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941.
Takashi Tamaki Midue Nagata Masato Ohashi Dr. Sensuke Ogoshi Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(39):10083-10091
Cyclopropanecarboxaldehyde ( 1 a ), cyclopropyl methyl ketone ( 1 b ), and cyclopropyl phenyl ketone ( 1 c ) were reacted with [Ni(cod)2] (cod=1,5‐cyclooctadiene) and PBu3 at 100 °C to give η2‐enonenickel complexes ( 2 a – c ). In the presence of PCy3 (Cy=cyclohexyl), 1 a and 1 b reacted with [Ni(cod)2] to give the corresponding μ‐η2:η1‐enonenickel complexes ( 3 a , 3 b ). However, the reaction of 1 c under the same reaction conditions gave a mixture of 3 c and cyclopentane derivatives ( 4 c , 4 c′ ), that is, a [3+2] cycloaddition product of 1 c with (E)‐1‐phenylbut‐2‐en‐1‐one, an isomer of 1 c . In the presence of a catalytic amount of [Ni(cod)2] and PCy3, [3+2] homo‐cycloaddition proceeded to give a mixture of 4 c (76 %) and 4 c′ (17 %). At room temperature, a possible intermediate, 6 c , was observed and isolated by reprecipitation at ?20 °C. In the presence of 1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene (IPr), both 1 a and 1 c rapidly underwent oxidative addition to nickel(0) to give the corresponding six‐membered oxa‐nickelacycles ( 6 ai , 6 ci ). On the other hand, 1 b reacted with nickel(0) to give the corresponding μ‐η2:η1‐enonenickel complex ( 3 bi ). The molecular structures of 6 ai and 6 ci were confirmed by X‐ray crystallography. The molecular structure of 6 ai shows a dimeric η1‐nickelenolate structure. However, the molecular structure of 6 ci shows a monomeric η1‐nickelenolate structure, and the nickel(II) 14‐electron center is regarded as having “an unusual T‐shaped planar” coordination geometry. The insertion of enones into monomeric η1‐nickelenolate complexes 6 c and 6 ci occurred at room temperature to generate η3‐oxa‐allylnickel complexes ( 8 , 9 ), whereas insertion into dimeric η1‐nickelenolate complex 6 ai did not take place. The diastereoselectivity of the insertion of an enone into 6 c having PCy3 as a ligand differs from that into 6 ci having IPr as a ligand. In addition, the stereochemistry of η3‐oxa‐allylnickel complexes having IPr as a ligand is retained during reductive elimination to yield the corresponding [3+2] cycloaddition product, which is consistent with the diastereoselectivity observed in Ni0/IPr‐catalyzed [3+2] cycloaddition reactions of cyclopropyl ketones with enones. In contrast, reductive elimination from the η3‐oxa‐allylnickel having PCy3 as a ligand proceeds with inversion of stereochemistry. This is probably due to rapid isomerization between syn and anti isomers prior to reductive elimination. 相似文献
942.
Pablo J. Alonso Prof. Dr. Ana B. Arauzo Dr. María Angeles García‐Monforte Dr. Antonio Martín Dr. Babil Menjón Dr. Conrado Rillo Prof. Dr. Milagros Tomás Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(41):11020-11030
Homoleptic perhalophenyl derivatives of divalent nickel complexes with the general formula [NBu4]2[NiII (C6X5)4] [X=F ( 1 ), Cl ( 2 )] have been prepared by low‐temperature treatment of the halo‐complex precursor [NBu4]2[NiBr4] with the corresponding organolithium reagent LiC6X5. Compounds 1 and 2 are electrochemically related by reversible one‐electron exchange processes with the corresponding organometallate(III) compounds [NBu4][NiIII (C6X5)4] [X=F ( 3 ), Cl ( 4 )]. The potentials of the [NiIII (C6X5)4]?/[NiII (C6X5)4]2? couples are +0.07 and ?0.11 V for X=F or Cl, respectively. Compounds 3 and 4 have also been prepared and isolated in good yield by chemical oxidation of 1 or 2 with bromine or the amminium salt [N(C6H4Br‐4)3][SbCl6]. The [NiIII (C6X5)4]? species have SP‐4 structures in the salts 3 and 4 , as established by single‐crystal X‐ray diffraction methods. The [NiII (C6F5)4]2? ion in the parent compound 1 has also been found to exhibit a rather similar SP‐4 structure. According to their SP‐4 geometry, the NiIII compounds (d7) behave as S=1/2 systems both at microscopic (EPR) and macroscopic levels (ac and dc magnetization measurements). The spin Hamiltonian parameters obtained from the analysis of the magnetic behavior of 3 and 4 within the framework of ligand field theory show that the unpaired electron is centered mainly on the metal atom, with >97 % estimated d contribution. Thermal decomposition of 3 and 4 proceeds with formation of the corresponding C6X5? C6X5 coupling compounds. 相似文献
943.
Vilas B. Phapale Manuel Guisán‐Ceinos Elena Buñuel Prof. Dr. Diego J. Cárdenas Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(46):12681-12688
Optimal conditions for a general Ni‐catalysed Negishi cross‐coupling of alkyl zinc halides with aryl, heteroaryl and alkenyl halides have been determined. These conditions allow the reaction to take place smoothly, with low catalyst loading, and in the presence of a wide variety of functional groups to afford products in good yields at room temperature. DFT studies on the mechanism support the occurrence of a catalytic cycle involving transmetalation of the alkyl zinc halide to NiI followed by oxidative addition of the haloarene and C? C reductive elimination. 相似文献
944.
磷酸铝镍介孔催化材料的低热固相合成及形成机理 总被引:3,自引:0,他引:3
以十六烷基三甲基溴化铵为模板,通过二水磷酸二氢钠、六水氯化铝与六水氯化镍的固相反应直接合成了磷酸铝镍(NiAlPO)介孔材料。用X-射线衍射、高分辨透射电镜、N2脱附-吸附、红外光谱仪等分析技术对材料进行了物相与表面织构表征,通过电感耦合等离子发射光谱仪对材料的元素组成进行分析;探讨了磷酸铝镍介孔材料的形成机理。结果表明,金属镍已进入了磷酸铝骨架,镍的含量为5.15wt%;所得介孔材料呈蠕虫状、无定形的六面体结构;其BET比表面积为157.3 m2·g-1,孔径分布中心为3.65和5.3 nm。P(Al)-O-Ni键伸缩振动所产生的吸收峰为983.7 cm-1。 相似文献
945.
946.
Kaoru Honda Jaeheung Cho Prof. Dr. Takahiro Matsumoto Dr. Jungyun Roh Hideki Furutachi Dr. Takehiko Tosha Dr. Minoru Kubo Dr. Shuhei Fujinami Prof. Takashi Ogura Prof. Teizo Kitagawa Prof. Masatatsu Suzuki Prof. 《Angewandte Chemie (International ed. in English)》2009,48(18):3304-3307
In the nick(el) of time : Bis(μ‐oxo) dinickel(III) complexes 2 (see scheme), generated in the reaction of 1 with H2O2, are capable of hydroxylating the xylyl linker of the supporting ligand to give 3 . Kinetic studies reveal that hydroxylation proceeds by electrophilic aromatic substitution. The lower reactivity than the corresponding μ‐η2:η2‐peroxo dicopper(II) complexes can be attributed to unfavorable entropy effects.
947.
Meghan E. Doster Samuel A. Johnson Prof. Dr. 《Angewandte Chemie (International ed. in English)》2009,48(12):2185-2187
N, not NHC : A neutral, basic, strong σ‐donor nitrogen ancillary ligand with properties analogous to those of N‐heterocyclic carbenes (NHCs) was developed to aid in the oxidative additions of challenging substrates to late transition metals. Selective, room‐temperature C? F bond activation was observed with hexa‐, penta‐, and all three isomers of tetrafluorobenzene using a nickel(0) source in the presence of this donor.
948.
The antibandwidth problem consists of placing the vertices of a graph on a line in consecutive integer points in such a way that the minimum difference of adjacent vertices is maximised. The problem was originally introduced in [J.Y.-T. Leung, O. Vornberger, J.D. Witthoff, On some variants of the bandwidth minimisation problem, SIAM Journal of Computing 13 (1984) 650-667] in connection with the multiprocessor scheduling problems and can also be understood as a dual problem to the well-known bandwidth problem, as a special radiocolouring problem or as a variant of obnoxious facility location problems. The antibandwidth problem is NP-hard, there are a few classes of graphs with polynomial time complexities. Exact results for nontrivial graphs are very rare. Miller and Pritikin [Z. Miller, D. Pritikin, On the separation number of a graph, Networks 19 (1989) 651-666] showed tight bounds for the two-dimensional meshes and hypercubes. We solve the antibandwidth problem precisely for two-dimensional meshes, tori and estimate the antibandwidth value for hypercubes up to the third-order term. The cyclic antibandwidth problem is to embed an n-vertex graph into the cycle Cn, such that the minimum distance (measured in the cycle) of adjacent vertices is maximised. This is a natural extension of the antibandwidth problem or a dual problem to the cyclic bandwidth problem. We start investigating this invariant for typical graphs and prove basic facts and exact results for the same product graphs as for the antibandwidth. 相似文献
949.
The Lamm equation is a fundamental differential equation in analytical ultracentrifugation, for describing the transport of solutes in an ultracentrifuge cell. In this article, we present a characteristic finite element method with local mesh refinements for solving the Lamm equation. The numerical method is mass‐conservative by design and allows relatively large time steps to be used. Numerical experiments indicate that the numerical solutions are oscillation‐free in the region near the cell bottom, where mass build up and large concentration gradients occur. Positivity of solutions is also well kept. © 2008 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2009 相似文献
950.
Beckman RA Moreland D Louise-May S Humblet C 《Journal of computer-aided molecular design》2006,20(5):263-279
Nuclear magnetic resonance (NMR) provides structural and dynamic information reflecting an average, often non-linear, of multiple solution-state conformations. Therefore, a single optimized structure derived from NMR refinement may be misleading if the NMR data actually result from averaging of distinct conformers. It is hypothesized that a conformational ensemble generated by a valid molecular dynamics (MD) simulation should be able to improve agreement with the NMR data set compared with the single optimized starting structure. Using a model system consisting of two sequence-related self-complementary ribonucleotide octamers for which NMR data was available, 0.3 ns particle mesh Ewald MD simulations were performed in the AMBER force field in the presence of explicit water and counterions. Agreement of the averaged properties of the molecular dynamics ensembles with NMR data such as homonuclear proton nuclear Overhauser effect (NOE)-based distance constraints, homonuclear proton and heteronuclear 1H–31P coupling constant (J) data, and qualitative NMR information on hydrogen bond occupancy, was systematically assessed. Despite the short length of the simulation, the ensemble generated from it agreed with the NMR experimental constraints more completely than the single optimized NMR structure. This suggests that short unrestrained MD simulations may be of utility in interpreting NMR results. As expected, a 0.5 ns simulation utilizing a distance dependent dielectric did not improve agreement with the NMR data, consistent with its inferior exploration of conformational space as assessed by 2-D RMSD plots. Thus, ability to rapidly improve agreement with NMR constraints may be a sensitive diagnostic of the MD methods themselves. 相似文献