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551.
W. P. Loh K. Inderfurth M. Hollinger P. Hammann H. Meyer zu Selhausen H. Dellwing H. Späth H. -J. Lenz 《Mathematical Methods of Operations Research》1976,20(4):B168-B174
Ohne Zusammenfassung 相似文献
552.
G.L. Borchert D. Anagnostopoulos M. Augsburger C. Castelli D. Chatellard J.P. Egger P. El Khoury M. Elble H. Gorke D. Gotta P. Hauser P. Indelicato K. Kirch S. Lenz N. Nelms K. Rashid O.W.B. Schult Th. Siems L.M. Simons 《Hyperfine Interactions》2000,127(1-4):149-155
At the LEAR facility, CERN, antiprotonic Lα transitions in light elements have been investigated with a focussing crystal
spectrometer. The high resolution of the experiment allowed for the first time to resolve in
H the 23P0 state from the close lying states 23P2, 21P1, and 23P1. In
D the corresponding transitions were found to be more than an order of magnitude broader. To a large extent the results for
H support the meson exchange model.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
553.
Delone sets of finite local complexity in Euclidean space are investigated. We show that such a set has patch counting and
topological entropy zero if it has uniform cluster frequencies and is pure point diffractive. We also note that the patch
counting entropy vanishes whenever the repetitivity function satisfies a certain growth restriction.
相似文献
554.
This article is concerned with crossed products and their applications to random operators. We study the von Neumann algebra of a dynamical system using the underlying Hilbert algebra structure. This gives a particularly easy way to introduce a trace on this von Neumann algebra. We review several formulas for this trace, show how it comes as an application of Connes" noncommutative integration theory and discuss Shubin"s trace formula. We then restrict ourselves to the case of an action of a group on a group and include new proofs for some theorems of Bellissard and Testard on an analogue of the classical Plancherel theorem. We show that the integrated density of states is a spectral measure in the periodic case, thereby generalizing a result of Kaminker and Xia. Finally, we discuss duality results and apply a method of Gordon et al. to establish a duality result for crossed products by Z. 相似文献
555.
Clauwaert KM Van Bocxlaer JF Major HJ Claereboudt JA Lambert WE Van den Eeckhout EM Van Peteghem CH De Leenheer AP 《Rapid communications in mass spectrometry : RCM》1999,13(14):1540-1545
This paper describes the investigation of the potential of a quadrupole orthogonal acceleration time-of-flight mass spectrometer (Q-TOF) equipped with an atmospheric pressure ionisation interface for quantitative measurements of small molecules separated by reversed phase liquid chromatography. To this end, the detection limits and linear dynamic range in particular were studied in an LC/MS/MS experiment using 3,4-methylenedioxymethamphetamine standards and 3,4-methylenedioxyethylamphetamine for internal standardisation. In a second phase, the experiment was repeated with real biological extracts (whole blood, serum, and vitreous humour). A calibration for 3,4-methylenedioxymethamphetamine and its metabolite 3,4-methylenedioxyamphetamine was prepared in each of these matrices again using 3,4-methylenedioxyethylamphetamine as internal standard. The resulting quantitative data were compared with those obtained by liquid chromatography with fluorescence detection for the same extracts. The Q-TOF results revealed excellent sensitivity and a linear dynamic range of nearly four decades (2-10 000 pg on-column, r(2) = 0.9998, 1/x weighting). Furthermore, all the calibration curves prepared in biological material were superimposable, LC/MS/MS and LC-fluorescence, and the quantitative results for actual samples compared very favourably. It was concluded that the Q-TOF achieves a linear dynamic range for quantitative LC/MS/MS work exceeding that of fluorescence detection and at much better absolute sensitivity. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
556.
Stefan A. P. Lenz Stacey D. Wetmore 《Journal of computer-aided molecular design》2018,32(12):1375-1388
Parasitic protozoa rely on nucleoside hydrolases that play key roles in the purine salvage pathway by catalyzing the hydrolytic cleavage of the N-glycosidic bond that connects nucleobases to ribose sugars. Cytidine–uridine nucleoside hydrolase (CU–NH) is generally specific toward pyrimidine nucleosides; however, previous work has shown that replacing two active site residues with Tyr, specifically the Thr223Tyr and Gln227Tyr mutations, allows CU–NH to process inosine. The current study uses molecular dynamics (MD) simulations to gain atomic-level insight into the activity of wild-type and mutant E. coli CU–NH toward inosine. By examining systems that differ in the identity and protonation states of active site catalytic residues, key enzyme-substrate interactions that dictate the substrate specificity of CU–NH are identified. Regardless of the wild-type or mutant CU–NH considered, our calculations suggest that inosine binding is facilitated by interactions of the ribose moiety with active site residues and Ca2+, and π-interactions between two His residues (His82 and His239) and the nucleobase. However, the lack of observed activity toward inosine for wild-type CU–NH is explained by no residue being correctly aligned to stabilize the departing nucleobase. In contrast, a hydrogen-bonding network between hypoxanthine and a newly identified general acid (Asp15) is present when the two Tyr mutations are engineered into the active site. Investigation of the single CU–NH mutants reveals that this hydrogen-bonding network is only maintained when both Tyr mutations are present due to a π-interaction between the residues. These results rationalize previous experiments that show the single Tyr mutants are unable to efficiently hydrolyze inosine and explain how the Tyr residues work synergistically in the double mutant to stabilize the nucleobase leaving group during hydrolysis. Overall, our simulations provide a structural explanation for the substrate specificity of nucleoside hydrolases, which may be used to rationally develop new treatments for kinetoplastid diseases. 相似文献
Graphical Abstract
557.
In this paper we consider bounded operators on infinite graphs, in particular Cayley graphs of amenable groups. The operators
satisfy an equivariance condition which is formulated in terms of a colouring of the vertex set of the underlying graph. In
this setting it is natural to expect that the integrated density of states (IDS), or spectral distribution function, exists.
We show that it can be defined as the uniform limit of approximants associated to finite matrices. The proof is based on a
Banach space valued ergodic theorem which even allows explicit convergence estimates. Our result applies to a variety of group
structures and colouring types, in particular to periodic operators and percolation-type Hamiltonians. 相似文献
558.
Xuereb F Chaignepain S Breilh D Godde F Saux MC Lenz C Glueckmann M Schmitter JM 《Analytical and bioanalytical chemistry》2011,400(7):2073-2084
The extended use of protein drugs in therapeutics has created the need for their quantification in human plasma. A methodology
using the therapeutic protein itself as internal standard for quantitative analysis by multiple reaction monitoring (MRM)
has been designed and applied to epoetin beta, a recombinant human erythropoietin (rhEPO). After depletion of major proteins,
plasma samples were desalted and enriched in rhEPO by reversed phase liquid chromatography prior to tryptic cleavage. Differential
isotopic labeling of peptides was performed by derivatization with 2-methoxy-4,5-dehydro-imidazole. A light version (four
hydrogen atoms) of this reagent was used for plasma peptides. Tryptic peptides obtained from pure rhEPO were derivatized with
a heavy version (four deuterium atoms) of the same reagent and used as internal standards. Two rhEPO tryptic peptides with
three MRM transitions per peptide were selected for quantification. This strategy provided a quantification limit close to
50 amol of epoetin beta per microliter of plasma (equivalent to 1.7 ng/mL), i.e., well below the expected therapeutic concentrations
in plasma (around 100–500 amol/μL). 相似文献
559.
Markus Lenz Arne Gmerek 《International journal of environmental analytical chemistry》2013,93(9):615-627
Chromatographic (IC-CD, GC-FID) and spectroscopic (XRD) techniques that allow the specific determination of several selenium species present or formed during bioremediation processes of selenate contaminated drinking, ground, or wastewaters have been established. The developed techniques are shown to be applicable in determining selenium species in the range of target concentrations for emissions and are thus appropriate to characterize bioremediation processes. The applied techniques offer advantages regarding short analytical times without loss of satisfactory accurateness towards more sophisticated methods. By means of IC-CD, selenate and selenite can be detected specifically to concentrations far below allowance levels for metal finishing industries (20?µg?L?1 selenate, 40?µg?L?1 selenite) within 16.0?min. Thus, the removal of selenate from the liquid phase by anaerobic granular sludge was quantified by IC-CD, and the concomitantly formed red precipitates were analysed by XRD. Hexagonal elemental selenium was found to be present in the XRD analysis. Even if the precipitate contained iron and zinc, as shown by ICP-OES, no iron- or zinc-containing selenium minerals were detected by XRD. The GC-FID method described determines dimethylselenide and dimethyldiselenide at a detection limit of 1?ng and 2?ng, respectively, without further chemical derivatization within 7.4?min. Thus, the GC-FID offers adequate detection of two major volatile organic selenium species potentially formed during bioremediation of selenium contaminated waters. 相似文献
560.
C. Gemmel W. Heil S. Karpuk K. Lenz Ch. Ludwig Yu. Sobolev K. Tullney M. Burghoff W. Kilian S. Knappe-Grüneberg W. Müller A. Schnabel F. Seifert L. Trahms St. Bae?ler 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,57(3):303-320
We discuss the design and performance of a very sensitive low-field magnetometer based on the detection of free spin precession of gaseous, nuclear polarized 3He or 129Xe samples with a SQUID as magnetic flux detector. The device will be employed to control fluctuating magnetic fields and gradients in a new experiment searching for a permanent electric dipole moment of the neutron. Furthermore, with the detection of the free precession of co-located 3He/129Xe nuclear spins it can be used as ultra-sensitive probe for non-magnetic spin interactions, since the magnetic dipole interaction (Zeeman-term) drops out. Characteristic spin precession times T2 * of up to 60 h were measured. The achieved signal-to-noise ratio of more than 5000:1 leads to an expected sensitivity level (Cramer-Rao lower bound) of δB≈1 fT after an integration time of 220 s and of δB≈10-4 fT after one day. By means of a co-located 3He/129Xe magnetometer, noise sources inherent in the magnetometer could be investigated, showing that CRLB is fulfilled, at least down to δB≈10-2 fT. The reason for such a high sensitivity is that free precessing 3He (129Xe) nuclear spins are almost completely decoupled from the environment. Therefore, this type of magnetometer is particularly attractive for precision field measurements where long-term stability is required. 相似文献