全文获取类型
收费全文 | 3402篇 |
免费 | 130篇 |
国内免费 | 19篇 |
专业分类
化学 | 2132篇 |
晶体学 | 9篇 |
力学 | 100篇 |
综合类 | 1篇 |
数学 | 459篇 |
物理学 | 850篇 |
出版年
2023年 | 24篇 |
2021年 | 54篇 |
2020年 | 68篇 |
2019年 | 65篇 |
2018年 | 45篇 |
2017年 | 44篇 |
2016年 | 95篇 |
2015年 | 83篇 |
2014年 | 82篇 |
2013年 | 175篇 |
2012年 | 153篇 |
2011年 | 207篇 |
2010年 | 108篇 |
2009年 | 86篇 |
2008年 | 194篇 |
2007年 | 181篇 |
2006年 | 155篇 |
2005年 | 140篇 |
2004年 | 145篇 |
2003年 | 96篇 |
2002年 | 103篇 |
2001年 | 62篇 |
2000年 | 60篇 |
1999年 | 24篇 |
1998年 | 37篇 |
1997年 | 38篇 |
1996年 | 62篇 |
1995年 | 68篇 |
1994年 | 51篇 |
1993年 | 52篇 |
1992年 | 54篇 |
1991年 | 32篇 |
1990年 | 30篇 |
1989年 | 30篇 |
1988年 | 31篇 |
1987年 | 33篇 |
1986年 | 26篇 |
1985年 | 31篇 |
1984年 | 28篇 |
1983年 | 28篇 |
1982年 | 27篇 |
1981年 | 46篇 |
1980年 | 26篇 |
1979年 | 29篇 |
1978年 | 29篇 |
1977年 | 35篇 |
1976年 | 39篇 |
1975年 | 33篇 |
1974年 | 26篇 |
1973年 | 30篇 |
排序方式: 共有3551条查询结果,搜索用时 37 毫秒
71.
72.
M. Ceulemans R. obiski W. M. R. Dirkx F. C. Adams 《Fresenius' Journal of Analytical Chemistry》1993,347(6-7):256-262
Summary A rapid, simple and sensitive method has been developed for the simultaneous determination of butyl- and phenyltin species in environmental waters. The ionic organotin compounds are ethylated in the aqueous phase using sodium tetraethylborate (NaBEt4) and extracted with hexane. A 25 l aliquot of the extract is injected at a low temperature into a Tenax filled liner. After solvent venting the analytes are transferred onto the capillary column using programmed temperature vaporization (PTV) injection. Detection is done by means of a microwave induced plasma atomic emission detector (MIP AED). The method allows the determination of butyl- and phenyltin compounds in water samples down to the level of 0.1 ng/l (as Sn) while 50 ml of sample is sufficient for analysis. The accuracy of the method was confirmed by GC-AAS after chelation and Grignard derivatization. 相似文献
73.
74.
A flow injection on-line sorption preconcentration method for the electrothermal AAS determination of platinum has been developed. The pyrrolidine dithiocarbamate complexes of either Pt4+ or Pt2+, formed in 0.7 mol L–1 HNO3, are on-line adsorbed on the inner walls of a PTFE knotted reactor and subsequently eluted with methanol. An enhancement factor of 112 and a detection limit (3 σ) of 10 ng L–1 along with a sampling frequency of 21 h–1 are achieved with a 90 s preconcentration time at a sample flow rate of 8.8 mL min–1. The relative standard deviation is 2.5% for 0.4 μg L–1 Pt. The method has been applied to the determination of platinum in blood samples. 相似文献
75.
M. Cameron Sullards Jeanette Adams 《Journal of the American Society for Mass Spectrometry》1995,6(7):608-610
The use of sector mass spectrometers to study metastable ion decompositions of peptide metal-ion complexes formed by electrospray ionization is discussed. Products that are formed by charge-separation reactions are characterized by large kinetic energy release distributions. This causes scans at a constant B/E to give incorrect product ion abundances and possibly incorrect mass assignments. Two instrumental methods exist that can be used either to detect the ions or to estimate relative ion abundances: a floated collision cell or mass-analyzed ion kinetic energy spectrometry (MIKES) scans. The floated collision cell, by virtue of an altered B/E scan law, however, discriminates against important metastable ion reactions that occur outside the cell. MIKES scans provide a clearer estimate of product ions that arise by metastable ion charge-separation reactions. Problems with pseudotandem (first field-free region) experiments are also discussed. 相似文献
76.
Reaction of CpMoMn(CO)(8) with elemental selenium and Me(3)NO in the absence of light yielded the diselenido complex CpMoMn(CO)(5)(mu-Se(2)), 2. Compound 2 contains a bridging diselenido ligand lying perpendicular to the Mo-Mn bond, Mo-Mn = 2.8421(10) A. In the presence of room light, the reaction yielded the tetranuclear metal complex Cp(2)Mo(2)Mn(2)(CO)(7)(mu(3)-Se)(4), 3 (36% yield), and 2 (7% yield). Compound 2 reacted with ethylene to yield the ethanediselenato complex CpMoMn(CO)(5)(mu-SeCH(2)CH(2)Se), 4, by insertion of ethylene into the Se-Se bond. Compound 2 also reacted with (PPh(3))(2)Pt(PhC(2)Ph) and CpCo(CO)(2) to yield the complexes CpMoMnPt(PPh(3))(2)(CO)(5)(mu(3)-Se)(2), 5, and Cp(2)CoMoMn(CO)(5)(mu(3)-Se)(2), 6, respectively, by insertion of the metal groupings CpCo and Pt(PPh(3))(2) into the Se-Se bond of 2. The oxo compound Cp(2)CoMo(O)Mn(CO)(5)(mu(3)-Se)(2), 7, was obtained from 6 by decarbonylation at molybdenum by using Me(3)NO. The molecular structures of the complexes 2-7 were established by single-crystal X-ray diffraction analyses. 相似文献
77.
The determination of beryllium and manganese in air particulate matter collected on filter material is discussed. Destruction by digestion with nitric and perchloric acids and by low-temperature ashing with dissolution of the ash in a hydrofluoric-nitric acid mixture were tested. The graphite furnace parameters were investigated for different acid solutions. Interferences of some cations and anions that are abundant in aerosol material are described. Accuracy was checked against standard samples. For manganese, the results are compared with those obtained by energy-dispersive x-ray fluorescence. 相似文献
78.
Gianfranco Denti Mauro Ghedini Jon A. McCleverty Harry Adams Neil A. Bailey 《Transition Metal Chemistry》1982,7(4):222-224
Summary Treatment of [Mo{HB(3,5-Me2C3HN2)3}(NO)I2] with one or two moles of AgPF6 in acetonitrile afforded the paramagnetic (one unpaired electron) complex [Mo{HB(3,5-Me2C3NH2)3}(NO)(NCMe)2][PF6]. The structure of this complex was determined crystallographically, and the six-coordinate geometry of the complex cation confirmed. 相似文献
79.
The reaction of Os3(CO)10(NCMe)[Si(OMe)3](-H),1, with PMe2Ph yielded the new complex Os3(CO)10(PMe2Ph)[Si(OMe)3](-H),2 by substitution of the MeCn ligand with the phosphine ligand. When heated to 125°C compound2 was decarbonylated and transformed into the new unsaturated cluster complex Os3(CO)8[-PMe2(C6H4)][Si(OMe)3](-H)2,3 in 54% yield. Compound3 was characterized by a single crystal X-ray diffraction analysis, osmium bonds. The phenyl ring of the phosphine ligand has undergoneortho-metallation by a neighboring metal atom. A terminally coordinated Si(OMe)3 ligand is coordinated to the third osmium atom. The cluster is unsaturated by the amount of 2 electrons, and there is an open coordination site on the siloxyl substituted osmium atom that is partially filled by a weak interaction with one of the -bonds of theortho-metalled phenyl ring. Complex3 reacts with CO at 1 atm to reform compound2 in 85% yield in 5 h at 40°C. Crystal Data: for3: space group = P21/n,a = 9.911(2) Å,b = 18.451(6) Å,c = 14.872(2) Å, = 95.64(2)°,Z = 4, 1994 reflections,R = 0.028. 相似文献
80.
Applications of the laser microprobe mass analyzer for characterizing the surface of chemically modified minerals (crown ether/montmorillonite and organosilane/sepiolite) and for detecting micro-crystallites at the surface of an inorganic matrix (brucite surface layer of chrysotile fibers) were investigated using laser desorption conditions. The laser microprobe is shown to be a versatile tool for these applications. 相似文献