全文获取类型
收费全文 | 33036篇 |
免费 | 2437篇 |
国内免费 | 1927篇 |
专业分类
电工技术 | 1320篇 |
技术理论 | 1篇 |
综合类 | 1832篇 |
化学工业 | 11688篇 |
金属工艺 | 1818篇 |
机械仪表 | 977篇 |
建筑科学 | 1059篇 |
矿业工程 | 405篇 |
能源动力 | 707篇 |
轻工业 | 5162篇 |
水利工程 | 366篇 |
石油天然气 | 2103篇 |
武器工业 | 235篇 |
无线电 | 2618篇 |
一般工业技术 | 2598篇 |
冶金工业 | 902篇 |
原子能技术 | 561篇 |
自动化技术 | 3048篇 |
出版年
2024年 | 63篇 |
2023年 | 404篇 |
2022年 | 983篇 |
2021年 | 2321篇 |
2020年 | 922篇 |
2019年 | 845篇 |
2018年 | 788篇 |
2017年 | 946篇 |
2016年 | 1165篇 |
2015年 | 1248篇 |
2014年 | 1694篇 |
2013年 | 2008篇 |
2012年 | 2273篇 |
2011年 | 2644篇 |
2010年 | 1815篇 |
2009年 | 1978篇 |
2008年 | 1839篇 |
2007年 | 1927篇 |
2006年 | 1803篇 |
2005年 | 1449篇 |
2004年 | 1242篇 |
2003年 | 1054篇 |
2002年 | 901篇 |
2001年 | 718篇 |
2000年 | 606篇 |
1999年 | 564篇 |
1998年 | 426篇 |
1997年 | 404篇 |
1996年 | 381篇 |
1995年 | 361篇 |
1994年 | 310篇 |
1993年 | 209篇 |
1992年 | 176篇 |
1991年 | 151篇 |
1990年 | 137篇 |
1989年 | 105篇 |
1988年 | 79篇 |
1987年 | 49篇 |
1986年 | 71篇 |
1985年 | 49篇 |
1984年 | 54篇 |
1983年 | 34篇 |
1982年 | 39篇 |
1981年 | 30篇 |
1980年 | 34篇 |
1979年 | 34篇 |
1978年 | 14篇 |
1977年 | 11篇 |
1976年 | 10篇 |
1975年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
112.
通过对 HL- 1M装置真空运行模式、真空运行参数、氦辉光放电清洗和硅化壁处理手段等的规范化 ,显著地改善了装置的真空壁出气、本底杂质浓度、托卡马克放电杂质出气比和再循环 ,成功地实现了高参数放电、长脉冲放电和装置暴露大气后快速恢复放电 ,并成功地为演证低混杂电流驱动、离子回旋共振加热、电子回旋共振加热、中性束注入、弹丸注入和分子束注入实验和升级等离子体运行等提供了良好的真空壁条件。描述了 HL- 1M装置真空系统、壁出气和再循环控制、质谱诊断和程序脉冲送气等方面的主要实验成果 ,并为 HL- 2 A装置的真空系统研制和运行提供了有益的参考 相似文献
113.
Let us consider n data measurements of a univariate process that have been altered by random errors. We assume that an underlying model function has a substantially smaller number of turning points than the observed ones. We propose algorithms that make least the sum of the moduli of the errors by requiring k monotonic sections, alternately increasing and decreasing, in the sequence of the smoothed values. The main difficulty in this calculation is that the optimal positions of the joins of the monotonic sections have to be found automatically among so many combinations that it is impossible to test each one separately. Moreover, the calculation seems to be very intractable to general optimization techniques because O(nk ) local minima can occur. It is shown that dynamic programming can be used for separating the data into optimal disjoint sections of adjacent data, where each section requires a single L1 monotonic calculation. This procedure is highly efficient, requiring at most O(kn2 ) computer operations and O(n) best L1 monotonic calculations to subranges of data for a global minimum. 相似文献
114.
115.
Wu Ting M. Badaye T. Morishita N. Koshizuka S. Tanaka 《Journal of Superconductivity》1996,9(6):637-645
Recently, superconducting Nd1Ba2Cu3Oy (Ndl23) thin films with high superconducting transition temperature (T
c) have been successfully fabricated at our institute employing the standard laser ablation method. In this paper, we report the results of surface characterization of the Nd123 thin films using an ultrahigh vacuum scanning tunneling microscope/spectroscopy (UHV-STM/STS) and an atomic force microscope (AFM) system operated in air. Clear spiral pattern is observed on the surfaces of Nd123 thin films by STM and AFM, suggesting that films are formed by two-dimensional island growth mode. Contour plots of the spirals show that the step heights of the spirals are not always the integer or half-integer number of thec-axis parameter of the structure. This implies that the surface natural termination layer of the films may not be unique. This result is supported byI-V STS measurements. The surface morphology of the Nd123 thin films is compared with that of thec-axis-oriented Y1Ba2Cu3Sy thin films. Surface atomic images of the as-prepared Nd123 thin films are obtained employing both STM and AFM. STS measurements show that most of the surfaces are semiconductive. The results of STS measurements together with the fact that we are able to see the surface atomic images using scanning probe microscopes suggest that exposure to air does not cause serious degradation to the as-prepared surfaces of Nd123 thin films. 相似文献
116.
首先从CDMA1X网络结构进行详细分析,引出CDMA1X网络安全风险分析。根据网络安全原理,联系江西联通现在CDMA1X网络结构,采取对每层安全进行预防,提出较详细的网络安全解决方案,最后对现网进行安全评估。 相似文献
117.
Christina Dirk‐Faitakis D Grant Allen 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(7):737-745
This paper describes the development and simulation of an unsteady state biofilter model used to predict dynamic behaviour of cyclically‐operated biofilters and compares it with experimental results obtained from three, parallel, bench‐scale biofilters treating both periodically fluctuating concentrations and constant concentrations of an α‐pinene‐laden gas stream. The dynamic model, using kinetic parameters estimated from the constant concentration biofilter, was able to predict the performance of cyclic biofilters operating at short cycle periods (ie, in the order of minutes and hours). Steady state kinetic data from a constant concentration biofilter can be used to predict unsteady state biofilter operation. At a 24 h cycle period, the dynamic model compared well with experimental results. For long cycle periods (ie, hours and days), removal efficiency decreased after periods of non‐loading: the longer the period of non‐loading, the poorer the biofilter's performance at the re‐commencement of pollutant loading. At longer time scales the model did not effectively predict transient behaviour, as adsorption and changes in kinetic parameters were not accounted for. Modelling results showed that similar biofiltration performance for the cyclic and constant concentration biofiltration of α‐pinene is expected for biofilters operating solely in the first order kinetics regime. Poorer performance for cyclic biofilters following Monod kinetics spanning the entire kinetics range is expected as the cycle amplitude increases. The most important parameters affecting the performance of a cyclically‐operated biofilter with short cycle periods are: amplitude of cyclic fluctuations, Cg, max/Cg, relative value of the half‐saturation constant in the Monod expression, Ks, and effective diffusivity of α‐pinene in the biofilm, De. Copyright © 2005 Society of Chemical Industry 相似文献
118.
RM Martín‐Aranda E Ortega‐Cantero ML Rojas‐Cervantes MA Vicente‐Rodríguez MA Baares‐Muoz 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(2):234-238
α,β‐Unsaturated nitriles have been synthesized by Knoevenagel condensation of a carbonylic compound with malononitrile, assisted by sonochemical irradiation. Two alkaline‐promoted clays (Li+‐ and Cs+‐exchanged saponites) have been employed as catalysts. The influence of the carbonylic compound (benzaldehyde or cyclohexanone) and the use of a solvent on the catalytic activity have been studied. Remarkable increase in the conversion values has been found when the reaction is activated by ultrasound, as compared with the thermal activation. In this green, solvent‐free procedure, α,β‐unsaturated nitriles have been produced in very high yields (97%) when the Cs+‐saponite is used as catalyst. Copyright © 2004 Society of Chemical Industry 相似文献
119.
以硫酸、磷钨酸、ZRP-5分子筛为催化剂,研究了二甘醇(DEG)脱水环化的反应规律。结果表明,DEG发生分子内脱水环化反应,生成1,4-二氧六环(DOX),DEG分子间脱水不仅可以生成四甘醇、六甘醇等,同时可生成三甘醇、五甘醇等一系列的多甘醇(PEG)。不仅DEG可以脱水环化生成DOX,在反应中生成的PEG也同样可以进行生成DOX的反应。对于二甘醇(DEG)脱水环化反应,硫酸是性能优良的催化剂,反应可以在较低的温度下进行,馏出产物中DOX选择性大于95%。 相似文献
120.
通过对常减压蒸馏装置阻垢剂进料管的材质、性能、工作条件及腐蚀形貌、腐蚀产物的全面分析,找出了使进料管发生大面积腐蚀的腐蚀介质为环烷酸.并提出了减缓阻垢剂进料管环烷酸腐蚀的措施,主要包括选用更耐蚀的316或316 L材质以及改进三通结构等. 相似文献