全文获取类型
收费全文 | 2005篇 |
免费 | 81篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 23篇 |
综合类 | 6篇 |
化学工业 | 512篇 |
金属工艺 | 29篇 |
机械仪表 | 40篇 |
建筑科学 | 120篇 |
矿业工程 | 32篇 |
能源动力 | 37篇 |
轻工业 | 154篇 |
水利工程 | 29篇 |
石油天然气 | 4篇 |
无线电 | 135篇 |
一般工业技术 | 311篇 |
冶金工业 | 147篇 |
原子能技术 | 5篇 |
自动化技术 | 508篇 |
出版年
2023年 | 23篇 |
2022年 | 43篇 |
2021年 | 60篇 |
2020年 | 28篇 |
2019年 | 26篇 |
2018年 | 60篇 |
2017年 | 51篇 |
2016年 | 79篇 |
2015年 | 69篇 |
2014年 | 81篇 |
2013年 | 95篇 |
2012年 | 110篇 |
2011年 | 135篇 |
2010年 | 78篇 |
2009年 | 116篇 |
2008年 | 103篇 |
2007年 | 89篇 |
2006年 | 99篇 |
2005年 | 69篇 |
2004年 | 63篇 |
2003年 | 46篇 |
2002年 | 53篇 |
2001年 | 31篇 |
2000年 | 28篇 |
1999年 | 36篇 |
1998年 | 32篇 |
1997年 | 37篇 |
1996年 | 37篇 |
1995年 | 38篇 |
1994年 | 30篇 |
1993年 | 20篇 |
1992年 | 15篇 |
1991年 | 17篇 |
1990年 | 13篇 |
1989年 | 6篇 |
1988年 | 8篇 |
1987年 | 14篇 |
1985年 | 13篇 |
1984年 | 13篇 |
1983年 | 12篇 |
1982年 | 5篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1978年 | 11篇 |
1977年 | 6篇 |
1976年 | 13篇 |
1975年 | 9篇 |
1973年 | 4篇 |
1971年 | 6篇 |
排序方式: 共有2092条查询结果,搜索用时 15 毫秒
311.
Ronacher Bernhard; Wohlgemuth Sandra; Vogel Astrid; Krahe Rüdiger 《Canadian Metallurgical Quarterly》2008,122(3):252
A characteristic feature of hearing systems is their ability to resolve both fast and subtle amplitude modulations of acoustic signals. This applies also to grasshoppers, which for mate identification rely mainly on the characteristic temporal patterns of their communication signals. Usually the signals arriving at a receiver are contaminated by various kinds of noise. In addition to extrinsic noise, intrinsic noise caused by stochastic processes within the nervous system contributes to making signal recognition a difficult task. The authors asked to what degree intrinsic noise affects temporal resolution and, particularly, the discrimination of similar acoustic signals. This study aims at exploring the neuronal basis for sexual selection, which depends on exploiting subtle differences between basically similar signals. Applying a metric, by which the similarities of spike trains can be assessed, the authors investigated how well the communication signals of different individuals of the same species could be discriminated and correctly classified based on the responses of auditory neurons. This spike train metric yields clues to the optimal temporal resolution with which spike trains should be evaluated. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
312.
A method for fully automated morphological and topological quantification of microvascular structures in confocal laser scanning microscopy (CLSM) volume datasets is presented. Several characteristic morphological and topological quantities are calculated in a series of image-processing steps and can be used to compare single components as well as whole networks of microvascular structures to each other. The effect of the individual image-processing steps is illustrated and characteristic quantities of measured volume datasets are presented and discussed. 相似文献
313.
314.
Philipp B Hoff M Germa F Schink B Beimborn D Mersch-Sundermann V 《Environmental science & technology》2007,41(4):1390-1398
Prediction of the biodegradability of organic compounds is an ecologically desirable and economically feasible tool for estimating the environmental fate of chemicals. We combined quantitative structure-activity relationships (QSAR) with the systematic collection of biochemical knowledge to establish rules for the prediction of aerobic biodegradation of N-heterocycles. Validated biodegradation data of 194 N-heterocyclic compounds were analyzed using the MULTICASE-method which delivered two QSAR models based on 17 activating (OSAR 1) and on 16 inactivating molecular fragments (GSAR 2), which were statistically significantly linked to efficient or poor biodegradability, respectively. The percentages of correct classifications were over 99% for both models, and cross-validation resulted in 67.9% (GSAR 1) and 70.4% (OSAR 2) correct predictions. Biochemical interpretation of the activating and inactivating characteristics of the molecular fragments delivered plausible mechanistic interpretations and enabled us to establish the following biodegradation rules: (1) Target sites for amidohydrolases and for cytochrome P450 monooxygenases enhance biodegradation of nonaromatic N-heterocycles. (2) Target sites for molybdenum hydroxylases enhance biodegradation of aromatic N-heterocycles. (3) Target sites for hydratation by an urocanase-like mechanism enhance biodegradation of imidazoles. Our complementary approach represents a feasible strategy for generating concrete rules for the prediction of biodegradability of organic compounds. 相似文献
315.
The interaction between learning and evolution has elicited much interest particularly among researchers who use evolutionary algorithms for the optimization of neural structures. In this article, we will propose an extension of the existing models by including a developmental phase – a growth process – of the neural network. In this way, we are able to examine the dynamical interaction between genetic information and information learned during development. Several measures are proposed to quantitatively examine the benefits and the effects of such an overlap between learning and evolution. The proposed model, which is based on the recursive encoding method for structure optimization of neural networks, is applied to the problem domain of time series prediction. Furthermore, comments are made on problem domains which associate growing networks (size) during development with problems of increasing complexity. 相似文献
316.
Making your system safe is no cinch, but here's a guide to getting started. The article examines various system security methods, including: identification and authentication techniques; firewalls; audit trails; and automated intrusion detection systems 相似文献
317.
Ayman Al-Shurbaji Elisabet Humble Mats Rudling Bernhard Lindenthal Lars Berglund 《Lipids》1998,33(2):165-169
Hypercholesterolemia is a consistent feature of the nephrotic syndrome. However, the mechanisms underlying this perturbation
are unclear. In the present work, we have investigated different factors that influence hepatic cholesterol metabolism using
the nephrotic rat as a model. The induction of nephrosis resulted in a severe and sustained hypercholesterolemia. However,
no effect on the rate-limiting enzyme in cholesterol synthesis, 3-hydroxy-3-methylglutaryl CoA reductase, could be detected.
Further, plasma lathosterol/cholesterol ratio, a measure of cholesterol synthesis, was not altered. Also, plasma levels of
mevalonate, both a substrate for cholesterogenesis beyond the rate-limiting step and a marker for cholesterol synthesis, did
not differ between control rats and those with established hypercholesterolemia. There was no detectable change in the expression
of low density lipoprotein (LDL) receptor between the two experimental groups. We conclude that the early increase in cholesterol
synthesis reported after the induction of nephrosis is not necessary for the maintenance of hypercholeserolemia. Established
hypercholesterolemia of the nephrotic syndrome seems to represent a steady state in which neither enhanced hepatic cholesterol
synthesis nor retarded LDL cholesterol clearance is of major importance. 相似文献
318.
Confocal microscopy is increasingly becoming recognized as a valuable analytical tool in material science although long established in life sciences. It is shown that this technique can be employed successfully in investigating polymers, coatings, emulsions, etc. Using the scattered light not only for imaging but also for analysis in a Raman spectrometer chemical information from an exactly defined volume smaller than 1 μm3 within the sample can be achieved. 相似文献
319.
Thomas Brümmer Friedrich Meuser Bernhard van Lengerich Claudia Niemann 《Starch - St?rke》2002,54(1):1-8
By using a systems analytical model (SAM) and a fuzzy logic control software (fuzzy CIM) extrusion experiments were designed, that enabled a differentiation of the influence of the thermal energy input, expressed by the product temperature (PT), and the influence of the specific mechanical energy input (SME) on the molecular structure of extruded starch. The chromatographic examination of the molecular changes in the starch clearly revealed the influence of the extrusion cooking conditions on molecular degradation. The molecular size of extruded starch, expressed as the weight average of the molecular weight (M̄ w), decreased exponentially when SME increased. In the range of 110—180 °C, PT had no significant influence on M̄ w so that the observed reduction of M̄ w was primarily dependent on the increase in SME. By contrast, the polydispersity depended both on PT and SME. The influence of PT on the polydispersity was of minor significance up to 160 °C, increasing more steeply at higher temperatures. PT increase above 180 °C resulted in increasing reducing power of the extruded starch, whereas SME had almost no effect on reducing power. Only at a PT of more than 180 °C small amounts of short chain molecules with a degree of polymerisation (DP) smaller than 6 could be determined. 相似文献
320.