全文获取类型
收费全文 | 1246篇 |
免费 | 119篇 |
国内免费 | 105篇 |
专业分类
化学 | 352篇 |
晶体学 | 58篇 |
力学 | 43篇 |
综合类 | 12篇 |
数学 | 17篇 |
物理学 | 484篇 |
综合类 | 504篇 |
出版年
2024年 | 2篇 |
2023年 | 10篇 |
2022年 | 23篇 |
2021年 | 11篇 |
2020年 | 15篇 |
2019年 | 19篇 |
2018年 | 20篇 |
2017年 | 41篇 |
2016年 | 47篇 |
2015年 | 51篇 |
2014年 | 58篇 |
2013年 | 120篇 |
2012年 | 98篇 |
2011年 | 76篇 |
2010年 | 71篇 |
2009年 | 72篇 |
2008年 | 85篇 |
2007年 | 70篇 |
2006年 | 88篇 |
2005年 | 60篇 |
2004年 | 44篇 |
2003年 | 41篇 |
2002年 | 54篇 |
2001年 | 23篇 |
2000年 | 37篇 |
1999年 | 30篇 |
1998年 | 17篇 |
1997年 | 24篇 |
1996年 | 11篇 |
1995年 | 12篇 |
1994年 | 21篇 |
1993年 | 16篇 |
1992年 | 13篇 |
1991年 | 12篇 |
1990年 | 11篇 |
1989年 | 13篇 |
1988年 | 16篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
排序方式: 共有1470条查询结果,搜索用时 15 毫秒
991.
《Physics and Chemistry of Liquids》2012,50(2):215-220
Precise densities and viscosities at 298.15, 303.15, and 308.15?K for solutions of nicotine in water and in 0.02?mmol aqueous ethyl alcohol were measured for limiting apparent molal volume and B-coefficients calculations, respectively. These data are rationalized to illustrate hydrophilic and hydrophobic interactions between various functional groups present in these solutions. 相似文献
992.
Hiromichi Kamo Takayuki IsonoKazuyuki Takahashi Hatsumi Mori 《Tetrahedron letters》2012,53(33):4385-4388
Catechol-fused tetrathiafulvalene (TTF) derivatives have been designed and synthesized as a new type of π-electron donor molecules having two phenolic hydroxyl groups. Cyclic voltammetry measurements and quantum chemical calculations demonstrated the electronic effect of the direct fusion of the catechol unit to the TTF π-skeleton. In the charge-transfer (CT) salts with bromide or chloride anions, a one-dimensional hydrogen-bonded chain was formed by the intermolecular OH?X network between the catechol moieties and the halide anions. The slight dissimilarity of the hydrogen-bond distances for the two CT salts gave rise to the significant differences in their overall molecular arrangements and intermolecular interactions as well as the electrical resistivities. 相似文献
993.
应用在位电阻率测量方法研究高压下锐钛矿TiO2的电学性质。通过研究电阻率随压力变化的异常变化点,观察到了TiO2从锐钛矿-柯铁矿-斜锆石的相变。卸压后,电阻率数值和初始值相差2个数量级,说明该相变为不可逆相变。结合第一性原理计算结果表明,柯铁矿结构更小的带隙是导致TiO2电阻率减小的根本原因。 相似文献
994.
Chao Ma Yan-jun Li Chun-shu Pan He Wang Jian Wang Shi-yue Chen Jian-ping Lu 《Magnetic resonance imaging》2014
Diffusion weighted magnetic resonance imaging (DWI) has been mostly acquired using single-shot echo-planar imaging (ss EPI) to minimize motion induced artifacts. The spatial resolution, however, is inherently limited in ss EPI especially for abdominal imaging, even with the advances in parallel imaging. A novel method of reduced Field of View ss EPI (rFOV ss EPI) has achieved high resolution DWI in human carotid artery, spinal cord with reduced blurring and higher spatial resolution than conventional ss EPI, but it has not been used to pancreas imaging. In the work, comparisons between the full FOV ss-DW EPI and rFOV ss-DW EPI in image qualities and ADC values of pancreatic tumors and normal pancreatic tissues were performed to demonstrate the feasibility of pancreatic high resolution rFOV DWI. There were no significant differences in the mean ADC values between full FOV DWI and rFOV DWI for the 17 subjects using b = 600 s/mm2 (P = 0.962). However, subjective scores of image quality was significantly higher at rFOV ss DWI (P = 0.008 and 0.000 for b-value = 0 s/mm2 and 600 s/mm2 respectively). The spatial resolution of DWI for pancreas was increased by a factor of over 2.0 (from almost 3.0 mm/pixel to 1.25 mm/pixel) using rFOV ss EPI technique. Reduced FOV ss EPI can provide good DW images and is promising to benefit applications for pancreatic diseases. 相似文献
995.
A.L. Nikolaev 《哲学杂志》2013,93(12):1017-1033
Electrical resistivity recovery (RR) data for irradiated concentrated alloys typically consist of two inseparable parts, one resulting from defect annihilation and the other from short-range order (SRO) effects. These parts exhibit different behaviour and often follow opposite trends. Therefore, in this case, analysis of RR data within the conventional method is too complicated. A new approach to data analysis of such a two-component RR is proposed. The approach involves a new quantity, the difference RR (DRR), which is composed of RR dependences of two similar samples irradiated to different defect concentrations. It is shown that the SRO formation proper and the stages corresponding to the onset of long-range migration of Frenkel pair defects, formed in each part of RR, can be clearly related to certain features of the DRR plots. This interrelationship allows detecting and identifying these stages in each part of RR separately. The validity of the approach is illustrated by analysis of the available pairwise RR data for Fe–16Cr–20Ni and Fe–4Cr alloys. It makes it possible to detect the small contribution from the SRO formation to RR in Fe–4Cr, which we failed to observe previously. It is shown that stage III of Fe–4Cr, which has a negligible contribution to the part of RR induced by defect annihilation, is clearly observed in the part induced by SRO formation. 相似文献
996.
G. T. Condo 《辐射效应与固体损伤》2013,168(2):125-126
Abstract It is shown that the use of negative muons as solid state probes is complicated by the de-excitation scheme of muonic atoms. A comparison with some recent radiation damage experiments suggest that the μ? atom (at least in silicon) is displaced to an interstitial position. 相似文献
997.
Alloys of composition Sn–8.5Sb–5.5Cu (in atomic percent) were rapidly solidified by a melt-spinning technique. The samples were irradiated at room temperature with GeV uranium ions of fluences between 9×108 and 9×1011 ions cm?2. X-ray diffraction analysis revealed the formation of a new-phase Cu11Sb3 as well as a reduction in the axial ratio (c/a) of the matrix (β -Sn) indicating the regular re-arrangement of atoms. Scanning force microscopy showed no surface topographic changes with the ion fluence. The mechanical properties (Young's modulus and hardness) of the irradiated alloys were studied as a function of ion fluence. The radiation-annealing process is discussed in terms of the evolution of both resistivity and hardness as a function of ion fluence. 相似文献
998.
999.
在以往的随钻电磁波电阻率测井仪器检波系统中,仪器采样过程大多为均匀采样,检波方法多采用数字相关法或数字相敏检波(DPSD)法,其检波结果往往受采样量化误差以及频谱泄漏影响。针对这一问题,提出一种基于非均匀采样的模拟退火(SA)检波方法,并研制快速检波电路系统,选取基于均匀采样的DPSD检波结果进行对比。结果表明,基于非均匀采样的SA检波方法选频能力强,能更加有效地抑制量化误差相关性以及频谱泄漏带来的检波误差,更适用于恶劣多变环境下的随钻测井仪器检波。 相似文献
1000.
The classical Chapman–Enskog expansion is performed for the recently proposed finite-volume formulation of lattice Boltzmann equation (LBE) method [D.V. Patil, K.N. Lakshmisha, Finite volume TVD formulation of lattice Boltzmann simulation on unstructured mesh, J. Comput. Phys. 228 (2009) 5262–5279]. First, a modified partial differential equation is derived from a numerical approximation of the discrete Boltzmann equation. Then, the multi-scale, small parameter expansion is followed to recover the continuity and the Navier–Stokes (NS) equations with additional error terms. The expression for apparent value of the kinematic viscosity is derived for finite-volume formulation under certain assumptions. The attenuation of a shear wave, Taylor–Green vortex flow and driven channel flow are studied to analyze the apparent viscosity relation. 相似文献