全文获取类型
收费全文 | 332039篇 |
免费 | 26539篇 |
国内免费 | 13871篇 |
学科分类
工业技术 | 372449篇 |
出版年
2024年 | 1061篇 |
2023年 | 5091篇 |
2022年 | 9340篇 |
2021年 | 13617篇 |
2020年 | 10272篇 |
2019年 | 8415篇 |
2018年 | 10137篇 |
2017年 | 11227篇 |
2016年 | 10158篇 |
2015年 | 12527篇 |
2014年 | 16022篇 |
2013年 | 19414篇 |
2012年 | 21086篇 |
2011年 | 22436篇 |
2010年 | 19187篇 |
2009年 | 18447篇 |
2008年 | 17889篇 |
2007年 | 16627篇 |
2006年 | 16200篇 |
2005年 | 13872篇 |
2004年 | 9878篇 |
2003年 | 8989篇 |
2002年 | 8583篇 |
2001年 | 7815篇 |
2000年 | 7146篇 |
1999年 | 7277篇 |
1998年 | 5901篇 |
1997年 | 5003篇 |
1996年 | 4561篇 |
1995年 | 3835篇 |
1994年 | 3151篇 |
1993年 | 2476篇 |
1992年 | 2192篇 |
1991年 | 1810篇 |
1990年 | 1624篇 |
1989年 | 1444篇 |
1988年 | 1241篇 |
1987年 | 1062篇 |
1986年 | 943篇 |
1985年 | 830篇 |
1984年 | 803篇 |
1982年 | 744篇 |
1981年 | 730篇 |
1979年 | 764篇 |
1978年 | 802篇 |
1977年 | 763篇 |
1976年 | 781篇 |
1975年 | 729篇 |
1974年 | 728篇 |
1973年 | 729篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
本文报导了甲基环氧丙酸钾的合成方法、农田应用,IR、NMR分析数据及与环氧丙酸钾的性能比较。 相似文献
992.
CPVC的力化学改性 总被引:6,自引:0,他引:6
着重研究了氯化聚氯乙烯(CPVC)与多种单体进行力化学接枝、嵌段的过程。红外光谱测试证明,通过力化学方法可以合成CPVC的共聚物。在CPVC侧基或端部接上其它单体成为一种共聚物时,将大大改善材料的加工性、透明性等某些性能。实验结果表明,力化学改性对改善CPVC的加工性能是一种简易、有效的方法。改性后的CPVC其加工温度可降低许多,为一种较易加工的材料。 相似文献
993.
N. N. Ajitanand A. Narayanan T. Ethvignot H. Yu J. M. Alexander 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1992,320(3):596-599
A close-geometry experimental technique has been developed and used to measure thick target fission yields for protons on 238U from 4.2 to 12 MeV. Fission fragments were detected at back angles by an annular photo-voltaic detector in coincidence with γ-ray registered in large NaI(Tl) detector. The neutron induced fission background was monitored by a detector on the downstream side of the thick target. Measured yields compare well with those calculated from published thin target cross sections. This method has the required sensitivity to carry out measurements at still lower energies where recent measurements give conflicting findings. 相似文献
994.
The bond strength and slip of epoxy-coated reinforcing bars in concrete have been evaluated by carrying out single pullout and double pullout tests. In extended single pullout tests, slip measurements were made while tensile force was applied to reinforcing bars embedded in concrete. In double pullout tests, 20 cycles of load were applied at levels of steel stress between zero and 0·5 times characteristic steel strength. Strains were measured by electrical resistance strain gauges glued inside the bars. Both epoxy-coated and uncoated bars were used in the investigation, to obtain comparative results. The strain gradient along the bar was found to be less for the coated reinforcement. In general, the epoxy coating was found to increase slip in bond and thereby reduce the bond performance of coated bars. 相似文献
995.
The use of the analytically decoupled near-tip displacement solutions as an alternative approach, is presented in this paper for the efficient finite element evaluation of the decoupled weight functions for an orthotropic 2-D crack. This alternative approach has been validated by directly comparing the prior weight function results with a symmetric mesh approach in the crack-tip neighborhood, and indirectly by comparing the calculated stress intensity factors (KI(II)) values using the computed weight functions with available KI(II) solutions of the 2-D mixed mode orthotropic cracks. In addition, this approach with analytically decoupled near-tip displacement solutions for calculating weight functions at all locations, can facilitate further extension of weight function evaluations to a more general 2-D anisotropic crack. 相似文献
996.
997.
998.
Yu. Medvedevskikh A. Bratus G. Hafiychuk A. Zaichenko A. Kytsya A. Turovski G. Zaikov 《应用聚合物科学杂志》2002,86(14):3556-3569
The kinetics of glycidyl methacrylate block polymerization to high conversion was experimentally investigated with variations of the photoinitiator concentration, temperature, and power of UV illumination. The kinetic curves of this polymerization process contain three characterized sections of coordinates of “conversion–time,” namely: The first one is practically linear to a conversion of ≈0.5, the second represents, by itself, the autoacceleration process, and the third presents the autodecelation process. An additional peculiarity of such a polymerization process is poor reproduction of the kinetic measurements. This reproduction does not correspond to instrumental error. Derivation of a kinetic model for block linear polymerization was done. This model is, quantitatively, in good agreement with all the data of the experimental material. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3556–3569, 2002 相似文献
999.
1000.
低压铝箔交流腐蚀研究 总被引:4,自引:2,他引:2
在30Hz频率下,通过铝箔在HCl+H2SO4+HNO3+H3PO4体系中的交流腐蚀,研究腐蚀液组成中腐蚀主体及缓蚀剂对铝箔腐蚀的作用,探讨腐蚀过程中电源频率、腐蚀液温度、电流密度及腐蚀时间对铝箔腐蚀的影响。腐蚀液组成的配比恰当,有利于比容的提高。在特定的频率下采用合适的腐蚀液温度、适宜的电流密度和腐蚀时间可以提高铝箔的静电容量。 相似文献