全文获取类型
收费全文 | 345240篇 |
免费 | 4142篇 |
国内免费 | 1073篇 |
专业分类
化学 | 175264篇 |
晶体学 | 5473篇 |
力学 | 15953篇 |
综合类 | 7篇 |
数学 | 41317篇 |
物理学 | 112441篇 |
出版年
2021年 | 3430篇 |
2020年 | 3699篇 |
2019年 | 4134篇 |
2018年 | 5443篇 |
2017年 | 5648篇 |
2016年 | 7943篇 |
2015年 | 4591篇 |
2014年 | 7576篇 |
2013年 | 16754篇 |
2012年 | 13449篇 |
2011年 | 16067篇 |
2010年 | 11660篇 |
2009年 | 11487篇 |
2008年 | 14161篇 |
2007年 | 14119篇 |
2006年 | 13054篇 |
2005年 | 11340篇 |
2004年 | 10507篇 |
2003年 | 9182篇 |
2002年 | 9195篇 |
2001年 | 10583篇 |
2000年 | 7823篇 |
1999年 | 6116篇 |
1998年 | 5092篇 |
1997年 | 4943篇 |
1996年 | 4656篇 |
1995年 | 3989篇 |
1994年 | 3937篇 |
1993年 | 3825篇 |
1992年 | 4191篇 |
1991年 | 4407篇 |
1990年 | 4182篇 |
1989年 | 4083篇 |
1988年 | 3864篇 |
1987年 | 3993篇 |
1986年 | 3760篇 |
1985年 | 4738篇 |
1984年 | 4793篇 |
1983年 | 3954篇 |
1982年 | 4090篇 |
1981年 | 3826篇 |
1980年 | 3748篇 |
1979年 | 4001篇 |
1978年 | 4024篇 |
1977年 | 3998篇 |
1976年 | 3954篇 |
1975年 | 3750篇 |
1974年 | 3687篇 |
1973年 | 3725篇 |
1972年 | 2630篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
Daniel W. Stroock 《Journal of Functional Analysis》2007,242(1):295-303
The purpose of this note is to describe a procedure for transferring familiar estimates for transition probabilities on RN to transition probabilities on compact manifolds. 相似文献
995.
Polyvinyl alcohol (PVA)-based proton conducting polymer electrolytes have been prepared by the solution cast technique. The
conductivity is observed to increase from 10−9 to 10−4 S cm−1 as a result of orthophosphoric acid (H3PO4) addition. The plot of conductivity vs temperature shows that a phase transition occurred at 343 K in the sample PVA-33 wt%
H3PO4. The β-relaxation peak is observed at 313 K. The glass transition temperature of PVA-33 wt% H3PO4 is 343 K. Orthophosphoric acid seems to play a dual role, i.e., as a proton source and as a plasticizer. The ac conductivity
σ
ac = Aω
s was also calculated in the temperature range from 303 to 353 K. The conduction mechanism was inferred by plotting the graph
of s vs T from which the conduction mechanism for sample PVA-17 wt% H3PO4 was inferred to occur by way of the overlapping large polaron tunneling (OLPT) model and the conduction mechanism for the
sample PVA-33 wt% H3PO4 by way of the correlated barrier height (CBH) model. 相似文献
996.
In this paper, an adaptive FE analysis is presented based on error estimation, adaptive mesh refinement and data transfer for enriched plasticity continua in the modelling of strain localization. As the classical continuum models suffer from pathological mesh-dependence in the strain softening models, the governing equations are regularized by adding rotational degrees-of-freedom to the conventional degrees-of-freedom. Adaptive strategy using element elongation is applied to compute the distribution of required element size using the estimated error distribution. Once a new mesh is generated, state variables and history-dependent variables are mapped from the old finite element mesh to the new one. In order to transfer the history-dependent variables from the old to new mesh, the values of internal variables available at Gauss point are first projected at nodes of old mesh, then the values of the old nodes are transferred to the nodes of new mesh and finally, the values at Gauss points of new elements are determined with respect to nodal values of the new mesh. Finally, the efficiency of the proposed model and computational algorithms is demonstrated by several numerical examples. 相似文献
997.
In this note we study uncertainty sequencing situations, i.e., one-machine sequencing situations in which no initial order
is specified. We associate cooperative games with these sequencing situations, study their core, and provide links with the
classic sequencing games introduced by Curiel et al. (Eur J Oper Res 40:344–351, 1989). Moreover, we propose and characterize
two simple cost allocation rules for uncertainty sequencing situations with equal processing times. 相似文献
998.
V. N. Sorokoumov S. N. Morozkina I. A. Balova 《Chemistry of Heterocyclic Compounds》2006,42(5):615-624
An investigation of the reaction of 1-lithio-1,3-diynes, generated in situ, with nitriles has been carried out. In the case
of aromatic nitriles 1-arylalk-1-ene-3,5-diynylamines are formed, which undergo dimerization and cyclization on isolation,
giving 3-(alka-1,3-diynyl)-4-(alk-2-ynyl)-2,6-diarylpyridines. The effect of the nature of the substituent in the benzonitrile
molecule on the selectivity of the reaction and the yield of the products has been determined. A scheme is proposed for the
conversions and the structures of the intermediates have been established.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 701–710, May, 2006. 相似文献
999.
S. A. Egorov 《Technical Physics》2006,51(8):999-1003
Calorimetric studies of titanium nickelide show that thermally reversible prestraining does not affect the heat of the B2 → R and R → B2 martensitic transformations. At the same time, reactive stresses induced by straining under constrained conditions are found to decrease the heat of the B19′ → B2, R → B19′, B2 → R, and R → B2 transformations by a factor of 1.16–1.40. A formula describing this effect is proposed. 相似文献
1000.
J. Łukasik G. Auger M. L. Begemann-Blaich N. Bellaize R. Bittiger F. Bocage B. Borderie R. Bougault B. Bouriquet J. L. Charvet A. Chbihi R. Dayras D. Durand J. D. Frankland E. Galichet D. Gourio D. Guinet S. Hudan P. Lautesse F. Lavaud A. Le Fèvre R. Legrain O. Lopez U. Lynen W. F. J. Müller L. Nalpas H. Orth E. Plagnol E. Rosato A. Saija C. Schwarz C. Sfienti B. Tamain W. Trautmann A. Trzciński K. Turzó E. Vient M. Vigilante C. Volant B. Zwiegliński 《Acta Physica Hungarica A》2006,25(2-4):229-239
Directed and elliptic flow for the 197Au+197Au system at incident energies between 40 and 150 MeV per nucleon has been measured using the INDRA 4π multi-detector. For semi-central collisions, the excitation function of elliptic flow shows a transition from in-plane to out-of-plane emission at around 100 MeV per nucleon. The directed flow changes sign at a bombarding energy between 50 and 60 MeV per nucleon and remains negative at lower energies. Molecular dynamics calculations (CHIMERA) indicate sensitivity of the global squeeze-out transition on the σ NN and demonstrate the importance of angular momentum conservation in transport codes at low energies. 相似文献