全文获取类型
收费全文 | 3048篇 |
免费 | 502篇 |
国内免费 | 85篇 |
专业分类
化学 | 298篇 |
晶体学 | 13篇 |
力学 | 680篇 |
综合类 | 91篇 |
数学 | 1659篇 |
物理学 | 894篇 |
出版年
2025年 | 20篇 |
2024年 | 66篇 |
2023年 | 57篇 |
2022年 | 88篇 |
2021年 | 88篇 |
2020年 | 114篇 |
2019年 | 103篇 |
2018年 | 100篇 |
2017年 | 105篇 |
2016年 | 132篇 |
2015年 | 93篇 |
2014年 | 159篇 |
2013年 | 191篇 |
2012年 | 161篇 |
2011年 | 187篇 |
2010年 | 144篇 |
2009年 | 149篇 |
2008年 | 157篇 |
2007年 | 150篇 |
2006年 | 157篇 |
2005年 | 174篇 |
2004年 | 153篇 |
2003年 | 118篇 |
2002年 | 120篇 |
2001年 | 77篇 |
2000年 | 83篇 |
1999年 | 65篇 |
1998年 | 65篇 |
1997年 | 48篇 |
1996年 | 52篇 |
1995年 | 41篇 |
1994年 | 42篇 |
1993年 | 22篇 |
1992年 | 20篇 |
1991年 | 18篇 |
1990年 | 16篇 |
1989年 | 14篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1982年 | 11篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1959年 | 3篇 |
1936年 | 1篇 |
排序方式: 共有3635条查询结果,搜索用时 15 毫秒
21.
Rational drug design involves finding solutions to large combinatorial problems for which an exhaustive search is impractical. Genetic algorithms provide a novel tool for the investigation of such problems. These are a class of algorithms that mimic some of the major characteristics of Darwinian evolution. LEA has been designed in order to conceive novel small organic molecules which satisfy quantitative structure-activity relationship based rules (fitness). The fitness consists of a sum of constraints that are range properties. The algorithm takes an initial set of fragments and iteratively improves them by means of crossover and mutation operators that are related to those involved in Darwinian evolution. The basis of the algorithm, its implementation and parameterization, are described together with an application in de novo molecular design of new retinoids. The results may be promising for chemical synthesis and show that this tool may find extensive applications in de novo drug design projects. 相似文献
22.
23.
《Analytical letters》2012,45(10):2153-2167
Abstract Three single‐chain fragment variable (scFv) fusion structures were constructed for use in rapid and sensitive detection of nucleocapsid protein (NP) of Hantaan virus. The detection of NPs on glass chips was signalized by enzyme labeling or fluorescence dye Cy3, or Cy5 cluster nanoparticles. The sensitivity of the methods with different signal systems was evaluated and compared. The detection limits of scFv‐alkaline phosphatase fusion, fluorescence labeling (scFv‐Cy3), and nanoparticles labeling (scFv‐SBP‐streptavidin‐nanoparticle) were 0.1 µg/mL, 1 ng/mL, and 0.1 ng/mL NP, respectively, which were all lower than that in a conventional enzyme‐linked immunosorbent assay (ELISA) (1 µg/mL). Twenty Hantaan virus isolates were detected using the proposed methods. 相似文献
24.
Kasani Aparna Professor Setharampattu S. Krishnamurthy Munirathinam Nethaji 《无机化学与普通化学杂志》1995,621(11):1913-1921
Lanthanide nitrate complexes of diphosphazane dioxides Ph2P(O)N(Pri)P(O)Ph2 ( 1 ) and (PhO)2P(O)N(Me)P(O)(OPh)2 ( 2 ) have been synthesised and studied by conductometry, IR, multinuclear NMR spectroscopic methods and X-ray diffraction. Ligand 2 is accessible by two different methods, viz., by direct oxidation of the phosp(III)azane ligand or by starting from phosph(V)azane chloro precursor. The structure of 2 is confirmed by X-ray diffraction. Crystallographic data for 2 : Triclinic, Space group P1 , a = 10.078(1), b = 10.575(3), c = 12.364(4) Å, α = 75.70(2)°, α = 75.56(1)°, γ = 77.68(1)°, Z = 2, V = 1 220 Å3; structure refined to RF = 0.0459 on 3 495 data with F > 3σ(F). The diphosphazane dioxide ligand exhibits trans geometry in the solid state. The structure of a lanthanide complex, [Pr(NO3)3( 2 )2] ( 14 ) is also determined by X-ray diffraction. Crystallographic data for 14 : Trigonal, Space group P32, a = b = 15.710(2), c = 40.067(2) Å, Z = 6, V = 8 564 Å3; structure refined to RF = 0.0430 on 8 077 data with F > 5σ(F). The two diphosphazane dioxide ligands and the nitrate groups are coordinated to praseodymium in a bidentate chelate fashion. The geometry around the ten coordinated metal is distorted bicapped square antiprism. 相似文献
25.
Helen Stoeckli‐Evans Olha Sereda Antonia Neels Sebastien Oguey Catherine Ionescu Yvan Jacquier 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(11):1057-1063
The one‐dimensional coordination polymer catena‐poly[diaqua(sulfato‐κO)copper(II)]‐μ2‐glycine‐κ2O:O′], [Cu(SO4)(C2H5NO2)(H2O)2]n, (I), was synthesized by slow evaporation under vacuum of a saturated aqueous equimolar mixture of copper(II) sulfate and glycine. On heating the same blue crystal of this complex to 435 K in an oven, its aspect changed to a very pale blue and crystal structure analysis indicated that it had transformed into the two‐dimensional coordination polymer poly[(μ2‐glycine‐κ2O:O′)(μ4‐sulfato‐κ4O:O′:O′′:O′′)copper(II)], [Cu(SO4)(C2H5NO2)]n, (II). In (I), the CuII cation has a pentacoordinate square‐pyramidal coordination environment. It is coordinated by two water molecules and two O atoms of bridging glycine carboxylate groups in the basal plane, and by a sulfate O atom in the apical position. In complex (II), the CuII cation has an octahedral coordination environment. It is coordinated by four sulfate O atoms, one of which bridges two CuII cations, and two O atoms of bridging glycine carboxylate groups. In the crystal structure of (I), the one‐dimensional polymers, extending along [001], are linked via N—H...O, O—H...O and bifurcated N—H...O,O hydrogen bonds, forming a three‐dimensional framework. In the crystal structure of (II), the two‐dimensional networks are linked via bifurcated N—H...O,O hydrogen bonds involving the sulfate O atoms, forming a three‐dimensional framework. In the crystal structures of both compounds, there are C—H...O hydrogen bonds present, which reinforce the three‐dimensional frameworks. 相似文献
26.
Nargis Jamila Melati Khairuddean Sadiq Noor Khan Naeem Khan 《Magnetic resonance in chemistry : MRC》2014,52(7):345-352
The genus Garcinia is reported to possess antimicrobial, anti‐inflammatory, anticancer, hepatoprotective and anti‐HIV activities. Garcinia hombroniana in Malaysia is used to treat itching and as a protective medicine after child birth. This study was aimed to isolate the chemical constituents from the bark of G. hombroniana and explore their possible pharmacological potential. Ethyl acetate extract afforded one new (1) and six (2–7) known 3 → 8 rotameric biflavonoids. Their structures were elucidated by UV, IR and NMR (1D and 2D) spectroscopy together with electron ionization/ESI mass spectrometric techniques and were identified as (2R, 3S) volkensiflavone‐7‐O‐rhamnopyranoside (1), volkensiflavone (2), 4″‐O‐methyl‐volkensiflavone (3), volkensiflavone‐7‐O‐glucopyranoside (4), morelloflavone (5), 3″‐O‐methyl‐morelloflavone (6) and morelloflavone‐7‐O‐glucopyranoside (7). The absolute configuration of compound 1 was assigned by circular dichroism spectroscopy as 2R, 3S. The coexistence of conformers of isolated biflavonoids in solution at 25 °C in different solvents was confirmed by variable temperature NMR studies. At room temperature (25 °C), compounds 1–7 exhibited duplicate NMR signals, while at elevated temperature (90 °C), a single set of signals was obtained. Compound 5 showed significant in vitro antioxidant activities against 1,1‐diphenyl‐2‐picrylhydrazyl and 2,2′‐azino‐bis‐3‐ethyl benzthiazoline‐6‐sulfonic acid radicals. The antibacterial studies showed that compounds 5 and 6 are the most active against Staphylococcus aureus, Bacillus subtilis and Escherichia coli. Compounds 3 and 6 also showed moderate antituberculosis activity against H38Rv. Based on the research findings, G. hombroniana could be concluded as a rich source of flavanone–flavone (3 → 8) biflavonoids that exhibit rotameric behaviour at room temperature and display significant antioxidant and antibacterial activities. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
27.
Norio Hasebe Seiji Kato 《ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik》2015,95(12):1477-1489
A closed form solution is derived for the bonded bimaterial planes at two interfaces. The bonded planes with two interfaces are symmetric with respect to the interface, which is straight. A rational mapping function and complex stress functions are used for the analysis. The problem is reduced to a Riemann‐Hilbert problem. Two interfaces problem to derive the general solution is more difficult than one interface problem. As a demonstration of geometry, semi‐strips bonded at two parts at the ends of strips are considered. The solution of different geometrical shapes can be obtained by changing the mapping function. Concentrated forces and couples are applied to the each strip. The first derivative of complex stress functions which does not include integral terms with regard to variable of the mapping plane is achieved. Therefore, there is no need of numerical integration to calculate stress components and to determine unknown coefficients in complex stress function. This is very benefit. All elastic constants in complex stress functions are expressed by Dundurs’ parameters. Stress distributions are shown for different lengths of the interface. 相似文献
28.
X. Wang P. Schiavone 《ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik》2013,93(8):520-549
In this work a simple and effective method is proposed to solve the problem corresponding to plane strain deformations of an N‐phase decagonal quasicrystalline circular inclusion‐matrix system in which the circular inclusion is bonded to the surrounding matrix through (N‐2) co‐axial interphase layers. We consider three kinds of thermomechanical loadings: (i) the matrix is subjected to a remote uniform stress field; (ii) the composite undergoes a uniform temperature change; (iii) the matrix is subjected to a uniform heat flux at infinity. We find that it is sufficient to manipulate three 8 × 8 real matrices, a 5 × 5 real matrix, and another 4 × 4 real matrix to arrive at the complete temperature and thermoelastic fields within the circular inclusion and the surrounding matrix, irrespective of the number of interphase layers existing within the composite system. Our results clearly indicate that the existence of the intermediate interphase layer(s) mean that the internal stresses within the circular inclusion are: (i) sextic functions of the two coordinates x1 and x2 under the loading of a remote uniform stress field; (ii) quadratic functions of the two coordinates under the loading of a uniform temperature change; (iii) cubic functions of the two coordinates under the loading of a remote uniform heat flux. The design of neutral and harmonic coated circular inclusions is also discussed as an application of the derived solution. Our analysis suggests that a coated inclusion can be made neutral only to a remote isotropic phonon stress field; whereas it can be made harmonic to any remote uniform phonon stress field. 相似文献
29.
In this article we have studied the peristaltic motion of an incompressible Williamson fluid with constant and radially varying magnetohydrodynamics (MHD) in an endoscope. Using the low Reynolds and long wavelength assumptions, the equations of Williamson fluid model in simplified form are solved using (i) the HAM method and (ii) the Shooting method. The comparisons of both solutions have been found a very good agreement. Graphical results have been presented for various emerging parameters. © British Crown Copyright 2010/MOD. Reproduced with permission. Published by John Wiley & Sons, Ltd. 相似文献
30.
The effect of variable viscosity on the peristaltic motion of MHD third‐order fluid in a channel is studied using slip condition. The series solution for stream function, longitudinal velocity and pressure gradient are first derived and then discussed in detail. The pressure rise and frictional forces are monitored through numerical integration. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献