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   15398篇
  免费   1599篇
  国内免费   819篇
电工技术   1242篇
技术理论   2篇
综合类   1119篇
化学工业   2359篇
金属工艺   845篇
机械仪表   918篇
建筑科学   1106篇
矿业工程   452篇
能源动力   496篇
轻工业   1389篇
水利工程   335篇
石油天然气   784篇
武器工业   162篇
无线电   1765篇
一般工业技术   1825篇
冶金工业   717篇
原子能技术   204篇
自动化技术   2096篇
  2024年   97篇
  2023年   270篇
  2022年   617篇
  2021年   739篇
  2020年   560篇
  2019年   430篇
  2018年   496篇
  2017年   594篇
  2016年   542篇
  2015年   700篇
  2014年   823篇
  2013年   925篇
  2012年   1115篇
  2011年   1076篇
  2010年   995篇
  2009年   948篇
  2008年   850篇
  2007年   829篇
  2006年   747篇
  2005年   616篇
  2004年   526篇
  2003年   484篇
  2002年   536篇
  2001年   480篇
  2000年   341篇
  1999年   315篇
  1998年   207篇
  1997年   159篇
  1996年   178篇
  1995年   141篇
  1994年   144篇
  1993年   76篇
  1992年   48篇
  1991年   44篇
  1990年   38篇
  1989年   34篇
  1988年   18篇
  1987年   19篇
  1986年   14篇
  1985年   6篇
  1984年   7篇
  1982年   5篇
  1981年   2篇
  1980年   5篇
  1977年   2篇
  1976年   1篇
  1975年   5篇
  1973年   1篇
  1969年   3篇
  1951年   6篇
排序方式: 共有10000条查询结果,搜索用时 33 毫秒
11.
Least mean p-power error criterion for adaptive FIR filter   总被引:1,自引:0,他引:1  
An adaptive FIR filter based on the least mean p-power error (MPE) criterion is investigated. First, some useful properties of MPE function are studied. Three main results are as follows: 1) MPE function is a convex function of filter coefficients; so it has no local minima. 2) When input process and desired process are both Gaussian processes, then MPE function has the same optimum solution as the conventional Wiener solution for any p. 3) When input process and desired process are non-Gaussian processes, then MPE function may have better optimum solution than Wiener solution. Next, a least mean p-power (LMP) error adaptive algorithm is derived and some application examples are presented. Consequently, when the signal is corrupted by an impulsive noise, the adaptive algorithm with p=1 is preferred. Furthermore, when the signal is corrupted by noise or interference, the adaptive algorithm with proper choice of p may be preferred  相似文献   
12.
用屏蔽暂堵技术封堵水平井裂缝性漏层   总被引:1,自引:1,他引:0  
克拉玛依油田HW702水平井的大斜度段和水平段,将穿越纵向裂缝发育的二叠系佳木河组储层。为安全钻进和保护油层,用超细碳酸钙和磺化沥青复配后加入复合离子钻井液中成屏蔽暂堵的堵漏钻井液。室内用岩心试验,屏蔽暂堵后渗透率可降为0,暂堵深度小于3cm,可用酸化和射孔解堵。现场使用效果也很好,使HW702水平井顺利完钻,并获得工业油气流。  相似文献   
13.
在统计分析、正交多项式回归和模拟试验的基础上,建立了高精度的屈强比预报模型,并运用多元函数极值原理,求导极值点及相应的工艺参数,为优化工艺制度,提高热焊弯管用钢(L360-WG系列)性能合格率提供了定量依据。  相似文献   
14.
To assess the effects of diabetes mellitus on renal osteodystrophy, we examined the database of 256 patients (45% on hemodialysis and 55% on peritoneal dialysis) who were prospectively studied in three Toronto dialysis centers between October of 1987 and 1989. All patients had serial documentation of their clinical, laboratory and risk parameters of bone disease, and completed a series of investigations that included the deferoxamine test, measurement of intact 1-84 PTH levels, and an iliac crest bone biopsy. Twenty-five percent of these patients were diabetic. When compared to non-diabetic patients, they were on dialysis for a shorter duration (2.4 +/- 0.3 vs. 4.7 +/- 0.3 years; P < 0.0002), used calcium carbonate as the only phosphate binder more frequently (40 vs. 25%; P < 0.007), and had lower parathyroid hormone levels (12 +/- 1.4 vs. 24 +/- 2.3 pmol/liter; P < 0.002). High-turnover bone disorders (that is, osteitis fibrosa and mixed disorder) were distinctly uncommon (8 vs. 33%; P < 0.01 by Fisher's exact test), while the mild (19 vs. 9%; P = NS) and the aplastic disorders (with mean stainable bone surface aluminum of 6.5 +/- 0.7%) (46 vs. 31%; P = NS) tended to be more common in diabetic patients. The prevalence of aluminum bone disease was the same in both groups (27%). Diabetic patients ingested a smaller cumulative dose of aluminum gels (3.7 +/- 0.6 vs. 9.3 +/- 1.1 kg; P < 0.005), yet had a higher rate of aluminium accumulation on bone surfaces than non-diabetic patients (1.5 +/- 0.19 vs. 0.96 +/- 0.10% per month on dialysis; P < 0.015).(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
15.
瞬态光的光电摄谱测量   总被引:3,自引:0,他引:3  
“光电摄谱法”是一种辐射光谱计量参数的测量方法,此法解决了单次脉冲闪光灯辐射光谱相对能量分布的精确测量问题。本文介绍了这种方法的测量原理、方法和特点,同时阐述了对接收器件、光路系统和时控电器系统的要求,并以自行研制的闪光光谱测定仪为例,对其计量参数波长和相对能量的标定与校正给予了必要的讨论,最后以实测结果证实了该方法的可靠性。  相似文献   
16.
This paper presents a recurrent neural-network model for solving a special class of general variational inequalities (GVIs), which includes classical VIs as special cases. It is proved that the proposed neural network (NN) for solving this class of GVIs can be globally convergent, globally asymptotically stable, and globally exponentially stable under different conditions. The proposed NN can be viewed as a modified version of the general projection NN existing in the literature. Several numerical examples are provided to demonstrate the effectiveness and performance of the proposed NN.  相似文献   
17.
含油废水处理   总被引:10,自引:0,他引:10  
赵亚乾  徐培 《水处理技术》1995,21(4):227-230
在水量水质调查的基础上,本文提出了以出水回用为目的的含油废水隔油调节沉淀-混凝沉淀-砂滤处理工艺,动态模型试验表明,废水中油和COD的去除率分别达到95%和90%,出水浊度低于2,此水质完全可回用于有关生产车间。  相似文献   
18.
Skyline and top-k queries are two popular operations for preference retrieval. In practice, applications that require these operations usually provide numerous candidate attributes, whereas, depending on their interests, users may issue queries regarding different subsets of the dimensions. The existing algorithms are inadequate for subspace skyline/top-k search because they have at least one of the following defects: 1) they require scanning the entire database at least once, 2) they are optimized for one subspace but incur significant overhead for other subspaces, or 3) they demand expensive maintenance cost or space consumption. In this paper, we propose a technique SUBSKY, which settles both types of queries by using purely relational technologies. The core of SUBSKY is a transformation that converts multidimensional data to one-dimensional (1D) values. These values are indexed by a simple B-tree, which allows us to answer subspace queries by accessing a fraction of the database. SUBSKY entails low maintenance overhead, which equals the cost of updating a traditional B-tree. Extensive experiments with real data confirm that our technique outperforms alternative solutions significantly in both efficiency and scalability.  相似文献   
19.
Structured adaptive mesh refinement (SAMR) techniques provide an effective means for dynamically concentrating computational effort and resources to appropriate regions in the application domain. However, due to their dynamism and space-time heterogeneity, scalable parallel implementation of SAMR applications remains a challenge. This paper investigates hybrid runtime management strategies and presents an adaptive hierarchical multipartitioner (AHMP) framework. AHMP dynamically applies multiple partitioners to different regions of the domain, in a hierarchical manner, to match the local requirements of the regions. Key components of the AHMP framework include a segmentation-based clustering algorithm (SBC) that can efficiently identify regions in the domain with relatively homogeneous partitioning requirements, mechanisms for characterizing the partitioning requirements of these regions, and a runtime system for selecting, configuring, and applying the most appropriate partitioner to each region. Further, to address dynamic resource situations for long-running applications, AHMP provides a hybrid partitioning strategy (HPS) that involves application-level pipelining, trading space for time when resources are sufficiently large and underutilized, and an application-level out-of-core strategy (ALOC), trading time for space when resources are scarce in order to enhance the survivability of applications. The AHMP framework has been implemented and experimentally evaluated on up to 1,280 processors of the IBM SP4 cluster at the San Diego Supercomputer Center.  相似文献   
20.
The effects of N-methyl-D-aspartate (NMDA) on opioid receptor-mediated G protein activation were explored in neuroblastoma X glioma hybrid (NG108-15) cells. Treatment of the cells with NMDA resulted in a remarkable attenuation of [35S]guanosine-5'-O-(3-thio)triphosphate binding stimulated by [D-Pen2,D-Pen5]-enkephalin (DPDPE), a delta-opioid receptor agonist. The effects of NMDA were dose and time dependent with an IC50 value of 5 nM and could be blocked by NMDA receptor antagonists. After NMDA treatment, the DPDPE dose-response curve shifted to the right (EC50 value increased approximately 7-fold, from 6 to 40 nM), and the maximal response induced by DPDPE was reduced by approximately 60%. The effects of NMDA were reversible, and the DPDPE response could recover within 60 min. The functional responses of delta-, mu-, and kappa-opioid receptors in primarily cultured neurons also were attenuated significantly by NMDA treatment. The inhibitory effects of NMDA on opioid receptor-mediated G protein activation could be blocked by coadministration of the protein kinase C (PKC) inhibitors or by elimination of the extracellular Ca2+. Correspondingly, NMDA treatment of NG108 cells significantly elevated cellular PKC activity and stimulated Gialpha2 phosphorylation. Transient transfection into NG108-15 cells of the wild-type Gialpha2 and a mutated Gialpha2 (Ser144Ala) resulted in a 2-fold increase in DPDPE-stimulated G protein activation. The DPDPE responses were greatly inhibited by NMDA treatment in the wild-type Gialpha2-transfected cells but much less affected in the mutant Gialpha2-transfected cells. In summary, NMDA attenuates opioid receptor/G protein coupling, and this process requires activation of PKC.  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