全文获取类型
收费全文 | 6916篇 |
免费 | 168篇 |
国内免费 | 27篇 |
专业分类
化学 | 4796篇 |
晶体学 | 22篇 |
力学 | 118篇 |
数学 | 1190篇 |
物理学 | 985篇 |
出版年
2020年 | 69篇 |
2019年 | 59篇 |
2016年 | 112篇 |
2015年 | 107篇 |
2014年 | 122篇 |
2013年 | 218篇 |
2012年 | 211篇 |
2011年 | 280篇 |
2010年 | 149篇 |
2009年 | 141篇 |
2008年 | 268篇 |
2007年 | 252篇 |
2006年 | 266篇 |
2005年 | 287篇 |
2004年 | 224篇 |
2003年 | 200篇 |
2002年 | 213篇 |
2001年 | 102篇 |
2000年 | 101篇 |
1999年 | 96篇 |
1998年 | 66篇 |
1997年 | 86篇 |
1996年 | 89篇 |
1995年 | 99篇 |
1994年 | 64篇 |
1993年 | 90篇 |
1992年 | 84篇 |
1991年 | 75篇 |
1990年 | 90篇 |
1989年 | 61篇 |
1988年 | 74篇 |
1987年 | 87篇 |
1986年 | 55篇 |
1985年 | 113篇 |
1984年 | 76篇 |
1983年 | 71篇 |
1982年 | 82篇 |
1981年 | 82篇 |
1980年 | 67篇 |
1979年 | 74篇 |
1978年 | 86篇 |
1977年 | 81篇 |
1976年 | 92篇 |
1975年 | 88篇 |
1974年 | 64篇 |
1973年 | 61篇 |
1971年 | 50篇 |
1970年 | 57篇 |
1967年 | 51篇 |
1966年 | 56篇 |
排序方式: 共有7111条查询结果,搜索用时 15 毫秒
1.
2.
Vereshchagin Anatoly N. Karpenko Kirill A. Elinson Michail N. Minaeva Alexandra P. Goloveshkin Alexander S. Hansford Karl A. Egorov Mikhail P. 《Molecular diversity》2020,24(4):1327-1342
Molecular Diversity - A novel five-component diastereoselective synthesis of polysubstituted 2-piperidinones is reported. The Knoevenagel condensation–Michael addition–Mannich cascade... 相似文献
3.
Dr. Man-Bo Li Daniels Posevins Dr. Karl P. J. Gustafson Dr. Cheuk-Wai Tai Dr. Andrey Shchukarev Dr. Youai Qiu Dr. Jan-E. Bäckvall 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(1):210-215
A highly selective and efficient oxidative carbocyclization/borylation of enallenols catalyzed by palladium immobilized on amino-functionalized siliceous mesocellular foam (Pd-AmP-MCF) was developed for diastereoselective cyclobutenol synthesis. The heterogeneous palladium catalyst can be recovered and recycled without any observed loss of activity or selectivity. The high diastereoselectivity of the reaction is proposed to originate from a directing effect of the enallenol hydroxyl group. Optically pure cyclobutenol synthesis was achieved by the heterogeneous strategy by using chiral enallenol obtained from kinetic resolution. 相似文献
4.
Ralf Freund Christos Allagiannis Peter Schnholzer Karl Bernauer 《Helvetica chimica acta》1994,77(3):615-621
A crude hydrate 6 and a crystalline hemiacetal 7 of glyoxylamide 4 were prepared from crotonamide 5 (Scheme 2). Particularly hemiacetal 7 , but also 6 and the ‘dimer’ 8 (obtained from 7 ) may serve as homochiral auxiliaries. The structure of 8 was determined by X-ray analysis. By arenesulfonyl halides, tryptimines 12–14 of 4 were diastereoselectively transformed into spirotricycles 15–17 and 19 . 相似文献
5.
The rotational spectra of the deuterium cyanide isotopic species DCN, D13CN, DC15N, and D13C15N were recorded in the vibrational ground and first excited bending state (v2=1) up to 2 THz. The R-branch transitions from J=3←2 to J=13←12 were measured with sub-Doppler resolution. These very high resolution (∼70 kHz) and precise (±3-10 kHz) saturation dip measurements allowed for resolving the underlying hyperfine structure due to the 14N nucleus in DCN and D13CN for transitions as high as J=10←9. Additional high JR-branch (J=25←24 to J=28←27) transitions around 2 THz and direct l-type (ΔJ=0, J=19 to J=25) transitions from 66 to 118 GHz were recorded in Doppler-limited resolution. For the ground state of D13C15N, the J=1←0 transition was measured for the first time. The transition frequency accuracies for the other deuterated species were significantly improved. These new experimental data, together with the available infrared rovibrational data and previously measured direct l-type transitions, were subjected to a global least squares analysis for each isotopomer. This yielded precise sets of molecular constants for the ground and first excited vibrational states, including the nuclear quadrupole and magnetic spin-rotation coupling constants of the 14N nucleus for DCN and D13CN. The hyperfine structure due to the D, 13C, and 15N nuclei have not been resolved, but led to a broadening of the observed saturation dips. 相似文献
6.
Karl Peters 《Monatshefte für Chemie / Chemical Monthly》1886,7(1):552-555
Ohne Zusammenfassung 相似文献
7.
Karl Dörge 《Mathematische Annalen》1941,118(1):310-311
Ohne Zusammenfassung 相似文献
8.
9.
Karl Heinrich Weise 《Mathematische Zeitschrift》1938,43(1):469-480
Ohne Zusammenfassung 相似文献
10.
Karl Gustafson 《Numerical Linear Algebra with Applications》2004,11(7):649-659
Given the operator product BA in which both A and B are symmetric positive‐definite operators, for which symmetric positive‐definite operators C is BA symmetric positive‐definite in the C inner product 〈x, y〉C? This question arises naturally in preconditioned iterative solution methods, and will be answered completely here. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献