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941.
Apffel A Yin H Hancock WS McManigill D Frenz J Wu SL 《Journal of chromatography. A》1999,832(1-2):149-163
A system is described which allows operation of a range of capillary based liquid phase separations including capillary electrophoresis, isocratic and gradient capillary electrochromatography, isocratic and gradient capillary liquid chromatography and electrically assisted gradient capillary liquid chromatography. The system was coupled to electrospray ionization mass spectrometry in the electrically assisted capillary liquid chromatography mode to investigate the effect of applied voltage on the selectivity in peptide mapping separations. Analyses were performed on tryptic digests of recombinant human growth hormone and tissue plasminogen activator. The results show a small but useful effect on selectivity that can be used to fine tune specific separations. 相似文献
942.
The photostimulated reaction of halonaphthalene with a series of carbanions derived from,propionic acid derivatives in liquid ammonia led to the naphthylation at a-carbon of the carbanions inan isolated yield ranging from 25% to 86%.In all cases,the dehalonaphthalenes were found to,be by-products and the reaction was inhibited by p-dinitrobenzere.An electron transfer from thecarbanion to the halonaphthalene followed by ejection of halogen led to naphtbyl radical,as predictedby comparing the LUMOs of the carbanions and the halonaphthalenes,was involved in the process.Absence of the alkylnaphthalene and 1,2-dinaphthylalkane in the products indicates the smoothelectron transfer between(Naph-Nu)~+ and Naph-X.C-vs.O-naphthylation is fully addressed interms of MNDO calculations and acid-base principle. 相似文献
943.
Upper-critical-solution-temperature (UCST) behavior in a ternary blend of poly(2,6-dimethyl-1,4-phenylene oxide), poly(4-methyl
styrene), and polystyrene is reported. The as-cast ternary blend is immiscible at ambient conditions and comprises two different
phases, and, however, turns into a miscible system above the “clarity point” ranging from 160 to 300 °C for different ternary
compositions. The maximum clarity point is labeled as the UCST for the ternary system, which is about 295 °C. Above the clarity
point, the originally immiscible ternary blend turned into one miscible phase. Owing to the thermodynamic UCST behavior and
kinetic hindrance, the immiscible ternary polymer blend can be locked into a pseudo-miscible state if it is heated to a temperature
above the clarity point followed by a rapid-cooling processing scheme. The quenched ternary blend can remain in a pseudo-miscible
state as long as the service temperature does not exceed the glass-transition temperature of the blend.
Received: 17 July 2001 Accepted: 3 October 2001 相似文献
944.
DFT study on the geometric, electronic structure and Raman spectra of 5,15-diphenylporphine 总被引:1,自引:0,他引:1
Zhang YH Li ZY Wu Y Zhu YZ Zheng JY 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,62(1-3):83-91
The ground state geometric, electronic structure and Raman spectra of 5,15-diphenylporphine (H(2)DPP) have been studied using B3LYP/6-31G(d) method and compared with that of well-studied free base porphine (H(2)P) and meso-tetraphenylporphine (H(2)TPP). Calculation shows that 5,15-substitution causes remarkable in-plane distortion, whereas the resulting out-of-plane distortion is negligible. The calculated electronic structure of H(2)DPP is consistent with the absorption spectra compared with H(2)P and H(2)TPP. The calculated vibrational frequencies of H(2)DPP scaled with a single factor of 0.971 agree well with experimental data (the rms error is 8.0 cm(-1)). The assignment of experimental Raman bands of H(2)DPP was discussed on the basis of theoretical calculation and the comparison with that of H(2)P and H(2)TPP. The splitting of some vibrational modes involving the motion of C(m) atom, such as nu(1), nu(8), and nu(10), was observed and was attributed to the diversification of the environment around C(m) atoms. As the shift of absorption peaks, the shift of some structure-sensitive Raman bands of H(2)DPP form that of H(2)TPP and H(2)P was attributed to the in-plane nuclear reorganization (IPNR) induced by phenyl-substitution, though the contribution of nonplanarity mechanism could not be excluded completely. 相似文献
945.
New solid-gas metathetical synthesis of binary metal polysulfides and sulfides at intermediate temperatures: utilization of boron sulfides 总被引:1,自引:0,他引:1
A new simple synthetic method for binary metal polysulfides and sulfides was developed by utilizing an in situ formation of boron sulfides and their subsequent reactions with metal-source oxides in a closed container at intermediate temperatures above 350 degrees C at which the boron sulfides react in a gaseous form. The versatility of the new method is demonstrated with oxides of various transition metals (Ti, V, Mn, Fe, Ni, Nb, Mo, Ru, and W) and rare-earth metals (Y, Ce, Nd, Sm, Eu, Tb, and Er) as starting materials that exhibit different chemical characteristics. Regardless of the oxidation states of metals in the starting materials, the sulfidation reactions occurred quantitatively with stoichiometric mixtures of boron and sulfur, and within 24 h the reactions yielded pure products of TiS(2), TiS(3), VS(4), FeS(2), NiS(2), NbS(3), MoS(2), RuS(2), WS(2), Y(2)S(3), and RS(2) (R = Ce, Nd, Sm, Eu, Tb, and Er) which were the thermodynamically stable phases under the reaction conditions. The scope and implications of the new sulfidation method are also discussed. 相似文献
946.
LIU Si-Min WU Xiao-Jun YAO Jun-Hua WU Cheng-Tai 《有机化学》2003,23(Z1):261-262
Non-covalent attractive forces are commonly employed in biological systems to drive the assembly of highly orga nized supramolecular entities from relatively simple subunits. 相似文献
947.
玉米叶片残体腐解过程的傅里叶变换红外光谱研究 总被引:10,自引:2,他引:10
采用傅里叶变换红外光谱对玉米植株叶片残体腐解过程进行了研究。结果表明,随着玉米叶片残体腐解的进行,羟基,酮碳基,甲基,在和次甲基的含量逐渐降收据 的含量增加。 相似文献
948.
Xin-Jian Lei Fei-Long Jiang Da-Xu Wu Mac-Chun Hong Zhi-Ying Huang Han-Qin Liu 《中国化学》1993,11(1):40-44
[V_2(μ-S_2)_2(S_2CNEt_2)_4].2CH_3Cl was synthesized by the reaction of NaS_2CNEt_2,Li_2S andVOCl_3 at room temperature.Crystal data:M=1061.3,space group Pbca,with the orthorhombicparameters:a=20.123(3),b=20.485(4),c=10.911(3),V=4497.7,Z=4,D_c=1.57g/cm~3,Mo Kσradiation(λ=0.71069()?),μ=13.2 cm~(-1),F(000)=2168.Final R=0.041 and R_w=0.047 for 2288 ob-served reflections with I>3σ(1).The coordination sphere of each V atom in title compound is a dis-torted tetragonal prism composed of two bidentate dithiocarbamate and two S_(2~((2-)) ligands.The V—Vdistance is 2.890 while the V—S distances fall in the range of 2.422—2.505. 相似文献
949.
950.
With the accelerated accumulation of genomic sequence data, there is a pressing need to develop computational methods and advanced bioinformatics infrastructure for reliable and large-scale protein annotation and biological knowledge discovery. The Protein Information Resource (PIR) provides an integrated public resource of protein informatics to support genomic and proteomic research. PIR produces the Protein Sequence Database of functionally annotated protein sequences. The annotation problems are addressed by a classification-driven and rule-based method with evidence attribution, coupled with an integrated knowledge base system being developed. The approach allows sensitive identification, consistent and rich annotation, and systematic detection of annotation errors, as well as distinction of experimentally verified and computationally predicted features. The knowledge base consists of two new databases, sequence analysis tools, and graphical interfaces. PIR-NREF, a non-redundant reference database, provides a timely and comprehensive collection of all protein sequences, totaling more than 1,000,000 entries. iProClass, an integrated database of protein family, function, and structure information, provides extensive value-added features for about 830,000 proteins with rich links to over 50 molecular databases. This paper describes our approach to protein functional annotation with case studies and examines common identification errors. It also illustrates that data integration in PIR supports exploration of protein relationships and may reveal protein functional associations beyond sequence homology. 相似文献