全文获取类型
收费全文 | 50743篇 |
免费 | 6674篇 |
国内免费 | 8247篇 |
专业分类
化学 | 38352篇 |
晶体学 | 1562篇 |
力学 | 2541篇 |
综合类 | 395篇 |
数学 | 7221篇 |
物理学 | 15593篇 |
出版年
2024年 | 77篇 |
2023年 | 521篇 |
2022年 | 1181篇 |
2021年 | 1288篇 |
2020年 | 1698篇 |
2019年 | 1670篇 |
2018年 | 1510篇 |
2017年 | 1862篇 |
2016年 | 2028篇 |
2015年 | 1824篇 |
2014年 | 2548篇 |
2013年 | 4516篇 |
2012年 | 3094篇 |
2011年 | 3567篇 |
2010年 | 3019篇 |
2009年 | 3476篇 |
2008年 | 3575篇 |
2007年 | 3507篇 |
2006年 | 3198篇 |
2005年 | 2864篇 |
2004年 | 2570篇 |
2003年 | 2173篇 |
2002年 | 1838篇 |
2001年 | 1611篇 |
2000年 | 1504篇 |
1999年 | 1296篇 |
1998年 | 1119篇 |
1997年 | 927篇 |
1996年 | 854篇 |
1995年 | 823篇 |
1994年 | 762篇 |
1993年 | 609篇 |
1992年 | 482篇 |
1991年 | 347篇 |
1990年 | 237篇 |
1989年 | 238篇 |
1988年 | 196篇 |
1987年 | 131篇 |
1986年 | 131篇 |
1985年 | 122篇 |
1984年 | 107篇 |
1983年 | 49篇 |
1982年 | 87篇 |
1981年 | 87篇 |
1980年 | 83篇 |
1979年 | 69篇 |
1978年 | 49篇 |
1977年 | 37篇 |
1976年 | 23篇 |
1973年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
主要介绍了一个引理,这个引理奠定了K4-同胚图K4(α,1,1,δ,ε,η)色性研究的基础。 相似文献
62.
The paper proposes a rational method to derive fairness measures for surfaces. It works in cases where isophotes, reflection lines, planar intersection curves, or other curves are used to judge the fairness of the surface. The surface fairness measure is derived by demanding that all the given curves should be fair with respect to an appropriate curve fairness measure. The method is applied to the field of ship hull design where the curves are plane intersections. The method is extended to the case where one considers, not the fairness of one curve, but the fairness of a one parameter family of curves. Six basic third order invariants by which the fairing measures can be expressed are defined. Furthermore, the geometry of a plane intersection curve is studied, and the variation of the total, the normal, and the geodesic curvature and the geodesic torsion is determined. 相似文献
63.
64.
烷基硫酸盐表面张力的量子化学研究 总被引:1,自引:0,他引:1
用AMl量子化学计算法优化了十三烷基硫酸根阴离子和——CH3在不同取代位的十二烷基硫酸根阴离子的几何构型,得到最优构型时最高占据分子轨道能级EHOMO、最低空轨道能级ELUMO、电子能量Eele和偶极矩μ等数据.将这些电子结构数据分别与表面张力相拟合,得到很好的相关性。文中讨论了——CH3在不同位置取代对表面张力的影响。 相似文献
65.
本文首先将文[1]中的BLD映射推广为弱(L1,L2)-BLD映射,并证明了如下正则性结果:存在两个可积指数 P1=P1(n,L1,L2)<n<q1=q1(n,L1,L2),使得对任意弱(L1,L2)-BLD映射f∈(Ω,Rn),都有f∈(Ω,Rn),即f为(L1,L2)-BLD映射. 相似文献
66.
一阶形式系统K~*及其完备性 总被引:2,自引:0,他引:2
裴道武 《数学年刊A辑(中文版)》2002,(6)
模糊命题演算的形式系统L*已经在模糊逻辑与模糊推理的结合研究中得到了成功的应用.本文考虑与系统L*相应的一阶逻辑理论,建立了一阶形式系统K*,并证明了这个系统的完备性. 相似文献
67.
68.
The MPEG-1 Layer 3 compression schema of audio signal, commonly known as mp3, has caused a great impact in recent years as it has reached high compression rates while conserving a high sound quality. Music and speech samples compressed at high bitrates are perceptually indistinguishable from the original samples, but very little was known about how compression acoustically affects the voice signal. A previous work with normal voices showed a high fidelity at high-bitrate compressions both in voice parameters and the amplitude-frequency spectrum. In the present work, dysphonic voices were tested through two studies. In the first study, spectrograms, long-term average spectra (LTAS), and fast Fourier transform (FFT) spectra of compressed and original samples of running speech were compared. In the second study, intensities, formant frequencies, formant bandwidths, and a multidimensional set of voice parameters were tested in a set of sustained phonations. Results showed that compression at high bitrates (96 and 128 kbps) preserved the relevant acoustic properties of the pathological voices. With compressions at lower bitrates, fidelity decreases, introducing some important alterations. Results from both works, Gonzalez and Cervera and this paper, open up the possibility of using MPEG-compression at high bitrates to store or transmit high-quality speech recordings, without altering their acoustic properties. 相似文献
69.
P. R. Latthe P. S. Shinge Bharati V. Badami P. B. Patil S. N. Holihosur 《Journal of Chemical Sciences》2006,118(3):249-256
3-[4-(Azidocarbonyl)]phenylsydnone (2) obtained from 3-(4-hydrazinocarbonyl) phenylsydnone (1) on Curtius rearrangement with alcohols, water and amines afforded the corresponding carbamates (3a-h), 4,4′-(sydnone-3-yl) diphenyl urea (4) and 4-(heterocyclyl)phenyl ureas (5a-l). Compounds (5a-l) on one-pot ring conversion yielded the 1,3,4-oxadiazolin-2-one derivatives (6a-l), which on reaction with N2H4 gave the 4-amino-1,2,4-triazolin-3-ones (7a-l). All these compounds exhibited moderate antimicrobial activity against the few microbes tested. The carbamates have been
found to be more toxic against fourth instar larvae ofAedes aegypti, in particular, then-butyl derivative (3e). 相似文献
70.
R. J. Saykally K. M. Evenson D. A. Jennings L. R. Zink A. Scalabrin 《International Journal of Infrared and Millimeter Waves》1987,8(6):653-662
Twenty new cw FIR laser lines in CD3OH, optically pumped by a CO2 laser, are reported. The frequencies of 39 of the stronger laser lines were measured relative to stabilized CO2 lasers with a fractional uncertainty, as determined by the reproducibility of the FIR frequency itself, of 2 parts in 107.Contribution of the U.S. Government, not subject to copyright. 相似文献