全文获取类型
收费全文 | 7589篇 |
免费 | 1116篇 |
国内免费 | 540篇 |
专业分类
化学 | 1896篇 |
晶体学 | 50篇 |
力学 | 1477篇 |
综合类 | 60篇 |
数学 | 903篇 |
物理学 | 2220篇 |
无线电 | 2639篇 |
出版年
2024年 | 18篇 |
2023年 | 106篇 |
2022年 | 212篇 |
2021年 | 282篇 |
2020年 | 324篇 |
2019年 | 213篇 |
2018年 | 218篇 |
2017年 | 279篇 |
2016年 | 338篇 |
2015年 | 295篇 |
2014年 | 453篇 |
2013年 | 542篇 |
2012年 | 445篇 |
2011年 | 504篇 |
2010年 | 422篇 |
2009年 | 455篇 |
2008年 | 406篇 |
2007年 | 425篇 |
2006年 | 389篇 |
2005年 | 353篇 |
2004年 | 279篇 |
2003年 | 289篇 |
2002年 | 234篇 |
2001年 | 190篇 |
2000年 | 206篇 |
1999年 | 176篇 |
1998年 | 178篇 |
1997年 | 150篇 |
1996年 | 111篇 |
1995年 | 107篇 |
1994年 | 111篇 |
1993年 | 106篇 |
1992年 | 80篇 |
1991年 | 75篇 |
1990年 | 59篇 |
1989年 | 41篇 |
1988年 | 31篇 |
1987年 | 20篇 |
1986年 | 16篇 |
1985年 | 27篇 |
1984年 | 13篇 |
1983年 | 10篇 |
1982年 | 16篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1971年 | 5篇 |
1957年 | 6篇 |
排序方式: 共有9245条查询结果,搜索用时 140 毫秒
81.
Jon Samseth Richard J. Spontak Kell Mortensen 《Journal of Polymer Science.Polymer Physics》1993,31(4):467-474
Poly(siloxaneimide) (PSI) segmented copolymers exhibit organized microdomains if the blocks are sufficiently incompatible. As with neat diblock and triblock copolymers, the processing route employed to prepare films of PSI materials is expected to influence the dimensions and/or morphology of the resultant microstructure. In this work, small-angle neutron scattering (SANS) is utilized to characterize the disordered microstructure found in films of a series of PSI copolymers which are subjected to solvent casting and various thermal treatments. Microstructural dimensions such as the periodicity and correlation length are deduced from the Teubner-Strey (TS) model for disordered microemulsions. The scattering intensity of each copolymer up to q = 5.0 nm?1, where q is the scattering vector, is found to scale as q?2.8+?0.1. Results indicate that processing the materials as cast films or as melt-pressed films allowed to cool slowly has a small, but discernible, effect on microstructural characteristics. SANS profiles of films quenched from elevated temperatures reveal a clear transition in microdomain periodicity, which correlates well with the glass transition temperature of the imide microphase in these and other materials of similar chemical structure. © 1993 John Wiley & Sons, Inc. 相似文献
82.
离子注入硅的线源非相干光瞬时退火温度计算 总被引:1,自引:0,他引:1
本文利用高温模型,计算了在我们的实验条件下对离子注入硅进行线源非相干光瞬时退火的退火温度,并与实验结果比较,两者符合得较好。 相似文献
83.
本文介绍了一个可对含连接线的电路进行瞬态分析的电路模拟器,该模拟器是在SPICE基础上经修改扩充而成的,连接线的处理采用了文献[1]的方法.文中介绍了方法的基本原理,讨论了数值Laplace反变换时参数的选择与误差的控制.实际VHSIC电路的试算结果表明,该模拟器是相当有效的. 相似文献
84.
This paper reports on the experimental investigation of the dynamic large deflection response of a portal frame impacted at its midspan by a body moving at a certain speed. Both the deflection and velocity vs. time curves of the midspan and the dynamic history of a number of desired locations were recorded during the process of response. On the basis of the test data, the momentum and kinetic energy conversion between the frame and the moving body in the impact process are realized, and the occurrence and expansion of plastic regions are described. Investigation results show that the initial collision is approximately ideally inelastic, and that the elastic deformation plays a considerable role in the response though the input energy is much larger than the maximum elastic energy capacity of the beam member; therefore, in a general impact, the energy ratio should not be regarded as a sufficient criterion for a rigid—plastic solution. The ratios of the impulse transferred to and the energy absorbed by the frame in the initial collision to that carried by the moving body before impact is only related to the ratiobetween the equivalent mass of the frame paticipating in the initial collision and the mass of the impacting body, having nothing to do with the impacting velocity to a certain extent. 相似文献
85.
On the reliability of unsaturated hydraulic conductivity calculated from the moisture retention curve 总被引:7,自引:0,他引:7
In comparison with direct measurements of unsaturated hydraulic conductivity, the methods of calculations from the moisture retention curve are attractive for their fast and simple use and low cost. These are the main reasons for their increasing use, mainly in spatial variability studies. On the other hand, it is known that their applicability is limited. The possibility of the use of the retention curve to indirectly determine hydraulic conductivities is analyzed as follows. The theoretical derivation of the relationK(h) – (h) is briefly discussed with regards to potential sources of inaccuracy. The sensitivity of the algorithm forK(h) calculation is studied as a response to possible inaccuracies in the retention curve determination. Conclusions about the usability of calculated hydraulic conductivities are drawn. 相似文献
86.
以碳酸锶为甲烷吸附活化的模型催化剂,用切换变应答、CH4(CO2)-TPD等技术,对甲烷的吸附、碱性对催化剂性能的影响进行了研究,结果表明,甲烷在碳酸锶上的活化显示出明显的酸碱活化机理特征,瞬变应答及TPD结果均证明,甲烷在碳酸锶表面有较强的吸附,其脱附温度约310℃,关联结果表明,甲烷转化率及C2烃收率与催化剂表面SrO碱性中心浓度有非常一致的顺变关系,因此催化剂表面的酸碱中心可能是甲烷的选择活 相似文献
87.
The dynamic viscoelastic response of the two-phase polymer blend systems shows the characteristics of the thermorheologically complex materials. In this paper theoretical equations for describing the dynamic viscoelastic response of such polymer blend systems have been established by means of the mechanical modeling technique. The dynamic viscoelastic response of the blend systems at any blend composition can be predicted theoretically by using the equations established, provided that the dynamic viscoelastic response of the two pure components and the mechanical model parameters are known in advance. Thus, we provide an effective method for studying the dynamic mechanical properties and the molecular relaxation characteristics of the two-phase polymer blend systems. 相似文献
88.
低电流密度下恒电流法制备的聚苯胺修饰电极 总被引:3,自引:1,他引:3
研究了低电流密度下恒电流法制备的聚苯(PA)修饰电极的性质及其影响因素,探讨了低电流密度聚合的PA膜的优点。发现此种条件下聚合的PA膜具有较好的电荷传输能力,它不仅对Br^-,Tl^+/Tl等电对的氧化还原反应有更好的电催化活性,而且对H^+的Nernast响应也更接近理论值。 相似文献
89.
90.
Fast atom bombardment mass spectra of a series of arenediazonium salts with various substituents complexed with 18-crown-6 and dibenzo-24-crown-8 ethers were examined. The correlation between quasi-molecular ion abundance of various complexes and the properties, coordination ability of donor-acceptor linkages in the complexes were studied. By using molecular orbital calculation we have successfully demonstrated that the correlation cited is related to the electron cloud densities on the heteroatoms α-N and β-N of arenediazonium salts. 相似文献