全文获取类型
收费全文 | 175889篇 |
免费 | 21957篇 |
国内免费 | 13699篇 |
专业分类
化学 | 97434篇 |
晶体学 | 2083篇 |
力学 | 18809篇 |
综合类 | 2027篇 |
数学 | 49022篇 |
物理学 | 42170篇 |
出版年
2024年 | 212篇 |
2023年 | 1114篇 |
2022年 | 2237篇 |
2021年 | 2609篇 |
2020年 | 3283篇 |
2019年 | 4973篇 |
2018年 | 4599篇 |
2017年 | 5719篇 |
2016年 | 6405篇 |
2015年 | 8129篇 |
2014年 | 9623篇 |
2013年 | 14418篇 |
2012年 | 10681篇 |
2011年 | 11320篇 |
2010年 | 9577篇 |
2009年 | 10898篇 |
2008年 | 11524篇 |
2007年 | 11094篇 |
2006年 | 10320篇 |
2005年 | 9220篇 |
2004年 | 8044篇 |
2003年 | 7625篇 |
2002年 | 7753篇 |
2001年 | 5611篇 |
2000年 | 5331篇 |
1999年 | 4168篇 |
1998年 | 3417篇 |
1997年 | 2823篇 |
1996年 | 2464篇 |
1995年 | 2175篇 |
1994年 | 1949篇 |
1993年 | 1616篇 |
1992年 | 1623篇 |
1991年 | 1261篇 |
1990年 | 1012篇 |
1989年 | 850篇 |
1988年 | 716篇 |
1987年 | 586篇 |
1986年 | 467篇 |
1985年 | 558篇 |
1984年 | 543篇 |
1983年 | 274篇 |
1982年 | 426篇 |
1981年 | 452篇 |
1980年 | 336篇 |
1979年 | 352篇 |
1978年 | 257篇 |
1977年 | 244篇 |
1976年 | 175篇 |
1974年 | 125篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
112.
In this study, stoichiometric protonation constants of L-tyrosine, L-cysteine, L-tryptophane, L-lysine, and L-histidine, and
their methyl and ethyl esters in water and ethanol–water mixtures of 30, 50, and 70% ethanol (v/v), were determined potentiometrically
using a combined pH electrode system calibrated as the concentration of hydrogen ion. Titrations were performed at 25∘C and the ionic strength of the medium was maintained at 0.10 mol⋅L−1 using sodium chloride. Protonation constants were calculated by using the BEST computer program. The effect of solvent composition
on the protonation constants is discussed. The log10 K2 values of esters generally decreased with increasing ethanol content. However, the log10 K1 values of the esters of L-tyrosine, L-cysteine, and L-tryptophane were found to increase with increasing ethanol content
in contrast those of L-lysine and L-histidine esters. 相似文献
113.
114.
In this paper, we study the existence of the uniformly minimum risk equivariant (UMRE) estimators of parameters in a class
of normal linear models, which include the normal variance components model, the growth curve model, the extended growth curve
model, and the seemingly unrelated regression equations model, and so on. The necessary and sufficient conditions are given
for the existence of UMRE estimators of the estimable linear functions of regression coefficients, the covariance matrixV and (trV)α, where α > 0 is known, in the models under an affine group of transformations for quadratic losses and matrix losses, respectively.
Under the (extended) growth curve model and the seemingly unrelated regression equations model, the conclusions given in literature
for estimating regression coefficients can be derived by applying the general results in this paper, and the sufficient conditions
for non-existence of UMRE estimators ofV and tr(V) are expanded to be necessary and sufficient conditions. In addition, the necessary and sufficient conditions that there
exist UMRE estimators of parameters in the variance components model are obtained for the first time. 相似文献
115.
M.A. Tawhid 《Journal of Optimization Theory and Applications》2002,113(1):149-164
In this paper, we give some sufficient conditions for the local uniqueness of solutions to nonsmooth variational inequalities where the underlying functions are H-differentiable and the underlying set is a closed convex set/polyhedral set/box/polyhedral cone. We show how the solution of a linearized variational inequality is related to the solution of the variational inequality. These results extend/unify various similar results proved for C
1 and locally Lipschitzian variational inequality problems. When specialized to the nonlinear complementarity problem, our results extend/unify those of C
2 and C
1 nonlinear complementarity problems. 相似文献
116.
非线性互补问题的一种全局收敛的显式光滑Newton方法 总被引:2,自引:0,他引:2
本针对Po函数非线性互补问题,给出了一种显式光滑Newton方法,该方法将光滑参数μ进行显式迭代而不依赖于Newton方向的搜索过程,并在适当的假设条件下,证明了算法的全局收敛性。 相似文献
117.
G. Montero L. Gonzlez E. Flrez M. D. García A. Surez 《Numerical Linear Algebra with Applications》2002,9(3):239-247
Parallel preconditioners are presented for the solution of general linear systems of equations. The computation of these preconditioners is achieved by orthogonal projections related to the Frobenius inner product. So, minM∈??∥AM?I∥ F and matrix M0∈?? corresponding to this minimum (?? being any vectorial subspace of ??n(?)) are explicitly computed using accumulative formulae in order to reduce computational cost when subspace ?? is extended to another one containing it. Every step, the computation is carried out taking advantage of the previous one, what considerably reduces the amount of work. These general results are illustrated with the subspace of matrices M such that AM is symmetric. The main application is developed for the subspace of matrices with a given sparsity pattern which may be constructed iteratively by augmenting the set of non‐zero entries in each column. Finally, the effectiveness of the sparse preconditioners is illustrated with some numerical experiments. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
118.
Pulse radiolysis with kinetic spectroscopic detection was applied to study the kinetics of the first steps of radiation induced polymerization of cyclohexyl acrylate and cyclohexyl methacrylate in cyclohexane solvent. The reactions were initiated by cyclohexyl radicals produced in the radiolysis of the solvent. The transient absorption spectra of the -carboxyalkyl type radicals produced in addition reaction show maxima around 300 nm. This shifts to longer wavelength with time after the pulse. This phenomenon was explained by the oligomerization reaction. From the kinetic curves average rate coefficients of termination for the oligomer radicals (2kt) were determined as a function of time elapsed after the electron pulse. The values obtained were compared with those calculated for other (acrylate and methacrylate type) monomers. 相似文献
119.
电路过渡过程所列方程是微分方程,本文中采用的是方框图模型分析法,即将微分方程的复杂示解分解成最基本的加(减)、乘(除)、积分(微分)、增益等运算,采用VB设计用户界面产进行计算,并给出了一算例。 相似文献