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51.
Ortho‐Quinone Methides as Reactive Intermediates in Asymmetric Brønsted Acid Catalyzed Cycloadditions with Unactivated Alkenes by Exclusive Activation of the Electrophile 下载免费PDF全文
MSc. Chien‐Chi Hsiao Dr. Sadiya Raja MSc. Hsuan‐Hung Liao Prof. Dr. Magnus Rueping 《Angewandte Chemie (International ed. in English)》2015,54(19):5762-5765
An efficient method for the highly enantioselective synthesis of chiral chromanes bearing multiple stereogenic centers was developed. A chiral BINOL‐based N‐triflylphosphoramide proved to be an effective catalyst for the in situ generation of ortho‐quinone methides (o‐QMs) and their subsequent cycloaddition reaction with unactivated alkenes provided chromanes with excellent diastereo‐ and enantioselectivity. 相似文献
52.
Revealing the Preferred Interlayer Orientations and Stackings of Two‐Dimensional Bilayer Gallium Selenide Crystals 下载免费PDF全文
Dr. Xufan Li Dr. Leonardo Basile Dr. Mina Yoon Dr. Cheng Ma Dr. Alexander A. Puretzky Dr. Jaekwang Lee Dr. Juan C. Idrobo Dr. Miaofang Chi Dr. Christopher M. Rouleau Dr. David B. Geohegan Dr. Kai Xiao 《Angewandte Chemie (International ed. in English)》2015,54(9):2712-2717
Characterizing and controlling the interlayer orientations and stacking orders of two‐dimensional (2D) bilayer crystals and van der Waals (vdW) heterostructures is crucial to optimize their electrical and optoelectronic properties. The four polymorphs of layered gallium selenide (GaSe) crystals that result from different layer stackings provide an ideal platform to study the stacking configurations in 2D bilayer crystals. Through a controllable vapor‐phase deposition method, bilayer GaSe crystals were selectively grown and their two preferred 0° or 60° interlayer rotations were investigated. The commensurate stacking configurations (AA′ and AB stacking) in as‐grown bilayer GaSe crystals are clearly observed at the atomic scale, and the Ga‐terminated edge structure was identified using scanning transmission electron microscopy. Theoretical analysis reveals that the energies of the interlayer coupling are responsible for the preferred orientations among the bilayer GaSe crystals. 相似文献
53.
White‐Light Emission Strategy of a Single Organic Compound with Aggregation‐Induced Emission and Delayed Fluorescence Properties 下载免费PDF全文
Dr. Zongliang Xie Dr. Chengjian Chen Shidang Xu Jun Li Prof. Yi Zhang Prof. Siwei Liu Prof. Jiarui Xu Prof. Zhenguo Chi 《Angewandte Chemie (International ed. in English)》2015,54(24):7181-7184
A novel white‐light‐emitting organic molecule, which consists of carbazolyl‐ and phenothiazinyl‐substituted benzophenone (OPC) and exhibits aggregation‐induced emission‐delayed fluorescence (AIE‐DF) and mechanofluorochromic properties was synthesized. The CIE color coordinates of OPC were directly measured with a non‐doped powder, which presented white‐emission coordinates (0.33, 0.33) at 244 K to 252 K and (0.35, 0.35) at 298 K. The asymmetric donor–acceptor–donor′ (D‐A‐D′) type of OPC exhibits an accurate inherited relationship from dicarbazolyl‐substituted benzophenone (O2C, D‐A‐D) and diphenothiazinyl‐substituted benzophenone (O2P, D′‐A‐D′). By purposefully selecting the two parent molecules, that is, O2C (blue) and O2P (yellow), the white‐light emission of OPC can be achieved in a single molecule. This finding provides a feasible molecular strategy to design new AIE‐DF white‐light‐emitting organic molecules. 相似文献
54.
Chih‐Hsien Wang Chia‐Chi Huang Long‐Liu Lin Wenlung Chen 《Journal of Raman spectroscopy : JRS》2016,47(8):940-947
Disulfide bond is relevant to many protein folding/unfolding functions and conformational diseases. To elucidate the effects of disulfide bonds on protein folding, unfolding, and misfolding, we performed Fourier transform–Raman measurements on serial chemical‐induced denaturations of bovine serum albumin (BSA). By directly monitoring Raman stretching at S–S (~507 cm−1), S–H (~2566 cm−1), amide I (1655 cm−1 for α‐helix; 1667 cm−1 for β‐sheet structure), and amide III (>1300 cm−1 for α‐helix; 1246 cm−1 for β‐sheet structure), the status of disulfide bonds and secondary structure of BSA at different states were elucidated. Both disulfide bonds and secondary structure (mostly in α‐helix) of BSA appeared relatively stable even when the protein was unfolded by urea solution. However, disulfide bonds were completely reduced and protein secondary structure changed from α‐helix to a relatively β‐sheet dominant when the protein was modified by the mixed solution of urea and dithiothreitol (urea/DTT). Adhering to these structural changes, the protein proceeded to different degrees of polymerization. BSA would aggregate into a high molecular mass (over 700 kDa) of protein ensemble when it was exposed to the mixed urea/DTT solution. An irreversible change in S–S/S–H conversion and secondary structure was responsible for protein misfolding. We demonstrate here that Fourier transform–Raman directly probe S–S/S–H conversion and secondary structural change of BSA at different states, and these results clearly indicate that disulfide bonds and secondary structure of BSA serve as concrete frameworks to stabilize protein structure. As the frameworks collapse, the protein undergoes an irreversible structural change and results in protein misfolding. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
55.
Chi Tien 《Applied Scientific Research》1967,17(3):233-248
Summary Approximate solutions for laminar natural convection heat transfer between a vertical plate and a power-law fluid with high Prandtl number were obtained using an integral method for cases with various types of boundary conditions. The results were found in good agreement with available experimental evidence.Nomenclature
a
exponent defined by equations (28) and (29)
-
A, B, C, D, E
constants defined by equations (15) to (19)
-
C
1, C
2, M
1, M
2
coefficients for Nusselt number expression defined by (32b), (33b)
-
f
temperature difference, equal to T
s–T
-
f
+
dimensionless temperature difference
-
g
gravitational acceleration
-
Gr
Grashof number defined by (25), (50) and (66), respectively
-
H
heat flux at plate surface
-
h
x
local heat transfer coefficient
-
K
consistency index for Power-law fluid
-
k
thermal conductivity of fluid
-
K
1, K
2
constants defined by (50) and (51)
-
L
height of plate
-
n
flow behavior index for Power-law fluid
-
P
a quantity defined by (54a)
-
T
temperature
-
T
s
plate temperature
-
T
temperature of the bulk of fluid
-
s
constant given by (35)
-
u
velocity component along x-direction
-
u
x
maximum velocity induced by natural convection current, (10)
-
v
velocity component along y-direction
-
x
distance measured along direction parallel to that of gravitational force
-
x
+
dimensionless quantity, defined as x/L
-
y
distance measured away from plate
-
Nu
x
local Nusselt number
-
Nu
av
average Nusselt number
-
Pr
Prandtl number defined by (24)
-
T
temperature difference according to boundary conditions
-
thermal diffusivity of fluid
-
coefficient of thermal expression of fluid
-
boundary layer thickness
-
+
dimensionless boundary layer thickness
-
dimensionless velocity profile
-
dimensionless variable, defined as y/
-
dimensionless temperature difference 相似文献
56.
Mu‐Huan Chi Chun‐Hsien Su Ming‐Hsiang Cheng Pei‐Yun Chung Chi‐How Peng Jiun‐Tai Chen 《Macromolecular rapid communications》2016,37(24):2037-2044
To manipulate the functions of nanomaterials more precisely for diverse applications, the controllability and critical influencing factors of their properties must be thoroughly investigated. In this work, the macroscopic and microscopic effects are studied on the photophysical properties of various pyrene‐ended poly(styrene‐block‐methyl methacrylate) nanostructures. Fluorescent polymer nanospheres, nanorods, and nanotubes are prepared by different template‐based methods using anodic aluminum oxide membranes. Chain arrangements and conformations are determined as the key factors affecting the photophysical properties of the fluorescent polymer nanostructures. This work not only gives a deeper understanding of the effects on the photophysical properties of polymer nanomaterials influenced by morphologies, chain arrangements, and chain conformations, but also provides a reference for designing proper fluorescent nanostructures for specific applications.
57.
Ki Mun Jung Lyn C Thomas Mee Chi So 《The Journal of the Operational Research Society》2015,66(10):1656-1668
Data-based scorecards, such as those used in credit scoring, age with time and need to be rebuilt or readjusted. Unlike the huge literature on modelling the replacement and maintenance of equipment there have been hardly any models that deal with this problem for scorecards. This paper identifies an effective way of describing the predictive ability of the scorecard and from this describes a simple model for how its predictive ability will develop. Using a dynamic programming approach one is then able to find when it is optimal to rebuild and when to readjust a scorecard. Failing to readjust or rebuild a scorecard when they aged was one of the defects in credit scoring identified in the investigations into the sub-prime mortgage crisis. 相似文献
58.
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