomic rearrangement and is essential for adaptive immunity in vertebrates. This gene is also expressed in the olfactory epithelium, but its function there is unknown. 相似文献993.
Background
Autosomal recessive juvenile parkinsonism (AR-JP) is caused by mutations in the parkin gene which encodes an E3 ubiquitin-protein ligase. Parkin is thought to be critical for protecting dopaminergic neurons from toxic insults by targeting misfolded or oxidatively damaged proteins for proteasomal degradation. Surprisingly, mice with targeted deletions of parkin do not recapitulate robust behavioral or pathological signs of parkinsonism. Since Parkin is thought to protect against neurotoxic insults, we hypothesized that the reason Parkin-deficient mice do not develop parkinsonism is because they are not exposed to appropriate environmental triggers. To test this possibility, we challenged Parkin-deficient mice with neurotoxic regimens of either methamphetamine (METH) or 6-hydroxydopamine (6-OHDA). Because Parkin function has been linked to many of the pathways involved in METH and 6-OHDA toxicity, we predicted that Parkin-deficient mice would be more sensitive to the neurotoxic effects of these agents. 相似文献994.
E. ?ernošková T. Qu Z. ?ernošek P. Boolchand 《Journal of Physics and Chemistry of Solids》2005,66(1):185-189
Thermoanalytical characteristics and Raman scattering of high purity sulfur and ternary bulk glasses GexAsxS(100−2x) for x=4-22 at. % were studied. The intermediate phase characterized by vanishing of non-reversing heat flow ΔHnr, i.e. so-called the thermally reversing window was found between mean coordination number 〈r〉∼2.28-2.47. Separated phase of non-crystalline cycloocta-S, manifesting itself by λ-transition at ∼155 °C, was found for glasses with sulfur content higher than ∼80 at.%. Raman spectra of studied Ge-As-S glasses showed different shapes in three different areas according to three distinct phases of network glasses-floppy, intermediate, rigid. 相似文献
995.
We have explored the opportunities for enhanced ratiometric pH sensing using the well-known carboxy seminaphthofluorescein (SNAFL-2) and silver island films (SiFs). Our results show that the metallic surfaces can provide up to a 40-fold increase in probe fluorescence intensity as compared to nonmetallic surfaces with the same probe coverage. However, while the S/N is significantly better for pH sensing, the emission wavelength ratiometric values are similar to that obtained in solution, due to the fact that the emission of both the acidic and basic forms of the probe are enhanced to similar extents. To the best of our knowledge this is the first report of enhanced ratiometric fluorescence sensing on metallic surfaces. 相似文献
996.
Michael?HellerEmail author Leszek?Pysiak Wies?w?Sasin 《International Journal of Theoretical Physics》2005,44(6):619-628
We continue our program of unifying general relativity and quantum mechanics in terms of a noncommutative algebra А on a transformation groupoid Γ = E × G where E is the total space of a principal fibre bundle over spacetime, and G a suitable group acting on Γ . We show that every a ∊ А defines a random operator, and we study the dynamics of such operators. In the noncommutative regime, there is no usual time but, on the strength of the Tomita–Takesaki theorem, there exists a one-parameter group of automorphisms of the algebra А which can be used to define a state dependent dynamics; i.e., the pair (А, ϕ), where ϕ is a state on А, is a “dynamic object.” Only if certain additional conditions are satisfied, the Connes–Nikodym–Radon theorem can be applied and the dependence on ϕ disappears. In these cases, the usual unitary quantum mechanical evolution is recovered. We also notice that the same pair (А, ϕ) defines the so-called free probability calculus, as developed by Voiculescu and others, with the state ϕ playing the role of the noncommutative probability measure. This shows that in the noncommutative regime dynamics and probability are unified. This also explains probabilistic properties of the usual quantum mechanics. 相似文献
997.
Lev?B.?Levitin Tom?ToffoliEmail author Zac?Walton 《International Journal of Theoretical Physics》2005,44(2):219-228
We consider a fixed quantum measurement performed over n identical copies of quantum states. Using a rigorous notion of distinguishability based on Shannon’s 12th theorem, we show that in the case of a single qubit, the number of distinguishable states is
, where (α1,α2) is the angle interval from which the states are chosen. In the general case of an N-dimensional Hilbert space and an area Ω of the domain on the unit sphere from which the states are chosen, the number of distinguishable states is
. The optimal distribution is uniform over the domain in Cartesian coordinates. 相似文献
998.
We present the full set of evolution equations for the spatially homogeneous cosmologies of type VIh filled with a tilted perfect fluid and we provide the corresponding equilibrium points of the resulting dynamical state space. It is found that only when the group parameter satisfies h > –1 a self-similar solution exists. In particular we show that for h > –
there exists a self-similar equilibrium point provided that
whereas for h < –
the state parameter belongs to the interval (1,
. This family of new exact self-similar solutions belongs to the subclass n = 0 having non-zero vorticity. In both cases the equilibrium points have a six-dimensional stable manifold and may act as future attractors at least for the models satisfying n = 0. Also we give the exact form of the self-similar metrics in terms of the state and group parameter. As an illustrative example we provide the explicit form of the corresponding self-similar radiation model ( =
), parametrised by the group parameter h. Finally we show that there are no tilted self-similar models of type III and irrotational models of type VIh. 相似文献
999.
Frederick?M.?KronzEmail author Tracy?A.?Lupher 《International Journal of Theoretical Physics》2005,44(8):1239-1258
It has been maintained that the physical content of a model of a system is completely contained in the C∗-algebra of quasi-local observables
that is associated with the system. The reason given for this is that the unitarily inequivalent representations of
are physically equivalent. But, this view is dubious for at least two reasons. First, it is not clear why the physical content
does not extend to the elements of the von Neumann algebras that are generated by representations of
. It is shown here that although the unitarily inequivalent representations of
are physically equivalent, the extended representations are not. Second, this view detracts from special global features
of physical systems such as temperature and chemical potential by effectively relegating them to the status of fixed parameters.
It is desirable to characterize such observables theoretically as elements of the algebra that is associated with a system
rather than as parameters, and thereby give a uniform treatment to all observables. This can be accomplished by going to larger
algebras. One such algebra is the universal enveloping von Neumann algebra, which is generated by the universal representation
of
; another is the direct integral of factor representations that are associated with the set of values of the global features.
Placing interpretive significance on the von Neumann algebras mentioned earlier sheds light on the significance of unitarily
inequivalent representations of
, and it serves to show the limitations of the notion of physical equivalence. 相似文献
1000.
The quantum discrete kinetic equations are solved to study the propagation of plane waves in a system of composite particles
with hard-sphere interactions and the filling factor (ν) being 1/2. We compare the dispersion relations thus obtained by the
relevant Pauli-blocking parameter B which describes the different-statistics particles for the quantum analog of the discrete Boltzmann system when B is positive (Bose gases), zero (Boltzmann gases), and negative (Fermi Gases). We found, as the effective magnetic field being
zero (ν = 1/2 using the composite fermion formulation), the electric field effect will induce anomalous dispersion relations. 相似文献