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991.
Well-defined perfluoroalkyl-terminated poly(glycerol methacrylate) (R F-PGMA) semitelechelics are prepared by atom transfer radical polymerization and copper(I)-catalyzed alkyne–azide cycloaddition reaction. R F-PGMA has a similar architecture as the well-studied perfluorinated poly(ethylene oxide) (R F-PEO) semitelechelics but bears two hydroxyl groups on each glycerol methacrylate unit. Because of the strong hydrophobic interaction of the perfluoroalkyl group, R F-PGMA semitelechelics self-associate to form core–corona spherical micelles in water above the critical micellization concentration (cmc) which depends on poly(glycerol methacrylate) (PGMA) content and temperature. For comparison, the R F-PEO semitelechelics with the same perfluoroalkyl terminal group as R F-PGMA are also prepared. The cmc values of R F-PGMA semitelechelics are found to increase with increasing temperature in water, which is opposite to the tendency of R F-PEO semitelechelics. According to the thermodynamic studies, the micellization process of R F-PGMA in aqueous solution is driven by both a negative enthalpy and an increase of entropy, whereas the micellization of R F-PEO is an entropy-driven process exhibiting a positive micellization enthalpy. This striking different behavior originates from intra-/intermolecular hydrogen bonds between the hydroxyl groups of the PGMA chains. These strong inter- and intramolecular hydrogen bonds between PGMA segments lead to a self-aggregation of R F-PGMA evident in temperature-dependent 1H and 19F NMR spectroscopy and dynamic light scattering measurements. 相似文献
992.
Hong Zheng Ning Lian Sui Wang Yuemei Cui Yunhui Zhai 《International journal of environmental analytical chemistry》2013,93(6):431-441
In this article, a new method that utilizes a diethyldithiocarbamate-modified nanometre TiO2 (TiO2–DDTC) as solid-phase extractant has been developed for simultaneous preconcentration of trace Cu(II), Pb(II), Zn(II), and Cd(II) prior to measurement by inductively coupled plasma atomic emission spectrometry (ICP-AES). The separation/preconcentration conditions of analytes, which include the effects of pH, sample flow rate and volume, elution conditions, and interfering ions on the recovery of the analytes, were investigated. At pH 5, the adsorption capacity of modified nanometre TiO2–DDTC was found to be 6.2, 19, 4.7, and 6.0?mg/g for Cu(II), Pb(II), Zn(II), and Cd(II), respectively. According to the definition of IUPAC, the detection limits (3σ) of this method for Cu(II), Pb(II), Zn(II), and Cd(II) were 0.41, 1.7, 0.39, and 0.52?ng/mL, respectively. The proposed method achieved satisfied results when applied to the determinations of trace Cu(II), Pb(II), Zn(II), and Cd(II) in biological and natural water samples. 相似文献
993.
使用近红外光谱分析方法测量培养后的胚胎培养液,结合偏最小二乘判别分析对胚胎发育潜能进行评价,鉴别具有妊娠能力与不具妊娠能力的胚胎。为了提高模型的判别能力,消除无信息变量对模型稳定性影响,分别采用基于蒙特卡罗的无信息变量消除法(MC-UVE)、竞争性自适应加权抽样法(CARS)与基于变量稳定性的竞争性自适应加权抽样法(SCARS),对光谱进行波长选择。结果表明,与采用全谱74%的正判率相比较,采用这3种波长选择方法,模型独立检验集的正判率分别提高至74.24%,77.12%与80.10%,建模使用变量数降至50以内。比较发现,SCARS的模型优化能力和稳定性均好于MC-UVE和CARS方法。采用近红外光谱结合化学计量学方法预测胚胎的发育潜能是可行的。 相似文献
994.
新型磺酸盐型Gemini表面活性剂的合成及其与聚合物相互作用 总被引:1,自引:0,他引:1
以溴代正烷烃、乙二胺、1,3-丙磺内酯合成了一系列新型磺酸盐型Gemini表面活性剂(SGS-8、SGS-10、SGS-12、SGS-14);采用IR、1H NMR及元素分析等手段对合成产物进行结构表征,并研究了其表面活性,采用等温滴定微量热技术、表面张力法和稳态荧光光谱法研究了SGS-12与聚丙烯酰胺(PAM)的相互作用规律及热力学参数。结果表明,合成的产物纯度较高,具有较低的cmc值和较好的表面活性;SGS-12/PAM混合体系的表面张力曲线和芘探针在体系中微极性的变化表明,二者发生相互作用且形成混合胶束;SGS-12与PAM结合是一个由焓驱动的自发过程,△H和△S均小于0,表明相互作用力以氢键和范德华力为主,合成产物在聚丙烯酰胺分子上的平均结合数为287。 相似文献
995.
Qihui Wang Zheng Hu Dandan Li Zhifeng Tu 《International journal of environmental analytical chemistry》2013,93(11):1289-1301
A chelating matrix prepared by immobilising folic acid on silica gel-bound amine phase was used as a new solid-phase extractant. This sorbent has been developed only for preconcentration of trace Pb(II) prior to determination by inductively coupled plasma atomic emission spectrometry (ICP-AES). Experimental conditions were investigated by batch and column procedures. The optimum pH value for the separation of Pb(II) on the new sorbent was 4.0. The adsorbed Pb(II) was quantitatively eluted by 2.0?cm3 of 0.5?mol?dm?3 of HCl. Common coexisting ions did not interfere with the separation and determination of Pb(II). The maximum static adsorption capacity of the sorbent under optimum conditions was found to be 69.23?mg?g?1 for Pb(II). The detection limit of the method defined by International Union of Pure and Applied Chemistry was 0.28?ng?cm?3. The relative standard deviation (RSD) of the method was lower than 2.0% (n?=?8). The developed method has been validated by analysing certified reference materials and successfully applied to the determination of Pb(II) in water samples with satisfactory results. 相似文献
996.
Hong Zheng Shuling Yang Jianchao Wang Wenfeng Sun 《International journal of environmental analytical chemistry》2013,93(11):1013-1023
A novel Rh(III)-imprinted amino-functionalised silica gel sorbent was prepared by a surface imprinting technique for preconcentration and separation of Rh(III) prior to its determination by inductively coupled plasma atomic emission spectrometry (ICP-AES). Compared with the traditional solid sorbents and non-imprinted polymer particles, the ion-imprinted polymers (IIPs) had higher adsorption capacity and selectivity for Rh(III). The maximum static adsorption capacity of the imprinted and non-imprinted sorbent for Rh(III) was 29.86?mg?g?1 and 11.23?mg?g?1, respectively. The imprinted Rh(III) was removed with 2?mL of 3% thiourea?+?2?mol?L?1 HCl. The obtained imprinted particles exhibited excellent selectivity and rapid kinetics process for Rh(III). The relatively selective factor (αr) values of Rh(III)/Ru(III), Rh(III)/Au(III), Rh(III)/Pt(IV), Rh(III)/Ir(IV), Rh(III)/Pd(II) were 26.7, 39.0 29.2, 28.1, 43.7, respectively, which were greater than 1. The detection limit (3σ) of the method was 0.26?µg?L?1. The relative standard deviation of the method was 1.79% for eight replicate determination of 10?µg of Rh3+ in 200?mL water sample. The method was validated by analysing standard reference material (GBW 07293), the results obtained is in good agreement with standard values. The developed method was also successfully applied to the determination of trace rhodium(III) in geological samples with satisfactory results. 相似文献
997.
Kongkai Zhu Junyan Lu Zhongjie Liang Xiangqian Kong Fei Ye Lu Jin Heji Geng Yong Chen Mingyue Zheng Hualiang Jiang Jun-Qian Li Cheng Luo 《Journal of computer-aided molecular design》2013,27(3):247-256
New Delhi metallo-β-lactamase-1 (NDM-1) has emerged as a major global threat to human health for its rapid rate of dissemination and ability to make pathogenic microbes resistant to almost all known β-lactam antibiotics. In addition, effective NDM-1 inhibitors have not been identified to date. In spite of the plethora of structural and kinetic data available, the accurate molecular characteristics of and details on the enzymatic reaction of NDM-1 hydrolyzing β-lactam antibiotics remain incompletely understood. In this study, a combined computational approach including molecular docking, molecular dynamics simulations and quantum mechanics/molecular mechanics calculations was performed to characterize the catalytic mechanism of meropenem catalyzed by NDM-1. The quantum mechanics/molecular mechanics results indicate that the ionized D124 is beneficial to the cleavage of the C–N bond within the β-lactam ring. Meanwhile, it is energetically favorable to form an intermediate if no water molecule coordinates to Zn2. Moreover, according to the molecular dynamics results, the conserved residue K211 plays a pivotal role in substrate binding and catalysis, which is quite consistent with previous mutagenesis data. Our study provides detailed insights into the catalytic mechanism of NDM-1 hydrolyzing meropenem β-lactam antibiotics and offers clues for the discovery of new antibiotics against NDM-1 positive strains in clinical studies. 相似文献
998.
Gadolinium(III)‐Hydroxy Ladders Trapped in Succinate Frameworks with Optimized Magnetocaloric Effect
Yan‐Cong Chen Fu‐Sheng Guo Prof. Dr. Yan‐Zhen Zheng Jun‐Liang Liu Ji‐Dong Leng Róbert Tarasenko Prof. Dr. Martin Orendáč Dr. Jan Prokleška Prof. Dr. Vladimír Sechovský Prof. Dr. Ming‐Liang Tong 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(40):13504-13510
Two kinds of inorganic gadolinium(III)‐hydroxy “ladders”, [2×n] and [3×n], were successfully trapped in succinate (suc) coordination polymers, [Gd2(OH)2(suc)2(H2O)]n ? 2n H2O ( 1 ) and [Gd6(OH)8(suc)5(H2O)2]n ? 4n H2O ( 2 ), respectively. Such coordination polymers could be regarded as alternating inorganic–organic hybrid materials with relatively high density. Magnetic and heat capacity studies reveal a large cryogenic magnetocaloric effect (MCE) in both compounds, namely (ΔH=70 kG) 42.8 J kg?1 K?1 for complex 1 and 48.0 J kg?1 K?1 for complex 2 . The effect of the high density is evident, which gives very large volumetric MCEs up to 120 and 144 mJ cm?3 K?1 for complexes 1 and 2 , respectively. 相似文献
999.
Dr. Yaqi Jiang Yanyan Jia Jiawei Zhang Lei Zhang Huang Huang Prof. Dr. Zhaoxiong Xie Prof. Dr. Lansun Zheng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(9):3119-3124
Pt? Cu alloy octahedral nanocrystals (NCs) have been synthesized successfully by using N,N‐dimethylformamide as both the solvent and the reducing agent in the presence of cetyltrimethylammonium chloride. Cu underpotential deposition (UPD) is found to play a key role in the formation of the Pt? Cu alloy NCs. The composition in the Pt? Cu alloy can be tuned by adjusting the ratio of metal precursors in solution. However, the Cu content in the Pt? Cu alloy NCs cannot exceed 50 %. Due to the fact that Cu precursor cannot be reduced to metallic copper and the Cu content cannot exceed 50 %, we achieved the formation of the Pt? Cu alloy by using Cu UPD on the Pt surface. In addition, the catalytic activities of Pt? Cu alloy NCs with different composition were investigated in electrocatalytic oxidation of formic acid. The results reveal that the catalytic performance is strongly dependent on Pt? Cu alloy composition. The sample of Pt50Cu50 exhibits excellent activity in electrocatalytic oxidation of formic acid. 相似文献
1000.
Prof. Mengtao Sun Dr. Zhenglong Zhang Prof. Zee Hwan Kim Prof. Hairong Zheng Prof. Hongxing Xu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(44):14958-14962
Heterogeneous catalysts play an important role in surface catalytic reactions, but selective bond breaking and control of reaction products in catalytic processes remain significant challenges. High‐vacuum tip‐enhanced Raman spectroscopy (HV‐TERS) is one of the best candidates to realize surface catalytic reactions. Herein, HV‐TERS was employed in a new method to control dissociation by using hot electrons, generated from plasmon decay, as plasmonic scissors. In this method, the N?N bond in 4,4′‐dimercaptoazobenzene was selectively dissociated by plasmonic scissors, and the reaction products formed from the radical fragment (SC6H5N) were controlled by varying the pH value. Under acidic conditions, p‐aminothiophenol was produced from the radical fragment by attachment of hydrogen ions, whereas under alkaline conditions, 4‐nitrobenzenethiol was obtained by attachment of oxygen ions to the substrate. 相似文献