全文获取类型
收费全文 | 699篇 |
免费 | 36篇 |
国内免费 | 1篇 |
专业分类
化学 | 489篇 |
晶体学 | 2篇 |
力学 | 5篇 |
数学 | 102篇 |
物理学 | 138篇 |
出版年
2023年 | 12篇 |
2022年 | 8篇 |
2021年 | 15篇 |
2020年 | 33篇 |
2019年 | 30篇 |
2018年 | 12篇 |
2017年 | 12篇 |
2016年 | 25篇 |
2015年 | 22篇 |
2014年 | 39篇 |
2013年 | 41篇 |
2012年 | 43篇 |
2011年 | 44篇 |
2010年 | 16篇 |
2009年 | 14篇 |
2008年 | 36篇 |
2007年 | 27篇 |
2006年 | 32篇 |
2005年 | 19篇 |
2004年 | 17篇 |
2003年 | 10篇 |
2002年 | 5篇 |
2000年 | 11篇 |
1999年 | 4篇 |
1997年 | 5篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1986年 | 4篇 |
1978年 | 7篇 |
1975年 | 3篇 |
1954年 | 4篇 |
1949年 | 6篇 |
1931年 | 4篇 |
1928年 | 6篇 |
1927年 | 9篇 |
1925年 | 10篇 |
1924年 | 8篇 |
1923年 | 6篇 |
1921年 | 4篇 |
1913年 | 6篇 |
1912年 | 4篇 |
1909年 | 4篇 |
1908年 | 4篇 |
1907年 | 10篇 |
1906年 | 4篇 |
1904年 | 4篇 |
1903年 | 3篇 |
1885年 | 3篇 |
1883年 | 4篇 |
1874年 | 3篇 |
排序方式: 共有736条查询结果,搜索用时 187 毫秒
11.
Chepanoske CL Richardson BE von Rechenberg M Peltier JM 《Rapid communications in mass spectrometry : RCM》2005,19(1):9-14
The quantity and variable quality of data that can be generated from liquid chromatography (LC)/mass spectrometry (MS)-based proteomics analyses creates many challenges in interpreting the spectra in terms of the actual proteins in a complex sample. In spite of improvements in algorithms that match putative peptide sequences to MS/MS spectra, the assembly of these lists of possible or probable peptides into a 'correct' set of proteins is still problematic. We have observed a trend in a simple relationship, derived from standard database search outputs, which can be useful in assessing the quality of a MS/MS-based protein identification. Specifically, the ratio of the protein score and number of non-redundant peptides, or average peptide score (APS), can facilitate initial filtering of database search results in addition to providing a useful measure of confidence for the proteins identified. This parameter has been applied to results from the analysis of multi-protein complexes derived from pull-down experiments analyzed using a two-dimensional LC/MS/MS workflow. In particular, the complex list of protein identifications derived from a drug affinity pull-down with immobilized ampicillin and an E. coli lysate was greatly simplified by applying the APS as a filter, allowing for facile identification of the penicillin-binding proteins known to interact with ampicillin. Furthermore, an APS threshold can be used for any data sets derived from electrospray ionization (ESI)- or matrix-assisted laser desorption/ionization (MALDI)-MS/MS experiments and is also not specific to any database search program. 相似文献
12.
Dr. Moritz Armsen 《manuscripta mathematica》1977,20(3):245-253
The classical Gauss-Bonnet formula has the form I(gij)=2, where I(gij) represents a sum of three terms each of which depends on the metric tensor gij. It is shown that the first variation I of I(gij) with respect to the metric gij vanishes and that for the Euclidean metric ij we have I(ij)=2. From this the formula I(gij)=2 follows. In the process, explicit expressions are obtained for the first variation of each of the three terms which comprise I(gij). Furthermore, a general expression for the first variation of a multiple integral whose integrand is a scalar density depending on the metric tensor gij and its derivatives up to the second order is obtained with the aid of results of Rund [1]. 相似文献
13.
Ternary Rare-Earth Halides of the A2MX5 Type (A = K, In, NH4, Rb, Cs; X = Cl, Br, I) Ternary rare-earth (=M) chlorides, bromides, and iodides In2MCl5, (NH4)2MCl5, Rb2MCl5, Cs2MCl5, CsRbMCl5, K2MBr5, Rb2MBr5, K2MI5, and Rb2MI5 have been synthesized. Single crystals of In2PrCl5, Rb2PrCl5, K2PrBr5, and K2PrI5 were grown and the structures refined. The other halides were characterized by x-ray powder patterns. They are isotypic either with K2PrCl5(orthorhombic, Pnma, Z = 4, hexagonal arrangement of chains of edge-connected polyhedra [PrX7]) or with Cs2DyCl5 (orthorhombic, Pbnm, Z = 4, hexagonal arrangement of cis-corner-connected octahedra [DyCl6]) which may be discriminated in structure field diagrams. The thermal expansion was investigated für Cs2LuCl5 and Rb2PrX5 (X = Cl, Br, I). 相似文献
14.
A continuous gradient elution method for capillary column (less than 0.32 mm I.D.) liquid chromatography was developed. Gradient eluent from a microbore liquid chromatograph was split ahead of the injector so that an accurate percentage (2-3%) of the mobile phase delivered by the pump flowed through the capillary column. The outlet of the column was connected to a length of 0.075 mm I.D. fused-silica capillary tubing which, in turn, was connected to a 6-mm optical path length longitudinal capillary flow cell. Fused-silica capillary columns of 0.32 mm I.D. were slurry-packed efficiently with 7-microns spherical, 300 A pore size, C8 bonded-phase particles, and evaluated in terms of their ability to resolve mixtures of proteins, peptides or phenylthiohydantoin (PTH)-amino acid derivatives. The gradient elution profiles agreed with those obtained using microbore (less than 2.1 mm I.D.) and larger bore columns. The minimum detectable amounts for proteins and PTH-amino acids on 0.32 mm I.D. capillary columns were 50 pg and 25 fmol, respectively. At a flow-rate of 3.6 microliters/min, proteins and peptides were recovered from the capillary columns in volumes of about 2-8 microliters. The use of a multiple-wavelength, forward-optics detector for identifying tryptophan- and tyrosine-containing peptides is discussed. 相似文献
15.
16.
17.
18.
F. Moritz M. Dey K. Zipperer S. Prinke J. Grotemeyer 《Journal of mass spectrometry : JMS》1993,28(12):1467-1475
Some details of the generation of electrons by impinging a laser beam on a metal surface are described. It is shown that highly efficient electron generation is observed only during the laser pulse. Therefore, this technique delivers intense pulses of electrons. The process is investigated and different ion source set-ups are discussed. In conjunction with a time-of-flight mass spectrometer this technique can be used to produce mass spectra of different samples ranging from simple organic molecules to peptides. 相似文献
19.
Ferricyan can be determined in the presence of copper, silver and cadmium by addition of potassium ferrocyanide, filtration of the ferrocyanides of copper, silver and cadmium formed in this reaction, and titration of the potassium ferricyanide contained in the filtrate. In the case of silver, the ferricyan can also be determined without filtration by addition of potassium iodide and titration of the ferricyanide. In the case of zinc, potassium, ferrocyanide is added and without filtration the ferricyanide titrated. 相似文献
20.
Sarah Eichenberger Moritz Hnig Matthieu J. R. Richter Renana Gershoni-Poranne Erick M. Carreira 《Chemical science》2020,11(20):5294
A novel Lewis acid-catalyzed cycloisomerization of alkylidenecyclopropane acylsilanes is disclosed. The readily available starting materials participate in tandem Prins addition/ring expansion/1,2-silyl shift to grant access to bicyclo[4.2.0]octanes and bicyclo[3.2.0]heptanes, which are common motifs in terpenoid natural products. Notably, the transformation relies on the ability of acylsilanes to act sequentially as acceptors and donors on the same carbon atom.A novel Lewis acid-catalyzed cycloisomerization of alkylidenecyclopropane acylsilanes is disclosed that involves tandem Prins addition/ring expansion/1,2-silyl shift to grant access to bicyclo[4.2.0]octanes and bicyclo[3.2.0]heptanes. 相似文献