全文获取类型
收费全文 | 256538篇 |
免费 | 3423篇 |
国内免费 | 994篇 |
专业分类
化学 | 139704篇 |
晶体学 | 3776篇 |
力学 | 10265篇 |
综合类 | 2篇 |
数学 | 29652篇 |
物理学 | 77556篇 |
出版年
2021年 | 1849篇 |
2020年 | 2128篇 |
2019年 | 2368篇 |
2018年 | 2702篇 |
2017年 | 2602篇 |
2016年 | 4359篇 |
2015年 | 3021篇 |
2014年 | 4411篇 |
2013年 | 11937篇 |
2012年 | 9066篇 |
2011年 | 11140篇 |
2010年 | 7151篇 |
2009年 | 6994篇 |
2008年 | 9837篇 |
2007年 | 9954篇 |
2006年 | 9186篇 |
2005年 | 8566篇 |
2004年 | 7611篇 |
2003年 | 6637篇 |
2002年 | 6593篇 |
2001年 | 7354篇 |
2000年 | 5495篇 |
1999年 | 4359篇 |
1998年 | 3650篇 |
1997年 | 3691篇 |
1996年 | 3445篇 |
1995年 | 3227篇 |
1994年 | 3050篇 |
1993年 | 3110篇 |
1992年 | 3375篇 |
1991年 | 3415篇 |
1990年 | 3207篇 |
1989年 | 3163篇 |
1988年 | 3239篇 |
1987年 | 3096篇 |
1986年 | 2991篇 |
1985年 | 4073篇 |
1984年 | 4242篇 |
1983年 | 3454篇 |
1982年 | 3852篇 |
1981年 | 3755篇 |
1980年 | 3604篇 |
1979年 | 3624篇 |
1978年 | 3878篇 |
1977年 | 3690篇 |
1976年 | 3878篇 |
1975年 | 3452篇 |
1974年 | 3573篇 |
1973年 | 3881篇 |
1972年 | 2346篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
972.
N. Chai W.D. Kulatilaka S.V. Naik N.M. Laurendeau R.P. Lucht J.P. Kuehner S. Roy V.R. Katta J.R. Gord 《Applied physics. B, Lasers and optics》2007,88(1):141-150
We report the application of electronic-resonance-enhanced coherent anti-Stokes Raman scattering (ERE-CARS) for measurements
of nitric oxide concentration ([NO]) in three different atmospheric pressure flames. Visible pump (532 nm) and Stokes (591 nm)
beams are used to probe the Q-branch of the Raman transition. A significant resonance enhancement is obtained by tuning an
ultraviolet probe beam (236 nm) into resonance with specific rotational transitions in the (v’=0, v”=1) vibrational band of
the A2Σ+–X2Π electronic system of NO. ERE-CARS spectra are recorded at various heights within a hydrogen-air flame producing relatively
low concentrations of NO over a Hencken burner. Good agreement is obtained between NO ERE-CARS measurements and the results
of flame computations using UNICORN, a two-dimensional flame code. Excellent agreement between measured and calculated NO
spectra is also obtained when using a modified version of the Sandia CARSFT code for heavily sooting acetylene-air flames
(φ=0.8 to φ=1.6) on the same Hencken burner. Finally, NO concentration profiles are measured using ERE-CARS in a laminar,
counter-flow, non-premixed hydrogen-air flame. Spectral scans are recorded by probing the Q1 (9.5), Q1 (13.5) and Q1 (17.5) Raman transitions. The measured shape of the [NO] profile is in good agreement with that predicted using the OPPDIF
code, even without correcting for collisional effects. These comparisons between [NO] measurements and predictions establish
the utility of ERE-CARS for detection of NO in flames with large temperature and concentration gradients as well as in sooting
environments.
PACS 07.88.+y; 42.62.Fi; 42.65.Dr 相似文献
973.
In single-objective optimization it is possible to find a global optimum, while in the multi-objective case no optimal solution is clearly defined, but several that simultaneously optimize all the objectives. However, the majority of this kind of problems cannot be solved exactly as they have very large and highly complex search spaces. Recently, meta-heuristic approaches have become important tools for solving multi-objective problems encountered in industry as well as in the theoretical field. Most of these meta-heuristics use a population of solutions, and hence the runtime increases when the population size grows. An interesting way to overcome this problem is to apply parallel processing. This paper analyzes the performance of several parallel paradigms in the context of population-based multi-objective meta-heuristics. In particular, we evaluate four alternative parallelizations of the Pareto simulated annealing algorithm, in terms of quality of the solutions, and speedup. 相似文献
974.
975.
976.
Bianchi type-III magnetized cosmological model when the field of gravitation is governed by either a perfect fluid or cosmic
string is investigated in Rosen’s [1] bimetric theory of gravitation. To complete determinate solution, the condition, viz.,
A=(BC)
n
, where n is a constant, between the metric potentials is used. We have assumed different equations of state for cosmic string [2]
for the complete solution of the model. Some physical and geometrical properties of the exhibited model are discussed and
studied. 相似文献
977.
In this short communication, we have evaluated the effect of thermal velocity of the plasma particles on the energy of resonantly
interacting energetic electrons with the propagating whistler mode waves as a function of wave frequency and L-value for the
normal and disturbed magnetospheric conditions. During the disturbed conditions when the magnetosphere is depleted in electron
density, the resonance energy of the electron enhances by an order of magnitude at higher latitudes, whereas the effect is
small at low latitudes. An attempt is made to explain the enhanced wave activity observed during magnetic storm periods. 相似文献
978.
This paper is concerned with demand-driven production scheduling in a commercial environment where smoothed production plans generation over a rolling horizon is desirable as new observations of demand are received through time. Demands are assumed to be normally distributed and dependent on the previous observed levels. The method of chance constraint of Charnes and Cooper is extended to multi-product production planning with variable workforce, back-ordered inventory, and nonstationary stochastic demand process. Bayesian procedures for revising the chance constraints and several variants of linear-programming-based production planning models are presented. In all cases the proposed methodology ensures that demands are satisfied, at a given level of confidence, while achieving smooth production. 相似文献
979.
C. A. Ballentine R. L. Fink J. Araya-Pochet J. L. Erskine 《Applied Physics A: Materials Science & Processing》1989,49(5):459-466
We describe magneto-optic Kerr effect studies of ultrathin Fe and Ni films on single crystal surfaces of Ag and Cu. Monolayer Fe films on Ag(100) exhibit the theoretically predicted spin-orbit anisotropy, but also yield some interesting discrepancies between behavior predicted by Kerr effect and by spin-polarized photoemission experiments. Layer-dependent studies of the magnetic moment of Ni on Ag(111) and Ag(100) suggest sp-d hybridization effects quench the first layer magnetic moment on Ag(111) but not on Ag(100). Temperature dependent studies of thin film magnetization obtained from Kerr effect measurements yield thickness dependent Curie temperatures, and critical exponents for several thin film systems. 相似文献
980.
H.D. Fonseca Filho R. Prioli M.P. Pires A.S. Lopes P.L. Souza F.A. Ponce 《Applied Physics A: Materials Science & Processing》2007,89(4):945-949
Atomic-force nanolithography was used to control the nucleation sites of InAs nanostructures on InP substrates. Indentations
with a wide range of dimensions were produced on InP. InAs nanostructures were selectively grown by metal organic vapor phase
epitaxy. It is shown that the number of active nucleation sites depends on the normal force applied during nanoindentation.
Crystalline defects introduced by nanoindentation are shown to be nucleation sites for these nanostructures. The presence
of screw dislocations within the grown nanostructures further supports this observation.
PACS 81.07.-b; 68.37.Ps; 81.16.Nd 相似文献