全文获取类型
收费全文 | 2803篇 |
免费 | 84篇 |
国内免费 | 9篇 |
专业分类
化学 | 1970篇 |
晶体学 | 30篇 |
力学 | 52篇 |
数学 | 402篇 |
物理学 | 442篇 |
出版年
2023年 | 13篇 |
2022年 | 32篇 |
2021年 | 31篇 |
2020年 | 46篇 |
2019年 | 48篇 |
2018年 | 24篇 |
2017年 | 32篇 |
2016年 | 66篇 |
2015年 | 57篇 |
2014年 | 67篇 |
2013年 | 113篇 |
2012年 | 164篇 |
2011年 | 159篇 |
2010年 | 98篇 |
2009年 | 77篇 |
2008年 | 113篇 |
2007年 | 142篇 |
2006年 | 161篇 |
2005年 | 155篇 |
2004年 | 128篇 |
2003年 | 110篇 |
2002年 | 110篇 |
2001年 | 43篇 |
2000年 | 16篇 |
1998年 | 28篇 |
1997年 | 36篇 |
1996年 | 35篇 |
1995年 | 24篇 |
1994年 | 29篇 |
1993年 | 38篇 |
1992年 | 35篇 |
1991年 | 25篇 |
1990年 | 25篇 |
1989年 | 33篇 |
1988年 | 25篇 |
1987年 | 18篇 |
1986年 | 27篇 |
1985年 | 50篇 |
1984年 | 22篇 |
1983年 | 22篇 |
1982年 | 38篇 |
1981年 | 43篇 |
1980年 | 37篇 |
1979年 | 41篇 |
1978年 | 49篇 |
1977年 | 25篇 |
1976年 | 46篇 |
1975年 | 28篇 |
1974年 | 20篇 |
1973年 | 24篇 |
排序方式: 共有2896条查询结果,搜索用时 15 毫秒
961.
Dan Li Anthony D. Rands Scott C. Losee Brian C. Holt John R. Williams Stephen A. Lammert Richard A. Robison H. Dennis Tolley Milton L. Lee 《Analytica chimica acta》2013
An automated sample preparation system was developed and tested for the rapid detection of Bacillus anthracis endospores by gas chromatography–mass spectrometry (GC–MS) for eventual use in the field. This reactor is capable of automatically processing suspected bio-threat agents to release and derivatize unique chemical biomarkers by thermochemolysis (TCM). The system automatically controls the movement of sample vials from one position to another, crimping of septum caps onto the vials, precise delivery of reagents, and TCM reaction times and temperatures. The specific operations of introduction of sample vials, solid phase microextraction (SPME) sampling, injection into the GC–MS system, and ejection of used vials from the system were performed manually in this study, although they can be integrated into the automated system. Manual SPME sampling is performed by following visual and audible signal prompts for inserting the fiber into and retracting it from the sampling port. A rotating carousel design allows for simultaneous sample collection, reaction, biomarker extraction and analysis of sequential samples. Dipicolinic acid methyl ester (DPAME), 3-methyl-2-butenoic acid methyl ester (a fragment of anthrose) and two methylated sugars were used to compare the performance of the autoreactor with manual TCM. Statistical algorithms were used to construct reliable bacterial endospore signatures, and 24 out of 25 (96%) endospore-forming Bacillus species were correctly identified in a statistically designed test. 相似文献
962.
L. M. Dennis 《Fresenius' Journal of Analytical Chemistry》1899,38(2):103-104
Ohne Zusammenfassung 相似文献
963.
964.
Ohne Zusammenfassung 相似文献
965.
Newcomb K. Chaney L. Compagno W. Judson Marsh J. G. Fairchild L. Bertiaux G. W. Morden B. P. Richardson A. K. Balls C. C. McDonell W. H. Ross W. S. Hendrikson Le Roy W. McCay L. M. Dennis B. J. Lemon P. A. von der Meulen Easton O. L. Shinn Ch. A. Peters 《Analytical and bioanalytical chemistry》1917,56(6-7):317-318
966.
Dr. Michiel Langerman Micha van Dorth Dr. Dennis G. H. Hetterscheid 《欧洲无机化学杂志》2023,26(24):e202300218
The pyridylalkylamine copper complex [Cu(tmpa)(L)]2+ has previously been proposed to reduce dioxygen via a dinuclear resting state, based on experiments in organic aprotic solvents using chemical reductants. Conversely, a mononuclear reaction mechanism was observed under electrochemical conditions in a neutral aqueous solution. We have investigated the electrochemical oxygen and hydrogen peroxide reduction reaction catalyzed by [Cu(tmpa)(L)]2+ in acetonitrile, using several different acids over a range of pKa. We demonstrate that strong acids lead to the loss of redox reversibility and to the destabilization of the copper complex under non-catalytic conditions. Under milder conditions, the electrochemical oxygen reduction reaction (ORR) was shown to proceed via a mononuclear catalytic intermediate, similar to what we have previously observed in water. However, in acetonitrile the catalytic rate constants of the ORR are dramatically lower by a factor 105, which is caused by the unfavorable equilibrium of formation of [CuII(O2⋅−)(tmpa)]+ in acetonitrile. This results in higher catalytic rates for the reduction of hydrogen peroxide than for the ORR. 相似文献
967.
A new distyryl boron dipyrromethene (BODIPY) with two bis(1,2,3‐triazole)amino substituents has been prepared by typical Knoevenagel condensation followed by click reaction. The compound selectively binds to Cu2+ and Hg2+ ions in CH3CN/H2O (1:1 v/v) to give remarkably blueshifted electronic absorption and fluorescence bands as a result of inhibition of the intramolecular charge‐transfer process upon binding to these metal ions. The color changes can be easily seen by the naked eye. The binding stoichiometry between this probe and Cu2+ ions has been determined to be 1:2 by a Job plot of the fluorescence data with a binding constant of ((6.2±0.6)×109) M ?2. The corresponding value for Hg2+ ions is about sixfold smaller. 相似文献
968.
Heitmann D Pape T Hepp A Mück-Lichtenfeld C Grimme S Hahn FE 《Journal of the American Chemical Society》2011,133(29):11118-11120
Reaction of the N,N'-diisobutyl-substituted benzannulated N-heterocyclic plumbylene (NHPb) 1 with [Pd(PPh(3))(4)] and [Pt(PPh(3))(4)] gave the complexes [M(NHPb)(PPh(3))(3)] (M = Pd [2], Pt [3]). X-ray diffraction studies of both complexes showed an angle of ~125° between the plumbylene plane and the transition-metal-Pb axis, indicating coordination of the transition metal to the empty π orbital of the plumbylene Pb atom. The experimentally determined metric parameters of complexes [2] and [3] are discussed on the basis of DFT calculations. 相似文献
969.
Even though quantum mechanical tunnelling has been appearing recurrently mostly in theoretical studies that emphasize its decisive role for many chemical reactions, it still appears suspicious to most organic chemists. Recent experiments in combination with powerful computational approaches, however, have demonstrated that tunnelling must be included to fully understand chemical reactivity. Here we provide an overview of the importance of tunnelling in organic chemical reactions. 相似文献
970.
Everson Kandare Baljinder K. Kandola Dennis Price Shonali Nazaré Richard A. Horrocks 《Polymer Degradation and Stability》2008,93(11):1996-2006
The thermal degradation behaviours of flame-retarded unsaturated polyester resin formulations containing ammonium polyphosphate (APP), Cloisite 25A nanoclay and zinc based smoke suppressants have been studied using thermogravimetric analysis (TGA) combined with infrared analysis of the evolved gases (EGA) and pyrolysis/gas chromatography-mass spectrometry (GC/MS). In TGA-EGA experiments, the mass loss as a function of temperature has been correlated with the evolution of carbon monoxide (CO) and carbon dioxide (CO2) and oxygen (O2) consumption as measured by an oxygen analyser. The effect of APP, Cloisite 25A and the smoke suppressants on the evolution of CO and CO2 has been examined. The decomposition behaviour of flame-retarded polyester resins under isothermal pyrolytic conditions was investigated and the evolved gaseous products were collected and qualitatively and semi-quantitatively analysed via GC/MS. The addition of APP does not yield many new gaseous products relative to the unmodified polyester resin neither does the presence of zinc borate (ZB) and zinc stannate (ZS) together with APP. Possible chemical interactions are discussed in an attempt to explain the observed results. 相似文献