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971.
Binamé J Meurice N Leherte L Glasgow J Fortier S Vercauteren DP 《Journal of chemical information and computer sciences》2004,44(4):1394-1401
In this paper, we propose a reduced representation of molecules of pharmacological interest based on their chemical functions. The proposed representations of the molecules are obtained by a topological analysis of their electron density maps at medium resolution, leading to graphs of critical points. The distribution of the different types of critical points are compared at various levels of resolution for a training set of 22 molecules in order to define the optimal resolution level leading to the best representation of the various chemical functions. The reduced representations can in the future be used for molecular similarity research and pharmacophore proposals. 相似文献
972.
Pisula W Kastler M Wasserfallen D Pakula T Müllen K 《Journal of the American Chemical Society》2004,126(26):8074-8075
The substitution of a hexa-peri-hexabenzocoronene by bulky, space-demanding, 2-decyltetradecyl side chains proved to be an effective procedure to influence the thermal and self-aggregation behavior. The extremely large steric requirement of the introduced side chains modulated the aggregation and resulted in a dramatic lowering of the isotropization temperature and a higher solubility. As an additional consequence of the exceptional, long-range self-aggregation of the discotic molecule, spherulite formation was observed during crystallization by polarized light microscopy. Macroscopic self-assembly was induced by zone crystallization of the material, leading to aligned columnar superstructures as revealed by 2D-WAXS experiments. These extraordinary properties have not yet been reported for a discotic columnar material, making this compound very promising for application in electronic devices. 相似文献
973.
The syntheses of new cyano-substituted derivatives of arachno-6,8-C(2)B(7)H(13) have been achieved through the addition reactions of the arachno-6,8-C(2)B(7)H(12)(-) (1-) anion with cyano-activated olefins. The reaction of PSH+1- with tetracyanoethylene (TCNE) yielded the unusual bridging compound PSH(+)endo-6-endo-7-[micro(2)-(C(CN)(2))(2)]-arachno-6,8-C(2)B(7)H(12)(-) (PSH+2-)) resulting from cycloaddition of the TCNE at the C6-B7 edge of the anion. Consistent with its hypho skeletal electron count, an X-ray crystallographic study and DFT/GIAO calculations confirm 2(-) has a more open structure than 1-. The reaction of 1- with acrylonitrile resulted in the formation of endo-6-(NCCH(2)CH(2))-arachno-6,8-C(2)B(7)H(11)(-) (3-), which, upon acidification, afforded endo-6-(NCCH(2)CH(2))-arachno-6,8-C(2)B(7)H(12) (3) in high yield. X-ray crystallographic and DFT/GIAO studies established that the cyanoethyl fragment in 3 is substituted at the endo-position of the C6 cage-carbon. Heating 3 in THF at 50 degrees C or in toluene at 110 degrees C resulted in the quantitative isomerization of the cyanoethyl-substituent from the endo- to the exo-position at C6 to yield exo-6-(NCCH(2)CH(2))-arachno-6,8-C(2)B(7)H(12) (4). This is the first example of an endo to exo isomerization to be observed at a cage-carbon of a carborane. While heating 3 resulted in isomerization to 4, heating 3- in the presence of a small amount of 3 yielded the new ethylene-bridged 10-vertex tricarbaborane micro(6,9)-(CH(2)CH(2))-arachno-5,6,9-C(3)B(7)H(11) (5) resulting from reduction of the 3- pendant nitrile group, followed by deammination and carbon insertion. 相似文献
974.
The preparation, characterization, and electronic structure of homoleptic complexes of molybdenum and tungsten bridged by bis(alkylamido)phenylboranes, M(2)[RN-B(Ph)-NR](3) (M = Mo, R = Et (1), (i)Pr (2); M = W, R = Et (3), (i)Pr (4)), are described. These triple metal-metal bond species (i) exhibit a nearly eclipsed ligand geometry and (ii) possess the shortest metal-metal bonds of neutral dimolybdenum and ditungsten M(2)X(6) complexes observed to date (d(Mo-Mo) = 2.1612(6) A (1); d(W-W) = 2.2351(7) A (4)). 相似文献
975.
A series of pyrroles incorporating N-tethered acrylates and related groups has been prepared and examined for their capacity to undergo intramolecular Michael addition reactions to form, in a diastereo- or enantio-selective fashion, the corresponding 8-substituted tetrahydroindolizidine or homologues thereof. 相似文献
976.
Niu W Wong EH Weisman GR Hill DC Tranchemontagne DJ Lam KC Sommer RD Zakharov LN Rheingold AL 《Dalton transactions (Cambridge, England : 2003)》2004,(21):3536-3547
Ethylene cross-bridging of the popular tetraazamacrocyclic ligand cyclam has led to metal complexes with enhanced kinetic inertness. The synthesis and spectral characterization of zinc(II), cadmium(II), and mercury(II) complexes of cross-bridged cyclam (L1) as well as cross-bridged cyclen (L2) are reported along with the details of our synthetic route to L2. X-ray structural studies revealed that all Zn(II) and Cd(II) cations are fully kappa(4)N-coordinated inside the respective ligand's molecular cleft with L1 providing the better fit for Zn(II). While Hg(II) is similarly coordinated to L2, it has been found to complex L1 outside the ligand cleft in a novel exo-kappa(2)N-mode. Solution NMR data of the kappa(4)N complexes are consistent with the presence of only a single cis-folded isomer in each case. Ligand (1)H and (13)C coupling to both (111,113)Cd and (199)Hg in their complexes can be clearly discerned. The relative kinetic inertness of representative cross-bridged complexes in acidic aqueous solution has been assessed and found to be in the following order: Zn(II) > Cd(II)[dbl greater-than] Hg(II). The data also reaffirm that cross-bridged cyclam ligand L1 forms a substantially more inert complex with zinc(II) than either the smaller cyclen analogue L2 or the unbridged 1,4,8,11-tetramethyl-cyclam L3. 相似文献
977.
A natural-product-inspired photonic logic gate based on photoinduced electron-transfer-generated dual-channel fluorescence 总被引:1,自引:0,他引:1
[structure: see text] Modified 1-benzylisoquinoline N-oxides can operate as molecular logic gates. The combination of dual-channel fluorescence emissions and the preferred interaction for selected chemical inputs allows one to design multifunction and self-reprogrammable molecular logic gates. 相似文献
978.
Dennis W. Bennett Tasneem A. Siddiquee Daniel T. Haworth Shariff E. Kabir Farzana K. Camellia 《Journal of chemical crystallography》2004,34(6):343-345
Other Index
Index abstracts 相似文献979.
Pancyclicity of Strong Products of Graphs 总被引:1,自引:0,他引:1
Daniel?KrálEmail author Jana?Maxová Pavel?Podbrdsky Robert??ámal 《Graphs and Combinatorics》2004,20(1):91-104
We prove that the strong product of graphs G1××Gn is pancyclic, in particular hamiltonian, for nc for any cln(25/12)+1/640.75 whenever all Gi are connected graphs with the maximum degree at most .This research was supported by KONTAKT ME 337 as a part of REU programme and in part by GACR 201/99/0242The author acknowledges partial support by NSF grant DMS-9900969 and by Institute for Theoretical Computer ScienceThe author acknowledges partial support by Institute for Theoretical Computer ScienceInstitute for Theoretical Computer Science is supported by Ministry of Education of Czech Republic as project LN00A056Final version received: August 6, 2003 相似文献
980.
Daniel?HugEmail author Rolf ?SchneiderEmail author 《Discrete and Computational Geometry》2004,31(4):503-514
It is proved that the shape of the typical cell of
a Delaunay tessellation, derived from a stationary Poisson point process in d-dimensional Euclidean space, tends to the shape of a regular simplex, given
that the volume of the typical cell tends to infinity. This follows from an
estimate for the probability that the typical cell deviates by a given amount
from regularity, given that its volume is large. As a tool for the proof,
a stability result for simplices is established. 相似文献