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   4535篇
  免费   158篇
  国内免费   23篇
电工技术   45篇
综合类   12篇
化学工业   566篇
金属工艺   41篇
机械仪表   60篇
建筑科学   67篇
矿业工程   4篇
能源动力   127篇
轻工业   304篇
水利工程   16篇
石油天然气   47篇
武器工业   1篇
无线电   516篇
一般工业技术   435篇
冶金工业   2039篇
原子能技术   10篇
自动化技术   426篇
  2023年   14篇
  2022年   33篇
  2021年   50篇
  2020年   32篇
  2019年   49篇
  2018年   65篇
  2017年   128篇
  2016年   57篇
  2015年   56篇
  2014年   100篇
  2013年   191篇
  2012年   131篇
  2011年   191篇
  2010年   143篇
  2009年   142篇
  2008年   129篇
  2007年   104篇
  2006年   103篇
  2005年   134篇
  2004年   127篇
  2003年   98篇
  2002年   74篇
  2001年   62篇
  2000年   64篇
  1999年   126篇
  1998年   685篇
  1997年   397篇
  1996年   250篇
  1995年   146篇
  1994年   118篇
  1993年   176篇
  1992年   54篇
  1991年   39篇
  1990年   24篇
  1989年   45篇
  1988年   28篇
  1987年   33篇
  1986年   24篇
  1985年   20篇
  1984年   13篇
  1983年   14篇
  1982年   16篇
  1981年   22篇
  1980年   30篇
  1979年   8篇
  1978年   11篇
  1977年   36篇
  1976年   80篇
  1975年   10篇
  1970年   10篇
排序方式: 共有4716条查询结果,搜索用时 0 毫秒
31.
32.
33.
Summary form only given. An edge-emitting strained AlGaAs/InGaAs/GaAs quantum-well laser structure is reported. It has a periodic index separate confinement heterostructure (PINSCH) optical confinement layers for a small beam divergence and high output power. Preliminary measurements of AR/HR-coated self-aligned ridge waveguide lasers show a CW output power of up to 350 mW and a 20° transverse beam divergence at a 980-nm lasing wavelength. This low beam divergence results in a high coupling efficiency of 51% into single-mode fibers. The expanded optical field in PINSCH confinement layers significantly pinches the transverse beam divergence and increases the maximum output power  相似文献   
34.
Kim  J.D. Ryu  M. Kim  J. Chin  H.U. 《Electronics letters》2006,42(14):792-793
An impedance matching technique using series condensers for the power receivers of in vivo robotic capsules is proposed. The power delivery function of the condenser ratio and its optimal ratio are derived. Experimental results validate the derived function.  相似文献   
35.
36.
The simultaneous contrast effect is investigated in this article. A total of 174 and 154 test/induction combinations were studied for CRT and surface colours respectively. Each combination was assessed by nine observers using a matching technique. The test and induction colours used for CRT colours were similar to surface colours using fabric samples. The results indicated a strong lightness contrast effect for both CRT and surface media; that is, the lightness of a test colour surrounded by a lighter induction colour was reduced for both CRT and surface colours. However, the effect in CRT medium was more pronounced than in the surface medium. © 2004 Wiley Periodicals, Inc. Col Res Appl, 30, 13–20, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20074  相似文献   
37.
Poly(arylene ether benzonitrile) (PAEBN) was synthesized with 2,6‐dichlorobenzonitrile and biphenol. PAEBNs with various molecular weights (MWs), 1,640,000 and 185,000 g/mol, were synthesized by control of the stoichiometry of the monomers and were blended with sulfonated poly(ether ether ketone) (SPEEK). The effects of MW on the water uptake, swelling, methanol permeability, and proton conductivity of the SPEEK/PAEBN blend membranes were investigated. The molecular mobility of the SPEEK/PAEBN blends was also examined in this study. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008  相似文献   
38.
39.
While the osteopenia associated with oestrogen deficiency is thought to arise from a relative defect in bone formation with respect to resorption, oestrogen administration itself leads to a decrease, rather than an increase, in bone formation. This decrease in bone formation, which arises from oestrogen's inhibitory effect on bone turnover, presumably masks any underlying tendency of oestrogen treatment towards stimulation of bone formation. To investigate this further, we have examined the early effect of discontinuing the administration of oestradiol-17 beta (OE2; 40 micrograms/kg) on bone formation indices in ovariectomized 13-week-old rats, before the turnover-induced increase in formation occurs. Histomorphometric indices were assessed at the proximal tibial metaphysis 0, 7, 10, 13 and 16 days following discontinuation of OE2 treatment. Measurements of body weight, uterine weight and longitudinal growth rate confirmed that there were rapid effects of OE2 deficiency on these parameters. We could detect no significant increase in bone resorption, as measured by osteoclast surface and number, until 16 days after ending treatment with OE2; this was coincidental with a reduction in bone volume. Shorter periods of OE2 deficiency were associated with a marked decrease in bone formation, as assessed by dynamic histomorphometric indices. This inhibition of bone formation was largely due to a reduction in double fluorochrome-labeled trabecular surfaces, which were decreased by approximately 70%. We conclude that ending OE2 administration in ovariectomized rats caused a striking decrease in trabecular bone formation, if such indices are assessed prior to the subsequent turnover-induced increase in formation.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
40.
The role of gender was examined in the process and outcome of therapy in the treatment of depressed outpatients seen in the National Institute of Mental Health Treatment of Depression Collaborative Research Program. Patients received either interpersonal therapy, cognitive-behavioral therapy, imipramine plus clinical management, or placebo plus clinical management. None of the therapist-patient by gender groupings (i.e., therapist gender, therapist-patient gender matching vs. mismatching, or patients' beliefs about whether a male or female therapist would be more helpful) were significantly related to measures of treatment process and outcome, controlling for type of treatment and severity of pretreatment depressive symptoms. Findings were duplicated when examining the effects of gender within only the psychotherapeutic modes of treatment for the groupings of therapist gender and therapist-patient gender matching versus mismatching.  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