全文获取类型
收费全文 | 5539篇 |
免费 | 506篇 |
国内免费 | 256篇 |
专业分类
化学 | 3633篇 |
晶体学 | 24篇 |
力学 | 241篇 |
综合类 | 23篇 |
数学 | 718篇 |
物理学 | 1662篇 |
出版年
2023年 | 66篇 |
2022年 | 99篇 |
2021年 | 105篇 |
2020年 | 110篇 |
2019年 | 114篇 |
2018年 | 96篇 |
2017年 | 80篇 |
2016年 | 173篇 |
2015年 | 141篇 |
2014年 | 189篇 |
2013年 | 330篇 |
2012年 | 403篇 |
2011年 | 414篇 |
2010年 | 267篇 |
2009年 | 238篇 |
2008年 | 336篇 |
2007年 | 289篇 |
2006年 | 275篇 |
2005年 | 252篇 |
2004年 | 229篇 |
2003年 | 211篇 |
2002年 | 175篇 |
2001年 | 137篇 |
2000年 | 112篇 |
1999年 | 107篇 |
1998年 | 68篇 |
1997年 | 80篇 |
1996年 | 86篇 |
1995年 | 88篇 |
1994年 | 78篇 |
1993年 | 73篇 |
1992年 | 72篇 |
1991年 | 40篇 |
1990年 | 45篇 |
1989年 | 33篇 |
1988年 | 35篇 |
1987年 | 33篇 |
1986年 | 29篇 |
1985年 | 53篇 |
1984年 | 39篇 |
1983年 | 32篇 |
1982年 | 43篇 |
1981年 | 34篇 |
1980年 | 31篇 |
1979年 | 40篇 |
1978年 | 32篇 |
1977年 | 28篇 |
1976年 | 28篇 |
1975年 | 26篇 |
1974年 | 34篇 |
排序方式: 共有6301条查询结果,搜索用时 921 毫秒
51.
52.
Chen-Yuan Tu Ying-Ling Liu Min-Tzu Luo Kueir-Rarn Lee Juin-Yih Lai 《Chemphyschem》2006,7(6):1355-1360
Poly(glycidyl methacrylate), PGMA, chains in linear and arborescent structures were incorporated onto surfaces of poly(tetrafluoroethylene), PTFE, films by hydrogen plasma and ozone treatment and atom transfer radical polymerization. The epoxide groups of the PGMA chains were further reacted with acetic acid (AAc), oxalic acid (XAc), allyl amine (AA), and ethylenediamine (EDN) to introduce hydroxyl and amine groups to the surfaces of the PTFE films. Surface characterizations performed by Fourier Transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed the surface modification and the chemical structure. The PGMA chains in arborescent structures show a high effectiveness for the enhancement of the adhesion of PTFE films. The adhesion of PTFE films was also significantly enhanced by ring-opening reactions of the PGMA epoxide groups with acetic acid and amine compounds. A high value of 9.5 N cm(-1) in the optimum 180 degrees peel strength test was observed with PTFE/copper assemblies. 相似文献
53.
随着基因技术的发展,人们几乎已经可以任意替换蛋白质序列中的特定残基。由于理论上对蛋白质性能的预测工作还远远跟不上实验的发展,只能花费大量的人力、物力利用实验方法筛选突变体。这就迫切需要建立一套能够正确预测蛋白质性质的方法。静电作用在酶促反应中起到了重要作用。基于表面带电残基对酶活性部位残基pK_α的影响,可利用替换表面残基的方法改变酶促反应随pH的变化趋势,是蛋白质工程研究中的一种有效方法。由于表面极性残基处于高介电常数的溶剂(水)与低介电常数的蛋白质的界面上,对此问题尚未有圆满的理论方法进行解决。我们利用Kirkwood理论定量地表述了表面荷电残基的替换对酶活性部位残基pK_α的影响,为研究酶突变体的性质,如突变体的电化学性质、酶催化反应随pH变化趋势的改变,酶专一性的改变等提供了一种简便的方法。 相似文献
54.
55.
The equilibrium volatilities at near infinite dilution of various solutes absorbed in molten polystyrene have been determined by a gas chromatographic technique. This method is much more rapid, although, with the present apparatus, probably less accurate than conventional static techniques. The primary parameters obtained from measurements of retention volumes are the Henry's law constants, from which are derived the weight and volume fraction activity coefficients, the Flory-Huggins interaction parameters, and the heats of dilution and solution. Of the solutes investigated, 2-butanone (MEK) was the least, and benzene the most compatible (highest and lowest volume fraction activity coefficients, respectively) with molten polystyrene. A small, but definite, variation of the activity coefficients with polystyrene molecular weight was observed. 相似文献
56.
57.
58.
John T. W. Lai Frankie W. Lau Damon Robb Peter Westh Gerda Nielsen Christa Trandum Aase Hvidt Yoshikata Koga 《Journal of solution chemistry》1995,24(1):89-102
The excess partial molar enthalpies, the vapor pressures, and the densities of dimethylsulfoxide (DMSO)–H2O mixtures were measured and the excess partial molar Gibbs energies and the partial molar volumes were calculated for DMSO and for H2O. The values of the excess partial molar Gibbs energies for both DMSO and H2O are negative over the entire composition range. The results for the water-rich region indicated that the presence of DMSO enhances the hydrogen bond network of H2O. Unlike monohydric alcohols, however, the solute-solute interaction is repulsive in terms of the Gibbs energy. This was a result of the fact that the repulsion among solutes in terms of enthalpy surpassed the attraction in terms of entropy. The data in the DMSO-rich region suggest that DMSO molecules form clusters which protect H2O molecules from exposure to the nonpolar alkyl groups of DMSO. 相似文献
59.
King RB 《Dalton transactions (Cambridge, England : 2003)》2004,(21):3420-3424
Nickel and palladium atoms with their closed-shell d(10) electronic configurations are encapsulated in the icosahedral clusters [Ni@Ni(10)E(2)(CO)(18)](4-)(E = Sb, Bi, Sb[rightward arrow]Ni(CO)(3), CH(3)Sn and n-C(4)H(9)Sn) and the geometrically related pentagonal antiprismatic cluster Pd@Bi(10)(4+) found in Bi(14)PdBr(16). Such endohedral d(10) atoms in pentagonal antiprismatic clusters are donors of zero skeletal electrons and interact only weakly with the atoms in the surrounding polyhedron so that they may be regarded as analogous to endohedral noble gases in fullerenes such as He@C(60). On the other hand, endohedral nickel and palladium atoms in 10- and 11-vertex flattened deltahedral bare metal clusters of group 13 metals without five-fold symmetry, such as Ni@E(10)(10-) found in Na(10)NiE(10)(E = Ga, In) and Pd@Tl(11)(7-) found in A(8)Tl(11)Pd (A = Cs, Rb, K), interact significantly with the cluster atoms, particularly those at the flattened vertices of the deltahedron. The role of endohedral d(10) atoms Ni and Pd in polyhedra with five-fold symmetry as "pseudo-noble-gases" can be related to their positions at the "composite divide" of the "Metallurgists' Periodic Table" proposed by H. E. N. Stone on the basis of alloy systematics as well as the equivalence of the five d orbitals in polyhedra with five-fold symmetry. 相似文献
60.
This paper describes the synthesis of three neutral water soluble poly(amidoamine) (PAMAM) dendrimer derivatives. The ability of the two larger dendrimers to bind small acidic hydrophobic molecules is reported. Spectroscopic data and pH behaviour suggested that the acidic hydrophobes were forming stable ion pairs with the dendrimer's internal, basic tertiary nitrogens. With respect to forming 1:1 and 2:1 substrate/dendrimer complexes, both of the larger dendrimers were equally efficient at binding. All dendrimer/substrate complexes were completely miscible with water in all proportions (i.e. infinitely water soluble). When the bound substrates are drug moieties, then the resulting complexes could be considered as potential drug delivery systems. Flow calorimetry demonstrated that the dendrimers were able to release their hydrophobic guests when in contact with a biological cell. 相似文献