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   88458篇
  免费   1119篇
  国内免费   432篇
电工技术   842篇
综合类   2325篇
化学工业   12339篇
金属工艺   4910篇
机械仪表   3128篇
建筑科学   2205篇
矿业工程   576篇
能源动力   1406篇
轻工业   3825篇
水利工程   1297篇
石油天然气   362篇
无线电   9881篇
一般工业技术   17382篇
冶金工业   3366篇
原子能技术   289篇
自动化技术   25876篇
  2024年   45篇
  2023年   82篇
  2022年   108篇
  2021年   197篇
  2020年   164篇
  2019年   133篇
  2018年   14563篇
  2017年   13487篇
  2016年   10099篇
  2015年   710篇
  2014年   404篇
  2013年   600篇
  2012年   3338篇
  2011年   9612篇
  2010年   8446篇
  2009年   5791篇
  2008年   6928篇
  2007年   7888篇
  2006年   239篇
  2005年   1314篇
  2004年   1223篇
  2003年   1261篇
  2002年   624篇
  2001年   165篇
  2000年   243篇
  1999年   130篇
  1998年   206篇
  1997年   137篇
  1996年   166篇
  1995年   94篇
  1994年   101篇
  1993年   93篇
  1992年   71篇
  1991年   92篇
  1990年   70篇
  1989年   48篇
  1988年   55篇
  1987年   46篇
  1986年   43篇
  1985年   48篇
  1981年   36篇
  1968年   45篇
  1967年   35篇
  1966年   50篇
  1965年   46篇
  1959年   35篇
  1958年   37篇
  1957年   36篇
  1955年   66篇
  1954年   68篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
There is difficulty for distinguishing of river and shadow in Synthetic Aperture Radar (SAR) images. A method of river segmentation in SAR images based on wavelet energy and gradient is proposed in this paper. It mainly includes two algorithms: coarse segmentation and refined segmentation. Firstly, The river regions are coarsely segmented by the wavelet energy feature,and then refined segmented accurately by the gradient threshold which is got adaptively. The experimental results show the validity of the method, which provides a good foundation for targets detection above the river.  相似文献   
33.
After a thorough review of some controllable parameters, which included field investigations, cavern dimensions, explosive, rock strength etc., cut, contour, lifters and stoping holes were introduced for blasting cavern of nucleus submarine. These design were conducted using a U. Langefors and B. Kihlstrom theory. Supported by the Navy Cavern Project Foundation of China (02)  相似文献   
34.
Neurofilament light chain (Nf-L) is a well-known biomarker for axonal damage; however, the corresponding circulating Nf-L analyte in cerebrospinal fluid (CSF) is poorly characterized. We therefore isolated new monoclonal antibodies against synthetic peptides, and these monoclonals were characterized for their specificity on brain-specific intermediate filament proteins. Two highly specific antibodies, ADx206 and ADx209, were analytically validated for CSF applications according to well-established criteria. Interestingly, using three different sources of purified Nf-L proteins, a significant impact on interpolated concentrations was observed. With a lower limit of analytical sensitivity of 100 pg/mL using bovine Nf-L as the calibrator, we were able to quantify the Nf-L analyte in each sample, and these Nf-L concentrations were highly correlated to the Uman diagnostics assay (Spearman rho = 0.97, p < 0.001). In the clinical diagnostic groups, the new Nf-L ELISA could discriminate patients with Alzheimer’s disease (AD, n = 20) from those with frontotemporal lobe dementia (FTD, n = 20) and control samples with subjective cognitive decline (SCD, n = 20). Henceforth, this novel Nf-L ELISA with well-defined specificity and epitopes can be used to enhance our understanding of harmonizing the use of Nf-L as a clinically relevant marker for neurodegeneration in CSF.  相似文献   
35.
36.
The Cu-Zr binary system is re-investigated via experiment and thermodynamic modeling. Four alloys were prepared by arc melting in order to check the controversial phase equilibria reported in the literature. Both as-cast and annealed alloys were examined by optical microscopy, x-ray diffraction and electron probe microanalysis, and the phase transformation temperatures were measured by differential scanning calorimetry. The intermetallic compounds, Cu24Zr13, Cu2Zr and Cu5Zr8, were demonstrated to be not the stable phases. Based on the literature information and present experimental data, the Cu-Zr system was critically evaluated by means of CALculation of PHAse Diagram approach. A set of self-consistent thermodynamic parameters was obtained, and the calculated phase diagram and thermodynamic properties are in a satisfactory agreement with the experimental data.  相似文献   
37.
In this report, a combination of the diffusion multiple technique and the recently developed pragmatic numerical inverse method was employed for a high-throughput determination of interdiffusivity matrices in Co-Cr-FeMn-Ni high-entropy alloys (HEAs). Firstly, one face-centered cubic (fcc) quinary Co-Cr-Fe-Mn-Ni diffusion multiple at 1373 K was carefully prepared by means of the hot-pressing technique. Based on the composition profiles measured by the field emission electron probe micro analysis (FE-EPMA), the composition-dependent interdiffusivity matrices in quinary Co-Cr-Fe-Mn-Ni system at 1373 K were then efficiently determined using the pragmatic numerical inverse method. The determined interdiffusivities show good agreement with the limited results available in the literature. Moreover, the further comparison with the interdiffusivities in the lower-order systems indicates the sluggish diffusion effect in Co-Cr-Fe-Mn-Ni HEAs, which is however not observed in tracer diffusivities. In order for the convenience in further analysis, a generalized transformation relation among interdiffusivities with different dependent components in multicomponent systems was finally derived.  相似文献   
38.
The successful replacement of the present generation of corrosion-resistant materials (nitric acid-grade stainless steel and Ti) by Ti-5Ta-1.8Nb, which has better corrosion resistance, depends on its weldability characteristics. This article presents the results of a study on the fabrication, qualification, and microstructural characterization of the welds. Welding was carried out using the direct current electrode negative (DCEN) polarity tungsten inert gas (TIG) (manual) welding method with high-purity Ar shielding. Testing was carried out as per the ASME standard (section IX, welding and brazing). Qualification tests found that the weldment met the required properties. The weldment showed heterogeneous microstructures, which are rationalized based on differences in phase transformation mechanisms that are dictated by the thermal cycles experienced by various microscopic regions. The results, described in this article, confirm that the weldability of the developmental Ti-Ta-Nb alloy is excellent. A preliminary evaluation of the corrosion behavior of the welds showed rates comparable to that of the base metal, establishing that this alloy could be considered as an alternative material for use in highly corrosive environments.  相似文献   
39.
Large-scale single-crystalline SnO2 nanocauliflowers were successfully synthesized using a hydrothermal growth method without any template. The samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). FE-SEM images show that the as-grown SnO2 nanocauliflowers are constructed of tetragonal prisms with a width of 500–600 nm. XRD, EDS, and SAED results indicate that the as-grown SnO2 nanocauliflowers are single crystalline with the tetragonal rutile crystalline structure. The growth mechanism of SnO2 nanocauliflowers is also preliminarily discussed on the basis of different Sn(OH)62− concentrations, and it is found that Sn(OH)62− concentration plays an important role in determining the shape of the prepared SnO2. Room temperature photoluminescence was further carried out on SnO2 nanocauliflowers to investigate their optical properties. An intense blue luminescence centered at a wavelength of 424 nm is observed in the as-grown SnO2 nanocauliflowers.  相似文献   
40.
For the multi-item and small lot size production mode and single machine job shop scheduling sequence independent setup time, many setup times are difficult to estimate accurately, which influences the ability to achieve accurate production cycles and costs of products. The survey shows that the length of the setup time depends on the level of employee’s knowledge. Therefore, a method for determining the standard setup time quota based on the level of employees’ knowledge is proposed. First, an evaluation index system for the level of employee’s knowledge is built; the level of employee’s knowledge is estimated by the masses and experts fuzzy comprehension evaluation and entropy method. Second, the range and definition of the level of employees’ knowledge index are developed. Third, the relational model of the employee’s knowledge level and the level of employees’ knowledge index is constructed through the least squares method. Finally, an example application is presented to verify the feasibility and effectiveness of the proposed model.  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