全文获取类型
收费全文 | 32940篇 |
免费 | 2832篇 |
国内免费 | 3683篇 |
专业分类
化学 | 21004篇 |
晶体学 | 474篇 |
力学 | 2205篇 |
综合类 | 456篇 |
数学 | 4598篇 |
物理学 | 10718篇 |
出版年
2022年 | 444篇 |
2021年 | 565篇 |
2020年 | 663篇 |
2019年 | 774篇 |
2018年 | 741篇 |
2017年 | 799篇 |
2016年 | 1014篇 |
2015年 | 903篇 |
2014年 | 1194篇 |
2013年 | 1648篇 |
2012年 | 1732篇 |
2011年 | 1857篇 |
2010年 | 1768篇 |
2009年 | 1741篇 |
2008年 | 1888篇 |
2007年 | 1820篇 |
2006年 | 1642篇 |
2005年 | 1389篇 |
2004年 | 1154篇 |
2003年 | 1119篇 |
2002年 | 1128篇 |
2001年 | 1009篇 |
2000年 | 775篇 |
1999年 | 570篇 |
1998年 | 444篇 |
1997年 | 391篇 |
1996年 | 358篇 |
1995年 | 339篇 |
1994年 | 314篇 |
1993年 | 340篇 |
1992年 | 330篇 |
1991年 | 334篇 |
1990年 | 329篇 |
1989年 | 309篇 |
1987年 | 270篇 |
1985年 | 295篇 |
1984年 | 295篇 |
1983年 | 275篇 |
1982年 | 278篇 |
1979年 | 304篇 |
1978年 | 333篇 |
1977年 | 325篇 |
1976年 | 404篇 |
1975年 | 360篇 |
1974年 | 388篇 |
1973年 | 398篇 |
1972年 | 370篇 |
1971年 | 333篇 |
1970年 | 315篇 |
1969年 | 298篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
Chin‐Ping Yang Ruei‐Shin Chen Kuei‐Hung Chen 《Journal of polymer science. Part A, Polymer chemistry》2003,41(7):922-938
To investigate the position and amount of the CF3 group affecting the coloration of polyimides (PIs), we prepared 2,2‐bis[4‐(4‐amino‐2‐trifluoromethylphenoxy)phenyl]hexafluoropropane ( 2 ) with four CF3 groups with 2‐chloro‐5‐nitrobenzotrifluoride and 2,2‐bis(4‐hydroxyphenol)hexafluoropropane. A series of soluble and light‐colored fluorinated PIs ( 5 ) were synthesized from 2 and various aromatic dianhydrides ( 3a – 3f ). 5a – 5f had inherent viscosities ranging from 0.80 to 1.19 dL/g and were soluble in amide polar solvents and even in less polar solvents. The glass‐transition temperatures of 5 were 221–265 °C, and the 10% weight‐loss temperatures were above 493 °C. Their films had cutoff wavelengths between 343 and 390 nm, b* values (a yellowness index) ranging from 5 to 41, dielectric constants of 2.68–3.01 (1 MHz), and moisture absorptions of 0.03–0.29 wt %. In a comparison of the PI series 6 – 8 based on 2,2‐bis[4‐(4‐aminophenoxy)phenyl]hexafluoropropane, 2,2‐bis[4‐(4‐amino‐2‐trifluoromethylphenoxy)phenyl]propane, and 2,2‐bis[4‐(4‐aminophenoxy)phenyl]propane, we found that the CF3 group close to the imide group was more effective in lowering the color; this means that CF3 of 5 , 7 , and 8f was more effective than that of 6c . The color intensity of the four PI series was lowered in the following order: 5 > 7 > 6 > 8 . The PI 5f , synthesized from diamine 2 and 4,4′‐hexafluoroisopropylidenediphthalic anhydride, had six CF3 groups in a repeated segment, so it exhibited the lightest color among the four series. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 922–938, 2003 相似文献
63.
64.
This Note addresses the derivation of an improved On-Surface Radiation Condition for the numerical solution of the exterior Helmholtz equation at high-frequencies. This condition is built as an approximation of the Neumann-to-Dirichlet map by using a local regularization of its principal classical symbol in the gliding zone for modelling the creeping waves. The numerical simulation of this pseudodifferential operator is efficiently realized with a linear cost according to the dimension of the boundary element approximation space using suitable complex Padé approximants. A numerical example is provided. To cite this article: X. Antoine et al., C. R. Acad. Sci. Paris, Ser. I 340 (2005). 相似文献
65.
M. P. Nosov V. A. Smirnova Yu. F. Zabashta A. Ya. Fridman M. P. Mokhnach 《Mechanics of Composite Materials》1989,25(1):8-12
Conclusion A method was proposed which makes it possible to study the low-frequency internal friction of complex fibers. This method was used to study the internal friction of complex composite fibers based on PCA and PE. We observed a relaxation process which is typical of the composite and is absent in the pure materials.Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 11–15, January–February, 1989. 相似文献
66.
P. P. Kirpichok N. B. Voronina A. F. Sitnikov V. Ya. Garmash 《Russian Physics Journal》1989,32(1):26-30
The effect of rare-earth oxides on the properties of anisotropic barium ferrites has been studied by x-ray structural and Mössbauer methods. Additions of SrCO3, as well as SrCO3 and La2O3, SrCO3 and Pr6O11, SrCO3 and Nd2O3, SrCO3 and Sm2O3 in amounts of 7.5 mole % Sr and 10 mole % rare-earth element to grade-A barium powder results in the substitution of barium ions by Sr and rare-earth ions; consequently, the energy of magnetic anisotropy changes and the technically important parameters Br and (BH)max increase.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 34–39, January, 1989. 相似文献
67.
The method of nonlinear moments, when used to solve the Boltzmann equation, necessitates the calculation of collision integral
matrix elements. The matrix elements are hard to calculate numerically, especially at large indices. The asymptotics of the
matrix elements are constructed. In terms of the model of pseudopower particle interaction, a formula free of summation is
derived. This makes it possible to find the asymptotic behavior of linear and nonlinear elements when two indices are large.
For an arbitrary interaction cross section, asymptotic expansions of linear and nonlinear matrix elements in one index are
obtained. For Maxwellian molecules, asymptotic formulas are derived for three large indices. 相似文献
68.
69.
70.
Ping Li Fei Rong Yibing Xie Van Hu Chunwei Yuan 《Journal of Analytical Chemistry》2004,59(10):939-944
S-naproxen imprinted polymer was prepared with acrylamide as a functional monomer, 1,4-butanediyl diacrylate as a new kind of crossliner, and 2,4,6-trimethylbenzoylphenyl-phosphinic acid ethyl ester as photoinitiator. Their UV and IR spectra were applied to study the interactions between the template and the monomer. Binding experiments showed that the S-naproxen imprinted polymer had better recognition capability for the template than that of a blank polymer. The adsorption distribution coefficient KD of S-naproxen on molecularly-imprinted polymer was 153.2 g/mL, and the separation factor was 1.95 when the initial concentration of substrate was 2.0 mmol/L. Scatchard curves suggested that there were two classes of binding sites in the imprinted polymer and only one class in the blank polymer. Computer simulation using Hyperchem showed the existence of the interactions between the template and the functional monomer as well as the models of the complexes formed by the template and the monomer. 相似文献