全文获取类型
收费全文 | 101394篇 |
免费 | 18114篇 |
国内免费 | 9186篇 |
专业分类
化学 | 85288篇 |
晶体学 | 1127篇 |
力学 | 4219篇 |
综合类 | 591篇 |
数学 | 9655篇 |
物理学 | 27814篇 |
出版年
2024年 | 221篇 |
2023年 | 1358篇 |
2022年 | 2536篇 |
2021年 | 2787篇 |
2020年 | 3829篇 |
2019年 | 4877篇 |
2018年 | 3166篇 |
2017年 | 2844篇 |
2016年 | 6304篇 |
2015年 | 6515篇 |
2014年 | 7003篇 |
2013年 | 8746篇 |
2012年 | 8774篇 |
2011年 | 8073篇 |
2010年 | 6825篇 |
2009年 | 6594篇 |
2008年 | 6539篇 |
2007年 | 5499篇 |
2006年 | 4927篇 |
2005年 | 4634篇 |
2004年 | 3709篇 |
2003年 | 3186篇 |
2002年 | 3767篇 |
2001年 | 2744篇 |
2000年 | 2546篇 |
1999年 | 1714篇 |
1998年 | 1114篇 |
1997年 | 1039篇 |
1996年 | 999篇 |
1995年 | 915篇 |
1994年 | 776篇 |
1993年 | 660篇 |
1992年 | 543篇 |
1991年 | 473篇 |
1990年 | 402篇 |
1989年 | 300篇 |
1988年 | 230篇 |
1987年 | 219篇 |
1986年 | 200篇 |
1985年 | 185篇 |
1984年 | 125篇 |
1983年 | 114篇 |
1982年 | 88篇 |
1981年 | 74篇 |
1980年 | 55篇 |
1979年 | 59篇 |
1978年 | 40篇 |
1977年 | 52篇 |
1976年 | 46篇 |
1975年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Stopped-flow was used to evaluate the methylation and reduction kinetics of the isolated alpha subunit of acetyl-Coenzyme A synthase from Moorella thermoacetica. This catalytically active subunit contains a novel Ni-X-Fe4S4 cluster and a putative unidentified n = 2 redox site called D. The D-site must be reduced for a methyl group to transfer from a corrinoid-iron-sulfur protein, a key step in the catalytic synthesis of acetyl-CoA. The Fe4S4 component of this cluster is also redox active, raising the possibility that it is the D-site or a portion thereof. Results presented demonstrate that the D-site reduces far faster than the Fe4S4 component, effectively eliminating this possibility. Rather, this component may alter catalytically important properties of the Ni center. The D-site is reduced through a pathway that probably does not involve the Fe4S4 component of this active-site cluster. 相似文献
992.
993.
Thecurrentsurgeofinterestinthefield0fnon-linearoptics(NL0)isderivedbothfromaquestforafundamentalunderstanding0fthenon-linearprocess,anditSimPortanceinthetechn0logyofphotonics.Amongnon-linearphen0mena,thethird-ordernon-linearophcsoccuPyanimPortantp0sihonbecauseitprovidesthemechanicsforophcalswitching,ophcallogic,andreal-hmeholograPhy"'.0rganicmaterialwithextendednconjugahonsandlargeRdelocalizahonsarewellknownastheimPortantmaterialsofachievinglargethird-ordernonlinearihes3.ForexamPle,thiosen… 相似文献
994.
首次将微量热用于亚细胞层次的研究,测定了鲤鱼肝脏线粒体和亚线粒体代谢的热谱及其漆树漆酶的影响,并用MTD方程和演化计算技术对它们的代谢热动力学参数进行了全局优化。 相似文献
995.
Jung SY Lim SM Albertorio F Kim G Gurau MC Yang RD Holden MA Cremer PS 《Journal of the American Chemical Society》2003,125(42):12782-12786
The molecular level details of the displacement of surface adsorbed fibrinogen from silica substrates were studied by atomic force microscopy, immunochemical assays, fluorescence microscopy, and vibrational sum frequency spectroscopy. The results showed that human plasma fibrinogen (HPF) can be readily displaced from the interface by other plasma proteins near neutral pH because the positively charged alpha C domains on HPF sit between the rest of the macromolecule and the underlying surface. The alpha C domains make weak electrostatic contact with the substrate, which is manifest by a high degree of alignment of Lys and Arg residues. Upon cycling through acidic pH, however, the alpha C domains are irreversibly removed from this position and the rest of the macromolecule is free to engage in stronger hydrogen bonding, van der Waals, and hydrophobic interactions with the surface. This results in a 170-fold decrease in the rate at which HPF can be displaced from the interface by other proteins in human plasma. 相似文献
996.
Pinnaduwage LA Yi D Tian F Thundat T Lareau RT 《Langmuir : the ACS journal of surfaces and colloids》2004,20(7):2690-2694
We measured the adsorption characteristics of trinitrotoluene (TNT) on piezoresistive silicon microcantilever surfaces under ambient air using a well-characterized TNT vapor generator. This allowed us to quantify the adsorption parameters and to estimate the sticking coefficient. The sticking coefficient initially increases with TNT exposure time and then levels off around 0.3. Atomic force microscopy images of silicon surfaces exposed to TNT revealed "island" formation of the adsorbate on the silicon surface. At low exposure times, mainly the number density of islands increased with exposure time; at longer exposure times, the size (in particular, height) of the islands grew, corresponding to the higher sticking coefficients. These observations can be qualitatively explained via the difference between TNT-surface and TNT-TNT interactions mediated by water molecules. 相似文献
997.
H2PtCl6可被一系列的酸处理定形聚偕胺肟树脂所吸附,吸附容量的大小与处理树脂的质子酸的Pka值有关.认为是解高度低的酸所处理的树脂上的伯胺基成盐的机会较少,即树脂的吸附中心保留着较多的空穴,有利于H2PtCl6的接近而被吸附下来.吸附动力学的研究表明化学反应是吸附速度的控制因素。 相似文献
998.
Yi Liu 《Tetrahedron letters》2007,48(22):3871-3874
Ring-in-ring nanostructures can be assembled from readily available starting materials, including dipyridyl ligands, (en)Pd(NO3)2, and β-cyclodextrin (β-CD). When a series of dipyridyl ligands are mixed with β-CD and Pd(II) in aqueous solution, various self-assembled geometries can be obtained as a result of a combination of hydrobic interactions and metal-ligand coordinations. In the cases of dipyridyl ligands with flexible linker, dinuclear coordination macrocycles M2L2 are formed and included in the cavity of β-CD to form ring-in-ring complexes. When more rigid dipyridyl ligands are used, a tetranuclear coordination macrocycle M4L4 prevails and shows no interaction with β-CD, as apposed to the flexible ones. 相似文献
999.
1000.
J. S. Bradshaw J. Y. Hui Y. Chan B. L. Haymore R. M. Izatt J. J. Christensen 《Journal of heterocyclic chemistry》1974,11(1):45-49
Macroeyclic polyether sulfides have been prepared by reacting an oligoethylene glycol dichloride with a dimercaptan or sodium sulfide as reported in a previous paper (6). The following new compounds were prepared: 1,4,7-trithia(15-crown-5) (1); 1,4,10-trithia(15-crown-5) (II): 1,4,7,10-tetrathia(15-crown-5) (III); I-thia(18-crown-6) (IV); 1,4-dithia(18-crown-6) (V); 1,7-dithia(18-crown-6) (VI); 1,4,7-trithia(18-crown-6) (VII); 1,7-dithia(21-crown-7) (VIII); and 1,4,7-trithia(21-crown-7) (IX). The melting points of these and previously reported thia-crown compounds correlate with their structures. X-ray analyses of two thia-crown compounds indicate that the large sulfur atoms are directed away from the center of the ring. 相似文献