全文获取类型
收费全文 | 78401篇 |
免费 | 920篇 |
国内免费 | 689篇 |
专业分类
电工技术 | 1492篇 |
综合类 | 60篇 |
化学工业 | 11581篇 |
金属工艺 | 3500篇 |
机械仪表 | 2689篇 |
建筑科学 | 1997篇 |
矿业工程 | 506篇 |
能源动力 | 1947篇 |
轻工业 | 6886篇 |
水利工程 | 873篇 |
石油天然气 | 2306篇 |
武器工业 | 41篇 |
无线电 | 7416篇 |
一般工业技术 | 16893篇 |
冶金工业 | 13560篇 |
原子能技术 | 2682篇 |
自动化技术 | 5581篇 |
出版年
2022年 | 555篇 |
2021年 | 968篇 |
2020年 | 722篇 |
2019年 | 814篇 |
2018年 | 1602篇 |
2017年 | 1605篇 |
2016年 | 1821篇 |
2015年 | 994篇 |
2014年 | 1619篇 |
2013年 | 3655篇 |
2012年 | 2474篇 |
2011年 | 2988篇 |
2010年 | 2486篇 |
2009年 | 2747篇 |
2008年 | 2741篇 |
2007年 | 2825篇 |
2006年 | 2268篇 |
2005年 | 1999篇 |
2004年 | 1917篇 |
2003年 | 1870篇 |
2002年 | 1783篇 |
2001年 | 1734篇 |
2000年 | 1739篇 |
1999年 | 1651篇 |
1998年 | 4041篇 |
1997年 | 2813篇 |
1996年 | 2068篇 |
1995年 | 1632篇 |
1994年 | 1413篇 |
1993年 | 1433篇 |
1992年 | 1029篇 |
1991年 | 1092篇 |
1990年 | 1114篇 |
1989年 | 1094篇 |
1988年 | 968篇 |
1987年 | 904篇 |
1986年 | 901篇 |
1985年 | 968篇 |
1984年 | 804篇 |
1983年 | 787篇 |
1982年 | 695篇 |
1981年 | 719篇 |
1980年 | 691篇 |
1979年 | 681篇 |
1978年 | 637篇 |
1977年 | 807篇 |
1976年 | 987篇 |
1975年 | 598篇 |
1974年 | 571篇 |
1973年 | 568篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
141.
Tuning-current splitting network for three-section DBR lasers 总被引:1,自引:0,他引:1
A simple current-splitting network for DBR-laser frequency tuning is proposed that distributes a single control current among two tuning sections and can adjust the current distribution without yielding impedance mismatching. The nonlinear characteristics of the tuning sections realise the non-proportional current splitting suitable for continuous tuning; 470 GHz (3.8 nm) tuning range is achieved 相似文献
142.
Most divers and diving medicine specialists know that application of normobaric oxygen as first aid after a bubble disease incident is highly effective. However, as yet technical difficulties acted as a deterrent to using normobaric oxygen at the diving site. This can now be overcome by a newer technique. To be efficient, any therapy of bubble disease should follow three main principles: maximal partial pressure of inhaled oxygen (i.e. 100 kpa in normobaric, and 280 kpa in hyperbaric conditions); minimal partial pressure of inhaled nitrogen, which should ideally be near zero; immediate start of therapy, if possible at the diving site, but not later than 2 hours after the onset of the first symptoms. However, it has to be borne in mind that for an efficient normobaric oxygenation (100%), the standard apparatus design without oxygen reservoir is obsolete, for it offers at most 40% oxygen to the lungs. Currently the following technical approaches for an efficient normobaric oxygenation are available: open one-way systems with tightly fitting mask and oxygen reservoir bag (type Ambu or Leardal, etc.); open systems with on-demand regulation and tightly fitting mouth piece (type SCUBA, or Bird-respirator); closed systems with CO2 absorber (type oxygen rebreathing diving gear). The closed system is a genuine technical advance, because it needs 15 times less oxygen than open systems (about 90 liters oxygen for a 3-hours oxygenation run). Such an apparatus is thus of light weight, far less cumbersome, and nevertheless highly efficient. The therapy should start immediately at the site of the mishap and be maintained during the transport to the next HBO-unit (usually 3 to 6 hours).(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
143.
Metal Science and Heat Treatment - 相似文献
144.
O. Perat J. M. Dorkel E. Scheid P. Temple Boyer Y. S. Chung A. Peyre-Lavigne M. Zecri P. Tounsi 《Microelectronics Reliability》2002,42(7):1053-1058
Reliability of thermomechanical simulations is critically linked to the accuracy of the mechanical properties that govern the behaviour of structure, like Young's modulus (E) and coefficient of thermal expansion (CTE). For many cases, the values found in literatures are dealing with bulk properties without detailed information on temperature effects. To address such issues, it is necessary to measure the materials parameters as a function of temperature. The measurement of CTE is usually accomplished by evaluating the thermal deflections of a subjected material layer deposited on a substrate, providing that E is known at a specific temperature of experiment. A bilayer method, based on theory of elasticity, is proposed to determine both E and CTE for a given temperature with a good resolution. This paper presents the theoretical analysis, the design and process of the microsystem test structures, and the main calculation results. 相似文献
145.
146.
147.
The heterogeneous enantioselective hydrogenation of activated ketones over chirally modified platinum is reviewed with emphasis on identifying the role of the various species observed in this catalytic system. The past years have witnessed a continuous broadening of the scope of this catalytic system including new reactants and modifiers affording over 97% ee. New reaction pathways have been uncovered and the kinetic and mechanistic studies have been faced with a number of complicating factors caused by spectator species and interactions in solution and on the Pt surface. The previously proposed mechanistic models are critically assessed in the light of these new findings. 相似文献
148.
Charles O. Okafor 《Dyes and Pigments》1985,6(6):405-415
The synthesis of three new azaphenothiazine ring systems and an evaluation of their use as intermediates for new dyes and pigments is described. 2-Amino-5-bromopyrazine-3[4H]-thione (11) was prepared and converted to the novel 1,4,6,9-tetraazaphenothiazine ring system. The reaction of 4,5-diaminopyrimidine-6[1H]-thione (15) with 2,3-dichloropyrazines gave the isomeric 1,4,6,8-tetraazaphenothiazine ring system, another new heterocycle in this series. With 2,3-dichloroquinoxaline a previously unknown tetracyclic tetraazaphenothiazine ring system was isolated in satisfactory yields. The properties and reactions of these new heterocyclic systems are presented. Mixed nitric and sulphuric acids convert them to their 5-sulphoxides. Structural assignments were based on chemical evidence and their UV, IR, NMR and mass spectra. Mechanistic pathways to these compounds are also proposed. 相似文献
149.
K. A. Abdikalikov V. K. Zadiraka O. S. Kondratenko S. S. Mel'nikova 《Cybernetics and Systems Analysis》1991,27(3):414-419
A fast algorithm is proposed for estimating the auto- and cross-correlation functions of a large signal. The algorithm is based on the sectioning method by the fast Fourier transform. We determine the optimal length of the portion of data read from external memory into RAM which achieves Tmin—a minimum processing time. An estimate of Tmin is obtained.Translated from Kibernetika, No. 3, pp. 78–81, May–June, 1991. 相似文献
150.