全文获取类型
收费全文 | 3265篇 |
免费 | 162篇 |
国内免费 | 207篇 |
专业分类
化学 | 1015篇 |
晶体学 | 2篇 |
力学 | 60篇 |
综合类 | 51篇 |
数学 | 1941篇 |
物理学 | 565篇 |
出版年
2024年 | 7篇 |
2023年 | 33篇 |
2022年 | 71篇 |
2021年 | 108篇 |
2020年 | 63篇 |
2019年 | 81篇 |
2018年 | 60篇 |
2017年 | 128篇 |
2016年 | 134篇 |
2015年 | 77篇 |
2014年 | 166篇 |
2013年 | 309篇 |
2012年 | 160篇 |
2011年 | 172篇 |
2010年 | 148篇 |
2009年 | 199篇 |
2008年 | 168篇 |
2007年 | 207篇 |
2006年 | 172篇 |
2005年 | 139篇 |
2004年 | 131篇 |
2003年 | 91篇 |
2002年 | 94篇 |
2001年 | 82篇 |
2000年 | 66篇 |
1999年 | 87篇 |
1998年 | 75篇 |
1997年 | 51篇 |
1996年 | 48篇 |
1995年 | 39篇 |
1994年 | 38篇 |
1993年 | 28篇 |
1992年 | 34篇 |
1991年 | 32篇 |
1990年 | 16篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 14篇 |
1986年 | 10篇 |
1985年 | 14篇 |
1984年 | 18篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1974年 | 1篇 |
1973年 | 3篇 |
排序方式: 共有3634条查询结果,搜索用时 15 毫秒
71.
The adsorption of complexes formed by sodium, potassium, and rubidium cations with macrobicyclic ligand (kryptofix 222 with C18H36N2O6 composition) is studied as a function of the ligand concentration on a stationary mercury drop in 0.1 M solutions of corresponding sulfates and chlorides by using the differential capacitance technique. Based on the model of two parallel capacitors supplemented by the Frumkin isotherm, the adsorption parameters of studied cryptates are estimated by using the regression analysis technique. Differential capacitance curves calculated with the parameters found are compared with experimental data. The comparison of the found adsorption parameters makes it possible to reveal the effects of the nature of included cations and specifically adsorbed supporting-electrolyte anions on the adsorption behavior of cryptates under study.__________Translated from Elektrokhimiya, Vol. 41, No. 4, 2005, pp. 475–481.Original Russian Text Copyright © 2005 by Stenina, Sviridova. 相似文献
72.
Simultaneous measurement of glucose and glutamine in aqueous solutions by near infrared spectroscopy 总被引:1,自引:0,他引:1
Hoeil Chung Mark A. Arnold Martin Rhiel David W. Murhammer 《Applied biochemistry and biotechnology》1995,50(2):109-125
A method is described for measuring the concentrations of both glucose and glutamine in binary mixtures from near infrared
(NIR) absorption spectra. Spectra are collected over the range from 5000–4000/cm (2.0–2.5μm) with a 1-mm optical path length.
Glucose absorbance features at 4710, 4400, and 4300/cm and glutamine features at 4700, 4580, and 4390/cm provide the analytical
information required for the measurement. Multivariate calibration models are generated by using partial least squares (PLS)
regression alone and PLS regression combined with a preprocessing digital Fourier filtering step. The ideal number of PLS
factors and spectral range are identified separately for each analyte. In addition, the optimum Fourier filter parameters
are established for both compounds. The best overall analytical performance is obtained by combining Fourier filtering and
PLS regression. Glucose measurements are established over the concentration range from 1.66–59.91 mM, with a standard error of prediction (SEP) of 0.32 mM and a mean percent error of 1.84%. Glutamine can be measured over the
concentration range from 1.10–30.65 mM with a SEP of 0.75 mM and a mean percent error of 6.67%. These results demonstrate
the analytical utility of NIR spectroscopy for monitoring glucose and glutamine levels in mammalian and insect cell cultures. 相似文献
73.
B. B. Damaskin 《Russian Journal of Electrochemistry》2006,42(9):990-994
Based on the results of the regression analysis of differential capacitance curves of a mercury electrode in solutions of cyclobutane carboxylic acid (CBCA) at 25, 50, and 75°C, the adsorption parameters that enter into both the Frumkin isotherm and the model of two parallel capacitors are estimated. The free energies of adsorption found from the analysis of the temperature dependence of these parameters are incorrect due to the partial blowing out of CBCA during the deaeration of the solutions. The corresponding adsorption parameters are corrected under the assumption that the hydrophobic effect associated with the increase in the liquid-water entropy at the removal from it of CBCA molecules is the same as for n-valeric acid. The physical meaning of the squeezing-out effect is revised. 相似文献
74.
一个多元校正的稳健诊断新方法 总被引:1,自引:0,他引:1
提出一种新的稳健诊断方法,与最小二乘估计结合进行混合物光谱中非线性点的诊断。文中探讨了该方法的性能,用计算机数字模拟及实际多组分光谱体系夺其进行检验,展示了此诊断方法在分析化学计量学中实际应用的可行性。 相似文献
75.
The computation ofL
1 smoothing splines on large data sets is often desirable, but computationally infeasible. A locally weighted, LAD smoothing spline based smoother is suggested, and preliminary results will be discussed. Specifically, one can seek smoothing splines in the spacesW
m
(D), with [0, 1]
n
D. We assume data of the formy
i
=f(t
i
)+
i
,i=1,..., N with {t
i
}
i=1
N
D, the
i
are errors withE(
i
)=0, andf is assumed to be inW
m
. An LAD smoothing spline is the solution,s
, of the following optimization problem
相似文献
76.
We propose an algorithm for the computation ofL
1 (LAD) smoothing splines in the spacesW
M
(D), with
. We assume one is given data of the formy
i
=(f(t
i
) +
i
, i=1,...,N with {itti}
i=1
N D
, the
i
are errors withE(
i
)=0, andf is assumed to be inW
M
. The LAD smoothing spline, for fixed smoothing parameter0, is defined as the solution,s
, of the optimization problem
(1/N)
i=1
N
¦y
i
–g(t
i
¦+J
M
(g), whereJ
M
(g) is the seminorm consisting of the sum of the squaredL
2 norms of theMth partial derivatives ofg. Such an LAD smoothing spline,s
, would be expected to give robust smoothed estimates off in situations where the
i
are from a distribution with heavy tails. The solution to such a problem is a thin plate spline of known form. An algorithm for computings
is given which is based on considering a sequence of quadratic programming problems whose structure is guided by the optimality conditions for the above convex minimization problem, and which are solved readily, if a good initial point is available. The data driven selection of the smoothing parameter is achieved by minimizing aCV() score of the form
.The combined LAD-CV smoothing spline algorithm is a continuation scheme in 0 taken on the above SQPs parametrized in, with the optimal smoothing parameter taken to be that value of at which theCV() score first begins to increase. The feasibility of constructing the LAD-CV smoothing spline is illustrated by an application to a problem in environment data interpretation. 相似文献
77.
78.
79.
Zusammenfassung Die alternierende Copolymerisation von Styrol und Benzylmethacrylat in Gegenwart von Ethylaluminiumsesquichlorid als Katalysator zeigt im Anfangsstadium der Reaktion ein vom weiteren Verlauf abweichendes Verhalten. So nehmen die Zusammensetzung und die Grenzviskositäten der Produkte sowie die Reaktionsgeschwindigkeit erst nach der Anfangsphase konstante Werte an.Die1H-NMR-Spektren von alternierenden und statistischen Copolymeren gleicher Bruttozusammensetzung zeigen deutliche Unterschiede. Das Spektrum des alternierenden Copolymeren bestätigt die alternierende Struktur und spricht gleichzeitig für einen ataktischen Kettenaufbau.
The alternating copolymerization of styrene and benzylmethacrylate shows a different behaviour at the beginning of the reaction and later on. Thus the composition and the intrinsic viscosity of the products as well as the reaction rate become constant only after the initial stage.The1H-NMR-spectra of alternating and statistical copolymers with equal composition show distinct differences. The spectrum of the alternating copolymer confirms the alternating structure as well as an atactic chain configuration.相似文献 80.
稳定回归法用于复方氯丙嗪片的测定 总被引:1,自引:1,他引:1
本文应用稳定回归法用于紫外重叠光谱的分析。以复方氯丙嗪为例,不经分离,测定了盐酸氯丙嗪和盐酸异丙嗪的含量。与最小二乘回归法比较,提高了测定结果的准确度和精密度。结果满意。 相似文献
|