全文获取类型
收费全文 | 16569篇 |
免费 | 3835篇 |
国内免费 | 908篇 |
专业分类
化学 | 2881篇 |
晶体学 | 93篇 |
力学 | 2153篇 |
综合类 | 348篇 |
数学 | 7285篇 |
物理学 | 8552篇 |
出版年
2024年 | 39篇 |
2023年 | 204篇 |
2022年 | 496篇 |
2021年 | 564篇 |
2020年 | 502篇 |
2019年 | 483篇 |
2018年 | 473篇 |
2017年 | 774篇 |
2016年 | 851篇 |
2015年 | 771篇 |
2014年 | 1083篇 |
2013年 | 1373篇 |
2012年 | 1009篇 |
2011年 | 1106篇 |
2010年 | 939篇 |
2009年 | 965篇 |
2008年 | 998篇 |
2007年 | 1129篇 |
2006年 | 929篇 |
2005年 | 736篇 |
2004年 | 675篇 |
2003年 | 706篇 |
2002年 | 590篇 |
2001年 | 465篇 |
2000年 | 497篇 |
1999年 | 435篇 |
1998年 | 340篇 |
1997年 | 282篇 |
1996年 | 258篇 |
1995年 | 224篇 |
1994年 | 164篇 |
1993年 | 142篇 |
1992年 | 123篇 |
1991年 | 112篇 |
1990年 | 96篇 |
1989年 | 83篇 |
1988年 | 86篇 |
1987年 | 64篇 |
1986年 | 51篇 |
1985年 | 84篇 |
1984年 | 44篇 |
1983年 | 29篇 |
1982年 | 44篇 |
1981年 | 36篇 |
1980年 | 52篇 |
1979年 | 47篇 |
1978年 | 31篇 |
1977年 | 38篇 |
1976年 | 39篇 |
1974年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
The educational system has gradually shifted from a face-to-face to an e-learning system, which has become prevalent in advanced countries with the advance of information technology, and connection of global networks. Accordingly, a growing demand is emerging for more reliable individual certification with technical precision in order to measure and record learning achievements and credentials of participants. The present system has a limit in terms of registration capacity, therefore, its accuracy has often been questioned. Against this background, an individual certification system is proposed particularly for access control in e-learning. Under our proposed system, a compact optical correlator for facial recognition is employed. This correlator was previously tested for of biometrics authentication accuracy and proved highly reliable, having recorded remarkably low error rates (below 1%). The recorded error rate is sufficiently robust that the system itself can be regarded as a valid and practical viable attestation system. 相似文献
143.
X. Y. You 《Heat and Mass Transfer》2003,40(1-2):75-81
Active feedback control for the onset of Rayleigh-Bénard Convection in temperature-dependent-viscosity liquids is investigated.
In this paper, three major problems are addressed: (1) The results of Tang-Bau control are improved by considering the effects
of temperature-dependent viscosity; (2) A more efficient two-plate control strategy is presented. A phenomenon of coalescence
of the unstable modes is observed as the controller gain is large enough; (3) A simple way to estimate the critical Rayleigh
number under the effects of temperature-dependent viscosity is described. Numerical results show that the effects of temperature-dependent
viscosity on the critical Rayleigh number should be taken into account in some cases and the onset of Rayleigh-Bénard convection
can be effectively delayed or advanced by the active feedback control strategies studied here. 相似文献
144.
El Kebir Boukas Peng Shi Sing Kiong Nguang 《Journal of Mathematical Analysis and Applications》2003,282(1):241-255
This paper studies the problem of stochastic stability and disturbance attenuation for a class of linear continuous-time uncertain systems with Markovian jumping parameters. The uncertainties are assumed to be nonlinear and state, control and external disturbance dependent. A sufficient condition is provided to solve the above problem. An H∞ controller is designed such that the resulting closed-loop system is stochastically stable and has a disturbance attenuation γ for all admissible uncertainties. It is shown that the control law is in terms of the solutions of a set of coupled Riccati inequalities. A numerical example is included to demonstrate the potential of the proposed technique. 相似文献
145.
W. Götze 《Journal of statistical physics》1996,83(5-6):1183-1197
146.
Frank Rutz Martin Koch Shilpa Khare Martin Moneke Heike Richter Uwe Ewert 《International Journal of Infrared and Millimeter Waves》2006,27(4):547-556
We report on experiments that evaluate the potential of terahertz (THz) time-domain spectroscopy (TDS) for quality control
of polymeric compounds. We investigate specimens out of a polyethylene compound with silver-coated titanium dioxide nanospheres
and a glass-fiber reinforced epoxy composite. We further examine an industrial polymer product produced by injection molding.
Our data demonstrates that THz imaging is a powerful tool for contactless quality control in the polymer industry. 相似文献
147.
Marek Pękała Jan Mucha Benedicte Vertruyen Rudi Cloots Marcel Ausloos 《Journal of magnetism and magnetic materials》2006
Samples of La0.7Ca0.3Mn1−xGaxO3 with x=0, 0.025, 0.05 and 0.10 were prepared by standard solid-state reaction. They were first characterized chemically, including the microstructure. The magnetic properties and various transport properties, i.e. the electrical resistivity, magnetoresistivity (for a field below 8 T), thermoelectric power and thermal conductivity measured each time on the same sample, are reported. The markedly different behaviour of the x=0.1 sample from those with a smaller Ga content, is discussed. The dilution of the Mn3+/Mn4+ interactions with Ga doping considerably reduces the ferromagnetic double exchange interaction within the manganese lattice leading to a decrease of the Curie temperature. The polaron binding energy varies from 224 to 243 meV with increased Ga doping. 相似文献
148.
第Ⅰ种强度不对称三态叠加多模叠加态光场N次方Y压缩—第一正交相位分量的压缩情况 总被引:2,自引:0,他引:2
根据量子力学中的线性叠加原理,构造了由三个强度不等的多模相干态光场|{Zj(A)}>q、|{Zj(B)}>q和|{Zj(C)}>q的线性叠加所组成的第Ⅰ种强度不对称三态叠加多模叠加态光场|ψl(ABC)>q.利用多模压缩态理论,研究了态|ψl(ABC)>q的第一正交方分量(即磁场分量)的广义非线性等幂次N次方Y压缩特性.结果发现:①在上述各多模相干态光场中各模的强度和各模的初始相位各不相等的情况下,态|ψl(ABC)>q的第一正交分量-磁场分量在一定的条件下,总可呈现出周期性变化的、任意等幂次的N次方Y压缩效应;②当上述各多模相干态光场的强度和各模的初始相位相等时,态|ψl(ABC)>q的磁场分量的N次方Y压缩现象消失,态|ψl(ABC)>q可恒处于等幂次N-Y最小测不准态. 相似文献
149.
A class of long-range predictive adaptive fuzzy relational controllers is presented. The plant behavior is described over an extended time horizon by a fuzzy relational model which is identified based on input-output closed-loop observations of the plant variables. In this class of adaptive controllers the control law attempts to minimize a quadratic cost over an extended control horizon. When used with linear models, this approach has revealed a significant potential for overcoming the limitations of one-step ahead schemes, such as the stabilization of non-minimum phase plants. Here, a uniform framework is adopted for implementing both the fuzzy model and the fuzzy controller, namely distributed fuzzy relational structures gaining from their massive parallel processing features and from the learning capabilities typical of the connectivist approaches. Issues such as maintenance during the adaptation process of the meaning of linguistic terms used at both fuzzy systems interfaces are addressed, namely by introducing a new design methodology for on-line fuzzy systems interface adaptation. The examples presented reinforce the claim of the usefulness of this new approach. 相似文献
150.
The solvability of a class of forward-backward stochastic differential equations (SDEs for short) over an arbitrarily prescribed time duration is studied. The authors design a stochastic relaxed control problem, with both drift and difftusion all being controlled, so that the solvability problem is converted to a problem of finding the nodal set of the viscosity solution to a certain Hamilton-Jacobi-Bellman equation. This method overcomes the fatal difficulty encountered in the traditional contraction mapping approach to the existence theorem of such SDEs. 相似文献