全文获取类型
收费全文 | 184223篇 |
免费 | 36928篇 |
国内免费 | 26854篇 |
专业分类
化学 | 121504篇 |
晶体学 | 2098篇 |
力学 | 12143篇 |
综合类 | 848篇 |
数学 | 23046篇 |
物理学 | 88366篇 |
出版年
2024年 | 734篇 |
2023年 | 2792篇 |
2022年 | 4487篇 |
2021年 | 4611篇 |
2020年 | 5048篇 |
2019年 | 5298篇 |
2018年 | 4842篇 |
2017年 | 5145篇 |
2016年 | 6982篇 |
2015年 | 7318篇 |
2014年 | 8166篇 |
2013年 | 11772篇 |
2012年 | 13534篇 |
2011年 | 15100篇 |
2010年 | 15434篇 |
2009年 | 15385篇 |
2008年 | 9764篇 |
2007年 | 8766篇 |
2006年 | 8007篇 |
2005年 | 7561篇 |
2004年 | 7295篇 |
2003年 | 5756篇 |
2002年 | 5281篇 |
2001年 | 5287篇 |
2000年 | 4262篇 |
1999年 | 4748篇 |
1998年 | 3986篇 |
1997年 | 3647篇 |
1996年 | 4027篇 |
1995年 | 4230篇 |
1994年 | 4133篇 |
1993年 | 3924篇 |
1992年 | 3400篇 |
1991年 | 2965篇 |
1990年 | 2494篇 |
1989年 | 2449篇 |
1988年 | 2289篇 |
1987年 | 1577篇 |
1986年 | 1570篇 |
1985年 | 1247篇 |
1984年 | 1231篇 |
1983年 | 600篇 |
1982年 | 1063篇 |
1981年 | 874篇 |
1980年 | 872篇 |
1979年 | 592篇 |
1978年 | 593篇 |
1977年 | 702篇 |
1976年 | 1111篇 |
1972年 | 573篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
The semi‐iterative method (SIM) is applied to the hyper‐power (HP) iteration, and necessary and sufficient conditions are given for the convergence of the semi‐iterative–hyper‐power (SIM–HP) iteration. The root convergence rate is computed for both the HP and SIM–HP methods, and the quotient convergence rate is given for the HP iteration. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
92.
93.
The Iyengar Type Inequalities with Exact Estimations and the Chebyshev Central Algorithms of Integrals 总被引:3,自引:0,他引:3
Xing Hua WANG Shi Jun YANG 《数学学报(英文版)》2005,21(6):1361-1376
In this paper, both low order and high order extensions of the Iyengar type inequality are obtained. Such extensions are the best possible in the same sense as that of the Iyengar inequality. hzrthermore, the Chebyshev central algorithms of integrals for some function classes and some related problems are also considered and investigated. 相似文献
94.
Compact, time‐harmonic, acoustic sources produce waves that decay too slowly to be square‐integrable on a line away from the sources. We introduce an inner product, arising directly from Green's second theorem, to form a Hilbert space of these waves and present examples of its computation.1 © 2005 Wiley Periodicals, Inc. 相似文献
95.
96.
K. C. Kumara Swamy E. Balaraman M. Phani Pavan N. N. Bhuvan Kumar K. Praveen Kumar N. Satish Kumar 《Journal of Chemical Sciences》2006,118(6):495-501
The diversity of products in the reaction of diethyl azodicarboxylate (DEAD)/diisopropyl azodicarboxylate (DIAD) and activated
acetylenes with PIII compounds bearing oxygen or nitrogen substituents is discussed. New findings that are useful in understanding the nature
of intermediates involved in the Mitsunobu reaction are highlighted. X-ray structures of two new compounds (2-t-Bu-4-MeC6H3O)P (μ-N-t-Bu)2P+[(NH-t-Bu)N[(CO2]-i-Pr)(HNCO2-i-Pr)]](Cl-)(2-t-Bu-4-MeC6H3OH)(23)and [CH2(6-t-Bu-4-Me-C6H2O)2P(O)C(CO2Me)C-(CO2Me)CClNC(O)Cl] (33) are also reported. The structure of23 is close to one of the intermediates proposed in the Mitsunobu reaction. 相似文献
97.
Kristian Hougaard Frederik D. Nielsen 《Journal of Optical and Fiber Communications Reports》2004,1(1):63-83
In this paper we will present an overview of the use
of photonic crystal fibers as fiber amplifiers. We
will describe the basic concepts of optical
amplification, and how to do numerical modelling of
such components. We will then identify advantages
and disadvantages of amplifiers based on PCF
technology compared to conventional fibers, and then
go into greater detail on some of these specific
applications, such as low pump power amplifiers, and
high-power double-clad amplifiers and lasers. 相似文献
98.
Hong-Xing Zheng Dao-Yin Yu 《International Journal of Infrared and Millimeter Waves》2005,26(9):1343-1353
In this paper, a very useful numerical technique has been developed for analyzing the transient characteristics of a planar-spiral inductor on-chip. A locally conformal technique and an alternating-direction implicit scheme are applied to the finite-difference time-domain method. A formulation for solving three dimensional Maxwell’s equations is proposed. Using the proposed method, various parameters of the planar-spiral inductors have been analyzed and an equivalent circuit, which includes frequency-independent circuit elements, has been introduced. Highly computational efficiency is implemented. Numerical results show excellent agreement with the measured data over a wide frequency range. 相似文献
99.
T Utsunomiya M. Sekine 《International Journal of Infrared and Millimeter Waves》2005,26(11):1651-1660
We have conducted a millimeter wave propagation experiment at 103 GHz (2.9 mm) on a propagation path of 390 m. The results
were compared with the rain attenuation calculations from the Marshall-Palmer, Best, Joss-Thomas-Waldvogel and Weibull distributions
for raindrop-size. It has been shown that the Weibull distribution has a good agreement with the experiments. 相似文献
100.
Junhua Chen 《Journal of organometallic chemistry》2006,691(3):470-474
Four novel hexadentate imidazolium salts were synthesized from hexakis(bromomethyl)benzene and 1-substituted imidazole. The arylation of aldehydes with arylboronic acids was effected conveniently and in high yields by a catalyst system generated in situ from these hexadentate imidazolium salts, [Rh(COD)Cl]2 and a base. 相似文献