全文获取类型
收费全文 | 21181篇 |
免费 | 2318篇 |
国内免费 | 1880篇 |
专业分类
化学 | 13621篇 |
晶体学 | 564篇 |
力学 | 869篇 |
综合类 | 99篇 |
数学 | 730篇 |
物理学 | 9496篇 |
出版年
2024年 | 75篇 |
2023年 | 214篇 |
2022年 | 551篇 |
2021年 | 514篇 |
2020年 | 682篇 |
2019年 | 629篇 |
2018年 | 624篇 |
2017年 | 800篇 |
2016年 | 1030篇 |
2015年 | 913篇 |
2014年 | 1137篇 |
2013年 | 2025篇 |
2012年 | 1426篇 |
2011年 | 1662篇 |
2010年 | 1238篇 |
2009年 | 1444篇 |
2008年 | 1327篇 |
2007年 | 1409篇 |
2006年 | 1164篇 |
2005年 | 928篇 |
2004年 | 862篇 |
2003年 | 743篇 |
2002年 | 829篇 |
2001年 | 497篇 |
2000年 | 427篇 |
1999年 | 379篇 |
1998年 | 319篇 |
1997年 | 226篇 |
1996年 | 202篇 |
1995年 | 166篇 |
1994年 | 169篇 |
1993年 | 108篇 |
1992年 | 126篇 |
1991年 | 65篇 |
1990年 | 50篇 |
1989年 | 43篇 |
1988年 | 57篇 |
1987年 | 45篇 |
1986年 | 39篇 |
1985年 | 34篇 |
1984年 | 39篇 |
1983年 | 18篇 |
1982年 | 30篇 |
1981年 | 24篇 |
1980年 | 12篇 |
1979年 | 22篇 |
1978年 | 12篇 |
1977年 | 10篇 |
1974年 | 6篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
《Physics and Chemistry of Liquids》2012,50(5):561-569
Some new 1,2,4-triazole derivatives have been synthesized and characterized by TLC, IR, NMR and mass spectra. Densities, viscosities and ultrasonic velocities of these compounds have been measured over the wide composition range at 308.15?K in dimethyl formamide (DMF) and tetrahydro furan (THF). From these data, various acoustical and thermodynamic parameters (C.V. Suryanarayana, J. Kuppuswamy. J. Acoust. Soc. Ind., 4, 75 (1976); H. Erying, M.S. John, Significance of Liquid Structures, Wiley, New York (1969); G.K. Johri, R.C. Misra. Acustica, 56, 66 (1989)) were evaluated. Some of these parameters are isentropic compressibility (κs), intermolecular free length (L f), relaxation strength (r), relative association (R A), Rao's molar constant (R m), van der Waal's constant (b), molar compressibility (W), internal pressure (π), free volume (V f), solvation number (S n) etc. The behavior of solutions of these compounds in DMF and THF are explained from the evaluated parameters. 相似文献
102.
N.Tz. Dintcheva S. AlessiR. Arrigo G. PrzybytniakG. Spadaro 《Radiation Physics and Chemistry》2012,81(4):432-436
In this paper two systems, polyethylene (LDPE) and polyethylene/commercial organo-modified montmorillonite (LDPE/OMMT) nanocomposite, were subjected to e-beam irradiation at different doses and both the molecular modifications and mechanical properties have been investigated through solubility, FT-IR, calorimetric and tensile tests. Moreover, in some of the irradiated systems photo-oxidation aging was performed and its effects were studied. The results show an enhancement with irradiation of the positive effect of the nano-filler loading, related to the increase of the mechanical properties, due to the increase of the nano-filler polymer interaction.Nevertheless calorimetric and FT-IR data indicate that the well known reduction of LDPE/OMMT nanocomposite resistance to photo-oxidation ageing, with respect to LDPE, is amplified by ionizing radiation. 相似文献
103.
The Young's modulus of graphene with various rectangular and circular vacancy defects is investigated by molecular dynamics simulation. By comparing with the results calculated from an effective spring model, it is demonstrated that the Young's modulus of graphene is largely correlated to the size of vacancy defects perpendicular to the stretching direction. And a linear reduction of Young's modulus with the increasing concentration of mono‐atomic‐vacancy defects (i.e., the slope of ?0.03) is also observed. The fracture behavior of graphene, including the fracture strength, crack initiation and propagation are then studied by the molecular dynamics simulation, the effective spring model, and the quantized fracture mechanics. The blunting effect of vacancy edges is demonstrated, and the characterized crack tip radius of 4.44 Å is observed. 相似文献
104.
105.
Jennifer N. Cambre Debashish Roy Brent S. Sumerlin 《Journal of polymer science. Part A, Polymer chemistry》2012,50(16):3373-3382
A detailed study of the pH‐ and sugar‐responsive behavior of poly(3‐acrylamidophenylboronic acid pinacol ester)‐b‐poly(N,N‐dimethylacrylamide) (PAPBAE‐b‐PDMA) block copolymers is presented. Reversible addition‐fragmentation chain transfer (RAFT) polymerization of the pinacol ester of 3‐acrylamidophenylboronic acid resulted in homopolymers with molecular weights between 12,000 and 37,000 g/mol. The resulting homopolymers were employed as macro‐chain transfer agents during the polymerization of N,N‐dimethylacrylamide (DMA). Successful chain extension and removal of the pinacol protecting groups to yield poly(3‐acrylamidophenylboronic acid)‐b‐PDMA (PAPBA‐b‐PDMA) with free boronic acid moieties resulted in pH‐ and sugar‐responsive block copolymers that were subsequently investigated for their behavior in aqueous solution. The PAPBA‐b‐PDMA block copolymers were capable of solution self‐assembly due to the PAPBA block being water‐insoluble below its pKa. The resulting aggregates were demonstrated to solubilize and release model hydrophobic compounds, as demonstrated by fluorescence studies. Dissociation of the aggregates was induced by raising the pH above the pKa of the boronic acid residues or by adding sugars capable of forming boronate esters. Aggregate size, dissociation kinetics, and the effect of various sugars were considered. The critical sugar concentration needed to induce aggregate dissociation was tuned by incorporation of hydrophilic DMA units within the PAPBA responsive segment to yield PDMA‐b‐poly(3‐acrylamidophenylboronic acid‐co‐DMA) block copolymers. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
106.
《Journal of Coordination Chemistry》2012,65(21):3764-3771
The crystal structure of [Zn2(2-pmOpe)2Cl4] (2-pmOpe?=?diethyl (pyridin-2-ylmethyl)phosphate) was determined by X-ray-diffraction method. The compound was also characterized by IR, far-IR, 1H, and 31P NMR spectroscopy. In this compound, 2-pmOpe is a bidentate N,O-bridging ligand and Zn(II) are slightly distorted tetrahedral ZnNOCl2. Zn(II) ions are doubly bridged by the 2-pmOpe ligands, resulting in a dinuclear species. The structure is stabilized by intermolecular C–H?···?O and C–H?···?Cl hydrogen bonds. The spectral properties are in agreement with the structural data. 相似文献
107.
《Journal of Coordination Chemistry》2012,65(20):3560-3574
A new coordination complex, aqua bis(o-phenanthroline) cadmium(II) sulfate cyanoguanidine pentahydrate, [Cd(o-phen)2(SO4)(H2O)](cnge)?·?5H2O, was synthesized and characterized. The crystal structure was solved by X-ray diffraction methods. It crystallizes in the monoclinic space group P21/n with a?=?13.7650(2) Å, b?=?10.2796(2) Å, c?=?21.4418(3) Å, β?=?90.106(2)°, and Z?=?4 molecules per cell unit. The cadmium(II) is in a distorted octahedral environment coordinated to two nearly planar and mutually perpendicular o-phenanthrolines, one oxygen atom of sulfate, and a water molecule. Non-bonded and planar cyanoguanidine and five crystallization water molecules complete the asymmetric unit. Vibrational (FT-IR and FT-Raman) spectroscopies and thermogravimetric determinations support this structure. Intensity enhancement of the fluorescence spectrum may be a demonstration of the interaction of the metal with phenanthroline. In solution the coordination behavior is rather different, and the speciation studies point to coordination of both cnge and phenanthroline to cadmium. The improvement of the antibacterial activity of cadmium upon complexation has been determined. 相似文献
108.
《Journal of Coordination Chemistry》2012,65(11):1953-1962
Two new discrete Btz-bridged pentanuclear metal complexes, [HDMF][NaHg4(Btz)6I4] (1) and [Zn5(Btz)6(L)3(Ac)]?·?0.5MeOH?·?0.5H2O (2) (Btz?=?deprotonated benzotriazole, L?=?p-aminobenzoate, HDMF?=?protonated DMF, and Ac?=?acetate), were synthesized using three-layered diffusion and natural evaporation methods, respectively. In 1, the pentanuclear anion [NaHg4(Btz)6I4]? is composed of a tetrahedral arrangement of four four-coordinate Hg(II) ions centered on the six-coordinate Na(I), and thereby forming a rare Btz-bridged hetero-metal complex. Compound 2 is a neutral pentanuclear homo-metal complex, consisting of a tetrahedral arrangement of four five-coordinate Zn(II) ions centered on the fifth six-coordinate Zn(II). The thermal stabilities and solid-state photoluminescence of the two complexes have been investigated. 相似文献
109.
In a previous paper we studied the Young's and shear modulus of a high-angle twist grain boundary (5) in Cu, using the EAM, and related it to the uniaxial strain derivatives of single crystals. In this paper, we discuss elastic properties of ten additional twist grain boundaries, from 8.8–43.6°. The monolayer Young's modulus at each boundary was calculated and found to be 20–50% higher than the bulk value for all eleven boundaries for both csl and type1 structures. The monolayer shear modulus at each boundary was calculated and found to be 93–98% lower than the bulk value for six grain boundaries with csl structure and found to decrease with increasing twist angle. The critical shear stress was also calculated for eleven boundaries with csl structure and found to roughly decrease with increasing twist angle. 相似文献
110.
L. Fionova O. Konokenko V. Matveev L. Priester S. Lartigue F. Dupau 《Interface Science》1994,1(3):207-211
Data on mutual arrangements of different types of grain boundaries in polycrystals are presented. The heterogeneity in grain boundary distribution, namely, the effect of gathering low-angle or special tilt grain boundaries is found in pure aluminum thin films, in sheets of Fe-3% Si alloy and in Al2O3 doped with MgO or MgO and Y
2O3. The local texture, i.e., formation of colonies or clusters of close-oriented grains is considered as a reason of this heterogeneity. The influences of grain boundary gathering on the transport properties of polycrystals and on the crack propagation are discussed. A new concept of effective grain size is suggested to analyze the relationship between material microstructures and material properties. 相似文献