全文获取类型
收费全文 | 471篇 |
免费 | 22篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 3篇 |
综合类 | 1篇 |
化学工业 | 147篇 |
金属工艺 | 16篇 |
机械仪表 | 17篇 |
建筑科学 | 11篇 |
能源动力 | 17篇 |
轻工业 | 34篇 |
水利工程 | 3篇 |
无线电 | 26篇 |
一般工业技术 | 101篇 |
冶金工业 | 44篇 |
原子能技术 | 6篇 |
自动化技术 | 68篇 |
出版年
2024年 | 2篇 |
2023年 | 8篇 |
2022年 | 16篇 |
2021年 | 21篇 |
2020年 | 19篇 |
2019年 | 13篇 |
2018年 | 24篇 |
2017年 | 29篇 |
2016年 | 22篇 |
2015年 | 4篇 |
2014年 | 24篇 |
2013年 | 42篇 |
2012年 | 26篇 |
2011年 | 27篇 |
2010年 | 21篇 |
2009年 | 15篇 |
2008年 | 20篇 |
2007年 | 15篇 |
2006年 | 18篇 |
2005年 | 9篇 |
2004年 | 6篇 |
2003年 | 2篇 |
2002年 | 5篇 |
2001年 | 7篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 12篇 |
1997年 | 4篇 |
1996年 | 10篇 |
1995年 | 9篇 |
1994年 | 11篇 |
1993年 | 10篇 |
1992年 | 3篇 |
1991年 | 6篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1980年 | 8篇 |
1979年 | 1篇 |
1976年 | 2篇 |
1973年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有494条查询结果,搜索用时 31 毫秒
21.
Mohd. Hashim Sagar E. Shirsath S.S. Meena Pramod Bhatt R.K. Kotnala Shalendra Kumar Ravi Kumar Dachepalli Ravinder Alimuddin 《Ceramics International》2014
The Cr3+ ions doped multi-oxide ZnFe2−xCrxO4 ferrite nanoparticles have been synthesized by chemical co-precipitation method. Site occupancies of Zn2+, Cr3+ and Fe3+ ions were analyzed using X-ray diffraction data and Buerger's method. The effect of the constituent phase variation on the magnetic hysteresis behavior was examined by saturation magnetization which decreases with the increase in Cr3+ content in place of Fe3+ ions at octahedral B-site. Typical blocking temperature (TB) around 90 K was observed by zero field cooling and field cooling magnetization study. Room temperature Mössbauer spectra show two paramagnetic doublets (tetrahedral and octahedral sites). The isomer shifts of both doublets decrease whereas quadrupole splitting and relative area of tetrahedral A-site increases with increasing Cr3+ substitution. The dielectric constant (measured on compositions x=0, 0.4, 0.8 and 1.0) increases when the temperature increases as in the semiconductor. This behavior is attributed to the hopping of electrons between Fe2+ and Fe3+ ions with a thermal activation. 相似文献
22.
Sagar Pal 《应用聚合物科学杂志》2009,111(5):2630-2636
Guar gum was partially carboxymethylated by the reaction of the base polysaccharide with the sodium salt of monochloroacetic acid in presence of sodium hydroxide. The resulting products (carboxymethyl guar with different degrees of substitution) were characterized by a variety of material characterization techniques, such as intrinsic viscosity measurement, determination of molecular weight, elemental analysis, thermal analysis, 13C‐NMR spectra, and Fourier transform infrared analysis. Various grades of carboxymethyl guar gum, which were synthesized in the laboratory, were studied for their suitability as flocculants and viscosifiers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 相似文献
23.
Blends of linear low density polyethylene (LLDPE) and ethylene-co-methyl acrylate (EMA) having 60/40 composition was studied
with and without compatibilizing agent. The compatibilizing agent used was maleic anhydride grafted linear low density polyethylene
(LLDPE-g-MA). The LLDPE backbones of the compatibilizer are compatible with LLDPE blend component, whereas the maleic anhydride
is affinated with carbonyl groups of EMA. The effectiveness of the compatibilizing agent was evaluated using different techniques
like mechanical, thermal, scanning electron microscopy and rheological studies. Best compatibilization effect was found in
the blend at a loading of 3 wt% of compatibilizer since at this level of compatibilizer complex viscosity, tensile strength,
modulus, elongation at break, impact strength was found to be higher. The increase in the melt viscosity, storage modulus
and thermal stability of the compatibilized blends indicated enhanced interactions between the discrete LLDPE and EMA phases
induced by the functional compatibilizer. 相似文献
24.
25.
Sagar Shankar Jagtap Rupali B. Awhad B. Santosh Pandit B. Vidyasagar 《Microgravity science and technology》2011,23(1):41-48
Microgravity, as a different environment, has been shown to affect plant growth and development (Sievers et al. 1996; Sack 1997). In the present study, effects of slow clinorotation (2 rpm) on growth and chlorophyll content in rice (variety: PRH-10)
seedlings were investigated. Rice seeds were clinorotated continuously for 3, 5 and 7 days under ambient conditions. Root
and shoot lengths and weights of rice seedlings were measured on the third, fifth and seventh day. Chlorophyll was extracted
using N, N-Dimethylformamide (DMF). Absorption and fluorescence spectra of chlorophyll were recorded. Chlorophyll a, chlorophyll
b and total chlorophyll contents were calculated from absorption spectra using Arnon’s method. Results showed an increase
in root and shoot lengths in clinorotated samples. Similar results were obtained for root and shoot weights. Absorption spectra
of chlorophyll showed no shift in the absorption peaks. Chlorophyll content was increased in clinorotated samples as compared
to the controls. Interestingly, the difference between chlorophyll content in control and clinorotated samples decreased as
the number of days of clinorotation increased. Chlorophyll a/b ratio was lowered in clinorotated samples as compared to the
controls. These results suggest that slow clinorotation (2 rpm) affects plant growth and chlorophyll content in rice seedlings. 相似文献
26.
Sagar S Pandit Ram S Kulkarni Hemangi G Chidley Ashok P Giri Keshav H Pujari Tobias G Köllner Jörg Degenhardt Jonathan Gershenzon Vidya S Gupta 《Journal of the science of food and agriculture》2009,89(12):2071-2081
BACKGROUND: Volatile blends of five developing and five ripening stages of mango (Mangifera indica L. cv. Alphonso) were investigated along with those of flowers and leaves. Raw and ripe fruits of cv. Sabja were also used for comparison. RESULTS: A total of 55 volatiles belonging to various chemical classes such as aldehydes, alcohols, mono‐ and sesquiterpene hydrocarbons, lactones and furanones were identified. In all Alphonso tissues monoterpenes quantitatively dominated, with 57–99% contribution; in particular, (Z)‐ocimene was found in the highest amount. Ripeness was characterized by the de novo appearance of lactones and furanones in the blend of monoterpenes. Sabja was distinguished by the abundance of monoterpene hydrocarbons in the raw fruit, and that of sesquiterpene hydrocarbons and their derivatives in the ripe stage. CONCLUSION: Various stages of the Alphonso fruit during transition from flower to ripe fruit are characterized by unique volatile signatures that are distinguished from each other by the qualitative and quantitative appearance of different volatile compounds. Thus volatiles can be highly informative markers while studying the development and ripening of mango. Copyright © 2009 Society of Chemical Industry 相似文献
27.
Sagar Raj Satyal Ben Leshchinsky Jie Han Madan Neupane 《Geotextiles and Geomembranes》2018,46(2):190-205
Due to extensive right-of-way, railroads are inevitably subject to poor subgrade conditions and interrupted service for significant maintenance due to excessive deformations and loss of track geometry. Geocell confinement presents itself as a possible solution for improving performance of ballasted railroad embankments over weak subgrade. To investigate the efficacy of geocell confinement on ballasted railway embankments, a set of well-instrumented, large-scale cyclic plate loading tests and numerical simulations were performed on geocell-confined ballast overlaying a weak subgrade material. The agreement of results from tests and simulations served as a basis for simulating practical track geometry and performance for various geocell configurations and subgrades using three-dimensional (3D) finite element (FE) analyses. The study showed that geocell reinforcement significantly decreased track settlement, decreased subgrade deformations with lower and uniform distribution of vertical stresses on subgrade and inhibited lateral deformation and serviceability under cyclic loading. These results demonstrate that geocell confinement can be an effective alternative to subsurface improvement or shorter maintenance cycles, particularly on weak subgrades. 相似文献
28.
BACKGROUND: The technical properties of polyolefinic thermoplastic elastomer (TPE) systems can be modified significantly using fillers like nano‐silica. Controlled irradiation can potentially be an effective way of tailoring the technical properties of such nano‐silica‐filled TPE systems. RESULTS: The effect of controlled electron‐beam irradiation on the properties of a pristine silica nanoparticle‐filled model low‐density polyethylene/ethylene–(vinyl acetate) (LDPE/EVA) TPE system is explored in this paper. The morphology of such a filled system was investigated using scanning electron microscopy (SEM) and field‐emission SEM. The dispersion of silica particles was analysed using transmission electron microscopy which clearly indicates that at low loading a fine dispersion of silica occurs in the polymer matrix. Swelling studies and Fourier transform infrared analyses indicate the occurrence of a favourable EVA–silica interaction. On the whole, it is observed that electron‐beam irradiation induces a high degree of reinforcement in all the silica‐filled samples through interfacial crosslinking as well as controlled crosslinking in the two polymer phases. In a few samples the processing characteristics are remarkably preserved following concurrent nano‐silica reinforcement and irradiation, while the technical properties of TPE systems, including set, solvent swelling and mechanical properties, are improved. However, the improvement in properties is a strong function of sequence of addition of filler in the LDPE/EVA blends. CONCLUSION: The green technique studied can be potentially extended for the improvement of the technical properties of conventional TPE systems. Copyright © 2009 Society of Chemical Industry 相似文献
29.
Sagar Chaki Edmund Clarke Joël Ouaknine Natasha Sharygina Nishant Sinha 《Formal Aspects of Computing》2005,17(4):461-483
We present a framework for model checking concurrent software systems which incorporates both states and events. Contrary
to other state/event approaches, our work also integrates two powerful verification techniques, counterexample-guided abstraction
refinement and compositional reasoning. Our specification language is a state/event extension of linear temporal logic, and
allows us to express many properties of software in a concise and intuitive manner. We show how standard automata-theoretic
LTL model checking algorithms can be ported to our framework at no extra cost, enabling us to directly benefit from the large
body of research on efficient LTL verification.
We also present an algorithm to detect deadlocks in concurrent message-passing programs. Deadlock- freedom is not only an
important and desirable property in its own right, but is also a prerequisite for the soundness of our model checking algorithm.
Even though deadlock is inherently non-compositional and is not preserved by classical abstractions, our iterative algorithm
employs both (non-standard) abstractions and compositional reasoning to alleviate the state-space explosion problem. The resulting
framework differs in key respects from other instances of the counterexample-guided abstraction refinement paradigm found
in the literature.
We have implemented this work in the magic verification tool for concurrent C programs and performed tests on a broad set
of benchmarks. Our experiments show that this new approach not only eases the writing of specifications, but also yields important
gains both in space and in time during verification. In certain cases, we even encountered specifications that could not be
verified using traditional pure event-based or state-based approaches, but became tractable within our state/event framework.
We also recorded substantial reductions in time and memory consumption when performing deadlock-freedom checks with our new
abstractions. Finally, we report two bugs (including a deadlock) in the source code of Micro-C/OS versions 2.0 and 2.7, which
we discovered during our experiments.
This research was sponsored by the National Science Foundation (NSF) under grants no. CCR-9803774 and CCR-0121547, the Office
of Naval Research (ONR) and the Naval Research Laboratory (NRL) under contract no. N00014-01-1-0796, the Army Research Office
(ARO) under contract no. DAAD19-01-1-0485, and was conducted as part of the Predictable Assembly from Certifiable Components
(PACC) project at the Software Engineering Institute (SEI).
This article combines and builds upon the papers (CCO+04) and (CCOS04).
Received December 2004
Revised July 2005
Accepted July 2005 by Eerke A. Boiten, John Derrick, Graeme Smith and Ian Hayes 相似文献
30.
Murray Stokely Sagar Chaki Joël Ouaknine 《Electronic Notes in Theoretical Computer Science》2006,157(1):77
In this paper we investigate how formal software verification systems can be improved by utilising parallel assignment in weakest precondition computations.We begin with an introduction to modern software verification systems. Specifically, we review the method in which software abstractions are built using counterexample-guided abstraction refinement (CEGAR). The classical NP-complete parallel assignment problem is first posed, and then an additional restriction is added to create a special case in which the problem is tractable with an O(n2) algorithm. The parallel assignment problem is then discussed in the context of weakest precondition computations. In this special situation where statements can be assumed to execute truly concurrently, we show that any sequence of simple assignment statements without function calls can be transformed into an equivalent parallel assignment block.Results of compressing assignment statements into a parallel form with this algorithm are presented for a wide variety of software applications. The proposed algorithms were implemented in the ComFoRT reasoning framework [J. Ivers and N. Sharygina. Overview of ComFoRT: A model checking reasoning framework. Technical Report CMU/SEI-2004-TN-018, Carnegie Mellon Software Engineering Institute, 2004] and used to measure the improvement in the verification of real software systems. This improvement in time proved to be significant for many classes of software. 相似文献