全文获取类型
收费全文 | 2226篇 |
免费 | 284篇 |
国内免费 | 237篇 |
专业分类
化学 | 1610篇 |
晶体学 | 24篇 |
力学 | 139篇 |
综合类 | 17篇 |
数学 | 259篇 |
物理学 | 698篇 |
出版年
2024年 | 8篇 |
2023年 | 57篇 |
2022年 | 64篇 |
2021年 | 75篇 |
2020年 | 125篇 |
2019年 | 109篇 |
2018年 | 77篇 |
2017年 | 78篇 |
2016年 | 125篇 |
2015年 | 104篇 |
2014年 | 124篇 |
2013年 | 174篇 |
2012年 | 187篇 |
2011年 | 220篇 |
2010年 | 116篇 |
2009年 | 113篇 |
2008年 | 152篇 |
2007年 | 119篇 |
2006年 | 82篇 |
2005年 | 72篇 |
2004年 | 62篇 |
2003年 | 66篇 |
2002年 | 66篇 |
2001年 | 66篇 |
2000年 | 45篇 |
1999年 | 49篇 |
1998年 | 26篇 |
1997年 | 29篇 |
1996年 | 23篇 |
1995年 | 19篇 |
1994年 | 22篇 |
1993年 | 14篇 |
1992年 | 16篇 |
1991年 | 6篇 |
1990年 | 12篇 |
1988年 | 8篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1957年 | 3篇 |
排序方式: 共有2747条查询结果,搜索用时 15 毫秒
951.
In this paper, the boundedness and unboundedness of solutions of the oscillator
are discussed under some suitable conditions. 相似文献
x″+ax+−bx−+φ(x)ψ(x′)+f(x)+g(x′)=p(t)
952.
The inclusive production of doubly heavy baryons Ξcc and Ξbb at γγ collider is investigated. It is found that the contribution from the heavy quark pair QQ in color triplet and color sextet are important. 相似文献
953.
M.W. Krasny F. Fayette W. Płaczek A. Siódmok 《The European Physical Journal C - Particles and Fields》2007,51(3):607-617
In this paper we propose a strategy for measuring the inclusive W boson production processes at LHC. This strategy exploits
simultaneously the unique flexibility of the LHC collider in running variable beam particle species at variable beam energies,
and the configuration flexibility of the LHC detectors. We propose their concrete settings for a precision measurement of
the standard model parameters. These dedicated settings optimise the use of the Z boson and Drell–Yan-pair production processes
as “the standard reference candles”. The presented strategy allows one to factorise and to directly measure those of the QCD
effects that affect differently the W and Z production processes. It reduces to a level of the impact of uncertainties in the partonic distribution functions (PDFs) and in the transverse momentum of the quarks on
the measurement precision. Last but not the least, it reduces by a factor of 10 the impact of systematic measurement errors,
such as the energy scale and the measurement resolution, on the W boson production observables. 相似文献
954.
Si Ahmed K Tazerouti F Badjah-Hadj-Ahmed AY Meklati BY 《Journal of separation science》2007,30(13):2025-2036
A phenylcarbamate derivative of 2-hydroxypropyl-beta-CD bonded stationary phase was prepared by a previously described method. Its enantiomeric recognition abilities were evaluated as chiral stationary phase (CSP) in normal, polar organic and RP conditions by HPLC. The relevant structural features of the prepared stationary phase which make it an effective chiral selector are discussed. This material seems to have an excellent enantioselectivity for a variety of racemic analytes in the three modes. Hence it can be considered a highly effective multimodal column. Retention factor (k), selectivity (alpha) and resolution (R(s)) were the chosen parameters to describe the column performance. Optimization of these separations was discussed in terms of mobile phase composition, flow rate and structural patterns of the injected analytes. 相似文献
955.
This paper is concerned with a functional differential equation of the form
x′(z)=1/x(az+bx′(z)) 相似文献
956.
Wei‐Guang Shan Shi‐Lei Wang Huang‐Yan Lang Si‐Mei Chen You‐Min Ying Zha‐Jun Zhan 《Helvetica chimica acta》2015,98(4):552-556
Two new norfumiquinazolines, cottoquinazolines E and F ( 1 and 2 , resp.), together with pyripyropene A ( 3 ), were isolated from the fungus Neosartorya fischeri NRRL 181. The structures of the new isolates were established by spectroscopic methods, including UV, IR, HR‐ESI‐MS, and extensive 1D‐ and 2D‐NMR techniques. To the best of our knowledge, this is the first report on norfumiquinazolines and pyripyropenes produced by the genus Neosartorya. 相似文献
957.
958.
Using first-principles pseudo-potential plane wave method, the formation enthalpy ΔH, binding energy ΔE, elastic constants, and electronic structure were calculated and analyzed carefully for NiTiX (X = Cu, Fe) shape memory alloy. The results show that the Cu or Fe element prefers to occupy the Ni site in the NiTi matrix phase respectively. Compared with the NiTi matrix phase, the ΔH, ΔE, c 44 and c′ of NiTi (Cu) are similar to each other. However, the structural stability of the NiTi phase is improved obviously by the Fe alloying process. Simultaneously, the shear modulus c 44 and c′ of NiTi (Fe) are larger than those of the NiTi matrix phase. Furthermore, Milliken population results indicate that Q Cu–Ti is smaller than Q Ni–Ti after the Cu alloying process, but Q Fe–Ti is larger than Q Ni–Ti. The electron density difference shows that some covalent bonding exists between Fe and Ti elements. Based on the upward analysis, the difference in the phase stability and elastic constants of NiTiX (X = Cu, Fe) is the substantial mechanism for the different M s of NiTiX (X = Cu, Fe) although Cu or Fe substitutes for the same atom Ni elements in the NiTi matrix phase. 相似文献
959.
Tong Zhang Zu-Qiang Zhang Lu Lin Si Li Xin-Juan Yan Hai-Ou Liu Xiong-Fu Zhang 《Chemical Papers》2015,69(12):1556-1562
Core-shell composite beads comprising a Pd-loaded Al2O3 core and a shell of inter-grown silicalite-1 (siliceous ZSM-5) crystals were synthesised. The incompatibility between the Pd/Al2O3 core and the zeolite shell was circumvented by a layer-by-layer self-assembly of polyelectrolyte to adsorb nanosized silicalite-1 seeds onto the core surface, followed by a secondary solvo-thermal treatment to form the continuous and well-intergrown silicalite-1 shell. The thickness of the outer zeolite shell could be tuned by monitoring the secondary growth time. When employed as catalyst for the hydrogenation reaction of alkenes to explore its full potential use, the Pd/Al2O3@silicalite-1 core-shell catalyst exhibited excellent size-selectivity, poison-resistance and leaching-proof properties. Such a catalyst@zeolite core-shell structure is expected to find promising applications in heterogeneous catalysis and adsorption. 相似文献
960.
Jin-Ping Si Wen-Jing Wang Jun Chang Kun-Lin Huang Zhi-Hui Zhang Sheng-Chun Chen Ming-Yang He Qun Chen 《无机化学与普通化学杂志》2020,646(21):1739-1747
Reactions of the aromatase inhibitor letrozole derivative 4,4'-(1H-1,2,4-triazol-1-yl)methylene-bis(benzonic acid) (H2tzmb) with ZnII, CdII, or PbII salts under similar conditions resulted in the generation of three coordination polymers, namely, {[Zn(tzmb)(H2tzmb)] · H2O}n ( 1 ), [Cd(tzmb)(H2O)2]n ( 2 ), and {[Pb(tzmb)(H2O)] · DMF}n ( 3 ), respectively. Their structures were determined by single-crystal X-ray diffraction analyses and further characterized by elemental analysis, IR spectroscopy, powder X-ray diffraction, and thermogravimetric analyses. Complex 1 features a twofold 2D → 2D interpenetrated network based on corrugated 63- hcb layers, and complex 2 exhibits a flat 2D 4.82- fes network, whereas complex 3 presents a 3D hex net based on infinite rod-shaped secondary building units. The remarkable structural diversity may illustrate the powerful effect of metal ions on coordination assemblies. The spectroscopic, thermal, and photoluminescent properties of complexes 1 – 3 were investigated. In addition, the catalytic activity of 1 in the solvent-free ring-opening polymerization of ε-caprolactone was also discussed. 相似文献