全文获取类型
收费全文 | 437198篇 |
免费 | 3413篇 |
国内免费 | 1197篇 |
专业分类
化学 | 234858篇 |
晶体学 | 6719篇 |
力学 | 18992篇 |
综合类 | 15篇 |
数学 | 50488篇 |
物理学 | 130736篇 |
出版年
2019年 | 4018篇 |
2018年 | 5556篇 |
2017年 | 5464篇 |
2016年 | 7806篇 |
2015年 | 4567篇 |
2014年 | 7309篇 |
2013年 | 18198篇 |
2012年 | 13571篇 |
2011年 | 16559篇 |
2010年 | 11793篇 |
2009年 | 11508篇 |
2008年 | 15672篇 |
2007年 | 15924篇 |
2006年 | 14864篇 |
2005年 | 13452篇 |
2004年 | 12123篇 |
2003年 | 11052篇 |
2002年 | 10939篇 |
2001年 | 11814篇 |
2000年 | 9289篇 |
1999年 | 7098篇 |
1998年 | 6232篇 |
1997年 | 6250篇 |
1996年 | 5856篇 |
1995年 | 5165篇 |
1994年 | 5359篇 |
1993年 | 5116篇 |
1992年 | 5682篇 |
1991年 | 5707篇 |
1990年 | 5593篇 |
1989年 | 5427篇 |
1988年 | 5465篇 |
1987年 | 5355篇 |
1986年 | 5118篇 |
1985年 | 6770篇 |
1984年 | 7129篇 |
1983年 | 5858篇 |
1982年 | 6255篇 |
1981年 | 6070篇 |
1980年 | 5842篇 |
1979年 | 6024篇 |
1978年 | 6390篇 |
1977年 | 6315篇 |
1976年 | 6377篇 |
1975年 | 5954篇 |
1974年 | 5994篇 |
1973年 | 6282篇 |
1972年 | 4392篇 |
1971年 | 3722篇 |
1967年 | 3695篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Daria E. Lonsdale Geoffrey Johnston‐Hall Amanda Fawcett Craig A. Bell Carl N. Urbani Michael R. Whittaker Michael J. Monteiro 《Journal of polymer science. Part A, Polymer chemistry》2007,45(16):3620-3625
In this work, we propose that retardation in vinyl acetate polymerization rate in the presence of toluene is due to degradative chain transfer. The transfer constant to toluene (Ctrs) determined using the Mayo method is equal to 3.8 × 10?3, which is remarkably similar to the value calculated from the rate data, assuming degradative chain transfer (2.7 × 10?3). Simulations, including chain‐length‐dependent termination, were carried out to compare our degradative chain transfer model with experimental results. The conversion–time profiles showed excellent agreement between experiment and simulation. Good agreement was found for the Mn data as a function of conversion. The experimental and simulation data strongly support the postulate that degradative chain transfer is the dominant kinetic mechanism. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3620–3625, 2007 相似文献
122.
Bahattin Gümgüm Nermin Biricik Feyyaz Durap Ismail Özdemir Nevin Gürbüz Wee Han Ang Paul J. Dyson 《应用有机金属化学》2007,21(8):711-715
Palladium(II) complexes with N,N‐bis(diphenylphosphino)aniline ligands catalyse the Heck reaction between styrene and aryl bromides, affording stilbenes in good yield. The structures of two of the complexes used as pre‐catalysts have been determined by single‐crystal X‐ray diffraction. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
123.
A modernized conception of hierarchical structure of reality is proposed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 3–6, December, 1980. 相似文献
124.
125.
Pál Sohár Gábor Bernáth Géza Stájer Angela E. Szabo 《Magnetic resonance in chemistry : MRC》1989,27(9):872-876
Pentacyclic isoxazolines were obtained by the cycloaddition of benzonitrile oxide to norbornene-azetidinone-fused 3,1-oxazines. The constitutions of two of the isomers obtained, and the configurations and conformations of all products, were determined by means of 1H and 13C NMR spectroscopy and DNOE experiments. 相似文献
126.
127.
Lerner E.J. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1989,17(2):259-263
A cosmological model is presented that produces He, C, O, D, Li, Be, and B in their observed abundances without a Big Bang. The elements are produced during the 1.5-Gy formation period of a galaxy, with C, O, and other heavy elements produced by stars of M >12 M3 , He by stars of 6 Ms<M <12 Ms, and D, Li, Be, and B by cosmic-ray reactions in a nearly pure H plasma halo. Thus, the model shows that the major elements used in astrophysical studies can be produced during galactic formation by exactly the same processes known to function today at much lower rates 相似文献
128.
E. Goering M. Justen J. Geissler U. Rüdiger M. Rabe G. Güntherodt G. Schütz 《Applied Physics A: Materials Science & Processing》2002,74(6):747-753
Highly a-axis-textured CrO2 films have been deposited on Al2O3 (0001) substrates by chemical vapor deposition. CrO2 has been found to have highly a-axis (010)-oriented columnar growth on a Cr2O3 (0001) initial layer. The six-fold surface symmetry of the Cr2O3 initial layer leads to three equivalent in-plane orientations of the a-axis-oriented CrO2 unit cell. We report Cr L2,3 X-ray magnetic circular dichroism data along the surface normal and at 60° off-normal sample orientation. For a 60° sample
alignment, a strong increase of the projected orbital moment could be observed for unoccupied majority t2g states using moment analysis. Therefore, the c axis is identified as the intrinsic magnetic easy axis of CrO2. In addition, a small spin moment and a very strong magnetic dipole term Tz have been found.
Received: 8 January 2002 / Accepted: 8 January 2002 相似文献
129.
The long-range sound propagation from a deep ocean to a receiving system located on the shelf is modeled. The waveguide model is constructed on the basis of the data of an acoustic-oceanographic experiment carried out in the northwestern Pacific. The sensitivity and the frequency dependence of the difference in the sound field levels at the crossing of the frontal zone on the geoacoustic characteristics of the bottom of the shelf and the continental slope are investigated. It is shown that the level difference decreases by 8.2 dB as the velocity of longitudinal waves increases by 100 m/s in the range within 1490–1820 m/s. 相似文献
130.