全文获取类型
收费全文 | 2880篇 |
免费 | 99篇 |
国内免费 | 16篇 |
专业分类
化学 | 2023篇 |
晶体学 | 20篇 |
力学 | 79篇 |
数学 | 281篇 |
物理学 | 592篇 |
出版年
2023年 | 13篇 |
2022年 | 66篇 |
2021年 | 48篇 |
2020年 | 43篇 |
2019年 | 47篇 |
2018年 | 36篇 |
2017年 | 46篇 |
2016年 | 100篇 |
2015年 | 66篇 |
2014年 | 87篇 |
2013年 | 157篇 |
2012年 | 173篇 |
2011年 | 193篇 |
2010年 | 100篇 |
2009年 | 94篇 |
2008年 | 172篇 |
2007年 | 154篇 |
2006年 | 132篇 |
2005年 | 126篇 |
2004年 | 133篇 |
2003年 | 113篇 |
2002年 | 103篇 |
2001年 | 58篇 |
2000年 | 63篇 |
1999年 | 46篇 |
1998年 | 17篇 |
1997年 | 27篇 |
1996年 | 45篇 |
1995年 | 66篇 |
1994年 | 52篇 |
1993年 | 48篇 |
1992年 | 53篇 |
1991年 | 26篇 |
1990年 | 30篇 |
1989年 | 19篇 |
1988年 | 19篇 |
1987年 | 20篇 |
1986年 | 23篇 |
1985年 | 29篇 |
1984年 | 26篇 |
1983年 | 10篇 |
1982年 | 23篇 |
1981年 | 18篇 |
1980年 | 12篇 |
1979年 | 13篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1975年 | 6篇 |
1974年 | 5篇 |
1973年 | 7篇 |
排序方式: 共有2995条查询结果,搜索用时 31 毫秒
11.
12.
A systematic study of the efficiency of protons, Ni, Pd and Th as chemical modifiers for the determination of cadmium by electrothermal atomic absorption spectrometry (ETAAS) using fast temperature programs was made for platform atomization. A comparison was made in terms of the salt type, absorbance-time profiles and elimination of the sodium chloride interference. The results were adapted to develop a method for the ETAAS determination of cadmium in biological and environmental samples. The highest sensitivity to determine cadmium in biological and environmental samples was obtained using nickel (together with protons) as a chemical modifier. The accuracy of the method was tested by the determination of cadmium in different certified reference materials. The best detection limit and the characteristic mass of Cd were found to be 0.03 ng mL(-1) and 0.35 pg, respectively. 相似文献
13.
Muhammad Faisal Nobuaki Sato Armando T. Quitain Hiroyuki Daimon Koichi Fujie 《国际化学动力学杂志》2007,39(3):175-180
The kinetics and pathway of hydrothermal decomposition of aspartic acid were studied using a continuous‐flow tubular reactor. The reaction was carried out in the temperature range of 200–260°C and at a pressure of 20 MPa. Deamination was the primary reaction, indicated by the presence of significant amount of ammonia, fumaric acid, or maleic acid in the products. Other reaction products were pyruvic acid, malic acid, and traces of succinic and lactic acid. Traces of alanine were also detected, showing the possibility of decomposing high‐molecular weight amino acids to obtain simple amino acids such as glycine or alanine. Results on the effect of reaction parameters demonstrated that decomposition of aspartic acid is highly temperature dependent under hydrothermal conditions. For a slight temperature difference of 60°C (from 200 to 260°C), the first‐order reaction rate constants of 0.003 significantly increased to 0.231 s?1. The activation energy was 144 kJ/mol, as calculated by the Arrhenius equation. No significant effect was exhibited by other reaction parameters such as pH and pressure. The results are useful in controlling the hydrolysis of proteinaceous materials toward high yield of aspartic acid under hydrothermal conditions. © 2007 Wiley Periodicals, Inc. 39: 175–180, 2007 相似文献
14.
Dimitri Markushevich Vladimir B. Matveev Armando Treibich 《Letters in Mathematical Physics》2006,76(2-3):109-109
15.
In this paper we approximate the solution of a linear initial-value problem, making use of a Schauder basis for certain Banach space associated with such a differential problem. In addition, we apply that results in order to calculate numerically the response from a structure modelled by a three degree-of-freedom mass–damper–spring system. 相似文献
16.
We report a rigorous theory to show the origin of the unexpected periodic behavior seen in the consecutive differences between prime numbers. We also check numerically our findings to ensure that they hold for finite sequences of primes, that would eventually appear in applications. Finally, our theory allows us to link with three different but important topics: the Hardy–Littlewood conjecture, the statistical mechanics of spin systems, and the celebrated Sierpinski fractal. 相似文献
17.
Dore Augusto Clemente Armando Marzotto Giovanni Valle 《Journal of chemical crystallography》1988,18(2):147-156
The crystal and molecular structure of thiamine monochloride (C12H17N4OSCl) was determined by X-ray diffraction and refined to a finalR value of 0.042. The compound crystallizes in the monoclinic system, space groupP21/a, with cell constantsa=18.929(4),b=11.663(2),c=6.376(2) Å and=96.72(8)°. The thiamine molecule is anhydrous and unprotonated, and the torsion angles at the methylene carbon show that it possesses anF conformation. The dihedral angle value of 84.16(6)° between thiazolium and pyrimidine rings is in the normal range found for the thiamine withF conformation, protonated or not, hydrated or not. Thiamine therefore has the same conformation notwithstanding protonation or hydration, with the rings similarly oriented in all the crystal structures containing thiamine. 相似文献
18.
D. Bisello G. Busetto A. Castro M. Nigro M. Penzo L. Pescara M. Posocco P. Sartori L. Stanco Z. Ajaltouni A. Falvard J. Jousset B. Michel J. C. Montret A. Antonelli R. Baldini A. Calcaterra G. Capon M. Schioppa J. -E. Augustin G. Cosme F. Couchot B. Dudelzak F. Fulda G. Grosdidier B. Jean-Marie S. Jullian D. Lalanne V. Lepeltier F. Manè C. Paulot R. Riskalla Ph. Roy G. Szklarz DM Collaboration 《Zeitschrift fur Physik C Particles and Fields》1988,39(1):13-19
Thee + e ?→K + K ? cross section has been measured from about 750 events in the energy interval \(1350 \leqq \sqrt s \leqq 2400 MeV\) with the DM2 detector at DCI. TheK ± form factor |F F ±| cannot be explained by the ρ, ω, ? and ρ′(1600). An additional resonant amplitude at 1650 MeV has to be added as suggested by a previous experiment. 相似文献
19.
An automatic continuous-flow photometric method for the determination of ammonia is proposed. It is based on the Berthelot reaction, the product of which is temporarily immobilized on a suitable support (Sephadex QAE) located in the flow-cell. The retained product is eluted after measurement by a cationic surfactant contained in the carrier solution. The method allows the determination of the analyte between 0.4 and 20.0 gmg/ml, with an RSD of 0.8%, at a sampling frequency of 13/hr. The determination limit can be reduced by a factor of ten by using a flow-cell with a two-fold longer path length, but the sampling frequency is also reduced as a result. The method was applied to the determination of this analyte in agricultural samples (plants and soils) and compared with standard methods for these types of samples. 相似文献
20.
The kinetics of carbon deposition over a Ni/α-Al2O3 commercial catalyst, has been studied using CH4−H2 gas mixtures in the range of 748–873 K. A Hougen-Watson type model gives good agreement with the experimental rates. 相似文献