全文获取类型
收费全文 | 1082篇 |
免费 | 56篇 |
国内免费 | 7篇 |
专业分类
化学 | 702篇 |
晶体学 | 30篇 |
力学 | 57篇 |
综合类 | 2篇 |
数学 | 153篇 |
物理学 | 201篇 |
出版年
2023年 | 7篇 |
2022年 | 34篇 |
2021年 | 44篇 |
2020年 | 36篇 |
2019年 | 32篇 |
2018年 | 40篇 |
2017年 | 27篇 |
2016年 | 58篇 |
2015年 | 40篇 |
2014年 | 57篇 |
2013年 | 105篇 |
2012年 | 83篇 |
2011年 | 91篇 |
2010年 | 57篇 |
2009年 | 49篇 |
2008年 | 41篇 |
2007年 | 56篇 |
2006年 | 43篇 |
2005年 | 36篇 |
2004年 | 20篇 |
2003年 | 23篇 |
2002年 | 24篇 |
2001年 | 9篇 |
1999年 | 8篇 |
1998年 | 9篇 |
1997年 | 6篇 |
1996年 | 13篇 |
1995年 | 9篇 |
1994年 | 5篇 |
1993年 | 11篇 |
1992年 | 6篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 9篇 |
1982年 | 9篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1973年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1964年 | 2篇 |
1962年 | 1篇 |
排序方式: 共有1145条查询结果,搜索用时 15 毫秒
961.
We consider weak sharp solutions for the generalized variational inequality problem, in which the underlying mapping is set-valued, and not necessarily monotone. We extend the concept of weak sharpness to this more general framework, and establish some of its characterizations. We establish connections between weak sharpness and (1) gap functions for variational inequalities, and (2) global error bound. When the solution set is weak sharp, we prove finite convergence of the sequence generated by an arbitrary algorithm, for the monotone set-valued case, as well as for the case in which the underlying set-valued map is either Lipschitz continuous in the set-valued sense, for infinite dimensional spaces, or inner-semicontinuous when the space is finite dimensional. 相似文献
962.
Hasan Furkan 《Journal of the Egyptian Mathematical Society》2017,25(1):37-42
In the present paper, the difference sequence spaces and bsλ(Δ) of nonabsolute type are generalized by introducing a generalized Λ difference operator . Also, their Schauder basis are calculated and α-, β- and γ-duals of these spaces are investigated. Finally, some matrix transformations between these spaces and the basic sequence spaces ?p, c and c0 are characterized, where 1 ≤ p ≤ ∞. 相似文献
963.
Hassan Keypour Mohammad Hasan Zebarjadian Majid Rezaeivala Mojtaba Shamsipur Hamid Reza Bijanzadeh 《Journal of solution chemistry》2014,43(7):1218-1231
Lithium-7 NMR spectroscopy was used to investigate the stoichiometry and stability of a Li+ complex with two new branched amines, 4,7-bis(2-pyridylmethyl)-4,7-diazadecane-1,10-diamine (L1) and 4,8-bis(2-pyridylmethyl)-4,8-diazaundecane-1,11-diamine (L2), in acetonitrile and nitromethane. A competitive 7Li NMR method was also employed to probe the complexation of Mn2+, Zn2+ and Cd2+ ions with L1 and L2 in the same solvent systems. The formation constants of the resulting complexes were evaluated from computer fitting of the mole ratio data with an equation that relates the observed chemical shifts to the formation constant. In both solvents, the stability of the resulting 1:1 complexes was found to vary in the order Cd2+ > Zn2+ > Mn2+ > Li+. 相似文献
964.
Faisal N. Al-Obaidi Hasan Atabey Mustafa Macit Hayati Sari 《Journal of solution chemistry》2014,43(5):989-999
The protonation equilibria of (2Z, 3Z)-2H-benzo[b][1,4]thiazine-2,3(4H)-dionedioxime (BTDH2) together with the equilibria of its bis- binary complexes of Co(II), Ni(II), Cu(II) and Zn(II) were investigated potentiometrically. The investigation was carried out at 25 ± 0.1 °C, in aqueous solution, with a constant ionic strength of 0.100 mol·dm?3 NaCl. The protonation constants of the ligand together with the stability constants of a variety of complexes were determined potentiometrically in 10 % ethanol–water mixed solution using the SUPERQUAD computer program. Theoretical calculations were set up to assist in understanding the protonation sequence in the ligand molecule via the semi-empirical molecule orbital method of parameterized model number 3. Results are discussed in connection to the basicity of the donor atoms and structural arrangement of the ligand. Although BTDH2 has two dissociable protons, four protonation constants can be measured under the experimental conditions presented. These four protonation constants (as log10 βs) are 10.245, 19.397, 22.414 and 25.176. 相似文献
965.
Hui Chen Qiang Han Kevin Daniel Richard Venditti Hasan Jameel 《Applied biochemistry and biotechnology》2014,174(6):2096-2113
Paper sludge is an attractive biomass source for the conversion to ethanol due to its low cost and the lack of severe pretreatment required. Four sludges from pulp and paper operations including both virgin kraft (VK) and recycled and deinking (RD) paper mills were analyzed. A fractionation process using a laboratory screen was utilized to produce a fiber-rich stream for enzymatic hydrolysis. This process removed 82–98 % of the ash with fiber yields from 39 to 69 %. Even though sludges in both non-fractionated and fractionated scenarios were pH-adjusted, total sugar conversion was still improved by 12–27 % by fractionation with 4.5 times less acid required for pH adjustment. Fermentation of the fractionated sludges showed very high ethanol yields. Acid insoluble clay adsorbs 3–5 mg enzyme per gram of clay depending on enzyme dosage. Acid soluble CaCO3 adsorbs about half of the enzyme compared to clay. Fractionation efficiency was also evaluated by testing different size mesh screen openings (100 to 500 mesh). The 400-mesh screen presented the best fiber yield, ash removal and ash fractionation ratio for both VK and RD sludges. The ash-rich streams have a lower C/N ratio than the original sludge which improves its suitability as soil amendment. 相似文献
966.
Emilia Kiersikowska Hasan Marai Magdalena Mątewska Grzegorz Wrzeszcz Ewa Kita 《Transition Metal Chemistry》2014,39(4):361-371
Two aqua derivatives of [Cr(Ala)3] were characterized in solution. Acid-catalyzed aquation of cis-[Cr(Ala)2(H2O)2]+ leads to inert [Cr(Ala)(H2O)4]2+, whereas base hydrolysis of cis-Cr(Ala)2(OH)2]? causes dissociation of both the Ala ligands and formation of chromates(III). Kinetics of these processes have been studied spectrophotometrically in both 0.1–1.0 M HClO4 and 0.2–0.9 M NaOH under first-order conditions. A linear dependence of the k obs,H on [H+] and a small dependence of the (k obs)OH on [OH?] were established. In the proposed mechanism, the rate determining step is Cr–N bond breaking in the reactive form of the substrate, i.e., in the protonated aqua- or dihydroxo complex. The effect of pH on the complex reactivity is discussed. The kinetic results are compared with those determined previously for analogous glycine and asparagine complexes. Additionally, oxidation of tris- and bis-Aa–chromium(III) complexes, where Aa = Gly, Ala or Asn, by hydrogen peroxide in alkaline medium was studied. Two reaction products were detected: thermodynamically stable CrO4 2? and [Cr(O2)4]3? that under a large excess of hydrogen peroxide is metastable. The rate-limiting stage of this process is an inner sphere two-electron transfer within the peroxido intermediate. 相似文献
967.
Hassan?KeypourEmail author Mohammad?Hasan?Zebarjadian Seyyed?Javad?Sabounchei 《Journal of the Iranian Chemical Society》2015,12(1):121-126
The reaction of phosphorus ylide, acetylmethylenetriparatolylphosphorane (L) with HgX2 (X = Cl, Br, I and NO3) in equimolar ratios using acetone and dimethylformamide as solvents leads to binuclear products. 31P NMR spectroscopy was used to investigate the stoichiometry and stability of a HgX2 complex with CH3COCHP(p-tolyl)3 (L) in binary acetone–dimethylformamide mixtures of varying composition. In all cases studied, the variation of 31P NMR chemical shift with the [HgX2]/[L] mole ratio indicated the formation of 1:1 complexes. The formation constants of the resulting complexes were evaluated from computer fitting of the mole ratio data to an equation that relates the observed chemical shifts to the formation constant. In all mercuric salts used, the stabilities of the resulting 1:1 complexes varied in the order Hg(NO3)2 > HgCl2 > HgBr2 > HgI2. It was found that, in the case of all complexes, an increase in the percentage of dimethylformamide in the solvent mixtures significantly decreases the stability of the complexes. 相似文献
968.
On the respective terms of the derived and the polycentral series of a free lie algabra and an ideal
Let F be a free Lie algebra of rank> 1 and S be an ideal of F. Denote by Fm and Fn l,…,nk the terms of the lower central and the polycentral series of F. The aim of this paper is to provide a sufficient condition for the quotient algebra Fn l,…,nk/Sn l,…,nk to be infinitely generated. The case Fm/Sm was studied in [6] for free groups and in [ 2 ] for free Lie algebras. In this paper the following main theorem is proved : If F = F2 = S, k > 1 and ni > 1 for i=l,…, k, then Fn l…,nk/Sn l is infinitely generated. 相似文献
969.
970.
Hasan Tuner 《辐射效应与固体损伤》2013,168(5-6):397-405
ABSTRACTThe effect of gamma radiation on lithium trifluoromethanesulfonate (LiTf) was investigated in detail using electron spin resonance (ESR) spectroscopy. The experimental spectra consisted of complex overlapped signals. Simulations of both the 1st- and 10th-day ESR spectra gave valuable information about the spectroscopic and structural features of radiation-induced radicals. More information about the qualitative and quantitative features of the radicals were gathered from the microwave power, storage time and dosimetric feature findings. In the light of the information obtained, four radicals were accepted to be produced after irradiation of LiTf. 相似文献