全文获取类型
收费全文 | 290047篇 |
免费 | 3064篇 |
国内免费 | 836篇 |
专业分类
化学 | 157207篇 |
晶体学 | 3230篇 |
力学 | 12520篇 |
综合类 | 10篇 |
数学 | 34664篇 |
物理学 | 86316篇 |
出版年
2020年 | 2364篇 |
2019年 | 2571篇 |
2018年 | 3366篇 |
2017年 | 3376篇 |
2016年 | 5010篇 |
2015年 | 3221篇 |
2014年 | 4885篇 |
2013年 | 11989篇 |
2012年 | 9312篇 |
2011年 | 11415篇 |
2010年 | 7935篇 |
2009年 | 7620篇 |
2008年 | 10612篇 |
2007年 | 10805篇 |
2006年 | 10261篇 |
2005年 | 9310篇 |
2004年 | 8597篇 |
2003年 | 7698篇 |
2002年 | 7556篇 |
2001年 | 7734篇 |
2000年 | 6024篇 |
1999年 | 4714篇 |
1998年 | 4206篇 |
1997年 | 4122篇 |
1996年 | 3607篇 |
1995年 | 3523篇 |
1994年 | 3711篇 |
1993年 | 3390篇 |
1992年 | 3827篇 |
1991年 | 3847篇 |
1990年 | 3757篇 |
1989年 | 3625篇 |
1988年 | 3694篇 |
1987年 | 3584篇 |
1986年 | 3413篇 |
1985年 | 4600篇 |
1984年 | 4913篇 |
1983年 | 4081篇 |
1982年 | 4251篇 |
1981年 | 4139篇 |
1980年 | 4142篇 |
1979年 | 4061篇 |
1978年 | 4415篇 |
1977年 | 4318篇 |
1976年 | 4339篇 |
1975年 | 3977篇 |
1974年 | 4042篇 |
1973年 | 4162篇 |
1972年 | 2927篇 |
1971年 | 2441篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Kentsch U. Zschornack G. Grossmann F. Ovsyannikov V. P. Ullmann F. 《Hyperfine Interactions》2003,148(1-4):237-242
Hyperfine Interactions - It is well known that many reinforced concrete structures are at risk of deterioration due to chloride ion contamination of the concrete or atmospheric carbon dioxide... 相似文献
992.
Mary E. Neubert DAVID G. ABDALLAH Jr Sandra S. Keast Julie M. Kim Soonnam Lee Ryan M. Stayshich Margaret E. Walsh Rolfe G. Petschek Shin-Tson Wu 《Liquid crystals》2003,30(6):711-731
New diphenyldiacetylenes of the type with A, B = H and/or F; m = 0, 1; n = 1-4; and X = C n H 2n + 1 , F, CF 3 or CN were synthesized and their mesomorphic properties determined by hot stage polarizing microscopy and DSC. When m = 0, all of these compounds showed only a nematic phase except when X = CF 3 when both nematic and smectic A phases were seen. Both clearing and melting temperatures were higher than those reported for substitution with the corresponding alkyl chains but the much larger increase in clearing temperatures produced considerably wider nematic phases. Eutectic mixtures of a few of these olefins yielded nematic materials also having much wider temperature ranges and higher clearing temperatures than the eutectic mixtures of the alkyl compounds, while retaining their high birefringence and low viscosities. Such materials are of interest for beam-steering devices.
Four of the diacetylenes with m = 1 ( A, B = H) were also prepared ( X = C 6 H 13 , F, n = 2, 3). When X was C 6 H 13 ( n = 2), the nematic range was smaller in the 2- than in the 1-olefin but wider than in the alkyl series. When X = F, either no nematic phase or a monotropic one was observed, whereas the 1-olefins gave a much wider nematic phase. Both transition temperatures were lower than those for the corresponding 1-olefin and alkyl analogues. The compound with X = C 6 H 13 and n = 2 had a melting temperature below room temperature. 相似文献
Four of the diacetylenes with m = 1 ( A, B = H) were also prepared ( X = C 6 H 13 , F, n = 2, 3). When X was C 6 H 13 ( n = 2), the nematic range was smaller in the 2- than in the 1-olefin but wider than in the alkyl series. When X = F, either no nematic phase or a monotropic one was observed, whereas the 1-olefins gave a much wider nematic phase. Both transition temperatures were lower than those for the corresponding 1-olefin and alkyl analogues. The compound with X = C 6 H 13 and n = 2 had a melting temperature below room temperature. 相似文献
993.
994.
995.
Peter Amrhein 《Annals of the Institute of Statistical Mathematics》1995,47(1):167-170
Although the theory of rank tests is rather complete in the one-sided case, it was not even known in 1959, whether the Wilcoxon two-sample test and other similar tests are unbiased against the two-sided alternatives (Lehmann (1959,Testing Statistical Hypotheses, p. 240, Wiley, New York)). A partial answer to this question was given by Sugiura in 1965, who found, that the test named above may be biased (Sugiura (1965,Ann. Inst. Statist. Math.,17, 261–263)). According to Lehmann (1986,Testing Statistical Hypotheses, 2nd ed., pp. 322–324, Wiley, New York) it seems to be still open, whether the same is true for the WILCOXON one-sample test, which is also known as WILCOXON signed rank test. This will be shown in the present paper. 相似文献
996.
V. G. Lakhtin V. L. Ryabkov A. V. Kisin V. M. Nosova M. V. Polyakova E. A. Chernyshev 《Russian Chemical Bulletin》1995,44(11):2163-2167
Liquid-phase chlorination of a number of chloro(chlorovinyl)methylsilanes was investigated. A number of novelC-chlorosilanes were characterized by IR and1H NMR spectra. Some regularities of these reactions were determined; correlations between the structure of chloro(chlorovinyl)methylsilanes and their reactivities were identified.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2256–2260, November, 1995. 相似文献
997.
Sans résumé
相似文献
相似文献
998.
A finite element solution of the Navier-Stokes equations for steady flow under the magnetic effect through a double-branched two-dimensional section of a three-dimensional model of the canine aorta is discussed. The numerical scheme involves transforming the physical co-ordinates to a curvilinear boundary-fitted co-ordinate system. The shear stress at the wall is calculated for a Reynolds number of 1000 with the branch-to-main aortic flow rate ratio as a parameter. The results are compared with earlier works involving experimental data and found to be in reasonable qualitative agreement. The steady flow, shear stress and branch flow under the effect of a magnetic field have been discussed in detail. 相似文献
999.
1000.