首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1755篇
  免费   22篇
  国内免费   1篇
电工技术   32篇
化学工业   356篇
金属工艺   28篇
机械仪表   27篇
建筑科学   79篇
矿业工程   7篇
能源动力   47篇
轻工业   106篇
水利工程   24篇
石油天然气   4篇
无线电   123篇
一般工业技术   241篇
冶金工业   480篇
原子能技术   14篇
自动化技术   210篇
  2021年   30篇
  2020年   20篇
  2019年   23篇
  2018年   25篇
  2017年   20篇
  2016年   22篇
  2015年   19篇
  2014年   31篇
  2013年   94篇
  2012年   47篇
  2011年   83篇
  2010年   63篇
  2009年   42篇
  2008年   58篇
  2007年   69篇
  2006年   41篇
  2005年   35篇
  2004年   35篇
  2003年   36篇
  2002年   37篇
  2001年   27篇
  2000年   30篇
  1999年   25篇
  1998年   90篇
  1997年   65篇
  1996年   43篇
  1995年   42篇
  1994年   40篇
  1993年   32篇
  1992年   19篇
  1991年   15篇
  1990年   26篇
  1989年   20篇
  1988年   27篇
  1987年   31篇
  1986年   27篇
  1985年   33篇
  1984年   17篇
  1983年   24篇
  1982年   25篇
  1981年   23篇
  1980年   19篇
  1979年   26篇
  1978年   17篇
  1977年   29篇
  1976年   23篇
  1975年   26篇
  1974年   14篇
  1973年   15篇
  1971年   13篇
排序方式: 共有1778条查询结果,搜索用时 15 毫秒
11.
A feature of the empirical literature in colour psychology is that little attention has been given to how people in real settings engage in colour selection. Surprisingly, with rare exceptions, we know almost nothing about this. Besides its theoretical significance within psychology, this question has practical implications for industries where colour choice is important. A study is reported into that most ubiquitous of activities, selecting a paint colour for the home. This used a retrospective method supported by qualitative data analysis (NVivo) in which participants described their process of colour selection. The results indicate a process that is far from uniform, but one that consists of two essential stages. The first involves arriving at what we refer to as an affective specification of the qualities sought. Once constructed, this leads to the second stage of matching colour attributes to that specification. Selecting a wall colour emerges as a surprisingly complex process, and one that corresponds more closely to a search than to a simple affective choice. A parallel is drawn with decision research, particularly the field of naturalistic decision‐making. From participants' reports, colour selection also emerges as a process that women appear to understand better than men. © 2007 Wiley Periodicals, Inc. Col Res Appl, 33, 55–60, 2008  相似文献   
12.
This paper reviews available information on the state of practice of inservice material property monitoring performed in European energy industries. Current practice includes a range of standard nondestructive testing and monitoring methods, improved remote sampling and surveillance specimen testing, and new monitoring techniques which are emerging from ongoing development programs. These new technologies include ultrasonic, positron annihilation, neutron diffraction, and magnetic techniques.  相似文献   
13.
Immunocytochemistry and retrograde labeling were used to define the thalamic projections of calbindin- and parvalbumin-containing cells in superficial layers of the rat's superior colliculus (SC). Quantitative analysis revealed that 90.8 +/- 2.2% (mean +/- standard deviation) of the calbindin-immunoreactive neurons in the stratum griseum superficiale (SGS) projected to the dorsal lateral geniculate nucleus (LGNd) and that 91.3 +/- 4.3% of calbindin-immunoreactive neurons in the stratum opticum (SO) projected to the lateral posterior nucleus (LP). In contrast, only 17.3 +/- 2.5% of parvalbumin-immunoreactive neurons in the SGS were found to project to the LGNd and 16.5 +/- 3.1% of the parvalbumin-immunoreactive SO cells were retrogradely labeled after LP injections. Few of the parvalbumin-immunoreactive neurons in either the SGS (7.2 +/- 2.5%) or the SO (9.2 +/- 2.5%) were GABA positive. The retrograde-labeling results suggest that parvalbumin-immunoreactive neurons in the rat's SO and SGS may either be primarily interneurons or have descending projections, while calbindin-containing cells are primarily thalamic projection neurons. These results are consistent with data from other rodents, but almost exactly the opposite of data that have been reported for the cat for these same populations of SC projection neurons. Such interspecies differences raise questions regarding the functional importance of expressing one calcium-binding protein versus another in a specific neuronal population.  相似文献   
14.
All fields of engineering, whether chemical, civil, electrical, materials, mechanical, etc., encompass a common body of essential mathematics and science. In the freshman year of Drexels E4 program, this common mathematical and scientific foundation is cultivated in the Mathematical and Scientific Foundations of Engineering I, II and III (MSFE I, MSFE II, MSFE III). In an integrated fashion, MSFE I presents the essential calculus, physics and engineering mechanics vital to the freshman engineering student. In the first two quarters, MSFE II presents chemistry with clearly defined engineering applications and significance: in the third quarter, MSFE II presents living systems with the same thrust. Also in the third quarter, MSFE III presents basic circuits and circuit elements, and a brief introduction to electromagnetic theory.  相似文献   
15.
16.

Introduction

Hyperglycaemia is a common complication of stress and prematurity in extremely low-birth-weight infants. Model-based insulin therapy protocols have the ability to safely improve glycaemic control for this group. Estimating non-insulin-mediated brain glucose uptake by the central nervous system in these models is typically done using population-based body weight models, which may not be ideal.

Method

A head circumference-based model that separately treats small-for-gestational-age (SGA) and appropriate-for-gestational-age (AGA) infants is compared to a body weight model in a retrospective analysis of 48 patients with a median birth weight of 750 g and median gestational age of 25 weeks. Estimated brain mass, model-based insulin sensitivity (SI) profiles, and projected glycaemic control outcomes are investigated. SGA infants (5) are also analyzed as a separate cohort.

Results

Across the entire cohort, estimated brain mass deviated by a median 10% between models, with a per-patient median difference in SI of 3.5%. For the SGA group, brain mass deviation was 42%, and per-patient SI deviation 13.7%. In virtual trials, 87–93% of recommended insulin rates were equal or slightly reduced (Δ < 0.16 mU/h) under the head circumference method, while glycaemic control outcomes showed little change.

Conclusion

The results suggest that body weight methods are not as accurate as head circumference methods. Head circumference-based estimates may offer improved modelling accuracy and a small reduction in insulin administration, particularly for SGA infants.  相似文献   
17.
Microsomal membrane preparations from the developing seeds of safflower (Carthamus tinctorius, var. Gila) and turnip-rape (Brassica campestris, var. Bele) catalyzed the assembly of triacylglycerols (triglycerides) from sn-glycerol 3-phosphate and acyl-CoA. The membrane preparations were used to assess the acyl specificity properties of the initial acylating enzymes—glycerol 3-phosphate acyltransferase (GPAT) and 1-acylglycerol 3-phosphate acyltransferase (lysophosphatidic acid acyltransferase, LPAAT)—that are responsible for the fatty acids at positions sn-1 and sn-2 of the sn-triacylglycerol, respectively. In spectrophotometric assays it was possible to evaluate, to some extent, how these enzymes will utilize unusual and foreign fatty acids that are not normally found in these particular plant species. The acylating enzymes from both plants used, to varying extents, a comprehensive range of acyl-CoA donor species and some kinetic properties of the substrates involved are presented. The enzymes from safflower, however, were generally the more selective, whereas the turnip-rape was less particular and could utilize a range of acyl substrates. The enzymes from both plants hardly utilized erucate (C22∶1), and the significance of this is discussed in terms of mechanisms which have evolved in order to exclude certain, perhaps detrimental, fatty acids from structural membrane lipids and dedicate them to storage lipid assembly. The ability of the microsomal preparations, from the developing seeds of both plants, to synthesize cocoabutter type fats was investigated. Microsomal membranes were incubated with glycerol 3-phosphate and equimolar amounts of palmitate, oleate and stearate. Safflower preparations catalyzed the construction of sn-triacylglycerol with largely palmitate, oleate and stearate in positions sn-1, 2 and 3, respectively. The selectivity for acyl species in rape was less pronounced, however, substantial saturated-unsaturated-saturated oils were still produced. The results are discussed in terms of the acyl selectivity properties of the glycerol acylating enzymes. It is evident that given the correct composition of fatty acids, the plant can produce cocoabutter or other exotic fats.  相似文献   
18.
The Soil and Water Assessment Tool (SWAT), a physically-based watershed-scale model, holds promise as a means to predict tributary sediment and nutrient loads to the Laurentian Great Lakes. In the present study, model performance is compared across six watersheds draining into Lake Erie to determine the applicability of SWAT to watersheds of differing characteristics. After initial model parameterization, the Huron, Raisin, Maumee, Sandusky, Cuyahoga, and Grand SWAT models were calibrated (1998-2001) and confirmed, or validated (2002-2005), individually for stream water discharge, sediment loads, and nutrient loads (total P, soluble reactive P, total N, and nitrate) based on available datasets. SWAT effectively predicted hydrology and sediments across a range of watershed characteristics. SWAT estimation of nutrient loads was weaker although still satisfactory at least two-thirds of the time across all nutrient parameters and watersheds. SWAT model performance was most satisfactory in agricultural and forested watersheds, and was less so in urbanized settings. Model performance was influenced by the availability of observational data with high sampling frequency and long duration for calibration and confirmation evaluation. In some instances, it appeared that parameter adjustments that improved calibration of hydrology negatively affected subsequent sediment and nutrient calibration, suggesting trade-offs in calibrating for hydrologic vs. water quality model performance. Despite these considerations, SWAT accurately predicted average stream discharge, sediment loads, and nutrient loads for the Raisin, Maumee, Sandusky, and Grand watersheds such that future use of these SWAT models for various scenario testing is reasonable and warranted.  相似文献   
19.
Labour force participation of adolescents in Australia is growing at an unprecedented rate. This increased participation is coupled with a growing realisation of the vulnerability of adolescents in the labour market in terms of occupational injury. Despite recent evidence that time of day may be an important determinant of adolescent injuries, the impact of non-standard and night work on adolescent injury rates has received scant attention to date. The current study addresses this shortcoming by examining injury patterns of 3201 working adolescents in Queensland. Results revealed that female adolescents are 2.5 times more likely to sustain an injury on day shift and 4.71 times more likely to sustain an injury on night shift than their adult counterparts when total work hours are taken into consideration. Similar results were found for male adolescents with an injury to work hours ratio of 2.19 on day shift and 3.05 on night shift. These findings point to the value of considering the temporal pattern of adolescent work in future research aimed at minimising injuries at work and improving the work experience of tomorrow's workforce.  相似文献   
20.
The subject matter and trends of presentations made at ASHP Midyear Clinical Meetings (MCMs) were studied. A computerized database of information from MCM and Annual Meeting (AM) program and abstract books was created. The data were analyzed to determine the distribution of MCM presentations by subject and by author for the period 1967 to 1990, determine if there were differences in subjects covered between MCMs and AMs, explore the proposition that there has been duplication of material in MCM presentations, and evaluate the frequency with which MCM presentations have been published in ASHP journals. The total number of presentations made at MCMs from 1967 through 1990 was 8180, while the total for the AMs was 1547 for the two periods (1962-71 and 1985-90) studied. The most common keywords in titles were "pharmacy," "drug," "patient," "hospital," and "service." All International Pharmaceutical Abstracts subject categories and two other categories were represented; presentations in the institutional pharmacy practice category were the most frequent, while pharmacognosy-related presentations were least frequent. The overwhelming number of authors made only one presentation and were listed as the first author. The subjects of presentations were similar between AMs and MCMs. A tendency toward duplication of material was found. Of the 8180 MCM presentations, at least 1005 were published in an ASHP journal. Between 1967 and 1990, presentations at MCMs covered a wide range of subjects but were sometimes duplicative or not on the cutting edge.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号