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151.
Chen Feng 《中国有色金属学会会刊》1996,(3)
CORRECTIONOFDISCONTINUITYSPACINGBIASCAUSEDBYFINITELENGTHSCANLINESURVEY¥ChenFeng(TestingCenter,CentralSoutUniversityofTechnolo... 相似文献
152.
为了研究结构面对岩体稳定性的影响,需要清楚岩体结构面的发育规律。传统玫瑰花图、极点图和等密度图等岩体结构面产状优势分组方法较为粗糙,主观因素影响较大,而采用K均值聚类算法、FCM模糊聚类算法则可以得到较为准确的分组结果,但须事先指定聚类数量及初始聚类中心。初始划分对分组结果影响较大,因此提出一种基于K近邻改进密度峰值聚类分析法的岩体结构面产状优势分组的新方法,该方法优点在于无需迭代过程、计算速度快、可自动探测聚类中心数量,并可通过自动计算岩体结构面局部密度大小和聚类中心距离更加准确地确定聚类中心,实现结构面产状的合理划分。通过应用计算机模拟生成的结构面产状数据进行产状优势分组,验证了该方法的准确性和可靠性。最后将这种方法应用于怒江松塔水电站坝址区实测的结构面产状优势分组中,得到了较为符合实际的分组结果。 相似文献
153.
Spatial stability for the monolithic and sequential methods with various space discretizations in poroelasticity 下载免费PDF全文
Hyun C. Yoon Jihoon Kim 《International journal for numerical methods in engineering》2018,114(7):694-718
We investigate spatial stability with various numerical discretizations in displacement and pressure fields for poroelasticity. We study 2 sources of the early time instability: discontinuity of pressure and violation of the inf‐sup condition. We consider both compressible and incompressible fluids by employing the monolithic, stabilized monolithic, and fixed‐stress sequential methods. Four different spatial discretization schemes are used: Q1Q1, Q2Q1, Q1P0, and Q2P0. From mathematic analysis and numerical tests, the piecewise constant finite volume method for flow provides stability at the early time for the case of the pressure discontinuity. On the other hand, a piecewise continuous (or higher‐order) interpolation of pressure shows spatial oscillation, having lower limits of time step size, although lower approximations of pressure than displacement can alleviate the oscillation. For an incompressible fluid, Q2Q1 can be better than Q1P0, because Q1P0 might not satisfy the inf‐sup condition. However, regardless of fluid compressibility and the pressure discontinuity, the fixed‐stress method can effectively stabilize the oscillation without an artificial stabilizer. Even when Q1P0 and Q1Q1 with the monolithic method cannot satisfy the inf‐sup condition, the fixed‐stress method can yield the full‐rank linear system, providing stability. Thus, the fixed‐stress method with Q1P0 can effectively circumvent the aforementioned 2 types of instability. 相似文献
154.
155.
由内导体和空心外导体所组成的传输线是电磁工程中一类重要的传输线。提出应用LBEM角点弧形法处理传输线物理角节点问题,解决由于角节点边界条件不连续带来的方程求解困难问题。计算了一类特殊截面偏心传输线的特性阻抗,算例分析结果表明,该方法操作简单,计算便捷,能有效消除角点给边界计算带来的误差,可方便应用于工程问题的设计与计算,并为此类特种传输线加工制作精度提供理论参数。 相似文献
156.
Assessing the recovery of fish assemblages downstream of hydrological barriers in India's Western Ghats 下载免费PDF全文
River flow regulation by dams and barrages threatens freshwater fish diversity globally. However, factors contributing to the recovery of fish communities downstream of barriers to river flow are not well understood. It is crucial to identify processes that might enable river restoration despite the presence of river barriers. In this study, we assess recovery of fish species, including endemics, downstream of large and small barriers in the Malaprabha basin in the Western Ghats of India. We define “fish species recovery” as the proportion of fish species occurring in river reaches downstream of barriers, of the species pool occurring in upstream unregulated segments with similar elevation, stream order, and habitat characteristics. As per the serial discontinuity concept, we predicted that recovery will reduce immediately after, but gradually increase with, increasing distance downstream of barriers, due to contributions from unregulated streams joining the river. As expected, fish recovery decreased immediately downstream of barriers and increased at greater distances and declined when the number of upstream barriers increased, indicating cumulative impacts. Dissolved oxygen and total alkalinity were positively and negatively correlated with both recovery and distance from barrier. Water temperature and rocky instream habitat influenced recovery positively, but independent of distance from barriers. Recovery of fish species, including Western Ghats endemics, was promising even under the current level of river regulation in the area, mainly due to connectivity with undammed tributaries. Strict limits on future stream regulation within already regulated basins will be critical for conservation of freshwater fish biodiversity in this region. 相似文献
157.
Privacy-aware collection of aggregate spatial data 总被引:1,自引:0,他引:1
Hairuo Xie Author VitaeLars Kulik Author Vitae Egemen TaninAuthor Vitae 《Data & Knowledge Engineering》2011,70(6):576-595
Privacy concerns can be a major barrier to collecting aggregate data from the public. Recent research proposes negative surveys that collect negative data, which is complementary to the true data. This opens a new direction for privacy-aware data collection. However, the existing approach cannot avoid certain errors when applied to many spatial data collection tasks. The errors can make the data unusable in many real scenarios. We propose Gaussian negative surveys. We modulate data collection based on Gaussian distribution. The collected data can be used to compute accurate spatial distribution of participants and can be used to accurately answer range aggregate queries. Our approach avoids the errors that can occur with the existing approach. Our experiments show that we achieve an excellent balance between privacy and accuracy. 相似文献
158.
Robert?F.?O’Brien Deborah?K.?Carlson Richard?O.?GilbertEmail author John?E.?Wilson Derrick?J.?Bates Brent?A.?Pulsipher 《Sensing and Imaging: An International Journal》2005,6(3):251-270
The U.S. Department of Defense is in the process of assessing and remediating closed, transferred, and transferring military
training ranges across the United States. Many of these sites have areas that are known to contain unexploded ordnance (UXO).
Other sites or portions of sites are not expected to contain UXO, but some verification of this expectation using geophysical
surveys is needed. Many sites are so large that it is often impractical and/or cost prohibitive to perform surveys over 100%
of the site. In such cases, it is particularly important to be explicit about the performance required of the surveys. This
article presents the statistical algorithms developed to support the design of geophysical surveys along transects (swaths)
to find target areas (TAs) of anomalous geophysical readings that may indicate the presence of UXO. The algorithms described
here determine (1) the spacing between transects that should be used for the surveys to achieve a specified probability of
traversing the TA, (2) the probability of both traversing and detecting a TA of anomalous geophysical readings when the spatial
density of anomalies within the TA is either uniform (unchanging over space) or has a bivariate normal distribution, and (3)
the probability that a TA exists when it was not found by surveying along transects. These algorithms have been implemented
in the Visual Sample Plan (VSP) software to develop cost-effective transect survey designs that meet performance objectives. 相似文献
159.
岩体结构面连通率的研究一直是岩石力学研究领域的难点之一。一些学者已经相继提出了多种确定连通率的方法,但许多方法可能引起的误差较大,实用性也较差。广义H—H连通率公式和基于网络模拟的计算方法是近年发展起来的比较成熟且实用的方法。文章评述了各种方法的适用性和有效性,并采用基于结构面网络模拟的“带宽投影法”进行了实例分析,最后讨论了岩体结构面连通率的研究趋向。 相似文献
160.