全文获取类型
收费全文 | 437440篇 |
免费 | 6394篇 |
国内免费 | 2227篇 |
专业分类
电工技术 | 8944篇 |
技术理论 | 2篇 |
综合类 | 1816篇 |
化学工业 | 69419篇 |
金属工艺 | 17831篇 |
机械仪表 | 14089篇 |
建筑科学 | 12592篇 |
矿业工程 | 2816篇 |
能源动力 | 10654篇 |
轻工业 | 41159篇 |
水利工程 | 4504篇 |
石油天然气 | 8980篇 |
武器工业 | 209篇 |
无线电 | 50703篇 |
一般工业技术 | 83346篇 |
冶金工业 | 73283篇 |
原子能技术 | 9527篇 |
自动化技术 | 36187篇 |
出版年
2021年 | 3553篇 |
2019年 | 3117篇 |
2018年 | 5185篇 |
2017年 | 5237篇 |
2016年 | 5552篇 |
2015年 | 4173篇 |
2014年 | 6714篇 |
2013年 | 18910篇 |
2012年 | 10747篇 |
2011年 | 14580篇 |
2010年 | 11861篇 |
2009年 | 13322篇 |
2008年 | 14072篇 |
2007年 | 14050篇 |
2006年 | 12714篇 |
2005年 | 11918篇 |
2004年 | 10899篇 |
2003年 | 10593篇 |
2002年 | 10618篇 |
2001年 | 10435篇 |
2000年 | 9891篇 |
1999年 | 10029篇 |
1998年 | 20859篇 |
1997年 | 15879篇 |
1996年 | 12719篇 |
1995年 | 9987篇 |
1994年 | 9013篇 |
1993年 | 8684篇 |
1992年 | 6967篇 |
1991年 | 6775篇 |
1990年 | 6557篇 |
1989年 | 6552篇 |
1988年 | 6365篇 |
1987年 | 5473篇 |
1986年 | 5409篇 |
1985年 | 6318篇 |
1984年 | 5947篇 |
1983年 | 5514篇 |
1982年 | 5192篇 |
1981年 | 5274篇 |
1980年 | 5010篇 |
1979年 | 4979篇 |
1978年 | 4935篇 |
1977年 | 5687篇 |
1976年 | 7235篇 |
1975年 | 4488篇 |
1974年 | 4210篇 |
1973年 | 4251篇 |
1972年 | 3657篇 |
1971年 | 3396篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
801.
变结构变参数设计方法及其在机械CAD中的应用 总被引:4,自引:0,他引:4
提出了一种新颖的机械结构设计思想-变结构变参数设计方法,并结合实例,阐述了变结构变参数设计的概念、原则、实施措施和意义。由此对I-deas软件包进行了二次开发,编制了发动机曲轴专用CAD软件程序,并用某型号发动机曲轴进行了验证。 相似文献
802.
803.
Scientific-Technical Center “Atomtekhénergo.” Leningrad Nuclear Power Plant. N. V. Sultanov Institute of Nuclear Reactors,
Russian Scientific Center “Kurchatovskii institut.” Translated from Atomnaya énergiya, Vol. 76, No. 6, pp. 470–473, June,
1994. 相似文献
804.
G. P. Ledneva 《Journal of Engineering Physics and Thermophysics》1994,67(3-4):960-964
Heating of spherical alumina particles by high-intensity laser radiation under vacuum conditions to the melting temperature is investigated with account for the nonuniform distribution of energy sources with respect to the particle volume.B. I. Stepanov Institute of Physics, Academy of Sciences of Belarus, Minsk. Translated fron Inzhenerno-Fizicheskii Zhurnal, Vol. 67, Nos. 3–4, pp. 307–312, September–October, 1994. 相似文献
805.
Preparation of Metal-Coated Carbon Fiber Reinforced Composites and Their Electromagnetic Properties 总被引:1,自引:0,他引:1
Medium temperature curing by infrared radiation was used to prepare electromagnetic wave absorbing multilayered plastic matrix composite materials containing metal-coated carbon fibers (MCFs). The electromagnetic properties of the materials were investigated by frequency scanning tests with microwave vector network analyzer. It is found that the electromagnetic parameters, mainly permittivity of the composites increase significantly with the addition of MCFs, which gives the composites good designability as thin, light-weight EM wave absorbers. It is also shown that MCFs can improve on the EM wave energy attenuating property of the composites by widening the work frequency band width and raising the absorptive peak 相似文献
806.
Cook R.D. Saulnier G.J. Gisser D.G. Goble J.C. Newell J.C. Isaacson D. 《IEEE transactions on bio-medical engineering》1994,41(8):713-722
Presents the design, implementation, and performance of Rensselaer's third-generation adaptive current tomograph, ACT3. This system uses 32 current sources and 32 phase-sensitive voltmeters to make a 32-electrode system that is capable of applying arbitrary spatial patterns of current. The instrumentation provides 16 b precision on both the current values and the real and reactive voltage readings and can collect the data for a single image in 133 ms. Additionally, the instrument is able to automatically calibrate its voltmeters and current sources and adjust the current source output impedance under computer control. The major system components are discussed in detail and performance results are given. Images obtained using stationary agar targets and a moving pendulum in a phantom as well as in vivo resistivity profiles showing human respiration are shown 相似文献
807.
V. V. Veremey A. A. Kostenko I. K. Kuz'michev A. E. Poyedinchuk G. I. Khlopov 《Journal of Infrared, Millimeter and Terahertz Waves》1994,15(7):1283-1295
Reported here are the results on level and structure of the radiated field of an open resonator at and off resonance. On the basis of the modelling problem rigorous solution and the measurements at 4-millimeter wavelength we find there are no ways to compensate the radiated field from an open electromagnetic structure at resonance. Analysis of open resonator excitation efficiency shows that the mismatch loss of a slot-fed open resonator runs to 34% while at the aperture-feed excitation this is not more than 6% for the same-geometry resonator. 相似文献
808.
Howden W.E. Wieand B. 《IEEE transactions on pattern analysis and machine intelligence》1994,20(6):445-462
Formal verification of program properties may be infeasible or impractical, and informal analysis may be sufficient. Informal analysis involves the informal acceptance, by inspection, of the validity of program properties or steps in an analysis. Informal analysis may also involve abstraction. Abstraction can be used to eliminate details and concentrate on more general properties. Abstraction will result in informal analysis if it includes the use of undefined properties. A systematic, informal method for analysis called QDA (Quick Defect Analysis) is described. QDA is a comments analysis process based on facts and hypotheses. Facts are used to create an abstract program model, and hypotheses are selected, nonobvious program properties which are identified as needing verification. Hypotheses are proved from the facts that define an abstraction. QDA is hypothesis-driven in the sense that only those parts of an abstraction that are needed to prove hypotheses are created. The QDA approach was applied to a previously well tested operational flight program (OFP). The QDA method and the results of the OFP experiment are presented. The problems of incomplete or unsound informal analysis are analyzed, the relationship of QDA to other analysis methods is discussed, and suggested improvements to the QDA method are described 相似文献
809.
KW Scheller J G?rres JG Ross M Wiescher R Harkewicz DJ Morrissey BM Sherrill M Steiner NA Orr JA Winger 《Canadian Metallurgical Quarterly》1994,49(1):46-50
The shortage of suitable liver donors for children has motivated the use of ABO-incompatible (ABO-I) grafts for transplantation in urgent situations. However, survival after ABO-I liver grafts has been reported at about 30% as compared with 80% in cases of ABO-identical or -compatible liver grafts. This difference has been attributed to antibody-mediated, hyperacute or chronic liver rejection, due to preformed ABO antibodies (alloantibodies). In this study, we report our results with ABO-I livers in children without alloantibodies at the time of transplantation. From January 1988 to June 1993, 143 OLT were performed in 122 children. Eight children received 8 ABO-I liver grafts. Of these, 7 patients were included in the study. All 7 were alloantibody free before OLT. Five children were spontaneously alloantibody free, while in 2 children, the plasma alloantibodies were eliminated before and after transplantation using intravenous infusion of specific blood group antigens of the donor blood group (soluble antigens). Immunosuppression consisted of a triple-drug treatment combining CsA, AZA, and steroids. The follow-up period was between 10 and 48 months. One child died from a surgical complication. Six children survived, but 1 died 10 months later from intestinal obstruction. There were no graft losses and no episodes of hyperacute or chronic rejection. The graft and patient survival rate was 71%. There was a 28% incidence of rejection, but all were mild (requiring steroid boluses only). Our results suggest that the absence of ABO alloantibodies at the time of and after transplantation can protect ABO-I liver grafts against antibody-mediated rejection, whether hyperacute or chronic, and that soluble antigens are effective in eliminating alloantibodies in children. 相似文献
810.
The present study describes the development of an enzyme-linked immunosorbent assay capable of quantifying serum antibody of all four canine IgG subclasses. A panel of subclass-restricted and subclass-specific monoclonal antibodies was used to measure IgG subclasses in the serum of healthy dogs, as well as in dogs with a range of clinical diseases. The subclasses have been redefined as IgG1, IgG2, IgG3 and IgG4 based on a comparison with the relative concentration and electrophoretic mobilities of human IgG subclasses. In serum samples from healthy dogs, the concentration of IgG1 (mean, 8.17 +/- 0.95 mg ml-1) and IgG2 (mean, 8.15 +/- 3.16 mg ml-1) were very similar and considerably higher than the levels of IgG3 (mean, 0.36 +/- 0.43 mg ml-1) and IgG4 (mean, 0.95 +/- 0.45 mg ml-1). There was no apparent difference in the level of subclasses between the different breeds comprising this normal population. Sera from dogs with a range of immune-mediated or inflammatory diseases all had markedly elevated levels of IgG2 (more than 13 mg ml-1), but IgG1 decreased (less than 4 mg ml-1) to levels below the normal range. 相似文献