全文获取类型
收费全文 | 1756篇 |
免费 | 90篇 |
国内免费 | 11篇 |
专业分类
化学 | 1342篇 |
晶体学 | 37篇 |
力学 | 45篇 |
数学 | 109篇 |
物理学 | 324篇 |
出版年
2024年 | 15篇 |
2023年 | 18篇 |
2022年 | 106篇 |
2021年 | 89篇 |
2020年 | 54篇 |
2019年 | 63篇 |
2018年 | 87篇 |
2017年 | 62篇 |
2016年 | 84篇 |
2015年 | 64篇 |
2014年 | 65篇 |
2013年 | 136篇 |
2012年 | 131篇 |
2011年 | 126篇 |
2010年 | 82篇 |
2009年 | 68篇 |
2008年 | 82篇 |
2007年 | 74篇 |
2006年 | 47篇 |
2005年 | 41篇 |
2004年 | 29篇 |
2003年 | 31篇 |
2002年 | 56篇 |
2001年 | 36篇 |
2000年 | 41篇 |
1999年 | 12篇 |
1998年 | 18篇 |
1997年 | 10篇 |
1996年 | 6篇 |
1995年 | 10篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 8篇 |
1991年 | 5篇 |
1990年 | 12篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1974年 | 2篇 |
1937年 | 2篇 |
排序方式: 共有1857条查询结果,搜索用时 31 毫秒
921.
D. A. Bradley Ithnin Abdul Jalil M. Kremar A. Ljubicic 《Journal of Radioanalytical and Nuclear Chemistry》2000,244(3):475-478
In recent years, several groups have reported measurement of a finite non-resonant photoactivation cross section for 115In. Present evaluations of this same parameter have made use of an irradiation arrangement and detector which differ from those of other groups. Our values for the resonant and non-resonant contribution to the photoactivation cross-section are (1.6±0.3)·10–28 cm2 keV and (4.0±0.9)·10–32 cm2, respectively, comparing favourably with counterpart results by TUSTONIC et al.5 of (1.3±0.1)·10–28 cm2 keV and (5.5±0.8)·10–32 cm2. 相似文献
922.
Seik Weng Ng Suchada Chantrapromma Ibrahim Abdul Razak Hoong-Kun Fun 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(3):291-292
The triclinic cell of the title compound contains 2C12H24N+·2C6H5O2S− ion pairs that are linked by four hydrogen bonds [N⃛O = 2.728 (3) and 2.758 (3) Å] across a centre of inversion. 相似文献
923.
Barrie Kellam Paul A. Ward Aisyah S. Abdul Rahim Siri Ram Chhabra 《Tetrahedron letters》2005,46(10):1703-1706
Nα-(4,4-Dimethyl-2,6-dioxocyclohexylidenemethylene) (Dmc) protected l-serine, l-threonine and l-homoserine have been prepared as tert-butyl esters in excellent yields. These hydrogenolysis stable acceptors underwent efficient α-O-glycosylation with an l-fucopyranosyl bromide donor and also allowed convenient protecting group manipulations to ultimately deliver novel glycoamino acid building blocks suitable for Fmoc based solid-phase glycopeptide synthesis. 相似文献
924.
Farook Rahaman Nupur Paul S. S. De Saibal Ray Md. Abdul Kayum Jafry 《The European Physical Journal C - Particles and Fields》2015,75(11):564
We construct a toy model for compact stars based on the Finslerian structure of spacetime. By assuming a particular mass function, we find an exact solution of the Finsler–Einstein field equations with an anisotropic matter distribution. The solutions are revealed to be physically interesting and pertinent for the explanation of compact stars. 相似文献
925.
M. Jawaid Alothman Othman N. Saba Y. A. Shekeil M. T. Paridah H. P. S. Abdul Khalil 《International Journal of Polymer Analysis and Characterization》2014,19(5):391-403
Treatment of oil palm empty fruit bunch (EFB) and jute fibers is carried out by using 2-hydroxy ethyl acrylate (2-HEA) to increase the interfacial bonding of fibers with the epoxy matrix. Fourier transform-infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM) were used to measure the change of surface composition of the fibers after treatment. Modified oil palm and jute fibers were used as reinforcements for epoxy matrix to fabricate hybrid composites by the hand lay-up technique. Tensile and morphological properties of hybrid composites were studied, and tensile properties of hybrid composites prepared from chemically treated oil palm/jute fibers were found to be better than those of untreated hybrid composites. SEM micrographs disclose that interfacial bonding between fiber and matrix significantly improved in the hybrid composites. Developed hybrid composites can be exploited as alternative materials for development of automotive and structural components instead of synthetic fiber–reinforced polymer composites. 相似文献
926.
Benzaldehydes are important building blocks in synthetic organic chemistry that have wide applications for the synthesis of natural products and pharmaceutical drugs. Herein we report a general synthetic methodology for the synthesis of highly functionalized 2H and 13C labeled benzaldehydes in transfer of isotopic purity >99% via regio-selective formylation. Regio-selective deprotonation of substituted benzene 1 with LDA/n-BuLi at −78 °C and treatment with DMF-d7 or EtO-13CHO led to the synthesis of 2-deutero-1,3-disubstituted benzaldehydes 2/4 in moderate to good yields. The synthetic methodology described represents a simple yet versatile route to functionalized formyl-deuterated, tritiated 13C and 14C labeled benzaldehydes. 相似文献
927.
Abdul Majid Maryam Sana Salah Ud-Din Khan Naeem Ahmad 《International journal of quantum chemistry》2020,120(15):e26253
The time-dependent density functional theory approach, implemented at hybrid-B3LYP, GGA-PBE, and density functional-based tight binding levels of theory, was used to model photoinjection in organic dye/TiO2 quantum dot to explore the prospects of improvement of dye-sensitized solar cell (DSSC). The photosensitizer used in this study consisted of six carbazole-based organic dyes, a cyanoacrylic acid group as an acceptor and an oligothiophene π-bridge spacer. The modifications were made in the dyes by increasing the length of the spacer by adding thiophene and oxadiazole rings at different positions of the donor-acceptor bridge. The structural variations appeared to alter the electronic and optical properties of dyes studied via energy levels and excitation spectra. The UV-Vis spectra calculated for all the dyes in solvents exhibited a red shift in spectral peaks with an increase in the polarity of the solvents. The findings of the study pointed toward the indirect photoinjection of the dye-(TiO2)96 complex for six different dyes. The substitution of the oxadiazole ring at the center and addition of a thiophene ring at the edge of the spacer produced two dyes that exhibited the lowest injection energies of 0.11 and 0.17 eV, along with the regeneration energies of 1.18 and 1.12 eV, respectively. The dyes reported here may have promising applications in photoanode for enhancing the performance of DSSC. 相似文献
928.
This study presents an efficient synthesis of 3-[6-(substituted-phenyl)-[1,2,4]triazolo[3,4-b][1,3,4] thiadiazol-3-yl]-1H-indazole via dehydrative condensation with cyclization of 4-amino-5-(1H-indazol-3-yl)-4H-[1,2,4]triazole-3-thiol and fluorinated or nonfluorinated carboxylic acids in presence of phosphorous oxychloride. The multistep reaction pathway proceeds through different compounds. Present synthesis has the advantages of easily accessible starting materials, convenient synthesis, simple reaction condition, wider substrate scope, and higher yield (75% to 90% isolated). 相似文献
929.
Abdul‐Majid Wazwaz 《Mathematical Methods in the Applied Sciences》2019,42(5):1553-1560
In this work, we employ the recursion operator, the Burgers equation and its inverse operator, for constructing a hierarchy of negative‐order integrable Burgers equations of higher orders. The complete integrability of each established equation emerges by virtue of the correlation between integrability and recursion operators. We use the simplified Hirota's method to obtain multiple kink solutions for some of the derived equations, and in particular, for the generalized negative‐order Burgers equation. 相似文献
930.
Tractor beam for fully immersed multiple objects: Long distance pulling,trapping, and rotation with a single optical set‐up 下载免费PDF全文
Md. Masudur Rahman Ayed Al Sayem M. R. C. Mahdy Md. Ehsanul Haque Rakibul Islam S. Tanvir‐ur‐Rahman Chowdhury Md. Abdul Matin 《Annalen der Physik》2015,527(11-12):777-793
In this article, we have theoretically demonstrated the mechanism of an active tractor beam for multiple fully immersed objects with additional abilities to yielding stable long distance levitation, a controlled rotation and a desired 3D trapping. This is demonstrated with a single optical set‐up by using two coaxial, or even non‐coaxial, superimposed higher order monochromatic Bessel beams of reverse helical nature and different frequencies. The superimposed beams can possess periodic intensity variations both along and around the beam‐axis due to a difference in longitudinal wave‐numbers and beam orders, respectively. The difference in frequencies of the two laser beams makes the intensity pattern to move along and around the beam‐axis in a continuous way without manual ramping of phase, which allows for bidirectional movement of completely immersed multiple particles. The condition for increasing or decreasing the dimension of binding regions is also proposed here to manipulate multiple immersed objects of different sizes under dipole approximation.