全文获取类型
收费全文 | 41423篇 |
免费 | 5181篇 |
国内免费 | 6741篇 |
专业分类
化学 | 30789篇 |
晶体学 | 1336篇 |
力学 | 1568篇 |
综合类 | 531篇 |
数学 | 3375篇 |
物理学 | 15746篇 |
出版年
2024年 | 66篇 |
2023年 | 413篇 |
2022年 | 722篇 |
2021年 | 1141篇 |
2020年 | 1323篇 |
2019年 | 1306篇 |
2018年 | 1141篇 |
2017年 | 1605篇 |
2016年 | 1653篇 |
2015年 | 1515篇 |
2014年 | 2123篇 |
2013年 | 3477篇 |
2012年 | 2463篇 |
2011年 | 2875篇 |
2010年 | 2410篇 |
2009年 | 2807篇 |
2008年 | 2856篇 |
2007年 | 2889篇 |
2006年 | 2617篇 |
2005年 | 2459篇 |
2004年 | 2211篇 |
2003年 | 1862篇 |
2002年 | 1603篇 |
2001年 | 1300篇 |
2000年 | 1229篇 |
1999年 | 1025篇 |
1998年 | 894篇 |
1997年 | 800篇 |
1996年 | 690篇 |
1995年 | 663篇 |
1994年 | 577篇 |
1993年 | 485篇 |
1992年 | 384篇 |
1991年 | 297篇 |
1990年 | 193篇 |
1989年 | 190篇 |
1988年 | 169篇 |
1987年 | 122篇 |
1986年 | 109篇 |
1985年 | 111篇 |
1984年 | 77篇 |
1983年 | 45篇 |
1982年 | 68篇 |
1981年 | 76篇 |
1980年 | 62篇 |
1979年 | 57篇 |
1978年 | 45篇 |
1977年 | 41篇 |
1976年 | 29篇 |
1973年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 20 毫秒
81.
数码相机CMOS图像传感器的特性参数与选择 总被引:2,自引:0,他引:2
介绍了数码相机的核心器件———CMOS图像传感器的特性参数和在数码相机设计过程中CMOS图像传感器的选择。选择CMOS图像传感器,不仅需要考虑包括传感器的尺寸、像素总数和有效像素数、最小照度、动态范围、灵敏度、分辨力、光电响应不均匀性以及光谱响应等在内的特性参数,而且还要考虑电源管理和功耗、模数转换位数、开发的简便性以及成本等因素。 相似文献
82.
83.
Zavarzin I. V. Smirnova N. G. Chernoburova E. I. Yarovenko V. N. Krayushkin M. M. 《Russian Chemical Bulletin》2004,53(6):1257-1260
A method for syntheses of previously unknown derivatives of thieno[2,3-d]pyrimidines and quinazolines from monothiooxamides was proposed. 相似文献
84.
B. Saha S. Bhattacharyya T. K. Mukherjee P. K. Mukherjee 《International journal of quantum chemistry》2003,92(5):413-418
In the framework of nonrelativistic variational formalism a new type of basis set is proposed, to estimate separately the effect of radial and angular correlations on the ground‐state energy for helium isoelectronic sequence H? to Ar16+. Effect of radial correlation is incorporated by using multiexponential functions arising from product basis sets suitably formed out of Slater‐type one‐particle orbitals. The angular correlation can be switched on by incorporating an expansion in terms of basis involving interparticle coordinates. With a set of six‐term Slater‐type one‐particle basis and five‐term interparticle expansion, the ground‐state energy of helium is estimated as ?2.9037236 (a.u.) compared with the multiterm variational estimates ?2.9037244 (a.u.) due to Pekeris and Thakkar and Smith and Drake. Matrix elements of different operators in the ground state have been calculated and found to be in good agreement with available accurate results. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 相似文献
85.
86.
87.
Gowravaram Sabitha G.S.Kiran Kumar ReddyK.Bhaskar Reddy J.S. Yadav 《Tetrahedron letters》2003,44(34):6497-6499
The three component condensation of an aldehyde, a β-keto ester and urea (thiourea) in the presence of a catalytic amount of VCl3 is disclosed for the solution phase synthesis of dihydropyrimidinones. The ease of synthesis and work-up allowed the parallel synthesis of a 48-membered library of dihydropyrimidinones quickly and efficiently in good yields. 相似文献
88.
We carried out detailed calculations for photorefractive wave-mixing switches based on one of three crystals with high electro-optic coefficients, namely, BaTiO3, Strontium Barium Niobate (SBN (0.75)), and Potasium Sodium Strontium Barium Niobate (KNSBN). A comparison of results for the three crystals shows that a 0_-cut BaTiO3 crystal is suitable for a longitudinal switch and requires a voltage of about 80 for a 2-mm-thick crystal to induce sufficient phase mismatch. The electrodes must be transparent for the incident and diffracted beams. A 45_-cut SBN (0.75) crystal, however, is suitable for a lateral switch and requires a voltage of about 150 for a 1-mm-wide crystal. The electrodes do not need to be transparent. 相似文献
89.
Y. Guyot H. Loudyi S. Kazanskii J. C. Gcon C. Pdrini M. F. Joubert 《Radiation measurements》2004,38(4-6):753-757
Photoconductivity spectra of rare earth-doped insulating materials are measured using the resonant microwave cavity method. This technique is based on the detection of the cavity Q-factor changes induced by irradiation of the sample (inserted in the cavity) by a pulsed tunable laser. Results obtained with Lu2(SiO4)O:Ce3+ and BaF2:Eu2+ are presented and discussed. Photoionization thresholds at 400 nm (3.1 eV) and 310 nm (4.0 eV) are measured for Lu2(SiO4)O:Ce3+ and BaF2:Eu2+, respectively. 相似文献
90.
A solution to the phase problem in optics is considered within the context of the analysis of signals changing in time and of the effect of an object under investigation on the probing radiation. The solution is based on the use of a twin-wave interferometer with phase modulation in one of the channels and a spectrometer. The analysis is concerned, in particular, with signals and processes of ultrashort duration. To shift the frequency in the interferometer channel, an electrooptical crystal of ferroelectric perovskite is used as the modulator. Errors of amplitude and phase structures determined are analyzed. 相似文献