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   65230篇
  免费   5199篇
  国内免费   2869篇
电工技术   3684篇
技术理论   7篇
综合类   4282篇
化学工业   11088篇
金属工艺   3611篇
机械仪表   3991篇
建筑科学   5519篇
矿业工程   1877篇
能源动力   1895篇
轻工业   4137篇
水利工程   1174篇
石油天然气   4553篇
武器工业   459篇
无线电   7201篇
一般工业技术   8088篇
冶金工业   3203篇
原子能技术   723篇
自动化技术   7806篇
  2024年   243篇
  2023年   1087篇
  2022年   1801篇
  2021年   2506篇
  2020年   1942篇
  2019年   1691篇
  2018年   1896篇
  2017年   2129篇
  2016年   1934篇
  2015年   2394篇
  2014年   3243篇
  2013年   3719篇
  2012年   4120篇
  2011年   4456篇
  2010年   3901篇
  2009年   3708篇
  2008年   3636篇
  2007年   3536篇
  2006年   3591篇
  2005年   3106篇
  2004年   2116篇
  2003年   1897篇
  2002年   1669篇
  2001年   1606篇
  2000年   1674篇
  1999年   1811篇
  1998年   1406篇
  1997年   1194篇
  1996年   1076篇
  1995年   951篇
  1994年   783篇
  1993年   563篇
  1992年   436篇
  1991年   339篇
  1990年   316篇
  1989年   230篇
  1988年   177篇
  1987年   108篇
  1986年   105篇
  1985年   60篇
  1984年   41篇
  1983年   26篇
  1982年   33篇
  1981年   22篇
  1980年   13篇
  1979年   3篇
  1978年   1篇
  1976年   1篇
  1975年   1篇
  1959年   1篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
31.
Behavioral cues to deception are instrumental in detecting deception. As one of the primary sources of deception behavior, text has been analyzed at the level of sub-sentence or message but not the discourse of interaction. Additionally, empirical studies on cues to deception in the case of multiple receivers remain nonexistent. To fill these voids, we propose a discourse framework and six hypotheses about deception behaviors in a multi-receiver environment. The deception behaviors are operationalized by discourse features based on an analysis of real-world data. The results of statistical analysis validate the efficacy of discourse features in discriminating deceivers from truth-tellers.  相似文献   
32.
Poly(vinyl chloride)/wood fiber (flour) composites are currently experiencing a dramatic increase in use. Most of them are used to produce window/door profiles, decking, railing, and siding by using conical counterrotating intermeshing twin‐screw extruders. Heat stabilizers, processing aids, impact modifiers, lubricants, and pigments are still important for PVC/wood composite formulations. Poly[methylene(polyphenyl isocyanate)] (PMPPIC), γ‐aminopropyltriethoxysilane, maleated polypropylene (MAPP), and copper metallic complex have proved to be effective coupling agents for this composite system. Mechanical properties of PVC/wood composites can be enhanced by combining wood with mica or glass fibers to form hybrid reinforcements. Ultraviolet light resistance and weathering dimensional stabilities of PVC/wood composites are superior to those of natural wood. Density reduction can be achieved through the microcellular foaming technique by using chemical blowing agents, such as azodicarbonamide and sodium bicarbonate, or physical blowing agents, such as carbon dioxide. J. Vinyl Addit. Technol. 10:59–69, 2004. © 2004 Society of Plastics Engineers.  相似文献   
33.
In this paper, a new Chinese character recognition (CCR) approach is proposed based on the fuzzy clustering analysis theory. Chinese characters (CCs) have various similar radicals and stroke components, which make it difficult to recognize features in the CCR process. At the same time, the recognition accuracy and the efficiency are lower when the objects to be recognized are complex. In order to solve these problems, a fuzzy clustering analysis method is introduced to enhance the computing efficiency. At first, the CCs including learning samples and testing samples are transformed into binarization templates in the form of matrixes. Then, the minimum distance algorithm is applied to calculate ‘distances’ between the testing sample templates and the learning sample templates. At last, the character recognition can be achieved by searching the minimum distance from the results. The experiment results of the CCR process can prove the effectiveness and accuracy of the new method.  相似文献   
34.
With the fast explosive rate of the amount of image data on the Internet, how to efficiently utilize them in the cross-media scenario becomes an urgent problem. Images are usually accompanied with contextual textual information. These two heterogeneous modalities are mutually reinforcing to make the Internet content more informative. In most cases, visual information can be regarded as an enhanced content of the textual document. To make image-to-image similarity being more consistent with document-to-document similarity, this paper proposes a method to learn image similarities according to the relations of the accompanied textual documents. More specifically, instead of using the static quantitative relations, rank-based learning procedure by employing structural SVM is adopted in this paper, and the ranking structure is established by comparing the relative relations of textual information. The learning results are in more accordance with the human’s recognition. The proposed method in this paper can be used not only for the image-to-image retrieval, but also for cross-modality multimedia, where a query expansion framework is proposed to get more satisfactory results. Extensive experimental evaluations on large scale Internet dataset validate the performance of the proposed methods.  相似文献   
35.
In this paper, hyperbranched polyesters (HPs) were synthesized in the molten state from 2,2-bis(hydroxymethyl) propionic acid (bis-MPA) and 2-ethyl-2-hydroxymethyl-1,3-propanediol (TMP) using acid catalysis. The modified hyperbranched polyesters were obtained through the chemical modification of the hyperbranched polyester cores by substituting a controlled fraction of the terminal hydroxyl groups with touluene-4-sulfonyl chloride using triethylamine (TEA) as an acceptor of HCl. The resultant polyesters were characterized by 1H NMR, 13C NMR, FT-IR, UV and GPC and their self-assembly behaviors were investigated. The results revealed that self-assembled structures could be formed in selected solvents (trichloromethane/acetone or trichloromethane/n-hexane).  相似文献   
36.
Highly purified polycrystalline wafers of Zr and Hf were chosen as substrates for diamond deposition by means of the d.c. arc discharge plasma CVD method. Polycrystalline diamond films were formed on both substrates. Scanning electron microscopy and high resolution X-ray diffraction were used to investigate the surface morphology of the diamond films and the composition of the interface layers between the diamond films and substrates. The experiments showed that the transition layer between the diamond films and Zr substrates was ZrC, ZrH and ZrC0.32H1.2. For Hf substrates, in addition to HfC, it is supposed that there were also some hydrides or carbohydrides in the transition layer, because several X-ray reflections appeared which could not be assigned to Hf, HfC or diamond.  相似文献   
37.
Preparation of Titanium Nitride/Alumina Laminate Composites   总被引:2,自引:0,他引:2  
A preparation route for TiN/Al2O3 laminate composites has been described. A water-based process using Al2O3 and TiN slurries with solids contents of 40 and 35 vol%, respectively, was used to make TiN and Al2O3 tapes. The removal of the binder was monitored by weight-loss measurements in a thermogravimetry unit. Bodies composed of Al2O3 and TiN tapes were densified at temperatures of 1400° and 1500°C using the Spark Plasma Sintering® (SPS) technique. Densities of >98% of the theoretical densities were approached. Crack-free and almost fully densified TiN/Al2O3 compacts were prepared by heating the burned-out green bodies to the final sintering temperature (1500°C) at a rate of 100°C/min, and with a holding time of 5–10 min, under a pressure of 75 MPa. The microstructures of the obtained compacts were studied using scanning electron microscopy. Grain sizes in the sintered Al2O3 and TiN compacts were similar to those of the precursor powders. Hardness and indentation fracture toughness were measured at room temperature, and the monolithic compacts as well as the laminate composites exhibited anisotropic mechanical behavior; i.e., the cracks propagated much more easily in a direction parallel to the laminas than perpendicular to them.  相似文献   
38.
CaSO_4晶须对聚氨酯胶粘剂性能影响的研究   总被引:2,自引:1,他引:2  
用实验室自制的相对分子质量为2500的聚己二酸-1,4-丁二醇酯二醇和甲苯二异氰酸酯、混合扩链剂配制聚氨酯胶粘剂,并使用实验室自制的改性和未改性200nm硫酸钙晶须对聚氨酯胶粘剂进行改性,考察不同硫酸钙晶须及其加入量、加入方式对聚氨酯胶粘剂综合力学性能的影响。根据实验结果,200nm改性硫酸钙晶须当加入量为3%时,聚氨酯胶粘剂的拉伸强度、初粘性和最终剥离强度均有明显提高。  相似文献   
39.
〕介绍了轻质多孔复合隔墙板挤压成型机的构造原理、技术参数、使用方法与保养、经济分析和有关问题的探讨  相似文献   
40.
The Pr α-sialon powders prepared by self-propagating high-temperature synthesis (SHS), consisting of 55 wt% Pr α-sialon and 45 wt% of β-sialon (abbreviated as α' and β'), were hot-pressed at 1800°C for 1 h. The results showed that Pr α' phase would transfer to β' with the appearance of JEM phase (Pr(Si6− z Al z )(N10− z O z )) after sintering, thus resulting in the increase of β' phase to 86 wt%. The addition of Y2O3 into SHS-ed Pr α' powders as the starting materials restrains the transformation of α' to β' and prevents the formation of JEM phase as well. The nucleation mechanism of Pr α' grain during hot-pressing was investigated in terms of transmission electron microscope and energy-dispersive spectrometer analysis. Two nucleation modes of Pr α' grains were found, i.e., nucleating on the undissolved Pr α' grains and on the nuclei of (Pr, Y) α' grains precipitated from liquid phase.  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