全文获取类型
收费全文 | 108711篇 |
免费 | 14396篇 |
国内免费 | 8673篇 |
专业分类
化学 | 37441篇 |
晶体学 | 1813篇 |
力学 | 14634篇 |
综合类 | 1562篇 |
数学 | 30319篇 |
物理学 | 46011篇 |
出版年
2024年 | 131篇 |
2023年 | 960篇 |
2022年 | 1578篇 |
2021年 | 2907篇 |
2020年 | 2679篇 |
2019年 | 2479篇 |
2018年 | 2292篇 |
2017年 | 3102篇 |
2016年 | 3673篇 |
2015年 | 3191篇 |
2014年 | 4990篇 |
2013年 | 7852篇 |
2012年 | 5872篇 |
2011年 | 6635篇 |
2010年 | 5759篇 |
2009年 | 6740篇 |
2008年 | 6964篇 |
2007年 | 7036篇 |
2006年 | 6113篇 |
2005年 | 5228篇 |
2004年 | 4655篇 |
2003年 | 4409篇 |
2002年 | 6549篇 |
2001年 | 3774篇 |
2000年 | 3176篇 |
1999年 | 2728篇 |
1998年 | 2297篇 |
1997年 | 1958篇 |
1996年 | 1714篇 |
1995年 | 1560篇 |
1994年 | 1475篇 |
1993年 | 1319篇 |
1992年 | 1237篇 |
1991年 | 925篇 |
1990年 | 758篇 |
1989年 | 607篇 |
1988年 | 580篇 |
1987年 | 477篇 |
1986年 | 426篇 |
1985年 | 573篇 |
1984年 | 461篇 |
1983年 | 257篇 |
1982年 | 451篇 |
1981年 | 597篇 |
1980年 | 509篇 |
1979年 | 547篇 |
1978年 | 450篇 |
1977年 | 349篇 |
1976年 | 284篇 |
1973年 | 163篇 |
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
81.
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
82.
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
83.
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
84.
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
85.
It is proved that for any integerk≥ 54 000, there isN
k
>0 depending onk only such that every even integer ≥N
k
is a sum of two odd prime numbers andk powers of 2.
Project partially supported by RGC Research Grant (No.HKU 7122/97P) and Post-Doctoral Fellowship of the University of Hong
Kong. 相似文献
86.
FINITE GROUPS WHOSE AUTOMORPHISM GROUP HAS ORDER CUBEFREE 总被引:3,自引:0,他引:3
Li Shirong 《数学年刊B辑(英文版)》1997,18(3):301-308
FINITEGROUPSWHOSEAUTOMORPHISMGROUPHASORDERCUBEFREELISHIRONGAbstractLetGdenoteafinitegroup.Itisshownthatif|Aut(G)|iscubefre... 相似文献
87.
We investigate congruence classes and direct congruence classes of m-tuples in the complex projective space ℂP
n
. For direct congruence one allows only isometries which are induced by linear (instead of semilinear) mappings. We establish
a canonical bijection between the set of direct congruence classes of m-tuples of points in ℂP
n
and the set of equivalence classes of positive semidefinite Hermitean m×m-matrices of rank at most n+1 with 1's on the diagonal. As a corollary we get that the direct congruence class of an m-tuple is uniquely determined by the direct congruence classes of all of its triangles, provided that no pair of points of
the m-tuple has distance π/2. Examples show that the situation changes drastically if one replaces direct congruence classes by
congruence classes or if distances π/2 are allowed. Finally we do the same
kind of investigation also for the complex hyperbolic space ℂH
n
. Most of the results are completely analogous, however, there are also some interesting differences.
Received: 15 January 1996 相似文献
88.
Summary. We generalise and apply a refinement indicator of the type originally designed by Mackenzie, Süli and Warnecke in [15] and
[16] for linear Friedrichs systems to the Euler equations of inviscid, compressible fluid flow. The Euler equations are symmetrized
by means of entropy variables and locally linearized about a constant state to obtain a symmetric hyperbolic system to which
an a posteriori error analysis of the type introduced in [15] can be applied. We discuss the details of the implementation of the refinement
indicator into the DLR--Code which is based on a finite volume method of box type on an unstructured grid and present numerical results.
Received May 15, 1995 / Revised version received April 17, 1996 相似文献
89.
Rafael López 《Annals of Global Analysis and Geometry》1997,15(3):201-210
In this paper we study constant mean curvature compact surfaces with two Jordan curves in parallel planes as boundary and we investigate the point at which the surface inherits the symmetries of its boundary. 相似文献
90.