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91.
单柱离子色谱法测定茶叶中草酸根和硫酸根的研究 总被引:1,自引:1,他引:1
本文研究单柱离子色谱分离测定茶叶中微量草酸根和硫酸根的方法。样品水浸泡,酸化液。上ShimParskIC-A_2柱分离,用2.0mmol·L ̄(-1)H-2C_8O_4/1.9mmol·L ̄(-1)Tri淋洗液洗脱,电导检测器检测,检测灵敏度为1.6S/cm,最低检出限0.05μg/mL;线性范围L;相对标准偏差1.06%;平均回收车98.72%97.88/。该法简便、快速、准确、灵敏、选择性好。 相似文献
92.
Tu‐Gen Xu Duan‐Jun Xu Jing‐Yun Wu Michael Y. Chiang 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(12):m615-m616
The title complex, {[Fe(C4H4O4)(H2O)4]}n, is an infinite polymeric compound bridged by the succinate dianion. Two carboxylate groups coordinate in a monodentate manner to the FeII atom, in a trans fashion, with an O—Fe—O bond angle of 175.72 (6)° and Fe—O distances of 2.0886 (14) and 2.1008 (15) Å. One of the uncoordinated carboxylate O atom forms an intramolecular hydrogen bond with a coordinated water molecule. Extensive hydrogen bonding between parallel polymeric complex chains results in a three‐dimensional supramolecular structure. 相似文献
93.
The single electron emission behaviors and characteristics from the well-defined quantized energy levels, corresponding to localized electronic states at the dome-structure tips, in single-walled carbon nanotubes (SWNTs) are investigated and illuminated by use of the energy level emission model in combination with the first-principles calculations on the electronic structures. Under the external electric field, the confined electrons are emitted simultaneously from each quantized energy level by virtue of the resonant tunneling effects. With increasing applied voltage, the emission current increases monotonically and exponentially up to the first peak value, and then steps into the increasing and decreasing "sawtoothlike" variations in sequence. The negative differential resistance or conductivity and the maximum current for SWNTs are simulated. The influences of localized electronic states and curvatures of the different closed tips on the single electron emission behaviors of SWNTs are evaluated and discussed. Also a few issues and applications relevant to electron emission of carbon nanotubes are addressed. 相似文献
94.
去溶温度对微波诱导等离子体原子吸收光谱法分析性能影响的研究 总被引:1,自引:0,他引:1
本文研究了超声雾化微波诱导等离子体原子吸收光谱法(UN-MIP-AAS)中,去溶温度对选择载气流量、微波前向功率等因素的影响,并定量考察了去溶效果。通过改善去溶条件,提高了UN-MIP-AAS的分析性能。 相似文献
95.
Zou Jianzhong Wu Yong Duan Chunyin Liu Yongjiang Xu Zheng 《Transition Metal Chemistry》1998,23(3):305-308
Three binuclear copper(II) complexes bridged by three different bridging ligands: μ-TPHA (terephthalato), μ-PHTA (phthalato)
and μ-TCB (tetracarboxylatobenzene) have been synthesized. The crystal structure of [{Cu(dipn)}2(μ-TPHA)](ClO4)2 where dipn = N-(3-aminopropyl)-1,3-propanediamine was solved at room temperature. The [{Cudipn}2(μ-TPHA)](ClO4)2 complex consists of a μ-terephthalato bridging binuclear copper(II) cationic unit and two non-coordinated perchlorate anions.
The TPHA ligand bridges in a bismonodentate fashion. The environment of the copper(II) ion is a distorted plane-square-planar coordination sphere. The magnetic
properties of the three complexes have been investigated in the 75–300 K range, and show that the geometry of the CuII atom is the important factor for magnetic interactions in the terephthalato bridging binuclear copper(II) complexes.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
96.
97.
Lu Zhong-Lin Duan Chun-Ying Tian Yu-Peng You Xiao-Zeng Fun Hoong-Kun Yip Boon-Chuan 《Transition Metal Chemistry》1997,22(6):549-552
The [Cu(tren)(Im)Cu(tren)](ClO4)3·MeCN complex [tren=tris(2-aminoethyl)amine; Im=imidazolate anion] has been synthesized and
characterized spectrally. The X-ray crystal structure analysis reveals that the imidazolate anion serves as a bridge to form
a noncentrosymmetric dimeric structure in the complex. The co-ordination geometry about each copper(II) ion is a distorted
trigonal bipyramid with three primary amine groups of the tren ligand forming the equatorial plane. The tertiary amine group
and the imidazolate anion are in the axial positions.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
98.
Four new 28‐noroleanane‐derived spirocyclic triterpenoids, compounds 1 – 4 , were isolated from the rhizomes of Phlomis umbrosa. Their structures were elucidated on the basis of 1D‐ and 2D‐NMR analyses, in combination with high‐resolution MS experiments. 相似文献
99.
Yong Wu Hui-Biao Liu Yong-Jiang Liu Chun-Ying Duan Jun Hu Zheng Hu 《Journal of inclusion phenomena and macrocyclic chemistry》2000,36(4):473-478
A new facile method of synthesis of calix[4]arene amide via the aminolysis of the calix[4]arene esters was reported. One ethyl ester of the compound (2) was aminolysized byn-butylamine. The crystal structure of compound (1)shows that one ethyl ester of compound (1) enters into thecavity of another compound (1) forming a long chainhost-guest supramolecule. From the 2D NMR data, the compound(1) does not assemble in THF or CHCl3 solution. The CH- interaction and crystallization energy might be theimportant driving forces for forming the self-assembledcalix[4]arene. 相似文献
100.
The lower singlet excited states for dimethylaminobenzophenone have been investigated as a function of the twisting motion with inclusion of solvent effects. Theoretical calculations have been performed using time-dependent density functional theory. The B3LYP and MPW1PW91 functionals with a 6-311+G(2d,p) basis set have been used to compute transition energies. The solvent effects have been described within the polarizable continuum model. Ground-state geometries are optimized using density functional theory with both B3LYP and MPW1PW91 functionals combined with 6-31G(d) basis sets. Vertical absorption energy calculations characterize the lower singlet excited states both in vacuum and in different kinds of solvents. A large redshift of the absorption maximum in the polar solvent suggests an intramolecular charge transfer character of the excited state. We have constructed the potential energy curves of two possible twisting motions of the excited states both in vacuum and in the polar solvent of acetonitrile: the twisting of only the dimethylamino group and the twisting of the dimethylaminophenyl group with respect to the benzoyl group. Both twisting processes predict the formation of the twisted intramolecular charge transfer state associated with the crossing of a low barrier. The presence of the polar solvent significantly changes the shape of the energy curves. Calculated emission energies for both the isolated and the solvated systems show a large Stokes shift between the absorption and fluorescence maxima. Two possible twisting motions produce similar fluorescence spectroscopic consequences. Our results including solvent effects explain the weak "dual-fluorescence" feature of dimethylaminobenzophenone, and imply that the two possible twisting motions may occur in the excited-state relaxation dynamics, but the twisting of the dimethylamino group seems to take place easier. 相似文献