全文获取类型
收费全文 | 5508篇 |
免费 | 254篇 |
国内免费 | 20篇 |
专业分类
化学 | 4228篇 |
晶体学 | 45篇 |
力学 | 71篇 |
数学 | 554篇 |
物理学 | 884篇 |
出版年
2023年 | 44篇 |
2022年 | 75篇 |
2021年 | 166篇 |
2020年 | 149篇 |
2019年 | 125篇 |
2018年 | 85篇 |
2017年 | 74篇 |
2016年 | 180篇 |
2015年 | 149篇 |
2014年 | 165篇 |
2013年 | 277篇 |
2012年 | 405篇 |
2011年 | 418篇 |
2010年 | 214篇 |
2009年 | 166篇 |
2008年 | 334篇 |
2007年 | 317篇 |
2006年 | 289篇 |
2005年 | 252篇 |
2004年 | 232篇 |
2003年 | 183篇 |
2002年 | 191篇 |
2001年 | 67篇 |
2000年 | 55篇 |
1999年 | 41篇 |
1998年 | 38篇 |
1997年 | 40篇 |
1996年 | 71篇 |
1995年 | 63篇 |
1994年 | 49篇 |
1993年 | 62篇 |
1992年 | 62篇 |
1991年 | 53篇 |
1990年 | 51篇 |
1989年 | 53篇 |
1988年 | 34篇 |
1987年 | 37篇 |
1986年 | 31篇 |
1985年 | 42篇 |
1984年 | 36篇 |
1983年 | 30篇 |
1982年 | 28篇 |
1981年 | 26篇 |
1980年 | 31篇 |
1979年 | 24篇 |
1978年 | 28篇 |
1977年 | 21篇 |
1975年 | 22篇 |
1974年 | 31篇 |
1973年 | 31篇 |
排序方式: 共有5782条查询结果,搜索用时 31 毫秒
21.
C. Cooper 《Random Structures and Algorithms》1993,4(4):469-472
Let D 2(n) be the probability space of 2-regular digraphs on n vertices with the uniform measure. As n tends to infinity, the probability that the digraphs are 2-connected tends to 1. © 1993 John Wiley & Sons, Inc. 相似文献
22.
Experts were interviewed to identify criteria for evaluation of vocal performance. A scale was then constructed and inter- and intrajudge reliability assessed. Experts listened to 19 different performances, plus 6 presented a second time. Interjudge reliability for one judge was modest, but increased dramatically as the size of the judge panel increased. The most reliable items were overall score and intonation accuracy. Diction was less reliable than other items. Intrajudge reliability was higher for overall score than for any other item. A factor analysis on the test items yielded factors labelled intrinsic quality, execution, and diction. Another factor analysis, using the experts as variables, revealed two underlying evaluative dimensions. It was found that 13 experts were primarily influenced by execution, and that 8 were mainly affected by intrinsic quality. Interjudge and intrajudge reliabilities of these two groups differed. 相似文献
23.
24.
Gisha Elizabeth Luckachan C. K. S. Pillai 《Journal of polymer science. Part A, Polymer chemistry》2006,44(10):3250-3260
Novel multiblock poly(ester amide)s containing poly(L ‐lactide) and cycloaliphatic amide segments were synthesized from telechelic oligomer of α,ω‐hydroxyl terminated poly(L ‐lactide), 1,3‐cyclohexylbis(methylamine), and sebacoylchloride by the “two‐step” interfacial polycondensation method. The blocky nature of PEAs was established by FTIR and 1H NMR spectroscopies. The effect of relative content of ester and amide segments on the crystallization nature of PEAs was investigated by WAXD and DSC analyses. PEAs having lower content of PLLA, PEA 1 and PEA 2, showed a crystallization pattern analogous to polyamides, whereas PEA 3, having higher content of PLLA, showed two crystalline phases characterized by polyester and polyamide segments. Random nature of PEAs was observed from single Tg values. Biodegradation studies using the enzyme lipase from Candida Cylindracea showed higher degradation rate for PEA 3 than that for PEA 1 and PEA 2. FTIR, 1H NMR, and DSC analyses of the degraded products indicated the involvement of ester linkages in the degradation process. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3250–3260, 2006 相似文献
25.
Two problems in projectiles are discussed which generate interestingloci. 相似文献
26.
We show that the isotropy types of the singularities of Riemannian orbifolds are not determined by the Laplace spectrum. Indeed,
we construct arbitrarily large families of mutually isospectral orbifolds with different isotropy types. Finally, we show
that the corresponding singular strata of two isospectral orbifolds may not be homeomorphic.
Received: 6 October 2005 相似文献
27.
Abe F Amidei D Apollinari G Atac M Auchincloss P Baden AR Bamberger A Barbaro-Galtieri A Barnes VE Bedeschi F Behrends S Belforte S Bellettini G Bellinger J Bensinger J Beretvas A Berge JP Bertolucci S Bhadra S Binkley M Blair R Blocker C Booth AW Brandenburg G Brown D Buckley E Byon A Byrum KL Campagnari C Campbell M Carey R Carithers W Carlsmith D Carroll JT Cashmore R Cervelli F Chadwick K Chiarelli G Chinowsky W Cihangir S Clark AG Connor D Contreras M Cooper J Cordelli M Crane D Curatolo M 《Physical review letters》1990,65(18):2243-2246
28.
Elizabeth M. Holt Balawant S. Joshi Dilip H. Gawad S. William Pelletier 《Journal of chemical crystallography》1990,20(3):261-264
The crystal and molecular structure of 1-ethyl-4-methoxy-9H-pyrido[3,4b]indole (crenatine) carbonate C14H14N2O·H2CO3, (MS, m/z 226)M
R
288.3, a-carboline alkaloid, has been determined from X-ray diffraction data. The compound crystallizes in the space group Pbca with cell parameters:a=11.616(4),b=18.450(8),c=12.992(5)Å,V=2784(2)Å3,Z=8,D
calc=1.375 g cm–3, (MoK)=0.71069Å,(Mo K)=0.94 cm–1,F(000)=1216,R/R
w
=8.2/10.3% for 1099 reflections. The ring system of the-carboline nucleus is planar. The title compound shows a two center hydrogen bond between the indole N-H group and the oxygen atom of a carbonate group. The structure does not display hydrogen bonding between-carboline groups but rather a bonding network involving the carbonate group. 相似文献
29.
Abe F Amidei D Apollinari G Ascoli G Atac M Auchincloss P Baden AR Barbaro-Galtieri A Barnes VE Bedeschi F Behrends S Belforte S Bellettini G Bellinger J Bensinger J Beretvas A Berge P Bertolucci S Bhadra S Binkley M Blair R Blocker C Bofill J Booth AW Brandenburg G Brown D Byon A Byrum KL Campbell M Carey R Carithers W Carlsmith D Carroll JT Cashmore R Cervelli F Chadwick K Chapin T Chiarelli G Chinowsky W Cihangir S Cline D Connor D Contreras M Cooper J Cordelli M Curatolo M Day C DelFabbro R 《Physical review D: Particles and fields》1990,41(5):1722-1725
30.