全文获取类型
收费全文 | 2954篇 |
免费 | 61篇 |
国内免费 | 10篇 |
专业分类
化学 | 1791篇 |
晶体学 | 69篇 |
力学 | 98篇 |
数学 | 281篇 |
物理学 | 786篇 |
出版年
2023年 | 17篇 |
2022年 | 28篇 |
2020年 | 23篇 |
2019年 | 37篇 |
2018年 | 30篇 |
2017年 | 31篇 |
2016年 | 65篇 |
2015年 | 43篇 |
2014年 | 68篇 |
2013年 | 162篇 |
2012年 | 134篇 |
2011年 | 223篇 |
2010年 | 148篇 |
2009年 | 137篇 |
2008年 | 164篇 |
2007年 | 205篇 |
2006年 | 157篇 |
2005年 | 135篇 |
2004年 | 109篇 |
2003年 | 104篇 |
2002年 | 74篇 |
2001年 | 32篇 |
2000年 | 39篇 |
1999年 | 40篇 |
1998年 | 30篇 |
1997年 | 32篇 |
1996年 | 31篇 |
1995年 | 30篇 |
1994年 | 25篇 |
1993年 | 28篇 |
1992年 | 31篇 |
1991年 | 22篇 |
1990年 | 31篇 |
1989年 | 21篇 |
1988年 | 17篇 |
1987年 | 28篇 |
1986年 | 31篇 |
1985年 | 31篇 |
1984年 | 26篇 |
1983年 | 19篇 |
1982年 | 31篇 |
1981年 | 40篇 |
1980年 | 22篇 |
1979年 | 34篇 |
1978年 | 27篇 |
1976年 | 22篇 |
1975年 | 21篇 |
1974年 | 19篇 |
1973年 | 20篇 |
1972年 | 18篇 |
排序方式: 共有3025条查询结果,搜索用时 46 毫秒
891.
Richard A. Hancock Ray Walder Helmut Weigel Victor Gold Cristian M. Sghibartz 《Journal of mass spectrometry : JMS》1983,18(9):402-405
Isobutane chemical ionization mass spectrometry of crown ether acetals (M), derived from ethanal, give [MH]+ ions from which species corresponding to 44 u are successively eliminated. Mechanisms are presented in which these units correspond to (i) ethanal and (ii) oxirane. An accompanying process is the elimination of ethyne. Similar reactions occur in the chemical ionization mass spectrometry of benzo crown ether acetals. 相似文献
892.
Ray E. Artz 《Foundations of Physics》1981,11(9-10):679-697
Galilean space-time plays the same role in nonrelativistic physics that Minkowski space-time does in relativistic physics. In this paper, the fundamental concepts (velocity, momentum, kinetic energy, etc.) and principles (laws of motion and conservation laws) of classical physics are formulated in the language of Galilean space-time. Much of the development closely parallels the development of similar concepts and principles in the theory of special relativity. 相似文献
893.
Anthony J. Pearson Tapan Ray Ian C. Richards Jon Clardy Linda Silveira 《Tetrahedron letters》1983,24(52):5827-5830
Use of the title reactions for the regioselective, and stereoselective functionalization of a range of dienylacetic acids, available from simple organoiron chemistry, is presented. 相似文献
894.
Summary Two complextrans-NiL2 (NCS)2] (L =N, N-dimethyl-1,3-propanediamine) synthesised from solution in two isomeric forms (1) and (2), exhibit similar colours, magnetic moments and electronic spectra, but differ in their i.r. spectra and x-ray powder diffraction patterns. We suggest they possesstrans- chair-chair andcis-chair-chair chelate conformations, respectively. Complexes (1) (2) isomerise (temperature range 382–397.5 K; H = 5.12 kJ mol–1) in the solid state. Isomer (2) is converted into isomer (1) upon recrystallisation from chloroform. Thetrans-[NiL2NCSe)2] complex does not isomerise upon heating. The compound [NiL(NCS)2], prepared by thermal decomposition of [NiL2(NCS)2], possesses octahedral polymeric structure in which the diamine is chelated and all the thiocyanato groups are bridging. 相似文献
895.
896.
Colloid and Polymer Science - The kinetics of aqueous polymerization of acrylamide and methacrylamide initiated by potassium peroxydiphosphate has been investigated. The kinetic orders with respect... 相似文献
897.
The silver complex ofo-aminobenzenesulfonyl glycine crystallizes in the monoclinic space groupP21/n with two molecules of HAg[C6H4(NH2)SO2-NHCH2COO]2 per unit cell of dimensionsa=5.73(2),b=12.16(1),c=13.94(3) Å, and =94.9(1) °. The structure has been solved by the heavy-atom technique using three-dimensional photographic data, and refined by full-matrix least-squares methods, leading to a finalR value of 0.102. The two aminobenzenesulfonyl glycine ligands in the complex are centrosym-metrically arranged with the silver atom at the center of symmetry. The silver atom is surrounded in an approximately square-planar arrangement by two nitrogens (one each from the amino groups attached to benzene rings) and two oxygens (one each from the carboxyl groups) at distances of 2.280 and 2.599 Å, respectively. The glycine in this complex is not a zwitterion. The molecules are held together by a three-dimensional network of hydrogen bonds of the type N-H O. Both the -amino nitrogen and that attached to the benzene ring take part in the formation of hydrogen bonds. 相似文献
898.
APW-Xα calculations of a f.c.c.-b.c.c. phase transition in Xe prior to metallization give P ? 950 kbar, contrary to the 820 kbar result of Hama and Matsui; their use of non-touching APW spheres (f.c.c.) may be the crucial difference. Hartree-Fock plus correlation calculations in Kr indicate that f-bands play no role in rare gas crystal metallization. 相似文献
899.
Optical absorption and emission spectra are reported for single crystals of the cubic elpasolite Cs2NaSmCl6. The variable temperature spectra obtained at high resolution are assigned using energies and relative intensities. Transitions from the ground level, 6H to cystal fi levels of 6H-, 6F-, 4G-, 4F,, 4I, and 6P, are located and characterized. Intensity calculations are reported for magnetic dipole allowed transitions. The dominance of vibronic intensity in 6H→6F - and 6P, transitions is accounted for qualitatively through the ligand polarization model involving quadrupole metal (Sm3+)-ligand (Cl?) interaction mechanisms. The Eu″(6H)→E′(6H) Eu′(6F) no-phonon transition is postulated to be pure electric quadrupole allowed. The ground state magnetic moment is determined to be very small from magnetic circular dichroism (MCD) spectra.This study has led to the assignment of nearly all of the crystal field levels in the visible and IR region for Cs2NaSmCl6. A total of 27 such levels were identified, 17 from no-phonon transitions and the rest from vibronic transitions. The magnetic dipole intensity calculated using intermediate coupling Oh wavefunctions along with a crystal field analysis of the splitting pattern was used in the assignment of the levels. Vibronic bands were observed for all transitions and their vibrational symmetries were tentatively assigned. MCD data were used to determine the magnet moment of the ground state. 相似文献
900.
Condensation of the anions of acetone, acetophenone, acetylacetone and benzoylacetone with 4,6-dimethoxy-2-pyrone afforded good yields of the corresponding 6 substituted 4-methoxy-2-pyrones which were converted to the 4-hydroxy analogs by demethylation with iodotrimethylsilane. 相似文献