全文获取类型
收费全文 | 7594篇 |
免费 | 177篇 |
国内免费 | 53篇 |
专业分类
化学 | 4954篇 |
晶体学 | 61篇 |
力学 | 250篇 |
数学 | 825篇 |
物理学 | 1734篇 |
出版年
2022年 | 78篇 |
2021年 | 80篇 |
2020年 | 117篇 |
2019年 | 120篇 |
2018年 | 85篇 |
2017年 | 81篇 |
2016年 | 178篇 |
2015年 | 119篇 |
2014年 | 154篇 |
2013年 | 336篇 |
2012年 | 344篇 |
2011年 | 417篇 |
2010年 | 227篇 |
2009年 | 174篇 |
2008年 | 355篇 |
2007年 | 408篇 |
2006年 | 368篇 |
2005年 | 339篇 |
2004年 | 289篇 |
2003年 | 282篇 |
2002年 | 230篇 |
2001年 | 157篇 |
2000年 | 168篇 |
1999年 | 111篇 |
1998年 | 84篇 |
1997年 | 93篇 |
1996年 | 131篇 |
1995年 | 82篇 |
1994年 | 76篇 |
1993年 | 100篇 |
1992年 | 99篇 |
1991年 | 84篇 |
1990年 | 78篇 |
1989年 | 74篇 |
1988年 | 103篇 |
1987年 | 77篇 |
1986年 | 73篇 |
1985年 | 101篇 |
1984年 | 96篇 |
1983年 | 52篇 |
1982年 | 77篇 |
1981年 | 85篇 |
1980年 | 72篇 |
1979年 | 88篇 |
1978年 | 69篇 |
1977年 | 93篇 |
1976年 | 78篇 |
1975年 | 69篇 |
1974年 | 76篇 |
1973年 | 73篇 |
排序方式: 共有7824条查询结果,搜索用时 15 毫秒
1.
An optimal control model of exhaustible resources is used to clarify the long run relationship between mineral rent and depletion cost at the industry level. A standard first order condition of the time rate of change of rents is reformulated to reveal that rent data may be used to help forecast the rise in extraction costs resulting from resource depletion. This application of the theory of exhaustible resources is illustrated using historical mineral industry rent and extraction cost data. A forecast of U.S. coal extraction costs, following the method proposed in this paper, suggests that future rates of extraction cost increases will be similar to rates experienced in the past. 相似文献
2.
We analyze diffusion from a periodic array of hemispherical droplets through a membrane. We find that the multiple sources do not interact strongly, even when the droplets are closely spaced, so that the flux through the membrane appears nearly additive. 相似文献
3.
The basic features of a chemical measurement 总被引:2,自引:0,他引:2
4.
5.
D. Ohlberg J.J. Blackstock R. Ragan S. Kim R. Stanley Williams 《Applied Physics A: Materials Science & Processing》2005,80(6):1327-1334
A recently demonstrated [1] in-vacuo template-stripping process is applied to the study of platinum films stripped from ultra-flat silicon-oxide surfaces. Template-stripped (TS) Pt surfaces, prepared with a range of post-deposition annealing times prior to being stripped from the templating surface in an ultra-high vacuum (UHV) environment, are examined by UHV scanning tunneling microscopy (STM). These studies reveal that without post-deposition annealing, TS Pt surfaces are largely made up of poorly-ordered, granular nanostructures undesirable for many applications. The post-deposition annealing treatments explored in the study result in the emergence and continuous growth of large smooth crystallites. Issues with crystallite orientation relative to the TS surface and artefacts arising as a result of the epoxy used in the template-stripping process are presented and discussed in relation to optimizing the template-stripping procedure for specific applications such as self-assembled monolayer (SAM) formation for molecular electronics. PACS 68.37.Ef; 68.47.De; 68.55.Jk; 81.05.Bx; 81.15.Ef 相似文献
6.
Alex Hellsten 《Archive for Mathematical Logic》2006,45(6):705-714
We extract some properties of Mahlo’s operation and show that some other very natural operations share these properties. The weakly compact sets form a similar hierarchy as the stationary sets. The height of this hierarchy is a large cardinal property connected to saturation properties of the weakly compact ideal. 相似文献
7.
Frank H.G.M. Wijnands Charles G. Crookes Paul M. Charles Richard M. Ash Ian F. Lealman Michael J. Robertson Anthony E. Kelly Kevin A. Williams Aeneas B. Massara Richard V. Penty Ian H. White 《Optical and Quantum Electronics》2002,34(10):959-973
An anomalous modulation in the wavelength spectrum has been observed in lasers with spot-size converters. This intensity modulation is shown to be caused by beating between the fundamental lasing mode and radiation modes in the taper. This results in a periodic modulation in the net gain spectrum, which causes wavelength jumps between adjacent net gain maxima, and a drive current dependent spectral width that is expected to affect system performance. The amplitude of this spectral modulation is reduced significantly by either using an angled rear-facet which reflects the beating radiation modes away from the laser axis, or by using a nonlinear, adiabatic taper. 相似文献
8.
Yiming Huai Mahendra PakalaZhitao Diao Dmytro ApalkovYunfei Ding Alex Panchula 《Journal of magnetism and magnetic materials》2006
Spin-transfer driven switching was observed in MgO based magnetic tunnelling junctions (MTJ) with tunnelling magnetoresistance ratio of up to 160% and the average intrinsic switching current density (Jc0) down to 2 MA/cm2, which are the best known results reported in spin-transfer switched MTJ nanostructures. Based on a comparison of results both from MgO and AlOx MTJs, further switching current decrease via MgO dual structures with two pinned layers is discussed. 相似文献
9.
The stannous chloride dihydrate-mediated deprotection-bicyclisation of a range of amides possessing a pendant acetal group is reported. These mild reaction conditions have been used to prepare a number of ring-fused heterocyclic compounds, some in enantiomerically pure form, which should be of interest both in their own right and as building blocks for the production of more complex target molecules. 相似文献
10.
We study property (T) and the fixed-point property for actions on L
p
and other Banach spaces. We show that property (T) holds when L
2 is replaced by L
p
(and even a subspace/quotient of L
p
), and that in fact it is independent of 1≤p<∞. We show that the fixed-point property for L
p
follows from property (T) when 1<p< 2+ε. For simple Lie groups and their lattices, we prove that the fixed-point property for L
p
holds for any 1< p<∞ if and only if the rank is at least two. Finally, we obtain a superrigidity result for actions of irreducible lattices
in products of general groups on superreflexive spaces.
Bader partially supported by ISF grant 100146; Furman partially supported by NSF grants DMS-0094245 and DMS-0604611; Gelander
partially supported by NSF grant DMS-0404557 and BSF grant 2004010; Monod partially supported by FNS (CH) and NSF (US). 相似文献