全文获取类型
收费全文 | 2396篇 |
免费 | 95篇 |
国内免费 | 4篇 |
专业分类
化学 | 1768篇 |
晶体学 | 11篇 |
力学 | 77篇 |
数学 | 242篇 |
物理学 | 397篇 |
出版年
2023年 | 24篇 |
2022年 | 23篇 |
2021年 | 35篇 |
2020年 | 33篇 |
2019年 | 39篇 |
2018年 | 33篇 |
2017年 | 17篇 |
2016年 | 67篇 |
2015年 | 55篇 |
2014年 | 59篇 |
2013年 | 127篇 |
2012年 | 101篇 |
2011年 | 129篇 |
2010年 | 93篇 |
2009年 | 56篇 |
2008年 | 111篇 |
2007年 | 118篇 |
2006年 | 105篇 |
2005年 | 124篇 |
2004年 | 78篇 |
2003年 | 87篇 |
2002年 | 55篇 |
2001年 | 50篇 |
2000年 | 36篇 |
1999年 | 18篇 |
1998年 | 27篇 |
1997年 | 13篇 |
1996年 | 36篇 |
1995年 | 35篇 |
1994年 | 32篇 |
1993年 | 38篇 |
1992年 | 25篇 |
1991年 | 25篇 |
1990年 | 25篇 |
1989年 | 23篇 |
1988年 | 19篇 |
1987年 | 22篇 |
1986年 | 16篇 |
1985年 | 30篇 |
1984年 | 24篇 |
1983年 | 19篇 |
1982年 | 24篇 |
1981年 | 16篇 |
1980年 | 18篇 |
1978年 | 16篇 |
1977年 | 19篇 |
1967年 | 16篇 |
1966年 | 20篇 |
1965年 | 39篇 |
1964年 | 45篇 |
排序方式: 共有2495条查询结果,搜索用时 15 毫秒
41.
The possibility of lasing without inversion on the 1079.8 nm line of a HeNe laser is investigated. It is shown that a modified double- scheme can be realized by use of the 877.9 nm line for introducing Zeeman coherence. It is shown experimentally that Zeeman coherence can enforce laser action, even if the inversion is below threshold. A different choice of the polarization of the driving beam can result in suppression of laser action above threshold. The underlying mechanisms are examined. On the 611.8 nm line, laser action below threshold inversion is obtained with the driving beam tuned to 824.9 nm (up-conversion). 相似文献
42.
S. N. Tskhai Yu. B. Udalov P. J. M. Peters W. J. Witteman V. N. Ochkin 《Applied physics. B, Lasers and optics》1996,62(1):11-14
A radiofrequency excited atomic Xe slab laser with an active volume of 2 × 10 × 300 mm3 using a quartz envelope containing the laser-gas mixture shows a stable cw performance with an output power of almost 1 W. The free-running system oscillates, depending on gas composition and density, on several lines between 1.73 and 3.51 m. Line competition phenomena are observed. Single-line oscillation yields more than 500 mW. 相似文献
43.
44.
Jeroen Kuipers 《Mathematical Methods of Operations Research》1993,38(2):131-139
LetN=1,2,...,n be a set of customers andG=(N {0},E) an undirected connected graph with non-negative edge lengths. 0 is the home location of a salesman who visits the customers inN. Each subset
can invite the salesman to visit its members only. The costc(S) of coalitionS is the length of a shortest tour that starts in 0, visits each customer inS at least once and returns to 0. The cooperative cost game defined in this way is called a (symmetric) traveling salesman game (TSG).The core of a TSG can be empty when ¦N¦ 6 and it was proved that it always has a non-empty core when ¦N¦ 4. In this note we shall prove that a TSG always has a non-empty core when ¦N¦=5. 相似文献
45.
46.
47.
de Loos F Reynhout IC Cornelissen JJ Rowan AE Nolte RJ 《Chemical communications (Cambridge, England)》2005,(1):60-62
A series of mono-functionalized metallo-porphyrin polystyrenes have been synthesized using atom transfer radical polymerization and their self-assembling behavior was studied by electron microscopy showing that the polystyrene tail-length influences the aggregate architecture. 相似文献
48.
103Rh NMR Spectroscopic Evidence of Mixed Nonahalogenodirhodates(III), [Rh2ClnBr9–n]3?, n = 0–9 On heating a mixture of the tetrabutylammonium salts (TBA)3[Rh2Cl9] and (TBA)3[Rh2Br9] at 60°C in propylenecarbonate the complete system of the mixed nonahalogenodirhodates(III) [Rh2ClnBr9–n]3?, n = 0–9 is formed. In the 103Rh nmr spectra 40 different species have been detected, 16 with two equivalent 103Rh atoms each resulting in one singlet and 24 with inequivalent 103Rh atoms each pair giving two resonances. The signals of the geometric isomeres are not resolved. All 64 expected resonances are really observed. By additional measuring of the 103Rh nmr spectra of the fractions n = 0–4 separable by ion exchange chromatography on DEAE cellulose, and utilizing characteristic increments of chemical shifts the complete and unambiguous assignment of all signals is achieved. 相似文献
49.
Dan Peters Anna-Britta Hrnfeldt Salo Gronowitz 《Journal of heterocyclic chemistry》1991,28(6):1629-1631
5-Cyclopropyluracil and cyclopropylcytosine were prepared by the Pd(0)-catalyzed coupling reaction of 5-bromo-2,4-di(trimethylsilyloxy)pyrimidine and 5-bromo-2,4-O,N-bis-trimethylsilylcytosine with tributylstan-nylcyclopropane. The reactions also gave dehalogenated pyrimidine bases as by-products. Attempts to use 2,4-O,N-bis-trimethylsilyl-5-iodocytosine as the halide gave complete dehalogenation. 相似文献
50.
Tromp M van Bokhoven JA Arink AM Bitter JH van Koten G Koningsberger DC 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(24):5667-5678
Herein we describe a structural characterisation with EXAFS of copper(I) arenethiolate complexes in both the solid and liquid state. Previously noted difficulties in the detection of the Cu-Cu interaction have been attributed to anti-phase behaviour of different Cu-Cu neighbour contributions. A data analysis procedure solely based on EXAFS parameters is presented which resolves these problems. A careful analysis of the individual coordination shells and the use of different k-weightings during the data analysis are shown to be an absolute necessity to obtain reliable results. During R-space fitting, the difference file technique is used to separate, examine and compare the individual contributions. Using this technique their statistical significance and correctness can be determined. Anti-phase behaviour can be detected and accounted for in this way. An additional mixed organocopper aggregate [Cu4(SAr)2(Mes)2] with different Cu sites is analysed, which proves the value of the analysis procedure described above. Moreover, this newly developed EXAFS data analysis procedure is applicable to any other EXAFS spectrum obtained. The structural analysis of these organocopper complexes with EXAFS provides information about their actual structure and dynamic behaviour in solution. The technique can now be used to obtain insights into the reactivity of these complexes and the way in which they form catalytic reaction intermediates. 相似文献