全文获取类型
收费全文 | 45033篇 |
免费 | 9756篇 |
国内免费 | 1433篇 |
专业分类
化学 | 46620篇 |
晶体学 | 405篇 |
力学 | 819篇 |
数学 | 3672篇 |
物理学 | 4706篇 |
出版年
2022年 | 100篇 |
2021年 | 283篇 |
2020年 | 1364篇 |
2019年 | 2709篇 |
2018年 | 1132篇 |
2017年 | 749篇 |
2016年 | 3551篇 |
2015年 | 3665篇 |
2014年 | 3590篇 |
2013年 | 4616篇 |
2012年 | 3309篇 |
2011年 | 2628篇 |
2010年 | 3158篇 |
2009年 | 3075篇 |
2008年 | 2759篇 |
2007年 | 2107篇 |
2006年 | 1807篇 |
2005年 | 1945篇 |
2004年 | 1764篇 |
2003年 | 1572篇 |
2002年 | 2249篇 |
2001年 | 1545篇 |
2000年 | 1442篇 |
1999年 | 493篇 |
1998年 | 154篇 |
1997年 | 173篇 |
1996年 | 188篇 |
1995年 | 129篇 |
1994年 | 130篇 |
1993年 | 167篇 |
1992年 | 163篇 |
1991年 | 163篇 |
1990年 | 123篇 |
1989年 | 126篇 |
1988年 | 137篇 |
1987年 | 184篇 |
1986年 | 152篇 |
1985年 | 199篇 |
1984年 | 191篇 |
1983年 | 148篇 |
1982年 | 170篇 |
1981年 | 177篇 |
1980年 | 172篇 |
1979年 | 172篇 |
1978年 | 168篇 |
1977年 | 164篇 |
1976年 | 142篇 |
1975年 | 161篇 |
1974年 | 130篇 |
1973年 | 124篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
Beyond Stereoselectivity,Switchable Catalysis: Some of the Last Frontier Challenges in Ring‐Opening Polymerization of Cyclic Esters 下载免费PDF全文
Dr. Sophie M. Guillaume Dr. Evgueni Kirillov Dr. Yann Sarazin Prof. Dr. Jean‐François Carpentier 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(22):7988-8003
Metal‐based catalysts and initiators have played a pivotal role in the ring‐opening polymerization (ROP) of cyclic esters, thanks to their high activity and remarkable ability to control precisely the architectures of the resulting polyesters in terms of molar mass, dispersity, microstructure, or tacticity. Today, after two decades of extensive research, the field is slowly reaching maturity. However, several challenges remain, while original concepts have emerged around new types or new applications of catalysis. This Review is not intended to comprehensively cover all of these aspects. Rather, it provides a personal overview of the very recent progress achieved in some selected, important aspects of ROP catalysis—stereocontrol and switchable catalysis. Hence, the first part addresses the development of new metal‐based catalysts for the isoselective ROP of racemic lactide towards stereoblock copolymers, and the use of syndioselective ROP metal catalysts to control the monomer sequence in copolymers. A second part covers the development of ROP catalysts—primarily metal‐based catalysts, but also organocatalysts—that can be externally regulated by the use of chemical or photo stimuli to switch them between two states with different catalytic abilities. Current challenges and opportunities are highlighted. 相似文献
42.
43.
44.
45.
46.
47.
Hendrik Van Maldeghem 《Journal of Geometry》1997,58(1-2):192-202
We characterize in a geometrical way those Suzuki-Tits ovoids which are defined over a perfect fieidK (or equivalently living inside a self polar symplectic quadrangle). We simplify our axioms in the particular cases that (1) the associated Suzuki group has exactly two orbits in the set of lines ofPG(3,K), and (2) the ovoid is finite.Senior Research Associate at the Belgian National Fund for Scientific Research 相似文献
48.
Photobleaching was studied during recording of confocal scanning laser microscopy. Studies on fluorescent gels of FITC-labeled
dextran were used to evaluate differential bleaching along thez-axis. Differential bleaching along the z-axis was observed and it was seen that this was related to the numerical aperture
of the objective in use. This points to the conclusion that photon energy flux density is an important parameter in photobleaching.
To check if photon energy flux density heterogeneity is affected by local variation in the refractive index of the sample,
photobleaching rates were calculated for different fluorescent objects (sections of seeds, animal cells stained with nuclear
stains, immunocytochemistry preparations) and a pronounced similarity was found between photobleaching rates and DIC images. 相似文献
49.
C. Daum L. Hertzberger W. Hoogland R. Jongerius S. Peters P. Van Deurzen V. Chabaud A. Gonzalez-Arroyo B. Hyams H. Tiecke P. Weilhammer A. Dwurazny G. Polok M. Rozanska K. Rybicki M. Turala J. Turnau G. Ascoli H. Backer G. Blanar M. Cerrada H. Dietl J. Gallivan M. Glaubmann R. Klanner E. Lorenz G. Lütjens G. Lutz W. Männer U. Stierlin I. Blakey M. Bowler R. Cashmore J. Loken W. Spalding G. Thompson B. Alper C. Damerell A. Gillman C. Hardwick M. Hotchkiss F. Wickens ACCMOR Collaboration 《Zeitschrift fur Physik C Particles and Fields》1981,10(2):95-100
Muon electron pairs were detected in an Al multiplate spark chamber, exposed to a neutrino beam from the CERN PS. The leptons were not accompanied by other particles, except occasionally by protons. The background came mainly from muon associated π0 production, with one decay gamma lost. It was determined empirically, together with the small contribution from υ e reactions. For electron energies above 2 GeV the background is 5.7±1.5 events, whereas 18 (μe)-candidates have been observed. Hence the effect is established, with a rate of about 10?4 as compared to the muonic reactions above 3 GeV. Charm creation as the origin of this (μe)-production process is excluded; heavy neutral lepton production does not fit the kinematics observed. Instead the events are compatible with the two-body decay of an object with variable invariant mass of order 1 GeV, possibly resulting from axion interactions. 相似文献
50.