全文获取类型
收费全文 | 1064篇 |
免费 | 41篇 |
国内免费 | 41篇 |
专业分类
化学 | 277篇 |
晶体学 | 1篇 |
力学 | 51篇 |
综合类 | 10篇 |
数学 | 602篇 |
物理学 | 205篇 |
出版年
2024年 | 4篇 |
2023年 | 21篇 |
2022年 | 27篇 |
2021年 | 19篇 |
2020年 | 29篇 |
2019年 | 28篇 |
2018年 | 18篇 |
2017年 | 27篇 |
2016年 | 34篇 |
2015年 | 26篇 |
2014年 | 48篇 |
2013年 | 113篇 |
2012年 | 52篇 |
2011年 | 62篇 |
2010年 | 47篇 |
2009年 | 56篇 |
2008年 | 72篇 |
2007年 | 58篇 |
2006年 | 41篇 |
2005年 | 24篇 |
2004年 | 35篇 |
2003年 | 25篇 |
2002年 | 33篇 |
2001年 | 24篇 |
2000年 | 29篇 |
1999年 | 24篇 |
1998年 | 19篇 |
1997年 | 23篇 |
1996年 | 19篇 |
1995年 | 18篇 |
1994年 | 13篇 |
1993年 | 7篇 |
1992年 | 11篇 |
1991年 | 3篇 |
1990年 | 28篇 |
1989年 | 3篇 |
1988年 | 7篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有1146条查询结果,搜索用时 15 毫秒
171.
Coleman MD Brewer PJ Smith IM Harris PM Clift MG Milton MJ 《Analytica chimica acta》2007,601(2):189-195
We report the use of a calibration transfer strategy to correct for drift in the quantitative sensitivity of a portable quadrupole mass spectrometer (QMS) aimed at process monitoring applications. Gas mixtures of CH4/Ar/C2H6/CO2 were studied with calibration phase measurements made of the pure gases for a univariate analysis and of 40 multi-component mixtures for a multivariate approach. To evaluate calibrations, test set spectra of a CH4/Ar/C2H6/CO2 gas mixture were recorded bi-weekly over a period of 12 months. As part of the strategy a standard of pure argon was measured during both calibration and test phases so that correction factors could be calculated for each measurement day. It was shown that in the absence of a calibration transfer strategy quantifications of test set spectra could be inaccurate by more than an order of magnitude over 12 months. Furthermore, due to the effects of drift in the sensitivity over the 6 days required to record the training set in the calibration phase it was found that the multivariate analysis quantified test spectra less accurately than the univariate analysis. However, by applying the calibration transfer strategy across all measurements (both calibration and test phases) it was shown that the errors in prediction using the multivariate analysis previously seen after 2 weeks were not observed until approximately 12 months later. 相似文献
172.
On-line high performance liquid chromatography is used to monitor a steady state reaction over 35.2 h, with 197 chromatograms recorded as the reaction progresses. For each chromatogram, peaks are detected, baseline corrected, aligned and integrated to provide a peak table consisting of the intensities of 19 peaks, two corresponding to the reactants, one to the product and one to the solvent, the remaining being impurities, by-products or intermediates. D-charts and Q-charts from multivariate statistical process control are applied to the data to determine which samples are out of control and also provide diagnostic insight into why these samples are problematic. The D-chart is best at looking at overall performance issues such as problems with mixing or difficulties with instrument operation, whereas the Q-charts are best at detecting impurities during the reaction. 相似文献
173.
Bernd C. Kellner. 《Mathematics of Computation》2007,76(257):405-441
Let ( ) denote the usual th Bernoulli number. Let be a positive even integer where or . It is well known that the numerator of the reduced quotient is a product of powers of irregular primes. Let be an irregular pair with . We show that for every the congruence has a unique solution where and . The sequence defines a -adic integer which is a zero of a certain -adic zeta function originally defined by T. Kubota and H. W. Leopoldt. We show some properties of these functions and give some applications. Subsequently we give several computations of the (truncated) -adic expansion of for irregular pairs with below 1000.
174.
广义n阶Euler-Bernoulli多项式 总被引:25,自引:2,他引:23
刘国栋 《数学的实践与认识》1999,29(3):5-10
本文得到了广义n阶Euler数和广义n阶Bernoulli数,广义n阶Euler多项式和广义n阶Bernoulli多项式的关系式。 相似文献
175.
鲍玉芳 《数学物理学报(A辑)》1999,19(1):94-100
证明了分支特征为ψ(z)=z^2,底过程为d≤3的暂留Ornstein-Uhlenbeck(O.U.)过程的超过程Xt的占位时过程Y(t)=∫^t0Xsds关于Lebesgue测度绝对连续,且其密度过程Y(t,x)关于t≥0,x∈R^d联合连续。 相似文献
176.
L. I. Sazonov 《Mathematical Notes》1999,65(2):202-207
In the exterior domain Ω⊂ℝ2 we consider the two-dimensional Navier-stokes system Δu-▽p=(u,▽)u, div u=0 whose solution possesses a finite Dirichlet integral
and satisfies the condition lim|x|→∞
u(x)=(1, 0). For this solution, we establish the estimate |u(x)−(1, 0)|≤c|x|
−α, where α>1/4. This estimate implies an asymptotic expression for the solution indicating the presence of a track behind the
body.
Translated fromMatematicheskie Zametki, Vol. 65, No. 2, pp. 246–253, February, 1999. 相似文献
177.
在真空中解理后,用XPS测得了GaAs样品(110)断面能带弯曲的动态过程.两组重掺杂n型和p型GaAs样品的费米能级分别向禁带中间的方向移动了0.4eV和0.3eV.实验测得重掺杂n型和p型GaAs样品费米能级之差为1.3eV,它们的禁带宽度理论值为1.42eV,这说明结果是合理的.根据实验结果,对引起GaAs表面能带弯曲的可能原因进行了分析讨论.排除了本征表面态、真空中残留气体和X射线辐射等原因,认为解理过程在表面产生的缺陷和解理后表面晶格弛豫过程中产生的缺陷可能是导致能带弯曲的主要原因. 相似文献
178.
Vladimir V. Anisimov 《TOP》1999,7(2):169-186
Some special classes of Switching Processes such as Recurrent Processes of a Semi-Markov type and Processes with Semi-Markov
Switches are introduced. Limit theorems of Averaging Principle and Diffusion Approximation types are given. Applications to
the asymptotic analysis of overloading state-dependent Markov and semi-Markov queueing modelsM
SM,Q
/M
SM,Q
/1/∞ and retrial queueing systemsM/G/1/w.r in transient conditions are studied.
The paper was supported by INTAS Project 96-0828 相似文献
179.
180.
《Particuology》2023
Disodium 5′-ribonucleotide, which is composed of disodium 5′-inosine (IMP) and disodium 5′-guanosine (GMP), is an important food additive. The lack of kinetic studies of it causes a lack of clarity in understanding the complicated multi-solute crystallization of IMP + GMP in ethanol-water. In this work, process analytical technology tools were used to obtain the thermodynamics and kinetic data from the experiments, the kinetic parameters of anti-solvent and cooling crystallization were investigated. The crystal form of IMP + GMP mixed crystal was determined, which was consistent with the IMP whether crystallized from pure water or ethanol-water. The effects of different anti-solvent addition rates and cooling rates on the metastable zone widths were studied, and the opposite effect on metastable zone width was found. The modified exponential empirical function was developed to correlate nucleation and growth kinetic equations under different conditions. The kinetic data were well fitted with adjusted correlation coefficient (adj-R2 > 0.7), which is sufficient to provide a valid reference for process design and control. 相似文献