全文获取类型
收费全文 | 220727篇 |
免费 | 2980篇 |
国内免费 | 1319篇 |
专业分类
化学 | 122793篇 |
晶体学 | 3228篇 |
力学 | 8889篇 |
综合类 | 61篇 |
数学 | 24371篇 |
物理学 | 65684篇 |
出版年
2020年 | 1754篇 |
2019年 | 1896篇 |
2018年 | 2483篇 |
2017年 | 2532篇 |
2016年 | 3647篇 |
2015年 | 2425篇 |
2014年 | 3539篇 |
2013年 | 8876篇 |
2012年 | 7690篇 |
2011年 | 9398篇 |
2010年 | 6654篇 |
2009年 | 6454篇 |
2008年 | 8795篇 |
2007年 | 8913篇 |
2006年 | 8386篇 |
2005年 | 7714篇 |
2004年 | 6874篇 |
2003年 | 6061篇 |
2002年 | 5987篇 |
2001年 | 6703篇 |
2000年 | 5067篇 |
1999年 | 3673篇 |
1998年 | 3038篇 |
1997年 | 3009篇 |
1996年 | 3012篇 |
1995年 | 2620篇 |
1994年 | 2719篇 |
1993年 | 2582篇 |
1992年 | 2829篇 |
1991年 | 2894篇 |
1990年 | 2703篇 |
1989年 | 2617篇 |
1988年 | 2558篇 |
1987年 | 2498篇 |
1986年 | 2520篇 |
1985年 | 3300篇 |
1984年 | 3360篇 |
1983年 | 2804篇 |
1982年 | 3047篇 |
1981年 | 2811篇 |
1980年 | 2607篇 |
1979年 | 2790篇 |
1978年 | 2996篇 |
1977年 | 3032篇 |
1976年 | 3059篇 |
1975年 | 2793篇 |
1974年 | 2906篇 |
1973年 | 2956篇 |
1972年 | 2318篇 |
1971年 | 1845篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
121.
(S)-2-[2-(p-Tolylsulfinyl)phenyl]acetaldehyde reacts with different O-silylated ketenethioacetals in the presence of Yb(OTf)3 yielding β-hydroxythioesters in high yields and diastereoselectivities. The obtained compounds were readily transformed into β-hydroxyacids and their corresponding diols. These Mukaiyama aldol reactions are a direct evidence of the ability of the sulfinyl group to control 1,5- and 1,6-asymmetric induction processes. 相似文献
122.
F. Chen L. Liu Z. Shen G.Q. Xu T.S.A. Hor 《Applied Physics A: Materials Science & Processing》2002,74(2):317-319
Free-standing and supported hydrogenated amorphous carbon films (a:C–H) were prepared upon pyrolysis of the polymer formed
by ethanolamine (EA) and citric acid (CA), under an ambient atmosphere at 300 °C. EA facilitates the formation of the macroscopic
films, while CA is essential for obtaining the a:C–H microstructure, which comprises a mixture of sp2 and sp3 carbon.
Received: 29 May 2001 / Accepted: 17 August 2001 / Published online: 20 December 2001 相似文献
123.
An overview of theoretical and experimental studies of the coherent type-B e
+
e-pair production by photons in aligned crystals performed at Nuclear Physics Institute at Tomsk Polytechnic University is given. 相似文献
124.
N. L. Dmitruk O. Yu. Borkovskaya R. V. Konakova I. B. Mamontova S. V. Mamykin D. I. Voitsikhovskiy 《Technical Physics》2002,47(6):698-702
The effect of 60Co gamma irradiation at doses of 103-2×105 Gy on the photoconversion and dark I-V characteristics of Au/GaAs surface-barrier solar cells (SCs) is studied. The morphology of the interface microrelief is varied
to reach the highest photoconversion efficiency. Of the two types of microrelief morphology (dendritic and quasi-grating)
obtained by the chemical anisotropic etching of n-(100)GaAs, the latter is more promising, particularly for SCs designed for space application, since the associated SCs offer
higher efficiency and radiation resistance. 相似文献
125.
126.
127.
We analyze diffusion from a periodic array of hemispherical droplets through a membrane. We find that the multiple sources do not interact strongly, even when the droplets are closely spaced, so that the flux through the membrane appears nearly additive. 相似文献
128.
129.
130.
E. N. Sobol’ O. I. Baum A. V. Bol’shunov V. I. Sipliviy N. Yu. Ignat’eva O. L. Zakharkina V. V. Lunin A. I. Omel’chenko V. A. Kamenskiy A. V. Myakov 《Laser Physics》2006,16(5):735-740
A new approach to alterations in eye refraction upon nondestructive laser action on the sclera and cornea is studied. It is demonstrated in in vivo experiments on rabbit eyes that sequential laser irradiation of the sclera and cornea yields a significant alteration in the eye refraction. The collagen structure of the sclera and cornea is studied after the nondestructive laser action with noninvasive polarization-sensitive optical coherence tomography. It is demonstrated that collagen fibers that provide for the cornea tension and applanation partially survive in the zone of the local denaturation of sclera. An irradiation mode that corresponds to an increase in the cornea’s plasticity and does not cause visible structural changes is chosen. The simplest theoretical model for alterations in the eye refraction upon the nonablative laser action on sclera is analyzed. The alteration in the cornea curvature upon stretching resulting from the local sclera coagulation and the corresponding decrease in its volume is calculated. The model makes it possible to approximately estimate the laser irradiation modes that provide the desired alterations in eye refraction. 相似文献