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51.
The amorphous aluminum silicate (Al2O3)2(SiO2) [AS2] is investigated by means of large scale molecular dynamics computer simulations. We consider fully equilibrated melts in the temperature range 6100 K> or =T> or =2300 K as well as glass configurations that were obtained from cooling runs from T=2300 to 300 K with a cooling rate of about 10(12) K/s. Already at temperatures as high as 4000 K, most of the Al and Si atoms are fourfold coordinated by oxygen atoms. Thus, the structure of AS2 is that of a disordered tetrahedral network. The packing of AlO4 tetrahedra is very different from that of SiO4 tetrahedra in that Al is involved with a relatively high probability in small-membered rings and in triclusters in which an O atom is surrounded by four cations. We find as typical configurations two-membered rings with two Al atoms in which the shared O atoms form a tricluster. On larger length scales, the system shows a microphase separation in which the Al-rich network structure percolates through the SiO2 network. The latter structure gives rise to a prepeak in the static structure factor at a wave number q=0.5 A(-1). A comparison of experimental x-ray data with the results from the simulation shows good agreement for the structure function. The diffusion dynamics in AS2 is found to be much faster than in SiO2. We show that the self-diffusion constants for O and Al are very similar and that they are by a factor of 2-3 larger than the one for Si. 相似文献
52.
Stefan Müllegger Kathrin H?nel Thomas Strunskus Christof W?ll Adolf Winkler 《Chemphyschem》2006,7(12):2552-2558
Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy has been applied to reveal the molecular arrangement of ultrathin oligophenyl films [p-quaterphenyl (4P) and p-hexaphenyl (6P)] on Au(111). In the half-monolayer films the molecules lie flat on the surface but still have a considerable inter-ring twist of 30 degrees -40 degrees , similar to the gas-phase conformation. In the saturated monolayer film the second half of the molecules is side-tilted by an angle of less than 66 degrees with respect to the surface. This arrangement is already similar to that in bulk net planes of thicker films parallel to the surface, that is, the 4P(211) and 6P(21-3) planes, respectively. 相似文献
53.
W. Pilz und Ilse Johann 《Fresenius' Journal of Analytical Chemistry》1965,210(2):113-123
Zusammenfassung Es wird eine neue Methode zur spezifischen Bestimmung von freiem -Naphthol in Gegenwart eines großen Überschusses von -Naphthylesteremulsion beschrieben. Alle notwendigen reaktionskinetischen und optischen Bedingungen werden untersucht. Die Methode eignet sich besonders gut zur enzymatischen Analyse von Fermenten, die -Naphthylester hydrolysieren. Nach genauer Beschreibung von Arbeitsvorschriften werden folgende Anwendungsbeispiele ausgeführt: a) die Bestimmung von freiem -Naphthol in rohen -Naphthylesterpräparaten, b) die Bestimmung von Enzymaktivitäten: Substratvariation im menschlichen Serum, c) Verwendung als Suchreaktion: Ortung der -Naphthylpropionat spaltenden Fermente und Proteine des menschlichen Serums durch biologische Analyse der Eluate nach präparativer Stärkebreielektrophorese. Die Empfindlichkeit der Methode beträgt mindestens 0,1 Mol -Naphthol; die Störanfälligkeit ist minimal.
Meinem verehrten Lehrer Herrn Univ. Prof. Dr. Alois Musil zum 65. Geburtstag gewidmet. 相似文献
Summary A new method is described for the specific determination of free -naphthol in presence of a large excess of emulsions of -naphthol esters. The kinetics of the reaction and all optical conditions are tested. The method is applicable to the determination of esterases which hydrolyse -naphthol esters. The following examples for the use of the method are described: a) determination of free -naphthol in industrial -naphthol ester preparations, b) determination of esterase activities; c) application as finding test: localisation of the -naphthol propionic acid ester hydrolysing esterases and proteins of human serum by biological analysis of the eluates after preparative starch electrophoresis. The sensitivity is at least 0.1 Mol of -naphthol; the security is optimal.
Meinem verehrten Lehrer Herrn Univ. Prof. Dr. Alois Musil zum 65. Geburtstag gewidmet. 相似文献
54.
Helmut Simon Johann Bader Helmut Günther Stefan Neumann Jordanes Thanos 《Angewandte Chemie (International ed. in English)》1985,24(7):539-553
It has been known for many decades that chiral compounds can be obtained by stereospecific biocatalytic reduction. Further significant methodological developments in this field have, however, only been made during the past ten years; they include the application of previously unused microorganisms and electron donors, the discovery of additional substrates for the known reductases, the development of methods for regenerating reduced pyridine nucleotides, and the discovery of new reductases which were sought for specific preparative purposes. Many chiral compounds can now be synthesized by microbial hydrogenation using H2 and hydrogenase-containing microorganisms as well as by electromicrobial or electroenzymatic reduction. In the two latter methods, anaerobic or aerobic organisms are supplied with electrons from electrochemically reduced, artificial mediators, e.g., methyl viologen. Reductases that do not require pyridine nucleotides and can accept electrons directly from reduced viologens are especially useful. Two examples of this type of enzyme are described which are of preparative interest. Many cells contain methyl viologen-dependent NAD(P) reductases, a large number of which have still not been characterized. A productivity number is proposed which allows different methods of bioconversion with microorganisms to be compared. The productivity numbers of compounds synthesized by the methods described in this review are often 10- to 100-fold higher than those of substances obtained by conventional techniques. 相似文献
55.
56.
[reaction: see text] We describe a convergent and flexible synthesis of 15-deoxy-16-(m-tolyl)-17,18,19,20-tetranorisocarbacyclin (15-deoxy-TIC), a simple isocarbacyclin derivative. The synthesis takes advantage of two key step reactions: a regioselective deprotonation of the described ketone under substrate control which is then trapped, as the enol triflate, to generate the C6-C9alpha endocyclic double bond, followed by an sp2-sp3 Pd-catalyzed cross-coupling reaction (C5-C6) with a suitable primary alkyl Grignard reagent. Introduction of the C13-C14 (E)-double bond in the omega-side chain is performed by the Julia-Kocie?ski olefination. 相似文献
57.
58.
A model for describing sputter depth profiles on rough surfaces is presented; this is based on the assumption that sputter removal occurs at preferred sites due to the intrinsically rough surface. The progress of sputtering is described by the growth and overlap of statistically distributed holes in the surface layer. Within this assumption the variation of the Auger signal intensity during sputtering is described by simple functions. The model is applied to the sputter removal of oxide layers formed on INCOLOY 800 in hot water. 相似文献
59.
Rhodococcus equi A4, Rhodococcus erythropolis NCIMB 11540 and Rhodococcus sp. R312 were investigated towards their ability to produce β-amino amides and acids from β-amino nitriles. The microorganisms show comparable trends: five-membered alicyclic 2-amino nitriles were transformed significantly faster than the six-membered compounds and the products of trans-2-amino nitriles (amides and acids) were formed considerably faster than the cis-counterparts (amides). The trans-five membered nitriles gave the amides (1b, 5b) in excellent enantiomeric excess (94-99%), the biotransformation of trans-six membered substrates resulted in the formation of the acid (3c, 7c) in excellent ee (87-99%). The ee's of the cis-compounds were throughout lower. Fifteen new substances were synthesized and characterized in the course of this work. 相似文献
60.
M. Voss W. Weiss R. Winkler 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1986,1(2):157-166
From 17 transitions in the singly ionized Sb II spectrum the hyperfine structure (A andB splitting constants) of the complete excited configurations 5p6s and 5p6p were determined by means of optical interference spectroscopy. In addition, a theoretical analysis both of the fine structure and also of the hyperfine structure was carried out (in the case of 5p6p of the general typenpn′p for the first time in literature). For the 3 levels 5p6p 3 P 1, 5p7p 3 D 2 and 5p6p 1 P 1 a different classification was found and consistent values for the fine structure parameters, mixing coefficients and single electron hyperfine structure splitting parametersa nl ik andb nl ik were obtained. The three new determinations in Sb II of the quadrupole moment (in barn) of121Sb (Q(5p6s)=?0.55(5);Q(5p6p)=?0.57(5) from the 5p-electron andQ(5p6p)=?0.7(2) from the 6p-electron) are well agreeing with each other but differ to former values from SbI. The core polarization and isotope shift of the lines, however, are compatible with our former results in SbI. 相似文献