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971.
Four new methyloxorhenium(V) compounds were synthesized with these tridentate chelating ligands: 2-mercaptoethyl sulfide (abbreviated HSSSH), 2-mercaptoethyl ether (HSOSH), thioldiglycolic acid (HOSOH), and 2-(salicylideneamino)benzoic acid (HONOH). Their reactions with MeReO(3) under suitable conditions led to these products: MeReO(SSS), 1, MeReO(SOS), 2, MeReO(OSO)(PAr(3)), 3, and MeReO(ONO)(PPh(3)), 4. These compounds were characterized spectroscopically and crystallographically. Compounds 1 and 2 have a five-coordinate distorted square pyramidal geometry about rhenium, whereas 3 and 4 are six-coordinate compounds with distorted octahedral structures. The kinetics of oxidation of 2 and 3 in chloroform with pyridine N-oxides follow different patterns. The oxidation of 2 shows first-order dependences on the concentrations of 2 and the ring-substituted pyridine N-oxide. The Hammett analysis of the rate constants gives a remarkably large and negative reaction constant, rho = -4.6. The rate of oxidation of 3 does not depend on the concentration or the identity of the pyridine N-oxide, but it is directly proportional to the concentration of water, both an accidental and then a deliberate cosolvent. The mechanistic differences have been interpreted as reflecting the different steric demands of five- and six-coordinate rhenium compounds. 相似文献
972.
Zun Yao Wang Xue Dong Gong Jin Shan Li He Ming Xiao 《International journal of quantum chemistry》2002,87(4):192-197
The reaction mechanism of F2+Cl2→2ClF has been investigated with the density functional theory at the B3LYP/6‐311G* level. Six transition states have been found for the three possible reaction paths and verified by the normal mode vibrational and IRC analyses. Ab initio MP2/6‐311G* geometry optimizations and CCSD(T)/6‐311G(2df)//MP2/6‐311G* single‐point energy calculations have been performed for comparison. It is found that when the F2 (or Cl2) molecule decomposes into atoms first and then the F (or Cl) atom reacts with the molecule Cl2 (or F2) nearly along the molecular axis, the energy barrier is very low. The calculated energy barrier of F attacking Cl2 is zero and that of Cl attacking F2 is only 15.57 kJ?mol?1 at the B3LYP level. However, the calculated dissociation energies of F2 and Cl2 are as high as 145.40 and 192.48 kJ?mol?1, respectively. When the reaction proceeds through a bimolecular reaction mechanism, two four‐center transition states are obtained and the lower energy barrier is 218.69 kJ?mol?1. Therefore, the title reaction F2+Cl2→2ClF is most probably initiated from the atomization of the F2 molecule and terminated by the reaction of F attacking Cl2 nearly along the Cl? Cl bond. MP2 calculations lead to the same conclusion, but the geometry of TS and the energy barrier are somewhat different. © 2002 John Wiley & Sons, Inc. Int J Quantum Chem, 2002 相似文献
973.
We report on the application of the time-temperature superposition principle to supramolecular bond-rupture forces on the single-molecule level. The construction of force-loading rate master curves using atomic force microscopy (AFM)-based single-molecule force spectroscopy (SMFS) experiments carried out in situ at different temperatures allows one to extend the limited range of the experimentally accessible loading rates and hence to cross from thermodynamic nonequilibrium to quasi-equilibrium states. The approach is demonstrated for quadruple H-bonded ureido-4[1H]-pyrimidinone (UPy) moieties studied by variable-temperature SMFS in organic media. The unbinding forces of single quadruple H-bonding (UPy)2 complexes, which were identified based on a polymeric spacer strategy, were found to depend on the loading rate in the range of 5 nN/s to 500 nN/s at 301 K in hexadecane. By contrast, these rupture forces were independent of the loading rate from 5 to 200 nN/s at 330 K. These results indicate that the unbinding behavior of individual supramolecular complexes can be directly probed under both thermodynamic nonequilibrium and quasi-equilibrium conditions. On the basis of the time-temperature superposition principle, a master curve was constructed for a reference temperature of 301 K, and the crossover force (from loading-rate independent to -dependent regimes) was determined as approximately 145 pN (at a loading rate of approximately 5.6 nN/s). This approach significantly broadens the accessible loading-rate range and hence provides access to fine details of potential energy landscape of supramolecular complexes based on SMFS experiments. 相似文献
974.
975.
阻抑动力学光度法测定痕量间二硝基苯 总被引:2,自引:1,他引:2
在盐酸介质中,痕量间二硝基苯能灵敏地阻抑Fe^3 催化高碘酸钾氧化孔雀绿的反应。研究了该阻抑反应的最佳条件及动力学参数,建立了测定痕量间二硝基苯的新方法,间二硝基苯的线性范围为0.0-10.0μg/L,检出限为1.8μg/L。该法灵敏、简便,选择性好,用于环境水样中间二硝基苯的测定,结果准确。 相似文献
976.
Aziridines and epoxides were reacted with diphenyl diselenide in the presence of a stoichiometric amount of (n-Bu)3P, respectively, giving β-amino- or β-hydroxy selenides in moderate to excellent yields under mild conditions. In the reactions the (n-Bu)3P might act as a reductant though it was a nucleophilic catalyst in other similar ring-opening reactions. 相似文献
977.
Xiancui Zhu Yuzhe Jiang Jun Chen Shaowu Wang Zeming Huang Shan Zhu Xu Zhao Wenrun Yue Jun Zhang Weikang Wu Xiangyang Zhong 《中国化学》2020,38(5):478-488
A series of dinuclear rare‐earth metal alkyl complexes {[μ‐η2:η1:η1‐3‐( L NCH)(CH2SiMe3)Ind]RE(CH2SiMe3)(THF)}2 ( L 1 = 2‐tBuC6H4, RE = Y, Gd, Dy, Er, Yb; L 2 = 2,4,6‐Me3C6H2, RE = Dy, Er; Ind = indolyl) and {[μ‐η2:η1:η1‐3‐( L NCH2)Ind]RE(CH2SiMe3)(THF)}2 ( L 1, RE = Y, Dy, Er, Yb; L 2, RE = Er, Yb) bearing 3‐arylamido functionalized indolyl ligands having diverse bonding modes with metal ions were synthesized either by the insertion reaction of the imino group to the RE—C bond or by the alkane elimination reaction. In the preparation of above complexes, rare‐earth metal alkyl complexes [μ‐η5:η1:η1‐3‐( L 2NCH)(CH2SiMe3)Ind]Gd(CH2SiMe3)(THF)}2 with a μ‐η5:η1:η1 coordination mode to the gadolinium ion and {[μ‐η3:η1:η1‐3‐( L 2NCH2)Ind]Dy(CH2SiMe3)(THF)}2 with a μ‐η3:η1:η1 coordination mode to the dysprosium ion were unexpectedly isolated. The reactions of 3‐( L 2N=CH)Ind with Er(CH2SiMe3)3(THF)2 at room temperature, generated a tetranuclear imino‐indolyl erbium intermediate {[μ‐η1:η1‐3‐( L 2N=CH)Ind]Er(CH2SiMe3)2(THF)}4, which can transform into the amido functionalized indolyl erbium complex in hot toluene. Moreover, the reactivities of the newly synthesized ytterbium complex with N‐heterocyclic compounds were investigated, affording the corresponding products of the mixed pyridyl‐indolyl, imidazolyl‐indolyl, and ortho‐metalated complexes. The yttrium complexes showed a high regioselectivity and steroselectivity for the isoprene polymerization with 1,4‐trans selectivity up to 91.7% and 1,4‐cis selectivity up to 96.1% in the presence of cocatalysts, respectively. 相似文献
978.
979.
A novel coordination polymer of [Ca(2-OPA)2(H2O)2]n (2-OPA-=2-oxo-1(4H)-pyridineacetate anion) was synthesized and characterized by elemental analysis, IR, TG and single crystal X-ray diffraction. The title complex crystallizes in orthorhombic with space group Pna21, a=0.799 96(16) nm, b=0.823 77(16) nm, c=2.415 3(5) nm, V=1.591 6(6) nm3, Z=4, R=0.030 3, wR=0.070 0. The Ca atom is eight-coordinated by six O atoms of four 2-OPA- ligands and two water molecules, and displays a dodecahedron coordination geometry. Each 2-OPA- ligand bridges two adjacent Ca atoms, forming a infinite chain along the a direction. The Ca…Ca distance is 0.4102 2(8)nm. A two-dimensional supramolecular framework is further constructed by the hydrogen bonds and the weak π-π interactions. The results of TG analysis show the chain structure of the title complex was stable under 297.5 ℃. CCDC: 251669. 相似文献
980.
采用液-液萃取结合GC/MS选择离子的方法,建立了人尿中8种合成麻醉镇痛剂的分析方法,讨论了回收率和检测限问题,并成功地用于实际尿样检测。 相似文献