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991.
Yan-jun Min Wen-peng Yuan Dong-yuan Yang Dong-xu Dai Sheng-rui Yu Guo-rong Wu Xue-ming Yang 《化学物理学报(中文版)》2022,35(2):242-248
The S\begin{document}$_1$\end{document} state decay dynamics of 2-hydroxypyridine following UV excitation at a wavelength range of 276.9\begin{document}$-$\end{document} 250.0 nm is investigated using femtosecond time-resolved photoelectron imaging technique. Based on pump wavelength dependence of the decay dynamics, a refined decay picture is proposed. At pump wavelength of 276.9 nm, the S\begin{document}$_1$\end{document} state is depopulated through intersystem crossing to lower triplet state(s). At 264.0 nm, both intersystem crossing to lower triplet state(s) and internal conversion to the ground state are in operation. At 250.0 nm, internal conversion to the ground state becomes dominated. 相似文献
992.
细胞表面受体与配体之间的特异性相互作用在细胞生物学过程中起着重要作用。然而,与均相溶液不同,受体分子在细胞膜上的分布是非连续的、动态的,因此细胞表面的受体配体相互作用通常呈现复杂的非线性结合模式。框架核酸作为一类具有确定几何形状的DNA纳米支架,可用于多价配体的偶联,为深入揭示受体配体相互作用机制提供了可靠的工具。利用框架核酸纳米分辨率的可寻址特性,可实现对配体数目、间距及空间构象等参数的精确调控,进而研究细胞表面受体配体的结合特性及影响因素,优化结合条件最终实现高效的分子识别及靶向治疗。本文综述了基于框架核酸的细胞表面受体配体相互作用研究进展,通过探讨细胞表面受体配体相互作用的重要影响因素及生物学应用,对该研究领域的发展前景和未来趋势予以展望。 相似文献
993.
Ion-selective water treatment is needed to address emerging problems in an energy- and cost-efficient manner. Capacitive deionization (CDI) is a membraneless water treatment technology, which relies on storing ions in charged electric double layers (EDLs) of micropores. CDI has shown remarkable selectivity, with local density approximations (LDAs) showing some success in guiding selective separations. However, many underlying processes are represented by lumped fitting parameters in LDA models, hindering further progress. Atomistic models help unravel selectivity mechanisms, but are difficult to integrate with cell-level CDI theory. Here, we review and extend LDA models for CDI, highlight a knowledge gap in connecting between LDA and atomistic models for CDI, and emphasize and build upon analogies between micropore EDLs and nanofiltration membranes. 相似文献
994.
Yanqing Yang Joseph Cheramy Dr. Martin Brehm Prof. Dr. Yunjie Xu 《Chemphyschem》2022,23(11):e202200161
Raman and Raman Optical Activity (ROA) spectra of N-acetyl-L-cysteine (NALC), a flexible chiral molecule, were measured in water and in methanol to evaluate the solvent effects. Two different solvation approaches, that is, the DFT based “clusters-in-a-liquid” solvent model and the ab initio molecular dynamics (AIMD) simulations, were applied to simulate the Raman and ROA spectra. Systematic conformational searches were carried out using a recently developed conformational searching tool, CREST, with the inclusion of polarizable continuum model of water and of methanol. The CREST candidates of NALC and the NALC-solvent complexes were re-optimized and their Raman and ROA simulations were done at the B3LYP−D3BJ/def2-TZVP and the B3LYP-aug-cc-pVDZ//cc-pVTZ levels. Also, AIMD simulations, which includes some anharmonic effects and all intermolecular interactions in solution, were performed. By empirically weighting the computed Raman and ROA spectra of each conformer, good agreements with the experimental data were achieved with both approaches, while AIMD offered some improvements in the carbonyl and in the low wavenumber regions over the static DFT approach. The pros and cons of these two different approaches for accounting the solvent effects on Raman and ROA of this flexible chiral system will also be discussed. 相似文献
995.
高速铁路的出现,使得轮轨交通技术达到更高的层次.速度提升不仅对列车的牵引动力与动力学性能提出更高要求.而且,列车与线路、气流等运行环境的耦合作用加剧,并直接影响到了列车的运行品质和安全性.在高速列车发展初期,研究关注的是如何保证高速列车能高速、平稳和安全运行.随着运行速度的提高,系统间耦合加强,服役模拟也越来越受到重视... 相似文献
996.
997.
非线性时滞动力系统的研究进展 总被引:24,自引:1,他引:24
具有时滞的动力系统广泛存在于各工程领域.本文从动力学角度对时滞动力系统的研究进展作一综述,内容包括时滞动力系统的特点、研究方法、动力学热点问题的研究进展等.由于时滞动力系统的演化趋势不仅依赖于系统的当前状态,还依赖于系统过去某一时刻或若干时刻的状态,其运动方程要用泛国微分方程来描述,解空间是无穷维的.即使系统中的时滞非常小,在许多情况下也不能忽略不计.对于非线性时滞常微分方程,目前的研究思路基本上与常微分方程系统理论相平行.主要研究方法可分为时域法和频域法,前者包括Taylor级数法,中心流形法,Poincare映射法等,后者包括Nyquist法等.目前对这类系统的动力学研究主要集中在稳定性、Hopf分岔、混沌等方面.研究表明:时滞动力系统具有非常丰富和复杂的动力学行为,如单变量的一维非线性时滞动力系统可发生混沌现象,与用常微分方程描述的系统有本质性差别.另一方面,人们可巧妙地利用时滞来控制动力系统的行为,如时滞反馈控制是控制混饨的主要方法之一.最后,本文展望了存在的一些问题以及近期值得关注的研究. 相似文献
998.
本文用有限元方法分析了两种常见汽轮发电机定子结构模型的动力特性,建立了固有特性对集中质量、连接刚度及基础刚度的灵敏度分析方法,对这两种结构模型进行了振动实验研究,实验结果与有限元分析结果吻合较好.从避开共振的角度出发,对两种结构作了评价.本文的研究方法及实验结果对汽轮发电机结构设计、减振、隔振和降噪等方面的工作具有一定的参考价值和实际工程意义. 相似文献
999.
The behavior of a terminally anchored freely-jointed bead-rod chain, subjected to solvent shear flow, was investigated via Brownian dynamics simulations. Previous calculations have been improved by computing the segment density and fluid velocity profiles self-consistently. The segment density distributions, components of the radius of gyration, and chain attachment shear and normal stresses were found to be sensitive to low values of shear rate. Additionally, it was found that the thickness of a model polymer layer was a strong function of the shear rate, and that the functional dependence on shear rate changed dramatically as the chain length increased. For the longest chains studied, the thickness of the model polymer layer first increased as the shear rate increased, passed through a maximum, and then decreased at high shear rates, in accordance with experimental results in theta solvents. These results suggest that a dilute or semi-dilute layer model may explain hydrodynamic behavior previously thought to be due to the entanglements that occur in dense surface bound polymer layers.Nomenclature
a
i
acceleration of bead i
-
b
radius of the beads
-
d
length of the rods connecting the chain beads
-
d
i
vector from bead i to bead i + 1
-
F
i
external force applied to bead i
-
F
i
b
external force on bead i due to Brownian motion of surrounding fluid
-
F
i
h
external force on bead i due to viscous drag
-
F
i
s
external force on bead i due to surface interactions
-
f
Stokes drag coefficient
-
Boltzmann's constant
-
L
h
effective hydrodynamic thickness
-
m
i
mass of bead i
-
N
number of beads on a model chain
-
n
number of chains anchored to the surface per unit surface area
-
P
segment density distribution P pressure
-
Q
flow in a tube with no surface bound polymer layer
-
Q
a
flow in a tube with a surface bound polymer layer
-
R
g
vector representation of the radius of gyration
-
R
tube radius
-
r
radial coordinate in the tube geometry
-
S
ij
pair hydrodynamic interaction tensor for beads i and j
-
T
i
internal chain force in rod i connecting beads i and i + 1
-
T
X
component of the surface attachment force in the direction of the fluid flow
-
T
y
component of the surface attachment force perpendicular to the surface
-
T
temperature
-
v
i
velocity of the center of mass of bead i
-
V
if
average fluid velocity at the location of bead i
-
v
if
0
fluid velocity in the absence of a polymer chain
-
v
if
perturbation to the fluid velocity due to hydrodynamic interactions
-
V
b
bead volume = 4 b
3/3
-
scalar fluid speed in the axial direction down the tube
-
x
axial coordinate in the tube geometry
Greek symbols w
apparent shear rate
-
fluid viscosity
-
polymer layer permeability
-
volume fraction of space occupied by chain beads
- (w)a
chain attachment stress perpendicular to the surface
- (w)a
chain attachment stress in the plane of the surface and in the direction of fluid flow 相似文献
1000.