全文获取类型
收费全文 | 24061篇 |
免费 | 3993篇 |
国内免费 | 2496篇 |
专业分类
化学 | 13290篇 |
晶体学 | 195篇 |
力学 | 1049篇 |
综合类 | 103篇 |
数学 | 2114篇 |
物理学 | 7568篇 |
无线电 | 6231篇 |
出版年
2024年 | 58篇 |
2023年 | 611篇 |
2022年 | 647篇 |
2021年 | 955篇 |
2020年 | 899篇 |
2019年 | 878篇 |
2018年 | 849篇 |
2017年 | 734篇 |
2016年 | 1117篇 |
2015年 | 1051篇 |
2014年 | 1341篇 |
2013年 | 1721篇 |
2012年 | 2104篇 |
2011年 | 2139篇 |
2010年 | 1545篇 |
2009年 | 1459篇 |
2008年 | 1553篇 |
2007年 | 1420篇 |
2006年 | 1322篇 |
2005年 | 1131篇 |
2004年 | 840篇 |
2003年 | 629篇 |
2002年 | 582篇 |
2001年 | 474篇 |
2000年 | 424篇 |
1999年 | 549篇 |
1998年 | 409篇 |
1997年 | 386篇 |
1996年 | 387篇 |
1995年 | 325篇 |
1994年 | 285篇 |
1993年 | 277篇 |
1992年 | 202篇 |
1991年 | 205篇 |
1990年 | 156篇 |
1989年 | 126篇 |
1988年 | 113篇 |
1987年 | 77篇 |
1986年 | 80篇 |
1985年 | 65篇 |
1984年 | 65篇 |
1983年 | 34篇 |
1982年 | 38篇 |
1981年 | 31篇 |
1980年 | 29篇 |
1976年 | 17篇 |
1975年 | 16篇 |
1973年 | 16篇 |
1968年 | 14篇 |
1957年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
61.
Chunxia Zhao Guowang Xu Xianzhe Shi Jianmei Ma Yan Zhang Shen Lv Qianfeng Weng Qing Yang 《Analytical sciences》2004,20(7):1001-1005
Fluorescent-based single-strand conformation polymorphism (F-SSCP) analysis with capillary electrophoresis (CE) is the most common method for the detection of mutation because of its high sensitivity and resolution. In this study, we prepared an inexpensive linear polyacrylamide (LPA), and successfully applied it to CE-SSCP analysis and tandem CE-SSCP/heteroduplex analysis (HA) of the P53 gene on an ABI capillary genetic analyzer. A comparison of the sieving capabilities of a homemade LPA and commercial polydimethylacrylamide (PDMA) demonstrates that the homemade LPA has a higher resolution, a shorter analysis time, and is more suitable for tandem SSCP/HA than commercial PDMA. To show the usefulness, mutations of P53 gene exon 7 - 8 in 37 tumor samples were investigated by using homemade LPA. The results indicate that 10 mutations were found in 9 of 37 cases; the majority of P53 mutations were missense mutations, and 70% were located in exon 7, which plays an important role in neoplastic progression in human tumorigenesis. 相似文献
62.
在等离子体增强化学气相淀积系统中,采用aSi:H层淀积和原位等离子体氧化相结合的逐层生长技术制备了aSi:H/SiO_2多层膜.在激光诱导限制结晶原理基础上,使用KrF准分子脉冲激光为辐照源,对aSi:H/SiO_2多层膜进行辐照,使纳米级厚度的aSi:H子层晶化.Raman散射谱和电子衍射谱的结果表明,经过激光辐照后纳米Si颗粒在原始的aSi:H子层内形成,晶粒尺寸可以根据aSi:H层的厚度精确控制.还研究了样品的光致发光(PL)特性以及激光辐照能量密度对PL性质的影响.
关键词:
脉冲激光
多层膜
限制结晶 相似文献
63.
两段级联掺铒光纤放大器的优化研究 总被引:7,自引:4,他引:3
基于Giles模型,研究了980 nm和1480 nm泵浦的两段级联掺铒光纤放大器(EDFA)的设计,得出了掺铒光纤(EDF)的最佳长度和光隔离器的最佳位置随泵浦功率和信号功率的变化关系.比较980 nm和1480 nm泵浦的两段级联EDFA,可以发现,前者的最佳EDF长度短,而光隔离器最佳位置距EDFA输入端远. 相似文献
64.
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
65.
Ricardo Mañé 《Bulletin of the Brazilian Mathematical Society》1997,28(2):141-153
The objective of this note is to present some results, to be proved in a forthcoming paper, about certain special solutions of the Euler-Lagrange equations on closed manifolds. Our main results extend to time dependent periodic Lagrangians with minor modifications.We have chosen the autonomous case because this formally simpler framework allows to reach more easily the core of our concepts and results. Moreover the autonomous case exhibits certain special features involving the energy as a first integral that deserve special attention. They are closely related to the link found by Carneiro [C] between the energy and Mather's action function [Ma].Reprinted by permission of Addison Wesley Longman Ltd. 相似文献
66.
67.
介绍了深圳市邮电局计算机网络的体系结构与系统功能,并通过分析网络建设过程中所遇到的问题,指出了我国信息高速公路建设中可能出现和应该注意的问题。 相似文献
68.
Lizeng Wang Chengsong Ma Xiaoli Zhang Yibing Ren Yong Yu 《Fresenius' Journal of Analytical Chemistry》1995,351(7):689-691
The electrochemical behavior of the copper-tyrosine complex has been studied by linear-sweep adsorption voltammetry. In 0.02 mol/L Na2HPO4 buffer solution (pH=9.6), the complex can be adsorped on a hanging mercury drop electrode and reduced at a peak potential of about –0.42 V (vs. SCE). The secondary derivative peak height is linear proportional to the concentration of tyrosine in the range 1.0×10–7–5.0×10–5 mol/L. The detection limit is 5×10–8 mol/L.Project supported by the Provincial Science Foundation of Shandong Province 相似文献
69.
155Mb/s时分光交换系统 总被引:1,自引:0,他引:1
本文介绍了国内第一个155Mb/s时分光交换实验系统。系统以新型半导体光器件-半导体光开关门为核心构成,传输速度为155Mb/s。 相似文献
70.
Tao Liu Zuxiong Xu Zhongtao Zhao Ruzhang Ma Tiandou Hu Yaning Xie Yinghuan Guo 《中国科学A辑(英文版)》1997,40(4):395-399
The role of magnetoelastic coupling effects in nanocrystalline ferromagnets is investigated by means of high-field magnetization and Doppler-broadening spectrum measurements. For the nanocrystalline Fe73 5Cu1Nb3Si13.5B9 alloy, the results show that the pinning effects resulting from the quasidislocation dipole intensely influence the movement of domain wall; by coupling with the magnetostriction the defects-induced stress fields determine the magnetic properties at the early stage of crystallization. In view of the effective anisotropy and magnetoelastic coupling energy the optimal annealing conditions of alloys are discussed. 相似文献