全文获取类型
收费全文 | 3064篇 |
免费 | 167篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 43篇 |
综合类 | 2篇 |
化学工业 | 553篇 |
金属工艺 | 66篇 |
机械仪表 | 58篇 |
建筑科学 | 90篇 |
矿业工程 | 11篇 |
能源动力 | 100篇 |
轻工业 | 288篇 |
水利工程 | 23篇 |
石油天然气 | 8篇 |
无线电 | 305篇 |
一般工业技术 | 589篇 |
冶金工业 | 710篇 |
原子能技术 | 37篇 |
自动化技术 | 350篇 |
出版年
2023年 | 22篇 |
2022年 | 52篇 |
2021年 | 65篇 |
2020年 | 58篇 |
2019年 | 72篇 |
2018年 | 78篇 |
2017年 | 88篇 |
2016年 | 75篇 |
2015年 | 71篇 |
2014年 | 94篇 |
2013年 | 166篇 |
2012年 | 141篇 |
2011年 | 183篇 |
2010年 | 127篇 |
2009年 | 108篇 |
2008年 | 134篇 |
2007年 | 115篇 |
2006年 | 107篇 |
2005年 | 104篇 |
2004年 | 89篇 |
2003年 | 98篇 |
2002年 | 77篇 |
2001年 | 48篇 |
2000年 | 56篇 |
1999年 | 51篇 |
1998年 | 111篇 |
1997年 | 90篇 |
1996年 | 83篇 |
1995年 | 59篇 |
1994年 | 55篇 |
1993年 | 47篇 |
1992年 | 36篇 |
1991年 | 28篇 |
1990年 | 39篇 |
1989年 | 32篇 |
1988年 | 31篇 |
1987年 | 25篇 |
1986年 | 20篇 |
1985年 | 28篇 |
1984年 | 26篇 |
1983年 | 32篇 |
1982年 | 20篇 |
1981年 | 17篇 |
1980年 | 11篇 |
1979年 | 30篇 |
1978年 | 17篇 |
1977年 | 22篇 |
1976年 | 22篇 |
1975年 | 13篇 |
1973年 | 12篇 |
排序方式: 共有3233条查询结果,搜索用时 15 毫秒
1.
Joel Kuula Heino Kuuluvainen Jarkko V. Niemi Erkka Saukko Harri Portin Anu Kousa 《Aerosol science and technology》2020,54(2):190-202
AbstractLung deposited surface area (LDSA) is a relatively new metric that has been argued to be more accurate at predicting health effects from aerosol exposure. For typical atmospheric aerosol, the LDSA concentration depends mainly on the concentration of ultrafine particles (e.g. vehicular exhaust emissions and residential wood combustion) and therefore optical methods cannot be used to measure and quantify it. The objective of this study was to investigate and describe typical characteristics of LDSA under different urban environments and evaluate how a diffusion charging-based Pegasor AQ Urban sensor (Pegasor Ltd., Finland) can be used as an alternative to optical sensors when assessing local combustion emissions and respective LDSA concentrations. Long-term (12?months) sensor measurements of LDSA were carried out at three distinctly different measurement sites (four sensor nodes) in the Helsinki metropolitan area, Finland. The sites were affected mainly by vehicular exhaust emission (street canyon and urban background stations) and by residential wood combustion (two detached housing area stations). The results showed that the accuracy of the AQ Urban was good (R2 = 0.90) for the measurement of LDSA when compared to differential mobility particle sizer. The mean concentrations of LDSA were more than twice as high at the street canyon (mean 22 µm2 cm?3) site when compared to the urban background site (mean 9.4 µm2 cm?3). In the detached housing area, the mean concentrations were 12 µm2 cm?3, and wood combustion typically caused high LDSA peaks in the evenings. High correlations and similar diurnal cycles were observed for the LDSA and black carbon at street canyon and urban background stations. The utilization of a small-scale sensor network (four nodes) showed that the cross-station variability in hourly LDSA concentrations was significant in every site, even within the same detached housing area (distance between the two sites ~670?m). 相似文献
2.
3.
4.
Physical Stability of Octenyl Succinate–Modified Polysaccharides and Whey Proteins for Potential Use as Bioactive Carriers in Food Systems 下载免费PDF全文
The high cost and potential toxicity of biodegradable polymers like poly(lactic‐co‐glycolic)acid (PLGA) has increased the interest in natural and modified biopolymers as bioactive carriers. This study characterized the physical stability (water sorption and state transition behavior) of selected starch and proteins: octenyl succinate–modified depolymerized waxy corn starch (DWxCn), waxy rice starch (DWxRc), phytoglycogen, whey protein concentrate (80%, WPC), whey protein isolate (WPI), and α‐lactalbumin (α‐L) to determine their potential as carriers of bioactive compounds under different environmental conditions. After enzyme modification and particle size characterization, glass transition temperature and moisture isotherms were used to characterize the systems. DWxCn and DWxRc had increased water sorption compared to native starch. The level of octenyl succinate anhydrate (OSA) modification (3% and 7%) did not reduce the water sorption of the DWxCn and phytoglycogen samples. The Guggenheim–Andersen–de Boer model indicated that native waxy corn had significantly (P < 0.05) higher water monolayer capacity followed by 3%‐OSA‐modified DWxCn, WPI, 3%‐OSA‐modified DWxRc, α‐L, and native phytoglycogen. WPC had significantly lower water monolayer capacity. All Tg values matched with the solid‐like appearance of the biopolymers. Native polysaccharides and whey proteins had higher glass transition temperature (Tg) values. On the other hand, depolymerized waxy starches at 7%‐OSA modification had a “melted” appearance when exposed to environments with high relative humidity (above 70%) after 10 days at 23 °C. The use of depolymerized and OSA‐modified polysaccharides blended with proteins created more stable blends of biopolymers. Hence, this biopolymer would be suitable for materials exposed to high humidity environments in food applications. 相似文献
5.
6.
Joel P. Martin J. Edward Swan II Robert J. Moorhead II Zhanping Liu Shangshu Cai 《Computer Graphics Forum》2008,27(3):991-998
We present the results from a user study looking at the ability of observers to mentally integrate wind direction and magnitude over a vector field. The data set chosen for the study is an MM5 (PSU/NCAR Mesoscale Model) simulation of Hurricane Lili over the Gulf of Mexico as it approaches the southeastern United States. Nine observers participated in the study. This study investigates the effect of layering on the observer's ability to determine the magnitude and direction of a vector field. We found a tendency for observers to underestimate the magnitude of the vectors and a counter‐clockwise bias when determining the average direction of a vector field. We completed an additional study with two observers to try to uncover the source of the counter‐clockwise bias. These results have direct implications to atmospheric scientists, but may also be able to be applied to other fields that use 2D vector fields. 相似文献
7.
Seema Hiranandani Joel Saltz Piyush Mehrotra Harry Berryman 《Journal of Parallel and Distributed Computing》1991,12(4)
Many researchers approach the problem of programming distributed memory machines by assuming a global shared name space. Thus the user views the distributed memory of the machine as though it were shared. A major issue that arises at this point is how to manage the memory. When a processor accesses data stored on another processor's memory, data must be moved between the two processors. Once these data are retrieved from another processor's memory, several interesting issues are raised. Where should these data be stored locally? What transformations must be performed to the code to guarantee that the nonlocal accesses reference the correct memory location? What optimizations can be performed to reduce the time spent in accessing the nonlocal data? In this paper we examine various data migration mechanisms that allow an explicit and controlled mapping of data to memory. We describe, experimentally evaluate, and model a set of schemes for storing and retrieving off-processor array elements. The schemes are all based on using hash tables for efficient access of nonlocal data. The three different techniques evaluated are the basic hashed cache, partial enumeration, and full enumeration, the details of which are described in the paper. In all three schemes, nonlocal data are stored in hash tables—the difference is in the amount of memory used by the schemes and the retrieval mechanisms for nonlocal data. 相似文献
8.
Data compiled by the American Psychological Association (APA) revealed that 7%–10% of ethics complaints filed were against custody evaluators. Comparative data from various state and provincial psychology boards remain too sketchy to permit an accurate appraisal of this problem at the local level. Nevertheless, vulnerability to ethics complaints remains an occupational hazard for the private practitioner who engages in custody assessment. This article offers practitioners who conduct custody evaluations suggestions for reducing their risk of incurring an ethics complaint and discusses variables to consider when responding to a review board inquiry. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
9.
Two studies examined the relationship between the content of a self-threat and the attractiveness of available self-affirmations (C. M. Steele, 1988). After self-threat was induced by means of a cognitive dissonance procedure, participants' choices for affirmations were examined in order to explore whether the attractiveness of a given affirmation depends on its relevance to the threatened domain of the self-concept. The authors hypothesized that when faced with a threat to a specific self-conception or standard, individuals may forego affirmations within the threatened self-concept domain in favor of affirmations of unrelated, compensatory domains. Both studies supported this hypothesis and further suggested that such selective self-affirmation can lead individuals to modify their self-concepts by identifying with self-aspects that justify dissonant behavior and by disidentifying with the standards that such behavior violates. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
10.
A Burger D Voges P Demange CR Perez R Huber R Berendes 《Canadian Metallurgical Quarterly》1994,237(4):479-499
Annexin V binds to phospholipids in a calcium-dependent manner and exhibits calcium channel activity in vitro. We prepared a variety of mutants yielding information about the structure-function relationship of the ion channel activity. All mutants were characterized by X-ray crystallography, electron microscopy and electrophysiological measurements. Their structures are insignificantly changed whereas their electrophysiological properties are drastically different. Glu95, located in the central hydrophilic pore of the molecule, is crucial for the ion selectivity filter as its exchange leads to reduced calcium and increased sodium conductance. The removal of Glu17, located on the protein surface and far from the ion conduction pathway, leads to the appearance of a second conductance level of 9 pS in addition to the conductance level of about 30 pS in the wild-type molecule. This was also the case for Glu78, which is part of a weak calcium binding site. The exchange of Glu17 and Glu78 produced a mutant retaining only the smaller conductance level. We conclude that these two residues influence the angle between the two halves of the molecule, which determines the diameter of the ion conduction pathway, thereby leading to the occurrence of a second conductance level. 相似文献