全文获取类型
收费全文 | 513篇 |
免费 | 6篇 |
专业分类
化学 | 289篇 |
晶体学 | 1篇 |
力学 | 15篇 |
数学 | 44篇 |
物理学 | 170篇 |
出版年
2021年 | 5篇 |
2020年 | 3篇 |
2019年 | 7篇 |
2018年 | 6篇 |
2016年 | 7篇 |
2015年 | 6篇 |
2014年 | 3篇 |
2013年 | 33篇 |
2012年 | 20篇 |
2011年 | 25篇 |
2010年 | 22篇 |
2009年 | 14篇 |
2008年 | 19篇 |
2007年 | 27篇 |
2006年 | 17篇 |
2005年 | 13篇 |
2004年 | 18篇 |
2003年 | 20篇 |
2002年 | 17篇 |
2001年 | 11篇 |
2000年 | 16篇 |
1999年 | 13篇 |
1998年 | 7篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 8篇 |
1994年 | 9篇 |
1993年 | 12篇 |
1992年 | 12篇 |
1991年 | 8篇 |
1990年 | 8篇 |
1989年 | 9篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1977年 | 8篇 |
1976年 | 5篇 |
1974年 | 3篇 |
1973年 | 9篇 |
1933年 | 2篇 |
1904年 | 2篇 |
1878年 | 2篇 |
排序方式: 共有519条查询结果,搜索用时 109 毫秒
11.
Comprehensive studies have been carried out on the extraction behaviour of thorium matrix vis-a-vis 17 trace metallic elements using a novel extractant viz. Cyanex-923. The near total extraction of thorium and quantitative separation of these metals has been established using inductively coupled argon plasma–atomic emission spectrometry (ICP–AES). The recovery of few representative elements has been confirmed by radio-active tracer studies. The studies carried out here have enabled determination of μg/l amounts of all analyte elements with a precision of better than 1% RSD with prior chemical separation from as low as 1 g thorium sample in just five chemical extractions. 相似文献
12.
Roger J. Greathead Rod S. Mason Keith R. Jennings Janet A. Page Robert J. Pryce 《Journal of mass spectrometry : JMS》1985,20(2):110-114
The behaviour of gibberellic acid (GA3) under electron impact and chemical ionization conditions has been examined. The tendency of GA3 to undergo pyrolysis by the loss of the elements of water and carbon dioxide has been identified. Two methods of sample introduction can be used to minimize the occurrence of this pyrolysis. Accurate mass measurement allows the composition of the pyrolysis product to be determined and metastable techniques confirm the structure of this product to be epi-allogibberic acid rather than its isomer allogibberic acid. This result corrects a misconception in the literature and illustrates the advantage of metastable methods compared with accurate mass measurements, for the determination of small structural differences within a molecule. 相似文献
13.
M. Leino J. Uusitalo R. G. Allatt P. Armbruster T. Enqvist K. Eskola S. Hofmann S. Hurskanen A. Jokinen V. Ninov R. D. Page W. H. Trzaska 《Zeitschrift für Physik A Hadrons and Nuclei》1996,355(1):157-164
Neutron-deficient isotopes of radium have been produced in the reactions35Cl+175Lu,40Ar+170,171Yb, and36Ar+170,171Yb and separated in-flight with a gas-filled recoil separator. The activities have been identified on the basis of correlated alpha decay chains. The alpha particle energy Eα and the half-life T1/2 of an isomeric state of the new isotope,203m Ra, have been determined to be (7615±20) keV and (33 ?10 +22 ) ms, respectively. An assignment of another decay with Eα = (7577±20) keV and T1/2=(1.1 ?0.5 +5.0 ) ms to203g Ra is made on the basis of one observed three-decay chain. Tentative evidence for the production of the new isotope202Ra is also given. The values Eα = (7860±60) keV and T1/2=(0.7 ?0.3 +3.3 ) ms were measured. Improved decay data have been obtained for204Ra. The results are Eα = (7484±10) keV and T1/2=(59 ?9 +12 ) ms. Earlier findings concerning the decay of two states in205Ra and an isomer in207Ra have been confirmed. Approximate values for cross sections have been determined for202Ra, produced using the36Ar+170Yb reaction and for203Ra,204Ra, and205Ra using the35Cl+175Lu reaction. The results are 2 nb (202Ra), 4 nb (203Ra), 40 nb (204Ra), and 800 nb (205Ra). 相似文献
14.
15.
Information in black hole radiation 总被引:1,自引:0,他引:1
Page DN 《Physical review letters》1993,71(23):3743-3746
16.
17.
[reaction: see text] N-Acylsulfonamides usually react with nucleophiles by acyl transfer and C-N bond fission. However, the hydrolysis of N-acyl beta-sultams is a sulfonyl transfer reaction that occurs with S-N fission and opening of the four-membered ring. Similar to other beta-sultams, the N-acyl derivatives are at least 10(6)-fold more reactive than N-acyl sulfonamides. 3-Oxo-beta-sultams are both beta-lactams and beta-sultams but also hydrolyze with preferential S-N bond fission. 相似文献
18.
Jaan A. Pesti Jill A. Downard Mark D. Lauritsen Goss S. Kauffman Walter M. Bryant George F. Huhn John F. Arnett Robert E. Yule James Segretario Kimberly A. Nelson Edward F. Gorko Gary O. Page Lisa M. Lloyd Richard E. Olson Christopher S. Bamum Joseph J. Mrowca 《Journal of heterocyclic chemistry》1998,35(1):249-255
The methanesulfonates of (α-(4-chlorophenyl)-α-[1-(2-chlorophenyl)ethenyl]-1H-1,2,4-triazole-1-ethanol and α-[1-(2-chlorophenyl)ethenyl]-α-(2,4-difluorophenyl)-1H-1,2,4-triazole-1-ethanol ( 1a, b ) are orally effective α-styryl carbinol derivatives developed for the treatment and prevention of systemic fungal infections. Practical new processes amenable for the large-scale production of these compounds are described. Of note is the selection of dichlorostyrene as a convenient precursor of the styryl portion, modification of a sensitive Grignard addition into a realistic preparative reaction and the use of 1,2,4-triazole simultaneously as a base transfer agent and nucleophile. 相似文献
19.
20.
An adjustable low-mass filter has been developed for an electrospray ionization (ESI) source to block ions associated with unwanted background species from entering the mass spectrometer. The low-mass filter is made by using an adjustable potential energy barrier from the conductance-limiting plate of an electrodynamic ion funnel, which prohibits species with higher ion mobilities from exiting the ESI source. We show that this arrangement provides a linear voltage adjustment for low-mass filtering from m/z 0 to 500. Mass filtering above m/z 500 is also performed; however, higher-mass species are attenuated. The mass filter was tested with a liquid chromatography/mass spectrometry (LC/MS) analysis of a bovine serum albumin (BSA) tryptic digest and resulted in the ability to block low-mass, background species, which accounted for 40-70% of the total ion current immediately behind the ESI source during peak elution and detection. 相似文献