全文获取类型
收费全文 | 3417篇 |
免费 | 584篇 |
国内免费 | 279篇 |
专业分类
化学 | 1014篇 |
晶体学 | 38篇 |
力学 | 539篇 |
综合类 | 109篇 |
数学 | 341篇 |
物理学 | 2239篇 |
出版年
2024年 | 9篇 |
2023年 | 33篇 |
2022年 | 95篇 |
2021年 | 122篇 |
2020年 | 119篇 |
2019年 | 80篇 |
2018年 | 84篇 |
2017年 | 113篇 |
2016年 | 132篇 |
2015年 | 111篇 |
2014年 | 209篇 |
2013年 | 323篇 |
2012年 | 239篇 |
2011年 | 230篇 |
2010年 | 148篇 |
2009年 | 187篇 |
2008年 | 204篇 |
2007年 | 219篇 |
2006年 | 177篇 |
2005年 | 161篇 |
2004年 | 153篇 |
2003年 | 142篇 |
2002年 | 129篇 |
2001年 | 116篇 |
2000年 | 82篇 |
1999年 | 104篇 |
1998年 | 80篇 |
1997年 | 76篇 |
1996年 | 70篇 |
1995年 | 52篇 |
1994年 | 53篇 |
1993年 | 37篇 |
1992年 | 42篇 |
1991年 | 33篇 |
1990年 | 25篇 |
1989年 | 15篇 |
1988年 | 19篇 |
1987年 | 12篇 |
1986年 | 5篇 |
1985年 | 12篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1980年 | 1篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1973年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有4280条查询结果,搜索用时 31 毫秒
41.
A. E. Raevskaya A. L. Stroyuk S. Ya. Kuchmii Yu. M. Azhnyuk V. M. Dzhagan M. Ya. Valakh 《Theoretical and Experimental Chemistry》2006,42(3):162-168
The optical characteristics of CdSe nanoparticles, produced in aqueous solutions and polymer films in the reaction of cadmium
chloride and sodium selenosulfate, were studied. The main parameters that make it possible to vary the forbidden band width
were identified. The absorption, photoluminescence, Raman, and nonstationary decolorization spectra of CdSe nanoparticles
of various sizes were analyzed. It was demonstrated that under the conditions of pulsed irradiation the CdSe nanoparticles
are capable of accumulating excess electrons and inducing redox transformations in components of the solution (oxygen, methylviologen,
and sulfite ions).
__________
Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 3, pp. 150–155, May–June, 2006. 相似文献
42.
G. R. Sudhakaran J. C. Sarker R. L. Bhattacharjee L. H. Johnston 《International Journal of Infrared and Millimeter Waves》1987,8(12):1531-1540
Submillimeter laser-Stark spectra have been observed for the isotopic species of methyl fluoride,13CH3F, using the 337 m line of the HCN laser. We have identified the multiplet transitions as JK=18K17K in the ground vibrational state. Ten distinct families with K=8, 9, 10, 11, 12, 13, 14, 15, 16 and 17 have been observed. Zero-field frequencies for all the transitions are given and in most cases with better accuracy than predicted from the previous constants. 相似文献
43.
利用扫描电镜、热失重-红外、元素分析、低温氮吸附等技术和化学手段对聚羧酸基FFC-1离子交换纤维的结构与性能特点等进行了系统研究.结果表明:FFC-1离子交换纤维为含适量酰肼类交联键的聚羧酸(钠)型离子交换材料,外比表面积大和传质距离短是其反应动力学性能优异的主要原因,FFC-1纤维具有良好的化学与热稳定性。在5mol/L硫酸、硝酸、盐酸和2mol/L氢氧化钠溶液中浸泡,交换容量未见明显降低。但过氧化氢溶液对其功能基有明显破坏,CO2为FFC-1纤维在高温区间(300℃~350℃)的主要分解产物。 相似文献
44.
H.-J. Mai S. Wocadlo H.-C. Kang W. Massa K. Dehnicke C. Maichle-Mssmer J. Strhle D. Fenske 《无机化学与普通化学杂志》1995,621(5):705-712
Phosphanimine and Phosphoraneiminato Complexes of Iron. The Crystal Structures of [FeCl3(Me3SiNPEt3)], [FeCl2(Me3SiNPEt3)]2, [FeCl2(NPEt3)]2, and [Fe(O2C? CH3)2(NPEt3)]2 The phosphanimine complexes [FeCl3(Me3SiNPEt3)] (red-orange) and [FeCl2(Me3SiNPEt3)]2 (colourless) have been prepared by reactions of Me3SiNPEt3 with FeCl3 and FeCl2, respectively, in CH2Cl2 suspensions. Thermal decomposition of these donor-acceptor complexes in boiling toluene leads to the phosphoraneiminato complex [FeCl2(NPEt3)]2 (black), whereas [Fe(O2C? CH3)2(NPEt3)]2 (brown) is formed from iron(II) acetate and Me3SiNPEt3 in boiling acetonitrile. The complexes are characterized by IR spectroscopy and by crystal structure determinations. [FeCl3(Me3SiNPEt3)] (1) : Space group P21/c, Z = 8, structure determination with 4 673 unique reflections, R = 0.033. Lattice dimensions at ?15°C: a = 1 607.8, b = 1 602.0, c = 1 417.2 pm, β = 106.56°. 1 forms monomeric molecules with tetrahedrally coordinated iron atoms. Bond lengths in average: Fe? N = 196.9 pm, Fe? Cl = 219.7 pm. [FeCl2(Me3SiNPEt3)]2 (2) : Space group P21/c, Z = 4, structure determination with 4 992 unique reflections, R = 0.048. Lattice dimensions at 20°C: a = 1 457.9, b = 1 685.4, c = 1 507.3 pm, β = 116.74°. 2 forms dimeric molecules, which are associated by chloro bridges. The iron atoms are tetrahedrally coordinated with trans positions of the phosphanimine ligands. Both lengths in average: Fe? N = 202.2 pm, Fe? Clterminal = 224.7 pm, Fe? Cl bridge = 241.0 pm. [FeCl2(NPEt3)]2 (3): Space group P21/n, Z = 2, structure determination with 2763 unique reflections, R = 0.039. Lattice dimensions at ?70°C: a = 799.1, b = 1009.0, c = 1441.9 pm, β = 93.45°. 3 forms centrosymmetric dimeric molecules, in which the tetrahedrally coordinated iron atoms are associated by the nitrogen atoms of the phosphoraneiminato ligands. Bond lengths in average: Fe? N = 191.4 pm, Fe? Cl = 222.7 pm. [Fe(O2C? CH3)2(NPEt3]2 (4): Space group P21/n, Z = 2, structure determination with 3005 observed unique reflections, R = 0.034. Lattice dimensions at -65°C: a = 886.4, b = 1444.6 pm, β = 90.60°. 4 forms centrosymmetric dimeric molecules, in which the octahedrally coordinated iron atoms are associated by the nitrogen atoms of the phosphoraneiminato ligands with bond lengths Fe? N of 191.9 and 195.0 pm. The acetate groups are coordinated in a chelating fashion. 相似文献
45.
Ga^3+的新萃取体系的界面特性和胶团化作用研究 总被引:1,自引:0,他引:1
研究了Ga~(3+)协萃体系(Ga~(3+)-D_2EHPA-H_2MPA-正十二烷-H_2SO_4)的界面吸附和胶团形成热力学,发现该萃取体系中[H_2MPA]影响D_2EHPA和H_2MPA的界面吸附性质。在中、高[H_2MPA]范围内D_2EHPA与H_2MPA的界面吸附行为相反,D_2EHPA的存在也影响H_2MPA的界面吸附行为。研究了界面张力与各因素关系的数学模型,并获得某些胶团形成和界面吸附特性的物化参数。 相似文献
46.
Spectral quantities of cyclopropane, cyclobutane, cyclohexane, and of several derivatives, have been calculated by a semiempirical all-valence electron SCF-CI MO method. In cyclopropane, HOMO is practically localized in the carbon-frame, and LVMO is purely so. In cyclobutane, these two MO's are based on C-H bonds, while cyclohexane holds an intermediate position. Despite the overall similarity-experimental and computed-of the spectra of these molecules, assignments are non-parallel. Like cyclopropane, cyclobutane can extend conjugation, but to a diminished degree; cyclohexane behaves in this respect like an acyclic alkane. An interpretation of this gradation, in terms of the nature of high-lying MO's, is proposed. 相似文献
47.
Monodisperse poly(methyl methacrylate) (PMMA) particles containing various concentrations of stearyl methacrylate (SMA) were prepared, and a liquid crystal (LC) was swollen into the particles using a solute co-diffusion method (SCM). Phase separation behaviors between the polymer and LC were monitored by utilizing an optical and a polarized microscope (OM/POM). The monodisperse LC microcapsules were then applied to a polymer-dispersed liquid crystal (PDLC), and the electro-optical properties were investigated. As a result, the threshold and driving voltages were improved when the SMA content increased. The long alkyl chains of SMA in the capsules should exist at the interface of the LC and polymer resulting in an enhancement of phase separation between the polymer and LC, which largely influences the electro-optical properties of PDLC. 相似文献
48.
Gasphase Reactions. 92 Thermal Elimination of HCl from Alkyldichlorophosphanes (H3C/H)3C? PCl2 to Phosphaalkenes (H3C/H)2C?PCl and Phosphaalkines (H3C/H)C≡P The alkyldichlorophosphanes H3C? PCl2, ClH2? PCl2, (H3C)H2C? PCl2 and (H3C)2HC? PCl2 split off HCl on heating in a gasflow under reduced pressure. PE spectroscopic gas analysis proves that under these conditions the short-lived phosphaalkenes H2C?PCl, (H3C)H2C?PCl and – catalyzed by [MgCl2? MgO/SiO2]∞ – (H3C)2C?PCl as well as the phosphaalkines HC≡P and (H3C)C≡P are formed, all of which can be isolated by low temperature condensation. Based on the PES ionization patterns recorded and on the MNDO calculations for their assignment, the πCP multiple bonds are discussed. The presumable pathway of the HCl elimination is rationalized for (H3C)H2C? PCl2 by an approximate MNDO energy hypersurface. 相似文献
49.
A new potential tetradentate ligand, 1,4-bis(N-1-methylimidazol-2-ylmethyl)-1,4-diazacycloheptane (l), together with its CuII complex [CulCl]ClO4 (1), has been reported. The crystal structure of 1, determined by single-crystal X-ray analysis, shows that it is in chiral P212121 space group. The CuII centre is penta-coordinated in square pyramidal geometry and the diazacycloheptane (DACH) ring adopts normal boat configuration. The most striking feature of this complex is the formation of a 3D network bridged through the C-H?Cl hydrogen bonds with the perchlorate anions in the cavities, and stabilized via π-π stacking interactions along the a-direction. The solution behaviour of 1 has been further investigated by UV/Vis and ESR techniques. 相似文献
50.
Effect of the type and number of high-speed impellers installed on a common shaft on the power characteristics was investigated
in water and glucose solutions of different concentration. Different configurations of the Rushton or Smith turbines, pitched
blade turbines, propeller, and A 315 impeller were tested. Measurements of power consumption were carried out within the transitional
and turbulent regime of the fluid flow using the strain gauge method. Baffled agitated vessels with inner diameter of 0.288
m and 0.634 m were used for the experiments. Liquid height in the vessels was equal to the vessel diameter or it was twice
higher. The relative power consumption was compared for different configurations of the impellers.
Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 22–26 May
2006. 相似文献