全文获取类型
收费全文 | 9081篇 |
免费 | 795篇 |
国内免费 | 500篇 |
专业分类
电工技术 | 58篇 |
技术理论 | 1篇 |
综合类 | 750篇 |
化学工业 | 1610篇 |
金属工艺 | 425篇 |
机械仪表 | 190篇 |
建筑科学 | 572篇 |
矿业工程 | 305篇 |
能源动力 | 419篇 |
轻工业 | 3162篇 |
水利工程 | 367篇 |
石油天然气 | 641篇 |
武器工业 | 26篇 |
无线电 | 231篇 |
一般工业技术 | 704篇 |
冶金工业 | 473篇 |
原子能技术 | 211篇 |
自动化技术 | 231篇 |
出版年
2024年 | 45篇 |
2023年 | 133篇 |
2022年 | 240篇 |
2021年 | 301篇 |
2020年 | 321篇 |
2019年 | 314篇 |
2018年 | 296篇 |
2017年 | 317篇 |
2016年 | 379篇 |
2015年 | 305篇 |
2014年 | 528篇 |
2013年 | 549篇 |
2012年 | 647篇 |
2011年 | 680篇 |
2010年 | 435篇 |
2009年 | 474篇 |
2008年 | 391篇 |
2007年 | 527篇 |
2006年 | 475篇 |
2005年 | 404篇 |
2004年 | 363篇 |
2003年 | 325篇 |
2002年 | 299篇 |
2001年 | 242篇 |
2000年 | 192篇 |
1999年 | 196篇 |
1998年 | 148篇 |
1997年 | 133篇 |
1996年 | 102篇 |
1995年 | 117篇 |
1994年 | 60篇 |
1993年 | 79篇 |
1992年 | 70篇 |
1991年 | 52篇 |
1990年 | 48篇 |
1989年 | 44篇 |
1988年 | 25篇 |
1987年 | 21篇 |
1986年 | 18篇 |
1985年 | 19篇 |
1984年 | 17篇 |
1983年 | 13篇 |
1982年 | 11篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
摘要:为了研究退火温度对镀锌DP980+Z烘烤硬化值的影响,退火温度控制在760~820℃之间,系统分析退火温度对烘烤硬化值的影响。通过准静态拉伸试验机测量烘烤硬化值及抗拉强度,采用lepara试剂对组织中的马氏体进行着色,利用金相显微镜及图像处理软件测量马氏体的体积分数;采用扫描电镜观察DP980+Z的双相组织特点,并且将组织图片通过CAD转化成有限元图进行网格划分,建立代表性体积单元(RVE),通过有限元分析铁素体、马氏体强度对烘烤硬化值的影响。在同样的变形量情况下,DP980+Z的原始屈服强度越高,烘烤硬化值越高。 相似文献
12.
Effect of Different Cosolvents on Transesterification of Waste Cooking Oil in a Microreactor
下载免费PDF全文
![点击此处可从《化学工程与技术》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Biodiesel was prepared from waste cooking oil combined with methanol. The process was performed via transesterification in a microreactor using kettle limescale as a heterogeneous catalyst and various cosolvents under different conditions. n‐Hexane and tetrahydrofuran were selected as cosolvents to investigate fatty acid methyl esters (FAMEs). To optimize the reaction conditions, the main parameters affecting FAME% including reaction temperature, catalyst concentration, oil‐to‐methanol volumetric ratio, and cosolvent‐to‐methanol volumetric ratio were studied via response surface methodology. Under optimal reaction conditions and in the presence of the cosolvents n‐hexane and tetrahydrofuran, high FAME purities were achieved. Considering the experimental results, the limescale catalyst is a unique material, and the cosolvent method can reduce significantly the reaction time and biodiesel production cost. 相似文献
13.
Wyatt L. Brown Douglas A. Day Harald Stark Demetrios Pagonis Jordan E. Krechmer Xiaoxi Liu Derek J. Price Erin F. Katz Peter F. DeCarlo Catherine G. Masoud Dongyu S. Wang Lea Hildebrandt Ruiz Caleb Arata David M. Lunderberg Allen H. Goldstein Delphine K. Farmer Marina E. Vance Jose L. Jimenez 《Indoor air》2021,31(1):141-155
Understanding the sources and composition of organic aerosol (OA) in indoor environments requires rapid measurements, since many emissions and processes have short timescales. However, real-time molecular-level OA measurements have not been reported indoors. Here, we present quantitative measurements, at a time resolution of five seconds, of molecular ions corresponding to diverse aerosol-phase species, by applying extractive electrospray ionization mass spectrometry (EESI-MS) to indoor air analysis for the first time, as part of the highly instrumented HOMEChem field study. We demonstrate how the complex spectra of EESI-MS are screened in order to extract chemical information and investigate the possibility of interference from gas-phase semivolatile species. During experiments that simulated the Thanksgiving US holiday meal preparation, EESI-MS quantified multiple species, including fatty acids, carbohydrates, siloxanes, and phthalates. Intercomparisons with Aerosol Mass Spectrometer (AMS) and Scanning Mobility Particle Sizer suggest that EESI-MS quantified a large fraction of OA. Comparisons with FIGAERO-CIMS shows similar signal levels and good correlation, with a range of 100 for the relative sensitivities. Comparisons with SV-TAG for phthalates and with SV-TAG and AMS for total siloxanes also show strong correlation. EESI-MS observations can be used with gas-phase measurements to identify co-emitted gas- and aerosol-phase species, and this is demonstrated using complementary gas-phase PTR-MS observations. 相似文献
14.
孙新忠 《水利水电科技进展》2006,26(2):26-29
在运城市夹马口灌区和红旗灌区进行了1996,1997两个年度的玉米渗灌试验,研究了不同毛管间距条件下渗灌对其产量及水分生产率等的影响。结果表明,玉米渗灌毛管间距采用0.8~1.0 m较为适宜。毛管间距愈大,产量愈低;渗灌较地面灌平均减产7.23%,较旱地平均增产30.8%;玉米生长期内总耗水量地面灌最大,渗灌次之,旱地最小。渗灌可明显提高玉米水分生产率,渗灌处理水分生产率平均为1.65 kg/m3,是地面灌的1.2倍,是旱地的1.33倍;两年度渗灌较地面灌平均节水44.4%。 相似文献
15.
The analysis of 124 curves obtained in short-term tensile tests demonstrate that they can be described by varying strain hardening and softening characteristics. Different stress–strain curves can be produced at invariable yield strength and ultimate strength and interrelated proportional variations of the above characteristics. To determine some specific stress–strain curve, it is necessary to take account of yield strength and ultimate strength as well as strain corresponding to the latter. The relations between yield strength, ultimate strength and hardening and their practically complete absence between these parameters and softening were statistically established. 相似文献
16.
The tensile elastic modulus (E), yield stress (σY) and microhardness (MH) of neat and binary and ternary blends of glassy semicrystalline ethylene–vinyl alcohol copolymer (EVOH), a glassy amorphous polyamide and a semicrystalline nylon‐containing ionomer covering a broad range of properties were examined. The tests were carried out on dry and water‐equilibrated samples to produce stiffer and softer materials, respectively. From the results, more accurate linear correlations were found to describe adequately the microhardness, modulus and yield stress of these strongly self‐associated polymers through hydrogen bonding. Copyright © 2003 Society of Chemical Industry 相似文献
17.
现代电子工业Cpk评价中的特殊问题 总被引:2,自引:0,他引:2
现代电子工业生产具有许多新的特点,如果不针对具体情况,均采用传统工业生产中广泛使用的常规方法计算其工序能力指数,评价生产工艺水平,将可能导致错误的结论。总结了电子工业生产中工艺参数的典型特点,并讨论了工序能力指数的正确计算方法。 相似文献
18.
19.
介绍了利用现有的催化裂化装置 ,通过优化操作及运用MGD技术提高柴油和液化气收率的方法和技术措施。 相似文献
20.
Although the literature on the mechanics of cellular materials is vast, there is no theoretical model to account for the effects of axial yielding of struts aligned to the applied loading direction on the plastic yield surface under multiaxial loading conditions. An anisotropic hexagonal model having tapered strut morphology is developed to show these effects on the plastic yield surface under multiaxial tensile loading condition. This model covers several types of cellular structure such as two-dimensional (2D) hexagonal and square cellular materials, and three-dimensional (3D) hexagonal and rhombic cellular materials of rod-like columnar structure. A tetrahedral element with tapered strut morphology is also used for a foam model to illustrate these effects on the yield surface under axisymmetric loading condition. Plastic collapse due to bending moment in the inclined struts is a dominant mode. However, under multiaxial tensile loading, the collapse due to axial yielding of struts parallel to the loading direction is found to be an important mode. The shape of plastic yield surface was found to depend not only on relative density but also on the strut morphology. 相似文献