全文获取类型
收费全文 | 1167篇 |
免费 | 104篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 14篇 |
综合类 | 2篇 |
化学工业 | 355篇 |
金属工艺 | 17篇 |
机械仪表 | 24篇 |
建筑科学 | 38篇 |
矿业工程 | 4篇 |
能源动力 | 55篇 |
轻工业 | 112篇 |
水利工程 | 10篇 |
石油天然气 | 1篇 |
无线电 | 121篇 |
一般工业技术 | 220篇 |
冶金工业 | 52篇 |
原子能技术 | 9篇 |
自动化技术 | 239篇 |
出版年
2023年 | 22篇 |
2022年 | 64篇 |
2021年 | 83篇 |
2020年 | 50篇 |
2019年 | 32篇 |
2018年 | 59篇 |
2017年 | 47篇 |
2016年 | 45篇 |
2015年 | 46篇 |
2014年 | 69篇 |
2013年 | 88篇 |
2012年 | 105篇 |
2011年 | 87篇 |
2010年 | 75篇 |
2009年 | 62篇 |
2008年 | 50篇 |
2007年 | 54篇 |
2006年 | 32篇 |
2005年 | 29篇 |
2004年 | 21篇 |
2003年 | 22篇 |
2002年 | 19篇 |
2001年 | 9篇 |
2000年 | 5篇 |
1999年 | 10篇 |
1998年 | 13篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1994年 | 7篇 |
1993年 | 9篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有1273条查询结果,搜索用时 15 毫秒
1.
In recent years biodegradable polymers, particularly polyesters such as the poly(lactic acid) (PLA) and polycaprolactone (PCL), have gained high interests for their applicability in the biomedical and pharmaceutical fields where they're used for manufacturing various different resorbable devices, from tissue engineering scaffolds to controlled drug release systems. Despite many positive characteristics, processability of these materials still remains a critical issue as they easily tend to degrade during manufacturing. In this article we aimed to assess microextrusion as a nondegradative process for manufacturing PLA and PCL. The results we experimentally obtained, that are hereby presented, set a new point in the on‐going debate on degradation during processing of resorbable polymers as they allow to affirm that microextrusion leaves unmodified molecular weight distributions without producing any evident reductions in mean molecular weight. Microextrusion thus represents a risk‐free high molecular weight polymer processing solution for obtaining nondegraded products within pharmaceutical and biomedical production lines, such as for scaffolds for tissue engineering applications or drug delivery. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
2.
We analyze generalization in XCSF and introduce three improvements. We begin by showing that the types of generalizations evolved by XCSF can be influenced by the input range. To explain these results we present a theoretical analysis of the convergence of classifier weights in XCSF which highlights a broader issue. In XCSF, because of the mathematical properties of the Widrow-Hoff update, the convergence of classifier weights in a given subspace can be slow when the spread of the eigenvalues of the autocorrelation matrix associated with each classifier is large. As a major consequence, the system's accuracy pressure may act before classifier weights are adequately updated, so that XCSF may evolve piecewise constant approximations, instead of the intended, and more efficient, piecewise linear ones. We propose three different ways to update classifier weights in XCSF so as to increase the generalization capabilities of XCSF: one based on a condition-based normalization of the inputs, one based on linear least squares, and one based on the recursive version of linear least squares. Through a series of experiments we show that while all three approaches significantly improve XCSF, least squares approaches appear to be best performing and most robust. Finally we show how XCSF can be extended to include polynomial approximations. 相似文献
3.
Mayra Colardo Michele Petraroia Letizia Lerza Daniele Pensabene Noemi Martella Valentina Pallottini Marco Segatto 《International journal of molecular sciences》2022,23(9)
Cholesterol plays a crucial role in the brain, where its metabolism is particularly regulated by astrocytic activity. Indeed, adult neurons suppress their own cholesterol biosynthesis and import this sterol through ApoE-rich particles secreted from astrocytes. Recent evidence suggests that nerve growth factor (NGF) may exert neurotrophic activity by influencing cell metabolism. Nevertheless, the effect of NGF on glial cholesterol homeostasis has still not been elucidated. Thus, the aim of this project is to assess whether NGF could influence cholesterol metabolism in glial cells. To reach this objective, the U373 astrocyte-derived cell line was used as an experimental model. Immunoblot and ELISA analysis showed that proteins and enzymes belonging to the cholesterol metabolism network were increased upon NGF treatment in glial cells. Furthermore, NGF significantly increased ApoE secretion and the amount of extracellular cholesterol in the culture medium. Co-culture and U373-conditioned medium experiments demonstrated that NGF treatment efficiently counteracted rotenone-mediated cytotoxicity in N1E-115 neuronal cells. Conversely, neuroprotection mediated by NGF treatment was suppressed when N1E-115 were co-cultured with ApoE-silenced U373 cells. Taken together, these data suggest that NGF controls cholesterol homeostasis in glial cells. More importantly, NGF exerts neuroprotection against oxidative stress, which is likely associated with the induction of glial ApoE secretion. 相似文献
4.
5.
Abou-Rjeily C. Daniele N. Belfiore J.-C. 《Communications, IEEE Transactions on》2006,54(11):1960-1972
In this paper, we present the construction of full rate, fully diverse, and totally real space-time (ST) codes for ultra-wideband (UWB) transmissions. In particular, we construct two families of codes adapted to real carrierless UWB communications that employ pulse position modulation, pulse amplitude modulation, or a combination of the two. The first family encodes adjacent symbols and is constructed from totally real cyclic division algebras. The second family encodes the pulses used to convey one information symbol, and permits achieving high performance levels with reduced complexity. The first family of codes achieves only a fraction of the coding gain of the second one. Moreover, these coding gains are independent from the size of the transmitted constellation. For time-hopping multiple-access channels, the amplitude spreading code associated with the second family of codes is taken to be user-specific. In this case, a simple design criterion is proposed, and spreading matrices constructed according to this criterion permit reducing the level of multiple-access interference (MAI). Simulations performed over realistic indoor UWB channels verify the theoretical claims and show high performance levels and better immunity against MAI 相似文献
6.
Mario Caironi Matt Bird Daniele Fazzi Zhihua Chen Riccardo Di Pietro Christopher Newman Antonio Facchetti Henning Sirringhaus 《Advanced functional materials》2011,21(17):3371-3381
Charge transport is investigated in high‐mobility n‐channel organic field‐effect transistors (OFETs) based on poly{[N,N′‐bis(2‐octyldodecyl)‐naphthalene‐1,4,5,8‐bis(dicarboximide)‐2,6‐diyl]‐alt‐5,5′‐(2,2′‐bithiophene)} (P(NDI2OD‐T2), Polyera ActivInk? N2200) with variable‐temperature electrical measurements and charge‐modulation spectroscopy. Results indicate an unusually uniform energetic landscape of sites for charge‐carrier transport along the channel of the transistor as the main reason for the observed high‐electron mobility. Consistent with a lateral field‐independent transport at temperatures down to 10 K, the reorganization energy is proposed to play an important role in determining the activation energy for the mobility. Quantum chemical calculations, which show an efficient electronic coupling between adjacent units and a reorganization energy of a few hundred meV, are consistent with these findings. 相似文献
7.
8.
Tetiana Borzda Christoph Gadermaier Natasa Vujicic Peter Topolovsek Milos Borovsak Tomaz Mertelj Daniele Viola Cristian Manzoni Eva A. A. Pogna Daniele Brida Maria Rosa Antognazza Francesco Scotognella Guglielmo Lanzani Giulio Cerullo Dragan Mihailovic 《Advanced functional materials》2015,25(22):3351-3358
The 2D semiconductor MoS2 in its mono‐ and few‐layer form is expected to have a significant exciton binding energy of several 100 meV, suggesting excitons as the primary photoexcited species. Nevertheless, even single layers show a strong photovoltaic effect and work as the active material in high sensitivity photodetectors, thus indicating efficient charge carrier photogeneration. Here, modulation spectroscopy in the sub‐ps and ms time scales is used to study the photoexcitation dynamics in few‐layer MoS2. The results suggest that the primary photoexcitations are excitons that efficiently dissociate into charges with a characteristic time of 700 fs. Based on these findings, simple suggestions for the design of efficient MoS2 photovoltaic and photodetector devices are made. 相似文献
9.
Ivan Damgård Sebastian Faust Pratyay Mukherjee Daniele Venturi 《Journal of Cryptology》2017,30(1):152-190
Related key attacks (RKAs) are powerful cryptanalytic attacks where an adversary can change the secret key and observe the effect of such changes at the output. The state of the art in RKA security protects against an a-priori unbounded number of certain algebraic induced key relations, e.g., affine functions or polynomials of bounded degree. In this work, we show that it is possible to go beyond the algebraic barrier and achieve security against arbitrary key relations, by restricting the number of tampering queries the adversary is allowed to ask for. The latter restriction is necessary in case of arbitrary key relations, as otherwise a generic attack of Gennaro et al. (TCC 2004) shows how to recover the key of almost any cryptographic primitive. We describe our contributions in more detail below. (1) We show that standard ID and signature schemes constructed from a large class of \(\Sigma \)-protocols (including the Okamoto scheme, for instance) are secure even if the adversary can arbitrarily tamper with the prover’s state a bounded number of times and obtain some bounded amount of leakage. Interestingly, for the Okamoto scheme we can allow also independent tampering with the public parameters. (2) We show a bounded tamper and leakage resilient CCA-secure public key cryptosystem based on the DDH assumption. We first define a weaker CCA-like security notion that we can instantiate based on DDH, and then we give a general compiler that yields CCA security with tamper and leakage resilience. This requires a public tamper-proof common reference string. (3) Finally, we explain how to boost bounded tampering and leakage resilience [as in (1) and (2) above] to continuous tampering and leakage resilience, in the so-called floppy model where each user has a personal hardware token (containing leak- and tamper-free information) which can be used to refresh the secret key. We believe that bounded tampering is a meaningful and interesting alternative to avoid known impossibility results and can provide important insights into the security of existing standard cryptographic schemes. 相似文献
10.
Chiari L Dozza M Cappello A Horak FB Macellari V Giansanti D 《IEEE transactions on bio-medical engineering》2005,52(12):2108-2111
This paper introduces a prototype audio-biofeedback system for balance improvement through the sonification using trunk kinematic information. In tests of this system, normal healthy subjects performed several trials in which they stood quietly in three sensory conditions while wearing an accelerometric sensory unit and headphones. The audio-biofeedback system converted in real-time the two-dimensional horizontal trunk accelerations into a stereo sound by modulating its frequency, level, and left/right balance. Preliminary results showed that subjects improved balance using this audio-biofeedback system and that this improvement was greater the more that balance was challenged by absent or unreliable sensory cues. In addition, high correlations were found between the center of pressure displacement and trunk acceleration, suggesting accelerometers may be useful for quantifying standing balance. 相似文献