全文获取类型
收费全文 | 3744篇 |
免费 | 119篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 65篇 |
综合类 | 4篇 |
化学工业 | 1123篇 |
金属工艺 | 67篇 |
机械仪表 | 45篇 |
建筑科学 | 236篇 |
矿业工程 | 32篇 |
能源动力 | 49篇 |
轻工业 | 495篇 |
水利工程 | 13篇 |
石油天然气 | 1篇 |
无线电 | 229篇 |
一般工业技术 | 532篇 |
冶金工业 | 451篇 |
原子能技术 | 35篇 |
自动化技术 | 488篇 |
出版年
2022年 | 30篇 |
2021年 | 47篇 |
2020年 | 35篇 |
2019年 | 34篇 |
2018年 | 47篇 |
2017年 | 50篇 |
2016年 | 74篇 |
2015年 | 97篇 |
2014年 | 91篇 |
2013年 | 138篇 |
2012年 | 138篇 |
2011年 | 181篇 |
2010年 | 139篇 |
2009年 | 130篇 |
2008年 | 134篇 |
2007年 | 162篇 |
2006年 | 141篇 |
2005年 | 127篇 |
2004年 | 120篇 |
2003年 | 95篇 |
2002年 | 84篇 |
2001年 | 73篇 |
2000年 | 70篇 |
1999年 | 70篇 |
1998年 | 150篇 |
1997年 | 98篇 |
1996年 | 85篇 |
1995年 | 77篇 |
1994年 | 73篇 |
1993年 | 51篇 |
1992年 | 51篇 |
1991年 | 46篇 |
1990年 | 32篇 |
1989年 | 42篇 |
1988年 | 26篇 |
1987年 | 32篇 |
1986年 | 38篇 |
1985年 | 49篇 |
1984年 | 44篇 |
1983年 | 37篇 |
1982年 | 39篇 |
1981年 | 40篇 |
1980年 | 35篇 |
1978年 | 33篇 |
1977年 | 36篇 |
1976年 | 51篇 |
1975年 | 41篇 |
1974年 | 28篇 |
1973年 | 28篇 |
1970年 | 44篇 |
排序方式: 共有3865条查询结果,搜索用时 156 毫秒
41.
42.
Gerhard Jäger 《Journal of Logic, Language and Information》2002,11(4):427-451
In this paper, we discuss some formal properties of the model ofbidirectional Optimality Theory that was developed inBlutner (2000). We investigate the conditions under whichbidirectional optimization is a well-defined notion, and we give aconceptually simpler reformulation of Blutner's definition. In thesecond part of the paper, we show that bidirectional optimization can bemodeled by means of finite state techniques. There we rely heavily onthe related work of Frank and Satta (1998) about unidirectionaloptimization. 相似文献
43.
SA Kliewer JT Moore L Wade JL Staudinger MA Watson SA Jones DD McKee BB Oliver TM Willson RH Zetterstr?m T Perlmann JM Lehmann 《Canadian Metallurgical Quarterly》1998,92(1):73-82
PURPOSE: To determine the effects of 28 d of creatine supplementation during training on body composition, strength, sprint performance, and hematological profiles. METHODS: In a double-blind and randomized manner, 25 NCAA division IA football players were matched-paired and assigned to supplement their diet for 28 d during resistance/agility training (8 h x wk[-1]) with a Phosphagen HP (Experimental and Applied Sciences, Golden, CO) placebo (P) containing 99 g x d(-1) of glucose, 3 g x d(-1) of taurine, 1.1 g x d(-1) of disodium phosphate, and 1.2 g x d(-1) of potassium phosphate (P) or Phosphagen HP containing the P with 15.75 g x d(-1) of HPCE pure creatine monohydrate (HP). Before and after supplementation, fasting blood samples were obtained; total body weight, total body water, and body composition were determined; subjects performed a maximal repetition test on the isotonic bench press, squat, and power clean; and subjects performed a cycle ergometer sprint test (12 x 6-s sprints with 30-s rest recovery). RESULTS: Hematological parameters remained within normal clinical limits for active individuals with no side effects reported. Total body weight significantly increased (P < 0.05) in the HP group (P 0.85 +/- 2.2; HP 2.42 +/- 1.4 kg) while no differences were observed in the percentage of total body water. DEXA scanned body mass (P 0.77 +/- 1.8; HP 2.22 +/- 1.5 kg) and fat/bone-free mass (P 1.33 +/- 1.1; HP 2.43 +/- 1.4 kg) were significantly increased in the HP group. Gains in bench press lifting volume (P -5 +/- 134; HP 225 +/- 246 kg), the sum of bench press, squat, and power clean lifting volume (P 1,105 +/- 429; HP 1,558 +/- 645 kg), and total work performed during the first five 6-s sprints was significantly greater in the HP group. CONCLUSION: The addition of creatine to the glucose/taurine/electrolyte supplement promoted greater gains in fat/bone-free mass, isotonic lifting volume, and sprint performance during intense resistance/agility training. 相似文献
44.
S Ronsseray M Lehmann D Nouaud D Anxolabéhère 《Canadian Metallurgical Quarterly》1996,143(4):1663-1674
Genetic recombination was used in Drosophila melanogaster to isolate P elements, inserted at the telomeres of X chromosomes (cytological site IA) from natural populations, in a genetic background devoid of other P elements. We show that complete maternally inherited P repression in the germline (P cytotype) can be elicited by only two autonomous P elements at 1A and that a single element at this site has partial regulatory properties. The analysis of the surrounding chromosomal regions of the P elements at 1A shows that in all cases these elements are flanked by Telomeric Associated Sequences, tandemly repetitive noncoding sequences that have properties of heterochromatin. In addition, we show that the regulatory properties of P elements at 1A can be inhibited by some of the mutant alleles of the Su(var)205 gene and by a deficiency of this gene. However, the regulatory properties of reference P strains (Harwich and Texas 007) are not impaired by Su(var)205 mutations. Su(var)205 encodes Heterochromatin Protein 1 (HP1). These results suggest that the HP1 dosage effect on the P element properties is site-dependent and could involve the structure of the chromatin. 相似文献
45.
Susanna Eberhartinger Ingrid Steiner Josef Washüttl und Gerhard Kroyer 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1990,191(4-5):286-289
Zusammenfassung Mittels verschiedener Untersuchungen wurden Aussagen über das Migrationsverhalten von Acetaldehyd aus Polyethylenterephthalat (PET) getroffen. Die Analyse des Acetaldehyds erfolgte durch Kopfraum-Gaschromatographie mit Flammenionisationsdetektion. Die Bestimmung des Restgehaltes an Acetaldehyd in neuen PET-Flaschen ergab Werte um 6,3 mg/kg, woraus sich eine maximal mögliche Migratmenge von etwa 200 (g/L errechnen läßt. Migrationsstudien bei verschiedenen Temperaturen zeigten die für das Verpakkungssystem typischen Zeitverläufe. Die Diffusion des Acetaldehyds aus dem Kunststoff erreichte bei einer Inkubationstemperatur von 40 °C nach ca. 4 Tagen ein konstantes Niveau, welches ca. 10% des ermittelten Restgehaltes an Acetaldehyd beträgt. Bei einer Temperaturerhöhung um 20 °C kam es zu einer Erhöhung dieses Niveaus auf das 5fache. Die Versuchsergebnisse der Bestimmung des Acetaldehyds in Getränken zeigte, daß in der Praxis nur mit einer geringen Migration zu rechnen ist, die bei den kohlensäurehaltigen Erfrischungsgetränken wegen des intensiven Eigengeschmacks ohne Belang ist. Eine Geschmacksbeeinträchtigung könnte sich höchstens bei Mineral- und Sodawässern ergeben, wenn diese längerfristig, wie sich aus den Migrationsstudien ableiten läßt, Temperaturen um 40 °C ausgesetzt werden.
Study of the migration of acetaldehyde from PET bottles into soft drinks containing carbonic acid
Summary The migration of acetaldehyde from polyethyleneterephthalate (PET) under various conditions was analysed by headspace gas chromatography and flame ionisation detection. The residual amounts of new PET bottles were about 6.3 mg/kg with a migration value of 200 g/1. On studying the migration at different temperatures and times, behaviour curves characteristic of packing materials made from plastics are obtaind. The amount of acetaldehyde diffusing from PET at a temperature of 40° C reached a constant level after 4 days which was about 10% of the residual value of acetaldehyde. On increasing the temperature by 20° C, this level was raised up to 50%. The results of the analysis of acetaldehyde in soft drinks containing carbonic acid show that the migration in fact is not sufficiently high to influence the taste of these soft drinks. A negative effect on the taste may be recognized with mineral waters and soda when they are exposed to higher temperatures (e.g. 40° C or more) over a longer period of time.相似文献
46.
We address the problem of multi-label classification in heterogeneous graphs, where nodes belong to different types and different
types have different sets of classification labels. We present a novel approach that aims to classify nodes based on their
neighborhoods. We model the mutual influence of nodes as a random walk in which the random surfer aims at distributing class
labels to nodes while walking through the graph. When viewing class labels as “colors”, the random surfer is essentially spraying
different node types with different color palettes; hence the name Graffiti of our method. In contrast to previous work on
topic-based random surfer models, our approach captures and exploits the mutual influence of nodes of the same type based
on their connections to nodes of other types. We show important properties of our algorithm such as convergence and scalability.
We also confirm the practical viability of Graffiti by an experimental study on subsets of the popular social networks Flickr and LibraryThing. We demonstrate the superiority of our approach by comparing it to three other state-of-the-art techniques for graph-based
classification. 相似文献
47.
The shapes of our cities change very frequently. These changes have to be reflected in data sets representing urban objects.
However, it must be assured that frequent updates do not affect geometric-topological consistency. This important aspect of spatial data quality guarantees essential assumptions on which users and applications of 3D city
models rely: viz. that objects do not intersect, overlap or penetrate mutually, or completely cover one another. This raises
the question how to guarantee that geometric-topological consistency is preserved when data sets are updated. Hence, there
is a certain risk that plans and decisions which are based on these data sets are erroneous and that the tremendous efforts
spent for data acquisition and updates become vain. In this paper, we solve this problem by presenting efficient transaction rules for updating 3D city models. These rules guarantee that geometric-topological consistency is preserved (Safety) and allow for the generation of arbitrary consistent 3D city models (Completeness). Safety as well as completeness is proven with mathematical rigor, guaranteeing the reliability of our method. Our method
is applicable to 3D city models, which define—besides the terrain surface—complex spatial objects like buildings with rooms
and storeys as interior structures, as well as bridges and tunnels. Those objects are represented as aggregations of solids,
and their surfaces are complex from a topology point of view. 3D GIS models like CityGML, which are widely used to represent cities, provide the means to define semantics, geometry and topology, but do not address
the problem of maintaining consistency. Hence, our approach complements CityGML. 相似文献
48.
We present a filter-and-refine method to speed up nearest neighbor searches with the Kullback–Leibler divergence for multivariate
Gaussians. This combination of features and similarity estimation is of special interest in the field of automatic music recommendation
as it is widely used to compute music similarity. However, the non-vectorial features and a non-metric divergence make using
it with large corpora difficult, as standard indexing algorithms can not be used. This paper proposes a method for fast nearest
neighbor retrieval in large databases which relies on the above approach. In its core the method rescales the divergence and
uses a modified FastMap implementation to speed up nearest-neighbor queries. Overall the method accelerates the search for
similar music pieces by a factor of 10–30 and yields high recall values of 95–99% compared to a standard linear search. 相似文献
49.
Elisabeth M. Haberl Thomas S. Weiss Georg Peschel Kilian Weigand Nikolai Khler Josch K. Pauling Jürgen J. Wenzel Marcus Hring Sabrina Krautbauer Gerhard Liebisch Christa Buechler 《International journal of molecular sciences》2021,22(10)
Hepatocellular carcinoma (HCC) still remains a difficult to cure malignancy. In recent years, the focus has shifted to lipid metabolism for the treatment of HCC. Very little is known about hepatitis B virus (HBV) and C virus (HCV)-related hepatic lipid disturbances in non-malignant and cancer tissues. The present study showed that triacylglycerol and cholesterol concentrations were similar in tumor adjacent HBV and HCV liver, and were not induced in the HCC tissues. Higher levels of free cholesterol, polyunsaturated phospholipids and diacylglycerol species were noted in non-tumorous HBV compared to HCV liver. Moreover, polyunsaturated phospholipids and diacylglycerols, and ceramides declined in tumors of HBV infected patients. All of these lipids remained unchanged in HCV-related HCC. In HCV tumors, polyunsaturated phosphatidylinositol levels were even induced. There were no associations of these lipid classes in non-tumor tissues with hepatic inflammation and fibrosis scores. Moreover, these lipids did not correlate with tumor grade or T-stage in HCC tissues. Lipid reprogramming of the three analysed HBV/HCV related tumors mostly resembled HBV-HCC. Indeed, lipid composition of non-tumorous HCV tissue, HCV tumors, HBV tumors and HBV/HCV tumors was highly similar. The tumor suppressor protein p53 regulates lipid metabolism. The p53 and p53S392 protein levels were induced in the tumors of HBV, HCV and double infected patients, and this was significant in HBV infection. Negative correlation of tumor p53 protein with free cholesterol indicates a role of p53 in cholesterol metabolism. In summary, the current study suggests that therapeutic strategies to target lipid metabolism in chronic viral hepatitis and associated cancers have to consider disease etiology. 相似文献
50.