全文获取类型
收费全文 | 6282篇 |
免费 | 166篇 |
国内免费 | 15篇 |
专业分类
化学 | 4906篇 |
晶体学 | 70篇 |
力学 | 58篇 |
数学 | 314篇 |
物理学 | 1115篇 |
出版年
2023年 | 37篇 |
2022年 | 43篇 |
2021年 | 64篇 |
2020年 | 104篇 |
2019年 | 93篇 |
2018年 | 75篇 |
2017年 | 48篇 |
2016年 | 129篇 |
2015年 | 103篇 |
2014年 | 160篇 |
2013年 | 288篇 |
2012年 | 323篇 |
2011年 | 441篇 |
2010年 | 192篇 |
2009年 | 208篇 |
2008年 | 368篇 |
2007年 | 369篇 |
2006年 | 366篇 |
2005年 | 394篇 |
2004年 | 322篇 |
2003年 | 256篇 |
2002年 | 267篇 |
2001年 | 153篇 |
2000年 | 169篇 |
1999年 | 67篇 |
1998年 | 64篇 |
1997年 | 56篇 |
1996年 | 84篇 |
1995年 | 48篇 |
1994年 | 65篇 |
1993年 | 47篇 |
1992年 | 65篇 |
1991年 | 53篇 |
1990年 | 51篇 |
1989年 | 46篇 |
1988年 | 57篇 |
1987年 | 46篇 |
1986年 | 62篇 |
1985年 | 68篇 |
1984年 | 71篇 |
1983年 | 46篇 |
1982年 | 52篇 |
1981年 | 43篇 |
1980年 | 47篇 |
1979年 | 42篇 |
1978年 | 36篇 |
1977年 | 33篇 |
1976年 | 25篇 |
1975年 | 40篇 |
1974年 | 32篇 |
排序方式: 共有6463条查询结果,搜索用时 78 毫秒
981.
We demonstrate that ultrasmall double-layer photonic-crystal-slab cavities exhibit a very high-Q value for a wide range of the layer spacing, which enables us to realize unique optomechanical coupling. By mechanically varying the separation, we can achieve extraordinarily large wavelength conversion. In addition, the light stored in the cavity can generate a large radiation force. We show that this system exhibits extremely high energy conversion efficiency between optical and mechanical energy, leading to a novel approach for the optomechanical control of light and matter. 相似文献
982.
Tojo S Kitagawa M Enomoto K Kato Y Takasu Y Kumakura M Takahashi Y 《Physical review letters》2006,96(15):153201
We observed high-resolution photoassociation spectra of laser-cooled ytterbium (Yb) atoms in the spin-forbidden 1S0 - 3P1 intercombination line. The rovibrational levels in the 0u+ state were measured for red detunings of the photoassociation laser ranging from 2.9 MHz to 1.97 GHz with respect to the atomic resonance. The rotational splitting of the vibrational levels near the dissociation limit were fully resolved due to the sub-MHz linewidth of the spectra in contrast to previous measurements using the spin-allowed singlet transition. In addition, from a comparison between the spectra of 174Yb and those of 176Yb, a d-wave shape resonance for 174Yb is strongly suggested. 相似文献
983.
N,N‐Di(arenesulfonyl)‐N′,N′‐dimethyl‐hydrazines, readily prepared from arenesulfonyl chlorides and N,N‐dimethylhydrazine, were heated at 120°C in chlorobenzene to give S‐aryl arenethiosulfonates, ArSSO2Ar, in good yields. 相似文献
984.
Kenichi Imaeda Hiroo Inokuchi Kenji Ichimura Shinichi Inoue Satoshi Nakakita Hiroshi Okamoto 《Molecular Crystals and Liquid Crystals》2013,570(1):667-670
Abstract Solid state 1H NMR of (KH)3C60 was measured in the temperature range between ?80 and 60 °C. A doublet spectrum composed of main peak at ?7.0 ppm and shoulder peak at ~0 ppm was observed at room temperature. The negative chemical shift of the main peak indicates that hydrogen in (KH)3C60 exists as a hydride-like ion. The 60 °C spectrum became singlet at ?5.8 ppm due to motional narrowing. 相似文献
985.
Tomohiro Sato Katsuyoshi Ito Tsutomu Tamada Akihiko Kanki Shigeru Watanabe Hirotake Nishimura Daigo Tanimoto Hiroki Higashi Akira Yamamoto 《Magnetic resonance imaging》2013,31(8):1412-1417
ObjectivesTo quantify tissue gadolinium (Gd) deposition in renally impaired rats exposed to Gd-EOB-DTPA and other Gd-based MRI contrast agents by means of inductively coupled plasma mass spectrometry (ICP-MS), and to compare the differences in distribution among major organs as possible triggers for nephrogenic systemic fibrosis (NSF).MethodsA total of 15 renally impaired rats were injected with Gd-EOB-DTPA, Gd-DTPA-BMA and Gd-HP-DO3A. Gd contents of skin, liver, kidney, lung, heart, spleen, diaphragm and femoral muscle were measured by inductively coupled plasma mass spectrometry (ICP-MS). Histological assessment was also conducted.ResultsTissue Gd deposition in all organs was significantly higher (P = 0.005 ~ 0.009) in the Gd-DTPA-BMA group than in the Gd-HP-DO3A and Gd-EOB-DTPA groups. In the Gd-DTPA-BMA group, Gd was predominantly deposited in kidney (1306 ± 605.7 μg/g), followed by skin, liver, lung, spleen, femoral muscle, diaphragm and heart. Comparing Gd-HP-DO3A and Gd-EOB-DTPA groups, Gd depositions in the kidney, liver and lung were significantly lower (P = 0.009 ~ 0.011) in the Gd-EOB-DTPA group than in the Gd-HP-DO3A group although no significant differences were seen for any other organs.ConclusionsGd-EOB-DTPA is a stable and safe Gd-based contrast agent (GBCA) showing lower Gd deposition in major organs in renally impaired rats, compared with other GBCAs. This fact suggests that the risk of NSF onset would be low in the use of Gd-EOB-DTPA. 相似文献
986.
Satoshi Kakihara Atsumi Ohara Takashi Tsuchiya 《Journal of Optimization Theory and Applications》2013,157(3):749-780
We develop an information geometric approach to conic programming. Information geometry is a differential geometric framework specifically tailored to deal with convexity, naturally arising in information science including statistics, machine learning and signal processing etc. First we introduce an information geometric framework of conic programming. Then we focus on semidefinite and symmetric cone programs. Recently, we demonstrated that the number of iterations of Mizuno–Todd–Ye predictor–corrector primal–dual interior-point methods is (asymptotically) expressed with an integral over the central trajectory called “the curvature integral”. The number of iterations of the algorithm is approximated surprisingly well with the integral even for fairly large linear/semidefinite programs with thousands of variables. Here we prove that “the curvature integral” admits a rigorous differential geometric expression based on information geometry. We also obtain an interesting information geometric global theorem on the central trajectory for linear programs. Together with the numerical evidence in the aforementioned work, we claim that “the number of iterations of the interior-point algorithm is expressed as a differential geometric quantity.” 相似文献
987.
Necessary conditions for optimal control problems with state-control variable inequality constraints are obtained via mathematical programming formulation and functional analysis in Banach space. These conditions are general ones that hold without any constraint qualifications but differentiability. Furthermore, these conditions are shown to be equivalent to the classical result in the presence of the linear independence constraint qualification. 相似文献
988.
Y.?IzumidaEmail author N.?Ito 《The European Physical Journal B - Condensed Matter and Complex Systems》2013,86(10):431
We perform a molecular dynamics computer simulation of a heat engine model to study how the engine size difference affects its performance. Upon tactically increasing the size of the model anisotropically, we determine that there exists an optimum size at which the model attains the maximum power for the shortest working period. This optimum size locates between the ballistic heat transport region and the diffusive heat transport one. We also study the size dependence of the efficiency at the maximum power. Interestingly, we find that the efficiency at the maximum power around the optimum size attains a value that has been proposed as a universal upper bound, and it even begins to exceed the bound as the size further increases. We explain this behavior of the efficiency at maximum power by using a linear response theory for the heat engine operating under a finite working period, which naturally extends the low-dissipation Carnot cycle model [M. Esposito, R. Kawai, K. Lindenberg, C. Van den Broeck, Phys. Rev. Lett. 105, 150603 (2010)]. The theory also shows that the efficiency at the maximum power under an extreme condition may reach the Carnot efficiency in principle. 相似文献
989.
Takaaki Takatsuka Hideki Tomita Tetsu Sonoda Volker Sonnenschein Chika Sakamoto Hiroki Mita Takuma Noto Chikara Ito Shigetaka Maeda Tetsuo Iguchi Michiharu Wada Klaus Wendt Iain Moore 《Hyperfine Interactions》2013,216(1-3):41-46
93Nb(n, n′)93mNb reaction allows retrospective estimation of integrated fast neutron dose in nuclear reactor. We proposed isomer-selective trace analysis of 93mNb by Resonance Ionization Mass Spectrometry (RIMS) combined with a gas-jet atomic source and an injection locked Ti:Sapphire laser system operated at several kHz. Resonant ionization spectroscopy of Nb in gas-jet using Ti:Sapphire laser was demonstrated. 相似文献
990.
K. Miki A. Tamii N. Aoi T. Fukui T. Hashimoto K. Hatanaka T. Ito T. Kawabata H. Matsubara K. Ogata H. J. Ong H. Sakaguchi S. Sakaguchi T. Suzuki J. Tanaka I. Tanihata T. Uesaka T. Yamamoto 《Few-Body Systems》2013,54(7-10):1353-1356
Tensor correlations in 4He were studied via the (p, dp) reaction at the incident energy of 392 MeV with a focus on spin configurations of correlated pn pairs in 4He at high relative momenta ${(P_{\rm rel}^{\rm cor})}$ . The preliminary results show that the correlated pn pair at ${P_{\rm rel}^{\rm cor} = 310 {\rm MeV/c}}$ predominantly has the channel spin S = 1, which is consistent with the characteristics of tensor correlations. 相似文献