全文获取类型
收费全文 | 1623篇 |
免费 | 70篇 |
国内免费 | 166篇 |
专业分类
化学 | 1036篇 |
晶体学 | 18篇 |
力学 | 52篇 |
综合类 | 13篇 |
数学 | 277篇 |
物理学 | 463篇 |
出版年
2022年 | 16篇 |
2021年 | 23篇 |
2020年 | 19篇 |
2019年 | 23篇 |
2017年 | 22篇 |
2016年 | 27篇 |
2015年 | 32篇 |
2014年 | 51篇 |
2013年 | 98篇 |
2012年 | 72篇 |
2011年 | 101篇 |
2010年 | 48篇 |
2009年 | 54篇 |
2008年 | 83篇 |
2007年 | 81篇 |
2006年 | 91篇 |
2005年 | 93篇 |
2004年 | 72篇 |
2003年 | 80篇 |
2002年 | 51篇 |
2001年 | 44篇 |
2000年 | 30篇 |
1999年 | 21篇 |
1998年 | 16篇 |
1997年 | 13篇 |
1996年 | 30篇 |
1995年 | 23篇 |
1994年 | 23篇 |
1993年 | 23篇 |
1992年 | 23篇 |
1991年 | 20篇 |
1990年 | 19篇 |
1989年 | 19篇 |
1988年 | 24篇 |
1987年 | 15篇 |
1986年 | 21篇 |
1985年 | 29篇 |
1984年 | 26篇 |
1983年 | 14篇 |
1982年 | 15篇 |
1981年 | 17篇 |
1980年 | 13篇 |
1979年 | 20篇 |
1978年 | 19篇 |
1977年 | 19篇 |
1976年 | 27篇 |
1975年 | 25篇 |
1974年 | 21篇 |
1973年 | 17篇 |
1970年 | 10篇 |
排序方式: 共有1859条查询结果,搜索用时 62 毫秒
991.
Yuh HY Kaye SM Levinton FM Mazzucato E Mikkelsen DR Smith DR Bell RE Hosea JC LeBlanc BP Peterson JL Park HK Lee W 《Physical review letters》2011,106(5):055003
Negative magnetic shear is found to suppress electron turbulence and improve electron thermal transport for plasmas in the National Spherical Torus Experiment (NSTX). Sufficiently negative magnetic shear results in a transition out of a stiff profile regime. Density fluctuation measurements from high-k microwave scattering are verified to be the electron temperature gradient (ETG) mode by matching measured rest frequency and linear growth rate to gyrokinetic calculations. Fluctuation suppression under negligible E×B shear conditions confirm that negative magnetic shear alone is sufficient for ETG suppression. Measured electron temperature gradients can significantly exceed ETG critical gradients with ETG mode activity reduced to intermittent bursts, while electron thermal diffusivity improves to below 0.1?electron gyro-Bohms. 相似文献
992.
Glenzer SH MacGowan BJ Meezan NB Adams PA Alfonso JB Alger ET Alherz Z Alvarez LF Alvarez SS Amick PV Andersson KS Andrews SD Antonini GJ Arnold PA Atkinson DP Auyang L Azevedo SG Balaoing BN Baltz JA Barbosa F Bardsley GW Barker DA Barnes AI Baron A Beeler RG Beeman BV Belk LR Bell JC Bell PM Berger RL Bergonia MA Bernardez LJ Berzins LV Bettenhausen RC Bezerides L Bhandarkar SD Bishop CL Bond EJ Bopp DR Borgman JA Bower JR Bowers GA Bowers MW Boyle DT Bradley DK Bragg JL Braucht J 《Physical review letters》2011,106(8):085004
We demonstrate the hohlraum radiation temperature and symmetry required for ignition-scale inertial confinement fusion capsule implosions. Cryogenic gas-filled hohlraums with 2.2 mm-diameter capsules are heated with unprecedented laser energies of 1.2 MJ delivered by 192 ultraviolet laser beams on the National Ignition Facility. Laser backscatter measurements show that these hohlraums absorb 87% to 91% of the incident laser power resulting in peak radiation temperatures of T(RAD)=300 eV and a symmetric implosion to a 100 μm diameter hot core. 相似文献
993.
Guttenfelder W Candy J Kaye SM Nevins WM Wang E Bell RE Hammett GW LeBlanc BP Mikkelsen DR Yuh H 《Physical review letters》2011,106(15):155004
This Letter presents nonlinear gyrokinetic simulations of microtearing mode turbulence. The simulations include collisional and electromagnetic effects and use experimental parameters from a high-β discharge in the National Spherical Torus Experiment. The predicted electron thermal transport is comparable to that given by experimental analysis, and it is dominated by the electromagnetic contribution of electrons free-streaming along the resulting stochastic magnetic field line trajectories. Experimental values of flow shear can significantly reduce the predicted transport. 相似文献
994.
995.
Capdevila-Cortada M Novoa JJ Bell JD Moore CE Rheingold AL Miller JS 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(34):9326-9341
The α, β, and δ polymorphs of [TTF][TCNE] (TTF=tetrathiafulvalene; TCNE=tetracyanoethylene) exhibit a new type of long, multicenter bonding between the [TTF]δ+ and [TCNE]δ? moieties, demonstrating the existence of long, hetero‐multicenter bonding with a cationicδ+???anionicδ? zwitterionic‐like structure. These diamagnetic π‐[TTF]δ+[TCNE]δ? heterodimers exhibit a transfer of about 0.5 e? from the TTF to the TCNE fragments, as observed from experimental studies, in accord with theoretical predictions, that is, [TTFδ+???TCNEδ?] (δ?0.5). They have several interfragment distances <3.4 Å, and a computed interaction energy of ?21.2 kcal mol?1, which is typical of long, multicenter bonds. The lower stability of [TTF]δ+[TCNE]δ? with respect to typical ionic bonds is due, in part, to the partial electron transfer that reduces the electrostatic bonding component. This reduced electrostatic interaction, and the large interfragment dispersion stabilize the long, heterocationic/anionic multicenter interaction, which in [TTFδ+???TCNEδ?] always involves two electrons, but have ten, eight, and eight bond critical points (bcps) involving C? C, N? S, and sometimes C? S and C? N components for the α, β, and δ polymorphs, respectively. In contrast, γ‐[TTF][TCNE] possesses [TTF]22+ and [TCNE]22? dimers, each with long, homo‐multicenter 2e?/12c (c=center, 2 C+4 S) [TTF]22+ cationic+???cationic+ bonds, as well as long, homo‐multicenter 2e?/4c [TCNE]22? anionic????anionic? bonding. The MO diagrams for the α, β, and δ polymorphs have all of the features found for conventional covalent C? C bonds, and for all of the previously studied multicenter long bonds, for example, π‐[TTF]22+ and π‐[TCNE]22?. The HOMOs for α‐, β‐, and δ‐[TTF][TCNE] have 2c C? S and 3c C? C? C orbital‐overlap contributions between the [TTF]δ+? and [TCNE]δ? moieties; these are the shortest intra [TTF???TCNE] separations. Thus, from an orbital‐overlap perspective, the bonding has 2c and 3c components residing over one S and four C atoms. 相似文献
996.
研究了Fabry-Perot光学腔中包含一个光学参量放大器来增强腔场与机械振子之间的耦合的光机械动力学行为.在解析边带机制下用量子郎之万方程具体研究了振子的涨落光谱、光学多稳态行为、机械阻尼与修正共振频移和基态冷却,通过数值解讨论了辐射压力诱导机械振子和腔场的稳态振幅所展现的光学多稳态行为,同时也分析了辐射压力引起的修... 相似文献
997.
Mukundan Shilpaa Bell Jordan Teryek Matthew Hernandez Charles Love Andrea C. Parekkadan Biju Chan Leo Li-Ying 《Journal of fluorescence》2022,32(2):521-531
Journal of Fluorescence - Tumor spheroid models have proven useful in the study of cancer cell responses to chemotherapeutic compounds by more closely mimicking the 3-dimensional nature of tumors... 相似文献
998.
在高超声速静音风洞内, 通过基于纳米粒子示踪的平面激光散射(nano-tracer-based planar laser scattering, NPLS)技术、高频压力传感器和温敏漆(temperature sensitive paints, TSP)技术开展了0°攻角条件下7°直圆锥高超声速边界层转捩相关实验研究, 得到了圆锥边界层由层流发展至湍流完整过程的NPLS图像, 清晰地展示了第2模态波的"绳状"结构, 尖锥与钝锥边界层的NPLS结果表明尖锥边界层转捩中第2模态波占主导, 而钝锥边界层在转捩前出现波长约为第2模态波波长5倍(甚至更长)、特征频率不高于31 kHz的狭长涡结构; 采用功率谱密度(power spectrum density, PSD)分析、互相关和N值计算对高频脉动压力数据进行分析, 得到了边界层内扰动波的发展规律, 在尖锥和钝锥中均观察到了沿流向第2模态波幅值先增大后减小、特征频率逐渐降低, 低频成分逐渐增加, 表明边界层发展过程中第2模态率先发展达到饱和, 而后逐渐衰减, 而低频模态则逐渐发展; 通过TSP技术得到了不同单位Reynolds数下的圆锥表面温升分布, 结果表明, 随单位Reynolds数增大, 边界层转捩阵面前移. 相似文献
999.
In problem structuring methods, facilitators often ask of themselves questions such as: what makes a ‘good’ problem structuring group (PSG) and indeed what does ‘good’ mean? How can group dynamics be improved and does it matter in terms of the quality of the problem structuring that that group engages in? On the surface these questions seem to be straightforward. Indeed, those who have helped facilitate many participatory workshops will think they intuitively know the answers to these questions; they can, from their professional practice, ‘feel’ which PSGs are doing well and producing novel insights and those which are functioning less well and perhaps generating something that is less imaginative and more routine as a consequence. The intuitive, practice-learned insight will depend upon a rich array of visual signals that become more obvious with experience. This paper asks whether there is value in being much more open and analytical about these questions and answers. If so, then how can we make the unwritten processes and outcomes of PSGs written? Indeed, open to whom? Finally, how much of any insights learned by facilitators should be shared with those engaged in workshops? 相似文献
1000.
金瓷修复体兼具金属强度及陶瓷美观的优点,在口腔医学上得到了广泛应用,但临床上时有发生脱瓷并且又多发生在界面处,针对这种情况,通过研究不同层厚比的金瓷修复体试件梁的界面力学行为,以分析其破坏机理。采用云纹干涉法和电子散斑法对界面具有缺陷形式的试件进行了实验研究。得到裂纹尖端及界面处的位移场,计算了界面断裂强度等参量,并给出了试件制备、实验方法。实验结果表明不同层厚比的试件以及不同界面缺陷形式的试件对抵抗破坏能力均有不同影响;现代光力学实验方法对研究具有小变形的双材料结构力学行为可行、有效。 相似文献