全文获取类型
收费全文 | 2276篇 |
免费 | 209篇 |
国内免费 | 94篇 |
专业分类
化学 | 137篇 |
晶体学 | 3篇 |
力学 | 64篇 |
综合类 | 32篇 |
数学 | 227篇 |
物理学 | 264篇 |
无线电 | 1852篇 |
出版年
2024年 | 8篇 |
2023年 | 30篇 |
2022年 | 34篇 |
2021年 | 65篇 |
2020年 | 73篇 |
2019年 | 32篇 |
2018年 | 32篇 |
2017年 | 97篇 |
2016年 | 90篇 |
2015年 | 97篇 |
2014年 | 178篇 |
2013年 | 145篇 |
2012年 | 217篇 |
2011年 | 166篇 |
2010年 | 133篇 |
2009年 | 108篇 |
2008年 | 147篇 |
2007年 | 123篇 |
2006年 | 127篇 |
2005年 | 118篇 |
2004年 | 89篇 |
2003年 | 89篇 |
2002年 | 66篇 |
2001年 | 54篇 |
2000年 | 44篇 |
1999年 | 35篇 |
1998年 | 27篇 |
1997年 | 32篇 |
1996年 | 17篇 |
1995年 | 21篇 |
1994年 | 16篇 |
1993年 | 10篇 |
1992年 | 8篇 |
1991年 | 8篇 |
1990年 | 2篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1959年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有2579条查询结果,搜索用时 0 毫秒
61.
转子在线自动平衡及其工程应用研究的进展 总被引:2,自引:0,他引:2
转子在线自动平衡技术可以在旋转机械运行期间调整其不平衡量来及时降低振动, 使其始终稳定运行.早期的自动平衡装置始于19世纪末, 包括液体型、环型、球型和摆锤型;20世纪60年代开始研究的自动平衡装置主要包括喷涂型、电腐蚀型、电子光束型、激光型和电化学型;20世纪后期研究的自动平衡装置主要包括电动机型和遥控型;现代的自动平衡装置主要包括液压型、电磁型和电磁轴承型.综述了国内外各种旋转机械在线自动平衡装置的结构和工作原理, 重点介绍了液压型和电磁型自动平衡装置的结构和控制原理.讨论了在线自动平衡技术最新的研究成果, 列举了在线自动平衡技术的工程应用实例, 介绍了应用电磁型自动平衡装置解决柔性弯曲转子和立式超重力机转子振动的试验.转子在线自动平衡技术已经大量应用到机械加工设备, 如磨床等, 显著提高了加工精度;有些还应用于流程工业中大型的旋转机械上, 如汽轮机、风机和压缩机等, 取得了巨大的经济效益.高可靠性的平衡执行机构和高效的控制策略等关键问题尚未完全解决. 相似文献
62.
L. A. Pranoto-soetardhi M. A. H. Rijk N. De Kruijf R. H. De Vos 《International journal of environmental analytical chemistry》2013,93(1-3):151-159
Abstract The possibility was investigated to apply a commercially available automatic head-space sampler in trace analysis of ethylene dibromide (EDB, 1,2-dibromoethane), in cereals. Samples of rice and wheat flour were thermostatted in closed vials at 70[ddot]C for 30min. The top gas was then automatically introduced into a gas chromatograph equipped with an electron capture detector. Quantitation was performed using external standards (untreated samples spiked with solutions of EDB in N,N′-dimethylacetamide). The relative standard deviation of the method was 3.4% for rice and 4.5% for wheat flour, at a residue level of 0.008 mg/kg. The detection limit was 0.001 mg/kg (the official EC residue tolerance is 0.01 mg/kg). Preliminary experiments with other fumigants were carried out as well. The headspace technique in question has the following advantages over other methods for determining EDB residues in cereals: 1. No sample pre-treatment like extraction, steam distillation, purge and trap etc.; 2. Automated sample handling; 3. “Clean” chromatograms. 相似文献
63.
集成运算放大器具有成本低、功能多等优点,可广泛用于自动控制系统、测量仪表等其他电子设备中。近年来集成运放的指标在不断提高,性能也在不断提升,伴随着运算放大器的发展,对用来考核运算放大器指标的测试技术也提出了相应的要求,对测试系统(Automatic Testing Equipment,以下简称ATE)的性能要求也相应变高。阐述了单、双电源集成运算放大器在JC-5600ATE上的测试方法,并分析了两者的测试差异。 相似文献
64.
This work discusses efficient and automated methods for constructing a set of representative resonance structures for arbitrary chemical species, including radicals and biradicals, consisting of the elements H, C, O, N, and S. Determining the representative reactive structures of chemical species is crucial for identification of reactive sites and consequently applying the correct reaction templates to generate the set of important reactions during automated chemical kinetic model generation. We describe a fundamental set of resonance pathway types, accounting for simple resonating structures, as well as global approaches for polycyclic aromatic species. Automatically discovering potential localized structures along with filtration to identify the representative structures was shown to be robust and relatively fast. The algorithms discussed here were recently implemented in the Reaction Mechanism Generator (RMG) software. The final structures proposed by this method were found to be in reasonable agreement with quantum chemical computation results of localized structure contributions to the resonance hybrid. 相似文献
65.
Narges Mohamadshahi 《Journal of Dispersion Science and Technology》2013,34(6):821-826
The use of soluble amphiphiles oil types provide the most practical and economical solution for crude oil treatment in order to control the asphaltene precipitation phenomenon. In this article, the inhibition performance of a number of new chemical additives to asphaltene precipitation is examined on two types of Iranian crude oil. An automatic titration method is used in experimental evaluation. The vegetable oil types (hazelnut, wheat germ, and walnut), organic acids (oleic and linoleic) and chemical additives (4-dodecylresorcinol and benzyl alcohol) displayed the highest capacity to inhibit asphaltene precipitation. A remarkable onset displacement is displayed by dodecyl resorcinol. The results also revealed that the vegetable oil have high potential in delaying asphaltene precipitation. 相似文献
66.
In this paper, we establish uniform-in-bandwidth limit laws of the logarithm for nonparametric Inverse Probability of Censoring
Weighted (I.P.C.W.) estimators of the multivariate regression function under random censorship. A similar result is deduced
for estimators of the conditional distribution function. The uniform-in-bandwidth consistency for estimators of the conditional
density and the conditional hazard rate functions are also derived from our main result. Moreover, the logarithm laws we establish
are shown to yield almost sure simultaneous asymptotic confidence bands for the functions we consider. Examples of confidence
bands obtained from simulated data are displayed.
相似文献
67.
68.
69.
70.