全文获取类型
收费全文 | 406502篇 |
免费 | 4252篇 |
国内免费 | 1020篇 |
专业分类
化学 | 192891篇 |
晶体学 | 4609篇 |
力学 | 21296篇 |
综合类 | 6篇 |
数学 | 79154篇 |
物理学 | 113818篇 |
出版年
2021年 | 2237篇 |
2020年 | 2693篇 |
2019年 | 2972篇 |
2018年 | 19468篇 |
2017年 | 19766篇 |
2016年 | 13979篇 |
2015年 | 5257篇 |
2014年 | 5739篇 |
2013年 | 12798篇 |
2012年 | 16898篇 |
2011年 | 30316篇 |
2010年 | 18485篇 |
2009年 | 18455篇 |
2008年 | 25258篇 |
2007年 | 29873篇 |
2006年 | 10744篇 |
2005年 | 16445篇 |
2004年 | 12600篇 |
2003年 | 12127篇 |
2002年 | 9187篇 |
2001年 | 7094篇 |
2000年 | 5893篇 |
1999年 | 4115篇 |
1998年 | 3596篇 |
1997年 | 3550篇 |
1996年 | 3582篇 |
1995年 | 2809篇 |
1994年 | 2885篇 |
1993年 | 2948篇 |
1992年 | 3060篇 |
1991年 | 3025篇 |
1990年 | 2896篇 |
1989年 | 2867篇 |
1988年 | 2780篇 |
1987年 | 2769篇 |
1986年 | 2648篇 |
1985年 | 3476篇 |
1984年 | 3625篇 |
1983年 | 2861篇 |
1982年 | 3217篇 |
1981年 | 3093篇 |
1980年 | 2854篇 |
1979年 | 3069篇 |
1978年 | 3172篇 |
1977年 | 3075篇 |
1976年 | 3113篇 |
1975年 | 2943篇 |
1974年 | 2919篇 |
1973年 | 3111篇 |
1972年 | 1993篇 |
排序方式: 共有10000条查询结果,搜索用时 390 毫秒
981.
982.
V. O. Kur'yanov T. F. Zhelobetskaya A. E. Zemlyakov V. Ya. Chirva 《Chemistry of Natural Compounds》1993,29(1):103-106
The synthesis has been effected of derivatives of MDP having a spacer with an amino or carboxy group. The final stage of the synthesis was the condensation of Boc-L-Ala-D-iGln with 6-aminohexanol (followed by the two-stage replacement of the hydroxy by an azido group) or with benzyl 6-aminohexanoate.Simferopol' State University. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 122–125, January–February, 1993. 相似文献
983.
O. A. Rakitin E. A. Khaibullina T. I. Godovikova V. A. Ogurtsov L. I. Khimel'nitskii 《Chemistry of Heterocyclic Compounds》1993,29(8):952-954
Previously unreported furoxanenitrolic acids have been synthesized.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1117–1119, August, 1993. 相似文献
984.
985.
Yu. V. Belovitskaya I. V. Pekov E. R. Gobechiya N. A. Yamnova Yu. K. Kabalov N. V. Chukanov J. Schneider 《Crystallography Reports》2002,47(2):223-228
The crystal structures of two ancylite specimens from Khibiny massif (the Kola Peninsula, Russia)—ancylite-(Ce) from alkali hydrothermalites (Sr1.01Ca0.02Ba0.01)Σ1.04(Ce0.52La0.28Nd0.11Pr0.04 Sm0.01)Σ0.96(CO3)2(OH0.83F0.13)Σ0.96 · 0.9H2O and ancylite-(Ce) from carbonatites—have (Sr0.80Ca0.05Ba0.01)Σ0.86(Ce0.62La0.40Nd0.09Pr0.03) Σ1.14(CO3)2(OH0.99F0.15)Σ1.14 · 1.0H2O been refined by the Rietveld method. A focusing STOE-STADIP diffractometer with a bent Ge(111) primary monochromator was used (λ MoK α 1 radiation, 2.16° < 2θ < 54.98°; reflection number 237–437). All the computations for ancylite from alkali hydrothermalites were performed within the sp. gr. Pmc21, a = 5.0634(1) Å, b = 8.5898(1) Å, c = 7.2781(1) Å, V = 316.55(1) Å3, R wp = 1.90; the computations for ancylite from carbonatites were performed within the sp. gr. Pmcn, a = 5.0577(1) Å, b = 8.5665(2) Å, c = 7.3151(2) Å, V = 316.94(1) Å3, R wp = 2.38 in the anisotropic approximation of thermal vibrations of cations and oxygen atoms. 相似文献
986.
A generalization of strong regularity around a vertex subset C of a graph Γ, which makes sense even if Γis non-regular, is studied. Such a structure appears, together with a kind of distance-regularity around C , when an spectral bound concerning the so-called predistance polynomial of C is attained. As a main consequence of these results, it is shown that a regular (connected) graph Γwith d + 1 distinct eigenvalues is distance-regular, and its distance- d graph Γ d is strongly regular with parameters a = c , if and only if the number of vertices at distance d from each vertex satisfies an expression which depends only on the order of Γand the different eigenvalues of Γ. 相似文献
987.
The results of Monte Carlo simulations of the beta dose rate to enamel are presented. The dose rates are the most comprehensive to date, incorporating the beta spectrum from 21 different radionuclides, all internal conversion and Auger electrons, the majority of the bremsstrahlung radiation, effects due to radon loss in the uranium series, and variations in the moisture content of the sediment. Applications to a new dating technique in archaeology using electron spin resonance and beta-gradient isochrons are discussed. 相似文献
988.
K. Venkatakrishnan B.K.A. Ngoi P. Stanley L.E.N. Lim B. Tan N.R. Sivakumar 《Applied Physics A: Materials Science & Processing》2002,75(4):493-496
Photomasks are the backbone of microfabrication industries. Currently they are fabricated by a lithographic process, which
is very expensive and time consuming since it is a multi-step process. These issues can be addressed by fabricating photomasks
by direct femtosecond laser writing, which is a single-step process and comparatively cheaper and faster than lithography.
In this paper we discuss our investigations on the effect of two types of laser writing techniques, namely front- and rear-side
laser writing, with regard to the feature size and the edge quality of a feature. It is proved conclusively that for the patterning
of masks, front-side laser writing is a better technique than rear-side laser writing with regard to smaller feature size
and better edge quality. Moreover the energy required for front-side laser writing is considerably lower than that for rear-side
laser writing.
Received: 22 May 2001 / Accepted: 14 September 2001 / Published online: 17 October 2001 相似文献
989.
990.
S. Kwieciński M. Weychert A. Jasiński P. Kulinowski I. Wawer E. Sieradzki 《Applied magnetic resonance》2002,22(1):23-29
The disintegration of bromhexin tablets was monitored by magnetic resonance imaging. The fast imaging method FLASH with spoiling
gradients was used to obtain images of the tablets in short time intervals. The rate of the disintegration depends on the
preparation method, kind and percentage of the carrier (polyethylene glycol, lactose). Solid dispersion with slow evaporation
of solvent yields materials with decreased dissolution rate. Increasing molecular mass of polyethylene glycol and its percentage
content also hampers disintegration. 相似文献