全文获取类型
收费全文 | 607篇 |
免费 | 12篇 |
国内免费 | 4篇 |
专业分类
化学 | 316篇 |
晶体学 | 3篇 |
力学 | 33篇 |
数学 | 127篇 |
物理学 | 144篇 |
出版年
2023年 | 13篇 |
2022年 | 20篇 |
2021年 | 18篇 |
2020年 | 15篇 |
2019年 | 21篇 |
2018年 | 11篇 |
2017年 | 11篇 |
2016年 | 27篇 |
2015年 | 20篇 |
2014年 | 27篇 |
2013年 | 46篇 |
2012年 | 29篇 |
2011年 | 43篇 |
2010年 | 24篇 |
2009年 | 19篇 |
2008年 | 27篇 |
2007年 | 33篇 |
2006年 | 33篇 |
2005年 | 28篇 |
2004年 | 24篇 |
2003年 | 20篇 |
2002年 | 14篇 |
2001年 | 5篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1997年 | 9篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1982年 | 3篇 |
1980年 | 2篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1977年 | 7篇 |
1938年 | 2篇 |
1930年 | 1篇 |
1911年 | 1篇 |
1910年 | 1篇 |
1907年 | 1篇 |
1906年 | 2篇 |
1905年 | 1篇 |
1903年 | 1篇 |
1877年 | 1篇 |
1868年 | 1篇 |
排序方式: 共有623条查询结果,搜索用时 21 毫秒
531.
532.
Sara Gmez Natalia Rojas-Valencia Tommaso Giovannini Albeiro Restrepo Chiara Cappelli 《Molecules (Basel, Switzerland)》2022,27(2)
We unravel the potentialities of resonance Raman spectroscopy to detect ibuprofen in diluted aqueous solutions. In particular, we exploit a fully polarizable quantum mechanics/molecular mechanics (QM/MM) methodology based on fluctuating charges coupled to molecular dynamics (MD) in order to take into account the dynamical aspects of the solvation phenomenon. Our findings, which are discussed in light of a natural bond orbital (NBO) analysis, reveal that a selective enhancement of the Raman signal due to the normal mode associated with the C–C stretching in the ring, , can be achieved by properly tuning the incident wavelength, thus facilitating the recognition of ibuprofen in water samples. 相似文献
533.
Takashi Arima Maria Cristina Carrisi Sebastiano Pennisi Tommaso Ruggeri 《Entropy (Basel, Switzerland)》2022,24(1)
A relativistic version of the rational extended thermodynamics of polyatomic gases based on a new hierarchy of moments that takes into account the total energy composed by the rest energy and the energy of the molecular internal mode is proposed. The moment equations associated with the Boltzmann–Chernikov equation are derived, and the system for the first 15 equations is closed by the procedure of the maximum entropy principle and by using an appropriate BGK model for the collisional term. The entropy principle with a convex entropy density is proved in a neighborhood of equilibrium state, and, as a consequence, the system is symmetric hyperbolic and the Cauchy problem is well-posed. The ultra-relativistic and classical limits are also studied. The theories with 14 and 6 moments are deduced as principal subsystems. Particularly interesting is the subsystem with 6 fields in which the dissipation is only due to the dynamical pressure. This simplified model can be very useful when bulk viscosity is dominant and might be important in cosmological problems. Using the Maxwellian iteration, we obtain the parabolic limit, and the heat conductivity, shear viscosity, and bulk viscosity are deduced and plotted. 相似文献
534.
Considering the hyperbolic symmetric system of moments associated with the relativistic Boltzmann-Chernikov equation and closed
through procedures of Extended Thermodynamics, we determine numerically the maximum characteristic wave velocity for degenerate
and non-degenerate gases. As predicted by recent results, this velocity increases monotonically with respect to the number
of moments and tends asymptotically to the speed of light. We show that many moments are often required to approach with a
good approximation the speed of light. The dependence of the maximum characteristic wave velocity on the properties of the
materials is also investigated and it turns out that it depends significantly on the chemical potential only in the case of
Fermions gases.
Received April 24, 1999 相似文献
535.
Di Tommaso A. Neubauer U. Pantuso A. Rostasy F. S. 《Mechanics of Composite Materials》2001,37(4):327-338
This paper presents an evaluation of the results obtained from an initial study carried out at the IBMB, Technical University of Braunschweig, on the influence of temperature on adhesively bonded plate-concrete joint systems. The results of a theoretical model are also presented. The type of specimen used in this study is a three-point bending beam. The concrete specimens were prismatic in form, 100 × 100 × 700 mm without an internal steel reinforcement, strengthened at the intradoss with two types of UD CFRP lamina 20 mm wide and 590 mm long of thickness 1.4 mm for the E = 300 GPa type and 1.24 mm for the E = 175 GPa type. The plate-bonded specimens were designed to produce bending failure under a load, by not bonding the lamina and the concrete around the midspan of the specimens. The specimens were tested to failure at –100°, –30°, and +40°C after an approximately homogeneous temperature distribution within the concrete specimen has been reached. For comparison only, specimens of the same type were tested to failure at room temperature. The results obtained showed varying behavior of the bonded plate-concrete joint depending on variations in temperature. Furthermore, they showed different failure mechanisms. Greater reductions in the ultimate bond force were recorded for the test specimens strengthened with lamina having a high elastic modulus. A reasonable correlation was found between the experimental and theoretical results. 相似文献
536.
537.
Bowcock T Giles RT Hassard J Kinoshita K Pipkin FM Wilson R Gentile T Haas P Hempstead M Jensen T Kagan H Kass R Behrends S Guida JM Guida JA Morrow F Poling R Rosenfeld C Thorndike EH Tipton P Green J Sannes F Stone R Alam MS Katayama N Kim IJ Sun CR Tanikella V Bortoletto D Chen A Garren L Goldberg M Horwitz N Jawahery A Lubrano P Moneti GC Csorna SE Mestayer MD Panvini RS Word GB Bean A Bobbink GJ Brock I Engler A Ferguson T Kraemer R Rippich C Sutton R Vogel H Bebek C Berkelman K Blucher E 《Physical review letters》1986,56(25):2676-2679
538.
A sensitive and specific method for the determination of valproic acid in plasma has been developed. After the proteins in the plasma have been precipitated with a saturated solution of ammonium sulfate in 1N HCl, the valproic acid, together with the internal standard, is extracted from the plasma with dichloromethane. An aliquot of the organic solution is taken for derivatization of the valproic acid and the internal standard with O-p-nitrobenzyl-N,N′-diisopropylisourea. Separation is carried out by HPLC using two chromatographic systems: an adsorption system with a μ Porasil column, hexane-chloroform (94:6) as mobile phase, and caproic acid as internal standard and a partition reverse phase system comprising a μ Bondapak TM/C18 column, acetonitrile/methanol/0.0035 M phosphate buffer (60:10:30), and caprylic acid as internal standard. UV detection is at 254 nm. This method, developed in both systems, permits the determination of plasma levels of valproic acid in the reported range of 50-100 μg/mL. With adequate sensitivity, specificity, precision, and accuracy. The plasma levels of valproic acid may be determined by this method without interference from the commonest antiepileptic drugs. Good correlation is obtained with the enzymatic immune analytic method: EMIT. 相似文献
539.
Bianco G Schmitt-Kopplin P De Benedetto G Kettrup A Cataldi TR 《Electrophoresis》2002,23(17):2904-2912
Glycoalkaloids are naturally occurring nitrogen-containing compounds present in many species of the family Solanaceae, including cultivated and wild potatoes (Solanum spp.), tomatoes (Lycopersicon spp.), etc. These compounds have pharmacological and toxicological effects on humans due to their significant anticholinesterase activity and disruption of cell membranes. Herein is reported the development of a capillary electrophoresis (CE) method using nonaqueous (NA) separation solutions in combination with ion trap mass spectrometry (MS and MS/MS) detection for the identification and quantification of glycoalkaloids and their relative aglycones. A mixture 90:10 v/v of MeCN-MeOH containing 50 mM ammonium acetate and 1.2 M acetic acid (applied voltage of 25.5 kV) was selected as a good compromise for the separation and detection of these compounds. The electrospray MS measurements were carried out in the positive ionization mode using a coaxial sheath liquid, methanol-water (1:1) with 1% of acetic acid at a flow rate of 2.5 microL/min. Under optimized experimental conditions, the predominant ion was the protonated molecular ion ([M+H](+)) of solanidine (m/z = 398), tomatidine (m/z = 416), chaconine (m/z = 852), solanine (m/z = 868), and tomatine (m/z = 1034). MS/MS experiments were carried out systematically by changing the relative collisional energy and monitoring the intensities of the fragment ions that were not high enough to allow better quantification than with the mother ions. The method was used for analyzing glycoalkaloids in potato extracts. 相似文献
540.
Grazia M.L ConsoliCorrada Geraci Tommaso MeccaPlacido Neri 《Tetrahedron letters》2003,44(40):7467-7470
An efficient approach for the introduction of eight mono- or disaccharide sugar moieties (d-glucose, N-acetyl-d-glucosamine, d-galactose, l-fucose, d-maltose and d-cellobiose) at the upper rim of calix[8]arene 1, using thioureido linkers, is reported. The obtained water-soluble, nanosized glycocalix[8]arenes 5b-10b may act as biomimetic carbohydrate systems and as hosts for highly polar organic molecules. Preliminary 1H NMR complexation experiments of octaglycosyl derivative 7b and 10b with ionic guests are also reported. 相似文献