全文获取类型
收费全文 | 2783篇 |
免费 | 5篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 2篇 |
化学工业 | 66篇 |
金属工艺 | 2篇 |
机械仪表 | 5篇 |
建筑科学 | 13篇 |
能源动力 | 6篇 |
轻工业 | 42篇 |
水利工程 | 1篇 |
无线电 | 28篇 |
一般工业技术 | 42篇 |
冶金工业 | 2541篇 |
自动化技术 | 41篇 |
出版年
2022年 | 8篇 |
2021年 | 6篇 |
2020年 | 2篇 |
2019年 | 3篇 |
2018年 | 4篇 |
2017年 | 7篇 |
2016年 | 8篇 |
2015年 | 2篇 |
2014年 | 7篇 |
2013年 | 5篇 |
2012年 | 12篇 |
2011年 | 17篇 |
2010年 | 16篇 |
2009年 | 15篇 |
2008年 | 23篇 |
2007年 | 17篇 |
2006年 | 14篇 |
2005年 | 8篇 |
2004年 | 10篇 |
2003年 | 16篇 |
2002年 | 8篇 |
2001年 | 8篇 |
2000年 | 10篇 |
1999年 | 88篇 |
1998年 | 753篇 |
1997年 | 461篇 |
1996年 | 289篇 |
1995年 | 162篇 |
1994年 | 136篇 |
1993年 | 156篇 |
1992年 | 16篇 |
1991年 | 29篇 |
1990年 | 30篇 |
1989年 | 37篇 |
1988年 | 25篇 |
1987年 | 20篇 |
1986年 | 22篇 |
1985年 | 21篇 |
1984年 | 2篇 |
1983年 | 10篇 |
1982年 | 16篇 |
1981年 | 9篇 |
1980年 | 28篇 |
1979年 | 4篇 |
1978年 | 13篇 |
1977年 | 64篇 |
1976年 | 157篇 |
1975年 | 5篇 |
1974年 | 2篇 |
1972年 | 2篇 |
排序方式: 共有2789条查询结果,搜索用时 15 毫秒
51.
J KurdiA.Y Tremblay 《Polymer》2003,44(16):4533-4540
Polyetherimide (PEI) gas separation membranes were tailored, at the molecular scale, by the incorporation of nanostructured metallic complexes into the PEI network. The influence of these additives on the micropore size distributions of the membranes produced and on their performance for oxygen/nitrogen separation was investigated. Changing the metal within the same ligand had a significant influence on the microporosity and gas separation performance of these membranes. Magnesium (II) phathalocyanine (MgPc) in PEI membranes was found to be an excellent additive to increase membrane performance for air separation. The performance of these membranes increases with increasing additive concentrations. Membranes with this additive also exhibit an improved stability as determined through the annealing process. Annealing these membranes caused a slight decrease in their gas permeance and total micropore volume but a significant increase in their gas selectivity. The results show that the properties of the nanophase additive and nanophase-polymer interactions play a pivotal role in stabilizing and determining membrane performance for air separation. 相似文献
52.
Ming Hao Daniel A. Keim Umeshwar Dayal Daniela Oelke Chantal Tremblay 《Computer Graphics Forum》2008,27(3):895-902
In many business applications, large data workloads such as sales figures or process performance measures need to be monitored in real‐time. The data analysts want to catch problems in flight to reveal the root cause of anomalies. Immediate actions need to be taken before the problems become too expensive or consume too many resources. In the meantime, analysts need to have the “big picture” of what the information is about. In this paper, we derive and analyze two real‐time visualization techniques for managing density displays: (1) circular overlay d isplays which visualize large volumes of data without data shift movements after the display is full, thus freeing the analyst from adjusting the mental picture of the data after each data shift; and (2) variable resolution density displays which allow users to get the entire view without cluttering. We evaluate these techniques with respect to a number of evaluation measures, such as constancy of the display and usage of display space, and compare them to conventional d isplays with periodic shifts. Our real time data monitoring system also provides advanced interactions such as a local root cause analysis for further exploration. The applications using a number of real‐world data sets show the wide applicability and usefulness of our ideas. 相似文献
53.
The male-to-female ratio of patients requiring dialysis treatment commonly approaches 2:1. It is proposed that environmental factors, particularly occupational exposure to hydrocarbons, may account for the excess number of male patients. The term "hydrocarbon" refers to the aliphatic, alicyclic, aromatic, and halogenated hydrocarbons (carbon tetrachloride, chloroform); glycols (ethylene glycol, diethylene glycol, dioxane, glycerol); and organic solvents. Hydrocarbons commonly find use as solvents in industrial manufacturing practices because of their lipid solubility. Hydrocarbons have long been known to be neurotoxicants, affecting both peripheral and central nervous systems. Although benzene and its derivative have a known association with uroepithelial tumors, there is now a considerable body of evidence suggesting a possible role for hydrocarbon exposure in the development of non-neoplastic renal diseases. This article presents an epidemiological case for such an association and critically reviews the literature. 相似文献
54.
GM Weinstock JM Hardham MP McLeod EJ Sodergren SJ Norris 《Canadian Metallurgical Quarterly》1998,22(4):323-332
Covert brain activity related to task-free, spontaneous (i.e. unrequested), emotional evaluation of human face images was analysed in 27-channel averaged event-related potential (ERP) map series recorded from 18 healthy subjects while observing random sequences of face images without further instructions. After recording, subjects self-rated each face image on a scale from "liked" to "disliked". These ratings were used to dichotomize the face images into the affective evaluation categories of "liked" and "disliked" for each subject and the subjects into the affective attitudes of "philanthropists" and "misanthropists" (depending on their mean rating across images). Event-related map series were averaged for "liked" and "disliked" face images and for "philanthropists" and "misanthropists". The spatial configuration (landscape) of the electric field maps was assessed numerically by the electric gravity center, a conservative estimate of the mean location of all intracerebral, active, electric sources. Differences in electric gravity center location indicate activity of different neuronal populations. The electric gravity center locations of all event-related maps were averaged over the entire stimulus-on time (450 ms). The mean electric gravity center for disliked faces was located (significant across subjects) more to the right and somewhat more posterior than for liked faces. Similar differences were found between the mean electric gravity centers of misanthropists (more right and posterior) and philanthropists. Our neurophysiological findings are in line with neuropsychological findings, revealing visual emotional processing to depend on affective evaluation category and affective attitude, and extending the conclusions to a paradigm without directed task. 相似文献
55.
Members of a new molecular family of bacterial nonspecific acid phosphatases (NSAPs), indicated as class C, were found to share significant sequence similarities to bacterial class B NSAPs and to some plant acid phosphatases, representing the first example of a family of bacterial NSAPs that has a relatively close eukaryotic counterpart. Despite the lack of an overall similarity, conserved sequence motifs were also identified among the above enzyme families (class B and class C bacterial NSAPs, and related plant phosphatases) and several other families of phosphohydrolases, including bacterial phosphoglycolate phosphatases, histidinol-phosphatase domains of the bacterial bifunctional enzymes imidazole-glycerolphosphate dehydratases, and bacterial, eukaryotic, and archaeal phosphoserine phosphatases and threalose-6-phosphatases. These conserved motifs are clustered within two domains, separated by a variable spacer region, according to the pattern [FILMAVT]-D-[ILFRMVY]-D-[GSNDE]-[TV]-[ILVAM]-[AT S VILMC]-X-?YFWHKR)-X-?YFWHNQ?-X( 102,191)-?KRHNQ?-G-D-?FYWHILVMC?-?QNH?-?FWYGP?-D -?PSNQYW?. The dephosphorylating activity common to all these proteins supports the definition of this phosphatase motif and the inclusion of these enzymes into a superfamily of phosphohydrolases that we propose to indicate as "DDDD" after the presence of the four invariant aspartate residues. Database searches retrieved various hypothetical proteins of unknown function containing this or similar motifs, for which a phosphohydrolase activity could be hypothesized. 相似文献
56.
ER Smith GM Pesti RI Bakalli GO Ware JF Menten 《Canadian Metallurgical Quarterly》1998,77(11):1678-1687
An experiment was conducted to quantify genetic differences in response to dietary protein level of male vs female broilers. Broilers (1 d old) from a "high-yield" strain cross (Ross x Ross 208) and a "fast-growing" strain cross (Peterson x Arbor Acres) were placed on fresh pine shavings in floor pens. From Day 0 to 18, all birds were fed a 23% CP starter diet. During Days 18 to 53 male birds were fed either a 16, 18, 20, 22, 24, or 26% CP diet (3,200 kcal ME/kg) and female birds were fed the 16, 20, or 24% CP diet. Significant differences (P < 0.05) were noted in the performance of the different strains. Ross x Ross 208 male birds had a higher body weight (3.37 vs 3.16 kg), higher feed intake (7.08 vs 6.78 kg), higher breast yield (31.76 vs 29.25%), higher carcass yield (73.90 vs 71.85%), and a lower adjusted feed conversion ratio (FCR; 2.10 vs 2.16 g:g) than Peterson x Arbor Acres males at 53 d of age. As compared to Peterson x Arbor Acres females, Ross x Ross 208 female broilers also had a higher body weight (2.68 vs 2.55 kg), higher breast meat yield (33.61 vs 30.80%), higher carcass yield (75.31 vs 73.91%), and lower adjusted FCR (1.97 vs 2.04 g:g). Qualitative differences in the response of these strains were confirmed and better qualitative data is presented that can be used to predict the important output parameters from the import inputs in broiler production. 相似文献
57.
We have previously derived a theoretical measure of neural complexity (CN) in an attempt to characterize functional connectivity in the brain. CN measures the amount and heterogeneity of statistical correlations within a neural system in terms of the mutual information between subsets of its units. CN was initially used to characterize the functional connectivity of a neural system isolated from the environment. In the present paper, we introduce a related statistical measure, matching complexity (CM), which reflects the change in CN that occurs after a neural system receives signals from the environment. CM measures how well the ensemble of intrinsic correlations within a neural system fits the statistical structure of the sensory input. We show that CM is low when the intrinsic connectivity of a simulated cortical area is randomly organized. Conversely, CM is high when the intrinsic connectivity is modified so as to differentially amplify those intrinsic correlations that happen to be enhanced by sensory input. When the input is represented by an individual stimulus, a positive value of CM indicates that the limited mutual information between sensory sheets sampling the stimulus and the rest of the brain triggers a large increase in the mutual information between many functionally specialized subsets within the brain. In this way, a complex brain can deal with context and go "beyond the information given." 相似文献
58.
GM Roshchina EB Lishnevskaia IA Sizova VA Orlova IM Tereshin 《Canadian Metallurgical Quarterly》1980,25(11):850-854
The technique of accumulating preparation of the mucosa and "turned out sac" was used to show that levorin, a polyenic antibiotic in a concentration of 10(-6) M, lowered the transport rate and accumulation of glucose by the epithelial cells of the rat thin intestine under conditions of oxygenation. Suppression of the glucose transport in the first stages resulted in partial inhibition of the transmembrane transfer. It is suggested that levorin suppression of the glucose transport through the erythrocyte apical membrane in the thin intestine is associated with a decrease in the electrochemical gradient of Na+. 相似文献
59.
60.