全文获取类型
收费全文 | 2562篇 |
免费 | 224篇 |
国内免费 | 181篇 |
专业分类
化学 | 1840篇 |
晶体学 | 33篇 |
力学 | 58篇 |
综合类 | 37篇 |
数学 | 388篇 |
物理学 | 611篇 |
出版年
2024年 | 16篇 |
2023年 | 26篇 |
2022年 | 44篇 |
2021年 | 47篇 |
2020年 | 99篇 |
2019年 | 62篇 |
2018年 | 47篇 |
2017年 | 39篇 |
2016年 | 57篇 |
2015年 | 79篇 |
2014年 | 77篇 |
2013年 | 121篇 |
2012年 | 108篇 |
2011年 | 142篇 |
2010年 | 84篇 |
2009年 | 115篇 |
2008年 | 124篇 |
2007年 | 135篇 |
2006年 | 111篇 |
2005年 | 136篇 |
2004年 | 132篇 |
2003年 | 98篇 |
2002年 | 72篇 |
2001年 | 80篇 |
2000年 | 51篇 |
1999年 | 44篇 |
1998年 | 44篇 |
1997年 | 46篇 |
1996年 | 46篇 |
1995年 | 37篇 |
1994年 | 34篇 |
1993年 | 46篇 |
1992年 | 36篇 |
1991年 | 37篇 |
1990年 | 42篇 |
1989年 | 30篇 |
1988年 | 27篇 |
1987年 | 28篇 |
1986年 | 26篇 |
1985年 | 27篇 |
1984年 | 25篇 |
1983年 | 16篇 |
1982年 | 17篇 |
1981年 | 29篇 |
1979年 | 16篇 |
1978年 | 21篇 |
1977年 | 19篇 |
1976年 | 19篇 |
1974年 | 16篇 |
1973年 | 15篇 |
排序方式: 共有2967条查询结果,搜索用时 13 毫秒
991.
992.
Bon RS Hong C Bouma MJ Schmitz RF de Kanter FJ Lutz M Spek AL Orru RV 《Organic letters》2003,5(20):3759-3762
[reaction: see text] The three-component condensation between an amine, an aldehyde, and an alpha-acidic isocyanide efficiently provides substituted 2-imidazolines in a one-pot reaction under mild conditions. 相似文献
993.
Three new derivatives of the cytotoxic azole-bridged dinuclear platinum(II) complex [(cis-Pt(NH3)2)2(mu-OH)(mu-pz)][NO3]2 (1) have been prepared and structurally characterized. Their formulas are [(cis-Pt(NH3)2)2(mu-OH)(mu-1,2,3-ta)][NO3]2 (2) (1,2,3-ta = 1,2,3-triazolate), [(Pt(R,R-dach))(mu-OH)(mu-pz)(Pt(S,S- dach))][NO3]2 (3) (dach = 1,2-diaminocyclohexane, pz = pyrazolate), and [(Pt(R,R-dach))(mu-1,2,3- ta)2(Pt(S,S-dach))][NO3]2 (4). The compounds were characterized by 1H, 13C, and 195Pt NMR spectroscopy, and elemental analysis, and their crystal structures were determined. Relevant data for 2: triclinic, space group P1, a = 8.5225(15) A, b = 9.1977(18) A, c = 9.9771(7) A, alpha = 66.988(10) degrees, beta = 75.423(9) degrees, gamma = 67.321(13) degrees, Z = 2. 3: orthorhombic, space group Pca2(1), a = 17.7653(3) A, b = 12.4076(3) A, c = 10.7091(3) A, Z = 4. 4: orthorhombic, space group Pbca, a = 13.8944(1) A, b = 17.8668(1) A, c = 20.7647(2) A, Z = 8. In the crystal structures of 2, and 3, the intramolecular distances between the two Pt atoms are 3.4411(6) and 3.4873(5) A, and the dihedral angles between the platinum coordination planes are 14.1(3) and 9.3(4) degrees, respectively. In 2, an intramolecular hydrogen bond is observed between N9 of the ammine ligand and the noncoordinated nitrogen atom (N3) of the triazole ring (N9...N3: 2.962(10) A). 4 has a boat-form structure, and the two coordination planes cross at 83.64(10) degrees. A cytotoxicity assay of these dinuclear platinum(II) compounds on human tumor cell lines was performed. In most of the cell lines, 1 and 2 showed much higher cytotoxicity than those of cisplatin. On the other hand, 3 was found to be moderately active, and 4 was found only marginally cytotoxic. Implications of these findings are discussed in the context of a structure-activity relationship. 相似文献
994.
995.
Tris{2‐[ N ‐(diethylaminothiocarbonyl)benz(‐amidino; imidoxy; ‐imidothio)‐ N ′‐yl]ethyl}amines – New Tripodal Ligands. Synthesis, Complex Stability, and Extraction Behaviour of their Silver(I) Complexes N‐(Thiocarbamoyl)‐benzimidoylchlorides react with trivalent nucleophiles to give four novel tripodal ligands. Two of them have been characterized by X‐ray methods. The ligands form with silver(I) cationic mononuclear complexes in which the three arms of the ligand are coordinated monodentately via sulfur. The results of FAB and ESI mass spectrometry as well as ESCA and NMR investigations verify this binding mode. The protonation constants of the ligands and the stability constants of silver(I) complexes have been determined potentiometrically. The novel tripodal compounds behave as powerful extractands for silver(I). 相似文献
996.
W. Lutz W. Wieker D. Müller M. Schneider C. H. Rüscher J.‐Ch. Buhl 《无机化学与普通化学杂志》2000,626(6):1460-1467
The steaming of zeolite Y (here at 873 K for 7 hours) leads to the formation of an amorphous aluminium aluminosilicate in addition to the dealuminated zeolite (DAY). An alkaline treatment of DAY causes the transformation of the non‐framework phase into an alkali aluminosilicate and the partial desilication of the DAY framework. The alkali aluminosilicate is decomposed by a moderate acid leaching under the formation of silica gel. The 29Si MAS NMR and IR spectra of DAY and its chemically treated modifications are superimposed by the signals of the crystalline zeolite framework and the amorphous non‐framework materials whereas XRD measurements only characterize the current state of the framework. 相似文献
997.
J. Hanuza M. M
czka A. Wa
kowska W. Oganowski H. Ban-Oganowska E. T. G. Lutz J. H. van der Maas 《Journal of Molecular Structure》1998,450(1-3)
The crystal structure of 2,6-dimethyl-4-nitropyridine N-oxide (DMNPO) has been determined at ambient temperature. The compound crystallizes as a monoclinic structure, space group P2/n, with 12 molecules per unit cell. The unit cell contains three non-equivalent formula units. The nitro group is not coplanar with the pyridine ring. Through a system of =C–HO hydrogen bonds the molecules are arranged into a two-dimensional network of layers parallel to the axc plane.The IR and Raman spectra, measured in the 3500–100 cm−1 region at ambient temperature, are correlated with X-ray structural data. The assignment of IR and Raman bands is given. The appearance of characteristic vibrational features in the spectra of this compound and the observed shifts of the =C–H and N–O IR active stretching modes, when the sample is dissolved in CCl4, is discussed in terms of the relatively strong =C–HO hydrogen bonds present in this crystal. 相似文献
998.
999.
Maurice J. van Eis Corine M. D. Komen Franciscus J. J. de Kanter Willem H. de Wolf Koop Lammertsma Friedrich Bickelhaupt Martin Lutz Anthony L. Spek 《Angewandte Chemie (International ed. in English)》1998,37(11):1547-1550
Three novel aspects emerge for the reaction of [5]metacyclophane ( 1 ) with the (intermediate) phenylphosphinidene complex 2 to give the 7-phosphanorbornadiene 3 . It is the first 1,4-addition of a phosphinidene complex to an unsaturated system, the first addition of a phosphinidene complex to a benzene ring, and the first [4+1] cycloaddition to an aromatic compound. 相似文献
1000.
用固相反应法合成了锂离子二次电池正极材料LiAlyCo0.2Ni0.8-yO2(y=0,0.001,0.005,0.01,0.03),采用XRD、SEM、ICP-AES、差分计时电位法和充放电循环等对合成的材料的物理化学性质以及电化学性能进行了测试分析。结果表明所合成的产物均为α-NaFeO2型的层状结构,产物无杂质相,产物的表面形貌规则,颗粒大小均匀。实验结果证明经过Al掺杂后的材料的放电电压平台有所提高,容量也有所上升。并且随着Al含量的增加,材料在电化学充放电过程的结构稳定性在上升,因此电化学稳定性得到了提高。实验结果还表明低含量Al元素的掺杂既提高了LiNi0.8Co0.2O2的放电容量,又提高了其循环可逆性,使材料的容量保持率显著提高。 相似文献