全文获取类型
收费全文 | 34745篇 |
免费 | 1783篇 |
国内免费 | 30篇 |
专业分类
电工技术 | 254篇 |
综合类 | 17篇 |
化学工业 | 7065篇 |
金属工艺 | 665篇 |
机械仪表 | 701篇 |
建筑科学 | 952篇 |
矿业工程 | 76篇 |
能源动力 | 660篇 |
轻工业 | 5726篇 |
水利工程 | 326篇 |
石油天然气 | 131篇 |
武器工业 | 5篇 |
无线电 | 1406篇 |
一般工业技术 | 5755篇 |
冶金工业 | 8000篇 |
原子能技术 | 131篇 |
自动化技术 | 4688篇 |
出版年
2024年 | 80篇 |
2023年 | 299篇 |
2022年 | 381篇 |
2021年 | 845篇 |
2020年 | 703篇 |
2019年 | 801篇 |
2018年 | 1364篇 |
2017年 | 1319篇 |
2016年 | 1376篇 |
2015年 | 1070篇 |
2014年 | 1272篇 |
2013年 | 2654篇 |
2012年 | 2010篇 |
2011年 | 1875篇 |
2010年 | 1523篇 |
2009年 | 1367篇 |
2008年 | 1328篇 |
2007年 | 1256篇 |
2006年 | 867篇 |
2005年 | 744篇 |
2004年 | 707篇 |
2003年 | 623篇 |
2002年 | 611篇 |
2001年 | 447篇 |
2000年 | 420篇 |
1999年 | 465篇 |
1998年 | 2403篇 |
1997年 | 1647篇 |
1996年 | 1038篇 |
1995年 | 621篇 |
1994年 | 476篇 |
1993年 | 572篇 |
1992年 | 205篇 |
1991年 | 206篇 |
1990年 | 157篇 |
1989年 | 162篇 |
1988年 | 163篇 |
1987年 | 140篇 |
1986年 | 121篇 |
1985年 | 144篇 |
1984年 | 125篇 |
1983年 | 96篇 |
1982年 | 131篇 |
1981年 | 149篇 |
1980年 | 158篇 |
1979年 | 78篇 |
1978年 | 84篇 |
1977年 | 282篇 |
1976年 | 625篇 |
1973年 | 63篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
ABSTRACTIn this paper, we review some algebraic control system. Precisely, linear and bilinear systems on Euclidean spaces and invariant and linear systems on Lie groups. The fourth classes of systems have a common issue: to any class, there exists an associated subgroup. From this object, we survey the controllability property. Especially, from those coming from our contribution to the theory. 相似文献
2.
Kruk Menno R.; Halász József; Meelis Wout; Haller József 《Canadian Metallurgical Quarterly》2004,118(5):1062
Aggressive behavior induces an adrenocortical stress response, and sudden stressors often precipitate violent behavior. Experiments in rats revealed a fast, mutual, positive feedback between the adrenocortical stress response and a brain mechanism controlling aggression. Stimulation of the aggressive area in the hypothalamus rapidly activated the adrenocortical response, even in the absence of an opponent and fighting. Hypothalamic aggression, in turn, was rapidly facilitated by a corticosterone injection in rats in which the natural adrenocortical stress response was prevented by adrenalectomy. The rapidity of both effects points to a fast, mutual, positive feedback of the controlling mechanisms within the time frame of a single conflict. Such a mutual facilitation may contribute to the precipitation and escalation of violent behavior under stressful conditions. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
3.
Eduardo Freire Teodiano Bastos-Filho Mário Sarcinelli-Filho Ricardo Carelli 《IEEE transactions on systems, man, and cybernetics. Part B, Cybernetics》2004,34(1):419-429
This paper proposes an alternative approach to address the problem of coordinating behaviors in mobile robot navigation: fusion of control signals. Such approach is based on a set of two decentralized information filters, which accomplish the data fusion involved. Besides these two fusion engines, control architectures designed according to this approach also embed a set of different controllers that generate reference signals for the robot linear and angular speeds. Such signals are delivered to the two decentralized information filters, which estimate suitable overall reference signals for the robot linear and angular speeds, respectively. Thus, the background for designing such control architectures is provided by the nonlinear systems theory, which makes this approach different from any other yet proposed. This background also allows checking control architectures designed according to the proposed approach for stability. Such analysis is carried out in the paper, and shows that the robot always reaches its final destination, in spite of either obstacles along its path or the environment layout. As an example, a control architecture is designed to guide a mobile robot in an experiment, whose results allows checking the good performance of the control architecture and validating the design approach proposed as well. 相似文献
4.
Analogue switch for very low-voltage applications 总被引:2,自引:0,他引:2
Munoz F. Ramirez-Angulo J. Lopez-Martin A. Carvajal R.G. Torralba A. Palomo B. Kachare M. 《Electronics letters》2003,39(9):701-702
A new analogue switch suitable for operation at very low-voltage supply in a standard CMOS technology is presented. The proposed switch is based on 'quasi-floating-gate' transistors and has a simple and compact structure. For illustrative purposes, two sample-and-hold circuits operating from a single supply voltage close to the threshold voltage of a transistor, and using the proposed technique, are presented. Experimental results obtained from prototypes in a 1.5 /spl mu/m CMOS technology are provided. 相似文献
5.
Low supply voltage high-performance CMOS current mirror with low input and output voltage requirements 总被引:1,自引:0,他引:1
Ramirez-Angulo J. Carvajal R.G. Torralba A. 《Circuits and Systems II: Express Briefs, IEEE Transactions on》2004,51(3):124-129
This paper presents a scheme for the efficient implementation of a low supply voltage continuous-time high-performance CMOS current mirror with low input and output voltage requirements. This circuit combines a shunt input feedback and a regulated cascode output stage to achieve low input resistance and very high output resistance. It can be used as a high-precision current mirror in analog and mixed signal circuits with a power supply close to a transistor's threshold voltage. The proposed current mirror has been simulated and a bandwidth of 40 MHz has been obtained. An experimental chip prototype has been sent for fabrication and has been experimentally verified, obtaining 0.15-V input-output voltage requirements, 100-/spl Omega/ input resistance, and more than 200-M/spl Omega/ (G/spl Omega/ ideally) output resistance with a 1.2-V supply in a standard CMOS technology. 相似文献
6.
F Abadía-Molina R Calvente R Carmona R Luján F Abadía-Fenoll 《Canadian Metallurgical Quarterly》1993,8(2):297-304
In this study chick embryo optic cups at HH stage 13 of development were analyzed under normal conditions and after inoculation with colchicine for 1, 2, 4, and 8 h. Several changes were seen after these periods of treatment: 1) modifications of the structure, with thicker regions in the cup and a general decrease in the total volume according to the duration of exposure to the drug (about 4 times less than normal, 5,035 x 10(3) microns 3 vs 1,334 x 10(3) microns 3 after 8 h of treatment); 2) enlargement of the ventricular cavity and its closure, due to failure of approximation of retinal and pigmentary layers; 3) failure of lens development, with delay and impairment of pit formation and deformation of all structures; lens volume was less than normal (about 4 times less, 2,148 x 10(3) microns 3 vs 658 x 10(3) microns 3 after 8 h of treatment); 4) a general segregation of the cells making up the structure, principally in the more active proliferating zones. The local alterations found are described. 相似文献
7.
8.
Data from the past few years have shown that as caffeine metabolizes solely in the liver, caffeine elimination can serve as a liver function test. We have collected data by monitoring 40 persons with liver diseases (11 chronic alcoholic hepatitis, 24 liver cirrhosis, 5 non-cirrhotic liver disease). Eight subjects served as controls. The patients with liver cirrhosis were classified according to the Child--Pugh scoring system. To determine caffeine elimination blood samples were collected before and at 3, 6, 9 and 12 hours after oral administration of 0.2 g caffeine. Fasting serum caffeine concentration and concentration 12 hours after administration, serum clearance, half life, peak concentration and volume of distribution have been compared. The respective values measured in patients with non-cirrhotic liver diseases did not differ significantly from the controls. The disappearance of caffeine was significantly decreased in cirrhotics. Our results demonstrated a good correlation between impairment of caffeine elimination and assessment of severity of liver disease by the Child--Pugh classification. Measuring serum levels in samples taken 12 hours after caffeine administration is a simple and useful method in the diagnosis of liver diseases at cirrhotic stage. 相似文献
9.
Daniela M. Nevskaia Maria Luisa Rojas Cervantes Antonio Guerrero Ruíz Juan de Dios Lpez Gonzlez 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1995,63(3):249-256
Adsorption of Triton X-100 on various silica substrates has been investigated. A number of solids, including a natural quartz, this quartz washed with HCl acid and subsequently heated at 1273 K; two aerosils and one Kieselgel silicas were studied. These solids exhibit surface areas in the range of 5 to 430 m2 g?1. All the Triton adsorption isotherms display an S-shape at the adsorption temperatures studied (298 and 308 K). It has been found that the pretreatments of natural quartz (by water washing, impurities removed by acid and/or high temperature calcination) affect considerably the amounts of TX-100 adsorbed. Measurements of surface composition have been made by X-ray photoelectron spectroscopy (XPS) with particular emphasis on the presence of impurities and on the number of OH groups at the surface of the samples. The nature of the surface hydroxyl has also been studied by infrared spectroscopy. Furthermore, the specific number of hydroxyl groups on the surface of the silica samples has been determined by thermogravimetric analysis. Finally an attempt to correlate solid surface characteristics with adsorption isotherms has been developed. 相似文献
10.
ML Martínez-Frías E Bermejo Sánchez E Rodríguez Pinilla A Villa 《Canadian Metallurgical Quarterly》1997,46(6):593-596
INTRODUCTION: Even though there are few epidemiological studies evaluating the birth weights of different groups of malformed babies with chromosomal abnormalities, it is widely known that infants with trisomy 18, and to a lesser degree those with trisomy 13 and other chromosomal alterations, have low birth weights. PATIENTS AND METHODS: In this study we present the analysis of the birth weights and gestational ages of a large sample of babies (23,155 malformed and a similar number of nonmalformed babies), separating the different groups of chromosomal anomalies and comparing the weight in the clinical groups of malformed infants. RESULTS: Most of the groups with chromosomal abnormalities present lower birth weights in comparison to the other groups. CONCLUSIONS: The results of our study support the conclusion that the relationship between chromosomal alterations and low birth weight is sufficiently important that such a low birth weight in children with minor or major anomalies should be considered as one more indication to perform chromosomal analysis. 相似文献