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   2529篇
  免费   64篇
  国内免费   8篇
电工技术   11篇
综合类   12篇
化学工业   158篇
金属工艺   25篇
机械仪表   22篇
建筑科学   31篇
矿业工程   14篇
能源动力   11篇
轻工业   90篇
水利工程   1篇
石油天然气   7篇
武器工业   1篇
无线电   75篇
一般工业技术   113篇
冶金工业   1876篇
原子能技术   6篇
自动化技术   148篇
  2022年   8篇
  2021年   24篇
  2020年   9篇
  2019年   18篇
  2018年   17篇
  2017年   17篇
  2016年   15篇
  2015年   22篇
  2014年   39篇
  2013年   70篇
  2012年   33篇
  2011年   65篇
  2010年   41篇
  2009年   40篇
  2008年   20篇
  2007年   34篇
  2006年   28篇
  2005年   60篇
  2004年   15篇
  2003年   27篇
  2002年   12篇
  2001年   23篇
  2000年   11篇
  1999年   65篇
  1998年   520篇
  1997年   315篇
  1996年   213篇
  1995年   108篇
  1994年   101篇
  1993年   101篇
  1992年   14篇
  1991年   27篇
  1990年   23篇
  1989年   31篇
  1988年   38篇
  1987年   35篇
  1986年   27篇
  1985年   31篇
  1984年   7篇
  1983年   10篇
  1982年   14篇
  1981年   18篇
  1980年   28篇
  1979年   7篇
  1978年   14篇
  1977年   46篇
  1976年   111篇
  1975年   12篇
  1974年   4篇
  1972年   4篇
排序方式: 共有2601条查询结果,搜索用时 15 毫秒
71.
Cognitive impairment is well documented in schizophrenia, though some reports have been interpreted to suggest that it is possible to have schizophrenia without neuropsychological impairment. The authors tested this by comparing the neuropsychological profiles of closely matched patients with schizophrenia and healthy comparison participants. Sixty-four patients with schizophrenia and 64 healthy comparison cases, matched to within 3 Full-Scale IQ points, were tested using the Wechsler Adult Intelligence Scale (3rd ed.; D. Wechsler, 1997b) and the Wechsler Memory Scale (3rd ed.; D. Wechsler, 1997c). Neuropsychological profiles for these groups were markedly different, with the group of patients with schizophrenia exhibiting performance deficits in memory and speeded visual processing but superior verbal comprehension and perceptual organization relative to the group of healthy comparison participants matched on Full-Scale IQ. Thus, scoring in the normal range does not preclude neuropsychological abnormality in schizophrenia, confirming that neuropsychological impairment is a core feature of the illness. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
72.
For the first time in this innovative study, microorganisms such as Bacillus simplex bacteria, mostly used in biological activity studies, are used as a bio-supporter agent of iron to release hydrogen from sodium borohydride hydrolysis at 25.0 ± 0.1 °C. The goal is to investigate thoroughly sodium borohydride hydrolysis catalyzed by Fe2O3 nanoparticles impregnated on microorganism such as Bacillus simplex (BS) bacteria (Fe2O3@BS NPs) known with strong antibacterial properties, which makes innovative them a candidate for hydrolysis reaction. This study was focused on the preparation, identification, and catalytic use of biocatalyst-like Fe2O3@BS NPs for hydrogen release from the sodium borohydride hydrolysis at 25.0 ± 0.1 °C. The characterization results made after and before hydrolysis reaction using by SEM/SEM-EDX, FT-IR, XRD, UV–vis, XPS, DLS, ELS Zeta potential, ESR, and TEM techniques reveal the formation of highly active, stable, durable, and long-lived biocatalysts-like Fe2O3@BS NPs.  相似文献   
73.
74.
Principal among knowledge discovery tasks is recognition of insightful patterns or features from data that can inform otherwise challenging decisions. For the costly future decisions, there is little room for error. Features must provide substantial evidence to be robust for classification and dependable for important decisions. Here we seek statistical evidence for feature selection, that feature signals are of sufficient magnitude and frequency to be generalizable for classification. The Bayesian false discovery rate (bFDR) error control procedure is powerfully suited for this task. In realistic situations often encountered in practice, the bFDR procedure is biased, yielding a greater than desired FDR. In other less typical cases, the FDR is less than desired. We investigate the sources of bias in the bFDR procedure, and predict the direction of bias. A new algorithm has been developed to recover the bias in the bFDR control procedure. In simulation and real data mining examples, the new bFDR control algorithm shows promise. The strengths and limitations of the new approach are presented with examples and discussed.  相似文献   
75.
76.
77.
78.
Several current implementations of quantum circuits rely on the linear nearest neighbor restriction, which only allows interaction between adjacent qubits. Most methods that address the process of converting a generic circuit to an equivalent circuit which satisfies this restriction, minimize the number of additional SWAP gates required by this process. Moreover, most methods which address this problem are designed for 1D circuits. Considering the new and promising proposals for 2D quantum circuits, what we propose is a new perspective on this problem, namely that it can be seen as a multiobjective optimization problem. To test our hypothesis, we developed a multiobjective evolutionary algorithm that solves this problem by considering two objectives: minimizing the size of the 2D grid where the circuit is placed, and minimizing the number of additional SWAP gates. Of the methods designed for 2D circuits, only one considers different grid sizes which are much larger than strictly necessary. Consequently, our algorithm makes considerations which other methods do not make, since it naturally finds the grid which requires fewer SWAP gates for the circuit conversion, whether it is one-dimensional or two-dimensional. Our experimental results indicate that allowing a larger grid size results in fewer additional SWAP gates in about 73% of the tested circuits. Additionally, the average improvement we found when using larger grid sizes is about 30%, while the best improvement over using the smallest possible grid is 63.8%.  相似文献   
79.
80.
The passive fit between prosthesis and implant is a relevant factor for screw joint stability and treatment success. The aim of this study was to evaluate the influence of vertical misfit in abutment-implant interface on preload maintenance of retention screw of implant-supported crowns. The crowns were fabricated with different abutments and veneering materials and divided into 5 groups (n = 12): Gold UCLA abutments cast in gold alloy veneered with ceramic (Group I) and resin (Group II), UCLA abutments cast in titanium veneered with ceramic (Group III) and resin (Group IV), and zirconia abutments with ceramic veneering (Group V). The crowns were attached to implants by gold retention screws with 35-N cm insertion torque. Specimens were submitted to mechanical cycling up to 106 cycles. Measurements of detorque and vertical misfit in abutment-implant interface were performed before and after mechanical cycling. ANOVA revealed statistically significant difference (P < 0.05) among groups for vertical misfit measured before and after mechanical cycling. The abutments cast in titanium exhibited the highest misfit values. Pearson correlation test did not demonstrate significant correlation (P > 0.05) between vertical misfit and detorque value. It was concluded that vertical misfit did not influence torque maintenance and the abutments cast in titanium exhibited the highest misfit values.  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