全文获取类型
收费全文 | 9475篇 |
免费 | 1107篇 |
国内免费 | 678篇 |
专业分类
化学 | 6200篇 |
晶体学 | 95篇 |
力学 | 500篇 |
综合类 | 58篇 |
数学 | 1126篇 |
物理学 | 3281篇 |
出版年
2024年 | 29篇 |
2023年 | 170篇 |
2022年 | 345篇 |
2021年 | 344篇 |
2020年 | 418篇 |
2019年 | 350篇 |
2018年 | 315篇 |
2017年 | 256篇 |
2016年 | 444篇 |
2015年 | 422篇 |
2014年 | 448篇 |
2013年 | 636篇 |
2012年 | 721篇 |
2011年 | 827篇 |
2010年 | 511篇 |
2009年 | 534篇 |
2008年 | 583篇 |
2007年 | 522篇 |
2006年 | 471篇 |
2005年 | 396篇 |
2004年 | 320篇 |
2003年 | 268篇 |
2002年 | 235篇 |
2001年 | 197篇 |
2000年 | 136篇 |
1999年 | 153篇 |
1998年 | 100篇 |
1997年 | 85篇 |
1996年 | 118篇 |
1995年 | 80篇 |
1994年 | 100篇 |
1993年 | 71篇 |
1992年 | 64篇 |
1991年 | 54篇 |
1990年 | 52篇 |
1989年 | 40篇 |
1988年 | 30篇 |
1987年 | 26篇 |
1986年 | 22篇 |
1985年 | 31篇 |
1984年 | 41篇 |
1983年 | 18篇 |
1982年 | 36篇 |
1981年 | 19篇 |
1980年 | 22篇 |
1979年 | 37篇 |
1978年 | 26篇 |
1976年 | 23篇 |
1975年 | 15篇 |
1974年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
In this paper we present several results about local MV-algebras, extending existing results given for MV-chains. The role
of local MV-algebras in sheaf representation and weak boolean product is stressed and the relationship of local MV-algebras
with varieties of MV-algebras is analyzed.
Presented by S. Pulmannova.
Received November 11, 2005; accepted in final form December 20, 2005. 相似文献
52.
53.
Supply Chain Management (SCM) is an important activity in all producing facilities and in many organizations to enable vendors,
manufacturers and suppliers to interact gainfully and plan optimally their flow of goods and services. To realize this, a
dynamic modelling approach for characterizing supply chain activities is opportune, so as to plan efficiently the set of activities
over a distributed network in a formal and scientific way. The dynamical system will result so complex that it is not generally
possible to specify the functional forms and the parameters of interest, relating outputs to inputs, states and stochastic
terms by experiential specification methods. Thus the algorithm that will presented is Data Driven, determining simultaneously
the functional forms, the parameters and the optimal control policy from the data available for the supply chain. The aim
of this paper is to present this methodology, by considering dynamical aspects of the system, the presence of nonlinear relationships
and unbiased estimation procedures to quantify these relations, leading to a nonlinear and stochastic dynamical system representation
of the SCM problem. Moreover, the convergence of the algorithm will be proved and the satisfaction of the required statistical
conditions demonstrated. Thus SCM problems may be formulated as formal scientific procedures, with well defined algorithms
and a precise calculation sequence to determine the best alternative to enact. A “Certainty equivalent principle” will be
indicated to ensure that the effects of the inevitable uncertainties will not lead to indeterminate results, allowing the
formulation of demonstrably asymptotically optimal management plans. 相似文献
54.
Gui Qiao XU Yong Sheng SUN Yong Ping LIU 《数学学报(英文版)》2006,22(6):1667-1678
In this paper, we consider the n-widths and average widths of Besov classes in the usual Sobolev spaces. The weak asymptotic results concerning the Kolmogorov n-widths, the linear n-widths, the Gel'fand n-widths, in the Sobolev spaces on T^d, and the infinite-dimensional widths and the average widths in the Sobolev spaces on Ra are obtained, respectively. 相似文献
55.
We introduce a general scheme to realize perfect storage of quantum information in systems of interacting qubits. This novel approach is based on global external controls of the Hamiltonian that yield time-periodic inversions in the dynamical evolution allowing a perfect periodic quantum state reconstruction. We illustrate the method in the particularly interesting and simple case of spin systems affected by XY residual interactions with or without static imperfections. The global control is achieved by step time inversions of an overall topological phase of the Aharonov-Bohm type. Such a scheme holds both at finite size and in the thermodynamic limit, thus enabling the massive storage of arbitrarily large numbers of local states, and is stable against several realistic sources of noise and imperfections. 相似文献
56.
Debora Di Caprio 《Topology and its Applications》2006,153(14):2680-2702
We introduce and study some completeness properties for systems of open coverings of a given topological space. A Hausdorff space admitting a system of cardinality κ satisfying one of these properties is of type Gκ. Hence, we define several new variants of the ?ech number and use elementary submodels to determine further results. We introduce M-hulls and M-networks, for M elementary submodel. As an application, we give estimates for both the tightness and the Lindelöf number of a generic upper hyperspace. Two recent results of Costantini, Holá and Vitolo on the tightness of co-compact hyperspaces follow from ours as corollaries. 相似文献
57.
荧光光谱法研究蛋白质构象的电磁-温度协同效应 总被引:1,自引:1,他引:0
长期以来电磁生物效应受到人们普遍关注,近年来从各个角度进行了相关研究。电磁-温度协同效应是当前的热点。本研究通过电磁场及温度协同对蛋白质影响的研究,发现蛋白质在电磁场作用下的不可逆变性,而且这种变性也遵循Arrhenius规律,并进一步得出电磁-温度协同作用的蛋白质变性模型。本文从分子反应动力学的角度解释了电磁-温度协同效应,并对非热效应作了一定的探讨。 相似文献
58.
M. A. Macrì C. Del Gratta L. Di Donato S. Di Luzio G. L. Romani S. Della Penna A. Pasquarelli 《Il Nuovo Cimento D》1994,16(5):425-432
Summary A preliminary study is here reported on a new potential marker for biomagnetic measurements. The marker consists of superparamagnetic
polymer microspheres which were detected in the presence of external steady magnetic fields by means of an r.f.-SQUID magnetometer.
The particles were prepared in samples differing in the concentration value and immersed in a homogeneous magnetic field of
variable intensity. A simple model was taken into account for the distribution of the microspheres in the samples, so that
the theoretical values were compared to the marker field values measured by the biomagnetic sensor. The overall sensitivity
of the experimental apparatus and the minimum concentration value of the marker were then estimated. 相似文献
59.
影响海洋微藻生产麻痹性贝类毒素的重要生态因素 总被引:1,自引:0,他引:1
麻痹性贝类毒素是有害赤潮海洋微藻生产的重要毒素种类,本文综述了影响该类毒素的主要生态因素有光,温度,盐度和营养盐4类;弱光对毒素合成有抑制作用。低温下PSP毒素产量高,通过对营养盐吸收机制的离子效应,盐度可影响毒素的生命合成,不同种类和株系对N、P限制的反应有极大差异。 相似文献
60.
Summary Differential scanning calorimetric measurements in the early stage of isothermal crystal growth of polyethylene oxide are
analysed in the light of irreversible thermodynamics. An accurate evaluation of the equilibrium melting temperature is done
by fitting the thermograms obtained at different undercoolings and referring to the activation energy values already known
from the literature.
Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994. 相似文献