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Matthew J. Hills Irmgard Kiewitt Kumar D. Mukherjee 《Applied biochemistry and biotechnology》1991,27(2):123-129
Lipase from rape (Brassica napus L., immobilized onto celite, catalyzes esterification and transesterification reactions in hexane. The activity of the lipase is stimulated up to 35 fold by the addition of water (1.3% w/v). The activity of the lipase in hydrolysis is about 8 times higher than in the esterification reactions in hexane. Interesteri-fication reactions between mono- and diacylglycerols and transesterification reactions of mono- and diacylglycerols with alcohols were also catalyzed at relatively high rates but transesterification/esterification of these acylglycerols with fatty acids was comparatively slow. In transesterification reactions, triacylglycerols reacted rather slowly. 相似文献
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Studies of extractions of yttrium from aqueous solution into chloroform, benzene, methyl isobutyl ketone, and mixtures of these solvents, containing thenoyltrifluoroacetone are described. The effects of reagent concentration, added n-butylamine, and added fluoride were investigated. Values of pH and Pe were determined, and identifications of the involved species are suggested. 相似文献
7.
The application of parallel processing techniques to molecular mechanics calculations is evaluated. Using the standard molecular mechanics package, MM2, four different parallel versions of the program are implemented in a four-processor computing environment. A set of 529 test structures is used to compare the efficiency of the parallel versions of MM2 to a standard serial version of the program. Statistics describing execution times and program execution cycles are gathered and analyzed. The effects of parallel processing overhead and computer system load are explored, and the practical utility of parallel processing in molecular mechanics is estimated. The results of these parallelization experiments indicate that for geometry optimizations requiring significant amounts of computing time an improvement in program execution speed approaching 50% is realizable. © 1993 John Wiley & Sons, Inc. 相似文献
8.
Irmgard Heber 《Colloid and polymer science》1967,215(2):145-149
Zusammenfassung Steigert man für das Poly?thylen die Kristallisationstemperatur, so findet man Kristallformen in der folgenden Reihenfolge:
rautenf?rmige Einkristalle— rautenf?rmige Einkristalle mit abgeschnittenen spitzen Ecken (“truncated lozenge crystals”)-l?ngliche
sechseckf?rmige Einkristalle, bei denen die kristallographische b-Achse der orthorhombischen Elementarzelle in Richtung der l?ngsten Ausdehnung des Kristalls liegt. Diese l?nglichen Sechsecke
lagern sich zu Sph?rolithen zusammen, und zwar so, da? die kristallographische b-Achse radial liegt, wie es auch bei den aus der Schmelze gewachsenen Sph?rolithen der Fall ist. Damit sind für das Poly?thylen
übergangsformen zwischen den Einkristallen und Sph?rolithen aufgezeigt.
Sph?rolithe, die aus der L?sung gewachsen sind, zeigen im Polarisationsmikroskop nur dann ein konzentrisches Ringsystem, wenn
bei der Bildung der Sph?rolithe ein Mindestangebot an Substanz vorhanden ist. Die Ringbreite nimmt dann mit steigender Kristallisationstemperatur
zu. Bei aus der Schmelze gewachsenen Poly?thylen-Sph?rolithen ist mit der Bildung von nicht-kristallographischen Verzweigungen
eine Drehung der Indikatrix verbunden. Vermutlich wird also auch bei aus der L?sung gewachsenen Sph?rolithen das Ringsystem
auf dem Auftreten von Verzweigungen infolge hohen Angebotes von kristallisierender Substanz beruhen.
Summary With increasing temperature of crystallization polyethylene crystallizes from solution as lozenge single crystals, truncated lozenge crystals and longish hexagonal crystals, with the crystallographic b-axis along the long diagonal. In the solutions longish hexagonal crystal plates are able to cluster and to form spherulites, in which their crystallographic b-axes are oriented radially like the b-axes in spherulites grown from the melt. Various transition species have been observed. In polarised light the spherulites grown from solution show a concentric ring-system only, if during the crystallization a sufficient quantity of polyethylene is present. The ring-width increases with increasing crystallization temperature. Further it is shown that in polyethylene spherulites grown from the melt the rotation of the indicatrix is connected with a non-crystallographic branching. We suppose, that also for the solution-grown spherulites the ring-system depends on branching.相似文献
9.
Mg2Ru5B4 and Mg5Ru13B11, Two Ternary Magnesium Ruthenium Borides with Channel Structures The ternary borides Mg2Ru5B4 and Mg5Ru13B11, crystallizing in the orthorhombic space group Pbam, were prepared by reaction of the elementary components in sealed tantalum ampoules. Mg2Ru5B4 (a = 1000.0(2) pm, b = 837,6(1) pm, c = 295.42(3) pm, Z = 2, RW = 0.027 for 563 reflections) is homeotypic with Sc2Ru5B4. The structure contains BRu6-trigonal prisms, connected by faces and edges to form pentagonal channels filled with chains of magnesium atoms. Mg5Ru13B11 (a = 2190.1(2) pm, b = 996.7(2) pm, c = 294.65(3) pm, Z = 2, RW = 0.031 for 959 reflections) has a similar but so far unknown structure in which parts of the magnesium and boron atoms are disordered. 相似文献
10.
Extraction of radiolabeled cobalt(II) from aqueous solution into one or more solvents using 25 reagents was studied. Both reagent concentration and pH variation were investigated. The relevant association and partition constants for several of the better reagent-solvent systems were determined. These systems were hexanoic acid in I-hexanol, octanoic acid in I-octanol, and thenoyltrifluoroacetone in benzene. 相似文献