全文获取类型
收费全文 | 5500篇 |
免费 | 670篇 |
国内免费 | 304篇 |
专业分类
化学 | 2575篇 |
晶体学 | 58篇 |
力学 | 538篇 |
综合类 | 64篇 |
数学 | 534篇 |
物理学 | 2705篇 |
出版年
2024年 | 12篇 |
2023年 | 34篇 |
2022年 | 138篇 |
2021年 | 123篇 |
2020年 | 128篇 |
2019年 | 113篇 |
2018年 | 117篇 |
2017年 | 185篇 |
2016年 | 241篇 |
2015年 | 181篇 |
2014年 | 274篇 |
2013年 | 466篇 |
2012年 | 365篇 |
2011年 | 344篇 |
2010年 | 277篇 |
2009年 | 298篇 |
2008年 | 349篇 |
2007年 | 350篇 |
2006年 | 286篇 |
2005年 | 270篇 |
2004年 | 251篇 |
2003年 | 226篇 |
2002年 | 155篇 |
2001年 | 156篇 |
2000年 | 138篇 |
1999年 | 147篇 |
1998年 | 109篇 |
1997年 | 102篇 |
1996年 | 74篇 |
1995年 | 81篇 |
1994年 | 61篇 |
1993年 | 68篇 |
1992年 | 63篇 |
1991年 | 40篇 |
1990年 | 34篇 |
1989年 | 22篇 |
1988年 | 29篇 |
1987年 | 17篇 |
1986年 | 19篇 |
1985年 | 21篇 |
1984年 | 17篇 |
1983年 | 8篇 |
1982年 | 19篇 |
1981年 | 16篇 |
1980年 | 14篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1977年 | 12篇 |
1974年 | 4篇 |
1973年 | 3篇 |
排序方式: 共有6474条查询结果,搜索用时 0 毫秒
91.
Carlos Raimundo Andrade Lima Jefferson da Silva Martins Caroline Pinheiro Luis Fernando de Avila Roberto Rosas Pinho Maria Luiza Miranda Rocco Wilson de Souza Melo Fabio Zappa 《Journal of Polymer Science.Polymer Physics》2019,57(15):967-972
Photopolymerization is a phenomenon that is the basis of much of today's microfabrication technology and intense research is conducted to improve its control and the characteristics of end products for a variety of applications. The design of microscopic structures often relies on the accurate knowledge and modeling of photopolymer's behavior upon exposure, i.e. the Dill parameters, for each radiation species of interest and therefore the development of flexible characterization techniques is of great importance. SU‐8 is a popular compound that is representative of a whole class that relies on cationic polymerization, where an acid is obtained via photolysis of an onium salt during exposure. Here we report on the observation of SbF6? via laser desorption mass spectrometry on SU‐8 exposed to UV light at the wavelength of 365 nm and demonstrate that the yield of this counter‐anion as a function of exposure is consistent with the Dill C parameter value available in the literature. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 967–972 相似文献
92.
The lipophilicity of the series of alpha-(4-phenylpiperazin-1-yl)-gamma-phthalimido-butyramides (1-8) has been investigated. Several methods, like reversed-phase thin-layer chromatography and high-performance liquid chromatography using reversed-phase RP18 and IAM.DD2 columns, were applied to determine RMO, log k0 and log k(0IAM) factors. The RP-TLC investigations were performed in mixtures of acetone-water and acetonitrile-water. For RP-HPLC method mixtures of acetonitrile, water and 0.01% TFA were used as the mobile phases while for IAM.DD2 investigations mixtures of acetonitrile and water were applied. The partition coefficients of compounds (1-8) were also calculated with the Pallas and CAChe programs. All the obtained data, both from experimental methods and computational calculations, were compared and a suitable conclusion was reached. 相似文献
93.
The effect of injection procedures on efficiency in micellar electrokinetic capillary chromatography
Summary Micellar electrokinetic capillary chromatography (MECC) involves the application of a high voltage (10–30 KV) across a capillary
column (75μm i.d.) which is filled with a solution containing micelles. The mobile phase in this work consisted of sodium
dodecyl sulfate in an aqueous borate/phosphate buffer system. Injection parameters in MECC were investigated to minimize the
contribution to band-broadening resulting from the injection process. Efficiencies as high as 240,000 theoretical plates/meter
are reported. 相似文献
94.
Feasibility study on qualitative and quantitative analysis in tea by near infrared spectroscopy with multivariate calibration 总被引:2,自引:0,他引:2
This study attempted the feasibility to use near infrared (NIR) spectroscopy as a rapid analysis method to qualitative and quantitative assessment of the tea quality. NIR spectroscopy with soft independent modeling of class analogy (SIMCA) method was proposed to identify rapidly tea varieties in this paper. In the experiment, four tea varieties from Longjing, Biluochun, Qihong and Tieguanyin were studied. The better results were achieved following as: the identification rate equals to 90% only for Longjing in training set; 80% only for Biluochun in test set; while, the remaining equal to 100%. A partial least squares (PLS) algorithm is used to predict the content of caffeine and total polyphenols in tea. The models are calibrated by cross-validation and the best number of PLS factors was achieved according to the lowest root mean square error of cross-validation (RMSECV). The correlation coefficients and the root mean square error of prediction (RMSEP) in the test set were used as the evaluation parameters for the models as follows: R = 0.9688, RMSEP = 0.0836% for the caffeine; R = 0.9299, RMSEP = 1.1138% for total polyphenols. The overall results demonstrate that NIR spectroscopy with multivariate calibration could be successfully applied as a rapid method not only to identify the tea varieties but also to determine simultaneously some chemical compositions contents in tea. 相似文献
95.
Least-squares support vector machines and near infrared spectroscopy for quantification of common adulterants in powdered milk 总被引:5,自引:0,他引:5
This paper proposes the use of the least-squares support vector machine (LS-SVM) as an alternative multivariate calibration method for the simultaneous quantification of some common adulterants (starch, whey or sucrose) found in powdered milk samples, using near-infrared spectroscopy with direct measurements by diffuse reflectance. Due to the spectral differences of the three adulterants a nonlinear behavior is present when all groups of adulterants are in the same data set, making the use of linear methods such as partial least squares regression (PLSR) difficult. Excellent models were built using LS-SVM, with low prediction errors and superior performance in relation to PLSR. These results show it possible to built robust models to quantify some common adulterants in powdered milk using near-infrared spectroscopy and LS-SVM as a nonlinear multivariate calibration procedure. 相似文献
96.
Fatma M. Elzawawy 《Monatshefte für Chemie / Chemical Monthly》1991,122(11):921-925
Summary The stoichiometric stability constants for La(III) and Y(III)L-serine complexes were determined by potentiometric methods at different ionic strengths adjusted with NaClO4 and at different temperatures. The overall changes in free energy (G
o), enthalpy (H
o), and entropy (S
o) during the protonation ofL-serine and that accompanying the complex formation with the metal ions have been evaluated.
Komplexbildungskonstanten und thermodynamische Parameter für La(III)- und Y(III)-L-Serin-Komplexe
Zusammenfassung Die stöchiometrischen Komplexbildungskonstanten für La(III)- und Y(III)-L-Serin-Komplexe wurden mittels potentiometrischer Methoden bei verschiedenen Ionenstärken (mit NaClO4 adjustiert) und bei verschiedenen Temperaturen bestimmt. Die Änderungen in der freien Energie (G o), Enthalpie (H o) und Entropie (S o) während der Protonierung und der Komplexbildung mit den Metallionen wurden ermittelt.相似文献
97.
HDPE based composites were produced with 10-20-30 and 40% composite mass of wood fiber. The coupling agents were epolene and
silane. The thermal behavior of composite samples was analyzed as a function of the coupling agent content, the exposure time
and the wood fibers content by means of differential scanning calorimetry. Calorimetric curves of all samples of first and
second heating shows a similar behavior. Some significant relation has been observed between the exposure time and the degree
of crystallinity for the same percentage of fiber samples. A linear relation between the melting enthalpy average vs. content
in cellulosic fibers is detected. Nevertheless, the fibers non-pretreated with coupling agent show a lower loss of crystallinity
of the HDPE matrix at low wood fiber content (10%). A slight diminution of the melting peak temperature is detected as increasing
the exposure time.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
98.
Elena V. Parfenyuk Olga I. Davydova Nataliya Sh. Lebedeva 《Journal of solution chemistry》2004,33(1):1-10
Calorimetric titrations have been performed at 298.15 K in aqueous solutions to derive the stability constants and thermodynamic parameters of the interactions of D-maltose and sucrose with some amino acids (glycine, DL-alanine, DL-leucine, and L-serine). The apparent molal volumes of the disaccharides in dilute aqueous solutions of the amino acids have been determined from density measurements at 298.15 K. In contrast to D-maltose, sucrose was found to associate with the amino acids and these associated species are preferentially entropy stabilized. These results are interpreted in terms of the influence of the nature of the solutes, their specific conformations, and hydration, on the ability of the disaccharides to form associated complexes with the amino acids. 相似文献
99.
Based on the new draft of the EURACHEM/CITAC Guide Traceability in Chemical Measurement, this publication describes how traceability can be achieved for chemical measurements using a linear calibration function. Traceability can be accomplished without larger expenditure, if the measurement is calibrated on the basis of appropriate reference standards and the linear regression employed is selected and validated statistically in a suitable form. The determination of nickel in aqua regia eluates of sediment samples, employed for an ICP-OES measurement, is used as a practical illustration of this approach. 相似文献
100.
L. N. Ignatieva A. Yu. Beloliptsev S. G. Kozlova V. M. Buznik 《Journal of Structural Chemistry》2004,45(4):599-609
Quantum-chemical calculations of the geometrical structure and vibrational spectra of CnF2n+2 oligomers (n = 5–8) in the chain and branched conformations are reported. The lengthening of the chain of CnF2n+2 does not substantially affect the geometrical parameters of the oligomers. In all cases under study, the most optimal structure of the molecule is a zigzag chain with bond lengths R(C-C) = 1.53 –1.54 and R(C-F) = 1.36 –1.34 ; the chain is rolled into a helix, which makes an angle of 17° with the plane. The IR spectra are sensitive to the structural deficiency of oligomers CnF2n+2 associated with the lateral trifluoromethyl groups formed in the chain; the spectra can be used for revealing defects of this type in the structure of polytetrafluoroethylene (PTFE). The possibility of defects associated with the lateral CF3 groups in the structure of PTFE and its low-temperature modifications is explained based on the calculated total energies of CnF2
n+2.Original Russian Text Copyright © 2004 by L. N. Ignatieva, A. Yu. Beloliptsev, S. G. Kozlova, and V. M. BuznikTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 4, pp. 632–643, July–August, 2004.This revised version was published online in April 2005 with a corrected cover date. 相似文献