全文获取类型
收费全文 | 11945篇 |
免费 | 421篇 |
国内免费 | 51篇 |
专业分类
化学 | 7462篇 |
晶体学 | 58篇 |
力学 | 348篇 |
数学 | 2081篇 |
物理学 | 2468篇 |
出版年
2023年 | 69篇 |
2022年 | 87篇 |
2021年 | 174篇 |
2020年 | 187篇 |
2019年 | 185篇 |
2018年 | 201篇 |
2017年 | 177篇 |
2016年 | 336篇 |
2015年 | 321篇 |
2014年 | 345篇 |
2013年 | 692篇 |
2012年 | 789篇 |
2011年 | 871篇 |
2010年 | 471篇 |
2009年 | 419篇 |
2008年 | 695篇 |
2007年 | 665篇 |
2006年 | 648篇 |
2005年 | 618篇 |
2004年 | 507篇 |
2003年 | 439篇 |
2002年 | 357篇 |
2001年 | 236篇 |
2000年 | 192篇 |
1999年 | 149篇 |
1998年 | 102篇 |
1997年 | 116篇 |
1996年 | 96篇 |
1995年 | 99篇 |
1994年 | 92篇 |
1993年 | 76篇 |
1992年 | 89篇 |
1991年 | 86篇 |
1990年 | 86篇 |
1989年 | 79篇 |
1988年 | 71篇 |
1986年 | 65篇 |
1985年 | 91篇 |
1984年 | 122篇 |
1983年 | 79篇 |
1982年 | 114篇 |
1981年 | 90篇 |
1980年 | 89篇 |
1979年 | 85篇 |
1978年 | 89篇 |
1977年 | 97篇 |
1976年 | 73篇 |
1975年 | 72篇 |
1974年 | 74篇 |
1973年 | 69篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
11.
12.
13.
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
14.
15.
16.
It is proved that biorthogonal polynomials obey two different kinds of Christoffel-Darboux-type formulae, one linking polynomials with a different parameter and one combining polynomials with different degrees. This is used to produce a mixed recurrence relation, which is valid for all biorthogonal polynomials. This recurrence relation establishes several results on interlacing property of zeros of successive biorthogonal polynomials and leads to a new result on the interlace of zeros of orthogonal polynomials (of equal degrees) with respect to two distributionsdψ(x) andx p dψ(x), 0<p≤1, with support in either [0, 1] or [1, ∞). 相似文献
17.
Kasper K. Berthelsen Jesper Møller 《Bulletin of the Brazilian Mathematical Society》2002,33(3):351-367
This primer provides a self-contained exposition of the case where spatial birth-and-death processes are used for perfect
simulation of locally stable point processes. Particularly, a simple dominating coupling from the past (CFTP) algorithm and
the CFTP algorithms introduced in [13], [14], and [5] are studied. Some empirical results for the algorithms are discussed.
Received: 30 June 2002 相似文献
18.
We use the adiabatic hyperspheric expansion and the Faddeev decomposition of the wave function with only s-waves. We derive for a fixed hyperradius an integro-differential equation for the angular eigenvalue and wave function. The
correlations lower the interaction energy for N = 20 by about a factor of 5.
Received October 22, 2001; accepted for publication November 5, 2001 相似文献
19.
Kristian Hougaard Frederik D. Nielsen 《Journal of Optical and Fiber Communications Reports》2004,1(1):63-83
In this paper we will present an overview of the use
of photonic crystal fibers as fiber amplifiers. We
will describe the basic concepts of optical
amplification, and how to do numerical modelling of
such components. We will then identify advantages
and disadvantages of amplifiers based on PCF
technology compared to conventional fibers, and then
go into greater detail on some of these specific
applications, such as low pump power amplifiers, and
high-power double-clad amplifiers and lasers. 相似文献
20.
We predict ultraslow collapse of “tubular image states” (TIS) on material surfaces. TIS are bound Rydberg-like electronic states formed at large distances (∼30 nm) from the surfaces of suspended circularly-symmetric nanowires, such as metallic C nanotubes. The states are formed in potential wells, resulting from a combination of the TIS-electron attraction to image charges in the nanotube and its centrifugal repulsion, caused by spinning around the tube. We demonstrate that TIS can collapse on the tube surface by passing their angular momentum l to circularly polarized flexural phonons excited in the tube. Our analysis shows that for highly detached TIS with l ? 6 the relaxation lifetimes are of the order of 10 ns-1 μs, while for l < 6 these lifetimes are reduced by several orders of magnitude. 相似文献