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   3010篇
  免费   227篇
  国内免费   16篇
电工技术   42篇
综合类   8篇
化学工业   615篇
金属工艺   46篇
机械仪表   96篇
建筑科学   102篇
能源动力   137篇
轻工业   222篇
水利工程   15篇
石油天然气   10篇
无线电   578篇
一般工业技术   597篇
冶金工业   188篇
原子能技术   10篇
自动化技术   587篇
  2024年   4篇
  2023年   20篇
  2022年   59篇
  2021年   99篇
  2020年   67篇
  2019年   72篇
  2018年   90篇
  2017年   86篇
  2016年   100篇
  2015年   93篇
  2014年   141篇
  2013年   281篇
  2012年   197篇
  2011年   185篇
  2010年   176篇
  2009年   178篇
  2008年   167篇
  2007年   151篇
  2006年   119篇
  2005年   94篇
  2004年   76篇
  2003年   80篇
  2002年   78篇
  2001年   59篇
  2000年   56篇
  1999年   63篇
  1998年   92篇
  1997年   59篇
  1996年   41篇
  1995年   40篇
  1994年   34篇
  1993年   30篇
  1992年   23篇
  1991年   16篇
  1990年   15篇
  1989年   17篇
  1988年   8篇
  1987年   9篇
  1986年   7篇
  1985年   6篇
  1984年   11篇
  1983年   14篇
  1982年   5篇
  1981年   6篇
  1980年   4篇
  1979年   3篇
  1978年   3篇
  1977年   6篇
  1976年   3篇
  1970年   4篇
排序方式: 共有3253条查询结果,搜索用时 15 毫秒
101.
102.
选用28日龄断奶的三元杂交(杜×长×大)仔猪60头,随机分为饲喂发酵饲料的试验组和不合发酵料的对照组:每个处理3个重复,每个重复10头猪.试验结束前连续收集3天粪便,测定饲料养分的表观消化率;试验结束时前腔静脉采血,测定血清生化指标.结果:试验组比对照组显著降低了料肉比和腹泻指数(P<0.05),日增重提高,但显著不差异(P>0.05);血清碱性磷酸酶显著提高(P<0.05),而血清尿素氮、总蛋白、白蛋白、谷丙转氨酶均没有显著变化(P>0.05).饲料养分的表观消化率(CTTAD)试验组日粮磷的消化率显著提高(P<0.05),粗脂肪消化率显著下降(P<0.05),粗蛋白和钙的消化率提高,但无显著差异(P>0.05).结果表明,发酵饲料有利于提高仔猪的生长性能和饲料养分的表观消化率,对降低仔猪断奶应激性腹泻有较好效果.  相似文献   
103.
    
Drawing from the lessons learnt from the Fukushima nuclear disaster in Japan, the assessment of subsurface environmental hazard around nuclear power plants has emerged as a critical task. Consequently, aiming to better understand the possible environmental impact of radiation leaks into the groundwater, a prescreening programme was initiated in 2011 by the Taiwanese government. As part of this programme, this study conducted various borehole prospecting techniques to identify in situ hydrogeological characteristics at Chin‐Shan Nuclear Power Plant. Borehole electrical log, sonic log and temperature/conductivity log were conducted to explain the regional lithologic conditions and permeability of the formation. In conjunction with this, the interwell tracer and pumping test was carried out to simultaneously determine the hydraulic parameters. In our opinion, the implementation of such in situ end‐to‐end investigations is essential in interpreting in situ fluid and solute transport dynamics prior to programming any numerical scheme for early warning, vulnerability assessment and regular monitoring of a nuclear power plant site.  相似文献   
104.
一个被广泛用于验证实时系统的方法是根据被验证的实时性质,使用适当的双向模拟等价关系使无限的状态空间转化为有限的状态等价类空间.算法只需要在这个有限的等价类空间里搜索就可以得到正确答案.但是,这个等价类空间的规模一般随着系统规模的增大而产生爆炸性的增长,以至于在很多情况下,穷尽搜索这个空间是不现实的.该文引入了一个等价关系来验证一个由多个实时自动机通过共享变量组成的并发系统是否满足一个线性时段特性.同时,还引入了格局之间的兼容关系来避免对状态等价类空间的穷尽搜索.基于这两个关系,文章提出了一个算法来验证是否一个实时自动机网满足一个线性时段特性.实例研究显示,此算法在某些情况下比其他一些工具有更好的时间和空间效率.  相似文献   
105.
A carbon-containing CoCrFeNi high entropy alloy (HEA) with heterogeneous structures was obtained through thermome-chanical treatments,which induced concurrent recrystallization and carbide precipitation in the alloy.A combination of high yield strength (556 MPa) and large uniform elongation (45%) was achieved in the investigated alloy.The enhancement of the strength is attributed to the combined effects of grain refinement,precipitation strengthening and microstructural het-erogeneity.Our work demonstrated that the heterogeneity design could be realized by thermomechanical processes,which provided a practical strategy for producing HEAs with high performance.  相似文献   
106.
Fiber‐reinforced composite structures can be tailored to desire mechanical properties and to embed microstrip antenna in aerospace applications. The electromagnetic characteristics of a microstrip antenna on isotropic and uniaxial substrates have been known, but that embedded in composite laminated substrates remain unavailable to date. This work aims at analyzing the performance of microstrip antenna embedded in composite laminated substrates by spectral domain analysis. Parameter studies are conducted to investigate the effects of the substrate's dielectric constants, the fiber directions (the orientation between the antenna and the laminate layers), and the stacking sequence on antenna's resonant frequency and radiation pattern. The antenna size when embedded in composite laminated substrates is larger than that when attached on isotropic substrates, or conversely, the resonant frequency will deviate lower if assuming the substrate as isotropic. The far‐field pattern in composite laminated substrates is more ‘directional’ than that in isotropic substrates. The antenna gain in the substrates of symmetric stacking with ±45° fiber direction is 20 dB better than that in isotropic substrates in some elevations. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
107.
The batch shaking adsorption study was conducted to determine the potential of fly and volcanic ashes in removing organic pollutants from oxidation pond effluents. Factors affecting organic pollutant removals, such as concentrations and sizes of fly and volcanic ashes, initial pond effluent organic concentrations, washed and unwashed conditions of fly and volcanic ashes, were investigated. The TOC (total organic carbon) removal efficiency varied from 30 to 58 percent. The organic removal efficiency increased with increasing ash concentrations, with decreasing initial pond effluent organic concentrations and with decreasing sizes of ashes.  相似文献   
108.
A simple method which is much simpler than, while retaining the same degree of accuracy, as that of a large computer hydrocode has been developed for deducing the JWL equation of state (EOS) of high explosive detonation products from the cylinder expansion test. The radial expansion history of metal tube, which is recorded by the streak camera, is expressed as an appropriate fitting function with the aid of a nonlinear curve fitting procedure. The measured data with respect to Eulerian coordinate are transformed to that in Lagrangian coordinate so that the p-V relation of detonation products may be obtained from the differentiation of fitting function and equations of conservation law. Metal strength is also taken into consideration to reduce the deviation at the lower pressure region. JWL parameters are acquired through the p-V relations by another nonlinear curve fitting procedure. The computed results for Comp-B, TNT, HMX, PBX-9404 and nitromethane, which are in good agreement with Lawrence Livermore National Laboratory (LLNL) data, are listed for comparison with other procedures in literature which have been in use so far.  相似文献   
109.
The ability of Pluronic F127 (PF127) conjugated with tetrapeptide Gly-Arg-Gly-Asp (GRGD) as a sequence of Arg-Gly-Asp (RGD) peptide to form the investigated potential hydrogel (hereafter referred to as 3DG bioformer (3BE)) to produce spheroid, biocompatibility, and cell invasion ability, was assessed in this study. The fibroblast cell line (NIH 3T3), osteoblast cell line (MG-63), and human breast cancer cell line (MCF-7) were cultured in the 3BE hydrogel and commercial product (Matrigel) for comparison. The morphology of spheroid formation was evaluated via optical microscopy. The cell viability was observed through cell counting Kit-8 assay, and cell invasion was investigated via Boyden chamber assay. Analytical results indicated that 3BE exhibited lower spheroid formation than Matrigel. However, the 3BE appeared biocompatible to NIH 3T3, MG-63, and MCF-7 cells. Moreover, cell invasion ability and cell survival rate after invasion through the 3BE was displayed to be comparable to Matrigel. Thus, these findings demonstrate that the 3BE hydrogel has a great potential as an alternative to a three-dimensional cell culture for drug screening applications.  相似文献   
110.
A prominent feature of the skeleton is its ability to remodel in response to biophysical stimuli and to repair under varied biophysical conditions. This allows the skeleton considerable adaptation to meet its physiological roles of stability and movement. Skeletal cells and their mesenchymal precursors exist in a native environment rich with biophysical signals, and they sense and respond to those signals to meet organismal demands of the skeleton. While mechanical strain is the most recognized of the skeletal biophysical stimuli, signaling phenomena also include fluid flow, hydrostatic pressure, shear stress, and ion-movement-related electrokinetic phenomena including, prominently, streaming potentials. Because of the complex interactions of these electromechanical signals, it is difficult to isolate the significance of each. The application of external electrical and electromagnetic fields allows an exploration of the effects of these stimuli on cell differentiation and extra-cellular matrix formation in the absence of mechanical strain. This review takes a distinctly translational approach to mechanistic and preclinical studies of differentiation and skeletal lineage commitment of mesenchymal cells under biophysical stimulation. In vitro studies facilitate the examination of isolated cellular responses while in vivo studies permit the observation of cell differentiation and extracellular matrix synthesis.  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