全文获取类型
收费全文 | 4966篇 |
免费 | 119篇 |
国内免费 | 6篇 |
专业分类
化学 | 3938篇 |
晶体学 | 7篇 |
力学 | 42篇 |
数学 | 638篇 |
物理学 | 466篇 |
出版年
2019年 | 40篇 |
2018年 | 37篇 |
2017年 | 27篇 |
2016年 | 101篇 |
2015年 | 67篇 |
2014年 | 100篇 |
2013年 | 142篇 |
2012年 | 150篇 |
2011年 | 158篇 |
2010年 | 134篇 |
2009年 | 119篇 |
2008年 | 162篇 |
2007年 | 159篇 |
2006年 | 179篇 |
2005年 | 198篇 |
2004年 | 167篇 |
2003年 | 139篇 |
2002年 | 181篇 |
2001年 | 115篇 |
2000年 | 107篇 |
1999年 | 105篇 |
1998年 | 85篇 |
1997年 | 95篇 |
1996年 | 96篇 |
1995年 | 76篇 |
1994年 | 88篇 |
1993年 | 90篇 |
1992年 | 92篇 |
1991年 | 86篇 |
1990年 | 67篇 |
1989年 | 89篇 |
1988年 | 87篇 |
1987年 | 84篇 |
1986年 | 71篇 |
1985年 | 96篇 |
1984年 | 111篇 |
1983年 | 62篇 |
1982年 | 86篇 |
1981年 | 112篇 |
1980年 | 83篇 |
1979年 | 101篇 |
1978年 | 68篇 |
1977年 | 68篇 |
1976年 | 60篇 |
1975年 | 78篇 |
1974年 | 50篇 |
1973年 | 71篇 |
1972年 | 51篇 |
1971年 | 43篇 |
1970年 | 52篇 |
排序方式: 共有5091条查询结果,搜索用时 15 毫秒
111.
Priority queueing systems come natural when customers with diversified delay requirements have to wait to get service. The
customers that cannot tolerate but small delays get service priority over customers which are less delay-sensitive. In this
contribution, we analyze a discrete-time two-class preemptive repeat identical priority queue with infinite buffer space and
generally distributed service times. Newly arriving high-priority customers interrupt the on-going service of a low-priority
customer. After all high-priority customers have left the system, the interrupted service of the low-priority customer has
to be repeated completely. By means of a probability generating functions approach, we analyze the system content and the
delay of both types of customers. Performance measures (such as means and variances) are calculated and the impact of the
priority scheduling is discussed by means of some numerical examples. 相似文献
112.
We establish lower bounds on the matching number of graphs of given odd regularity d and odd girth g, which are sharp for many values of d and g. For d=g=5, we characterize all extremal graphs. 相似文献
113.
Mirjam Witthaut Rainer Cremer Klaus Reichert Dieter Neuschütz 《Mikrochimica acta》2000,133(1-4):191-196
(Al,Cr)2O3 layers were deposited on cemented carbide insert tips at a substrate temperature of 500 °C by means of reactive magnetron
sputtering. An Al target was sputtered in RF mode and a Cr target in DC mode simultaneously in an oxygen/argon plasma. The
influence of the Al and Cr sputter power and of the oxygen partial pressure on composition and structure of the (Al,Cr)2O3 layers as well as on the binding states of their components were investigated.
Special attention was paid to the interpretation of the O ls and O-KLL fine structure and peak shifts. For the binary phases
γ-Al2O3 and Cr2O3, a good agreement with literature values was observed in each case. In case of the ternary phases a continuous shift of the
energetic position of the O1s peak, the O-KL23L23 transition and the modified Auger parameter α ′ of oxygen between the two binary phases γ-Al2O3 and Cr2O3 could be detected, indicating a wide range of solid solubility between Al2O3 and Cr2O3. As revealed by grazing incidence X-ray diffraction, the crystallinity of the ternary phases is less pronounced as compared
to the binaries and increases with increasing oxygen flow rate. 相似文献
114.
115.
116.
Gerasko OA Mainicheva EA Naumova MI Neumaier M Kappes MM Lebedkin S Fenske D Fedin VP 《Inorganic chemistry》2008,47(19):8869-8880
Sandwich-type lanthanide complexes with macrocyclic ligand cucurbit[6]uril (C 36H 36N 24O 12, CB[6]) were synthesized under hydrothermal conditions from aqueous solutions of lanthanide(III) bromides, CB[6], and 4-cyanopyridine. According to X-ray analysis (Ln = La, Pr, Dy, Ho, Er, and Yb), the compounds with different structural types of lanthanide cores have a common fragment where the tetranuclear hydroxo complex is sandwiched between two macrocycles {(IN@CB[6])Ln 4(mu 3-OH) 4(IN@CB[6])} (6+) (IN = isonicotinate). The photoluminescence (for Ln = Eu) and Fourier transform ion cyclotron resonance mass spectra (for Ln = Pr, Dy, and Er) were studied. The compounds are used for the first time as precursors for the synthesis of lanthanide-silver heterometallic coordination polymers. The chainlike crystal structure of polymers (Ln = La, Pr, and Dy) is constituted by the sandwich complexes linked via the coordination of IN nitrogen atoms to the silver atoms. 相似文献
117.
Biopolymers represent an interesting class of polymers whose potential is not yet been fully realised. However, more recently, biopolymers are gaining impetus in the market. Among the biopolymers, polylactic acid (PLA) is being used successfully and is widely accepted because it is produced from natural raw material and is degradable. Furthermore, it has comparable properties to standard thermoplastic polymers and can also be processed using similar process channels as conventional thermoplastic synthetic materials. Biopolymer applications are manifold and range from foils, fruit and vegetable packaging to hygiene and medical products. It can be expected that in future the application spectrum of biopolymers will increase even further. 相似文献
118.
119.
Renate Borowski Dieter Rehder Klaus von Deuten 《Journal of organometallic chemistry》1981,220(1):45-54
Photo-reaction between the ligands Ph2ECH2EPh2 (E = P: dppm, E = As: dpam, E = Sb: dpsm), L, and the vanadium complexes η5-C5H5V(CO)4 and [Et4N][V(CO)6] yields monosubstituted mononuclear (dpsm) and dinuclear, ligand-bridged complexes (dpam, dpsm). With dppm, the final products are disubstituted chelate complexes, but monosubstituted mono- and dinuclear species are formed as intermediates.The shielding of the 51V nucleus decreases in the series dpsm > dppm > dpam and {M(CO)n} > {M(CO)n?1} L > {M(CO)n?1}2μ-L > {M(CO)n?2}dppm ({M(CO)n}[V(CO)6]?, η5-C5H5V(CO)4). The half-widths of the NMR signals are greater for dinuclear than for mononuclear complexes.The crystal and molecular structures of η5-C5H5V(CO)3As2Ph4 have been determined. The compound crystallizes in the space group P21/c with a = 1347.8, b = 1020.0, c = 2085.2 pm and β = 82.3°. Due to steric crowding, the 51V shielding is low composed to that of {η5-C5H5V(CO)3}2μ-dpam. 相似文献
120.
Ren Amstutz W. Bernd Schweizer Dieter Seebach Jack D. Dunitz 《Helvetica chimica acta》1981,64(8):2617-2621
The structures of the crystalline lithium enolates derived from 3, 3-dimethyl-2-butanone and from cyclopentanone have been determined by X-ray analysis. Both structures are tetrameric aggregates based on a Li4O4-cube, each Li+-ion being additionally bonded to the O-atom of a tetrahydrofuran solvent molecule. 相似文献