全文获取类型
收费全文 | 178412篇 |
免费 | 20014篇 |
国内免费 | 10948篇 |
专业分类
化学 | 123891篇 |
晶体学 | 2182篇 |
力学 | 8918篇 |
综合类 | 657篇 |
数学 | 19308篇 |
物理学 | 54418篇 |
出版年
2023年 | 1724篇 |
2022年 | 3580篇 |
2021年 | 4158篇 |
2020年 | 5288篇 |
2019年 | 6450篇 |
2018年 | 5317篇 |
2017年 | 4994篇 |
2016年 | 8676篇 |
2015年 | 7770篇 |
2014年 | 9191篇 |
2013年 | 11978篇 |
2012年 | 11927篇 |
2011年 | 11483篇 |
2010年 | 9725篇 |
2009年 | 9536篇 |
2008年 | 9515篇 |
2007年 | 8363篇 |
2006年 | 7441篇 |
2005年 | 6813篇 |
2004年 | 5795篇 |
2003年 | 5122篇 |
2002年 | 5815篇 |
2001年 | 4740篇 |
2000年 | 3995篇 |
1999年 | 2901篇 |
1998年 | 2358篇 |
1997年 | 2122篇 |
1996年 | 2061篇 |
1995年 | 1784篇 |
1994年 | 1745篇 |
1993年 | 1590篇 |
1992年 | 1479篇 |
1991年 | 1505篇 |
1990年 | 1434篇 |
1989年 | 1269篇 |
1988年 | 1082篇 |
1987年 | 1070篇 |
1986年 | 1032篇 |
1985年 | 1058篇 |
1984年 | 997篇 |
1983年 | 912篇 |
1982年 | 856篇 |
1979年 | 817篇 |
1978年 | 820篇 |
1977年 | 824篇 |
1976年 | 939篇 |
1975年 | 833篇 |
1974年 | 850篇 |
1973年 | 863篇 |
1972年 | 771篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
A. V. Ivanov M. Yu. Tsentalovich E. G. Kogan L. G. Tomilova N. S. Zefirov 《Russian Chemical Bulletin》2008,57(8):1676-1679
The chlorination of benzene, toluene, and o-xylene with molecular chlorine in the presence of the phthalocyanine complexes of different structures was studied. The transformations
of the catalysts during the reaction were investigated.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1644–1647, August, 2008. 相似文献
122.
123.
M. K. Bratenko Yu. V. Kadel’nik V. A. Chornous M. V. Vovk 《Russian Journal of Organic Chemistry》2008,44(2):247-250
Oximes of 4-(4-pyrazolyl)-3-buten-2-onees obtained by successive reaction of 3-aryl-4-formylpyrazoles with acetone and hydroxylamine at the treatment with iodine suffered an oxidative cyclization yielding 3-aryl-4-(5-isoxazolyl)pyrazoles. 相似文献
124.
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
125.
126.
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
127.
Z.J. Yang T.H. Johansen H. Bratsberg G. Helgesen A.T. Skjeltorp 《Physica C: Superconductivity and its Applications》1989,160(5-6):461-465
Based on a dipole-dipole interaction model, we discuss the levitation force and related vibration problems to understand the effects of flux pinning in type-II superconductors, and the applications of levitation in superconducting systems. 相似文献
128.
激光晶体YAG中Er3+的辐射跃迁 总被引:2,自引:0,他引:2
本文讨论和分析了激光晶体YAG中Er3+离子的激光上能级的4S3/2、4I11/2和4I13/2辐射跃迁的有关因素。 相似文献
129.
D. B. Kayumova Yu. P. Syrnikov N. V. Penkina M. N. Rodnikova 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2006,80(10):1634-1635
The structural relaxation time for series of various liquids (alkanes, aliphatic alcohols, and diols) are calculated from published data on the shear viscosity and the heat of evaporation per unit volume. Liquids having a 3D H-bond network (diols) are characterized by relaxation times one to two orders of magnitudes longer than those typical of liquids without such a network (alkanes and aliphatic alcohols). 相似文献
130.
A method of solving the problem of sound radiation from a plate with elements of different thickness in its plane is proposed, and the results obtained with this method are presented. It is shown that the main sources of sound radiation are the inhomogeneous flexural fields formed in the elements on both sides of their joint. 相似文献