全文获取类型
收费全文 | 37376篇 |
免费 | 575篇 |
国内免费 | 27篇 |
专业分类
电工技术 | 299篇 |
综合类 | 12篇 |
化学工业 | 8032篇 |
金属工艺 | 562篇 |
机械仪表 | 769篇 |
建筑科学 | 1127篇 |
矿业工程 | 62篇 |
能源动力 | 1009篇 |
轻工业 | 6832篇 |
水利工程 | 398篇 |
石油天然气 | 182篇 |
武器工业 | 3篇 |
无线电 | 1637篇 |
一般工业技术 | 5726篇 |
冶金工业 | 5844篇 |
原子能技术 | 142篇 |
自动化技术 | 5342篇 |
出版年
2024年 | 460篇 |
2023年 | 464篇 |
2022年 | 673篇 |
2021年 | 1159篇 |
2020年 | 996篇 |
2019年 | 1030篇 |
2018年 | 1477篇 |
2017年 | 1420篇 |
2016年 | 1577篇 |
2015年 | 1195篇 |
2014年 | 1466篇 |
2013年 | 2871篇 |
2012年 | 2262篇 |
2011年 | 2255篇 |
2010年 | 1769篇 |
2009年 | 1611篇 |
2008年 | 1583篇 |
2007年 | 1443篇 |
2006年 | 988篇 |
2005年 | 852篇 |
2004年 | 733篇 |
2003年 | 684篇 |
2002年 | 604篇 |
2001年 | 467篇 |
2000年 | 368篇 |
1999年 | 401篇 |
1998年 | 2074篇 |
1997年 | 1301篇 |
1996年 | 842篇 |
1995年 | 483篇 |
1994年 | 365篇 |
1993年 | 375篇 |
1992年 | 126篇 |
1991年 | 111篇 |
1990年 | 81篇 |
1989年 | 79篇 |
1988年 | 98篇 |
1987年 | 94篇 |
1986年 | 88篇 |
1985年 | 97篇 |
1984年 | 84篇 |
1983年 | 56篇 |
1982年 | 57篇 |
1981年 | 77篇 |
1980年 | 71篇 |
1979年 | 40篇 |
1977年 | 118篇 |
1976年 | 217篇 |
1975年 | 40篇 |
1973年 | 50篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
F. Martínez G. Calleja J.A. Melero R. Molina 《Applied catalysis. B, Environmental》2007,70(1-4):452-460
Iron-containing catalysts have been prepared following different synthesis routes and silica supports (amorphous, zeolitic and mesostructured materials). Activity and stability of these materials were assessed on the photo-Fenton degradation of phenolic aqueous solutions using near UV irradiation (higher than 313 nm) at room temperature and initial neutral pH. Their catalytic performance was monitored in terms of phenol and total organic carbon (TOC) conversions. Aromatic compounds and carboxylic acids as by-products coming from incomplete mineralization of phenol as well as the efficiency of each catalytic system in the use of the oxidant were also studied. Stability of the materials throughout the photo-Fenton reaction was evaluated in terms of metal leachibility. Activity and stability depend on the environment of iron species and features of silica support. The evolution of pH with the reaction time and their relationship with TOC degradation and leaching degree has been discussed. A nanocomposite material of crystalline iron oxides supported over mesostructured SBA-15 material is shown the most successful catalyst for degradation of phenolic aqueous solutions by photo-Fenton processes, achieving an outstanding overall catalytic performance accompanied with a noteworthy stability. 相似文献
22.
J. Hrivňák L. Soják J. Krupčík Y. P. Duchesne 《Journal of the American Oil Chemists' Society》1973,50(3):68-71
The influence of temperature on the gas chromatographic separation ofcis-trans isomers of the methyl esters of some monounsaturated fatty acids was studied on capillary columns coated with Apiezon L,
BDS and DEGS. As far as methyl oleate and methyl elaidate are concerned, the separation is better at lower temperatures on
Apiezon L (180–210 C) and at higher temperatures on polyester phases (BDS, DEGS; 150–180 C). The influence of temperature
on the separation ofcis-trans isomers on the three stationary phases under study is explained by the higher values of δECL/δt forcis isomers. The variation of the equivalent carbon chain length with temperature can be used for the identification ofcis-trans isomers in natural mixtures. 相似文献
23.
E. Castillo D.P. Morales G. Botella A. García L. Parrilla A.J. Palma 《Digital Signal Processing》2013,23(6):1897-1909
This paper describes a novel model for fetal heart rate (FHR) monitoring from single-lead mother?s abdomen ECG (AECG) measurements. This novel method is divided in two stages: the first step consists on a one-step wavelet-based preprocessing for simultaneous baseline and high-frequency noise suppression, while the second stage efficiently detects fetal QRS complexes allowing FHR monitoring. The presented structure has been simplified as much as possible, in order to reduce computational cost and thus enable possible custom hardware implementations. Moreover, the proposed scheme and its fixed-point modeling have been tested using real abdominal ECG signals, which allow the validation of the presented approach and provide high accuracy. 相似文献
24.
M Fernández J Cao MD Vázquez-Illanes JI Ramos-Martínez JA Villamarín 《Canadian Metallurgical Quarterly》1994,33(2):355-363
Phosphofructokinase purified from mantle tissue of the sea mussel Mytilus galloprovincialis, was phosphorylated "in vitro" by the catalytic subunit of cyclic AMP-dependent protein kinase. The incorporation of phosphate gave rise to an activation of the enzyme by increasing its affinity for fructose-6-phosphate, by decreasing its sensitivity to the inhibition by ATP and by enhancing the effect of allosteric activators (5'-AMP and fructose-2,6-bisphosphate). In addition, the effects of phosphorylation on the catalytic activity are pH-dependent. 相似文献
25.
A method for the calculation of the fractional Fourier transform (FRT) by means of the fast Fourier transform (FFT) algorithm is presented. The process involves mainly two FFT's in cascade; thus the process has the same complexity as this algorithm. The method is valid for fractional orders varying from -1 to 1. Scaling factors for the FRT and Fresnel diffraction when calculated through the FFT are discussed. 相似文献
26.
E Poves Martínez 《Canadian Metallurgical Quarterly》1996,88(10):677-686
In the last years different classification systems for hospitalized patients have been developed in the United States, that allow to evaluate different aspects of any Hospital: The quality, the efficacy and the efficiency. The classification of "The Diagnosis Related Groups" (DRG) relates the hospitalized patients with the expenses that they generate, and it is the most used in Europe. In the version DRG-All Patient, all the diagnoses and procedures of the hospitalized patients, using the International Classification of Diseases, are divided in to 25 Major Diagnostic Categories (MDC) where each one excludes all the others. We describe the behavior with respect to the age, sex and stay of all the GDR integrated in the CDM 6 and 7: diseases and disorders of the digestive tract, and diseases and disorders of the hepatobiliary system and the pancreas. The study has been carried out with a national data base of two millions of cases seen from 214 acute-care Hospitals. The MDC number 6 is the most frequent, with an important number of patients in the pediatric age; it is more frequent in males; the average stay is 8.59 days and 19 GDR (36.5%) have a variation coefficient greater than one. The other MDC, number 7 is less frequent, the majority of the patients are between 60-80 years of age, the average stay is 12.2 days with a coefficient of variation greater than one in 4 GDR (17.4%). Clinical Services should know the characteristics and behavior of their patients, as well as the comparison with the national data bases. This may allow a control of the quality and the costs by using a common "language" with the managers. 相似文献
27.
The additive model of multiattribute value theory is widely used in multicriteria choice problems. But often it is not easy to obtain precise values for the scaling weights or the alternatives’ value in each function. Several decision rules which require weaker information, such as ordinal information, have been proposed to select an alternative under these circumstances. We propose new decision rules and test them using Monte-Carlo simulation, considering that there is ordinal information both on the scaling weights and on the alternatives’ values. Results show the new rules constitute a good approximation. We provide guidelines about how to use these rules in a context of selecting a subset of the most promising alternatives, considering the contradictory objectives of keeping a low number of alternatives yet not excluding the best one. 相似文献
28.
An adaptive, real-time, traffic monitoring system 总被引:1,自引:0,他引:1
In this paper we describe a computer vision-based traffic monitoring system able to detect individual vehicles in real-time.
Our fully integrated system first obtains the main traffic variables: counting, speed and category; and then computes a complete
set of statistical variables. The objective is to investigate some of the difficulties impeding existing traffic systems to
achieve balanced accuracy in every condition; i.e. day and night transitions, shadows, heavy vehicles, occlusions, slow traffic
and congestions. The system we present is autonomous, works for long periods of time without human intervention and adapts
automatically to the changing environmental conditions. Several innovations, designed to deal with the above circumstances,
are proposed in the paper: an integrated calibration and image rectification step, differentiated methods for day and night,
an adaptive segmentation algorithm, a multistage shadow detection method and special considerations for heavy vehicle identification
and treatment of slow traffic. A specific methodology has been developed to benchmark the accuracy of the different methods
proposed. 相似文献
29.
MVB (Multifunction Vehicle Bus), defined in IEC 61375, has been broadly adopted as the communication standard between embedded control systems on-board modern trains. In this work a new method to take advantage of the full bandwidth of the channel using an OFDM technique is described. With this new method it is possible to share the physical medium between standard MVB traffic and new OFDM traffic. A 90 Mbps theoretical bitrate can be achieved. The results of this work have been validated in a test bench including standard MVB nodes transmitting on a line similar to a real vehicle bus. 相似文献
30.