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761.
762.
P.E. Rakita M.K. Hoffman M.N. Andrews M.M. Bursey 《Journal of organometallic chemistry》1973,49(1):213-218
A series of indanyl and indenyl derivaties of silicon and tin has been prepared and the molecular ionization potentials determined by electron impact mass spectrometry. Substitution of the hydrogen at C(1) by an organosilicon group results in a decrease of the ionization potential by ~0.6–0.8 eV, while extension of the π-system into the five-membered ring via the double bond produces a further decrease of the ionization potential by ~0.2–0.3 eV. The results are consistent with the postulate of a σ-gp hyperconjugative interaction between the β metal-carbon bond and the aromatic π-system. 相似文献
763.
Four new Mo(VI)-dioxo complexes of a family of N2X heteroscorpionate ligands are reported which, together with data already available for (TpR)-, provide a unique example of a comprehensive set of isostructural, isoelectronic complexes differing only in one biologically relevant donor atom. A study of these complexes allows for a direct comparison of structural, spectroscopic, and oxygen atom transfer reactivity properties of the Mo(VI)-dioxo center (of relevance to various families of molybdoenzymes) as a function of donor atom identity. 相似文献
764.
Itai Benjamini Noam Berger Christopher Hoffman Elchanan Mossel 《Transactions of the American Mathematical Society》2005,357(8):3013-3029
Consider the following method of card shuffling. Start with a deck of cards numbered 1 through . Fix a parameter between 0 and 1. In this model a ``shuffle' consists of uniformly selecting a pair of adjacent cards and then flipping a coin that is heads with probability . If the coin comes up heads, then we arrange the two cards so that the lower-numbered card comes before the higher-numbered card. If the coin comes up tails, then we arrange the cards with the higher-numbered card first. In this paper we prove that for all , the mixing time of this card shuffling is , as conjectured by Diaconis and Ram (2000). Our result is a rare case of an exact estimate for the convergence rate of the Metropolis algorithm. A novel feature of our proof is that the analysis of an infinite (asymmetric exclusion) process plays an essential role in bounding the mixing time of a finite process.
765.
A. Bendavid P.J. Martin J. Cairney M. Hoffman A.C. Fischer-Cripps 《Applied Physics A: Materials Science & Processing》2005,81(1):151-158
A hybrid technique is described for the synthesis of nanocomposite TiNSi3N4 thin films based on the reactive deposition of Ti produced from a cathodic arc source and Si from a liquid tetramethylsilane (TMS), precursor. The technique combines both the physical vapour of Ti and chemical vapour of silicon in a nitrogen background pressure in a single system. The influence of the TMS flow rate on the structure and mechanical properties has been investigated. The film structure was found to comprise of TiN crystallites and amorphous Si3N4. The X-ray diffraction data showed that with increasing TMS flow, there is a decrease in the TiN crystalline size from 33 nm to 4 nm. The hardness of the films was found to be strongly dependent on the Si content and reached a maximum value of 41 GPa at 5% Si content at a total pressure of nitrogen and TMS of 0.8 Pa. Hardness enhancement was found to arise from the nanostructural change induced due to the addition of an amorphous Si3N4 phase into the film. Transmission electron microscopy (TEM) analysis confirmed the structure of the ncTiN/aSi3N4 composites. Films with 4 at.% or more silicon were found to maintain the hardness after annealing at 500 °C in vacuum. PACS 68.55.Jk; 81.15.-z; 81.15.Ef 相似文献
766.
Marx KA O'Neil P Hoffman P Ujwal ML 《Journal of chemical information and computer sciences》2003,43(5):1652-1667
Using data mining techniques, we have studied a subset (1400) of compounds from the large public National Cancer Institute (NCI) compounds data repository. We first carried out a functional class identity assignment for the 60 NCI cancer testing cell lines via hierarchical clustering of gene expression data. Comprised of nine clinical tissue types, the 60 cell lines were placed into six classes-melanoma, leukemia, renal, lung, and colorectal, and the sixth class was comprised of mixed tissue cell lines not found in any of the other five classes. We then carried out supervised machine learning, using the GI(50) values tested on a panel of 60 NCI cancer cell lines. For separate 3-class and 2-class problem clustering, we successfully carried out clear cell line class separation at high stringency, p < 0.01 (Bonferroni corrected t-statistic), using feature reduction clustering algorithms embedded in RadViz, an integrated high dimensional analytic and visualization tool. We started with the 1400 compound GI(50) values as input and selected only those compounds, or features, significant in carrying out the classification. With this approach, we identified two small sets of compounds that were most effective in carrying out complete class separation of the melanoma, non-melanoma classes and leukemia, non-leukemia classes. To validate these results, we showed that these two compound sets' GI(50) values were highly accurate classifiers using five standard analytical algorithms. One compound set was most effective against the melanoma class cell lines (14 compounds), and the other set was most effective against the leukemia class cell lines (30 compounds). The two compound classes were both significantly enriched in two different types of substituted p-quinones. The melanoma cell line class of 14 compounds was comprised of 11 compounds that were internal substituted p-quinones, and the leukemia cell line class of 30 compounds was comprised of 6 compounds that were external substituted p-quinones. Attempts to subclassify melanoma or leukemia cell lines based upon their clinical cancer subtype met with limited success. For example, using GI(50) values for the 30 compounds we identified as effective against all leukemia cell lines, we could subclassify acute lymphoblastic leukemia (ALL) origin cell lines from non-ALL leukemia origin cell lines without significant overlap from non-leukemia cell lines. Based upon clustering using GI(50) values for the 60 cancer cell lines laid out by the RadViz algorithm, these two compound subsets did not overlap with clusters containing any of the NCI's 92 compounds of known mechanism of action, a few of which are quinones. Given their structural patterns, the two p-quinone subtypes we identified would clearly be expected to possess different redox potentials/substrate specificities for enzymatic reduction in vivo. These two p-quinone subtypes represent valuable information that may be used in the elucidation of pharmacophores for the design of compounds to treat these two cancer tissue types in the clinic. 相似文献
767.
A. Türler Ch.E. Düllmann H.W. Gäggeler U.W. Kirbach A.B. Yakushev M. Schädel W. Brüchle R. Dressler K. Eberhardt B. Eichler R. Eichler T.N. Ginter F. Glaus K.E. Gregorich D.C. Hoffman E. Jäger D.T. Jost D.M. Lee H. Nitsche J.B. Patin V. Pershina D. Piguet Z. Qin B. Schausten E. Schimpf H.-J. Schött S. Soverna R. Sudowe P. Thörle S.N. Timokhin N. Trautmann A. Vahle G. Wirth P.M. Zielinski 《The European Physical Journal A - Hadrons and Nuclei》2003,17(4):505-508
In bombardments of 248Cm with 143.7-146.8 MeV 26Mg ions the nuclides 269Hs and presumably 270Hs were produced. After chemical isolation, Hs atoms were identified by observing genetically linked nuclear-decay chains. Three chains originating from 269Hs confirmed the decay properties observed previously in the decay of 277112. Two chains exhibited the characteristics expected for the new nuclide 270Hs, which was predicted to be a deformed doubly magic nucleus. From the measured
MeV an
-decay half-life of 3.6+0.8-1.4 s was estimated.Received: 18 July 2002, Revised: 3 April 2003, Published online: 22 July 2003PACS:
23.60.+e Alpha decay - 25.70.Gh Compound nucleus - 25.85.Ca Spontaneous fission - 27.90.+b
相似文献
768.
The pseudozero set of a system of polynomials in complex variables is the subset of which is the union of the zero-sets of all polynomial systems that are near to in a suitable sense. This concept is made precise, and general properties of pseudozero sets are established. In particular it is shown that in many cases of natural interest, the pseudozero set is a semialgebraic set. Also, estimates are given for the size of the projections of pseudozero sets in coordinate directions. Several examples are presented illustrating some of the general theory developed here. Finally, algorithmic ideas are proposed for solving multivariate polynomials.
769.
770.