全文获取类型
收费全文 | 230199篇 |
免费 | 4519篇 |
国内免费 | 835篇 |
专业分类
电工技术 | 3799篇 |
综合类 | 345篇 |
化学工业 | 38069篇 |
金属工艺 | 8836篇 |
机械仪表 | 6235篇 |
建筑科学 | 6082篇 |
矿业工程 | 1021篇 |
能源动力 | 6088篇 |
轻工业 | 24450篇 |
水利工程 | 2189篇 |
石油天然气 | 3360篇 |
武器工业 | 13篇 |
无线电 | 22802篇 |
一般工业技术 | 41486篇 |
冶金工业 | 44941篇 |
原子能技术 | 4566篇 |
自动化技术 | 21271篇 |
出版年
2022年 | 1575篇 |
2021年 | 2652篇 |
2020年 | 1951篇 |
2019年 | 2471篇 |
2018年 | 3816篇 |
2017年 | 3822篇 |
2016年 | 3977篇 |
2015年 | 2932篇 |
2014年 | 4477篇 |
2013年 | 11246篇 |
2012年 | 7299篇 |
2011年 | 9349篇 |
2010年 | 7311篇 |
2009年 | 8040篇 |
2008年 | 7907篇 |
2007年 | 7712篇 |
2006年 | 6386篇 |
2005年 | 6029篇 |
2004年 | 5822篇 |
2003年 | 5411篇 |
2002年 | 5316篇 |
2001年 | 5116篇 |
2000年 | 4705篇 |
1999年 | 4866篇 |
1998年 | 13957篇 |
1997年 | 9817篇 |
1996年 | 7279篇 |
1995年 | 5303篇 |
1994年 | 4400篇 |
1993年 | 4453篇 |
1992年 | 2957篇 |
1991年 | 2949篇 |
1990年 | 2722篇 |
1989年 | 2745篇 |
1988年 | 2679篇 |
1987年 | 2388篇 |
1986年 | 2316篇 |
1985年 | 2648篇 |
1984年 | 2398篇 |
1983年 | 2168篇 |
1982年 | 2101篇 |
1981年 | 2172篇 |
1980年 | 2015篇 |
1979年 | 1954篇 |
1978年 | 1905篇 |
1977年 | 2471篇 |
1976年 | 3442篇 |
1975年 | 1669篇 |
1974年 | 1626篇 |
1973年 | 1711篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
21.
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
22.
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
23.
N. Mitchell A. Alekseev R. Gallix D. Holland R. Meyder A. Panin M. Shimada F. Wong E. Zapretelina 《Journal of Fusion Energy》1997,16(1-2):25-35
The ITER magnet system consists of structurally linked sets of toroidal (TF) and poloidal (PF) field coils, central solenoid (CS), and various support structures. The coils are superconducting, force flow Helium cooled with a Kapton-Glass-Epoxy multilayer insulation system. The stored magnetic energy is about 100GJ in the TF system and 20GJ in the PF-CS. Coils and structure are maintained at 4 K by enclosing them in a vacuum cryostat. The cryostat, comprising an outer envelope to the magnets, forms most of the second radioactivity confinement barrier. The inner primary barrier is formed by the vacuum vessel, its ports and their extensions. To keep the machine size within acceptable bounds, it is essential that the magnets are in close proximity to both of the nuclear confinement barriers. The objective of the magnet design is that, although local damage to one of the barriers may occur in very exceptional circumstances, large scale magnet structural or thermal failure leading to simultaneous breaching of both barriers is not credible. Magnet accidents fall into three categories: thermal (which includes arcing arising from insulation failure and local overheating due to discharge failure in the event of a superconductor quench), structural (which includes component mechanical failure arising from material inadequacies, design errors and exceptional force patterns arising from coil shorts or control failures), and fluid (Helium release due to cooling line failure). After a preliminary survey to select initial faults conceivable within the present design, these faults are systematically analyzed to provide an assessment of the damage potential. The results of this damage assessment together with an assessment of the reliability of the monitoring and protective systems, shows that the magnets can operate with the required safety condition. 相似文献
24.
This paper presents a new self-routing packet network called the plane interconnected parallel network (PIPN). In the proposed design, the traffic arriving at the network is shaped and routed through two banyan network based interconnected planes. The interconnections between the planes distribute the incoming load more homogeneously over the network. The throughput of the network under uniform and heterogeneous traffic requirements is studied analytically and by simulation. The results are compared with the results of the baseline network and another banyan network based parallel interconnection network. It is shown that, for the proposed design, a higher degree of heterogeneity results in better performance 相似文献
25.
Douay M. Xie W.X. Taunay T. Bernage P. Niay P. Cordier P. Poumellec B. Dong L. Bayon J.F. Poignant H. Delevaque E. 《Lightwave Technology, Journal of》1997,15(8):1329-1342
A comprehensive survey of photosensitivity in silica glasses and optical fiber is reviewed. Recent work on understanding the mechanisms contributing to germanium or aluminum doped fiber photosensitivity is discussed within the framework of photoelastic densification models 相似文献
26.
Sugawara F. Aoki K. Yamaguchi H. Sasaki K. Sasaki T. Fujisaki H. 《Electron Device Letters, IEEE》1997,18(10):483-485
A new lateral MOS-gated thyristor, called the Base-Current-Controlled Thyristor, is described. This device is designed so that most holes at the on-stage reach the P base through the floating P+ region adjacent to the P base and the on-state MOSFET. At the turn-off stage, the interruption of the hole current to the P base due to switching off the above MOSFET occurs simultaneously with the conventional turn-off operation. The concept of this device is verified experimentally by using the fabricated lateral device with the external MOSFET. This device exhibits a better trade-off relation between the on-state voltage and the turn-off time compared uith the conventional MOS-gated thyristor 相似文献
27.
28.
Cresswell M.W. Allen R.A. Guthrie W.F. Sniegowski J.J. Ghoshtagore R.N. Linholm L.W. 《Semiconductor Manufacturing, IEEE Transactions on》1998,11(2):182-193
The physical widths of reference features incorporated into electrical linewidth test structures patterned in films of monocrystalline silicon have been determined from Kelvin voltage measurements. The films in which the test structures are patterned are electrically insulated from the bulk-silicon substrate by a layer of silicon dioxide provided by SIMOX (Separation by the IMplantation of OXygen) processing. The motivation is to facilitate the development of linewidth reference materials for critical-dimension (CD) metrology-instrument calibration. The selection of the (110) orientation of the starting silicon and the orientation of the structures' features relative to the crystal lattice enable a lattice-plane-selective etch to generate reference-feature properties of rectangular cross section and atomically planar sidewalls. These properties are highly desirable for CD applications in which feature widths are certified with nanometer-level uncertainty for use by a diverse range of CD instruments. End applications include the development and calibration of new generations of CD instruments directed at controlling processes for manufacturing devices having sub-quarter-micrometer features 相似文献
29.
30.
Arguello F. Bruguera J.D. Doallo R. Zapata E.L. 《Parallel and Distributed Systems, IEEE Transactions on》1994,5(10):1091-1099
We present an unified parallel architecture for four of the most important fast orthogonal transforms with trigonometric kernel: Complex Valued Fourier (CFFT), Real Valued Fourier (RFFT), Hartley (FHT), and Cosine (FCT). Out of these, only the CFFT has a data flow coinciding with the one generated by the successive doubling method, which can be transformed on a constant geometry flow using perfect unshuffle or shuffle permutations. The other three require some type of hardware modification to guarantee the constant geometry of the successive doubling method. We have defined a generalized processing section (PS), based on a circular CORDIC rotator, for the four transforms. This PS section permits the evaluation of the CFFT and FCT transforms in n data recirculations and the RFFT and FHT transforms in n-1 data recirculations, with n being the number of stages of a transform of length N=rn. Also, the efficiency of the partitioned parallel architecture is optimum because there is no cycle loss in the systolic computation of all the butterflies for each of the four transforms 相似文献