全文获取类型
收费全文 | 24465篇 |
免费 | 2868篇 |
国内免费 | 2104篇 |
专业分类
化学 | 14626篇 |
晶体学 | 603篇 |
力学 | 1591篇 |
综合类 | 167篇 |
数学 | 1480篇 |
物理学 | 10970篇 |
出版年
2024年 | 82篇 |
2023年 | 258篇 |
2022年 | 643篇 |
2021年 | 619篇 |
2020年 | 795篇 |
2019年 | 738篇 |
2018年 | 739篇 |
2017年 | 960篇 |
2016年 | 1204篇 |
2015年 | 1050篇 |
2014年 | 1330篇 |
2013年 | 2309篇 |
2012年 | 1595篇 |
2011年 | 1870篇 |
2010年 | 1439篇 |
2009年 | 1602篇 |
2008年 | 1513篇 |
2007年 | 1615篇 |
2006年 | 1353篇 |
2005年 | 1077篇 |
2004年 | 986篇 |
2003年 | 857篇 |
2002年 | 934篇 |
2001年 | 590篇 |
2000年 | 506篇 |
1999年 | 478篇 |
1998年 | 384篇 |
1997年 | 272篇 |
1996年 | 247篇 |
1995年 | 212篇 |
1994年 | 204篇 |
1993年 | 143篇 |
1992年 | 155篇 |
1991年 | 91篇 |
1990年 | 61篇 |
1989年 | 56篇 |
1988年 | 74篇 |
1987年 | 52篇 |
1986年 | 47篇 |
1985年 | 44篇 |
1984年 | 49篇 |
1983年 | 20篇 |
1982年 | 35篇 |
1981年 | 33篇 |
1980年 | 19篇 |
1979年 | 26篇 |
1978年 | 15篇 |
1977年 | 12篇 |
1976年 | 8篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
B. Sourd P. André J. Aubreton M.-F. Elchinger 《Plasma Chemistry and Plasma Processing》2007,27(1):35-50
In this paper, calculated values of the viscosity and thermal conductivity of atomic nitrogen, taking into account three species
(the ground and two excited states), are presented. The calculations, which assume that the temperature dependent probability
of occupation of the states is given by the Boltzmann factor, are performed for atmospheric-pressure in the temperature range
from 1,000 to 20,000 K. Six collision integrals are used in calculating the transport coefficients and we have introduced
new averaged collision integrals where the weight associated at each interacting species pair is the probable collision frequency.
The influence of the collision integral values and energy transfer between two different species is studied. These results
are compared which those of published theoretical studies. 相似文献
992.
993.
《Journal of Coordination Chemistry》2012,65(14):2207-2215
Two aryl amide ligands, N-(p-tolyl)-2-(quinolin-8-yloxy)acetamide (L1 ) and N-(4-chlorophenyl)-2-(quinolin-8-yloxy)acetamide (L2 ), were synthesized. With these ligands, two series of lanthanide(III) complexes were prepared, Ln(L n )2(NO3)3 (n = 1, 2; Ln = La, Sm, Eu, Gd, Dy), and characterized by the elemental analyses, molar conductivity, 1H NMR spectra, IR spectra and TG-DTA. The fluorescence properties of the complexes and the triplet state energies of the ligands were studied in detail. In addition, the quantum yields of both Eu(III) complexes and Eu(L0)2(NO3)3 [where L0 is N-(phenyl)-2-(quinolin-8-yloxy)acetamide] 1 were calculated. The results indicate that among the lowest triplet energies (T) of the three ligands, that of L2 is most suitable to the resonance level (5D1) of Eu(III) ion. Furthermore, Eu(L2)2(NO3)3 has the highest fluorescence intensity and quantum yield of the three Eu(III) complexes. 相似文献
994.
《Journal of Coordination Chemistry》2012,65(7):1139-1146
A 1-D chain complex, cadmium(ΙΙ) chloride thiocyanate (1), [CdCl(SCN)] n was synthesized by evaporation and characterized by single-crystal X-ray diffraction and FT-IR techniques. The compound crystallizes in the space group Pnma of orthorhombic system with cell parameter a = 9.5967(7), b = 4.2595(3), and c = 10.1789(7) Å; V = 416.08(5) Å3 and Z = 4. The cadmium(ΙΙ) is five-coordinate, surrounded by one pair of (µ-1,1-NCS) bridging NCS? and three Cl? as a µ3-linker coordinating three Cd(ΙΙ) centers, approximately a severely distorted square-pyramidal configuration. Cd(ΙΙ), Cl?, and SCN? form an infinite 1-D chain with chair-like features, a new example of mixed Cd–NCS–Cl discrete compounds. The photophysical properties of the crystals have been investigated with one emission peak at 473 nm observed for the title complex in the solid state, which exhibits blue luminescence. The mechanical properties of the crystals have been studied using Vickers microhardness tester and the hardness was 78.6 kg mm?2. 相似文献
995.
《Journal of Coordination Chemistry》2012,65(17):3117-3126
A ligand containing different coordination groups, 5-([1,10]phenanthroline-[4,5-f]imidazo-2-yl)-8-hydroxyquinoline (PhenI8Q) has been synthesized and two corresponding polymeric metal complexes Cu(II) (1) and Zn(II) (2) were prepared by coordination polymerization of the ligand with copper(II) and zinc(II) halides, respectively. The ligand was characterized by 1H-NMR, 13C-NMR, and Fourier transform-infrared (FT-IR) and its corresponding polymeric metal complexes 1 and 2 were characterized by FT-IR, UV-Vis, elemental analysis, thermal gravimetric analysis, and conductivity measurements. The absorption spectra and luminescence of the ligand, 1, and 2 were investigated by UV-Vis and fluorescence spectroscopy at room temperature. Compared with the ligand, the fluorescence spectra of the polymeric metal complexes exhibit blue shifts in dimethyl sulfoxide (DMSO) solution and bathochromic shifts in the solid state. Complexes 1 and 2 emit blue light with emission maximum (λ f max) at 449 and 431 nm in DMSO solution and at 485 and 484 nm in the solid state, respectively. 相似文献
996.
《Journal of Coordination Chemistry》2012,65(1):155-168
A polymeric silver(I) complex, [Ag4(μ-pydc)2(μ-pm)2]n (1) (pydc = pyridine-3,5-dicarboxylate and pm = pyrimidine), has been synthesized and characterized by elemental analysis, IR spectroscopy, thermal analysis, and single-crystal X-ray diffraction. X-ray crystallographic data of 1 revealed that pydc exhibits two different coordinaton modes that play a key role in the construction of the 3-D crystal network including Ag–carboxylate clusters in which close Ag–Ag distances exist. The magnitudes of close Ag–Ag interactions in second-order energy (E2) have been revealed by natural bond orbital analysis performed with single point energy calculation using the experimental geometry of 1. Furthermore, the luminescent properties of 1 show strong fluorescence with two emission maxima in the visible region. Also, 1 has antifungal activity on Candida albicans (MIC value, 4 μg mL?1) and good antibacterial activity on micro-organisms (MIC value, 64–256 μg mL?1). 相似文献
997.
《Journal of Coordination Chemistry》2012,65(8):1412-1422
A family of phenoxo-bridged heterometallic Schiff base trinuclear complexes, [Fe2LnL2(C3H7COO)(H2O)]·CH3OH·CH3CN·H2O (Ln = Sm, 1; Gd, 2; Tb, 3; Dy, 4) is reported. Those complexes were afforded by “one-pot” reaction of a polydentate Schiff base ligand 2-hydroxy-3-methoxy-phenylsalicylaldimine (H2L) with Fe(NO3)3·9H2O, Ln(NO3)3·6H2O and sodium butyrate (C3H7COONa) in a mixture of methanol and acetonitrile in the presence of triethylamine as a base. Single-crystal X-ray diffraction analysis reveals that the structures of the four complexes are isomorphic. In each complex, two anionic [FeL2]? units coordinate to the central lanthanide ion as a tetradentate ligand using its four phenoxo oxygens, forming a two-blade propeller-like molecular shape. Magnetic properties of 1–4 were investigated using variable temperature magnetic susceptibility, and weak ferromagnetic exchange between the FeIII and LnIII ions has been established for the Gd derivative. The Tb and Dy complexes show no evidence of slow relaxation behavior above 2.0 K. 相似文献
998.
《Journal of Coordination Chemistry》2012,65(21):3600-3614
AbstractLanthanide complexes were prepared with 2,6-diacetylpyridinebis(benzoylhydrazone) (DAPBH2) and 7,7,8,8-tetracyano-p-quinodimethanide (TCNQ??). The complexes adopted one of two structure types depending on the reaction solvent. The complexes were categorized as Type I (i.e. bis{[2,6-diacetylpyridinebis(benzoylhydrazone)] methanollanthanide(III)}bis(µ2- 7,7,8,8-tetracyanoquinodimethanide(1?))bis(7,7,8,8-tetracyanoquinodimethanide(1?))bis(7,7,8,8-tetracyanoquinodimethanide(1?)) methanol disolvate, [Ln2(DAPBH2)2 (µ2-TCNQ??)2(TCNQ??)2(MeOH)2](TCNQ??)2·2MeOH (Ln?=?Gd, Tb, or Dy) or Type-II (i.e. [Ln2(DAPBH2)2(µ2-TCNQ??)2(TCNQ??)2(EtOH)2] (TCNQ??)2·solvent (Ln?=?Tb and Dy, solvent =4EtOH for the Tb and 2EtOH·2CH2Cl2 for the Dy complexes). These two complexes exhibit dramatically different molecular structures and packings. In all complexes, the strong intra- and intermolecular stacking interactions of the TCNQ?? radicals lead to the formation of 1D TCNQ chains. Magnetic susceptibility measurements for Type I and Type II complexes reveal that they exhibit paramagnetic behavior and that their magnetic properties originate from the lanthanide ions alone, owing to the diamagnetic nature of the TCNQ?? stacks. 相似文献
999.
《Physics and Chemistry of Liquids》2012,50(4):507-519
Abstract A new dye Trans-4-[p-(N-hydroxyethyl-N-ethyiamino)styryl]-N-methylpyridinium p-toluene sulfonate (HEASPS) was synthesized, and the two-photon absorption (TPA), TPA-induced frequency up-conversion emission, and two-photon pumped (TPP) frequency up-converted lasing properties of this new dye were experimentally studied. This new dye has a moderate TPA cross-section of\sigma2 = 4.7 × 10?48 cm4 .s/photon at 1064nm, but exhibits a high lasing efficiency. The net conversion efficiency from the absorbed 1064 nm pump pulse energy to the 626 nm up-converted lasing energy is 18.2% at the pump energy level of 1.9 mJ. 相似文献
1000.
《Physics and Chemistry of Liquids》2012,50(3):231-236
The dielectric relaxation study that is static dielectric permittivity (∈0) and relaxation time (τ) of amide of N-methyl formamide (NMF) with increasing volume percent propylene glycol (PLG) and BLG has been carried out at different temperatures. The time domain reflectometry (TDR) technique has been used to measure reflection coefficient in frequency range of 10 MHz to 20 GHz. The dielectric parameters have been obtained by fitting experimental data with the Havriliak–Negami equation. The experimental observation shows that the static dielectric permittivity and relaxation time decreases with increasing temperature. The experimental observation also shows that the static dielectric permittivity decreases and relaxation time increases with increasing percentage volume of Propylene glycol (PLG) and Butylene glycol (BLG) in NMF. The nature of (?0) and (τ) is same for the temperature ranges (20, 30, and 40°C). The thermodynamic parameters enthalpy (ΔH) and entropy (ΔS) of the binary mixture are also reported in this work. 相似文献