全文获取类型
收费全文 | 1639篇 |
免费 | 39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 | 470篇 |
金属工艺 | 33篇 |
机械仪表 | 17篇 |
建筑科学 | 88篇 |
矿业工程 | 8篇 |
能源动力 | 28篇 |
轻工业 | 256篇 |
水利工程 | 10篇 |
石油天然气 | 1篇 |
无线电 | 81篇 |
一般工业技术 | 233篇 |
冶金工业 | 252篇 |
原子能技术 | 8篇 |
自动化技术 | 150篇 |
出版年
2022年 | 24篇 |
2021年 | 34篇 |
2020年 | 23篇 |
2019年 | 28篇 |
2018年 | 21篇 |
2017年 | 15篇 |
2016年 | 31篇 |
2015年 | 29篇 |
2014年 | 37篇 |
2013年 | 54篇 |
2012年 | 50篇 |
2011年 | 66篇 |
2010年 | 58篇 |
2009年 | 45篇 |
2008年 | 49篇 |
2007年 | 62篇 |
2006年 | 45篇 |
2005年 | 36篇 |
2004年 | 40篇 |
2003年 | 39篇 |
2002年 | 35篇 |
2001年 | 16篇 |
2000年 | 28篇 |
1999年 | 15篇 |
1998年 | 35篇 |
1997年 | 37篇 |
1996年 | 30篇 |
1995年 | 24篇 |
1994年 | 30篇 |
1993年 | 27篇 |
1992年 | 40篇 |
1991年 | 19篇 |
1990年 | 31篇 |
1989年 | 22篇 |
1988年 | 14篇 |
1987年 | 24篇 |
1986年 | 15篇 |
1985年 | 30篇 |
1984年 | 24篇 |
1983年 | 25篇 |
1982年 | 16篇 |
1981年 | 27篇 |
1980年 | 14篇 |
1979年 | 15篇 |
1978年 | 24篇 |
1977年 | 16篇 |
1976年 | 18篇 |
1974年 | 17篇 |
1972年 | 15篇 |
1970年 | 16篇 |
排序方式: 共有1680条查询结果,搜索用时 0 毫秒
31.
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
32.
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
33.
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
34.
Holahan Charles J.; Moos Rudolf H.; Holahan Carole K.; Brennan Penny L.; Schutte Kathleen K. 《Canadian Metallurgical Quarterly》2005,73(4):658
This study examined (a) the role of avoidance coping in prospectively generating both chronic and acute life stressors and (b) the stress-generating role of avoidance coping as a prospective link to future depressive symptoms. Participants were 1,211 late-middle-aged individuals (500 women and 711 men) assessed 3 times over a 10-year period. As predicted, baseline avoidance coping was prospectively associated with both more chronic and more acute life stressors 4 years later. Furthermore, as predicted, these intervening life stressors linked baseline avoidance coping and depressive symptoms 10 years later, controlling for the influence of initial depressive symptoms. These findings broaden knowledge about the stress-generation process and elucidate a key mechanism through which avoidance coping is linked to depressive symptoms. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
35.
Since 1961, there have been a total of seven patients with small bowel perforation caused by metastatic lung carcinoma reported in the literature. Perforation of the small bowel to metastatic lung carcinoma must be considered when evaluating older patients who have histories of heavy cigarette smoking and signs and symptoms suggestive of pulmonary neoplasia. Primary resection and end-to-end anastomosis of the perforated bowel is the treatment of choice. No patient with small bowel perforation secondary to lung carcinoma has survived more than four months. 相似文献
36.
Replicates and extends the work of R. H. Moos and S. R. Clemes (see record 1967-07395-001) and F. van der Veen (see record 1965-08090-001). Each of 6 patients saw each of 4 therapists twice. The variables total activity, feeling words, action words, reinforcements each was scored separately for patient and therapist for each interview. Patient problem expression and therapist accurate empathy were rated for each interview. Consistent differences between patients accounted for substantially more variance than consistent differences between therapists on all variables. Patient * Therapist * Session interactions generally accounted for large proportions of the total variance. Results indicate that the therapist behaviors studied were not the result of a trait, of a given tendency to be empathic, or of a consistently applied therapeutic technique, but rather were very substantially situationally or patient determined. (23 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
37.
Nadine Kretschmer Christin Durchschein Antje Hufner Beate Rinner Birgit Lohberger Rudolf Bauer 《International journal of molecular sciences》2022,23(10)
Melanoma is a complex and heterogenous disease, displays the deadliest form of skin cancer, and accounts for approx. 80% of all skin cancer deaths. In this study, we reported on the synthesis and pharmacological effects of a novel shikonin derivative (SK119), which is active in a nano-molar range and exhibits several promising in vitro effects in different human melanoma cells. SK119 was synthesized from shikonin as part of our search for novel, promising shikonin derivatives. It was screened against a panel of melanoma and non-tumorigenic cell lines using XTT viability assays. Moreover, we studied its pharmacological effects using apoptosis and Western blot experiments. Finally, it was combined with current clinically used melanoma therapeutics. SK119 exhibited IC50 values in a nano-molar range, induced apoptosis and led to a dose-dependent increase in the expression and protein phosphorylation of HSP27 and HSP90 in WM9 and MUG-Mel 2 cells. Combinatorial treatment, which is highly recommended in melanoma, revealed the synergistic effects of SK119 with vemurafenib and cobimetinib. SK119 treatment changed the expression levels of apoptosis genes and death receptor expression and exhibited synergistic effects with vemurafenib and cobimetinib in human melanoma cells. Further research indicates a promising potential in melanoma therapy. 相似文献
38.
Suzanne N. Voorrips Huitzilihuitl Saucedo-Orozco Pablo I. Snchez-Aguilera Rudolf A. De Boer Peter Van der Meer B. Daan Westenbrink 《International journal of molecular sciences》2022,23(15)
Despite the constant improvement of therapeutical options, heart failure (HF) remains associated with high mortality and morbidity. While new developments in guideline-recommended therapies can prolong survival and postpone HF hospitalizations, impaired exercise capacity remains one of the most debilitating symptoms of HF. Exercise intolerance in HF is multifactorial in origin, as the underlying cardiovascular pathology and reactive changes in skeletal muscle composition and metabolism both contribute. Recently, sodium-related glucose transporter 2 (SGLT2) inhibitors were found to improve cardiovascular outcomes significantly. Whilst much effort has been devoted to untangling the mechanisms responsible for these cardiovascular benefits of SGLT2 inhibitors, little is known about the effect of SGLT2 inhibitors on exercise performance in HF. This review provides an overview of the pathophysiological mechanisms that are responsible for exercise intolerance in HF, elaborates on the potential SGLT2-inhibitor-mediated effects on these phenomena, and provides an up-to-date overview of existing studies on the effect of SGLT2 inhibitors on clinical outcome parameters that are relevant to the assessment of exercise capacity. Finally, current gaps in the evidence and potential future perspectives on the effects of SGLT2 inhibitors on exercise intolerance in chronic HF are discussed. 相似文献
39.
Zinc levels in serum and/or tissue are reported to be altered in melanoma with unknown effects on melanoma development and biology. The purpose of this study was to examine the effects of acute chelation of free intracellular zinc pools in melanoma cell lines Bowes and A375, as well as selected melanoma tissue explants with high or low intracellular free zinc. Zinc chelating agent TPEN at the concentration of 25 µM was employed during 48 h, which significantly reduced intracellular free zinc while decreasing melanoma cell proliferation, inducing G1/S arrest and cell damage leading to mitochondrial, caspase-dependent apoptosis. Chelation of free zinc was also associated with increased generation of superoxide in cell lines but not marked lysosomal membrane damage. Conversely, melanoma explant cultures mostly displayed time-dependent loss of lysosomal membrane integrity in the presence of slowly growing superoxide levels. Loss of free zinc-dependent p53 activity was similarly disparate in individual melanoma models. Surviving melanoma cells were arrested in the cell cycle, and varying proportions of them exhibited features characteristic of premature senescence, which increased in time despite zinc reloading. The present results show that melanoma cells with varying free zinc levels respond to its acute loss in a number of individual ways, reflecting activated mechanisms including oxidative stress, lysosomal damage, and p53 activity leading to heterogenous outcomes including cell death, transient, and/or permanent cell cycle arrest and premature senescence. 相似文献
40.
In current networks, packet losses can occur if routers do not
provide sufficiently large buffers. This paper studies how many
buffers should be provided in a router to eliminate packet losses.
We assume a network router has m incoming queues, each
corresponding to a single traffic stream, and must schedule
at any time on-line from which queue to take the next packet to
send out. To exclude packet losses with a small amount of
buffers, the maximum queue length must be kept low over the entire
scheduling period. We call this new on-line problem the balanced
scheduling problem (BSP). By competitive analysis, we measure the
power of on-line scheduling algorithms to prevent packet losses.
We show that a simple greedy algorithm is
Θ(log m)-competitive which is asymptotically optimal,
while Round-Robin scheduling is not better than
m-competitive, as actually is any deterministic on-line
algorithm for BSP.
We also give a polynomial time algorithm for
solving off-line BSP optimally.
We also study another on-line balancing problem that tries to
balance the delay among the m traffic streams. 相似文献