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41.
Gelebe AC Kaye PT Klein R Sewry JD Soper AG 《Magnetic resonance in chemistry : MRC》2005,43(11):952-955
The influence of substituents and structure on the 13C NMR spectra of four series of benzoxathiepine derivatives has been investigated. Signal assignments in the 13C NMR spectra have been facilitated by the use of several predictive methods, permitting comparison of their relative efficacy. 相似文献
42.
43.
本文提出了一种新的带有时间幂次项的灰色GM(1,1,k,k2)模型,给出了其灰微分方程和白化微分方程基本形式。基于最小二乘法获得了该模型参数估计值,并推导了该模型时间响应函数。鉴于GM(1,1,k,k2)模型灰微分方程与白化微分方程之间存在跳跃关系,首先对灰微分方程的背景值进行了优化,并推导了优化后的背景值计算公式。为了克服初始值的影响,根据误差平方和最小,进一步优化了GM(1,1,k,k2)模型时间响应函数。最后,该优化后的GM(1,1,k,k2)模型被应用于软土地基沉降预测,获得了较好的模拟预测效果,说明模型是可行的。 相似文献
44.
Least squares estimations have been used extensively in many applications, e.g. system identification and signal prediction. When the stochastic process is stationary, the least squares estimators can be found by solving a Toeplitz or near-Toeplitz matrix system depending on the knowledge of the data statistics. In this paper, we employ the preconditioned conjugate gradient method with circulant preconditioners to solve such systems. Our proposed circulant preconditioners are derived from the spectral property of the given stationary process. In the case where the spectral density functions() of the process is known, we prove that ifs() is a positive continuous function, then the spectrum of the preconditioned system will be clustered around 1 and the method converges superlinearly. However, if the statistics of the process is unknown, then we prove that with probability 1, the spectrum of the preconditioned system is still clustered around 1 provided that large data samples are taken. For finite impulse response (FIR) system identification problems, our numerical results show that annth order least squares estimator can usually be obtained inO(n logn) operations whenO(n) data samples are used. Finally, we remark that our algorithm can be modified to suit the applications of recursive least squares computations with the proper use of sliding window method arising in signal processing applications.Research supported in part by HKRGC grant no. 221600070, ONR contract no. N00014-90-J-1695 and DOE grant no. DE-FG03-87ER25037. 相似文献
45.
The COSMO-RS method, originally developed for the prediction of liquid-liquid and liquid-vapor equilibrium constants based on quantum chemical calculations, has been extended to solid compounds by addition of a heuristic expression for the Gibbs free energy of fusion. By this addition, COSMO-RS is now capable of a priori prediction of aqueous solubilities of a wide range of typical neutral drug and pesticide compounds. Only three parameters in the heuristic expression have been fitted on a data set of 150 drug-like compounds. On these data an rms deviation of 0.66 log-units was achieved. Later, the model was tested on a set of 107 pesticides, which have been critically selected based on two experimental data sources and by a crosscheck with an independent HQSAR model. On this data set an rms of 0.61 log-units was achieved, without any adjustments to the structurally extremely diverse pesticides. This result verifies the ability of this extended COSMO-RS to predict aqueous solubilities of drugs and pesticides of almost arbitrary structural classes. The new method is COSMO-RSol. 相似文献
46.
Summary A computer interactive identification system is proposed which is based on the relationship between retention and molecular
properties such as the size and shape of polycyclic aromatic hydrocarbons (PAHs). This system offers an automatic analytical
process for liquid chromatography, providing a reliable identification of the separated components. The identification can
be further enhanced by the use of multiple detectors such as a multichannel UV detector. The system can be used for optimization
procedures, resulting in a highly automatic complex analytical system. 相似文献
47.
Maria Concetta Bruzzoniti Edoardo Mentasti Corrado Sarzanini Peter Hajs 《Journal of chromatography. A》1997,770(1-2):13-22
The retention behavior of biologically relevant monovalent (formic, acetic, propionic, lactic and pyruvic) and divalent (oxalic, malonic, succinic, fumaric, maleic and tartaric acids) car☐ylic acids together with inorganic analytes (chloride and sulphate) has been studied. The separation was performed on a latex-based strong anion-exchange resin using carbonate buffer systems in suppressed IC. The retention behaviour of analytes was investigated at different pH values and [HCO3−]+[CO32−] concentrations. A theoretical model, involving ion-exchange equilibria of sample and eluent anions, was derived and applied to the chromatographic data obtained. Chromatographic ion exchange selectivity values were determined and retention data were calculated for the anions using different carbonate eluent conditions. The average of errors between the predicted and the measured retention volumes of the analytes studied does not exceed 4.0%. The study effectively characteristics the behaviour of different analytes under elution conditions of practical importance. 相似文献
48.
49.
Molecular parameters and retention characteristics of unsubstituted polyaromatic hydrocarbons in HPLC 总被引:1,自引:0,他引:1
Summary The present research studies the possibility of using the correlation dependence between molecular parameters of unsubstituted
polyaromatic hydrocarbons (PAH) and their retention in reversed-phase liquid chromatography to optimize the conditions for
the separation and identification of unknown peaks on the chromatograms of multicomponent mixtures. A linear correlation equation,
that takes the number and environment of the carbon atom in the PAH molecule into account as well as the differences in the
specific interactions of isomeric molecules with polar eluent, has been proposed. The adequacy of the proposed PAH retention
model was verified by comparing the calculated retention values with the experimental data. The possibility of identifying
unsubstituted PAH according to the number of carbon atoms of various types and according to the values of the molecules lengths
(calculated on the basis of the retention of these substances under different eluent compositions) was exemplified by various
chromatographic systems (reversed phase-eluent-PAH molecules). 相似文献
50.
高锰酸盐指数的灰色GM(1,1)预测 总被引:1,自引:0,他引:1
以中山市岐江河近7年的高锰酸盐指数监测数据为基础,采用灰色系统理论中的预测方法,建立了岐江河高锰酸盐指数的灰色预测模型。用该模型预测岐江河2006年、2007年、2008年高锰酸盐指数的值分别为5.3,5.4和5.4。 相似文献