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221.
Yi‐Zhen Tang Hao Sun Ya‐Ru Pan Xiu‐Mei Pan Rong‐Shun Wang 《International journal of quantum chemistry》2007,107(6):1495-1501
The mechanisms for the reaction of CH3S with NO2 are investigated at the QCISD(T)/6‐311++G(d,p)//B3LYP/6‐311++G(d,p) on both single and triple potential energy surfaces (PESs). The geometries, vibrational frequencies, and zero‐point energy (ZPE) correction of all stationary points involved in the title reaction are calculated at the B3LYP/6‐311++G(d,p) level. More accurate energies are obtained at the QCISD(T)/6‐311++G(d,p). The results show that 5 intermediates and 14 transition states are found. The reaction is more predominant on the single PES, while it is negligible on the triple PES. Without any barrier height for the whole process, the main channel of the reaction is to form CH3SONO and then dissociate to CH3SO+NO. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
222.
The crystallization processes of hydrated Mg-borates, boric, magnesium hydroxide and Mg-oxychloride from MgO-B2O3-18%MgCl2-H2O supersaturated solution at 20°C have been studied by kinetic method. The crystallization solid phases were characterized
by X-ray powder diffraction, IR spectra, thermal analysis and chemical analysis. The liquid-solid phase diagram of thermodynamic
nonequilibrium state has been given. In this phase diagram, there exist eight crystallization fields, boric acid(H3BO3), trigomagneborite(MgO · 3B2O3 · 7.5H2O, MgO · 3B2O3 · 7H2O), hungchaoite(MgO · 2B2O3 · 9H2O), inderite(2MgO · 3B2O3 · 15H2O), chloropinnoite(2MgO · 2B2O3 · MgCl2 · 14H2O), magnesium hydroxide(Mg(OH)2) and magnesium oxychloride (5Mg(OH)2 · MgCl2 · 8H2O). 相似文献
223.
Baeyer-Villiger单加氧酶在有机合成中的应用 总被引:3,自引:0,他引:3
综述了Baeyer-Villiger单加氧酶在有机合成中的应用.较之传统的化学反应, 氧化酶催化剂反应有较好的选择性、可控性和经济性. 环己酮加氧酶是一种还原型辅酶I (NADPH)依赖型氧化酶, 是最早被报道能够催化Baeyer-Villiger氧化的酶. 这些重要反应产生了合成化学家很感兴趣的扩环产物. 环己酮加氧酶也是有用的生物催化剂, 由于辅酶再生的问题已被工程菌克服了, 所以能像全细胞催化剂那样使用. 对酮包括杂环酮进行Baeyer-Villiger氧化和动态动力学拆分, 放大这种反应作为合成路线是很有前途的. 相似文献
224.
Paranemic crossover (PX) DNA is a four-stranded coaxial DNA complex containing a central dyad axis that relates two flanking parallel double helices. The strands are held together exclusively by Watson-Crick base pairing. The key feature of the structure is that the two adjacent parallel DNA double helices form crossovers at every point possible. Hence, reciprocal crossover points flank the central dyad axis at every major or minor groove separation. This motif has been modeled and characterized in an oligonucleotide system; a minor groove separation of five nucleotide pairs and major groove separations of six, seven, or eight nucleotide pairs produce stable PX DNA molecules; a major groove separation of 9 nucleotide pairs is possible at low concentrations. Every strand undergoes a crossover every helical repeat (11, 12, 13, or 14 nucleotides), but the structural period of each strand corresponds to two helical repeats (22, 24, 26, or 28 nucleotides). Nondenaturing gel electrophoresis shows that the molecules are stable, forming well-behaved complexes. PX DNA can be produced from closed dumbbells, demonstrating that the molecule is paranemic. Ferguson analysis indicates that the molecules are similar in shape to DNA double crossover molecules. Circular dichroism spectra are consistent with B-form DNA. Thermal transition profiles suggest a premelting transition in each of the molecules. Hydroxyl radical autofootprinting analysis confirms that there is a crossover point at each of the positions expected in the secondary structure. These molecules are generalized Holliday junctions. 相似文献
225.
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227.
Libera JA Cheng H Olvera de la Cruz M Bedzyk MJ 《The journal of physical chemistry. B》2005,109(48):23001-23007
We show an experimental approach for directly observing the condensation of polynucleotides and their electrolyte counterions at a liquid/solid interface. X-ray standing waves (XSW) generated by Bragg diffraction from a d = 20 nm Si/Mo multilayer substrate are used to measure the distinct distribution profiles of the polyanions and simple cations along the surface normal direction with subnanometer resolution. The 1D spatial sensitivity of this approach is enhanced by observing the XSW induced fluorescence modulations over multiple orders of Bragg peaks. We study the interesting divalent cation driven adsorption of anionic polynucleotides to anionic surfaces by exposing a hydroxyl-terminated silica surface to an aqueous solution with ZnCl2 and mercurated poly-uridylic acid (a synthetic RNA molecule). The in situ long-period XSW measurements are used to follow the evolution of both the Zn and Hg distribution profiles during the adsorption process. The conditions and physical mechanisms that govern the observed divalent cation adsorption and subsequent polynucleotide adsorption to an anionic surface are explained by a thermodynamic model that incorporates nonlinear electrostatic effects. 相似文献
228.
建立了用非水相体系高效毛细管电泳-紫外检测法同时测定苯甲酸和苯甲醛的新方法,考察了运行电压、非水相介质和电解质等因素的影响,在25℃下,以V(乙腈):V(碳酸丙烯酯)=1:1的混合液为溶剂,缓冲体系中含15mmol/L十六烷基三甲基溴化铵体积分数1%乙酸,重力进样30S,运行电压20kV,毛细管总长45cm有效长度30cm,φ75μm,检测波长285nm。苯甲酸线性范围为5~40μg/mL,线性方程为:Y=13.473ρ+13.336,相关系数r=0.9985,检出限为0.92μg/mL,RSD为3.8%。苯甲醛的线性范围75~1125μg/mL线性方程为:Y=5.2449ρ+564.01,相关系数r=0.9997,检出限为15.60μg/mL,RSD为3.5%。已用于经空气氧化后的苯甲醛中苯甲酸和苯甲醛的测定。 相似文献
229.
Nanocrystalline zirconium carbonitride (Zr‐C‐N) and zirconium oxide (ZrO2) films were deposited by chemical vapor deposition (CVD) of zirconium‐tetrakis‐diethylamide (Zr(NEt2)4) and ‐tert‐butyloxide (Zr(OBut)4), respectively. The films were deposited on iron substrates and characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS). The Zr‐C‐N films show blue, golden brown or bronze colours, with colour stability depending upon the precursor composition (pure metal amide or mixed with Et2NH). The deposition temperature showed no pronounced effect on the granular morphology of the Zr‐C‐N films. The XRD data of the films correspond to the formation of carbonitride phase whereas the XPS analyses revealed a strong surface oxidation and incorporation of oxygen in the film. The films deposited using a mixture of Zr(NEt2)4 and Et2NH showed higher N content, better adhesion and scratch resistance when compared to films obtained from the CVD of pure Zr(NEt2)4. Subject to the precursor composition and deposition temperature (550‐750 °C), the microhardness values of Zr‐C‐N films were found to be in the range 2.11‐5.65 GPa. For ZrO2 films, morphology and phase composition strongly depend on the deposition temperature. The CVD deposits obtained at 350 °C show tetragonal ZrO2 to be the only crystalline phase. Upon increasing the deposition temperature to 450 °C, a mixture of tetragonal and monoclinic modifications was formed with morphology made up of interwoven elongated grains. At higher temperatures (550 and 650 °C), pure monoclinic phase was obtained with facetted grains and developed texture. 相似文献
230.
The gas-phase proton affinity of the N-heterocyclic carbene, 1-ethyl-3-methylimidazol-2-ylidene, was determined to be 251.3 +/- 4 kcal/mol using the kinetic method, a value which makes the carbene one of the strongest bases reported thus far. Density functional theory calculations have been carried out at the B3LYP/6-31+G(d) level to compare the high experimental value with that estimated theoretically. Experimental results also show that two other N-heterocyclic carbenes with larger substituents have even higher proton affinities. [structure: see text] 相似文献