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921.
We report on chiral-nematic mixtures containing viscous chiral dopants, composed of rigid rod-like chiral molecules, in order to solve the problem of backflow in the middle layers of the liquid crystal cells. During the study, the viscoelastic properties of the liquid crystal compositions have been optimised, as well as the helical twisting power of the chiral compounds, the anchoring energy and the pre-tilt angle of alignment materials, the ratio between the cell gap and the helical pitch (d/P0). After optimisation, we prepared test cells with low operating voltage – from 1.5 till 5.0 V, fast response time (τon + τoff) – less than 1 ms, wide operating temperature range from ?40°C till +100°C, and good thermal stability. It should be noted that the response time of the new electro-optical mode does not strongly depend on the cell gap, which is in contrast to other known operating modes. We have achieved rather linear than quadratic dependence of the response time when changing the thickness of the cell.  相似文献   
922.
The combined use of the anion of phenyl(2-pyridyl)ketone oxime (ppko(-)) and azides (N(3)(-)) in nickel(II) carboxylate chemistry has afforded two new Ni(II)(5) clusters, [Ni(5)(O(2)CR')(2)(N(3))(4)(ppko)(4)(MeOH)(4)] [R' = H (1), Me (2)]. The structurally unprecedented {Ni(5)(μ-N(3))(2)(μ(3)-N(3))(2)}(6+) cores of the two clusters are almost identical and contain the five Ni(II) atoms in a bowtie topology. Two N(3)(-) ions are end-on doubly bridging and the other two ions end-on triply bridging. The end-on μ(3)-N(3)(-) groups link the central Ni(II) atoms with the two peripheral metal ions on either side of the molecule, while the Ni···Ni bases of the triangles are each bridged by one end-on μ-N(3)(-) group. Variable-temperature, solid-state direct- (dc) and alternating-current (ac) magnetic susceptibility, and magnetization studies at 2.0 K were carried out on both complexes. The data indicate an overall ferromagnetic behavior and an S = 5 ground state for both compounds. The ac susceptibility studies on 1 reveal nonzero, frequency-dependent out-of-phase (χ(M)") signals at temperatures below ~3.5 K; complex 2 reveals no χ(M)" signals. However, single-crystal magnetization versus dc field scans at variable temperatures and variable sweep rates down to 0.04 K on 1 reveal no noticeable hysteresis loops, except very minor ones at 0.04 K assignable to weak intermolecular interactions propagated by nonclassical hydrogen bonds.  相似文献   
923.
Absorption spectra of closed-shell Na(2), Na(3) (+), Na(4), Na(5) (+), Na(6), Na(7) (+), and Na(8) clusters are calculated using a complex Bethe-Salpeter equation derived using a conserving linear response method. In the framework of a quasiparticle approach, we determine electron-hole correlations in the presence of an external field. The calculated results are in excellent agreement with experimental spectra, and some possible cluster geometries that occur in experiments are analyzed. The position and the broadening of the resonances in the spectra arise from a consistent treatment of the scattering and dephasing contributions in the linear response calculation. Comparison between the experimental and the theoretical results yields information about the cluster geometry, which is not accessible experimentally.  相似文献   
924.
The reactions of [Re(CO)6]+, [FeCp(CO)2CS]+ and [FeCp(CNPh)3]+ with the metallo nitrile ylides [M{C+=N–C(H)CO2Et}(CO)5] (M = Cr, W) and the chromio nitrile imine [Cr{C+=N–NH}(CO)5] (generated by mono‐α‐deprotonation of the parent isocyanide complexes) to give neutral 5‐metallated 1,3‐oxazolin‐ ( 1 ), 1,3‐thiazolin‐ ( 2 ), imidazolin‐ ( 3 , 4 ), 1,3,4‐oxdiazolin‐ ( 5 ), 1,3,4‐thiadiazolin‐ ( 6 ) and 1,3,4‐triazolin‐2‐ylidene ( 8 ) chromium and tungsten complexes represent the first all‐organometallic versions of Huisgen’s 1,3‐dipolar cycloadditions. The formation of 6 and 8 is accompanied by partial decomposition to (OC)5Cr–C≡N–FeCpL2 {L = CO ( 7 ), CNPh ( 9 )}. The structures of 4a and 5 have been characterized by X‐ray diffraction.  相似文献   
925.
We synthesized melemium hydrogensulfate H3C6N7(NH2)3(HSO4)3 by reaction of melem with 70 % sulfuric acid. The crystal structure was elucidated by single‐crystal XRD (P21/n (no. 14), Z = 4, a = 10.277(2), b = 14.921(3), c = 11.771(2) Å, β = 99.24(3)°, V = 1781.5(6) Å3). H3C6N7(NH2)3(HSO4)3 is the first compound displaying a triple protonation of melem., In this contribution an overview of accessible melemium sulfates depending on the concentration of sulfuric acid is given. Two additional melemium sulfates were identified this way.  相似文献   
926.
927.
The semirigid tridentate 8-(2-pyridinylmethylthio)quinoline ligand (Q1) is shown to form the structurally characterized transition metal complexes [Cu(Q1)Cl2] (1), [Co(Q1)(NO3)2] (2), [Cd(Q1)(NO3)2] (3), [Cd(Q1)I2] (4). [Cu(Q1)2](BF4)2·(H2O)2 (5), [Cu(Q1)2](ClO4)2·(CH3COCH3)2 (6), [Zn(Q1)2](ClO4)2(H2O)2 (7), [Cd2(Q1)2Br4] (8), [Ag2(Q1)2(ClO4)2] (9), and [Ag2(Q1)2(NO3)2] (10). Four types of structures have been observed: ML-type in complexes 14, in which the anions Cl, NO3 or I also participate in the coordination; ML2 type in complexes 57 without direct coordination of the anions BF4 or ClO4 and with more (Cu2+) or less (Zn2+) distorted bis-fac coordinated Q1; M2L2-type in complex 8, in which two Br ions act as bridges between two metal ions; and M2(μ-L)2-type in complexes 9 and 10, in which the ligand bridges two anion binding and Ag–Ag bonded ions. Depending on electron configuration and size, different coordination patterns are observed with the bonds from the metal ions to Npyridyl longer or shorter than those to Nquinoline. Typically Q1 acts as a facially coordinating tridentate chelate ligand except for the compounds 9 and 10 with low-coordinate silver(I). Except for 6 and 8, the complexes exhibit distinct constraining effects against both G(+) and G(-) bacteria. Complexes 1, 3, 4, 5, 7 have considerable antifungal activities and complexes 1, 5, 7, and 10 show selective effects to restrain certain botanic bacteria. Electrochemical studies show quasi-reversible reduction behavior for the copper(II) complexes 1, 5 and 6.  相似文献   
928.
A density functional investigation into differently substituted silylenes with respect to the first step in the addition to white phosphorus is presented. The investigations include dispersion corrections in the density functional treatment. They become sizable for the transition state geometries for the silylenes as they become increasingly substituted by bulky groups. Hence, dispersion corrections are essential for a quantum chemical treatment of real molecules using density functional theory. The different singlet–triplet energy separations of differently substituted silylenes were also investigated and compared with calculated activation barriers for the first step in the addition reaction.  相似文献   
929.
930.
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