全文获取类型
收费全文 | 1020篇 |
免费 | 70篇 |
国内免费 | 5篇 |
专业分类
化学 | 706篇 |
晶体学 | 7篇 |
力学 | 27篇 |
数学 | 156篇 |
物理学 | 120篇 |
无线电 | 79篇 |
出版年
2023年 | 8篇 |
2021年 | 17篇 |
2020年 | 38篇 |
2019年 | 24篇 |
2018年 | 22篇 |
2017年 | 6篇 |
2016年 | 29篇 |
2015年 | 32篇 |
2014年 | 43篇 |
2013年 | 65篇 |
2012年 | 60篇 |
2011年 | 68篇 |
2010年 | 41篇 |
2009年 | 38篇 |
2008年 | 67篇 |
2007年 | 56篇 |
2006年 | 51篇 |
2005年 | 56篇 |
2004年 | 39篇 |
2003年 | 36篇 |
2002年 | 22篇 |
2001年 | 20篇 |
2000年 | 16篇 |
1999年 | 14篇 |
1998年 | 17篇 |
1997年 | 14篇 |
1996年 | 18篇 |
1995年 | 9篇 |
1994年 | 4篇 |
1993年 | 8篇 |
1992年 | 14篇 |
1991年 | 6篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1984年 | 13篇 |
1983年 | 10篇 |
1982年 | 6篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 3篇 |
1978年 | 7篇 |
1977年 | 9篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1970年 | 4篇 |
排序方式: 共有1095条查询结果,搜索用时 10 毫秒
1.
2.
Maria Chudnovsky Jim Geelen Bert Gerards Luis Goddyn Michael Lohman Paul Seymour 《Combinatorica》2006,26(5):521-532
Let G=(V,E) be an oriented graph whose edges are labelled by the elements of a group Γ and let A⊂V. An A-path is a path whose ends are both in A. The weight of a path P in G is the sum of the group values on forward oriented arcs minus the sum of the backward oriented arcs in P. (If Γ is not abelian, we sum the labels in their order along the path.) We are interested in the maximum number of vertex-disjoint
A-paths each of non-zero weight. When A = V this problem is equivalent to the maximum matching problem. The general case also includes Mader's S-paths problem. We prove that for any positive integer k, either there are k vertex-disjoint A-paths each of non-zero weight, or there is a set of at most 2k −2 vertices that meets each of the non-zero A-paths. This result is obtained as a consequence of an exact min-max theorem.
These results were obtained at a workshop on Structural Graph Theory at the PIMS Institute in Vancouver, Canada. This research
was partially conducted during the period the first author served as a Clay Mathematics Institute Long-Term Prize Fellow. 相似文献
3.
Yu Yang Hugo Bender Kai Arstila Bart Swinnen Bert Verlinden Ingrid De Wolf 《Microelectronics Reliability》2008,48(8-9):1517-1520
Focused ion beam (FIB) and nano-probing were applied for failure analysis of three-dimensional stacked circuits with copper through-silicon-vias between the stacked chips. The failure analysis was done after high temperature storage and thermal cycling tests. Passive voltage contrast in FIB allowed to pinpoint the open sites. FIB cross-sections showed the presence of opens at the bottom of the copper vias. The failure cause was suspected to be an interlayer particle, which was confirmed by optical profilometry. Nano-probing was used on another sample to pinpoint the failure location through the measurement of the local resistance within the daisy chains. The failure was traced out to be related with surface contamination. 相似文献
4.
5.
6.
A trade-off analysis on the cost and system packaging metrics of an electronic product aimed at the commercial/retail industry has been carried out. By comparing the system cost and packaging metrics with those of comparable consumer products, we have determined that there is opportunity for significant cost, size, and weight reduction of the overall electronics packaging system. These include the use of fine pitch IC packages, smaller discrete components, denser PCB wiring technology, double sided IC package surface mount, surface mount connectors, and improved plastics for the product housing. The analysis concluded that PCB area reduction of 40%, using a single PCB instead of three boards, reduction in board cost of over 50% and product weight reduction of over 28% are possible using available technologies. 相似文献
7.
N. A. Cherkashin M. V. Maksimov A. G. Makarov V. A. Shchukin V. M. Ustinov N. V. Lukovskaya Yu. G. Musikhin G. E. Cirlin N. A. Bert Zh. I. Alferov N. N. Ledentsov D. Bimberg 《Semiconductors》2003,37(7):861-865
The effect of the growth temperature on the density, lateral size, and height of InAs-GaAs quantum dots (QD) has been studied by transmission electron microscopy. With the growth temperature increasing from 450 to 520°C, the density and height of QDs decrease, whereas their lateral size increases; i.e., the QDs are flattened. The blue shift of the photoluminescence line indicates decreasing QD volume. The observed behavior is in agreement with the thermodynamic model of QD formation. The effect of lowering the substrate temperature immediately after the formation of QDs on the QD parameters has been studied. On lowering the temperature, the lateral size of QDs decreases and their density increases; i.e., the parameters of QD arrays tend to acquire the equilibrium parameters corresponding at the temperature to which the cooling is done. The QD height rapidly increases with cooling and may exceed the equilibrium value for a finite time of cooling, which enables fabrication of QD arrays with a prescribed ratio between height and lateral size by choosing the time of cooling. 相似文献
8.
9.
10.
VladimirA. Azov Franois Diederich Yoriko Lill Bert Hecht 《Helvetica chimica acta》2003,86(6):2149-2155
We report the synthesis of modified Cram‐type cavitands bearing one or two fluorescent labels for single‐molecule spectroscopic studies of vase? kite conformational switching (Scheme 3). Syntheses were performed by stepwise bridging of the four couples of neighboring H‐bonded OH groups of resorcin[4]arene bowls (Schemes 2 and 3). The new substitution patterns enable the construction of a large variety of future functional architectures. 1H‐NMR Investigations showed that the new partially and differentially bridged cavitands feature temperature‐ and pH‐triggered vase? kite conformational isomerism similar to symmetrical cavitands with four identical quinoxaline bridges (Table). It was discovered that vase? kite switching of cavitands is strongly solvent‐dependent. 相似文献