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991.
992.
A single-drop microextraction (SDME) procedure with a modified microsyringe was developed for the analysis of six organophosphorus pesticides (OPPs) in water. Microsyringe was modified by attaching a 2-mm cone onto the needle tip end. The conditions affecting SDME performance including microextraction solvent, stirring speed, extraction time, ionic strength and sample pH were optimized. Under the optimized conditions, the linear ranges of the SDME with ethion as internal standard were 0.05–50 μg L?1 (except for dimethoate 5–5,000 μg L?1) and limits of detection (LOD) were 0.012–0.020 μg L?1 (except for dimethoate 0.45 μg L?1). Recoveries of six pesticides were in the range of 70.6–107.5 % with relative standard deviation lower than 6.0 %. The modified method is simple, rapid and sensitive, and acceptable in the analysis of OPPs pesticides in water samples. 相似文献
993.
Synthesis of a Trisaccharide Related to the Cytotoxic Triterpenoid Saponins Isolated from the Bark of Albizia procera 下载免费PDF全文
Qing‐Chao Liu Tian‐Tian Guo Cong Zhao Jing Sun Wen‐Hong Li 《Helvetica chimica acta》2014,97(3):361-368
Chemical synthesis of a trisaccharide related to the cytotoxic triterpenoid saponins isolated from the bark of Albizia procera has been accomplished through a concise stepwise glycosylation strategy starting from commercially available D ‐xylose, 2‐acetamido‐2‐deoxy‐D ‐glucose and L ‐arabinose. The target trisaccharide was designed with a 4‐methoxyphenyl (MP) aglycone to extend the scope of conversion to suitable glycoconjugates via selective removal of 4‐methoxyphenyl (MP) group. An unexpected phenomenon, i.e., the arabinosyl residue assumed the 1C4 conformation instead of the typical 4C1 form, was observed. Deprotection could restore the normal conformation. 相似文献
994.
Tian‐hao Huang Ying‐hui Wang Zhi‐hui Kang Jin‐bo Yao Ran Lu Han‐zhuang Zhang 《Photochemistry and photobiology》2014,90(1):29-34
The effects of π‐spacer and electron donor groups on the photophysical behaviors of fluorenone‐based linear conjugated oligomers have been systemically investigated. Solvent‐dependent steady‐state measurements exhibit that the fluorene vinylene (FV) spacer and the electron‐donating ability of donor group are able to modulate the spectral features of oligomers and the fluorescence quantum yield could decrease with the increasing of the solvent polarity. Meanwhile, quantum chemical calculation simulates their absorption spectra, and analyzes their electron transition components simultaneously. The transient absorption measurements focus on the photoexcitation dynamics of these oligomers in the toluene solution, which show that an intramolecular charge transfer state exists in the relaxation process of excited states, and its generation process could accelerate with the introduction of FV spacer and the enhancement of donor strength. 相似文献
995.
A series of luminescent ion exchanged zeolite are synthesized by introducing various ions into NaY zeolite. Monometal ion (Eu3+, Tb3+, Ce3+, Y3+, Zn2+, Cd2+, Cu2+) exchanged zeolite, rare‐earth ion (Eu3+, Tb3+, Ce3+) exchanged zeolite modified with Y3+ and rare‐earth ion (Eu3+, Tb3+, Ce3+) exchanged zeolite modified with Zn2+ are discussed here. The resulting materials are characterized by Fourier transform infrared spectrum radiometer (FTIR), XRD, scanning electronic microscope (SEM), PLE, PL and luminescence lifetime measurements. The photoluminescence spectrum of NaY indicates that emission band of host matrix exhibits a blueshift of about 70 nm after monometal ion exchange process. The results show that transition metal ion exchanged zeolites possess a similar emission band due to dominant host luminescence. A variety of luminescence phenomenon of rare‐earth ion broadens the application of zeolite as a luminescent host. The Eu3+ ion exchanged zeolite shows white light luminescence with a great application value and Ce3+ exchanged zeolite steadily exhibits its characteristic luminescence in ultraviolet region no matter in monometal ion exchanged zeolite or bimetal ions exchanged zeolite. 相似文献
996.
Chemoselective hydrogenation of various aldehydes and ketones with methylamine borane (MeAB) in neat water was investigated. MeAB is suitable for green organic reactions, for MeAB is a nontoxic, environmentally benign, and easily handled reagent. Aldehydes were selectively and rapidly hydrogenated in excellent yields (86–97%) for 30 min, but hydrogenation of aromatic ketones needed over 20 h at room temperature because of their poor water solubility and steric hindrance. Thus we investigated polyethylene glycol (PEG400) and acidic cation-exchange D072 resin as catalysts to accelerate the hydrogenation reaction of aromatic ketones and achieved excellent yields within several hours. PEG 400 and D072 resin are both suitable for green organic reactions. The D072 resin was reused up to four times without any significance loss in activity. 相似文献
997.
998.
Hong Wu Xuecui WangBing Liu Yueling LiuShanshan Li Jusheng LuJiuying Tian Wenfeng ZhaoZonghui Yang 《Spectrochimica Acta Part B: Atomic Spectroscopy》2011,66(1):74-80
A new method was developed for the simultaneous speciation of inorganic arsenic and antimony in water by on-line solid-phase extraction coupled with hydride generation-double channel atomic fluorescence spectrometry (HG-DC-AFS). The speciation scheme involved the on-line formation and retention of the ammonium pyrrolidine dithiocarbamate complexes of As(III) and Sb(III) on a single-walled carbon nanotubes packed micro-column, followed by on-line elution and simultaneous detection of As(III) and Sb(III) by HG-DC-AFS; the total As and total Sb were determined by the same protocol after As(V) and Sb(V) were reduced by thiourea, with As(V) and Sb(V) concentrations obtained by subtraction. Various experimental parameters affecting the on-line solid-phase extraction and determination of the analytes species have been investigated in detail. With 180 s preconcentration time, the enrichment factors were found to be 25.4 for As(III) and 24.6 for Sb(III), with the limits of detection (LODs) of 3.8 ng L− 1 for As(III) and 2.1 ng L− 1 for Sb(III). The precisions (RSD) for five replicate measurements of 0.5 μg L−1 of As(III) and 0.2 μg L−1 of Sb(III) were 4.2 and 4.8%, respectively. The developed method was validated by the analysis of standard reference materials (NIST SRM 1640a), and was applied to the speciation of inorganic As and Sb in natural water samples. 相似文献
999.
采用水热反应合成了有机-无机杂化的Keggin型配合物(C12H9N2)3[PMo12O40],并通过X-射线单晶衍射对其结构进行了分析。该配合物为正交晶系P212121空间群,晶胞参数为a=1.20800(1)nm,b=2.10108(4)nm,c=2.24234(5)nm。配合物包含了孤立的Keggin型[PMo1... 相似文献
1000.