全文获取类型
收费全文 | 2531篇 |
免费 | 110篇 |
国内免费 | 10篇 |
专业分类
化学 | 1919篇 |
晶体学 | 10篇 |
力学 | 51篇 |
数学 | 286篇 |
物理学 | 385篇 |
出版年
2023年 | 40篇 |
2022年 | 41篇 |
2021年 | 62篇 |
2020年 | 106篇 |
2019年 | 88篇 |
2018年 | 59篇 |
2017年 | 37篇 |
2016年 | 92篇 |
2015年 | 65篇 |
2014年 | 75篇 |
2013年 | 117篇 |
2012年 | 203篇 |
2011年 | 270篇 |
2010年 | 97篇 |
2009年 | 80篇 |
2008年 | 160篇 |
2007年 | 145篇 |
2006年 | 153篇 |
2005年 | 97篇 |
2004年 | 94篇 |
2003年 | 77篇 |
2002年 | 54篇 |
2001年 | 18篇 |
2000年 | 33篇 |
1999年 | 16篇 |
1998年 | 20篇 |
1996年 | 25篇 |
1995年 | 10篇 |
1994年 | 19篇 |
1993年 | 28篇 |
1992年 | 21篇 |
1991年 | 14篇 |
1990年 | 15篇 |
1989年 | 14篇 |
1988年 | 15篇 |
1987年 | 16篇 |
1986年 | 16篇 |
1985年 | 17篇 |
1984年 | 15篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1976年 | 7篇 |
1975年 | 9篇 |
1973年 | 10篇 |
1968年 | 7篇 |
1967年 | 6篇 |
1966年 | 6篇 |
排序方式: 共有2651条查询结果,搜索用时 15 毫秒
101.
The accuracy, precision, and reproducibility of a rapid method for determination of fluoride in wine, using a fluoride selective ion electrode, were established by a collaborative study involving 12 laboratories, 5 in Europe and 7 in the United States. The laboratories assayed 6 Youden pairs of fluoride-fortified, red and white wine samples with fluoride concentrations ranging from 0.2 to 3.0 mg/L. The relative standard deviations of repeatability ranged from 1.94 to 4.88%; relative standard deviations of reproducibility ranged from 4.15 to 18.40%. HORRAT values ranged from 0.30 to 0.97. The average recovery was 99.97%. Based on the statistical results of this collaborative study, the Study Director recommends that this method be adopted First Action. 相似文献
102.
A model has been developed to describe the chemistry which occurs in SF6/O2 plasmas and the etching of silicon in these plasmas. Emphasis is placed nn the gas-phase free radical reactions, and the predictions n( the model are compared with experimental results. Forty-seven reactions are included, although a subset of 18 reactions describes the chemistry equally well. Agreement between the calculated and measured concentrations of stable products downstream of the plasma is better than a factor of 2. The need for additional kinetic data and fàr well-characterized diagnostic studies of SF6/O2 plasmas is discussed. 相似文献
103.
A model has been developed to describe the chemistry which occurs in CF4 plasmas and the etching of Si both in the plasma and downstream. One very important feature of this model is that for discharge residence times which vary by more than an order of magnitude, the amount of CF4 consumed is low and relatively constant. This is because the gas-phase combination reactions between F and both CF3 and CF2 lead to the rapid reforming of CF4. The model predicts that CF2 is a major species in the gas phase and that the [F] detected as a sample point downstream is a very sensitive function of [CF2]/[F] in the discharge. Even though the calculations show that [F] in the discharge varies only slightly over the wide range of experimental conditions considered, large variations in [F] at the sample point occur because the [CF2]/[F] ratio in the discharge changes. The concentrations of C2F6 and SiF4 are predicted to within a factor of 2 over a very wide range of experimental conditions. This confirms the importance of gas-phase free radical reactions in the etching of Si. 相似文献
104.
Warnick KF Francom SJ Humble PH Kelly RT Woolley AT Lee ML Tolley HD 《Electrophoresis》2005,26(2):405-414
The class of equilibrium gradient methods utilizes the opposition of two forces, at least one of which changes in magnitude with position, to separate and concentrate analytes. The drawback of many methods of this type is that the production of two opposing forces requires in comparison to standard methods, such as capillary electrophoresis, a relatively complex apparatus. In addition, for techniques such as electric field gradient focusing, hydrodynamic flow leads to Taylor dispersion, which limits the attainable concentration factor. We propose a new method, gradient field electrophoresis, which achieves analyte separation and focusing with only one spatially varying force, an electric field gradient. A model for the method is developed and used to analyze peak capacity. Experimental results for a protein (R-phycoerythrin) are given and compared to the model. 相似文献
105.
Electronically modified PHOX ligands 3a-e were synthesized to probe the mechanism of the enantioselective palladium-catalyzed allylic alkylation and amination reactions. Alkylation with dimethyl sodiomalonate produced only a small variation in the ee (89.3% to 93.4%), but amination with benzylamine gave a much wider variation in the ee (16.4% to 66.6%). Hammett analysis suggests that the substituents interact more significantly with phosphorus and supports a combined electronic and steric basis for enantioselection. [reaction: see text] 相似文献
106.
A method using capillary electrophoresis-mass spectrometry (CE-MS) was developed for the structural elucidation of bupivacaine and metabolites in rat urine. Prior to CE-MS analysis, solid-phase extraction (SPE) was used for sample cleanup and preconcentration purposes. Exact mass and tandem mass spectrometric (MS/MS) experiments were performed to obtain structural information about the unknown metabolites. Two instruments with different mass analyzers were used for mass spectrometric detection. A quadrupole time-of-flight (Q-TOF) and a magnetic sector hybrid instrument were coupled to CE and used for the analysis of urine extracts. Hydroxybupivacaine as well as five other isomerically different metabolites were detected including methoxylated bupivacaine. 相似文献
107.
108.
The cross-coupling of alkyl cyanamides with a number of aryl, heteroaryl, and vinyl halide and pseudohalide coupling partners has been developed via a modification of Pd-catalyzed amidation methods. The reactions proceed selectively under mild conditions with reasonable reaction times in moderate to excellent yields. 相似文献
109.
110.
Daniella Morgos Ivan Geroy Richard G. Sevier Molly M. Gribb Kevin P. Ryan Herbert H. Hill 《International Journal for Ion Mobility Spectrometry》2010,13(1):1-7
An ion mobility spectrometer (IMS) probe system for real-time, subsurface soil-gas sampling applications is presented. The
system includes an IMS and supporting electronics encased in a 51 mm diameter stainless steel probe housing. The IMS was challenged
in the laboratory with 2,6-di-tert-butylpyridine (DtBP) and tetrachloroethylene (PCE) in zero air yielding reduced ion mobility
constants (Ko) values of 1.42 cm2/Vs (n = 3) and 1.79 ± 0.01 cm2/Vs (n = 3), respectively. A resolving power of 38 and 31 was obtained for DtBP and PCE, respectively. The system was deployed at
a PCE-contaminated site to demonstrate its performance under field conditions. PCE was detected in the vapor samples as evidenced
by peaks with a Ko value of 1.80 ± 0.01 cm2/Vs for two measurements that were taken 6 min apart. The presence of PCE at the contaminated site was confirmed by GC-MS
analysis of a gas sample at an EPA-certified laboratory, suggesting that this IMS system can be used to detect PCE under field
conditions. 相似文献