全文获取类型
收费全文 | 1808篇 |
免费 | 33篇 |
国内免费 | 5篇 |
专业分类
化学 | 1252篇 |
晶体学 | 23篇 |
力学 | 38篇 |
数学 | 164篇 |
物理学 | 369篇 |
出版年
2021年 | 12篇 |
2020年 | 17篇 |
2019年 | 17篇 |
2018年 | 13篇 |
2017年 | 9篇 |
2016年 | 33篇 |
2015年 | 35篇 |
2014年 | 26篇 |
2013年 | 52篇 |
2012年 | 67篇 |
2011年 | 94篇 |
2010年 | 65篇 |
2009年 | 48篇 |
2008年 | 80篇 |
2007年 | 97篇 |
2006年 | 74篇 |
2005年 | 66篇 |
2004年 | 69篇 |
2003年 | 65篇 |
2002年 | 56篇 |
2001年 | 47篇 |
2000年 | 31篇 |
1999年 | 27篇 |
1998年 | 28篇 |
1997年 | 23篇 |
1996年 | 30篇 |
1995年 | 28篇 |
1994年 | 24篇 |
1993年 | 18篇 |
1992年 | 28篇 |
1991年 | 15篇 |
1990年 | 21篇 |
1989年 | 15篇 |
1987年 | 19篇 |
1986年 | 18篇 |
1985年 | 24篇 |
1984年 | 16篇 |
1983年 | 16篇 |
1982年 | 21篇 |
1981年 | 14篇 |
1980年 | 23篇 |
1979年 | 14篇 |
1978年 | 32篇 |
1977年 | 26篇 |
1976年 | 18篇 |
1975年 | 9篇 |
1974年 | 13篇 |
1973年 | 22篇 |
1972年 | 11篇 |
1968年 | 14篇 |
排序方式: 共有1846条查询结果,搜索用时 15 毫秒
51.
Oswald B Gruber M Böhmer M Lehmann F Probst M Wolfbeis OS 《Photochemistry and photobiology》2001,74(2):237-245
We describe a series of new long-wave absorbing and fluorescing cyanine dyes and labels (based on a general logic for the design of such dyes), their spectra, covalent and noncovalent linkage to proteins, their use in single molecule detection (SMD) and as donors and acceptors, respectively, in fluorescence resonance energy transfer studies. The new labels represent water-soluble and reactive fluorophores whose quantum yields increase substantially if noncovalently or covalently bound to proteins. Due to their strong absorptions between 550 and 700 nm they are excitable by light-emitting diodes or diode lasers. Their high absorbances (epsilon around 100,000) and adequate fluorescence quantum yields (phi up to 0.68 if bound to proteins) along with their availability as reactive NHS esters make them viable labels for proteins and oligomers, e.g. in context with SMD or fluorescence energy transfer immunoassay which is demonstrated for the system HSA/anti-HSA. 相似文献
52.
Fürstner A Ackermann L Gabor B Goddard R Lehmann CW Mynott R Stelzer F Thiel OR 《Chemistry (Weinheim an der Bergstrasse, Germany)》2001,7(15):3236-3253
Exchange of one PCy3 unit of the classical Grubbs catalyst 1 by N-heterocyclic carbene (NHC) ligands leads to "second-generation" metathesis catalysts of superior reactivity and increased stability. Several complexes of this type have been prepared and fully characterized, six of them by X-ray crystallography. These include the unique chelate complexes 13 and 14 in which the NHC- and the Ru-CR entities are tethered to form a metallacycle. A particularly favorable design feature is that the reactivity of such catalysts can be easily adjusted by changing the electronic and steric properties of the NHC ligands. The catalytic activity also strongly depends on the solvent used; NMR investigations provide a tentative explanation of this effect. Applications of the "second-generation" catalysts to ring closing alkene metathesis and intramolecular enyne cycloisomerization reactions provide insights into their catalytic performance. From these comparative studies it is deduced that no single catalyst is optimal for different types of applications. The search for the most reactive catalyst for a specific transformation is facilitated by IR thermography allowing a rapid and semi-quantitative ranking among a given set of catalysts. 相似文献
53.
54.
Pagels N Albrecht O Görlitz D Rogachev AY Prosenc MH Heck J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(15):4166-4176
The paramagnetic dinuclear complexes 1,8-bis(cobaltocenyl)naphthalene (2) and 1,8-bis[(pentamethyl-η(5)-cyclopentadienyl)(η(5)-cyclopentadiendiyl)cobalt(II)]naphthalene (4) were synthesized. The molecular structures were characterized by X-ray structure analysis and consisted of two cobaltocenes linked through a distorted naphthalene clamp. Electronic interactions between the two cobalt atoms were observed by cyclic voltammetric studies. Superconducting quantum interference device (SQUID) measurements of the pure compounds and diluted in their diamagnetic iron derivatives, as well as variable-temperature NMR spectroscopy experiments in solution are presented. Magnetic measurements revealed an antiferromagnetic coupling of the electrons in complexes 2 and 4. From NMR spectroscopy experiments, Curie behavior in the temperature range from -60 to +60 °C can be deduced. The electronic structure and magnetic behavior is supported by results of broken-symmetry DFT and multireference calculations along with UV/Vis spectroscopic data, which revealed an intramolecular through space π-π interaction between the cobaltocene units. 相似文献
55.
56.
57.
Eberhard H. Lehmann Werner Wagner 《Applied Physics A: Materials Science & Processing》2010,99(3):627-634
Neutron imaging as a method for non-destructive studies takes advantage of the alternative contrast mechanism of neutrons compared to X-rays: most of the light elements feature high contrast, whereas heavy elements are relatively transparent to neutrons. In the previous decade, the neutron imaging technique has made substantial progress in well-tailored and well-equipped beam lines, in improvements of the image recording quality and efficiency by new and modern imaging techniques, and in modern image processing tools. 相似文献
58.
59.
60.
The widespread occurrence of the neutral loss of one to six amino acid residues as neutral fragments from doubly protonated tryptic peptides is documented for 23 peptides with individual sequences. Neutral loss of amino acids from the N-terminus of doubly charged tryptic peptides results in doubly charged y-ions, forming a ladder-like series with the ions [M + 2H](2+) = y(max) (2+), y(max - 1) (2+), y(max - 2) (2+), etc. An internal residue such as histidine, proline, lysine or arginine appears to favor this type of fragmentation, although it was sometimes also observed for peptides without this structure. For doubly protonated non-tryptic peptides with one of these residues at or near the N-terminus, we observed neutral loss from the C-terminus, resulting in a doubly charged b-type ion ladder. The analyses were performed by Q-TOF tandem mass spectrometry, facilitating the recognition of neutral loss ladders by their 2+ charge state and the conversion of the observed mass differences into reliable sequence information. It is shown that the neutral loss of amino acid residues requires low collision offset values, a simple mechanistic explanation based on established fragmentation rules is proposed and the utility of this neutral loss fragmentation pathway as an additional source for dependable peptide sequence information is documented. 相似文献