全文获取类型
收费全文 | 7453篇 |
免费 | 1099篇 |
国内免费 | 778篇 |
专业分类
化学 | 5159篇 |
晶体学 | 74篇 |
力学 | 441篇 |
综合类 | 39篇 |
数学 | 860篇 |
物理学 | 2757篇 |
出版年
2024年 | 26篇 |
2023年 | 156篇 |
2022年 | 271篇 |
2021年 | 280篇 |
2020年 | 303篇 |
2019年 | 302篇 |
2018年 | 238篇 |
2017年 | 234篇 |
2016年 | 331篇 |
2015年 | 350篇 |
2014年 | 383篇 |
2013年 | 460篇 |
2012年 | 620篇 |
2011年 | 661篇 |
2010年 | 406篇 |
2009年 | 351篇 |
2008年 | 420篇 |
2007年 | 395篇 |
2006年 | 391篇 |
2005年 | 317篇 |
2004年 | 247篇 |
2003年 | 222篇 |
2002年 | 164篇 |
2001年 | 158篇 |
2000年 | 160篇 |
1999年 | 184篇 |
1998年 | 150篇 |
1997年 | 136篇 |
1996年 | 130篇 |
1995年 | 120篇 |
1994年 | 119篇 |
1993年 | 82篇 |
1992年 | 85篇 |
1991年 | 91篇 |
1990年 | 63篇 |
1989年 | 39篇 |
1988年 | 40篇 |
1987年 | 33篇 |
1986年 | 26篇 |
1985年 | 28篇 |
1984年 | 21篇 |
1983年 | 27篇 |
1982年 | 13篇 |
1981年 | 11篇 |
1979年 | 13篇 |
1978年 | 7篇 |
1977年 | 15篇 |
1975年 | 9篇 |
1974年 | 5篇 |
1972年 | 6篇 |
排序方式: 共有9330条查询结果,搜索用时 15 毫秒
31.
H. W. Sarkas S. T. Arnold J. H. Hendricks L. H. Kidder C. A. Jones K. H. Bowen 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,26(1):46-50
We present preliminary evidence for catalytic activity by unsupported mixed metal oxide nanocrystalline materials. The results of this study show that a nanophase form of Li-MgO has begun to exhibit catalytic activity by 300 °C. This is at least 200 degrees below the temperature at which conventional Li-MgO catalysts exhibit comparable activity. Furthermore, at higher temperatures, the same nanophase composition shows enhanced activities and somewhat improved hydrocarbon selectivities over conventional Li-MgO catalysts. 相似文献
32.
ZhiQuanZHAO LiZengPENG YuLinLI 《中国化学快报》2005,16(3):290-292
The phenomenon of migration of the silyl groups from α-oxygen to β-oxygen in sodium aldol reaction was observed for the first time in this paper. 相似文献
33.
Strategies for locating disulfide bonds in a monoclonal antibody via mass spectrometry 总被引:1,自引:0,他引:1
The location of the disulfide bonds in a recombinant monoclonal antibody was confirmed by matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) and electrospray ionization (ESI) mass spectrometry (MS). A non-reduced Endoproteinase Lys-C (Endo Lys-C) digest of the antibody was analyzed directly by MALDI-TOFMS. The sample was then reduced on-plate by depositing dithiothreitol (DTT) on the sample spot and re-analyzed by MALDI-TOFMS. The disulfide bonds were assigned based on the disappearance of certain mass ions in the non-reduced digest and the appearance of product ions in the reduced digest. A rapid LC/ESI-MS protocol was also developed to determine the location of the disulfide bonds. The peptides generated from the Endo Lys-C digest of the antibody were partially separated on a high performance liquid chromatography (HPLC) column by utilizing a steep gradient and analyzed by ESI-MS. The masses of the partially resolved peptides were determined by deconvoluting the mass spectra. 相似文献
34.
By means of a large-scale molecular dynamics simulation, we show that the Tolman length, although positive, is much smaller in magnitude than previously reported. We found that the range of interparticle interaction can significantly affect the magnitude of the Tolman length. When the range of interaction is longer than five molecular diameters, the Tolman length is on the order of a few hundredths of the molecular diameter, rather than a few tenths known previously. 相似文献
35.
South MS Case BL Dice TA Franklin GW Hayes MJ Jones DE Lindmark RJ Zeng Q Parlow JJ 《Combinatorial chemistry & high throughput screening》2000,3(2):139-151
A parallel solution-phase library synthesis of functionalized diaminobenzamides is described. The four-step library synthesis is accomplished using polymer-assisted solution-phase (PASP) synthesis techniques. This high-yielding, multi-step sequence utilizes sequestering resins for the removal of reactants, reactant by-products, and employs a resin capture/release strategy as a key library synthesis step. Step one of the sequence relies on the displacement of an activated fluoro-group from the aromatic ring of 1a, b with a variety of primary amines to introduce the first diversity position. Step two is hydrolysis of the benzoate ester to a benzoic acid which is subsequently captured on a polyamine resin, washed, and released to give 4a, b in pure form. Step three utilizes PASP resins to mediate the amide coupling of a benzoic acid with a variety of primary amines to give the aminonitrobenzamides 5a, b and introduces the second diversity position. Step four is the parallel reduction of the aminonitrobenzamides 5a, b to the functionalized diaminobenzamides 6a, b. This library synthesis proceeds with high overall purities which average 80 % over the 4-step sequence. 相似文献
36.
Xiu-Lin Zeng Wang-Hua Chen Jia-Cong Liu Jin-Lin Kan 《Journal of Molecular Structure》2007,810(1-3):47-51
Three density-functional methods (B3P86, B3PW91, and B3LYP) are employed to investigate the O–NO2 bond lengths, frontier orbital energies, and O–NO2 bond dissociation energies (BDEs) of n-propyl nitrate (NPN), isopropyl nitrate (IPN), 2-ethylhexyl nitrate (EHN), triethylene glycol dinitrate (Tri-EGDN), and tetraethylene glycol dinitrate (Tetra-EGDN). It is found that the O–NO2 bond lengthens (destabilizes) in the order of IPN, NPN, EHN, Tetra-EGDN, and Tri-EGDN. From the data of frontier orbital energies (EHOMO, ELUMO), and energy gaps (ΔE), we estimate the relative thermal stability ordering of five nitrates and their corresponding radicals. The predicted BDEs of O–NO2 bond in NPN, IPN, EHN, Tri-EGDN, and Tetra-EGDN, are 176.6, 174.5, 168.1, 156.1, and 159.3 kJ mol−1, respectively. Based on the finding that the present results of BDEs are well coincident with the experimental results of apparent activation energies from the literature, we can draw a conclusion that the experimental thermolysis of five nitrates is only unimolecular homolytical cleavage of the O–NO2 bonds. 相似文献
37.
The major slow unimolecular reactions undergone by C4H7+, C5H9+ and C6H+11 are discussed in terms of a potential surface approach and the organic chemist's concept of mechanism. It is shown that the observed decompositions which do not involve σ-bond formation in the dissociation step are precisely those expected from the model. Further use of the model correctly predicts the slow reactions of C7H+13 which have not previously been reported. The approach also permits useful limits to be set on the transition state energies for reactions involving σ-bond formation in the dissociation step (H2,CH4 loss). It is concluded that stepwise addition of ethylene to the allyl cation is preferred to a concerted 4-electron process which is symmetry forbidden. 相似文献
38.
A simple method was used to prepare a "switchable" electrode surface by using self-assembled monolayers of dodecanethiol on a gold electrode. The dodecane-modified electrode was electrochemically inactive until the monolayer was soaked in solutions of 1,10-phenanthroline or 2,2'-bipyridine. The electroactive form of the electrode could be reverted back to the nonelectroactive form by rinsing the electrode. Surface IR results showed that both dodecanethiol and 1,10-phenanthroline exist in the mixed monolayer. 相似文献
39.
A two-tiered organizing scheme with multiple-length scales for construction of dandelion-like hollow CuO microspheres has been elucidated: (1) mesoscale formation of rhombic building units from smaller nanoribbons via oriented aggregation and (2) macroscopic organization of these units into the CuO microspheres. This self-assembly concept may also be applicable to other metal oxides by creating geometric constraints for constructional units. 相似文献
40.