全文获取类型
收费全文 | 245052篇 |
免费 | 1472篇 |
国内免费 | 416篇 |
专业分类
化学 | 112483篇 |
晶体学 | 3815篇 |
力学 | 12987篇 |
综合类 | 3篇 |
数学 | 38003篇 |
物理学 | 79649篇 |
出版年
2021年 | 1021篇 |
2020年 | 1181篇 |
2019年 | 1251篇 |
2018年 | 10470篇 |
2017年 | 11333篇 |
2016年 | 6594篇 |
2015年 | 2410篇 |
2014年 | 2477篇 |
2013年 | 6159篇 |
2012年 | 9148篇 |
2011年 | 18481篇 |
2010年 | 11349篇 |
2009年 | 11421篇 |
2008年 | 16249篇 |
2007年 | 19688篇 |
2006年 | 5570篇 |
2005年 | 11731篇 |
2004年 | 7926篇 |
2003年 | 7548篇 |
2002年 | 5451篇 |
2001年 | 5711篇 |
2000年 | 4287篇 |
1999年 | 3117篇 |
1998年 | 2157篇 |
1997年 | 2224篇 |
1996年 | 2250篇 |
1995年 | 2022篇 |
1994年 | 2002篇 |
1993年 | 1806篇 |
1992年 | 2281篇 |
1991年 | 2372篇 |
1990年 | 2212篇 |
1989年 | 2179篇 |
1988年 | 2171篇 |
1987年 | 2175篇 |
1986年 | 1990篇 |
1985年 | 2464篇 |
1984年 | 2496篇 |
1983年 | 1996篇 |
1982年 | 2002篇 |
1981年 | 1844篇 |
1980年 | 1830篇 |
1979年 | 2136篇 |
1978年 | 2221篇 |
1977年 | 2080篇 |
1976年 | 2042篇 |
1975年 | 1912篇 |
1974年 | 1895篇 |
1973年 | 1969篇 |
1972年 | 1272篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
R. A. Ganeev A. I. Ryasnyanskii M. K. Kodirov Sh. R. Kamalov V. A. Li R. I. Tugushev T. Usmanov 《Technical Physics》2002,47(8):991-995
Nonlinear optical parameters (nonlinear refractive indices and nonlinear absorption coefficients) of solutions of polyvinylpyrrolidone doped by cobalt to various concentrations are measured at the lasing and second-harmonic wavelengths of a picosecond Nd:YAG laser (λ=1064 and 532 nm, respectively, and τ=35 ps). Data on optical limitation in these solutions are presented. The absence of nonlinear absorption in the IR spectral range and its significant effect in the visible range are demonstrated. Optical limitation at a wavelength of 1064 nm is related to defocusing, whereas at 532 nm, this effect is caused by two-photon absorption and partially by inverse saturated absorption and defocusing. Nonlinear optical parameters of metal-polymer complexes are reported. 相似文献
162.
B. Dubrulle F. Hersant 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):379-386
We generalize an analogy between rotating and stratified shear flows. This analogy is summarized in Table 1. We use this analogy
in the unstable case (centrifugally unstable flow vs. convection) to compute the torque in Taylor-Couette configuration, as a function of the Reynolds number. At low Reynolds
numbers, when most of the dissipation comes from the mean flow, we predict that the non-dimensional torque G = T/ν2
L, where L is the cylinder length, scales with Reynolds number R and gap width η, G = 1.46η3/2(1 - η)-7/4
R
3/2. At larger Reynolds number, velocity fluctuations become non-negligible in the dissipation. In these regimes, there is no
exact power law dependence the torque versus Reynolds. Instead, we obtain logarithmic corrections to the classical ultra-hard (exponent 2) regimes: G = 0.50
. These predictions are found to be in excellent agreement with avail-able experimental data. Predictions for scaling of velocity
fluctuations are also provided.
Received 7 June 2001 and Received in final form 7 December 2001 相似文献
163.
The influence of interatomic distances on magnetic ordering in RMnSi compounds (R=La, Y, Sm, and Gd)
S. A. Nikitin T. I. Ivanova Yu. A. Ovchenkova M. V. Maslennikova G. S. Burkhanov O. D. Chistyakov 《Physics of the Solid State》2002,44(2):308-311
Magnetic ordering in the RMnSi (R=La, Y, Sm, and Gd) compounds is investigated. It is found that the type of magnetic ordering depends on the d Mn-Mn distance between manganese atoms inside the magnetic layers located in the planes perpendicular to the c axis. This inference is based on the results of studies performed with SmMnSi and GdMnSi compounds in which the distances between manganese atoms are close to the critical value d Mn-Mn that corresponds to the crossover between ferromagnetic and antiferromagnetic ordering in RMnSi compounds. The introduction of lanthanum and yttrium atoms into the rare-earth sublattice leads to an increase and a decrease in the unit cell size, respectively, and brings about magnetic phase transitions in the compounds under investigation. 相似文献
164.
Sanzharov N. A. Yarovoi A. T. Bekhtereva E. S. Ulenikov O. N. 《Russian Physics Journal》2002,45(10):1024-1031
Analytical formulas are derived that describe the dependences of the transition probabilities in vibrational-rotational spectra of XY3-type molecules with C
3v
symmetry on the rotational quantum numbers. 相似文献
165.
The interaction between azathioprine (AZ) and bovine serum albumin (BSA) is mainly due to hydrophobic binding according to the dependence of the binding constant on the ionic strength obtained by equilibrium dialysis. The binding constant and partition coefficient of AZ were smaller than those of warfarin, phenylbutazone and ibuprofen. Little variation in the proton chemical shift of AZ was observed whether there was an absence or presence of BSA (7.25 x 10(-5) M). The spin-lattice relaxation time (T1) of AZ decreased in the presence of BSA to 6-22%. The spin-spin relaxation rate (1/T2) of AZ increased 16-24 times for the methyl group and the imidazole ring and 8-13 times for the purine ring in the presence of BSA. The ratio of the spin-spin relaxation rate of the free AZ to the bound AZ ((1/T2)b/(1/T2)f) of the methyl group and the imidazole ring was 2-3 times larger than that of the purine ring. The binding of AZ to BSA was concluded to be mainly at the methyl group on the imidazole ring of AZ. 相似文献
166.
167.
168.
S. P. Mukherjee A. K. Chattopadhyay 《The Journal of the Operational Research Society》1989,40(5):489-494
Consider an organization with several categories of staff, each having a specified number of members. The age of entry into service and the age of retirement are both specified. Withdrawals occur at time-independent rates. Under this set-up, the authors have computed the maximum ages at which promotions should take place, assuming that the staff members continuing at various ages are random. Some illustrative calculations have been carried out. 相似文献
169.
170.
A three-dimensional molecular dynamics (MD) model is utilized to investigate the effect of tool geometry on the deformation process of the workpiece and the nature of deformation process at the atomic-scale. Results show that different states exist between the atomic force microscope (AFM) pin tool and the workpiece surface, i.e. the non-wear state, the ploughing state, the state in which ploughing is dominant and the state in which cutting plays a key role. A relationship between the deformation process of the workpiece and the potential energy variation is presented. The potential energy variation of atoms in different deformed regions in the workpiece such as plastically deformed region, elastically deformed region and the mixed deformation region is different. The features of variations of potential energy are discussed. 相似文献