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101.
A. V. Harms 《Accreditation and quality assurance》2009,14(5):253-261
In this paper, a new data evaluation method for proficiency test exercises consisting of a combination of a z-test, a zeta test and an uncertainty outlier test is presented. This new method is compared with eight other evaluation methods
(both measurement uncertainty using and measurement uncertainty ignoring) in common use and/or recommended by ISO 13528. The
data set used to test the evaluation methods is real data and consists of the 95Nb results of the National Physical Laboratory Environmental Radioactivity Proficiency Test Exercise 2007. The evaluation
of 14 out of 32 results were affected by the choice of method. 相似文献
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105.
Thorsten Grb Christoph Müller W. Massa Thomas Miekisch Gert Seybert Klaus Harms Kurt Dehnicke 《无机化学与普通化学杂志》2001,627(9):2191-2197
Crystal Structures of the Phosphaneimine Complexes [NaI(HNPPh3)3] and [SrI2(HNPPh3)2(THF)2], as well as of Sodium Triphenylphosphoraneiminate [NaNPPh3]6 [NaI(HNPPh3)3] ( 1 ) has been obtained as yellow, moisture sensitive crystals as an intermediate product of the synthesis of sodium triphenylphosphoraneiminate, [NaNPPh3]6 ( 2 ) from Ph3PI2 and sodium amide in liquid ammonia. Correspondingly, colourless crystals of [SrI2(HNPPh3)2(THF)2] ( 3 ) are formed from strontium amide and Ph3PI2 in liquid ammonia and subsequent recrystallisation of the primary product [SrI2(HNPPh3)4] from thf solution. The complexes 1 – 3 are mainly characterized by crystal structure determinations. 1 · 0,5 thf: space group P3c1, Z = 4, lattice dimensions at 193 K: a = b = 1533.2(1); c = 2545.6(1) pm, R = 0.0417. 1 has a molecular structure in which the sodium atom is tetrahedrally coordinated by the iodine atom with a distance of 315.9 pm and by the nitrogen atoms of the three HNPPh3 molecules with a distance of 238.9 pm. 2 · C7H8: space group P1, Z = 1, lattice dimensions at 213 K: a = 1457.1(1), b = 1484.9(1), c = 1502.7(1) pm; α = 116.32(1)°, β = 115.358(10)°, γ = 93.585(14)°; R = 0.0520. 2 has a molecular structure in which the six sodium atoms and the six nitrogen atoms of the (NPPh3–) groups form a hexagonal prism with approximate D3d symmetry. 3 · 2 thf: space group P1, Z = 2, lattice dimensions at 193 K: a = 1042.9(1), b = 1337.4(1), c = 2095.1(1) pm; α = 90.130(8)°, β = 96.310(8)°, γ = 111.985(8)°; R = 0.0310. 3 has a molecular structure in which the strontium atom is octahedrally coordinated by the iodine atoms, by the nitrogen atoms of the HNPPh3 molecules and by the oxygen atoms of the thf molecules, all ligands being in trans‐position to one another. 相似文献
106.
A convergent total synthesis of the structurally unprecedented alkaloid lodopyridone was achieved using a cross-coupling of an iodopyridone fragment with a quinolinethiazolylstannane. Key features of the syntheses of the pentasubstituted 4-pyridone were a regioselective bromination of a 4-pyridone derived from kojic acid, a subsequent Cu-mediated introduction of the thioether, and a directed lithiation/iodination step. A chemoselective Negishi cross-coupling of a dibromothiazole and a quinolinylzinc reagent was used to assemble the chloroquinolinethiazol moiety. 相似文献
107.
Dr. Lars H. Finger Jannick Guschlbauer Dr. Klaus Harms Prof. Dr. Jörg Sundermeyer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(45):16292-16303
Depending on the amount of methanol present in solution, CO2 adducts of N‐heterocyclic carbenes (NHCs) and N‐heterocyclic olefins (NHOs) have been found to be in fully reversible equilibrium with the corresponding methyl carbonate salts [EMIm][OCO2Me] and [EMMIm][OCO2Me]. The reactivity pattern of representative 1‐ethyl‐3‐methyl‐NHO–CO2 adduct 4 has been investigated and compared with the corresponding NHC–CO2 zwitterion: The protonation of 4 with HX led to the imidazolium salts [NHO–CO2H][X], which underwent decarboxylation to [EMMIm][X] in the presence of nucleophilic catalysts. NHO–CO2 zwitterion 4 can act as an efficient carboxylating agent towards CH acids such as acetonitrile. The [EMMIm] cyanoacetate and [EMMIm]2 cyanomalonate salts formed exemplify the first C?C bond‐forming carboxylation reactions with NHO‐activated CO2. The reaction of the free NHO with dimethyl carbonate selectively led to methoxycarbonylated NHO, which is a perfect precursor for the synthesis of functionalized ILs [NHO–CO2Me][X]. The first NHO‐SO2 adduct was synthesized and structurally characterized; it showed a similar reactivity pattern, which allowed the synthesis of imidazolium methyl sulfites upon reaction with methanol. 相似文献
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109.
[reaction: see text] Two key photochemical reactions of prochiral 2-pyridones were studied in the presence of a chiral host. The [4 + 4]-photocycloaddition with cyclopentadiene (CpH) proceeded smoothly and with high enantioselectivity (84-87% ee). The absolute configuration of the endo-diastereoisomer was established by X-ray crystallography. The electrocyclic [4pi]-ring closure to 3-oxo-2-azabicyclo[2.2.0]-5-hexenes occurred with lower enantioselectivity (20-23% ee at -20 degrees C). The velocity of the latter reaction slowed significantly with decreasing temperature. 相似文献
110.
Qian Zhang Corinna Harms Jens Mitzel Pawel Gazdzicki K. Andreas Friedrich 《Current Opinion in Electrochemistry》2022
The durability of polymer electrolyte membrane fuel cells (PEMFCs) needs to be further improved to cope with application requirements and economic competitiveness. This article highlights the challenges in the reliable determination of degradation rates and lifetime. The reliable evaluation of performance degradation rates is fundamental to quantify and benchmark durability and to allow comparisons between PEMFC durability tests performed using different materials or in different laboratories. The use of efficient recovery procedures enables the discrimination of reversible and irreversible voltage losses and facilitates the understanding of recovery mechanisms. In the end, recent contributions about lifetime diagnoses and prediction are presented, which are promising to be implemented in PEMFC applications. 相似文献