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161.
162.
Haoshuang Gu Yongming Hu Hao Wang Xiangrong Yang Zhenglong Hu Ying Yuan Jin You 《Journal of Sol-Gel Science and Technology》2007,42(3):293-297
Single crystalline nanowires of lead titanate (PbTiO3) were fabricated by hydrothermal method at 200°C using lead acetate and n-tetrabutyl titanate as starting materials, where sodium hydroxide was served as a mineralizer. Crystalline phases, microstructure
and optical properties of PbTiO3 nanowires were investigated. The PbTiO3 nanowires were uniform and continuous along the long axis, and were composed of single crystalline PbTiO3 with a tetragonal perovskite structure. The diameter of a single nanowire was around 12 nm and the length reached up to 3 μm.
The chemical composition of the samples and the valence states of elements were determined by X-ray photoelectron spectroscopy
(XPS). The ultraviolet/visible absorption spectroscopic investigation suggested that the absorption edge of optical transition
of the first excitonic state occurred at around 320 nm. A blue-green light emission peaking at about 471 nm (2.63 eV) is observed
at room temperature, and the intensity of this emission increased with increasing excitation wavelength. Oxygen vacancies
are responsible for the light emission of PbTiO3 nanowires. 相似文献
163.
K. V. Zaitsev S. S. Karlov M. V. Zabalov A. V. Churakov G. S. Zaitseva D. A. Lemenovskii 《Russian Chemical Bulletin》2005,54(12):2831-2840
Titanatrane CpTi(OCH(CH3)CH2)3N (3) was prepared by the reaction of CpTiCl3 with N(CH2CH(CH3)OH)3 in the presence of triethylamine. The reaction of CpTi(OMe)3 (8) with N(CH2CH2OH)2(CH2CHPhOH), erythro-N(CH2CH2OH)2(CHPhCHPhOH), and N(CH2CH2OH)2(CH2CPh2OH) gave cyclopentadienyltitanatranes 12–14. Compound 8 reacts with threo-N(CH2CH2OH)2(CHPhCHPhOH) to give a mixture of threo-CpTi(OCH2CH2)2(OCHPhCHPh)N and threo-MeOTi(OCH2CH2)2(OCHPhCHPh)N. Slow hydrolysis of the latter product gave threo-[Ti3O(OMe){(OCH2CH2)2− (OCHPhCHPh)N} 3]2, which was studied by X-ray diffraction analysis. The crystal structures of 3 and 12 were also determined by X-ray diffraction analysis. The titanium coordination polyhedron in these complexes is a distorted
trigonal bipyramid in which the equatorial positions are occupied by three oxygen atoms and the axial positions contain the
N atom and the Cp group. The titanium—nitrogen distances (2.313(2), 2.291(2) Å in two independent molecules of 3 and 2.271(2) Å in compound 12) confirm the presence of Ti←N transannular interaction.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2736–2744, December, 2005. 相似文献
164.
Paavo?Mansikkam?ki Manu?Lahtinen Kari?RissanenEmail author 《Cellulose (London, England)》2005,12(3):233-242
The completeness of mercerisation can be evaluated by investigating the changes in the crystalline regions of cellulose from
cellulose I (C-I) to cellulose II (C-II) by the X-ray powder diffraction method. Mercerisation experiments in four different
solution systems: ethanol/water, acetone, DMSO and xylene, are reported. Also the effect of some additives, external pressure,
treatment time and alkalisation temperature were studied. In two-phase solvent systems, structural changes of cellulose crystallites
depended primarily on the distribution and solubility of sodium hydroxide in the solvent phases. The sodium hydroxide concentration
in the hydrophilic phase must exceed 7–8 w/w-% before complete crystal change from C-I to C-II can occur. The precipitation
of sodium hydroxide due to high concentration prevents the successful use of one-phase ethanol/water system in slurry process.
On the contrary, the 2-propanol/water/sodium hydroxide system separates into two layers; to the water-rich lower layer and
the 2-propanol-rich upper layer, where the sodium hydroxide remains mainly in the water-rich lower layer. This prevents the
precipitation of sodium hydroxide and promotes the alkalisation of cellulose. Ammonium chloride and ammonium hydroxide clearly
had a positive effect by promoting the crystal changes, however, the urea concentration used in this study was obviously too
small. In the advantageous two-phase 2-propanol/water systems, the alkalisation time was only 15 min when the treatment temperature
was kept between 0 and 10 °C. Reduced external pressure was found to have a small but still detectable positive effect on
cellulose alkalisation while over-pressure prevented crystal changes. 相似文献
165.
On Calcium Bromated and Iodates – Crystal Structure, X-Ray, IR and Raman Spectroscopical and Thermoanalytical Investigations The phase relationships (and both decomposition and disproportionation)of bromates and iodates of alkaline earth metals are studied by means of thermal analyses (DTA, DSC, TG) and (high-temperature) X-Ray, IR-, and (high-temperature) Raman spectroscopic measurements. The following compounds have been established: Ca(IO3)2 · 6 H2O oF 216, the isotypic Ca(BrO3)2 · H2O and Ca(IO3)2 · H2O mP 48, Ca(IO3)2 I (Lautarit) mP 36, Ca(IO3)2 II and Ca(BrO3)2. The Crystal structure of Ca(IO3)2 · H2O (brüggenite) (space group P21/c, Z = 4) has been determined by single crystal X-ray diffraction (MoKα). The final R value for 3888 reflections with Io > 3σ1 is 0.0487. The structures of bromates and iodates of alkaline earth metals known so far are discussed with respect to the energetic (mode frequencies) and geometric (bond lengths) distortion of the XO3–ions as well as the strengths of H-bonds present in the respective hydrates. 相似文献
166.
Z. A. Starikova A. I. Yanovsky Yu. T. Struchkov S. V. Zubkov I. I. Seifullina 《Russian Chemical Bulletin》1996,45(9):2157-2162
The crystal structure of the product of the condensation of (salicylideneamino)nitroguanidine with salicylaldehyde on a Ni2+ ion template, K[Ni(C15H10N5O4)] · DMF, has been studied. It was established that a planar Ni complex, consisting of isolated [NiL]– anions and solvated [K+ · DMF] cations, is formed. The negative charge of the anion is localized mainly on the O atoms of the nitro group. The nitroguanidine fragment of the ligand occurs in the tautomeric form, which was not reported previously.Deceased in 1995Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2273–2277, September, 1996. 相似文献
167.
In order to study the influence of the side-chain orientation on the peptide backbone conformation we have synthesised the model dipeptides t-BuCO-l-Pro-(1S,2R)-c6Phe-NHMe and t-BuCO-l-Pro-(1R,2S)-c6Phe-NHMe, incorporating each enantiomer of the trans cyclohexane analogue of phenylalanine (trans-1-amino-2-phenylcyclohexanecarboxylic acid). The orientation of the aromatic side-chain determines the β-turn type accommodated by these peptides to the point that the (1S,2R)-c6Phe derivative retains the type I β-turn in the crystalline state, in contrast to the behaviour exhibited by the natural counterpart t-BuCO-l-Pro-l-Phe-NHMe. 相似文献
168.
I. I. Ponomarey O. V. Shishkin S. V. Lindeman Yu. V. Volkova 《Russian Chemical Bulletin》1996,45(7):1711-1713
An X-ray structural investigation of 6-chloro- 2,3-trimethylene-4- phe nylquinoli ne obtained by the reaction of 2-amino-5-chlorobenzophenone with cyclopentanone was carried out. At 20 °C, a = 23.750,b = 9,242, c = 14.018 A, = 112,68° space group (21c,Z = 8, 2647 reflections,R = 0.047 He five-membered ring has an envelope conformation Conjugation between the quinohne fragment and the phenyl substituent is significantly distorted dm to the rotation of the latter by -62.9°Translated fromIzvestiya Akademii Nauk. Seriva Khimicheskaya, No. 7, pp. 1800–1802, July, 1996. 相似文献
169.
I. V. Ukrainets A. A. Tkach L. V. Sidorenko O. V. Gorokhova 《Chemistry of Heterocyclic Compounds》2006,42(10):1301-1307
1-R-4-Hydroxy-2-oxo-1,2-dihydroquinoline-3-carboxylic acid anilides have been prepared. It has been shown experimentally that
these compounds are brominated by molecular bromine in glacial acetic acid at position 4 of the anilide fragment. The antitubercular
properties of the compounds synthesized are discussed.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1508–1516, October, 2006. 相似文献
170.
六十年代后期,在Hartree-Fock-Slater法的基础上,提出了Xα法[1].用于原子结构计算的Xα法与HF(Hartree-Fock)法的主要区别在于:用简单的统计平均交换势替代了HF法中计算最为困难的电子交换势,从而在保持较高理论严谨性和计算精确度的同时,大大减少了计算工作量,近年来获得了广泛的应用.我们尝试用经过适当修改的Xα方法,计算原子参数,解决分子结构中的某些问题.用原子参数解决分子问题,历来是化学和物理工作者常用的方法.本工作的意图是引入一个比HF法简单的容易在微机上实现的某种表现原子参数的计算方法,提供… 相似文献