全文获取类型
收费全文 | 676篇 |
免费 | 37篇 |
国内免费 | 2篇 |
专业分类
化学 | 440篇 |
晶体学 | 8篇 |
力学 | 11篇 |
数学 | 58篇 |
物理学 | 198篇 |
出版年
2023年 | 6篇 |
2022年 | 11篇 |
2021年 | 13篇 |
2020年 | 20篇 |
2019年 | 24篇 |
2018年 | 22篇 |
2017年 | 23篇 |
2016年 | 27篇 |
2015年 | 25篇 |
2014年 | 25篇 |
2013年 | 65篇 |
2012年 | 46篇 |
2011年 | 49篇 |
2010年 | 34篇 |
2009年 | 33篇 |
2008年 | 38篇 |
2007年 | 38篇 |
2006年 | 29篇 |
2005年 | 22篇 |
2004年 | 21篇 |
2003年 | 12篇 |
2002年 | 14篇 |
2001年 | 6篇 |
2000年 | 5篇 |
1999年 | 7篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1995年 | 5篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 7篇 |
1987年 | 2篇 |
1986年 | 8篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1978年 | 1篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1975年 | 9篇 |
1974年 | 1篇 |
1971年 | 2篇 |
1970年 | 2篇 |
排序方式: 共有715条查询结果,搜索用时 15 毫秒
61.
Supramolecular calix[4]arene conjugate (L) has been developed as a sensitive and selective sensor for Zn(2+) in HEPES buffer among the 12 metal ion by using fluorescence, absorption and ESI MS and also by visual fluorescent color. The structural, electronic, and emission properties of the calix[4]arene conjugates L and its zinc complex, [ZnL], have been demonstrated using ab initio density functional theory (DFT) combined with time-dependent density functional theory (TDDFT) calculations. The TDDFT calculations reveal the switch on fluorescence behavior of L is mainly due to the utilization of the lone pair of electrons on imine moiety by the Zn(2+). The resultant fluorescent complex, [ZnL], has been used as a secondary sensing chemo-ensemble for the detection of -SH containing molecules by removing Zn(2+) from [ZnL] and forming {Cys/DTT·Zn} adducts as equivalent to those present in metallothioneins. The displacement followed by the release of the coordinated zinc from its Cys/DTT complex by heavy metal ion (viz. Cd(2+) and Hg(2+)), as in the metal detoxification process or by ROS (such as H(2)O(2)) as in the oxidative stress, has been well demonstrated using the conjugate L through the fluorescence intensity retrieval wherein the fluorescence intensity is the same as that observed with [ZnL], which in turn mimics the zinc sensing element (MTF) in biology. 相似文献
62.
Nucleophilic C-S bond formation using easily available β-hydroxysulfonate derivatives allowed direct access to new mono- and disubstituted divinyl sulfones. Our strategy uses thioethanol (HSCH(2)CH(2)OH) and its analogues such as HSCH(2)CH(Y)OH generated in situ. The strategy also allows the synthesis of modified divinyl sulfones attached to chiral appendages like carbohydrates. Bis-heteronucleophilic Michael addition reactions with 1 equiv of a primary amine afforded new generations of S,S-dioxothiomorpholine derivatives known for their therapeutic applications. Further synthetic manipulations of some of these cyclic compounds led to the synthesis of novel bicyclic derivatives. 相似文献
63.
Anant D. Kulkarni Dhurba Rai Libero J. Bartolotti Rajeev K. Pathak 《Journal of Molecular Structure》2007,824(1-3):32-38
Methyl hydrogen peroxide (MHP) exhibits a tendency to form a stable dimer by hydrogen-bonding. Ab initio theoretical investigations on methyl hydrogen peroxide dimer (MHPD) carried out herein lead to several energetically stable structures that have a direct bearing on the reactivity of the monomer in terms of its molecular electrostatic potential (MESP). To gauge the role played by the electron-correlation in lending stability to MHP and its dimer, we employ the density functional theory (DFT) (as implemented by B3LYP-functional), and subsequently second order Møller-Plesset (MP2) perturbation theory, using the basis sets 6-31G(d, p) and 6-311++G(2d, 2p). Simulated infra-red vibrational spectra lead to spectral intensity redistribution upon dimerization. Energetically the lowest MHPD is endowed with inversion symmetry and has two hydrogen bonds, while three other structures emerge: one energetically very close with two H-bonds, and the two others, with three H-bonds each, yet higher by about 2 kcal mol−1. 相似文献
64.
This paper presents the influence of magnetic field on heat due to viscous and electrical dissipations for an incompressible, viscous, electrically conducting fluid through a circular pipe in the presence of an applied (transverse) uniform magnetic field. The walls of the pipe are assumed to be non-conducting and kept at uniform temperature gradient in one case and at a constant temperature gradient in another case. The heat equation governing the present problem is solved exactly in hypergeometric series. The temperature at the centre of the pipe Te, unweighted mean temperature Tm and weight mean temperature TM are calculated. The temperature profiles are shown graphically for different values of Hartmann number M, Brinkman number Br and a non-dimensional number S. Numerical calculations are made for the Nusselt number and are entered in the table. 相似文献
65.
Non-isothermal studies of the dehydration of double salt hydrates of the type K2AB4·M(II)SO4·6H2O where AB4BeF2?4 or SeO2?4 and M(II)Mg(II), Co(II), Ni(II), Cu(II) or Zn(II) and their D2O analogues were carried out. Thermal parameters like activation energy, order of reaction, enthalpy change, etc., for each step of dehydration were evaluated from the analysis of TG, DTA and DTG curves. These parameters were compared with the corresponding double sulphate, i.e., K2SO4·M(II)SO4·6H2O and their D2O analogues. The role of divalent cation on the thermal properties of dehydration of the salt hydrates and also the effect on the thermal properties due to deuteration were discussed. The order of reaction was always found unity. The values of ΔH were within ~11-~19 kcal mol?1 相似文献
66.
Anirban Ganguly M. De Sarkar Anil K. Bhowmick 《Journal of Polymer Science.Polymer Physics》2007,45(1):52-66
Atomic force microscopy was successfully applied for comprehensive nanoscale surface and bulk morphological characterization of thermoplastic elastomeric triblock copolymers: poly[styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene] (SEBS) having different block lengths and their clay based nanocomposites. Commercially available Cloisite®20A and octadecyl (C18) ammonium ion modified montmorillonite clay (OC) prepared in our laboratory by cation exchange reaction were used. The phase detected images in the tapping mode atomic force microscopy exhibited a well‐ordered phase separated morphology consisting of bright nanophasic domains corresponding to hard component and darker domains corresponding to softer rubbery ethylene‐co‐butylene (PEB) lamella for all the neat triblock copolymers. This lamellar morphology gave a domain width of 19–23 nm for styrenic nanophase and 12–15 nm for ethylene‐co‐butylene phase of SEBS having end to mid block length ratio of 30:70 and block molecular weights of 8800–41,200–8800. On increasing the ratio of block lengths of the polymer matrix and the selectivity of the solvent toward the blocks used for casting, the morphological features of the resultant films altered along with change in domain thickness. The phase images showed position and distribution of the brightest clay stacks in the dark‐bright contrast of the base matrix of the nanocomposite. Exfoliated and intercalated‐exfoliated morphology obtained in the case of Cloisite®20A and OC‐based SEBS nanocomposites, respectively, is further supported by X‐ ray diffraction and transmission electron microscopy studies. The lamellar thickness of the soft phases widened to 50–75 nm, where the layered clay silicates (40–54 nm in length and 4–17 nm in width) were embedded in the soft rubbery phases in the block copolymeric matrix of the nanocomposite. The marginally thicker width of the hard styrenic phases and slightly shrinked width of the soft rubbery lamella can be observed from the regions where no nanofiller is present. Distinct differences in bulk morphologies of the nanocomposites prepared in the melt and the solution processes were obtained with nanocomposites. The presence of clay particles was evident from the almost zero pull‐off and snap‐in force in the force‐distance analysis of SEBS based nanocomposite. This analysis also revealed stronger tip interaction resulting in highest contact and adhesive forces with the softer PEB region relative to the harder PS region. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 52–66, 2007 相似文献
67.
68.
Radio pulses from extensive air showers (EAS) at 30, 44, and 60 MHz frequencies have been studied, using wide band broad-side
arrays of half-wave dipole antenna systems. The experimental results support the theoretical prediction that the field strength
of radio emission depends on the shower size. An asymmetry has been noticed in the pulse height distributions of radio pulses
detected by North-South and East-West directed arrays. These observations are in agreement with the theory that the charge
separation mechanism is predominant in generating radio pulses from EAS and radio emission is polarised in the East-West direction.
Experimental data are compared with those of earlier workers. 相似文献
69.
70.
The structure of129Ba is investigated through the beta decay of129La, whose half-life is measured to be 11.6±0.2 m. The decay properties are studied by means of beta, gamma and conversion electron spectroscopy techniques. Many transitions are observed and a level scheme of129Ba with deduced129Ba values is proposed. The total decay energy of129Ba is measured to be 3.72±0.05 MeV, which is compared with predictions of mass formulae. Low-lying structure of129Ba is discussed in terms of collective models. 相似文献