全文获取类型
收费全文 | 599439篇 |
免费 | 17467篇 |
国内免费 | 8547篇 |
专业分类
化学 | 318556篇 |
晶体学 | 8280篇 |
力学 | 30675篇 |
综合类 | 327篇 |
数学 | 75975篇 |
物理学 | 191640篇 |
出版年
2022年 | 6312篇 |
2021年 | 7777篇 |
2020年 | 8507篇 |
2019年 | 9068篇 |
2018年 | 10931篇 |
2017年 | 10871篇 |
2016年 | 15132篇 |
2015年 | 9590篇 |
2014年 | 14520篇 |
2013年 | 28737篇 |
2012年 | 24917篇 |
2011年 | 28334篇 |
2010年 | 20814篇 |
2009年 | 20444篇 |
2008年 | 25122篇 |
2007年 | 24489篇 |
2006年 | 22234篇 |
2005年 | 19631篇 |
2004年 | 17793篇 |
2003年 | 15796篇 |
2002年 | 15518篇 |
2001年 | 16112篇 |
2000年 | 12646篇 |
1999年 | 10258篇 |
1998年 | 8885篇 |
1997年 | 8740篇 |
1996年 | 8202篇 |
1995年 | 7296篇 |
1994年 | 7176篇 |
1993年 | 6759篇 |
1992年 | 7040篇 |
1991年 | 7435篇 |
1990年 | 7066篇 |
1989年 | 6866篇 |
1988年 | 6653篇 |
1987年 | 6403篇 |
1986年 | 6116篇 |
1985年 | 7607篇 |
1984年 | 7906篇 |
1983年 | 6631篇 |
1982年 | 6892篇 |
1981年 | 6393篇 |
1980年 | 6061篇 |
1979年 | 6532篇 |
1978年 | 6769篇 |
1977年 | 6670篇 |
1976年 | 6612篇 |
1975年 | 6323篇 |
1974年 | 6145篇 |
1973年 | 6453篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
The local vibrational spectra of copper crystals containing vacancies are calculated using the pair atomic potential derived in the framework of the resonance pseudopotential theory. The calculations are performed by a recursive method with due regard for the symmetry of the defect region. The frequencies of the vacancy-induced resonance vibrations of different symmetries are determined. 相似文献
993.
In-time motion adjustment in laser cladding manufacturing process for improving dimensional accuracy and surface finish of the formed part 总被引:2,自引:0,他引:2
This paper presents in-time motion adjustment in laser cladding manufacturing process as a means to improve dimensional accuracy and surface finish of the built part. Defects occurring during laser cladding degrade the part quality such as dimensional accuracy and surface finish. In this paper, in-time motion adjustment strategy was presented to remedy and eliminate defects occurring during laser cladding to improve the dimensional accuracy and surface finish. Based on the relationship between the motion of laser head relative to the growing part and other parameters in effects on clad profile, the laser traverse speed, stand-off distance and laser approach orientation to the existing clad layer were adjusted by instructions from a close-loop control system in real time to remedy and eliminate defects. The results of the experiments verified the effects of in-time motion adjustment on dimensional accuracy and surface finish. 相似文献
994.
S. P. Savin L. M. Zelenyi E. Amata J. Buechner J. Blecki S. I. Klimov B. Nikutowski J. L. Rauch S. A. Romanov A. A. Skalsky V. N. Smirnov P. Song K. Stasiewicz 《JETP Letters》2004,79(8):368-371
The study of the interaction between collisionless plasma flow and stagnant plasma revealed the presence of an outer boundary layer at the border of a geomagnetic trap, where the super-Alfvén subsonic laminar flow changes over to the dynamic regime characterized by the formation of accelerated magnetosonic jets and decelerated Alfvén flows with characteristic relaxation times of 10–20 min. The nonlinear interaction of fluctuations in the initial flow with the waves reflected from an obstacle explains the observed flow chaotization. The Cherenkov resonance of the magnetosonic jet with the fluctuation beats between the boundary layer and the incoming flow is the possible mechanism of its formation. In the flow reference system, the incoming particles are accelerated by the electric fields at the border of boundary layer that arise self-consistently as a result of the preceding wave-particle interactions; the inertial drift of the incoming ions in a transverse electric field increasing toward the border explains quantitatively the observed ion acceleration. The magnetosonic jets may carry away downstream up to a half of the unperturbed flow momentum, and their dynamic pressure is an order of magnitude higher than the magnetic pressure at the obstacle border. The appearance of nonequilibrium jets and the boundary-layer fluctuations are synchronized by the magnetosonic oscillations of the incoming flow at frequencies of 1–2 mHz. 相似文献
995.
Nešetřil and Sopena introduced the concept of oriented game chromatic number. They asked whether the oriented game chromatic
number of partial k-trees was bounded. Here we answer their question positively.
Received: January 12, 2001 Final version received: February 25, 2002 相似文献
996.
997.
It is a well-known feature of odd space-time dimensions d that there exist two inequivalent fundamental representations A and B of the Dirac gamma matrices. Moreover, the parity transformation swaps the fermion fields living in A and B. As a consequence, a parity-invariant Lagrangian can only be constructed by incorporating both the representations. Based upon these ideas and contrary to long-held belief, we show that in addition to a discrete exchange symmetry for the massless case, we can also define chiral symmetry provided the Lagrangian contains fields corresponding to both the inequivalent representations. We also study the transformation properties of the corresponding chiral currents under parity and charge-conjugation operations. We work explicitly in 2 + 1 dimensions and later show how some of these ideas generalize to an arbitrary number of odd dimensions. 相似文献
998.
V. A. Popov S. I. Lopatin L. Sh. Tsemekhman L. A. Pavlinova S. P. Kormilitsyn V. V. Barsegyan 《Russian Journal of Applied Chemistry》2003,76(10):1564-1567
Evaporation of chromium ore and concentrates was studied using high-temperature differential mass-spectrometry. The data obtained, concerning the component vapor pressures in evaporation of complex oxide systems in the range 1700-2100 K, can be used to calculate the evaporation loss in melting and to assess the possibility of utilization of the sublimates formed. 相似文献
999.
微模塑法制备PMMA/SiO2二氧化硅杂化材料微结构 总被引:1,自引:0,他引:1
以摩尔比为 1∶1的甲基丙烯酸甲酯 (MMA)、甲基丙烯酸 (3 三乙氧基硅烷基 )丙酯 (ESMA)单体、0 .2 %(单体总量的质量分数 )的偶氮二异丁腈AIBN引发剂和四氢呋喃 (THF)溶剂 ,及 2 0 % (总质量分数 )的正硅酸乙酯TEOS合成出PMMA/SiO2 有机 无机杂化的杂化溶胶 .将溶胶在洗净的普通光学玻璃基片表面甩膜 .利用软刻蚀中的微模塑法 ,把有机硅弹性印章复制有精细图纹一面轻放在杂化溶胶膜上进行微模塑 ,外加 1N压力于12 0℃下处理 2h使溶胶凝胶化 .印章剥离后在基片表面就形成了PMMA/SiO2 有机 无机杂化材料的微图纹结构 .从微图纹的光学显微镜照片可以看出微模塑方法制备杂化材料复制的图纹精细度高 ,操作简单易行 ,是一类比较理想的微细图纹结构加工的方法 . 相似文献
1000.
内部审核在计量体系中的作用 总被引:1,自引:0,他引:1
介绍内部审核制度在计量测试工作中的目的和作用,提出了内部审核工作应注意的事项,如内部审核工作计划的完整性,内部审核工作的有效性,管理者工作内容的全面性,以及后续工作的完善性。 相似文献