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The shell phase forms when certain picolinates are subjected to energy input (via sonication or vortexing) while exposed to a water/toluene mixture. A shell, about 600 A thick and containing the picolinate and (very likely) toluene, surround the water droplets that are always produced during the mixing process. Solubility in either phase appears to be deleterious to shell formation. The shells, stable for months, are not easily distorted but can be punctured, even skewered, with a syringe needle without destroying the sphere, yet there is enough mobility among the molecules to repair the physical damage after the needle is removed. This, plus the absence of evidence for crystallinity, suggests a solid or semisolid film forms when picolinates, with the aid of an aromatic solvent, are provided the energy to rearrange themselves on water droplet surfaces. Structure-activity comparisons among the 10 compounds studied indicate that chain-chain association and intermolecular hydrogen bonding are dominant forces in a side-by-side self-assembly of the molecules within the shells. 相似文献
3.
Karlberg M Stjerndahl M Lundberg D Piculell L 《Langmuir : the ACS journal of surfaces and colloids》2005,21(21):9756-9763
Mixtures of hydrophobically modified hydroxyethyl cellulose (HMHEC) and alkali-sensitive cleavable betaine ester surfactants have been studied by viscometry, 1H NMR, absorbance measurements, and birefringence determinations. Before the hydrolysis, the surfactants behaved as conventional nondegradable surfactants in terms of the effect on the viscosity of increasing surfactant concentration. As the surfactants were hydrolyzed, systems with time-dependent viscosity were obtained. The viscosity either decreased monotonically or went through a maximum as a function of time, depending on the initial surfactant concentration. Different surfactant chain lengths gave rise to different viscosity profiles. The rate of hydrolysis, and thus the time-dependency of the surfactant concentration, could be controlled by changing the pH of the solution. 相似文献
4.
T. L. Dawson R. D. Lundberg F. J. Welch 《Journal of polymer science. Part A, Polymer chemistry》1969,7(1):173-181
Trialkylboron–oxygen, an active, low-temperature free-radical initiator, has been employed to investigate the effects of very low temperatures on the copolymerizations of vinyl acetate with cis and trans-1,2-dichloroethylenes. The low temperatures favor the propagation rate relative to the transfer rate, such that high molecular weight copolymers containing substantial quantities of 1,2-dichloroethylene can be prepared. The molecular weights of the copolymers depend only on the amounts of 1,2-dichloroethylene in the copolymers, regardless of the isomer which takes part in the copolymerization. Since the double bond of the trans isomer is about six times as reactive as that of the cis isomer, this indicates that the dominating chain transfer reaction occurs by chlorine atom elimination subsequent to the addition of the dichloroethylene unit to the growing free radical chain. It is suggested that a similar chain-transfer mechanism occurs in the polymerization of vinyl chloride, wherein an infrequent head-to-head placement of monomer unit is followed by ejection of a chlorine atom to form an olefinic bond and termination of that growing chain. The presence of the 1,2-dichloroethylene unit in the copolymer increases the glass transition temperature approximately 1°C per weight per cent copolymerized with the vinyl acetate. 相似文献
5.
Information on the accuracy of DFT functionals for redox reactions in transition metal systems is rather limited. To analyze the performance of some popular functionals for redox reactions in manganese systems, calculated O--H bond dissociation enthalpies for Mn-ligands in six different complexes are compared to experimental results. In this benchmark, B3LYP performs well with a mean absolute error of 3.0 kcal/mol. B98 gives similar results to B3LYP (error of 3.8 kcal/mol). B3LYP* gives lower O--H bond strengths than B3LYP and has a mean error of 5.0 kcal/mol. Compared to B98 and B3LYP, B3LYP* has an error trend for the manganese ligands that is more similar to the error for a free water molecule. The nonhybrid functional BLYP consistently and significantly underestimates the O--H bond strengths by approximately 20 kcal/mol. HCTH407 has a rather large mean error of 9.4 kcal/mol and shows no consistent trend. The results support the use of hybrid functionals and the present computational method for large model systems containing manganese. An example is the oxygen evolving complex in photosystem II where hybrid functionals predict the appearance of a Mn(IV)-oxyl radical before the O--O bond formation step. 相似文献
6.
N. G. Thame R. D. Lundberg J. P. Kennedy 《Journal of polymer science. Part A, Polymer chemistry》1972,10(9):2507-2525
Cationically polymerizable olefins can be efficiently grafted onto poly(vinyl chloride) in the presence of alkylaluminum compounds. The substitution of labile chlorines in PVC by various branches yields a product of improved thermal stability as compared with unmodified PVC. Thus the grafting of a few per cent of polyisobutylene or poly-butadiene onto PVC gives graft copolymers superior in thermal stability to the PVC backbone, as determined by thermogravimetric and differential thermal analyses as well as color development of molded films. At advanced stages of thermal degradation the thermal stability of poly(vinyl chloride)-g-isobutylene) (PVC-g-PIB is some 40°C superior to the unmodified PVC. In addition to grafting of polymer chains onto the PVC backbone, other methods are also available to achieve improved thermal stability. In pentane suspension, alkylaluminum compounds efficiently alkylate labile chlorines in PVC, and the product exhibits improved thermal stability. Alternatively, PVC carbonium ions can alkylate aromatic compounds, and these products also exhibit high heat stability. Based on the assumption that certain alkylaluminums quantitatively react with labile chlorines in PVC, it was estimated that 2–3% of the chlorines present in suspension-grade PVC are labile. 相似文献
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8.
Daniel Roca‐Sanjuán Marcus Lundberg David A. Mazziotti Roland Lindh 《Journal of computational chemistry》2012,33(26):2124-2126
In the preceding paper results are presented, which are in serious conflict with state‐of‐the‐art ab initio method. Based on these new results the authors propose a new explanation of the reason for the preferential production of a phosphorescent state. Here we show that these controversial results are flawed, since the model use exclude biradical electron structures. © 2012 Wiley Periodicals, Inc. 相似文献
9.
Harry J. Whitlow Margaretha Andersson Mikael Hult Leif Persson Mohamed El Bouanani Mikael Östling Carina Zaring Nils Lundberg David D. Cohen Nick Dytlewski Peter N. Johnston Ian F. Bubb Scott R. Walker Erik Johanson Sture Hogmark P. Anders Ingemarsson 《Mikrochimica acta》1995,120(1-4):171-181
Recoil Spectrometry covers a group of techniques that are very similar to the well known Rutherford backscattering Spectrometry technique, but with the important difference that one measures the recoiling target atom rather than the projectile ion. This makes it possible to determine both the identity of the recoil and its depth of origin from its energy and velocity, using a suitable detector system. The incident ion is typically high-energy (30–100MeV)35C1,81Br or127I. Low concentrations of light elements such as C, O and N can be profiled in a heavy matrix such as Fe or GaAs. Here we present an overview of mass and energy dispersive recoil Spectrometry and illustrate its successful use in some typical applications. 相似文献
10.
Lars Lundberg 《BIT Numerical Mathematics》1993,33(2):190-213
In multiprocessors with static allocation of processes to processors, scheduling can be done locally for each processor. The scheduling strategy may have dramatic effect on the execution time of a parallel program. It is an NP-hard problem to find an optimal schedule, and very little is known of how close the heuristic solutions get.The major result here is a theorem stating that if certain program parameters, which can be obtained from an execution of the program on a single-processor, are known, the execution time of the optimal schedule can be calculated within a factor equal to the largest number of border processes on one processor. Border processes are processes which communicate with other processors. The program parameters are obtained using a previously developed tool.Due to the generality of this theorem, the proof is rather complex because it has to cover a large range of situations. The theorem itself, however, is easy to apply, making it possible to compare the performance of different scheduling strategies with the optimal case. The proof also gives important hints on how to design efficient scheduling algorithms for statically allocated programs. 相似文献