全文获取类型
收费全文 | 183篇 |
免费 | 15篇 |
国内免费 | 1篇 |
专业分类
化学 | 81篇 |
晶体学 | 2篇 |
力学 | 23篇 |
数学 | 39篇 |
物理学 | 54篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 6篇 |
2018年 | 6篇 |
2017年 | 3篇 |
2016年 | 10篇 |
2015年 | 13篇 |
2014年 | 7篇 |
2013年 | 19篇 |
2012年 | 12篇 |
2011年 | 25篇 |
2010年 | 13篇 |
2009年 | 12篇 |
2008年 | 5篇 |
2007年 | 4篇 |
2006年 | 5篇 |
2005年 | 5篇 |
2004年 | 4篇 |
2003年 | 3篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1984年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1941年 | 1篇 |
排序方式: 共有199条查询结果,搜索用时 31 毫秒
181.
Karbalaei-Heidari HR Habibi AE Khajeh K Ranjbar B Nemat-Gorgani M 《Applied biochemistry and biotechnology》2004,117(2):123-132
An intermediate form of alpha-amylase from Bacillus subtilis was prepared following a previously reported procedure. Stabilization of this protein structure by various additives and its interaction with alkyl-substituted Sepharose 4B (Sepharose-lipid), used to mimic the role of the alkyl chains of the phospholipid bilayer, were investigated. Exposure of hydrophobic clusters in the protein structure on denaturation was indicated by a greater affinity of the intermediate form for interaction with the alkyl chains on the matrix, as compared with the original native structure. Near- and far-ultraviolet circular dichroism studies supported loss of tertiary structure with retention of secondary structure, as expected from molten globular intermediate forms. Based on the results presented, we suggest that interaction of a protein in its native and nonnative forms with an alkyl-substituted matrix may provide useful information regarding its capacity for insertion into and translocation across the biologic membrane. 相似文献
182.
Precise measurements of electrical conductances of solutions of tetraethylammonium bromide, tetrapropylammonium bromide, tetrapentylammonium bromide, tetrahexylammonium bromide, tetraheptylammonium bromide, tetraocytylammonium bromide, sodium tetraphenylborate, and potassium tetraphenylborate in N,N-dimethylacetamide at 25°C are reported for the concentration range 0.005-0.015 mol-dm–3. The conductance data have been analyzed by the 1978 Fuoss conductance-concentration equation in terms of the limiting molar conductance, the association constant, and the association diameter. The limiting ionic conductances have been estimated from the appropriate division of the limiting molar conductivity value of the reference electrolyte Bu4NBPh4. Slight ionic association was found for all these salts in this solvent medium. Tetraalkylammonium ions are found to be unsolvated in N,N-dimethylacetamide, whereas significant solvation has been noticed for sodium and potassium ions. 相似文献
183.
Mozaffar Asadi Elham Safaei Bijan Ranjbar Leila Hasani 《Journal of Molecular Structure》2005,754(1-3):116-123
Interaction of N,N′,N″,N-tetramethyltetra-2,3-pyridinoporphyrazinatocopper(II), ([Cu(2,3-tmtppa)]4+) and N,N′,N″,N-tetramethyltetra-3,4-pyridinoporphyrazinatocopper(II), ([Cu(3,4-tmtppa)]4+) with calf thymus DNA was studied in 1 mM phosphate buffer and low ionic strength (5 mM NaCl) at various temperatures by UV-visible and circular dichroism (CD) spectroscopies and viscometric method. The binding constants were determined from the changes in the visible part of porphyrazine complexes spectra using SQUAD software. The values of K have been obtained (7.9±0.4)×104 and (2.2±0.1)×105 M−1 for [Cu(2,3-tmtppa)]4+ and [Cu(3,4-tmtppa)]4+, respectively at 27 °C. The higher affinity of 3,4-isomer of Cu complex towards DNA with respect to the 2,3-isomer was attributed to favorable external positioning of the cationic charges in former, which enables superior interaction with the DNA duplex. The thermodynamic parameters (ΔG°, ΔH°, ΔS°) were calculated by van't Hoff equation. The enthalpy and entropy changes were determined, +34.2±3.6 kJ mol−1 and +207.8±12.70 J mol−1 K−1 for [Cu(2,3-tmtppa)]4+ and +49.7±2.1 kJ mol−1 and +267.8±7.9 J mol−1 K−1 for [Cu(3,4-tmtppa)]4+. The existence of extensive hypochromicity, large red shift and negative CD in the visible part of [Cu(3,4-tmtppa)]4+ spectra suggested an intercalation binding mode. Analysis of the moderate hypochromicity, red shift and bisignate CD in the Q-band absorption region of [Cu(2,3-tmtppa)]4+ spectra possibly led us to the coexistence of intercalation and outside binding modes. The influence of the ionic strength on the binding parameters and binding modes was investigated. The results show that increase in ionic strength causes the decrease in the binding constants. It was also concluded that increase in ionic strength affects the binding characteristics of positively charged complexes with DNA.
The increase in DNA viscosity in the presence of Cu–tmtppa complexes is attributed to the lengthening of DNA helix due to the intercalation. This result is consistent with conclusions obtained from the spectroscopic techniques. 相似文献
184.
Sajedi RH Naderi-Manesh H Khajeh K Ranjbar B Ghaemi N Naderi-Manesh M 《Applied biochemistry and biotechnology》2004,119(1):41-50
A new α-amylase was extracted from a recently found strain of Bacillus sp. and purified by ion-exchange chromatography. Sodium dodecyl sulfate polyacrylamide gel electrophoresis showed a single
band for the purified enzyme with an apparent molecular weight of 59 kDa. The optimum temperature and pH range of the enzyme
were 40–60°C and 4.5–7.5, respectively, and its activation energy was 1.974 kcal/mol. The K
m
value for the enzyme activity on solubie starch was 4 mg/mL, and the T
m
values obtained from the circular dichroism (CD) results of thermal unfolding were 78.7 and 80.2°C in the absence and presence
of the calcium, respectively. The enzyme was almost completely inhibited by the addition of Fe3+, Mn2+, and Zn2+ and was activated by EDTA, Cr3+, and Al3+. Moreover, it was partially inhibited by Ca2+, Ba2+, Ni2+, and Co2+. Proteolytic digestion of the enzyme using trypsin combined with results from T
m
using CD and irreversible thermoinactivation suggests that this enzyme can be considered a moderate thermophile with both
mild flexibility and rigidity. 相似文献
185.
186.
In this paper, an adaptive fuzzy robust H
∞ controller is proposed for formation control of a swarm of differential driven vehicles with nonholonomic dynamic models.
Artificial potential functions are used to design the formation control input for kinematic model of the robots and matrix
manipulations are used to transform the nonholonomic model of each differentially driven vehicle into equivalent holonomic
one. The main advantage of the proposed controller is the robustness to input nonlinearity, external disturbances, model uncertainties,
and measurement noises, in a formation control of a nonholonomic robotic swarm. Moreover, robust stability proof is given
using Lyapunov functions. Finally, simulation results are demonstrated for a swarm formation problem of a group of six unicycles,
illustrating the effective attenuation of approximation error and external disturbances, even in the case of robot failure. 相似文献
187.
We consider a system of nonlinear spinor and scalar fields with minimal coupling in general relativity. The nonlinearity in the spinor field Lagrangian is given by an arbitrary function of the invariants generated from the bilinear spinor forms S= and P=i5; the scalar Lagrangian is chosen as an arbitrary function of the scalar invariant = ,,, that becomes linear at 0. The spinor and the scalar fields in question interact with each other by means of a gravitational field which is given by a plane-symmetric metric. Exact plane-symmetric solutions to the gravitational, spinor and scalar field equations have been obtained. Role of gravitational field in the formation of the field configurations with limited total energy, spin and charge has been investigated. Influence of the change of the sign of energy density of the spinor and scalar fields on the properties of the configurations obtained has been examined. It has been established that under the change of the sign of the scalar field energy density the system in question can be realized physically iff the scalar charge does not exceed some critical value. In case of spinor field no such restriction on its parameter occurs. In general it has been shown that the choice of spinor field nonlinearity can lead to the elimination of scalar field contribution to the metric functions, but leaving its contribution to the total energy unaltered. 相似文献
188.
Bijan Modak 《Pramana》1984,23(6):809-814
A solution of the Einstein field equation corresponding to a distribution of fluid with equation of stateρ = 3p but with a nonvanishing shear viscosity is presented. The solution is spherical symmetric and the flow lines are geodetic. 相似文献
189.
190.
Subrata Mahanta Bijan Kumar Paul Rupashree Balia Singh Nikhil Guchhait 《Journal of computational chemistry》2011,32(1):1-14
The inequivalence of substitution pair positions of naphthalene ring has been investigated by a theoretical measurement of hydrogen bond strength, aromaticity, and excited state intramolecular proton transfer (ESIPT) reaction as the tools in three substituted naphthalene compounds viz 1‐hydroxy‐2‐naphthaldehyde (HN12), 2‐hydroxy‐1‐naphthaldehyde (HN21), and 2‐hydroxy‐3‐naphthaldehyde (HN23). The difference in intramolecular hydrogen bond (IMHB) strength clearly reflects the inequivalence of substitution pairs where the calculated IMHB strength is found to be greater for HN12 and HN21 than HN23. The H‐bonding interactions have been explored by calculation of electron density ρ(r) and Laplacian ?2ρ(r) at the bond critical point using atoms in molecule method and by calculation of interaction between σ* of OH with lone pair of carbonyl oxygen atom using NBO analysis. The ground and excited state potential energy surfaces (PESs) for the proton transfer reaction at HF (6‐31G**) and DFT (B3LYP/6‐31G**) levels are similar for HN12, HN21 and different for HN23. The computed aromaticity of the two rings of naphthalene moiety at B3LYP/6‐31G** method also predicts similarity between HN12 and HN21, but different for HN23. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010 相似文献