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   378571篇
  免费   4319篇
  国内免费   1064篇
电工技术   7107篇
综合类   446篇
化学工业   60543篇
金属工艺   14625篇
机械仪表   11825篇
建筑科学   9522篇
矿业工程   1775篇
能源动力   8699篇
轻工业   39269篇
水利工程   3498篇
石油天然气   5675篇
武器工业   36篇
无线电   43043篇
一般工业技术   70323篇
冶金工业   69266篇
原子能技术   7881篇
自动化技术   30421篇
  2021年   2817篇
  2019年   2787篇
  2018年   4471篇
  2017年   4443篇
  2016年   4852篇
  2015年   3214篇
  2014年   5529篇
  2013年   16200篇
  2012年   9036篇
  2011年   12525篇
  2010年   9865篇
  2009年   11082篇
  2008年   11813篇
  2007年   12198篇
  2006年   10754篇
  2005年   9723篇
  2004年   9412篇
  2003年   9099篇
  2002年   9165篇
  2001年   9093篇
  2000年   8654篇
  1999年   8590篇
  1998年   19043篇
  1997年   13838篇
  1996年   11098篇
  1995年   8740篇
  1994年   7849篇
  1993年   7595篇
  1992年   6172篇
  1991年   5795篇
  1990年   5929篇
  1989年   5820篇
  1988年   5540篇
  1987年   4871篇
  1986年   4881篇
  1985年   5641篇
  1984年   5241篇
  1983年   4839篇
  1982年   4563篇
  1981年   4582篇
  1980年   4358篇
  1979年   4292篇
  1978年   4231篇
  1977年   4843篇
  1976年   6201篇
  1975年   3761篇
  1974年   3479篇
  1973年   3656篇
  1972年   3019篇
  1971年   2808篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Tachykinin immunoreactivity is found in a ventromedial spinal plexus in the lamprey. Neurons in this plexus project bilaterally and are thus in a position to modulate locomotor networks on both sides of the spinal cord. We have examined the effects of the tachykinin substance P on NMDA-evoked locomotor activity. Brief (10 min) application of tachykinin neuropeptides results in a prolonged concentration-dependent (>24 hr) modulation of locomotor activity, shown by the increased burst frequency and more regular burst activity. These effects are blocked by the tachykinin antagonist spantide II. There are at least two phases to the burst frequency modulation. An initial phase (approximately 2 hr) is associated with the protein kinase C-dependent potentiation of cellular responses to NMDA. The long-lasting phase (>2 hr) appears to be protein synthesis-dependent, with protein synthesis inhibitors causing the increased burst frequency to recover after washing for 2-3 hr. The modulation of the burst regularity is caused by a separate effect of tachykinins, because unlike the burst frequency modulation it does not require the modulation of NMDA receptors for its induction and is blocked by H8, an inhibitor of cAMP- and cGMP-dependent protein kinases. The effects of substance P were mimicked by the dopamine D2 receptor antagonist eticlopride. The effects of eticlopride were blocked by the tachykinin antagonist spantide II, suggesting that eticlopride may endogenously release tachykinins. Because locomotor activity in vitro corresponds to that during swimming in intact animals, we suggest that endogenously released tachykinins will result in prolonged modulation of locomotor behavior.  相似文献   
992.
Determined the comorbidity of psychopathy and alexithymia in 37 female inmates of a medium-security prison. The authors also investigated the association between psychopathy and alexithymia with the use of affective language in response to questions about an emotional event, and with their propensity for violence. The extent of psychopathy and alexithymia were assessed with the Hare Psychopathy Checklist—Revised (PCL-R) and the Toronto Alexithymia Scale (TAS), respectively. Using standard cutoff scores, 30% were identified as psychopaths, and 32% as alexithymics. Three Ss were both psychopaths and alexithymics. The correlation between PCL-R and TAS total scores was not significant, but the socially deviant impulsive factor of the PCL-R significantly correlated with the TAS items that reflect inability to discriminate feelings and bodily sensations. Alexithymia, but not psychopathy, was negatively related to measures of affective speech content. Both psychopathy and alexithymia were associated with a history of violence. In spite of several manifest similarities, psychopathy and alexithymia appear to be different clinical constructs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
993.
We present some novel expressions for the depolarization dyadics in uniaxial dielectric-magnetic media. These expressions were obtained by generalizing the Fikioris approach for extracting the singular behaviour of integrals involving the dyadic Green functions and the source current density distributions. Cubical, cylindrical and spherical geometries serve as examples for a discussion of the depolarization dyadics' dependence on geometry and anisotropy.  相似文献   
994.
A statistical study of the particle shape and size of pure V2O5 and TiO2, and samples of coprecipitated V2O5---TiO2 catalysts with different V/Ti ratios, has been performed. They were also characterized by XRD, EDAX, SEM and XPS. The results showed that pure vanadium pentoxide is compose by large square or needle-shaped particles, while pure titanium dioxide has small and rounded ones. VTiO samples presented an area and shape, depending on the V/Ti ratio.

These results and the spectroscopical characterization conducted to a particle model of the catalysts. Those VOTi samples with high V/Ti ratio would have large V2O5 crystals acting as support of a V/TiO2 solid solution. In contrast, those samples with a low V/Ti ratio, would have the solid solution supporting vanadium pentoxide crystals.  相似文献   

995.
996.
This paper investigates a method for predicting the generalization error that a multi-layer network of Sigma-pi units will, on average, exhibit. Theoretical values are compared with those obtained by the computer simulation of small networks learning parity and contiguity functions.  相似文献   
997.
998.
The effect of FEF carbon black as filler on the thermal capacity c, diffusivity a, and thermal conductivity λ, of styrene butadiene rubber (SBR) composites in the temperature range 300–420 K was studied. The filler strongly increases the thermal diffusivity, whilst strongly decreasing the thermal capacity and the thermal conductivity (except at high FEF content ≥80 phr). The influence of the filler on the thermoelastic behaviour of the same composites was also investigated. It was found that the thermoelastic temperature change (ΔT) increased with carbon black concentration as well as the entropy change per unit extension.  相似文献   
999.
In sheet stamping, friction appears between the tool and the deformed preform. It is of interest to evaluate the difference in the friction coefficient in stamping by tools subjected to different kinds of heat treatment and chemical heat treatment.  相似文献   
1000.
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