全文获取类型
收费全文 | 5824篇 |
免费 | 196篇 |
国内免费 | 52篇 |
专业分类
化学 | 4361篇 |
晶体学 | 42篇 |
力学 | 218篇 |
综合类 | 2篇 |
数学 | 779篇 |
物理学 | 670篇 |
出版年
2024年 | 11篇 |
2023年 | 61篇 |
2022年 | 308篇 |
2021年 | 307篇 |
2020年 | 207篇 |
2019年 | 230篇 |
2018年 | 218篇 |
2017年 | 168篇 |
2016年 | 292篇 |
2015年 | 202篇 |
2014年 | 210篇 |
2013年 | 533篇 |
2012年 | 359篇 |
2011年 | 383篇 |
2010年 | 238篇 |
2009年 | 204篇 |
2008年 | 258篇 |
2007年 | 259篇 |
2006年 | 207篇 |
2005年 | 181篇 |
2004年 | 165篇 |
2003年 | 140篇 |
2002年 | 144篇 |
2001年 | 56篇 |
2000年 | 63篇 |
1999年 | 44篇 |
1998年 | 30篇 |
1997年 | 44篇 |
1996年 | 40篇 |
1995年 | 32篇 |
1994年 | 39篇 |
1993年 | 31篇 |
1992年 | 32篇 |
1991年 | 28篇 |
1990年 | 43篇 |
1989年 | 26篇 |
1988年 | 22篇 |
1987年 | 26篇 |
1986年 | 27篇 |
1985年 | 33篇 |
1984年 | 19篇 |
1983年 | 17篇 |
1982年 | 25篇 |
1981年 | 20篇 |
1980年 | 14篇 |
1979年 | 16篇 |
1978年 | 11篇 |
1977年 | 12篇 |
1976年 | 9篇 |
1975年 | 6篇 |
排序方式: 共有6072条查询结果,搜索用时 15 毫秒
991.
Isab AA Wazeer MI 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2006,65(1):191-195
Complexation of Ag(+) with captopril, 1-[(2S)-3-mercapto-2-methylpropionyl]-L-proline, has been studied by (1)H and (13)C-NMR spectroscopy. The equilibrium constants for the trans to cis isomers of captopril bound to Ag(+) were measured by (1)H NMR spectroscopy. It is observed that the trans isomer of the drug binds more strongly to Ag(+) between pH 5 and 8, as shown by the broadening of the trans isomer's resonances in (13)C NMR spectra on complexation. A monodentate complexation of the trans captopril with Ag(+) via the thiol site is proposed based on the solid-state NMR and IR data. A superior antimicrobial activity is exhibited by the Cap-Ag(I) complex compared to captopril ligand itself against Heterotrotropic Plate Counts (HPC), Pseudomonas aeruginosa and Fecal streptococcus bacteria. 相似文献
992.
Metal complexes derived from 2,6-pyridinedicarboxaldehydebis(p-hydroxyphenylimine); L1, 2,6-pyridinedicarboxaldehydebis (o-hydroxyphenylimine); L2, are reported and characterized based on elemental analyses, IR, solid reflectance, magnetic moment, molar conductance and thermal analysis (TGA). The complexes are found to have the formulae [MX2(L1 or L2)] x nH2O, where M=Fe(II), Co(II), Ni(II), Cu(II) and Zn(II), X=Cl in case of Fe(II), Co(II), Ni(II), Cu(II) complexes and Br in case of Zn(II) complexes and n=0-2.5. The molar conductance data reveal that the chelates are non-electrolytes. IR spectra show that the Schiff bases are coordinated to the metal ions in a terdentate manner with NNN donor sites of the pyridine-N and two azomethine-N. From the magnetic and solid reflectance spectra, it is found that the geometrical structure of these complexes are trigonal bipyramidal (in case of Co(II), Ni(II), Cu(II) and Zn(II) complexes) and octahedral (in case of Fe(II) complexes). The thermal behaviour of these chelates shows that the hydrated complexes losses water molecules of hydration in the first step followed immediately by decomposition of the coordinated water, anions and ligands (L1 and L2) in the subsequent steps. The activation thermodynamic parameters, such as, E*, DeltaH*, DeltaS* and DeltaG* are calculated from the TG curves using Coats-Redfern method. The synthesized ligands, in comparison to their metal complexes also were screened for their antibacterial activity against bacterial species, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Fungi (Candida). The activity data show that the metal complexes to be more potent/antibacterial than the parent organic ligands against one or more bacterial species. 相似文献
993.
Mohamed Dhib 《Journal of Molecular Spectroscopy》2010,259(2):80-85
We present semiclassical calculations based on the Robert-Bonamy formalism of collisional broadening coefficients of ammonia by collision with He at room temperature. Calculations have been performed with the accurate ab initio potential of Hodges and Wheatley. The calculated line widths are compared to the available experimental data and a satisfactory agreement is found, although the model contains no adjustable parameters. However the calculations also exaggerate the K dependence of the broadenings, especially for lines with K = J − 1 or K = J. 相似文献
994.
A.K. Diab M.M. Wakkad E.Kh. Shokr W.S. Mohamed 《Journal of Physics and Chemistry of Solids》2010,71(9):1381-1387
Physical properties of In35Sb45Se20−xTex thin films with different compositions (x=2.5, 5, 7.5, 10, 12.5 and 15 at %) prepared by electron beam evaporation method are studied. X-ray diffraction results indicate that the as-evaporated films depend on the Te content and the crystallized compounds consist mainly of Sb2Se3 with small amount of Sb2SeTe2. Transmittance and reflectance of the films are found to be thickness dependent. Optical-absorption data indicate that the absorption mechanism is direct transition. Optical band gap values decrease with increase in Te content as well as with increase in film thickness. 相似文献
995.
This study presents a contribution to the tracking of a moving target during high-intensity focused ultrasound (HIFU) treatment. Indeed, HIFU has proved to be highly efficient in inducing homogeneous and reproducible tumor destruction by thermal coagulation necrosis. However, accurate targeting of human abdominal tumors is difficult to maintain due to the motion induced by breathing. An algorithm is presented to track a region of interest of fixed size in a sequence of images. This algorithm was evaluated on synthetic data and on in vivo sequences of ultrasound liver images acquired using 12 MHz ultrasound imaging probe at a rate of 16 frames/s.The algorithm presented here was derived from the non-linear constant brightness assumption. Since the motion was smooth it was possible to reduce the space of admissible displacements; hence the number of unknown parameters was small compared with the size of the data. The optimal displacement was estimated by a Gauss-Newton method, and the matrix required at each step was assembled by reading the data only once. This algorithm was applied to simulated data, where the true displacement was known and a precise evaluation was possible. The relative error was about 2%. The algorithm was also applied to a video sequence of sonograms acquired during in vivo experiments. These trials were conducted on porcine liver since its size and physiology are similar to humans. Movements were induced by breathing and heart-beating. Two particular frequencies representing breathing (0.26 Hz) and heart beat (1.14 Hz) were identified in the estimated displacement and were correlated with the monitored breathing (0.27 Hz) and electrocardiograms (1.28 Hz). In addition, a region of interest (ROI) modeling the focal zone of a HIFU transducer was tracked along time. Therefore this study provides a mean of determining the location of the targeted region in vivo during HIFU treatments. This can be applied to correct the location of the focal zone accordingly. This method can preferentially be applied to the liver or to any other moving organ. 相似文献
996.
Mohamed Bouali 《Mathematical Notes》2018,104(1-2):176-196
A β-matrix model with singular potential is described. A global asymptotic of the density of eigenvalues or the statistical density is obtained by using the equilibrium measure method. The large n-limit density of eigenvalues generalizes Wigner’s semicircle law. 相似文献
997.
998.
M. Ezzat Mohamed Mohammed M. Al-Shomrani M. I. Elashiry 《Periodica Mathematica Hungarica》2018,76(2):265-270
A subgroup H of a finite group G is quasinormal in G if it permutes with every subgroup of G. A subgroup H of a finite group G is \(\mathfrak {F}_{hq}\)-supplemented in G if G has a quasinormal subgroup N such that HN is a Hall subgroup of G and \((H\cap N)H_{G}/ H_{G} \le Z_{\mathfrak {F}}(G/H_{G})\), where \(H_{G}\) is the core of H in G and \({Z}_{\mathfrak {F}} (G/H_{G})\) is the \(\mathfrak {F}\)-hypercenter of \({G/H}_{G}\). This paper concerns the structure of a finite group G under the assumption that some subgroups of G are \(\mathfrak {F}_{hq}\)-supplemented in G. 相似文献
999.
On a resolvent approach for perturbed semigroups and application to $$L^1$$-neutron transport theory
We give new sufficient and practical conditions in terms of the generators ensuring the stability of the critical or the essential type of a perturbed \(C_0\)-semigroup in general Banach spaces. We apply our theoretical results in order to investigate the control and in particular the time asymptotic behavior of solutions to a broad class of transport equations in \(L^1\)-spaces and higher dimension. Our results improve, complete and enrich several earlier works. 相似文献
1000.
Abderrahim Aslimani Imad El Ghazi Mohamed El Kadiri Sabah Haddad 《Annali dell'Universita di Ferrara》2018,64(1):25-46
We study the existence and the regularity of the biharmonic Green kernel in a Brelot biharmonic space whose associated harmonic spaces have Green kernels. We show by some examples that this kernel does not always exist. We then introduce and study the adjoint of the given biharmonic space. This study was initiated by Smyrnelis, however, it seems that several results were incomplete and we clarify them here. 相似文献