全文获取类型
收费全文 | 1616篇 |
免费 | 41篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 36篇 |
综合类 | 2篇 |
化学工业 | 424篇 |
金属工艺 | 34篇 |
机械仪表 | 15篇 |
建筑科学 | 88篇 |
矿业工程 | 8篇 |
能源动力 | 29篇 |
轻工业 | 252篇 |
水利工程 | 10篇 |
石油天然气 | 1篇 |
无线电 | 74篇 |
一般工业技术 | 238篇 |
冶金工业 | 251篇 |
原子能技术 | 7篇 |
自动化技术 | 190篇 |
出版年
2021年 | 32篇 |
2020年 | 22篇 |
2019年 | 28篇 |
2018年 | 21篇 |
2017年 | 14篇 |
2016年 | 30篇 |
2015年 | 29篇 |
2014年 | 38篇 |
2013年 | 53篇 |
2012年 | 50篇 |
2011年 | 69篇 |
2010年 | 58篇 |
2009年 | 46篇 |
2008年 | 49篇 |
2007年 | 58篇 |
2006年 | 49篇 |
2005年 | 41篇 |
2004年 | 44篇 |
2003年 | 41篇 |
2002年 | 36篇 |
2001年 | 18篇 |
2000年 | 29篇 |
1999年 | 15篇 |
1998年 | 39篇 |
1997年 | 40篇 |
1996年 | 27篇 |
1995年 | 23篇 |
1994年 | 29篇 |
1993年 | 26篇 |
1992年 | 39篇 |
1991年 | 19篇 |
1990年 | 31篇 |
1989年 | 21篇 |
1988年 | 15篇 |
1987年 | 25篇 |
1986年 | 14篇 |
1985年 | 30篇 |
1984年 | 27篇 |
1983年 | 26篇 |
1982年 | 18篇 |
1981年 | 23篇 |
1978年 | 23篇 |
1977年 | 17篇 |
1976年 | 18篇 |
1974年 | 13篇 |
1973年 | 12篇 |
1972年 | 15篇 |
1970年 | 14篇 |
1963年 | 13篇 |
1943年 | 12篇 |
排序方式: 共有1659条查询结果,搜索用时 46 毫秒
31.
32.
Optimizing Safe Yield Policy Implementation 总被引:1,自引:1,他引:0
The presented method enhances groundwater-mandated safe yield management. It is useful for settings that prevent sustained
yield or integrated management. To protect hydraulically connected surface water rights, the Utah government’s Cache Valley
groundwater management plan proposes that total pumping increase not exceed 84,431 m3/day. To determine how best to spatially distribute additional allowable pumping, stakeholders quantified limits defining
acceptable impacts on selected water resource indicators. A new simulation–optimization (S–O) algorithm used these limits
while computing optimal spatially distributed perennial yield or safe yield groundwater pumping extraction strategies. The
limits prevent unacceptable decreases in: head and net flow between aquifer and surface waters (rivers, surface/subsurface
drains, springs, lakes). The optimization objective function maximizes weighted pumping to provide water for 18 growing municipalities.
For 16 perennial yield scenarios, computed optimal pumping increases differ in protectiveness toward senior water rights,
and range from 16% to 103% of the state plan-proposed increase. Implementing a protective strategy would achieve 90% of the
storage changes needed to reach equilibrium within 23 years. Indicator potentiometric heads would reach equilibrium within
10–40 years. At equilibrium, an optimal Cache Valley perennial yield strategy acceptably minimizes net annual non-pumping
discharges. By comparison, multi-period 20-year transient groundwater mining optimizations allow more pumping in early years.
Pumping then must decline to satisfy seepage and head constraints through year 20. Adverse seepage impact would increase for
years thereafter. For situations governed by safe or perennial yield policy, equilibrium-based (steady-state) optimization
is very useful. It effectively develops optimal perennial yield strategies. 相似文献
33.
Miodrag Čolić Sergej Tomić Rebeka Rudolf Evgenija Marković Ivana Šćepan 《Journal of materials science. Materials in medicine》2016,27(8):128
Superelastic (SE) and thermo-activated (TA) nickel–titanium (NiTi) archwires are used in everyday orthodontic practice, based on their acceptable biocompatibility and well-defined shape memory properties. However, the differences in their surface microstructure and cytotoxicity have not been clearly defined, and the standard cytotoxicity tests are too robust to detect small differences in the cytotoxicity of these alloys, all of which can lead to unexpected adverse reactions in some patients. Therefore, we tested the hypothesis that the differences in manufacture and microstructure of commercially available SE and TA archwires may influence their biocompatibility. The archwires were studied as-received and after conditioning for 24 h or 35 days in a cell culture medium under static conditions. All of the tested archwires, including their conditioned medium (CM), were non-cytotoxic for L929 cells, but Rematitan SE (both as received and conditioned) induced the apoptosis of rat thymocytes in a direct contact. In contrast, TruFlex SE and Equire TA increased the proliferation of thymocytes. The cytotoxic effect of Rematitan SE correlated with the higher release of Ni ions in CM, higher concentration of surface Ni and an increased oxygen layer thickness after the conditioning. In conclusion, the apoptosis assay on rat thymocytes, in contrast to the less sensitive standard assay on L929 cells, revealed that Rematitan SE was less cytocompatible compared to other archwires and the effect was most probably associated with a higher exposition of the cells to Ni on the surface of the archwire, due to the formation of unstable oxide layer. 相似文献
34.
We propose a user-centric rule filtering method that allows to identify association rules that exhibit a certain user-specified temporal behavior with respect to rule evaluation measures. The method can considerably reduce the number of association rules that have to be assessed manually after a rule induction. This is especially necessary if the rule set contains many rules as it is the case for the task of finding rare patterns inside the data. For the proposed method, we will reuse former work on the visualization of association rules [M. Steinbrecher, R. Kruse, Visualization of possibilistic potentials, in: Foundations of Fuzzy Logic and Soft Computing, in: Lecture Notes in Comput. Sci., vol. 4529, Springer-Verlag, Berlin/Heidelberg, 2007, pp. 295–303] and use an extension of it to motivate and assess the presented filtering technique. We put the focus on rules that are induced from a data set that contains a temporal variable and build our approach on the requirement that temporally ordered sets of association rules are available, i.e., one set for every time frame. To illustrate this, we propose an ad-hoc learning method along the way. The actual rule filtering is accomplished by means of fuzzy concepts. These concepts use linguistic variables to partition rule-related domains of interest, such as the confidence change rate. The original rule sets are then matched against these user concepts and result in only those rules that match the respective concepts to a predefined extent. We provide empirical evidence by applying the proposed methods to hand-crafted as well as real-world data sets and critically discuss the current state and further prospects. 相似文献
35.
36.
The World Wide Web has turned hypertext into a success story by enabling world-wide sharing of unstructured information and informal knowledge. The Semantic Web targets the sharing of structured information and formal knowledge pursuing objectives of achieving collective intelligence on the Web. Germane to the structure of the Semantic Web is a layering and standardization of concerns. These concerns are reflected by an architecture of the Semantic Web that we present through a common use case. Semantic Web data for the use case is now found on the Web and is part of a quickly growing set of Semantic Web resources available for formal processing. 相似文献
37.
Ontology learning for the Semantic Web 总被引:14,自引:0,他引:14
The Semantic Web relies heavily on formal ontologies to structure data for comprehensive and transportable machine understanding. Thus, the proliferation of ontologies factors largely in the Semantic Web's success. The authors present an ontology learning framework that extends typical ontology engineering environments by using semiautomatic ontology construction tools. The framework encompasses ontology import, extraction, pruning, refinement and evaluation. 相似文献
38.
Rudolf Treleano Hans-Dieter Belitz Harald Jugel und Herbert Wieser 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1978,167(5):320-323
Zusammenfassung 1-Aminocycloalkan-l-carbonsäuren mit Ringgrößen von 4–11 (ohne 10) wurden synthetisiert und auf ihre Geschmackseigenschaften untersucht. Süßer Geschmack tritt vom 4-Ring bis zum 8-Ring auf, beim 6-Ring ist der Schwellenwert minimal (c
Ssü=1–3 mmol/l). Bitter sind die Verbindungen vom 5-Ring bis zum 9-Ring, das Minimum des Schwellenwertes liegt beim 8-Ring (c
sbi=2–5 mmol/l). Die größeren Ringe sind bis zu Konzentrationen von 20 mmol/l ohne Geschmack. Beim 6-Ring löscht eine 2-Methylgruppe jeden Geschmackseindruck, während die 3- und 4-Methylverbindungen süß und bitter sind. Die 4-Äthylverbindung ist bitter aber nicht süß, die 4-tert.-Butylverbindung ist ohne Geschmack. 1-Aminonorbornan-1-carbonsäure ist süß (c
Ssü 50 mmol/l) und bitter (c
sbi=5–7mmo1/1), wobei der Schwellenwert für bitter fast eine Zehnerpotenz kleiner ist. tert.-Leucin ist ohne Geschmack. Die Ergebnisse werden im Zusammenhang mit früheren Untersuchungen an offenkettigen Aminosäuren diskutiert und in Modelle über sterische Voraussetzungen für Geschmack eingeordnet.
Relationsships between structure and taste in amino acids with cyclic side chains
Summary 1-Aminocycloalkane-1-carboxylic acids with ring sizes of 4–11 (excluding 10) were synthesized and tested for their taste properties. The compounds with 4- to 8-membered rings are sweet, with threshold values going through a minimum for the 6-membered ring (c tsw = l-3 mM/l). The compounds with 5- to 9-membered rings are bitter. Here the threshold value reaches a minimum for the 8-membered ring (c tbi=2–5 mM/l). The larger rings are without taste up to concentrations of 20 mmol/l. With the 6-membered ring a 2-methyl group abolishes any taste impression, whereas the 3- and 4-methyl compounds are sweet and bitter. The 4-ethyl compound is bitter but not sweet, the 4-tert.-butyl compound has no taste. 1-Aminonorbornane-l-carboxylic acid is sweet (c tsw 50mM/l) and bitter (c tbi= 5–7 mM/l), withc tbi being significantly smaller thanc tsw. tert-Leucine is without taste. The results are discussed in relation to previous investigations into steric prerequisites for taste in the amino acid series.相似文献
39.
We have found experimentally that rf SQUID's working in a nonhysteretic mode with small critical currents give exactly at resonance and at very low rf bias a triangular pattern with a period equal to half of one elementary quantum of magnetic flux. We discuss a possible explanation of this peculiar result. 相似文献
40.