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   580篇
  免费   62篇
  国内免费   47篇
化学   447篇
晶体学   1篇
力学   49篇
综合类   11篇
数学   68篇
物理学   113篇
  2023年   9篇
  2022年   16篇
  2021年   15篇
  2020年   12篇
  2019年   6篇
  2018年   11篇
  2017年   11篇
  2016年   16篇
  2015年   18篇
  2014年   29篇
  2013年   26篇
  2012年   40篇
  2011年   22篇
  2010年   29篇
  2009年   44篇
  2008年   45篇
  2007年   21篇
  2006年   33篇
  2005年   41篇
  2004年   28篇
  2003年   27篇
  2002年   16篇
  2001年   18篇
  2000年   14篇
  1999年   18篇
  1998年   8篇
  1997年   16篇
  1996年   17篇
  1995年   10篇
  1994年   9篇
  1993年   14篇
  1992年   14篇
  1991年   9篇
  1990年   11篇
  1989年   6篇
  1988年   3篇
  1987年   1篇
  1985年   1篇
  1984年   1篇
  1981年   2篇
  1980年   1篇
  1979年   1篇
排序方式: 共有689条查询结果,搜索用时 0 毫秒
631.
Commissioning of electron cooling in CSRm   总被引:1,自引:0,他引:1  
A new generation electron cooler has started operation in the heavy ion synchrotron CSRm which is used to increase the intensity of heavy ions. Transverse cooling of the ion beam after horizontal multi-turn injection allows beam accumulation at the injection energy. After optimization of the accumulation process an intensity increase in a synchrotron pulse by more than one order of magnitude has been achieved. In given accumulation time interval of 10 seconds, 108 particles have been accumulated and accelerated to the final energy. The momentum spread after accumulation and acceleration in the 10-4 range has been demonstrated in six species of ion beams. Primary measurements of accumulation process varying with electron energy, electron beam current, electron beam profile, expansion factor and injection interval have been performed. The lifetimes of ion beams in the presence of electron beams were roughly measured with the help of DCCT signal.  相似文献   
632.
本文把点集拓扑学中的C·T·Yang定理推广到模糊拓扑学中 ,并且获得了一些其它新的结果  相似文献   
633.
镉在自然水体生物膜生长过程中的积累   总被引:4,自引:0,他引:4  
镉在自然水体生物膜生长过程中的积累;吸附性积累  相似文献   
634.
The stimulant sibutramine is an anorexic agent found as an adulterant in natural products and multivitamins supplements used for weight‐loss. In this work, a carbon graphite screen‐printed electrode (SPE‐Gr) with adsorptive stripping pulse differential voltammetry (AdSDPV) is presented for the sensitive and simple detection of sibutramine in slimming tea beverages. The proposed electrochemical method shows a linear working range from 2.0 to 120 μM with a low LOD (0.3 μM) for sibutramine determination in slimming tea samples. The analytical performance of the SPE‐Gr with AdSDPV for sibutramine detection suggests its possible application as an easy, fast and low‐cost method to analyse adulterated tea samples with this stimulant at low levels (<0.1 %).  相似文献   
635.
In this study, broilers were fed with heavy-metal-containing diets (Zn, Cu, Pb, Cr, As, Hg) at three rates (T1: 5 kg premix/ton feed, T2: 10 kg premix/ton feed and T3: 15 kg premix/ton feed) and Doxycycline (DOX) and Gatifloxacin (GAT) at low or high doses (T4: 31.2 mg DOX/bird/day and 78 mg GAT/bird/day, T5: 15.6 mg DOX/bird/day and 48 mg GAT/bird/day) to assess the accumulation of various heavy metals and the fate of two antibiotics in broiler manure after 35 days of aerobic composting. The results indicated that the two antibiotics changed quite differently during aerobic composting. About 14.96–15.84% of Doxycycline still remained at the end of composting, while Gatifloxacin was almost completely removed within 10 days of composting. The half-lives of Doxycycline were 13.75 and 15.86 days, while the half-lives of Gatifloxacin were only 1.32 and 1.38 days. Based on the Redundancy analysis (RDA), the concentration of antibiotics was significantly influenced by physico-chemical properties (mainly temperature and pH) throughout the composting process. Throughout the composting process, all heavy metal elements remained concentrated in organic fertilizer. In this study the Cr content reached 160.16 mg/kg, 223.98 mg/kg and 248.02 mg/kg with increasing premix feed rates, similar to Zn, which reached 258.2 mg/kg, 312.21 mg/kg and 333.68 mg/kg. Zn and Cr concentrations well exceeded the United States and the European soil requirements. This experiment showed that antibiotic residues and the accumulation of heavy metals may lead to soil contamination and pose a risk to the soil ecosystem.  相似文献   
636.
钝顶螺旋藻对阴离子表面活性剂(LAS)的富集与降解   总被引:3,自引:0,他引:3       下载免费PDF全文
实验考察了使用钝顶螺旋藻富集与降解溶液中的阴离子表面活性剂(LAS).结果表明,溶液中不同浓度LAS存在下,钝顶螺旋藻的生长符合逻辑斯谛克方程;钝顶螺旋藻对LAS具有一定的富集能力,当LAS的质量浓度为0.5、1、2mg/L时,24h时富集量达到最大,分别为2.43、4.83、10.12mg/g;钝顶螺旋藻对LAS也具有一定的降解能力,当LAS的质量浓度分别为0.5、1、2mg/L时,5d内LAS的降解率分别为87%、80%和70.5%,其降解动力学方程可用二级反应动力学方程很好地拟合,拟合度达到87%以上.  相似文献   
637.
The paper explores the lability of DOC complexes of Co, Ni, Cu, and Zn in the mining effluent, and investigates the effects of dilution of the effluent on the release of metals from the metal-DOC complexes. This study was done using competing ligand exchange method in conjunction with adsorptive cathodic stripping voltammetry on effluent samples from Copper Cliff Mine, Sudbury, Canada, using two samples of the effluent: one, undiluted (100%) effluent, and the other, diluted (45%) effluent. The dilution was done with tap water in order to determine the effects of dilution on the metal complexes in the effluents when they were discharged into receiving streams of freshwaters. The dilution of the effluent had a small effect on release of Cu from the Cu-DOC complexes, but had a much greater effect on the release of Zn from the Zn-DOC complexes. The release of Ni and Co from their DOC complexes decreased drastically on dilution of the effluent. The much greater release of Cu from the Cu-DOC complexes compared to the release of Ni, Co, and Zn from their DOC complexes in both the undiluted and the diluted effluent was probably due to the higher absolute concentration of Cu and the higher [Cu]/[DOC] ratio. The drastic decrease in the release of Ni and Co from the Ni- and Co-DOC complexes in the diluted (45%) effluent compared with the undiluted (100%) effluent probably resulted from strengthening of the metal-DOC bond due to the reduced screening of charges by a smaller concentration of Ca2+ in the diluted (45%) effluent. This work also shows that change in the ionic strength produces conformational changes in and in aggregation and precipitation of the DOC and also changes in electrostatic interactions between the metal cations and the humate polyanions.  相似文献   
638.
Visual enhancement for infrared small dim targets is a standing problem in infrared image processing. Existing approaches cannot enhance the target well and suppress the background simultaneously, especially for targets which are so faint that they are hardly visible. This paper proposes a novel real-time visual enhancement algorithm for infrared small dim targets in video by introducing temporal cues. In this work, Dynamic Programming Algorithm (DPA) is used to detect the target’s trajectory in the video and the target is enhanced through energy accumulation along the trajectory. The shape prior of the small dim target is adopted for background suppression and adaptive merging. Experimental results on real infrared small dim target videos indicate that the proposed algorithm can improve the visual quality of these types of images notably, especially for cases in which the target is hardly visible. In addition, the proposed algorithm takes on average 8.35 ms to process a 320 1 256 image, and thus meets the needs of real-time applications.  相似文献   
639.
An alternative way of estimating the durability of structural plastics under stresses = const 0.4-0.8f(f is the failure stress) based on test data obtained in multiple rectangular loading-rest cycles is proposed. It is also suggested to employ the decrease in the instantaneous elastic modulus as a criterion for evaluating the residual service life of plastic parts and structures and elucidating the reasons for their early failure. For the first time, a possibility of considerably increasing the durability and endurance of structural plastics under short pulsed loadings with relatively long interruptions at the initial stage of stress concentration is considered. The cases of a significantly increased endurance of plastics caused by long interruptions after some fatigue loading by high-frequency tension cycles with a zero maximum stress are explained. First experimental confirmations of an increased durability and endurance of microcomposites subjected to short pulsed loadings alternating with long interruptions are obtained. The evolution of the effect of the loading-rest modes on the durability of massive specimens, microcomposites, and dry fibrous reinforcing fillers is demonstrated with examples of a glass-fabric laminate, a microcomposite, and a nonimpregnated glass strand.  相似文献   
640.
讨论Learning-by-doing随机经济增长模型,利用随机最优化方法,确定了均衡状态下的消费—财富比、期望经济增长率.讨论了差异性税率、随机扰动和技术积累参数对上述诸要素的影响.  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