全文获取类型
收费全文 | 32866篇 |
免费 | 942篇 |
国内免费 | 251篇 |
专业分类
化学 | 22717篇 |
晶体学 | 223篇 |
力学 | 770篇 |
数学 | 5446篇 |
物理学 | 4903篇 |
出版年
2022年 | 284篇 |
2021年 | 422篇 |
2020年 | 514篇 |
2019年 | 484篇 |
2018年 | 376篇 |
2017年 | 372篇 |
2016年 | 835篇 |
2015年 | 737篇 |
2014年 | 807篇 |
2013年 | 1729篇 |
2012年 | 1869篇 |
2011年 | 2357篇 |
2010年 | 1143篇 |
2009年 | 1008篇 |
2008年 | 2022篇 |
2007年 | 2023篇 |
2006年 | 2004篇 |
2005年 | 1867篇 |
2004年 | 1588篇 |
2003年 | 1385篇 |
2002年 | 1284篇 |
2001年 | 403篇 |
2000年 | 389篇 |
1999年 | 358篇 |
1998年 | 335篇 |
1997年 | 360篇 |
1996年 | 486篇 |
1995年 | 343篇 |
1994年 | 299篇 |
1993年 | 274篇 |
1992年 | 267篇 |
1991年 | 238篇 |
1990年 | 202篇 |
1989年 | 203篇 |
1988年 | 233篇 |
1987年 | 198篇 |
1986年 | 181篇 |
1985年 | 347篇 |
1984年 | 340篇 |
1983年 | 242篇 |
1982年 | 313篇 |
1981年 | 325篇 |
1980年 | 298篇 |
1979年 | 282篇 |
1978年 | 258篇 |
1977年 | 227篇 |
1976年 | 208篇 |
1975年 | 210篇 |
1974年 | 211篇 |
1973年 | 212篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Dr. David J. Lurie I. Nicholson J. S. McLay J. R. Mallard 《Applied magnetic resonance》1992,3(5):917-925
The technique of Field-Cycled Dynamic Nuclear Polarization (FC-DNP) involves the EPR irradiation of a free radical solution and the subsequent observation of the NMR signal, the experiment being carried out at a range of magnetic field strengths in order to measure the free radical’s EPR spectrum. In this work FC-DNP has been used to study the EPR spectrum of DMPO spin-trapped hydroxyl free radicals at magnetic field strengths between 0.5 mT and 13.0 mT (5–130 Gauss). The low-field EPR spectrum contains six separate EPR lines, in contrast to the well-known X-band spectrum where only four are seen. Knowledge of the spin-adduct’s EPR spectrum will be of use to workers involved in low-field EPR, especially those conducting biological or in-vivo spin-trapping experiments. 相似文献
12.
13.
Neutral Community Theory: How Stochasticity and Dispersal-Limitation Can Explain Species Coexistence
Neutral community theory explains biodiversity, i.e. the coexistence of several species, as the result of a stochastic balance
between immigration and extinction on a local level, and between speciation and extinction on a regional level. The most popular
model, presented by Hubbell in 2001, has seen many analytical developments in recent years, which can be used in model analysis,
model testing and model comparison. We review these developments here, and present alternative derivations and shine previously
unnoticed lights on them. 相似文献
14.
Background
The aim of the present study was to characterize the activation profiles of 15 opioid ligands in transfected human embryonic kidney cells expressing only δ opioid receptors. Activation profiles of most of these ligands at δ opioid receptors had not been previously characterized in vitro. Receptor activation was assessed by measuring the inhibition of forskolin-stimulated cAMP production. 相似文献15.
By optimizing pump power ratio between 1st order backward pump and 2nd order forward pump on discrete Raman amplifier, we demonstrated over 2dB noise figure improvement without excessive non-linearity degradation. 相似文献
16.
We exhibit timelike geodesic paths for a metric, introduced by Bonnor [11] and considered also by Steadman [13], and show that coordinate time runs backward along a portion of these geodesics. 相似文献
17.
One of the open questions in the geometry of line arrangements is to what extent does the incidence lattice of an arrangement determine its fundamental group. Line arrangements of up to 6 lines were recently classified by K.M. Fan (Michigan Math. J. 44(2) (1997) 283), and it turns out that the incidence lattice of such arrangements determines the projective fundamental group. We use actions on the set of wiring diagrams, introduced in (Garber et al. (J. Knot Theory Ramf.), to classify real arrangements of up to 8 lines. In particular, we show that the incidence lattice of such arrangements determines both the affine and the projective fundamental groups. 相似文献
18.
Alvaro P. Raposo Hans J. Weber David E. Alvarez-Castillo Mariana Kirchbach 《Central European Journal of Physics》2007,5(3):253-284
We briefly review the five possible real polynomial solutions of hypergeometric differential equations. Three of them are
the well known classical orthogonal polynomials, but the other two are different with respect to their orthogonality properties.
We then focus on the family of polynomials which exhibits a finite orthogonality. This family, to be referred to as the Romanovski
polynomials, is required in exact solutions of several physics problems ranging from quantum mechanics and quark physics to
random matrix theory. It appears timely to draw attention to it by the present study. Our survey also includes several new
observations on the orthogonality properties of the Romanovski polynomials and new developments from their Rodrigues formula. 相似文献
19.
20.
Gabor Schmera Adi Bulsara David Pierson Frank Moss Enrico Di Cera 《Journal of statistical physics》1993,71(5-6):1179-1190
We consider the class of experiments which can be characterized by a Fokker-PIanck dynamics corresponding to the overdamped motion of a state point in a suitable stochastic potential. We assume that the general form of the potential is known (or can be guessed with reasonable accuracy), but that its parameters are to be determined experimentally by measurements made with a noisy instrument. This possible method for determining the potential parameters, which exploits the system's own internal stochastic motion in order to explore rapidly its available parameter space, is substantially more efficient than traditional methods involving time averages of single point measurements, and yet does not appear to have been previously considered. The method could be important when, for example, the experiment must be completed in a limited time owing either to the expense of the experimental materials or to the temporary stationarity of the preparation, situations which are commonly encountered in experimental biochemistry and biology. 相似文献