全文获取类型
收费全文 | 6667篇 |
免费 | 347篇 |
国内免费 | 34篇 |
专业分类
化学 | 5194篇 |
晶体学 | 32篇 |
力学 | 136篇 |
数学 | 714篇 |
物理学 | 972篇 |
出版年
2023年 | 62篇 |
2022年 | 71篇 |
2021年 | 119篇 |
2020年 | 144篇 |
2019年 | 162篇 |
2018年 | 133篇 |
2017年 | 110篇 |
2016年 | 262篇 |
2015年 | 201篇 |
2014年 | 205篇 |
2013年 | 337篇 |
2012年 | 554篇 |
2011年 | 653篇 |
2010年 | 298篇 |
2009年 | 224篇 |
2008年 | 483篇 |
2007年 | 478篇 |
2006年 | 483篇 |
2005年 | 448篇 |
2004年 | 323篇 |
2003年 | 281篇 |
2002年 | 232篇 |
2001年 | 74篇 |
2000年 | 45篇 |
1999年 | 35篇 |
1998年 | 37篇 |
1997年 | 42篇 |
1996年 | 37篇 |
1995年 | 30篇 |
1994年 | 27篇 |
1993年 | 36篇 |
1992年 | 30篇 |
1991年 | 25篇 |
1990年 | 19篇 |
1989年 | 16篇 |
1988年 | 20篇 |
1987年 | 19篇 |
1986年 | 14篇 |
1985年 | 26篇 |
1984年 | 24篇 |
1983年 | 11篇 |
1982年 | 12篇 |
1981年 | 16篇 |
1979年 | 24篇 |
1978年 | 20篇 |
1977年 | 16篇 |
1976年 | 15篇 |
1975年 | 11篇 |
1974年 | 17篇 |
1973年 | 16篇 |
排序方式: 共有7048条查询结果,搜索用时 140 毫秒
31.
A semigroup S is said to have the ideal retraction property provided each of its ideals is the image of an idempotent endomorphism
of S. The main result of this work is a characterization of those bands which have the idempotent retraction property. All
such bands are normal. 相似文献
32.
N J Curtis P J Dortmans J Ciuk 《The Journal of the Operational Research Society》2006,57(11):1300-1312
The essential first step of any OR investigation is to ensure that the ‘right problem’ is studied. Our approach is to propose a set of six ‘rights’ or questions whereby achievement against particular aspects of a problem space is made and these provide the basis for scoping the context, understanding the system, and proposing sound options to the decision-maker. This style of problem structuring is an essential element of the Defence problem domain, and especially so for the Land Force, where there exist multiple degrees of freedom for poorly defined problems in an environment of uncertainty and ambiguity. Central to this is performing conceptual rather than analytical modelling, as perturbations then provide a basis for exploring a space, rather than solving a problem. 相似文献
33.
Xinyu Huang Roham Solasi Yue Zou Matthew Feshler Kenneth Reifsnider David Condit Sergei Burlatsky Thomas Madden 《Journal of Polymer Science.Polymer Physics》2006,44(16):2346-2357
The life of proton exchange membrane fuel cells (PEMFC) is currently limited by the mechanical endurance of polymer electrolyte membranes and membrane electrode assemblies (MEAs). In this paper, the authors report recent experimental and modeling work toward understanding the mechanisms of delayed mechanical failures of polymer electrolyte membranes and MEAs under relevant PEMFC operating conditions. Mechanical breach of membranes/MEAs in the form of pinholes and tears has been frequently observed after long‐term or accelerated testing of PEMFC cells/stacks. Catastrophic failure of cell/stack due to rapid gas crossover shortly follows the mechanical breach. Ex situ mechanical characterizations were performed on MEAs after being subjected to the accelerated chemical aging and relative humidity (RH) cycling tests. The results showed significant reduction of MEA ductility manifested as drastically reduced strain‐to‐failure of the chemically aged and RH‐cycled MEAs. Postmortem analysis revealed the formation and growth of mechanical defects such as cracks and crazing in the membranes and MEAs. A finite element model was used to estimate stress/strain states of an edge‐constrained MEA under rapid RH variations. Damage metrics for accelerated testing and life prediction of PEMFCs are discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2346–2357, 2006 相似文献
34.
Matthew D. Bailey Steven M. Shechter Andrew J. Schaefer 《Operations Research Letters》2006,34(3):307-315
We consider a general adversarial stochastic optimization model. Our model involves the design of a system that an adversary may subsequently attempt to destroy or degrade. We introduce SPAR, which utilizes mixed-integer programming for the design decision and a Markov decision process (MDP) for the modeling of our adversarial phase. 相似文献
35.
Ted K. Ralphs Matthew J. Saltzman Margaret M. Wiecek 《Annals of Operations Research》2006,147(1):43-70
A parametric algorithm for identifying the Pareto set of a biobjective integer program is proposed. The algorithm is based
on the weighted Chebyshev (Tchebycheff) scalarization, and its running time is asymptotically optimal. A number of extensions
are described, including: a technique for handling weakly dominated outcomes, a Pareto set approximation scheme, and an interactive
version that provides access to all Pareto outcomes. Extensive computational tests on instances of the biobjective knapsack
problem and a capacitated network routing problem are presented. 相似文献
36.
Gabriel M. Rebeiz Curtis C. Ling David B. Rutledge 《International Journal of Infrared and Millimeter Waves》1989,10(8):931-936
An accurate monolithic power meter has been developed for millimeter-wave applications. The detector is a large-area Bismuth bolometer, integrated on a fused-Quartz substrate. It simply measures the temperature change caused by the absorption of millimeter-wave radiation. The power meter is simple to fabricate, inexpensive, and can be easily calibrated using a low-frequency network. The measured responsivity for a 50 bolometer, with an area of 1×1cm, at a bias of 1V. and a video modulation of 100Hz, is 1mV/W. The noise spectrum exhibits a 1/f rolloff till 1KHz, and is limited by the Johnson noise for higher frequencies. The NEP of the detector is 3WHz–1/2 at a video modulation of 1KHz. It is possible to decrease the current NEP by fabricating bolometers with higher responsivities. Possible application areas are absolute power calibration and localized power density measurements at millimeter and submillimeter wavelengths. 相似文献
37.
Merkx M Kopp DA Sazinsky MH Blazyk JL Müller J Lippard SJ 《Angewandte Chemie (International ed. in English)》2001,40(15):2725
The cover picture shows in the background the whole cell of a methanotrophic bacterium on which are superimposed components of methane monooxygenase (the structure of the hydroxylase component (top), one of the two four-helix bundles that house the catalytic diiron centers (left)) and a schematic diagram of the catalytic cycle by which the enzyme converts dioxygen and methane into methanol and water. More about this unusual enzyme system is reported by Lippard et al. on p. 2782 ff. 相似文献
38.
39.
Palladium(II)-catalyzed oxidations constitute a paramount reaction class but have remained immature over the past few decades. Recently, this field has reappeared at the forefront of organometallic catalysis. This emerging area article outlines recent developments in palladium(II)-catalyzed oxidation chemistry with discussion of potential future growth. 相似文献
40.