全文获取类型
收费全文 | 113712篇 |
免费 | 7664篇 |
国内免费 | 6210篇 |
专业分类
化学 | 66794篇 |
晶体学 | 1510篇 |
力学 | 6396篇 |
综合类 | 391篇 |
数学 | 13331篇 |
物理学 | 39164篇 |
出版年
2023年 | 1031篇 |
2022年 | 2209篇 |
2021年 | 2598篇 |
2020年 | 2877篇 |
2019年 | 3093篇 |
2018年 | 3418篇 |
2017年 | 3293篇 |
2016年 | 4174篇 |
2015年 | 3101篇 |
2014年 | 4375篇 |
2013年 | 6024篇 |
2012年 | 6331篇 |
2011年 | 6725篇 |
2010年 | 5242篇 |
2009年 | 5109篇 |
2008年 | 5437篇 |
2007年 | 5064篇 |
2006年 | 4595篇 |
2005年 | 4048篇 |
2004年 | 3540篇 |
2003年 | 3137篇 |
2002年 | 3217篇 |
2001年 | 2826篇 |
2000年 | 2280篇 |
1999年 | 1844篇 |
1998年 | 1742篇 |
1997年 | 1517篇 |
1996年 | 1456篇 |
1995年 | 1214篇 |
1994年 | 1335篇 |
1993年 | 1219篇 |
1992年 | 1183篇 |
1991年 | 1213篇 |
1990年 | 1201篇 |
1989年 | 1122篇 |
1988年 | 962篇 |
1987年 | 945篇 |
1986年 | 915篇 |
1985年 | 949篇 |
1984年 | 937篇 |
1983年 | 831篇 |
1982年 | 814篇 |
1979年 | 808篇 |
1978年 | 816篇 |
1977年 | 808篇 |
1976年 | 929篇 |
1975年 | 819篇 |
1974年 | 852篇 |
1973年 | 854篇 |
1972年 | 754篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
L. A. Aslanov V. M. Ionov V. I. Andrianov Z. Sh. Safina A. Yu. Shashkov 《Chemistry of Heterocyclic Compounds》1977,13(12):1299-1303
The crystal and molecular structures of 2,10-diacetoxy-13-thiabicyclo[7.3.1]-cis-tridec-5-ene and 2,9-dichloro-13-thiablcyclo[8.2.1]-cis-tridec-5-ene sulfoxide were established. The conformations of the molecules are such that the unshared pairs of electrons of the sulfur atoms are directed to the carboncarbon double bonds of their molecules. It was observed that there are stereochemical conditions for transannular transformations under the influence of polarized molecules and cations.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1628–1632, December, 1977. 相似文献
992.
Conclusions A number of metal alloys in the Sb-Cd-Zn system was studied for the first time by the NQR method on the121,123Sb nuclei. The constants of the quadrupole bond and the asymmetry parameter of the compounds ZnSb were determined.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No; 7. pp. 1638–1640, July, 1977. 相似文献
993.
994.
Thiocarbamoyl derivatives of N-phenylpyrazolidines are converted under the influence of acidic agents to mixtures of tetrahydropyrimido[2,1-b]benzothiazoles
and 2-imino-3-aminoalkylbenzothiazoles and not only to tetrahydropyrimidobenzothiazoles, as previously assumed. The conditions
for the predominant formation of tetrahydropyrimidobenzothiazoles were found.
Deceased.
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 228–233, February, 1980. 相似文献
995.
996.
997.
B. A. Arbuzov A. O. Vizel' R. S. Giniyatullin Yu. F. Tarenko 《Russian Chemical Bulletin》1972,21(8):1786-1787
Conclusions A new and simple method has been found for the synthesis of 1-oxo-1-chlorophospholenes by the reaction of phosphorus trichloride, a diene, and an oxygen-donor compound, the best of which is acetone.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1847–1848, August, 1972. 相似文献
998.
Reaction of transition metal formate M(HCOO)(2).2H2O (M = Mn, Co, Ni) with 4,4'-bpy (4,4-bipyridine) has led to four new compounds with the formula M(HCOO)2(4,4'-bpy).nH2O (M = Mn, Co (1.Mn, 2.Co), n = 0; M = Co, Ni (3.Co, 4.Ni), n = 5). Compounds 1.Mn and 2.Co are isomorphous and crystallized in the tetragonal crystal system with the chiral space group P4(1)2(1)2. They are of three-dimensional diamondoid structure connected by anti-anti formate with 4,4'-bpy in the cavities of the framework reinforcing the intermetallic connections; the diamond-like net was observed also in their azide analogue (Mn(N3)2(4,4'-bpy)). Compounds 3.Co and 4.Ni are isomorphous also but crystallized in the monoclinic crystal system with the space group Cc. Both structures are uninterpenetrated 3D "CdSO4" type with big channels, constructed by anti-anti formate and 4,4'-bpy. This type of net was not observed in their azide analogue. Residing in the channels, water molecules form a new type of 1D tape constructed by vertex-sharing cyclic pentamers. Magnetic measurements were performed on all of these four compounds. 1.Mn and 2.Co are weak ferromagnets with the critical temperature Tc = 5.3 and 7.4 K, respectively. 3.Co is an antiferromagnet with Neel temperature TN = 3.0 K, and 4.Ni is a weak ferromagnet below 20 K. Hysteresis loop can be observed for 2.Co and 4.Ni at 1.8 K. As an analogue of azide, formate can be used to construct molecular architectures, which structurally and magnetically have great similarities to and also differences from those of azide. This offers a promising method for the design of new molecular architectures with formate. 相似文献
999.
1000.
Obushak N. D. Matiichuk V. S. Vasylyshin R. Ya. Ostapyuk Yu. V. 《Russian Journal of Organic Chemistry》2004,40(3):383-389
Meerwein reaction of arenediazonium chlorides with acrolein gave 3-aryl-2-chloropropanals which were brought into cyclocondensation with thiourea. The resulting 2-amino-5-benzyl-1,3-thiazoles were acylated with carboxylic acid chlorides and phthalic anhydride to afford, respectively, 2-acylamino-5-benzyl-1,3-thiazoles and N-(5-benzyl-1,3-thiazol-2-yl)phthalimides. 相似文献