全文获取类型
收费全文 | 38105篇 |
免费 | 2843篇 |
国内免费 | 1485篇 |
专业分类
电工技术 | 1890篇 |
技术理论 | 2篇 |
综合类 | 2283篇 |
化学工业 | 6425篇 |
金属工艺 | 2181篇 |
机械仪表 | 2300篇 |
建筑科学 | 2996篇 |
矿业工程 | 923篇 |
能源动力 | 906篇 |
轻工业 | 2293篇 |
水利工程 | 538篇 |
石油天然气 | 2595篇 |
武器工业 | 206篇 |
无线电 | 4638篇 |
一般工业技术 | 4779篇 |
冶金工业 | 2064篇 |
原子能技术 | 421篇 |
自动化技术 | 4993篇 |
出版年
2024年 | 117篇 |
2023年 | 602篇 |
2022年 | 863篇 |
2021年 | 1398篇 |
2020年 | 1043篇 |
2019年 | 873篇 |
2018年 | 967篇 |
2017年 | 1142篇 |
2016年 | 1045篇 |
2015年 | 1372篇 |
2014年 | 1740篇 |
2013年 | 2233篇 |
2012年 | 2203篇 |
2011年 | 2489篇 |
2010年 | 2254篇 |
2009年 | 2079篇 |
2008年 | 2071篇 |
2007年 | 2056篇 |
2006年 | 2079篇 |
2005年 | 1807篇 |
2004年 | 1240篇 |
2003年 | 1062篇 |
2002年 | 1030篇 |
2001年 | 883篇 |
2000年 | 914篇 |
1999年 | 1112篇 |
1998年 | 957篇 |
1997年 | 834篇 |
1996年 | 832篇 |
1995年 | 640篇 |
1994年 | 557篇 |
1993年 | 386篇 |
1992年 | 342篇 |
1991年 | 258篇 |
1990年 | 194篇 |
1989年 | 166篇 |
1988年 | 135篇 |
1987年 | 106篇 |
1986年 | 75篇 |
1985年 | 57篇 |
1984年 | 57篇 |
1983年 | 25篇 |
1982年 | 35篇 |
1981年 | 24篇 |
1980年 | 16篇 |
1979年 | 11篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1973年 | 5篇 |
1970年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
唐述宏 《计算机测量与控制》2008,16(7):917-919
为了提高现阶段XLPE电缆料杂质检测的精度与速度,运用TCD132D芯片,建立了杂质检测系统;运用虚拟示波器DSO2902对系统采集的数据进行分析和处理,从而有效地识别杂质颗粒的存在与否并能够准确地计算出存在杂质颗粒的尺寸、位置等;结果表明,该系统能够准确地测出XLPE电缆料的杂质颗粒的尺寸,并能够确定该杂质颗粒所处的准确位置与杂质颗粒的个数等特性,其分辨力可达到20μm,误差小于10%,杂质的检出率达100%。 相似文献
972.
在Ad hoc中,DBF、DSDV、AODV,DSR等都是基于最小跳路由协议.从能量的角度来看,最短路由并不一定是最佳的路由.为此在DSR按需驱动路由基础上提出了一种新的基于动态优先因子的路由策略EDSR.在这种协议中,综合考虑能耗低,链路容量大的路由,从而较好地节省网络能量. 相似文献
973.
介绍判定树归纳分类ID3算法,利用ID3算法,对有上机课的课程成绩分类,为学生和老师提供参考信息. 相似文献
974.
深入研究Windows server 2003 DDK 的passthru中间层驱动程序,并对该驱动程序进行扩展,使之能对底层的网络封包实现截获和过滤. 相似文献
975.
软件配置管理是通过技术或行政手段对软件产品及其开发过程和生命周期进行控制、规范的一系列措施.结合军用软件的特点提出一套软件配置管理实施流程,重点阐述如何制定软件配置管理计划、建立软件配置管理库、配置标识、版本控制、基线管理、变更控制、配置审核和配置管理记录等实践活动. 相似文献
976.
Wu CC Huang YS Lee LY Liang Y Tang RP Chang YS Hsieh LL Yu JS 《Proteomics. Clinical applications》2008,2(12):1586-1595
The cancer cell secretome may contain potentially useful biomarkers. Previously, we have analyzed the colorectal carcinoma (CRC) cell secretome. In this study, tumor‐associated antigen 90K (TAA90K)/Mac‐2 binding protein (Mac‐2BP), one of the CRC cell secreted proteins, was chosen for evaluation as a potential CRC biomarker because its mRNA level was also found to be significantly elevated in CRC tissues and in a more metastatic CRC cell line from the analysis of two public domain array‐based datasets. Immunohistochemical analysis of 241 CRC specimens showed that TAA90K/Mac‐2BP was positively detected in 52.7% of the tumors, but weakly or not detected in over 95% of the adjacent nontumor epithelial cells. The plasma TAA90K/Mac‐2BP levels were significantly higher in CRC patients (N = 280) versus healthy controls (N = 147) (7.77 ± 3.49 vs. 5.72 ± 2.67 μg/mL, p<0.001). Moreover, combination of TAA90K/Mac‐2BP and carcinoembryonic antigen (CEA) could outperform CEA alone in discriminating CRC patients from healthy persons in this case‐control study. Our results collectively indicate that analysis of cancer cell secretome is a feasible strategy for identifying cancer biomarker candidates, and the TAA90K/Mac‐2BP may be a potential CRC biomarker. 相似文献
977.
In quantitative models of visual search it has usually been assumed that visual lobe area shape was sufficiently regular to be approximated by a circle or ellipse. However, the irregularities in visual lobe shapes that have been found in studies involving extensive lobe mapping have suggested that lobe shape may have important implications for visual search performance and for the accuracy of mathematical models used for performance prediction. However, no systematic research on the relationship between the shape aspect of visual lobes and search performance seems to have been carried out and no comparisons of visual lobe shape characteristics under the effect of target difficulty have been reported. The current study was conducted to achieve two major objectives in two experiments. Experiment 1 used two different targets (letter 'O' and letter 'Y') to map the visual lobes of subjects in order to provide a systematic and quantitative comparison of lobe shape characteristics and experiment 2 was to investigate the correlation of visual lobe shape characteristics with visual search time under the effect of target difficulty. The visual lobes of 28 subjects were mapped on 24 imaginary and regularly spaced meridians originating from the centre of the visual field to resemble the full field mapping situation. Five categories of shape indices, viz. roundness, boundary smoothness, symmetry, elongation and shape regularity were investigated. The results of this study demonstrated that the visual lobe shapes of subjects elongate horizontally with medium level of roundness, high levels of boundary smoothness, symmetry and regularity for an easy target (O) against a homogeneous background of 'X's. When a difficult target (Y) was used, the visual lobes of the subjects were still elongated horizontally but to a smaller extent and with a low level of roundness, medium level of boundary smoothness and regularity and a similar high level of symmetry to the easy target. Moreover, significant correlations between shape indices and visual search time were found, suggesting mathematical models for predicting search time should not merely rely on area but also should consider visual lobe shape indices. Finally, a universal mathematical model containing several visual lobe shape indices was developed, which was applicable in the prediction of visual search time for a range of similar search tasks. 相似文献
978.
979.
In this paper, we extend a previous work on a compact scheme for the steady Navier–Stokes equations [Li, Tang, and Fornberg (1995), Int. J. Numer. Methods Fluids, 20, 1137–1151] to the unsteady case. By exploiting the coupling relation between the streamfunction and vorticity equations, the Navier–Stokes equations are discretized in space within a 3×3 stencil such that a fourth order accuracy is achieved. The time derivatives are discretized in such a way as to maintain the compactness of the stencil. We explore several known time-stepping approaches including second-order BDF method, fourth-order BDF method and the Crank–Nicolson method. Numerical solutions are obtained for the driven cavity problem and are compared with solutions available in the literature. For large values of the Reynolds number, it is found that high-order time discretizations outperform the low-order ones. 相似文献
980.
Java移动代码是一种可以通过网络从一台计算机传珐另一台计算机上运行的Java程序,在现代网络计算及电子商务中具有广泛应用,Java的这一显著特性也蕴藏着授权管理上的不足,未授权者可以很容易地非法使用这些程序,针对Java移动代码的这些不足之处,分别对Java Applet及Java Applet及Java Servlet提出了基于数字签名算法的授权与访问控制方案,安全,有效地解决了这种新兴的授权与访问控制问题。 相似文献