全文获取类型
收费全文 | 71845篇 |
免费 | 2382篇 |
国内免费 | 61篇 |
专业分类
化学 | 44600篇 |
晶体学 | 516篇 |
力学 | 1307篇 |
综合类 | 1篇 |
数学 | 12896篇 |
物理学 | 14968篇 |
出版年
2023年 | 496篇 |
2022年 | 433篇 |
2021年 | 772篇 |
2020年 | 1034篇 |
2019年 | 1010篇 |
2018年 | 1475篇 |
2017年 | 1314篇 |
2016年 | 2531篇 |
2015年 | 2089篇 |
2014年 | 2097篇 |
2013年 | 4589篇 |
2012年 | 4538篇 |
2011年 | 4517篇 |
2010年 | 2923篇 |
2009年 | 2442篇 |
2008年 | 3975篇 |
2007年 | 3768篇 |
2006年 | 3371篇 |
2005年 | 3206篇 |
2004年 | 2734篇 |
2003年 | 2170篇 |
2002年 | 1924篇 |
2001年 | 1461篇 |
2000年 | 1409篇 |
1999年 | 1005篇 |
1998年 | 770篇 |
1997年 | 649篇 |
1996年 | 887篇 |
1995年 | 634篇 |
1994年 | 706篇 |
1993年 | 690篇 |
1992年 | 683篇 |
1991年 | 556篇 |
1990年 | 591篇 |
1989年 | 496篇 |
1988年 | 471篇 |
1987年 | 446篇 |
1986年 | 431篇 |
1985年 | 597篇 |
1984年 | 566篇 |
1983年 | 449篇 |
1982年 | 433篇 |
1981年 | 438篇 |
1980年 | 365篇 |
1979年 | 372篇 |
1978年 | 377篇 |
1977年 | 361篇 |
1976年 | 373篇 |
1974年 | 329篇 |
1973年 | 347篇 |
排序方式: 共有10000条查询结果,搜索用时 781 毫秒
991.
King RC Gundersdorf R Fernández-Metzler CL 《Rapid communications in mass spectrometry : RCM》2003,17(21):2413-2422
A hybrid linear ion trap/triple quadrupole mass spectrometer was used to demonstrate the value of collecting full scan qualitative data during quantitative analysis of target compounds. We present examples of the additional information that can be obtained from plasma samples analyzed primarily for target compound concentrations. This information includes detection of circulating metabolites, dosing vehicle, interfering matrix components, and potential interfering drug conjugates. Additionally, the quantitative results from selected reaction monitoring (SRM) analysis and from combined full scan and SRM analysis (SRM/EMS) were compared. The quantitative data in both scan modes are acceptable in terms of sensitivity, accuracy and precision. One can conclude from this work that the hybrid linear ion trap/triple quadrupole mass analyzer can provide in a single analysis both useful qualitative data, and accurate and precise quantitative data from the samples routinely prepared and analyzed for target drug concentrations. 相似文献
992.
M. Harangozó V. Frank J. Tölgyessy M. Ondráček 《Journal of Radioanalytical and Nuclear Chemistry》1994,182(1):57-62
Radionuclide X-ray fluorescence method with a Si/Li semiconductor detector and238Pn exciting source was used in the study of Mn, Fe, Cu, Zn, and Pb content of solid emissions, raw and final materials of a brick factory. From the point of view of metal content, the working environment of the brick factory is safe for workers. 相似文献
993.
Summary A method is reported for the determination of dibutyltin (DBT), diphenyltin (DPhT), tributyltin (TBT), and triphenyltin (TPhT)
species at the nanogram per litre concentration level in natural water samples. Analytes were isolated from samples by solid-phase
extraction and analysed both off-line and on-line by reversed-phase high-performance liquid chromatography with post-column
derivatization and fluorimetric detection. Several SPE cartridges and eluents were evaluated; C18 enrichment and elution with a mixture of methanol, acetic acid, and water was found most suitable. Preconcentration factors
up to 250 can be achieved when a 500-mL sample is processed. Detection limits, recovery rates, and the precision of the whole
process have been determined. The method has been applied to the determination of organotin species in spiked natural water
samples collected on the NW Mediterranean coast. Recovery rates range from 75 to 110% and detection limits are at the low
ng L−1 level (1–3 ng Sn L−1 for DPhT, DBT, and PhT and 40 ng Sn L−1 for TBT when 250 mL spiked sea water is processed.) 相似文献
994.
Summary The ordering behavior of quenched Cu-12 at% Mn was investigated by differential scanning calorimetry (DSC) under increasing temperature conditions. The ordering process can be better explained in terms of a homogeneous short-range-order (SRO) rather than a disperse-short-range-order (DSRO) model as for concentrated Cu-γMn solid solutions. At the employed high quench rates ordering is established in one stage here termed stage 1, assisted by excess vacancies. This stage obeys a first order kinetics law, being the effective activation energy consistent with a weighed average sum of the activation energy for migration of free and bound vacancies. An estimated solute-vacancy binding energy of 15 kJ mol-1 seems quite reasonable for this alloy together with the assessed activation energy for complex migration of 92.6 kJ mol-1. By adopting a first SRO order parameter based in quasi-chemical theory in pair approximation and using boundary values calculated from displayed features of DSC traces, the retained degree of quenched-in order at room temperature was calculated. This procedure also enabled to estimate an ordering energy of -2.7 kJ mol-1. The effect of quenching temperature demonstrate that for smaller vacancy sink densities, the retained degree of order at room temperature goes through a minimum. 相似文献
995.
Borasio M Rodríguez de la Fuente O Rupprechter G Freund HJ 《The journal of physical chemistry. B》2005,109(38):17791-17794
Methanol decomposition and oxidation on Pd(111) at millibar pressure were studied by in situ polarization-modulation infrared reflection absorption spectroscopy (PM-IRAS), on-line gas chromatography and pre- and postreaction X-ray photoelectron spectroscopy (XPS). Various dehydrogenation products such as methoxy CH3O, formaldehyde CH2O, formyl CHO, and CO could be spectroscopically identified. Methanol oxidation proceeds via dehydrogenation to formaldehyde CH2O, which either desorbs or is further dehydrogenated to CO, which is subsequently oxidized to CO2. Carbonaceous overlayers that are present during the reaction may favorably affect the selectivity toward CH2O. The reaction takes place on metallic Pd, and no indications of an involvement of Pd surface oxide were observed. 相似文献
996.
Bond AD García F Jantos K Lawson GT McPartlin M Wright DS 《Chemical communications (Cambridge, England)》2002,(12):1276-1277
The novel, deca-lithium cage [(mtaNHLi)(As2(Nmta)5)-Li(4).2thf]2 (1) (mtaN = 5-methylthiazolyl, C4H4N2S) contains an imido-bridged tetraanion [(mtaN)2As(mu-Nmta)-As(Nmta)2]4-, which represents a new type of multi-functional imido group 15 ligand framework (homologous with group 15 anions of the type [As(NR)3]3-). 相似文献
997.
The kinetics of the reaction of manganese(III) with oxalic acid (OA) has been studied in H2SO4 solutions. Under the experimental conditions of 6 × 10–3 <>0 < 0.4=" mol=">–3 and [H2SO4]0 0.2 mol dm–3 the observed pseudo-first order rate constant k
obs follows the expression
相似文献
998.
M. Blanco J. Coello H. Iturriaga S. Maspoch E. Bertrán 《Fresenius' Journal of Analytical Chemistry》1991,340(7):410-414
Summary A procedure for the simultaneous spectrophotometric determination of organic additives and the quantitation of Ni(II) in Zn-Ni electrolytic baths is described. Organic additives were determined by resolving the mixed spectrum over the wavelength range 278–330 nm by applying a least-squares fitting computational program to the standard spectrum of each component. Spectra were recorded on a hydroalcoholic medium (15% methanol) containing 0.1 mol/l NH4Cl. The Ni(II) concentration was determined by applying the program to the first-derivative spectrum over the wavelength range 660–820 nm. 相似文献
999.
Summary New cyanato-copper(II) complexes with aminopyridines (ampy) were prepared and studied;viz. Cu(NCO)2(3-ampy)2 (- and -form), Cu(NCO)2(3-ampy)2(H2O), Cu(NCO)2(4ampy)2, and Cu(NCO)2(2-ampy). According to physical results, the Cu(NCO)2L2 complexes exhibitpseudo-octahedral structures with amine nitrogens or cyanate oxygens occupying axial sites. For - and -Cu(NCO)2(3-ampy)2 the crystal structure reorganization is connected with a change in axial distortion. The compound Cu(NCO)2(2-ampy) is square pyramidal or — more probably — rhombic octahedral and its strong antiferromagnetism reveals the N-bridging function of the NCO groups.Part XXII, Ref. 9. 相似文献
1000.
Summary Two new analytical techniques are described. The so-called injection technique operates on evaluating a dynamic concentration signal as a result of following the concentration change in a certain part of a flow-through channel after injecting a sample or reagent at a small volume into the current of an appropriate solution flowing at a constant rate.The second technique, the programmed coulometric titration technique, also uses the flow-through channel principle; that means this novel technique allows the more precise titrimetric way of analysis in flowing solutions. In the case of both techniques potentiometric and voltammetric detectors were involved. Several examples proved the multifold advantages of these techniques for environmental analysis.
Neue elektroanalytische Verfahren für die Umweltanalyse Zusammenfassung Zwei neue Methoden werden beschrieben. Die sog. Injektionstechnik wertet ein dynamisches Konzentrationssignal aus, das sich aus der Änderung in einem Durchflußkanal ergibt, wenn Probe oder Reagens in kleinen Volumina in einen konstant fließenden Flüssigstrom injiziert werden. Das zweite Verfahren, die programmierte coulometrische Titration, erlaubt die Anwendung der genaueren titrimetrischen Technik auf fließende Lösungen. Bei beiden Methoden werden potentiometrische und voltammetrische Detektoren verwendet. Mehrere Beispiele zeigen die vielfachen Vorteile dieser Verfahren bei der Anwendung auf die Analyse von Umweltmaterial. Presented at the 6th Annual Symposium on Recent Advances in the Analytical Chemistry of Pollutants, April 21–23, 1976; Vienna, Austria 相似文献 |