全文获取类型
收费全文 | 5119篇 |
免费 | 110篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 41篇 |
综合类 | 1篇 |
化学工业 | 1055篇 |
金属工艺 | 65篇 |
机械仪表 | 94篇 |
建筑科学 | 253篇 |
矿业工程 | 21篇 |
能源动力 | 84篇 |
轻工业 | 491篇 |
水利工程 | 37篇 |
石油天然气 | 20篇 |
无线电 | 249篇 |
一般工业技术 | 927篇 |
冶金工业 | 1270篇 |
原子能技术 | 34篇 |
自动化技术 | 591篇 |
出版年
2022年 | 34篇 |
2021年 | 46篇 |
2020年 | 48篇 |
2019年 | 50篇 |
2018年 | 59篇 |
2017年 | 44篇 |
2016年 | 75篇 |
2015年 | 69篇 |
2014年 | 129篇 |
2013年 | 288篇 |
2012年 | 199篇 |
2011年 | 266篇 |
2010年 | 182篇 |
2009年 | 192篇 |
2008年 | 252篇 |
2007年 | 209篇 |
2006年 | 228篇 |
2005年 | 198篇 |
2004年 | 148篇 |
2003年 | 146篇 |
2002年 | 135篇 |
2001年 | 95篇 |
2000年 | 106篇 |
1999年 | 81篇 |
1998年 | 134篇 |
1997年 | 118篇 |
1996年 | 109篇 |
1995年 | 83篇 |
1994年 | 92篇 |
1993年 | 92篇 |
1992年 | 84篇 |
1991年 | 57篇 |
1990年 | 83篇 |
1989年 | 80篇 |
1988年 | 59篇 |
1987年 | 86篇 |
1986年 | 78篇 |
1985年 | 84篇 |
1984年 | 83篇 |
1983年 | 62篇 |
1982年 | 65篇 |
1981年 | 67篇 |
1980年 | 44篇 |
1979年 | 57篇 |
1978年 | 53篇 |
1977年 | 44篇 |
1976年 | 45篇 |
1975年 | 37篇 |
1974年 | 30篇 |
1972年 | 30篇 |
排序方式: 共有5233条查询结果,搜索用时 15 毫秒
61.
Gary Felder 《Computer Physics Communications》2008,179(8):604-606
We describe an MPI C++ program that we have written and made available for calculating the evolution of interacting scalar fields in an expanding universe on parallel clusters. The program is a parallel programming extension of the simulation program LATTICEEASY. The ability to run these simulations on parallel clusters, however, greatly extends the range of scales and times that can be simulated. The program is particularly useful for the study of reheating and thermalization after inflation. The program and its full documentation are available on the Web at http://www.science.smith.edu/departments/Physics/fstaff/gfelder/latticeeasy/. In this paper we provide a brief overview of what the program does and what it is useful for.
Program summary
Program title: CLUSTEREASYCatalogue identifier: AEBJ_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEBJ_v1_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 7469No. of bytes in distributed program, including test data, etc.: 613 334Distribution format: tar.gzProgramming language: C++/MPIComputer: Cluster. Must have the library FFTW installedOperating system: AnyRAM: Typically 4 MB to 1 GB per processorClassification: 1.9External routines: A single-precision version of the FFTW library (http://www.fftw.org/) must be available on the target machine.Nature of problem: After inflation the universe consisted of interacting fields in a high energy, nonthermal state [1]. The evolution of these fields cannot be described with standard approximation techniques such as linearization, kinetic theory, or Hartree expansion, and must thus be simulated numerically. Fortunately, the fields rapidly acquire large occupation numbers over a range of frequencies, so their evolution can be accurately modeled with classical field theory [2]. The specific fields and interactions relevant at these high energies are not known, so different models must be tested phenomenologically. In many cases, e.g., those involving symmetry breaking, the wide range of physical time and length scales in the problem requires parallel computing.Solution method: CLUSTEREASY solves the equations of motion for interacting scalar fields in an expanding universe. The user describes a particular theory by entering the field potential and its derivatives in a model file and the program then uses a staggered leapfrog method to evolve the field equations and Friedmann equation for the fields and the expansion of the universe. Different processors compute the evolution on subgrids defined by block decomposition, and the processors exchange edge data after each time step to allow for calculation of spatial derivatives.Restrictions: In its current form CLUSTEREASY only includes scalar fields and does not include metric perturbations. For 2D and 3D simulations the cluster must already have the (free) libraries FFTW installed.Additional comments: CLUSTEREASY is the parallel form of the program LATTICEEASY (AEAW_v1_0), Comp. Phys. Comm. 178 (2008) 929.Note: The default installation type for FFTW is double-precision so care must be taken to specify single-precision when running the “configure” file associated with the FFTW software package installation.Running time: The running time can range from minutes to weeks.References:[1] A.D. Linde, Particle Physics and Inflationary Cosmology, Harwood, Chur, Switzerland, 1990.[2] S. Khlebnikov, I. Tkachev, Phys. Rev. Lett. 77 (1996) 219, hep-ph/9603378. 相似文献62.
Reports an error in the original article by M. A. Small and G. B. Melton (Professional Psychology: Research and Practice, 1994[August], Vol 25[3], 228–233). Footnote 1 incorrectly indicates that the Craig brief was written without the aid of private legal counsel. Though the brief in question was written with more APA member involvement than has been the case for other briefs, private legal counsel participated and was listed as a coauthor. (The following abstract of this article originally appeared in record 1994-43476-001.) States have passed legislation governing the procedures by which children may testify in cases of child abuse. In Maryland v. Craig (1990), the US Supreme Court reviewed the constitutionality of these procedures. As a result, psychologists may be asked to perform evaluations regarding the potential trauma a child faces in confronting a defendant in a criminal case. Specifically, opinions of psychologists may be sought as to the potential trauma a child may endure as a result of a face-to-face confrontation with a defendant. Research relevant to this assessment is reviewed, and it is suggested that psychologists may be of most help in preparing children to testify.… (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
63.
Engineering linear F(ab')2 fragments for efficient production in Escherichia coli and enhanced antiproliferative activity 总被引:1,自引:0,他引:1
Zapata Gerardo; Ridgway John B. B.; Mordenti Joyce; Osaka Gary; Wong Wai Lee T.; Bennett Gregory L.; Carter Paul 《Protein engineering, design & selection : PEDS》1995,8(10):1057-1062
We developed a novel bivalent antibody fragment, the linear(L-) F(ab')2, comprising tandem repeats of a heavy chain fragmentVHCH1VHCH1 cosecreted with a light chain.Functional humanized L-F(ab')2 directed against p185HER2 wassecreted from Escherichia coli at high titer (100 mg/l) andpurified to homogeneity. The L-F(ab')2 binds two equivalentsof antigen with an apparent affinity (Kd = 0.46 nM) that iswithin 3-fold of the corresponding thioether-linked F(ab')2fragment The N-terminal site binds antigen with an affinity(Kd = 1.2 nM) that is 4-fold greater than that for the C-terminalsite, as shown by the comparison of L-F(ab')2 variants containinga single functional binding site. L-F(ab')2 has greater antiproliferativeactivity than the thioether-linked F(ab')2 against the p185HER2-overexpressingtumor cell line BT474. Linear and thioether-linked F(ab')2 havevery similar pharmacokinetic properties in normal mice, andtheir serum permanence times are respectively 7- and 8-foldlonger than the corresponding Fab fragment L-F(ab')2 offersa facile route to bivalent antibody fragments that are potentiallysuitable for clinical applications, and that may have improvedbiological activity compared with thioether-linked F(ab')2 fragments. 相似文献
64.
The dynamics of avalanches of granular materials from initiation to runout. Part II. Experiments 总被引:1,自引:0,他引:1
Summary This paper describes a model to predict the flow of an initially stationary mass of cohesionsless granular material down a rough curved bed and checks it against laboratory experiments that were conducted with two different kinds of granular materials that are released from rest and travel in a chute consisting of a straight inclined section, a curved segment that is followed by a straight horizontal segment. This work is of interest in connection with the motion of landslides, rockfalls and ice and dense flow snow avalanches. Experiments were performed with two different granular materials, nearly spherical glass beads of 3 mm nominal diameter, Vestolen particles (a light plastic material) of lense type shape and 4 mm nominal diameter and 2,5 mm height. Piles of finite masses of these granular materials with various initial shapes and weight were released from rest in a 100 mm wide chute with the mentioned bent profile. The basal surface consisted of smooth PVC, but was in other experiments also coated with drawing paper and with sandpaper. The granular masses under motion were photographed and partly video filmed and thus the geometry of the avalanche was recorded as a function of position and time. For the two granular materials and for the three bed linings the angle of repose and the bed friction angle were determined. The experimental technique with which the laboratory avalanches were run are described in detail as is the reliability of the generated data. We present and use the depth-averaged field equations of balance of mass and linear momentum as presented by Savage and Hutter [28]. These are partial differential equations for the depth averaged streamwise velocity and the distribution of the avalanche depth and involve two phenomenological parameters, the internal angle of friction, ø, and a bed friction angle, , both as constitutive properties of Coulomb-type behaviour. We present the model but do not derive its equations. The numerical integration scheme for these equations is a Lagrangian finite difference scheme used earlier by Savage and Hutter [27],[28]. We present this scheme for completeness but do not discuss its peculiarities. Comparison of the theoretical results with experiments is commenced by discussing the implementation of the initial conditions. Observations indicate that with the onset of the motion a dilatation is involved that should be accomodated for in the definition of the initial conditions. Early studies of the temporal evolution of the trailing and leading edges of the granular avalanche indicate that their computed counterparts react sensitively to variations in the bed friction angle but not to those of the internal angle of friction. Furthermore, a weak velocity dependence of the bed friction angle, , is also scen to have a small, but negligible influence on these variables. We finally compare the experimental results with computational findings for many combinations of the masses of the granular materials and bed linings. It is found that the experimental results and the theoretical predictions agree satisfactorily. They thus validate the simple model equations that were proposed in Savage and Hutter [28]. 相似文献
65.
In this paper, we concentrate on justifying the decisions we made in developing the TEI recommendations for feature structure markup. The first four sections of this paper present the justification for the recommended treatment of feature structures, of features and their values, and of combinations of features or values and of alternations and negations of features and their values. Section 5 departs briefly from the linguistic focus to argue that the markup scheme developed for feature structures is in fact a general-purpose mechanism that can be used for a wide range of applications. Section 6 describes an auxiliary document called a feature system declaration that is used to document and validate a system of feature-structure markup. The seventh and final section illustrates the use of the recommended markup scheme with two examples, lexical tagging and interlinear text analysis.Terry Langendoen is Professor and Head of the Department of Linguistics at The University of Arizona. He was Chair of the TEI Committee on Analysis and Interpretation. He received his PhD in Linguistics from the Massachusetts Institute of Technology in 1964, and held teaching positions at The Ohio State University and the City University of New York (Brooklyn College and the Graduate Center) before moving to Arizona in 1988. He is author, co-author, or co-editor of six books in linguistics, and of numerous articles.Gary Simons is Director of the Academic Computing Department of the Summer Institute of Linguistics, Dallas, TX. He served on the TEI Committee on Analysis and Interpretation. He received his PhD in Linguistics (with minor emphasis in Computer Science) from Cornell University in 1979. Before taking up his current position in 1984, he spent five years in the Solomon Islands doing field work with SIL. He is author, co-author, or co-editor of eight books in the fields of linguistics and linguistic computing.The initial feature-structure recommendations were formulated by the Analysis and Interpretation Committee at a meeting in Tucson, Arizona in March 1990, following suggestions by Mitch Marcus and Beatrice Santorini. The authors received valuable help in the further revision and refinement of the recommendations from Steven Zepp. 相似文献
66.
Over the past decade, the call to foster computational thinking (CT) in every child has received considerable attention. However, there is little understanding of whether children are developmentally ready to think computationally and what specific CT concepts and skills can be developed at various ages. This study explored the developmental and gender differences in CT skills of 197 Grade 4–6 students (aged 9–13) before being exposed to instruction and investigated the age–gender interaction effects on their CT acquisition in an intervention combining both programming and non-programming (unplugged) activities. Results show that students' CT skills followed a developmental progression before instruction. Gender difference across ages was insignificant in conditionals, logical operators, pattern recognition and generalization skills. Additionally, students of different ages developed CT differently during the intervention, and their CT acquisition was unaffected by gender. Implications for practice and research in CT education were discussed. 相似文献
67.
68.
Biwei Deng Rong Xu Kejie Zhao Yongfeng Lu Sabyasachi Ganguli Gary J. Cheng 《Materials Today》2018,21(5):467-474
Manufacturing ultralight and mechanical reliable materials has been a long-time challenge. Ceramic-based mechanical metamaterials provide significant opportunities to reverse their brittle nature and unstable mechanical properties and have great potential as strong, ultralight, and ultrastiff materials. However, the failure of ceramics nanolattice and degradation of strength/modulus with decreasing density are caused by buckling of the struts and failure of the nodes within the nanolattices, especially during cyclic loading. Here, we explore a new class of 3D ceramic-based metamaterials with a high strength–density ratio, stiffness, recoverability, cyclability, and optimal scaling factor. Deformation mode of the fabricated nanolattices has been engineered through the unique material design and architecture tailoring. Bending-dominated hollow nanolattice (B-H-Lattice) structure is employed to take advantages of its flexibility, while a few nanometers of carbonized mussel-inspired bio-polymer (C-PDA) is coherently deposited on ceramics’ nanolayer to enable non-buckling struts and bendable nodes during deformation, resulting in reliable mechanical properties and outperforming the current bending-dominated lattices (B-Lattices) and carbon-based cellulose materials. Meanwhile, the structure has comparable stiffness to stretching-dominated lattices (S-Lattices) while with better cyclability and reliability. The B-H-Lattices exhibit high specific stiffness (>106?Pa·kg?1·m?3), low-density (~30?kg/m3), buckling-free recovery at 55% strain, and stable cyclic loading behavior under up to 15% strain. As one of the B-Lattices, the modulus scaling factor reaches 1.27, which is lowest among current B-Lattices. This study suggests that non-buckling behavior and reliable nodes are the key factors that contribute to the outstanding mechanical performance of nanolattice materials. A new concept of engineering the internal deformation behavior of mechanical metamaterial is provided to optimize their mechanical properties in real service conditions. 相似文献
69.
DI Blyth MS Pedrick TJ Savage H Bright JE Beesley S Sanjar 《Canadian Metallurgical Quarterly》1998,19(1):38-54
70.
A systematic approach to parameter-dependent control synthesis of a high-speed supercavitation vehicle (HSSV) is presented. The aim of the control design is to provide robust reference tracking across a large flight envelope, while directly accounting for the interaction of liquid and gas phases with the vehicle. A nonlinear dynamic HSSV model is presented and discussed relative to the actual vehicle. A linear, parameter-varying (LPV) controller is synthesized for angle rate tracking in the presence of model uncertainty. The control design takes advantage of coupling in the governing equations to achieve improved performance. Multiple LPV controllers synthesized for smaller overlapping regions of the parameter space are blended together, providing a single controller for the full flight envelope. Time-domain simulations implemented on high-fidelity simulations, provide insight into the performance and robustness of the proposed scheme. 相似文献