全文获取类型
收费全文 | 4564篇 |
免费 | 261篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 44篇 |
综合类 | 5篇 |
化学工业 | 1345篇 |
金属工艺 | 73篇 |
机械仪表 | 120篇 |
建筑科学 | 205篇 |
矿业工程 | 9篇 |
能源动力 | 160篇 |
轻工业 | 569篇 |
水利工程 | 28篇 |
石油天然气 | 15篇 |
无线电 | 295篇 |
一般工业技术 | 767篇 |
冶金工业 | 211篇 |
原子能技术 | 47篇 |
自动化技术 | 936篇 |
出版年
2024年 | 8篇 |
2023年 | 42篇 |
2022年 | 198篇 |
2021年 | 233篇 |
2020年 | 109篇 |
2019年 | 132篇 |
2018年 | 157篇 |
2017年 | 155篇 |
2016年 | 207篇 |
2015年 | 121篇 |
2014年 | 193篇 |
2013年 | 341篇 |
2012年 | 290篇 |
2011年 | 357篇 |
2010年 | 239篇 |
2009年 | 263篇 |
2008年 | 246篇 |
2007年 | 199篇 |
2006年 | 206篇 |
2005年 | 163篇 |
2004年 | 124篇 |
2003年 | 114篇 |
2002年 | 90篇 |
2001年 | 67篇 |
2000年 | 67篇 |
1999年 | 61篇 |
1998年 | 67篇 |
1997年 | 48篇 |
1996年 | 45篇 |
1995年 | 48篇 |
1994年 | 26篇 |
1993年 | 36篇 |
1992年 | 12篇 |
1991年 | 17篇 |
1990年 | 13篇 |
1989年 | 15篇 |
1988年 | 10篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1982年 | 16篇 |
1981年 | 11篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1973年 | 3篇 |
排序方式: 共有4829条查询结果,搜索用时 15 毫秒
71.
STUDY OBJECTIVE: To investigate social differences in cancer incidence in Turin, Italy in 1985-87. DESIGN: A cancer incidence follow up study of the turin population in relation to socioeconomic characteristics was performed through record linkage between the 1981 census and the cancer registry. A case-control study nested in the cohort was analysed, where cases were subjects with a new diagnosis of cancer in 1985-87 and controls were a sample of the Turin population, frequency matched by sex and age group. Incidence odd ratios (ORs) were calculated for social classes (defined by education, housing tenure, and socioeconomic group) using a logistic regression model. SETTING: The study population comprised subjects included in the 1981 Turin census (n approximately equal to 1,100,000) who were still alive, 20-69 years old, and were resident in Turin in the middle of study period. PARTICIPANTS: The analyses were based on 4215 male and 3451 female cases, and on 16,913 male and 13,838 female controls. MAIN RESULTS: Compared with the highest educational level, the men in the lowest one showed an OR > 2 for respiratory cancers; OR = 1.48 for stomach cancer; and ORs < 0.7 for skin, colorectal, and prostate cancers. Women with a primary school education were protected against colorectal (OR = 0.71), skin (OR = 0.59), and breast cancer (OR = 0.66) compared with university degree women, but were at risk for cancer of the cervix (OR = 2.33) and stomach cancer (OR = 2.84). The association between educational level (primary school v university) and lung cancer risk is negative for men (OR = 2.47) and positive for women (OR = 0.62), while the association with housing tenure is negative for both sexes (OR = 1.44). CONCLUSIONS: The socioeconomic distribution of some risk factors (for example smoking, alcohol, and diet) in Italy can partially explain the differences in respiratory and digestive cancers. "Unbalanced" health promotion interventions, targeted at social groups with the highest prevalences of risk factors, and national policies for increasing the level of education in the country may play an important role in reducing social differences in cancer risk. 相似文献
72.
Summary Distributed Mutual Exclusion algorithms have been mainly compared using the number of messages exchanged per critical section execution. In such algorithms, no attention has been paid to the serialization order of the requests. Indeed, they adopt FCFS discipline. Conversely, the insertion of priority serialization disciplines, such as Short-Job-First, Head-Of-Line, Shortest-Remaining-Job-First etc., can be useful in many applications to optimize some performance indices. However, such priority disciplines are prone to starvation. The goal of this paper is to investigate and evaluate the impact of the insertion of a priority discipline in Maekawa-type algorithms. Priority serialization disciplines will be inserted by means of agated batch mechanism which avoids starvation. In a distributed algorithm, such a mechanism needs synchronizations among the processes. In order to highlight the usefulness of the priority based serialization discipline, we show how it can be used to improve theaverage response time compared to the FCFS discipline. The gated batch approach exhibits other advantages: algorithms are inherently deadlock-free and messages do not need to piggyback timestamps. We also show that, under heavy demand, algorithms using gated batch exchange less messages than Maekawa-type algorithms per critical section excution.
Roberto Baldoni was born in Rome on February 1, 1965. He received the Laurea degree in electronic engineering in 1990 from the University of Rome La Sapienza and the Ph.D. degree in Computer Science from the University of Rome La Sapienza in 1994. Currently, he is a researcher in computer science at IRISA, Rennes (France). His research interests include operating systems, distributed algorithms, network protocols and real-time multimedia applications.
Bruno Ciciani received the Laurea degree in electronic engineering in 1980 from the University of Rome La Sapienza. From 1983 to 1991 he has been a researcher at the University of Rome Tor Vergata. He is currently full professor in Computer Science at the University of Rome La Sapienza. His research activities include distributed computer systems, fault-tolerant computing, languages for parallel processing, and computer system performance and reliability evaluation. He has published in IEEE Trans. on Computers, IEEE Trans. on Knowledge and Data Engineering, IEEE Trans. on Software Engineering and IEEE Trans. on Reliability. He is the author of a book titled Manufactoring Yield Evaluation of VLSI/WSI Systems to be published by IEEE Computer Society Press.This research was supported in part by the Consiglio Nazionale delle Ricerche under grant 93.02294.CT12This author is also supported by a grant of the Human Capital and Mobility project of the European Community under contract No. 3702 CABERNET 相似文献
73.
Nicola Pellicciotta Ojus Satish Bagal Viridiana Carmona Sosa Giacomo Frangipane Gaszton Vizsnyiczai Roberto Di Leonardo 《Advanced functional materials》2023,33(39):2214801
Biohybrid microbots integrate biological actuators and sensors into synthetic chassis with the aim of providing the building blocks of next-generation micro-robotics. One of the main challenges is the development of self-assembled systems with consistent behavior and such that they can be controlled independently to perform complex tasks. Herein, it is shown that, using light-driven bacteria as propellers, 3D printed microbots can be steered by unbalancing light intensity over different microbot parts. An optimal feedback loop is designed in which a central computer projects onto each microbot a tailor-made light pattern, calculated from its position and orientation. In this way, multiple microbots can be independently guided through a series of spatially distributed checkpoints. By exploiting a natural light-driven proton pump, these bio-hybrid microbots are able to extract mechanical energy from light with such high efficiency that, in principle, hundreds of these systems can be controlled simultaneously with a total optical power of just a few milliwatts. 相似文献
74.
Roberto C. Dante Francisco M. Sánchez-Arévalo Lazaro Huerta Florinella Muñoz-Bisesti Diana Marquez Pablo Martín-Ramos 《Fullerenes, Nanotubes and Carbon Nanostructures》2017,25(11):630-636
Polymeric carbon nitride was synthesized from urea and doped with Cu and Fe to act as co-catalysts. The material doped with Fe was a new composite material composed of Fe(III) oxides (acting as a co-catalyst) wrapped by the polymer layers and amorphous carbon. Furthermore, the copper doped material was described in a previous report. The photocatalytic degradation of the azo dye direct blue 1 (DB) was studied using as photocatalysts: pure carbon nitride (CN), carbon nitride doped with Cu (CN-Cu) and carbon nitride doped with Fe (CN-Fe). The catalysts were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), by X-ray photoelectron spectroscopy (XPS) and Brunauer–Emmett–Teller method (BET), etc. The adsorption phenomenon was studied using the Langmuir and Freundlich models. For the kinetic study, a solution of 500 mg L?1 of DB1 was treated with each catalyst, visible light and H2O2. The dye concentration was measured by spectrophotometry at the wavelength of 565 nm, and the removal of the total organic content (TOC) was quantified. BET analysis yielded surface areas of 60.029, 20.116 and 70.662 m2g?1 for CN, CN-Cu and CN-Fe, respectively. The kinetics of degradation were pseudo-first order, whose constants were 0.093, 0.039 and 0.110 min?1 for CN, CN-Cu and CN-Fe, respectively. The total organic carbon (TOC) removal reached the highest value of 14.46% with CN-Fe. 相似文献
75.
José Augusto de Oliveira Diogo Aparecido Lopes Silva Mariana Guardia Lillian do Nascimento Gambi Otávio José de Oliveira Aldo Roberto Ometto 《Clean Technologies and Environmental Policy》2017,19(6):1761-1774
The companies’ needs to adopt changes in their way of production to maximize the environmental performance required by their stakeholders, and at the same time, to maximize their economic and market performance, have made them seek for environmental strategies and certifications. In this sense, the Cleaner Production and the Environmental Management System based on ISO 14001 have been, respectively, presented, since the main objective of this research is to identify and analyze Cleaner Production contributions to comply with ISO 14001 requirements. For such, a survey research has been carried out in Brazilian industrial companies certified by ISO 14001. We have identified the main performance factors by leading practices and variables of Cleaner Production that contribute to the compliance with the standard requirements by companies. Thus, it has been noted that Cleaner Production is an important strategy for the preparation of companies for certification as well as for improving their environmental performance. 相似文献
76.
Engineered Multifunctional Albumin‐Decorated Porous Silicon Nanoparticles for FcRn Translocation of Insulin
下载免费PDF全文
![点击此处可从《Small (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
João P. Martins Roberto D'Auria Dongfei Liu Flavia Fontana Mónica P. A. Ferreira Alexandra Correia Marianna Kemell Karina Moslova Ermei Mäkilä Jarno Salonen Luca Casettari Jouni Hirvonen Bruno Sarmento Hélder A. Santos 《Small (Weinheim an der Bergstrasse, Germany)》2018,14(27)
The last decade has seen remarkable advances in the development of drug delivery systems as alternative to parenteral injection‐based delivery of insulin. Neonatal Fc receptor (FcRn)‐mediated transcytosis has been recently proposed as a strategy to increase the transport of drugs across the intestinal epithelium. FcRn‐targeted nanoparticles (NPs) could hijack the FcRn transcytotic pathway and cross the epithelial cell layer. In this study, a novel nanoparticulate system for insulin delivery based on porous silicon NPs is proposed. After surface conjugation with albumin and loading with insulin, the NPs are encapsulated into a pH‐responsive polymeric particle by nanoprecipitation. The developed NP formulation shows controlled size and homogeneous size distribution. Transmission electron microscopy (TEM) images show successful encapsulation of the NPs into pH‐sensitive polymeric particles. No insulin release is detected at acidic conditions, but a controlled release profile is observed at intestinal pH. Toxicity studies show high compatibility of the NPs with intestinal cells. In vitro insulin permeation across the intestinal epithelium shows approximately fivefold increase when insulin is loaded into FcRn‐targeted NPs. Overall, these FcRn‐targeted NPs offer a toolbox in the development of targeted therapies for oral delivery of insulin. 相似文献
77.
The semantic definition of action refinement on labelled configuration structures is compared with the notion ofsyntactic substitution, which can be used as another notion of action refinement in a process algebraic setting. The comparison is done by studying a process algebra equipped with sequential composition, parallel composition with an explicit synchronisation set, and an operator for action refinement. On the one hand, the language (including the refinement operator) is given a configuration structure semantics. On the other hand, a reduction procedure transforms a process termPinto aflatterm (i.e., with the refinement operator not occurring in it)red(P) by means of syntactic substitution, defined in a structural inductive way. The main aim of the paper is to investigate general conditions under which the termsPandred(P) have the same semantics. The results we present are essentially dependent on the question whether the refined action can be synchronised or not. In the latter case,Pandred(P) give rise to isomorphic configuration structures under mild assumptions. The former case is considerably more difficult, since then refinement cannot be expected to distribute over parallel composition. We give necessary and sufficientsemanticconditions under which distribution still holds up to semantic equivalence. Subsequently, we also give sufficient (but not necessary)syntacticconditions for reducible terms. Finally, we generalise these results to a language with recursion. 相似文献
78.
Ferreira N Lins L Fink D Kelling S Wood C Freire J Silva C 《IEEE transactions on visualization and computer graphics》2011,17(12):2374-2383
Birds are unrivaled windows into biotic processes at all levels and are proven indicators of ecological well-being. Understanding the determinants of species distributions and their dynamics is an important aspect of ecology and is critical for conservation and management. Through crowdsourcing, since 2002, the eBird project has been collecting bird observation records. These observations, together with local-scale environmental covariates such as climate, habitat, and vegetation phenology have been a valuable resource for a global community of educators, land managers, ornithologists, and conservation biologists. By associating environmental inputs with observed patterns of bird occurrence, predictive models have been developed that provide a statistical framework to harness available data for predicting species distributions and making inferences about species-habitat associations. Understanding these models, however, is challenging because they require scientists to quantify and compare multiscale spatialtemporal patterns. A large series of coordinated or sequential plots must be generated, individually programmed, and manually composed for analysis. This hampers the exploration and is a barrier to making the cross-species comparisons that are essential for coordinating conservation and extracting important ecological information. To address these limitations, as part of a collaboration among computer scientists, statisticians, biologists and ornithologists, we have developed BirdVis, an interactive visualization system that supports the analysis of spatio-temporal bird distribution models. BirdVis leverages visualization techniques and uses them in a novel way to better assist users in the exploration of interdependencies among model parameters. Furthermore, the system allows for comparative visualization through coordinated views, providing an intuitive interface to identify relevant correlations and patterns. We justify our design decisions and present case studies that show how BirdVis has helped scientists obtain new evidence for existing hypotheses, as well as formulate new hypotheses in their domain. 相似文献
79.
The introduction of Internet and Information and communication Technologies (ICT) in offices is a global phenomenon that transformed
white-collar worker job demands. Although there are several studies of e-skills and mental workload for central countries,
there is a lack of similar studies for the Latin American context. An online snowball sampled (n = 352) survey was developed and validated by the authors (internal consistency = 0.7). We characterized ICT worker profiles
from e-skills and these dimensions: attitudes toward, resources usage and technology dependency. Mental Strain was assessed with raw task load index (RTLX) and correlated with the proposed profiles by means of paired
T-tests and Mann–Whitney Tests. The sample was characterized by 7.2% of non visual display terminal users and 92.8% of visual
display terminal, ICT skilled users. Of the latter, 30.7% were ICT practitioners, 30.4% were ICT Users and 27.2% were E-Business
Users. Non VDT users’ mental strain was statistically meaningful smaller than VDT–ICT skilled users’ mental workload. No statistical
differences were found in RTLX results when comparing ICT skilled user profiles. Non VDT users can be identified from ICT
skilled Users by their lower ITC Dependency and minor use of ICT resources. There were no differences in those dimensions
among ICT skilled Profiles. Attitude toward these technologies was a distinct factor for ICT Users in relation to ICT Practitioners
and ITC Business Users. The application of this tool in peripheral and central countries would allow a complete ergonomical
characterization of white-collar workers within the Information Society. 相似文献
80.