全文获取类型
收费全文 | 2486篇 |
免费 | 84篇 |
国内免费 | 9篇 |
专业分类
化学 | 2056篇 |
晶体学 | 13篇 |
力学 | 26篇 |
数学 | 226篇 |
物理学 | 258篇 |
出版年
2023年 | 24篇 |
2022年 | 48篇 |
2021年 | 71篇 |
2020年 | 51篇 |
2019年 | 60篇 |
2018年 | 42篇 |
2017年 | 39篇 |
2016年 | 82篇 |
2015年 | 87篇 |
2014年 | 86篇 |
2013年 | 119篇 |
2012年 | 157篇 |
2011年 | 207篇 |
2010年 | 125篇 |
2009年 | 111篇 |
2008年 | 157篇 |
2007年 | 157篇 |
2006年 | 120篇 |
2005年 | 124篇 |
2004年 | 103篇 |
2003年 | 93篇 |
2002年 | 75篇 |
2001年 | 39篇 |
2000年 | 23篇 |
1999年 | 36篇 |
1998年 | 22篇 |
1997年 | 17篇 |
1996年 | 27篇 |
1995年 | 27篇 |
1994年 | 24篇 |
1993年 | 15篇 |
1992年 | 14篇 |
1991年 | 16篇 |
1990年 | 21篇 |
1989年 | 19篇 |
1988年 | 10篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 15篇 |
1984年 | 11篇 |
1983年 | 5篇 |
1982年 | 14篇 |
1980年 | 10篇 |
1979年 | 12篇 |
1978年 | 11篇 |
1976年 | 5篇 |
1975年 | 7篇 |
1974年 | 4篇 |
1970年 | 3篇 |
1879年 | 3篇 |
排序方式: 共有2579条查询结果,搜索用时 0 毫秒
11.
Benchmarking of ruthenium initiators for the ROMP of a norbornenedicarboxylic acid ester 总被引:1,自引:0,他引:1
Sandra Demel Wolfgang Schoefberger Christian Slugovc Franz Stelzer 《Journal of molecular catalysis. A, Chemical》2003,200(1-2):11-19
The kinetic study of ring-opening metathesis polymerization (ROMP) of a diester functionalised norbornene derivative, (±)-exo,endo-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid diethyl ester, with a series of ruthenium benzylidene complexes revealed the applicability of these initiators for well defined polymerization reactions. Values for the rate of initiation as well as the rate of propagation of the initiators were determined and correlated to the molecular weight and polydispersity of the isolated polymers. As the only initiator providing an entry to virtually monodisperse polymers the classical “first generation Grubbs-catalyst” was identified, while N-heterocyclic carbene based initiators polymerized with a rate of propagation much higher than the rate of initiation yielding polymers with a broader molecular weight distribution. 相似文献
12.
Capillary electrochromatography (CEC) has been utilized to analyze free fatty acids (FFAs) and fatty acid phenacyl esters (FAPEs) originating from vegetable oils and margarine. The analyses were performed on capillaries 25 and 40 cm long, 100 microm ID, and packed with 3 microm Hypersil ODS. Isocratic elution was achieved with the mobile phase acetonitrile/50 mM 2-(N-morpholino)ethane sulfonic acid (MES), pH 6, at a ratio of 9:1. For quantitative analysis, the formation of FAPE derivatives is preferred. Moreover, the number of double bonds in the FAPEs can be elucidated by measuring the UV absorbance ratio of 240:210 nm. For the determination of the oleate/elaidate ratio in margarines, the FFAs are analyzed because of overlap of elaidate/palmitate in FAPE analysis. Data obtained with CEC and micro liquid chromatography (LC) were compared and CEC was found to be far superior in terms of efficiency and speed of analysis. Important selectivity differences were noted between micro LC on highly endcapped ODS and CEC on the silanol-rich Hypersil ODS. 相似文献
13.
Sandra Ristori Grard Gebel Giacomo Martini 《Colloids and surfaces. A, Physicochemical and engineering aspects》1993,80(2-3):113-120
The aggregation properties of ammonium perfluorooctanoate (NH4-PFO) in concentrated aqueous phases have been investigated by magnetic resonance techniques and have been compared with the aggregation properties in dilute solutions. Magnetic resonance methods indicated that NH4-PFO—water systems with surfactant concentrations below 45% (w/w) behaved as isotropic purely micellar solutions in the temperature range 285–340 K. For higher concentrations the system exhibited a rather complex structure, having both isotropic and anisotropic components. The nematic nature of the anisotropic fraction was demonstrated by 19F NMR studies. The 19F NMR and EPR of nitroxides (TempTMA+, 5- and 16-DXSA) inserted as paramagnetic probes into the concentrated NH4-PFO—water systems allowed us to establish that the lamellar phase could be mechanically oriented between quartz slides. The EPR investigation also gave details concerning the dynamics of both the oriented and non-oriented structures. 相似文献
14.
W. Lautsch W. Broser W. Bandel W. Biedermann W. Gehrmann E. Schröder H. Gnichtel I. Zehmisch G. Kurth R. Krüger H. J. Kraege 《Colloid and polymer science》1954,138(3):129-142
Ohne Zusammenfassung
Die Arbeit wurde aus Mitteln des Marshall-Planes (ERP-Mittel) und mit Spenden aus dem „Fonds Chemie“ ausgeführt. Wir sprechen
den zust?ndigen Stellen für die Gew?hrung der Beihilfe unseren verbindlichsten Dank aus. Der Deutschen Forschungsgemeinschaft
danken wir für die überlassung einer Ultrazentrifuge, den Behring-Werken für die uns zur Verfügung gestellten Serumalbumin-
und -globulin-Pr?parate. 相似文献
15.
Rosenthal SJ Tomlinson I Adkins EM Schroeter S Adams S Swafford L McBride J Wang Y DeFelice LJ Blakely RD 《Journal of the American Chemical Society》2002,124(17):4586-4594
To explore the potential for use of ligand-conjugated nanocrystals to target cell surface receptors, ion channels, and transporters, we explored the ability of serotonin-labeled CdSe nanocrystals (SNACs) to interact with antidepressant-sensitive, human and Drosophila serotonin transporters (hSERT, dSERT) expressed in HeLa and HEK-293 cells. Unlike unconjugated nanocrystals, SNACs were found to dose-dependently inhibit transport of radiolabeled serotonin by hSERT and dSERT, with an estimated half-maximal activity (EC(50)) of 33 (dSERT) and 99 microM (hSERT). When serotonin was conjugated to the nanocrystal through a linker arm (LSNACs), the EC(50) for hSERT was determined to be 115 microM. Electrophysiology measurements indicated that LSNACs did not elicit currents from the serotonin-3 (5HT(3)) receptor but did produce currents when exposed to the transporter, which are similar to those elicited by antagonists. Moreover, fluorescent LSNACs were found to label SERT-transfected cells but did not label either nontransfected cells or transfected cells coincubated with the high-affinity SERT antagonist paroxetine. These findings support further consideration of ligand-conjugated nanocrystals as versatile probes of membrane proteins in living cells. 相似文献
16.
Martinez-López S Morales-Noé A Pastor-Garcia A Morales-Rubio A de la Guardia M 《Journal of AOAC International》2005,88(4):1247-1254
The determination of 15 polycyclic aromatic hydrocarbons (PAHs) in olive oil samples has been improved in order to obtain a fast methodology with a low limit of detection through the combination of liquid-liquid extraction with acetonitrile and preparative gel permeation chromatography (GPC) prior to the injection of purified extracts into a C18 column. Acetonitrile-water was used as the mobile phase with a gradient from 50 to 95%, w/w, acetonitrile in 30 min. The oven temperature was maintained at 15 degrees C, and fluorometric detection was made at a fixed excitation wavelength of 264 nm and variable, optimal emission wavelength for each analyte ranging from 352 nm for 11-H-benzo(b)fluorene to 500 nm for indeno(1,2,3-cd)pyrene. Recovery for all the compounds studied varied from 75 to 111%, and limit of detection values from 0.05 ng/g for benzo(k)fluoranthene to 0.48 ng/g for indeno(1,2,3-cd)pyrene, corresponding to 0.09 ng/g benzo(a)pyrene. Results were compared with those obtained by liquid-liquid extraction followed by a cleanup on silica and a direct GPC treatment of oil samples diluted in dichloromethane, 2 other methodologies that are appropriate for quantifying PAHs in olive oils. However, the proposed method improves the determination limits, reduces the time of analysis, and provides a highly stable baseline for sample chromatograms. 相似文献
17.
Magnani A Marchettini N Ristori S Rossi C Rossi F Rustici M Spalla O Tiezzi E 《Journal of the American Chemical Society》2004,126(37):11406-11407
The present work deals with the spatially extended oscillatory Belousov Zhabotinsky reaction-diffusion system carried out in an anisotropic environment of phosphatidylcholines/water binary system, which presents layered aqueous domains separated by lipid bilayers. We report the occurrence of stable Turing patterns, spiral waves, and other exotic structures in phospholipids bilayers that are generally used as a models for cell plasma membranes. 相似文献
18.
Sample evaporation in splitless injection of large volumes is rapid: depending on the experiment, results indicate that 200 μl of hexane, for instance, evaporates in 2–10 s, producing vapor at a rate of many hundreds of milliliters per minute. A 60 × 4 mm packed bed of 20–35 mesh Tenax TA enabled injection of 200 μl volumes of all solvents tested, and even 1 ml injections were possible provided they were performed over a period of 30 s. Retention of volatile sample components depends on the sample solvent, the injection volume, and the injection speed, but only little on the injector temperature. Losses of n-tridecane varied from hardly 15 % (when dissolved in pentane) to ca 60 % (ethyl acetate); losses of n-heptadecane were usually below 20 %. The column temperature during injection should be at least ca 20–30°C above the standard solvent boiling point. 相似文献
19.
De Vriendt K Sandra K Desmet T Nerinckx W Van Beeumen J Devreese B 《Rapid communications in mass spectrometry : RCM》2004,18(24):3061-3067
The use of electrospray ionization mass spectrometry (ESI-MS) for studying non-covalent interactions between macromolecules and ligands is well established. ESI-MS can be a useful tool for the determination of dissociation constants between molecules in the gas phase. We validate this method by studying the binding of the catalytic domain of cellobiohydrolase I (CBH I) from Trichoderma reesei to the disaccharide inhibitor cellobiose. The method was further applied to study two newly synthesized cellobiose derivatives (m-iodobenzyl 2-deoxy-2-azido-beta-cellobioside and p-benzyloxybenzyl beta-cellobioside). In a titration experiment, peak areas of different charge states of the free enzyme and the complex were summed in order to determine the dissociation constant. For cellobiose and m-iodobenzyl 2-deoxy-2-azido-beta-cellobioside, the calculated values are in good agreement with those reported from either displacement titration or equilibrium binding experiments in solution. Due to non-specific binding, the dissociation constant of p-benzyloxybenzyl beta-cellobioside does not correspond with the solution-based value. Our results indicate the need for careful interpretation of data sets when using nanoESI to study non-covalent interactions. 相似文献
20.
Most of the common classes of organic compounds chromatograph normally on Superoxes. There is no tailing or adverse effect from excessively different activity different activity coefficients. Superoxes are therefore universal phases for gas chromatography. This is also expressed by a wide useful temperature range from ~50° to ~300°. High MW Superox-4 has a MAOT about 20° higher than the lower MW Superox-0.1. Several applications illustrating the versatility of Superox phases in (GC)2 are presented. 相似文献