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991.
992.
A concise synthetic approach for constructing the oxapentacyclic framework of cortistatin A is described. The synthesis features a furan-oxyallyl [4 + 3] cycloaddition and double-intramolecular aldol reactions. In addition, an interesting core structure was obtained in 11 steps from furan by using our method. 相似文献
993.
Zhongchen Wu Konstantin Chingin Huanwen Chen Liang Zhu Bin Jia Renato Zenobi 《Analytical and bioanalytical chemistry》2010,397(4):1549-1556
The development of analytical techniques suitable for sensitive, high-throughput, and nondestructive food analysis has been
of increasing interest in recent years. In this study, mass-spectral fingerprints of various cheese products were rapidly
recorded in the mass range of m/z 50–300 Da without any sample pretreatment, using neutral desorption extractive electrospray ionization mass spectrometry
(ND-EESI-MS) in negative ion mode. The results demonstrate that both volatile and nonvolatile analytes on greasy cheese surfaces
can be directly sampled by a neutral desorption gas beam. The influence of the neutral desorption gas flow on the analyte
signal was systematically investigated. Under optimized experimental conditions, reproducible results were obtained using
ND-EESI-MS. Principal component analysis was applied to differentiate a total of 49 individual cheese samples (four different
types), which were purchased from three different supermarkets. All samples were successfully classified according to their
types; but distributors and sensory properties were not distinguishable from the spectra data. The principal components 2,
3, and 4 scores showed an excellent capacity of distinguishing types of cheese. Molecular markers of interest can be identified
using tandem mass spectrometry and matching the data with those from reference compounds. The experimental data show that
ND-EESI-MS is able to sensitively and directly detect analytes on greasy surfaces without chemical contamination, providing
a convenient method for high-throughput food analysis with a high degree of safety. 相似文献
994.
FAN Zhi GUO MinJie DONG Bin DIAO ChunHua JING ZuoLiang & CHEN Xin College of Sciences Tianjin University of Science Technology Tianjin China 《中国科学:化学》2010,(5)
The mono-modified β-cyclodextrin derivative,6-O-(4-aminobenzoyl)-β-cyclodextrin(1) ,was synthesized and characterized. We compared its self-assembling behavior with structurally related β-cyclodextrin derivative,6-O-(4-hydroxybenzoyl)-βcyclodextrin(2) ,in aqueous solution and in the solid state using NMR spectroscopy and single crystal X-ray structure analysis. The two complexes displayed different self-assembling behaviors.Complex 1 formed a head-to-tail helical columnar superstructure in which the substit... 相似文献
995.
The effects of β‐cyclodextrin containing silicone oligomer(CDS), as a synergistic agent, on the flame retardancy and mechanical properties of intumescent flame retardant polypropylene composites were studied by adding different amounts of CDS in intumescent flame retardants. The limiting oxygen index (LOI), UL‐94 test, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) were utilized to evaluate the synergistic effects of CDS in the composites. It was found that after a little amount of CDS partially replaced a charring‐foaming agent (CFA) in IFR, LOI values of the composites were enhanced and they obtained a UL‐94 V‐0 rating. IFR system containing 6.25wt% CDS presented the best flame retardancy in PP. The experimental results obtained from LOI and UL‐94, TGA, SEM, and mechanical properties indicated that the combination of CDS and CFA presents synergistic effects in flame retardancy, char formation, and mechanical properties of the composites. This is probably due to different structures of polyhydroxyl macromolecules (CDS and CFA), the existence of dimethyl silicone group in CDS, and the toughness of epoxy silicon chain in CDS. SEM results proved that the interfacial compatibility between IFR and PP was improved by CDS. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
996.
Fast quantitative detection of cocaine in beverages using nanoextractive electrospray ionization tandem mass spectrometry 总被引:1,自引:0,他引:1
Bin Hu Xuejiao Peng Shuiping Yang Haiwei Gu Huanwen Chen Yanfu Huan Tingting Zhang Xiaolin Qiao 《Journal of the American Society for Mass Spectrometry》2010,21(2):290-293
Without any sample pretreatment, effervescent beverage fluids were manually sprayed into the primary ion plume created by
using a nanoelectrospray ionization source for direct ionization, and the analyte ions of interest were guided into an ion
trap mass spectrometer for tandem mass analysis. Functional ingredients (e.g., vitamins, taurine, and caffeine, etc.) and
spiked impurity (e.g., cocaine) in various beverages, such as Red Bull energy drink, Coco-cola, and Pepsi samples were rapidly
identified within 1.5 s. The limit of detection was found to be 7 ∼ 15 fg (S/N = 3) for cocaine in different samples using the characteristic fragment (m/z 150) observed in the MS3 experiments. Typical relative standard deviation and recovery of this method were 6.9% ∼ 8.6% and 104% ∼ 108% for direct
analysis of three actual samples, showing that nanoextractive electrospray ionization tandem mass spectrometry is a useful
technique for fast screening cocaine presence in beverages. 相似文献
997.
Liu B Wang J Wang X Liu BM He LL Xu SK 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2010,77(5):1115-1121
The eight-coordinate (enH2)[YIII(pdta)(H2O)](2)·10H2O (en=ethylenediamine and H4pdta=1,3-propylenediamine-N,N,N',N'-tetraacetic acid) was synthesized, meanwhile its molecular and crystal structures were determined by single-crystal X-ray diffraction technology. The interaction between [Y(III)(pdta)(H2O)]2(2-) and bovine serum albumin (BSA) was investigated by UV-vis and fluorescence spectra. The results indicate that [YIII(pdta)(H2O)]2(2-) quenched effectively the intrinsic fluorescence of BSA via a static quenching process with the binding constant (Ka) of the order of 10(4). Meanwhile, the binding and damaging sites to BSA molecules were also estimated by synchronous fluorescence. Results indicate that the hydrophobic environments around Trp and Tyr residues were all slightly changed. The thermodynamic parameters (ΔG=-25.20 kJ mol(-1), ΔH=-26.57 kJ mol(-1) and ΔS=-4.58 J mol(-1) K(-1)) showed that the reaction was spontaneous and exothermic. What is more, both ΔH and ΔS were negative values indicated that hydrogen bond and Van der Waals forces were the predominant intermolecular forces between [YIII(pdta)(H2O)]2(2-) and BSA. 相似文献
998.
Yan Wu Gui‐Ge Hou Jian‐Ping Ma Yu‐Bin Dong 《Acta Crystallographica. Section C, Structural Chemistry》2010,66(6):m163-m165
The title molecular complex, [CoCl2(C22H18N6O)], features a novel 18‐membered Co‐containing metallocycle. The CoII atom lies in a fairly regular tetrahedral geometry defined by two imidazole N‐atom donors from one 2,5‐bis[3‐(1H‐1,3‐imidazol‐1‐ylmethyl)phenyl]‐1,3,4‐oxadiazole (L) ligand and two chloride anions. The coordinating orientation of the L ligand plays an important role in constructing the metallocycle complex. The complexes form a three‐dimensional supramolecular assembly via nonclassical C—H...Cl and C—H...N hydrogen bonds and π–π interactions. 相似文献
999.
1000.
液相色谱-氢化物发生-原子荧光联用同时测定洛克沙胂及其代谢物 总被引:4,自引:0,他引:4
利用液相色谱-氢化物发生-原子荧光联用技术同时检测5种砷形态化合物(亚砷酸、砷酸、一甲基胂酸、二甲基胂酸和洛克沙胂).结果表明,在梯度洗脱条件下,以C18反相柱作分离柱,含0.5 mmol/L四丁基溴化铵的NaH2PO4-CH3OH溶液为流动相,5种砷化合物得以完全分离;以20 g/L K2S2O8为氧化剂进行紫外消解,7% HCl为载流,20 g/L KBH4为还原剂,砷化合物形成最佳的原子荧光信号.5种砷化合物在一定的浓度范围内与荧光峰面积呈良好的线性关系; 检出限<10 μg/L; 加标回收率为81.4%~105.6%; 相对标准偏差RSD<4.0%.本方法适用于饲料、鸡粪、土壤和植物样品中洛克沙胂及其代谢物(亚砷酸、砷酸、一甲基胂酸和二甲基胂酸)的含量分析. 相似文献