首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   450138篇
  免费   7147篇
  国内免费   1411篇
电工技术   8968篇
综合类   963篇
化学工业   69762篇
金属工艺   15620篇
机械仪表   13229篇
建筑科学   12176篇
矿业工程   1314篇
能源动力   12076篇
轻工业   46568篇
水利工程   3618篇
石油天然气   4324篇
武器工业   23篇
无线电   56050篇
一般工业技术   84836篇
冶金工业   81394篇
原子能技术   7194篇
自动化技术   40581篇
  2021年   3487篇
  2019年   3211篇
  2018年   5277篇
  2017年   5053篇
  2016年   5338篇
  2015年   4107篇
  2014年   6704篇
  2013年   21079篇
  2012年   11033篇
  2011年   15032篇
  2010年   11773篇
  2009年   13428篇
  2008年   14368篇
  2007年   14428篇
  2006年   12675篇
  2005年   11666篇
  2004年   11262篇
  2003年   10993篇
  2002年   10766篇
  2001年   10789篇
  2000年   10296篇
  1999年   10729篇
  1998年   24409篇
  1997年   17867篇
  1996年   14269篇
  1995年   11121篇
  1994年   10098篇
  1993年   9672篇
  1992年   7520篇
  1991年   7203篇
  1990年   7006篇
  1989年   6813篇
  1988年   6598篇
  1987年   5656篇
  1986年   5732篇
  1985年   6733篇
  1984年   6145篇
  1983年   5794篇
  1982年   5272篇
  1981年   5408篇
  1980年   4978篇
  1979年   4903篇
  1978年   4625篇
  1977年   5596篇
  1976年   7184篇
  1975年   4009篇
  1974年   3767篇
  1973年   3884篇
  1972年   3123篇
  1971年   2821篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Wireless Personal Communications - A relatively new area of research and development is Swarm Robotics. It is a part of the swarm intelligence field. In the proposed paper, we shall use swarm...  相似文献   
82.
Atom scattering is becoming recognized as a sensitive probe of the electron–phonon interaction parameter λ at metal and metal-overlayer surfaces. Here, the theory is developed, linking λ to the thermal attenuation of atom scattering spectra (in particular, the Debye–Waller factor), to conducting materials of different dimensions, from quasi-1D systems such as W(110):H(1 × 1) and Bi(114), to quasi-2D layered chalcogenides, and high-dimensional surfaces such as quasicrystalline 2ML-Ba(0001)/Cu(001) and d-AlNiCo(00001). Values of λ obtained using He atoms compare favorably with known values for the bulk materials. The corresponding analysis indicates in addition, the number of layers contributing to the electron–phonon interaction, which is measured in an atom surface collision.  相似文献   
83.
Journal of Communications Technology and Electronics - This paper implements mathematically rigorous extended trial function algorithm to address cubic–quartic optical solitons in...  相似文献   
84.
The family of NAD(P)H-dependent short-chain dehydrogenases/reductases (SDRs) comprises numerous biocatalysts capable of C=O or C=C reduction. The highly homologous noroxomaritidine reductase (NR) from Narcissus sp. aff. pseudonarcissus and Zt_SDR from Zephyranthes treatiae, however, are SDRs with an extended imine substrate scope. Comparison with a similar SDR from Asparagus officinalis (Ao_SDR) exhibiting keto-reducing activity, yet negligible imine-reducing capability, and mining the Short-Chain Dehydrogenase/Reductase Engineering Database indicated that NR and Zt_SDR possess a unique active-site composition among SDRs. Adapting the active site of Ao_SDR accordingly improved its imine-reducing capability. By applying the same strategy, an unrelated SDR from Methylobacterium sp. 77 (M77_SDR) with distinct keto-reducing activity was engineered into a promiscuous enzyme with imine-reducing activity, thereby confirming that the ability to reduce imines can be rationally introduced into members of the “classical” SDR enzyme family. Thus, members of the SDR family could be a promising starting point for protein approaches to generate new imine-reducing enzymes.  相似文献   
85.
The paper describes the results of a study on the temperature and frequency dependences of the dielectric permeability and dielectric loss tangent of composite materials composed of low density polyethylene filled with cadmium sulfide (LDPE/CdS) and indium(III) selenide (LDPE/In2Se3) in the temperature range of 300–450 K and a frequency range of 0–1014 Hz. It is revealed that a variation in the filler content and the effect of external factors can yield novel composite materials with desired dielectric characteristics.  相似文献   
86.
JOM - Alpha-radiation damage in metals is a concern for long-term radioactive storage and systems that produce nuclear energy. Accurate prediction of irradiated material properties and failure...  相似文献   
87.
88.
89.
90.
The work reported involved the fabrication of an electrospun tubular conduit of a gelatin and polycaprolactone (PCL) blend as an adventitia‐equivalent construct. Gelatin was included as the matrix for increased biocompatibility with the addition of PCL for durability. This is contrary to most of the literature available for biomaterials based on blends of gelatin and PCL where PCL is the major matrix. The work includes the assiduous selection of key electrospinning parameters to obtain smooth bead‐free fibres with a narrow distribution of pore size and fibre diameter. Few reports elucidate the optimization of all electrospinning parameters to fabricate tubular conduits with a focus on obtaining homogeneous pores and fibres. This stepwise investigation would be unique for the fabrication of gelatin–PCL electrospun tubular constructs. The fabricated microfibrous gelatin–PCL constructs had pores of size ca 50–100 μm reportedly conducive for cell infiltration. The measured value of surface roughness of 57.99 ± 17.4 nm is reported to be favourable for protein adhesion and cell adhesion. The elastic modulus was observed to be similar to that of the tunica adventitia of the native artery. Preliminary in vitro and in vivo biocompatibility tests suggest safe applicability as a biomaterial. Minimal cytotoxicity was observed using MTT assay. Subcutaneous implantation of the scaffold demonstrated acute inflammation which decreased by day 15. The findings of this study could enable the fabrication of smooth bead‐free microfibrous gelatin–PCL tubular construct as viable biomaterial which can be included in a bilayer or a trilayer scaffold for vascular tissue engineering. © 2019 Society of Chemical Industry  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号