全文获取类型
收费全文 | 302599篇 |
免费 | 14681篇 |
国内免费 | 8044篇 |
专业分类
化学 | 165949篇 |
晶体学 | 4621篇 |
力学 | 15340篇 |
综合类 | 311篇 |
数学 | 33611篇 |
物理学 | 105492篇 |
出版年
2022年 | 3121篇 |
2021年 | 4145篇 |
2020年 | 4828篇 |
2019年 | 4866篇 |
2018年 | 5151篇 |
2017年 | 4893篇 |
2016年 | 7331篇 |
2015年 | 5659篇 |
2014年 | 7881篇 |
2013年 | 15149篇 |
2012年 | 13980篇 |
2011年 | 15952篇 |
2010年 | 11061篇 |
2009年 | 10801篇 |
2008年 | 13187篇 |
2007年 | 12735篇 |
2006年 | 11907篇 |
2005年 | 10529篇 |
2004年 | 9264篇 |
2003年 | 7965篇 |
2002年 | 7750篇 |
2001年 | 8492篇 |
2000年 | 6687篇 |
1999年 | 5735篇 |
1998年 | 4829篇 |
1997年 | 4732篇 |
1996年 | 4562篇 |
1995年 | 4046篇 |
1994年 | 3864篇 |
1993年 | 3775篇 |
1992年 | 3803篇 |
1991年 | 3899篇 |
1990年 | 3579篇 |
1989年 | 3405篇 |
1988年 | 3389篇 |
1987年 | 3221篇 |
1986年 | 3047篇 |
1985年 | 4003篇 |
1984年 | 4142篇 |
1983年 | 3297篇 |
1982年 | 3489篇 |
1981年 | 3402篇 |
1980年 | 3294篇 |
1979年 | 3365篇 |
1978年 | 3450篇 |
1977年 | 3389篇 |
1976年 | 3474篇 |
1975年 | 3162篇 |
1974年 | 3163篇 |
1973年 | 3220篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
P. V. Yagodovskii 《Journal of Mathematical Sciences》2003,113(5):728-730
A linear deformation of a discrete group G is a special deformation of the group algebra of G resulting in the group algebra of a multivalued group. Basic results on linear deformations are presented. Bibliography: 5 titles. 相似文献
992.
V. P. Belousov I. M. Belousova A. S. Grenishin O. B. Danilov V. M. Kiselev A. V. Kris’ko A. A. Mak T. D. Murav’eva V. N. Sosnov 《Optics and Spectroscopy》2003,95(6):830-832
The possibility of lasing in the fullerene-oxygen-iodine system with optical excitation of fullerene is studied. Laser radiation with an energy of 25 mJ and a pulse duration of 5–10 ms is obtained. 相似文献
993.
994.
995.
Time-resolved electron transport studies on InGaAs/GaAs-QWIPs 总被引:1,自引:0,他引:1
S. Steinkogler H. Schneider R. Rehm M. Walther P. Koidl P. Grant R. Dudek H. C. Liu 《Infrared Physics & Technology》2003,44(5-6):355-361
Due to the short internal response time, quantum-well infrared photodetectors (QWIPs) are interesting for high-speed applications such as heterodyne spectroscopy or laser pulse monitoring. We studied the photocurrent transients of InGaAs/GaAs-QWIPs after irradiation with infrared laser pulses of 250 fs duration. The excitation wavelength of about 9 μm matches the peak wavelength of the QWIP structure. The photocurrent transient consists of two different dynamical components, representing the fast photoionization in the quantum-wells and the slow injection current that compensates the remaining space charge. The investigations of the different components as a function of temperature and bias voltage were performed on a nanosecond time-scale. The experimental separation of the two photocurrent contributions allows us to determine the photoconductive gain. The Fourier transform of the photocurrent transient was compared with other experimental methods including heterodyne detection and microwave rectification. The quantitative agreement between these different measurement techniques is excellent. 相似文献
996.
N. Segovia M. A. Armienta C. Valdes M. Mena J. L. Seidel M. Monnin P. Pea M. B. E. Lopez A. V. Reyes 《Radiation measurements》2003,36(1-6):379-383
Soil radon has been monitored at two fixed stations in the northern flank of Popocatepetl Volcano, a high risk volcano located 60 km SE from Mexico City. Water samples from three springs were also studied for radon as well as major and trace elements. Radon in the soil was recorded using track detectors. Radon in the water samples was evaluated using the liquid scintillation method and an Alphaguard. The major elements were determined through conventional chemical methods and trace elements using an ICP-MS equipment. Soil radon levels were low, indicating a moderate diffuse degassing through the flanks of the volcano. Groundwater radon had almost no relation with the eruptive stages. Water chemistry was stable in the reported time (2000–2002). 相似文献
997.
Gu De-shan Jing Shi-wei Sang Hai-feng Qiao Shuang Liu Yu-ren Liu Lin-mao 《Journal of Radioanalytical and Nuclear Chemistry》2004,262(2):493-496
This paper introduces the analysis method and principle of pulse fast-thermal neutron analysis (PFTNA). A system for the measurement
of low caloric power of coal by PFTNA is also presented. The 14 MeV pulse neutron generator and BGO detector and 4096 MCA
were applied in this system. A multiple linear regression method applied to the data solved the interferential problem of
multiple elements. The error of low caloric power between chemical analysis and experiment was less than 0.4 MJ/kg.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
998.
A. V. Alatortsev R. N. Kuz'min O. G. Provorova N. P. Savenkova 《Computational Mathematics and Modeling》2004,15(4):350-364
We model the electrolysis of aluminum in specific electrolysis baths. A model of the physical process is proposed, allowing for the specific bath design, including the state of the bottom surface. The mathematical model utilizes the information capabilities of the Navier–Stokes equations written for the metal and the electrolyte media. The multidimensional system of equations enables us to consider the magnetohydrodynamic processes in two media and the interaction of the media. The problem is solved numerically. The calculations simulate the interface dynamics and the distribution of velocities and currents in the middle layer in both media. The numerical results are compared with physical experiments. 相似文献
999.
K. P. Kokhas 《Journal of Mathematical Sciences》2004,121(3):2371-2379
We consider a field F that is a direct limit of an increasing chain of finite fields, and describe the Bratteli diagram, complex factor-representations, and projective moduli of the Heisenberg group of 3 × 3 upper-triangular matrices with elements from F. Bibliography: 3 titles. 相似文献
1000.
Summary The solubility parameters of cationic surfactants were obtained using the inverse gas chromatographic technique. The surfactants
didodecyl dimethyl ammonium bromide, dioctadecyl dimethyl ammonium bromide and dodecyl pyridinium chloride were used as stationary
phase and retention data of different probe solutes were measured at different temperatures. The results were analysed by
the combination of Flory-Huggins and Hildebrand theories, and the solubility parameters of the surfactants were obtained in
a range of temperatures between 80–120°C. 相似文献