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排序方式: 共有1319条查询结果,搜索用时 15 毫秒
91.
Huber GW Cortright RD Dumesic JA 《Angewandte Chemie (International ed. in English)》2004,43(12):1549-1551
92.
Tris(oxalato)phosphorus acid and its lithium salt 总被引:1,自引:0,他引:1
Wietelmann U Bonrath W Netscher T Nöth H Panitz JC Wohlfahrt-Mehrens M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(10):2451-2458
The conversion of three equivalents of anhydrous oxalic acid with phosphorus pentachloride yields tris(oxalato)phosphorus acid 1, which crystallizes from diethyl ether solutions as protonated diethyl ether complex [(Et2O)2H](+)[P(C2O3)3)]-. The superacidic compound can be used as catalyst for Friedel-Crafts-type reactions. Upon neutralization with lithium hydride, the lithium salt Li[P(C2O3)3] 2 is obtained, which is highly soluble in aprotic solvents and which exhibits a wide voltage window. Thus, the lithium compound is a promising candidate as electrolyte for high performance non-aqueous batteries. 相似文献
93.
A set of experiments, using model compounds, was carried out in order to evaluate the influence of amide linkages on acidity measurements of humic substances (HS). Three benzene-carboxylic acids (2,4-dihydroxybenzoic acid; 3,5-dihydroxybenzoic acid, and phthalic acid) and two peptides (dl-alanyl-dl-alanine, and glycil-l-leucine) were employed to simulate the major acidic functional groups present in humic material. The acidity of the samples was measured, using the Schnitzer and Gupta methods, for each compound separately, as well as for selected mixtures with different compound combinations. General results showed that, in the absence of peptides, phenolic groups with high pKa values are not detected in the barium hydroxide reaction and the data so obtained do not represent the real concentrations of the acidic groups. For the mixtures containing peptides, the presence of amide linkages distorts the results relative to the total acidity (TA) mainly because under the extreme conditions of the reaction with Ba(OH)2 hydrolysis of the peptide occurs, consuming extra hydroxyl groups and increasing artificially the phenolic content. Such a condition is minimized by the reduction of the reaction time. 相似文献
94.
基于6S模型的遥感影像逐像元大气纠正算法 总被引:4,自引:0,他引:4
大气纠正的目的是从遥感影像中去除大气影响,并反演获取地物真实反射率。介绍了一种逐像元对遥感影像进行大气纠正的算法,该算法基于6S(Second Simulation of the Satellite Signal in the Solar Spectrum)大气辐射传输模型计算建立的查找表(look-up table),并利用地面暗目标(dark object)进行陆地气溶胶光学厚度的自动反演,由于气溶胶的分布具有空间连续性,在获取地面暗目标气溶胶光学厚度值后,通过空间插值的方法计算影像中非暗目标像元的气溶胶光学厚度值,经过查找表二次插值计算,逐像元进行大气纠正并获取像元地表反射率值。以Landsat5遥感影像为例,介绍了算法流程,展示了大气纠正的结果。结果显示,利用查找表逐像元大气纠正的算法,能够在一定程度上去除云雾对影像的影响,更加精确的对遥感影像进行大气纠正并获取地物的真实反射率。 相似文献
95.
Measuring particle size-dependent physicochemical structure in airborne
single walled carbon nanotube agglomerates 总被引:1,自引:1,他引:1
Andrew D. Maynard Bon Ki Ku Mark Emery Mark Stolzenburg Peter H. McMurry 《Journal of nanoparticle research》2007,9(1):85-92
As-produced single-walled carbon nanotube (SWCNT) material is a complex matrix of carbon nanotubes, bundles of nanotubes (nanoropes),
non-tubular carbon and metal catalyst nanoparticles. The pulmonary toxicity of material released during manufacture and handling
will depend on the partitioning and arrangement of these components within airborne particles. To probe the physicochemical
structure of airborne SWCNT aggregates, a new technique was developed and applied to aerosolized as-produced material. Differential
Mobility Analysis-classified aggregates were analyzed using an Aerosol Particle Mass Monitor, and a structural parameter Γ
(proportional to the square of particle mobility diameter, divided by APM voltage) derived. Using information on the constituent
components of the SWCNT, modal values of Γ were estimated for specific particle compositions and structures, and compared
against measured values. Measured modal values of Γ for 150 nm mobility diameter aggregates suggested they were primarily
composed of non-tubular carbon from one batch of material, and thin nanoropes from a second batch of material – these findings
were confirmed using Transmission Electron Microscopy. Measured modal values of Γ for 31 nm mobility diameter aggregates indicated
that they were comprised predominantly of thin carbon nanoropes with associated nanometer-diameter metal catalyst particles;
there was no indication that either catalyst particles or non-tubular carbon particles were being preferentially released
into the air. These results indicate that the physicochemistry of aerosol particles released while handling as-produced SWCNT
may vary significantly by particle size and production batch, and that evaluations of potential health hazards need to account
for this.
Disclaimer: The mention of any company or product does not constitute an endorsement by the Centers for Disease Control and
Prevention. The findings and conclusions in this paper are those of the authors and do not necessarily represent the views
of the National Institute for Occupational Safety and Health. 相似文献
96.
Jorge Antonio Guerrero‐Álvarez Wendy Paloma Mas‐Ku Cesar Garcías‐Morales Armando Ariza‐Castolo 《Magnetic resonance in chemistry : MRC》2010,48(5):356-361
The relative acidities of the cis and trans isomers of a series of 1,5‐oxazaspiro[5.5]undecane derivatives were determined by measuring ΔpK in acid‐base titrations followed by 1 H NMR. Relative structural stabilities were determined by measuring substituent chemical shift and γ‐gauche effects in 13C, 15N, and 17O NMR. Crystallographic characterization of a model spiro[5.5]undecane is presented to support the basicity in solid state. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
97.
98.
Scott D. Noblitt Florian M. Schwandner Susanne V. Hering Jeffrey L. Collett Jr. Charles S. Henry 《Journal of chromatography. A》2009,1216(9):1503-1510
A sensitive and selective separation of common anionic constituents of atmospheric aerosols, sulfate, nitrate, chloride, and oxalate, is presented using microchip electrophoresis. The optimized separation is achieved in under 1 min and at low background electrolyte ionic strength (2.9 mM) by combining a metal-binding electrolyte anion (17 mM picolinic acid), a sulfate-binding electrolyte cation (19 mM HEPBS), a zwitterionic surfactant with affinity towards weakly solvated anions (19 mM N-tetradecyl,N,N-dimethyl-3-ammonio-1-propansulfonate), and operation in counter-electroosmotic flow (EOF) mode. The separation is performed at pH 4.7, permitting pH manipulation of oxalate's mobility. The majority of low-concentration organic acids are not observed at these conditions, allowing for rapid subsequent injections without the presence of interfering peaks. Because the mobilities of sulfate, nitrate, and oxalate are independently controlled, other minor constituents of aerosols can be analyzed, including nitrite, fluoride, and formate if desired using similar separation conditions. Contact conductivity detection is utilized, and the limit of detection for oxalate (S/N = 3) is 180 nM without stacking. Sensitivity can be increased with field-amplified sample stacking by injecting from dilute electrolyte with a detection limit of 19 nM achieved. The high-sensitivity, counter-EOF operation, and short analysis time make this separation well-suited to continuous online monitoring of aerosol composition. 相似文献
99.
Z. Honglin Y. Xiufang Y. Li L. Fenghua N. Zhaodong S. Haitao 《Journal of Thermal Analysis and Calorimetry》2001,65(3):755-760
The power–time curves of a biological oscillation system were determined for different temperatures, acidities and carbon
sources, by using a 2277 thermal activity monitor. The apparent activation energy and order of the oscillation reaction were
calculated from the induction period (t
in) and the first oscillation period (t
p). The regularity of the biological oscillation system is discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
100.
Linear alkylbenzene sulfonic acid, the largest-volume synthetic surfactant, in addition to its excellent performance, is important
due to its biodegradable environmental friendliness, as it has a straight chain and is prepared by the sulphonation of linear
alkylbenzenes (LAB). To ensure environmental protection, the commercial benzene alkylation catalysts HF or AlCl3 are replaced and we have developed a clean LAB production process using a pillared clay catalyst capable of not only replacing
the conventional homogeneous catalysts, but also having high selectivity for the best biodegradable 2-phenyl LAB isomer. Pillared
clay catalysts having high Br?nsted acidity show efficient conversion in gas phase alkylation of benzene with 1-octene with
a good 2-phenyl octane selectivity. 相似文献