全文获取类型
收费全文 | 20399篇 |
免费 | 2746篇 |
国内免费 | 1699篇 |
专业分类
化学 | 9283篇 |
晶体学 | 236篇 |
力学 | 1951篇 |
综合类 | 30篇 |
数学 | 3058篇 |
物理学 | 10286篇 |
出版年
2024年 | 35篇 |
2023年 | 955篇 |
2022年 | 844篇 |
2021年 | 872篇 |
2020年 | 1098篇 |
2019年 | 639篇 |
2018年 | 742篇 |
2017年 | 984篇 |
2016年 | 1002篇 |
2015年 | 1026篇 |
2014年 | 1194篇 |
2013年 | 1203篇 |
2012年 | 1429篇 |
2011年 | 1182篇 |
2010年 | 1089篇 |
2009年 | 1078篇 |
2008年 | 744篇 |
2007年 | 854篇 |
2006年 | 953篇 |
2005年 | 590篇 |
2004年 | 391篇 |
2003年 | 400篇 |
2002年 | 397篇 |
2001年 | 587篇 |
2000年 | 274篇 |
1999年 | 535篇 |
1998年 | 354篇 |
1997年 | 268篇 |
1996年 | 166篇 |
1995年 | 147篇 |
1994年 | 97篇 |
1993年 | 105篇 |
1992年 | 110篇 |
1991年 | 84篇 |
1990年 | 78篇 |
1989年 | 104篇 |
1988年 | 484篇 |
1987年 | 798篇 |
1986年 | 758篇 |
1985年 | 98篇 |
1984年 | 49篇 |
1983年 | 20篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1971年 | 7篇 |
1963年 | 1篇 |
1959年 | 1篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
The classes ofL
1-matrices,L
2-matrices,L
3-matrices andW-matrices are introduced to study solvability of a linear complementarity problem via solving a linear program. Three sufficient
conditions are presented to guarantee that a linear complementarity problem is solvable via a linear program. The new sufficient
conditions are weaker than the ones introduced by Mangasarian. This fact is also illustrated by an example.
Partially supported by NSFC.
This author is also with College of Business Administration of Human University as a Lotus chair professor. 相似文献
82.
We report on Raman scattering of VO2 films prepared by radio frequency magnetron sputtering under different conditions. Our investigations revealed that the dominated Raman peaks shift towards high frequency for both V-rich and O-rich VO2 films, compared with the stoichiometry VO2 films. The experimental evidence is presented and the cause for nonstoichiometry dependence of Raman spectra of VO2 films is discussed. 相似文献
83.
Hui Zhang 《Journal of solid state chemistry》2004,177(3):772-780
A nano-scale magnetic solid base catalyst MgAl-OH-LDH/MgFe2O4 (where LDH denotes layered double hydroxide) composed of MgAl-OH-LDH Brønsted base catalytic layers coated on MgFe2O4 spinel cores has been prepared. A magnetic precursor MgAl-CO3-LDH/MgFe2O4 was prepared by a method involving separate nucleation and aging steps, and subsequently calcined to give a mixed metal oxide composite MgAl(O)/MgFe2O4 which was rehydrated to give MgAl-OH-LDH/MgFe2O4. The structure and magnetic properties of the nano-scale magnetic solid base MgAl-OH-LDH/MgFe2O4, together with those of the magnetic precursor MgAl-CO3-LDH/MgFe2O4 and MgFe2O4 were characterized by XRD, XPS, low temperature N2 adsorption and vibrating sample magnetometry (VSM). The MgAl-OH-LDH/MgFe2O4 composite possesses a mesoporous structure with pore size ranging from 2 to 20 nm with particle size mainly in the range 35-130 nm. The catalytic properties of MgAl-OH-LDH/MgFe2O4 were evaluated using the self-condensation of acetone at 273 K as a probe reaction. The results showed that the conversion of acetone to diacetone alcohol reached the thermodynamic equilibrium value of 23% at 273 K. The catalyst was easily recovered through application of an external magnetic field, and when the reclaimed catalyst was used in a second run for the same reaction, the reactivity remained unchanged. 相似文献
84.
《Electrochemistry communications》2007,9(8):1991-1997
The controllability of pore density and diameter is critical for emerging applications, e.g., non-lithographic photonic-crystal formation; however pore density and diameter could either increase or decrease self-orderedly with enhanced current density. In this letter, similar paradoxical phenomena were demonstrated; the etch rate as a function of field strength was evidenced and interpreted in light of current-burst-model. Based on a hybrid of SCR (space charge region) and breakdown effects, a semi-quantitative model was established in order to disentangle the paradox: such a model could also potentially serve as a design reference for various applications as far as breakdown comes into play. The paradox was finally found to be dominated by physics on patterned samples. 相似文献
85.
Applying the approximate Fokker-Planck equation we derived, we obtain the analytic expression of thestationary laser intensity distribution Pst(Ⅰ) by studying the single-mode laser cubic model subject to colored cross-correlation additive and multiplicative noise, each of which is colored. Based on it, we discuss the effects on the stationarylaser intensity distribution Pst(Ⅰ) by cross-correlation between noises and “color“ of noises (non-Markovian effect) whenthe laser system is above the threshold. In detail, we analyze two cases: One is that the three correlation-times (i.e.the self-correlation and cross-correlation times of the additive and multiplicative noise) are chosen to be the same value(τ1 = τ2 = τ3 = τ). For this case, the effect of noise cross-correlation is investigated emphatically, and we detect thatonly when λ≠ 0 can the noise-induced transition occur in the Pst(Ⅰ) curve, and only when τ≠ 0 and λ≠ 0, can the“reentrant noise-induced transition“ occur. The other case is that the three correlation times are not the same value,τ1 ≠τ2 ≠τ3. For this case, we find that the noise-induced transition occurring in the Pst (Ⅰ) curve is entirely differentwhen the values of τ1, τ2, and τ3 are changed respectively. In particular, when τ2 (self-correlation time of additivenoise) is changing, the ratio of the two maximums of the Pst(Ⅰ) curve R exhibits an interesting phenomenon, “reentrantnoise-induced transition“, which demonstrates the effect of noise “color“ (non-Markovian effect). 相似文献
86.
《Electrochemistry communications》2007,9(11):2725-2728
The electrocatalytic hydrogenation of ethyl pyruvate to yield S-ethyl lactate over palladium supported on carbon felt electrodes modified with cinchonidine has been found to yield an enantiomeric excess of 13%. The effect of electrode potential, ethyl pyruvate concentration and cinchonidine have been investigated. The experimental results reported in the present study are in good agreement with the previously reported heterogeneous enantioselective hydrogenation using molecular hydrogen at high pressure. The electrocatalytic driven reaction avoids the dissociation of molecular hydrogen and thus the use of high pressure hydrogen. 相似文献
87.
《Physica A》2006,365(1):190-196
The formula for probability density functions (PDFs) has been extended to include PDF for energy dissipation rates in addition to other PDFs such as for velocity fluctuations, velocity derivatives, fluid particle accelerations, energy transfer rates, etc., and it is shown that the formula actually explains various PDFs extracted from direct numerical simulations and experiments performed in a wind tunnel. It is also shown that the formula with appropriate zooming increment corresponding to experimental situation gives a new route to obtain the scaling exponents of velocity structure function, including intermittency exponent, out of PDFs of velocity fluctuations. 相似文献
88.
《Tetrahedron: Asymmetry》2006,17(14):2054-2058
The catalytic enantioselective addition of different organozinc reagents, such as diethylzinc, or in situ generated phenylzinc derivatives to simple ketones was accomplished using titanium tetraisopropoxide and supported chiral ligands derived from trans-1-phenylsulfonylamino-2-isoborneolsulfonylamidocyclohexane, to give the corresponding tertiary alcohols with enantioselectivities up to >99%. A simple and efficient procedure for the synthesis of the disulfonamide monomeric ligand and the corresponding polymerization is described. 相似文献
89.
《Physica A》2006,362(1):68-77
We use the lattice Boltzmann method (LBM) for analysis of high and moderate Knudsen number phenomena. Simulation results are presented for microscale Couette and Poiseuille flows. The slip velocity, nonlinear pressure drop, and mass flow rate are compared with previous numerical results and/or experimental data. The Knudsen minimum is successfully predicted for the first time within the LBM framework. These results validate the usage of the LBM based commercial, arbitrary geometry code PowerFLOW for simulating nanoscale problems. 相似文献
90.
《Physica A》2006,369(2):408-416
We show that the maximum entropy approach proposed by El-Wakil, Elhanbaly, and Abdou (from now on EEA) in [S.A. El-Wakil, A. Elhanbaly, M.A. Abdou, Physica A 323 (2003) 213] for solving approximately the collisional Vlasov equation actually can provide exact solutions if properly implemented. We consider here two alternative procedures for obtaining exact maximum entropy solutions of the aforementioned equation. On the one hand, after identifying an appropriate set of relevant mean values (moments), we show that there are exact maximum entropy solutions associated with that set of moments. These solutions can be studied focusing either on the equations of motion of the moments themselves, or on the equations of motion of the corresponding Lagrange multipliers. On the other hand, it is possible to find exact solutions of the reduced equation considered by EEA, if one takes explicitly into account the zeroth-order moment of the solutions. 相似文献