全文获取类型
收费全文 | 1384篇 |
免费 | 38篇 |
国内免费 | 6篇 |
专业分类
化学 | 1025篇 |
晶体学 | 10篇 |
力学 | 11篇 |
数学 | 25篇 |
物理学 | 276篇 |
无线电 | 81篇 |
出版年
2023年 | 12篇 |
2022年 | 10篇 |
2021年 | 21篇 |
2020年 | 38篇 |
2019年 | 38篇 |
2018年 | 12篇 |
2017年 | 14篇 |
2016年 | 24篇 |
2015年 | 30篇 |
2014年 | 38篇 |
2013年 | 62篇 |
2012年 | 82篇 |
2011年 | 80篇 |
2010年 | 34篇 |
2009年 | 49篇 |
2008年 | 100篇 |
2007年 | 77篇 |
2006年 | 67篇 |
2005年 | 70篇 |
2004年 | 56篇 |
2003年 | 43篇 |
2002年 | 56篇 |
2001年 | 20篇 |
2000年 | 29篇 |
1999年 | 11篇 |
1998年 | 14篇 |
1997年 | 8篇 |
1996年 | 14篇 |
1995年 | 9篇 |
1994年 | 14篇 |
1993年 | 14篇 |
1992年 | 18篇 |
1991年 | 18篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1988年 | 15篇 |
1987年 | 21篇 |
1985年 | 14篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 9篇 |
1981年 | 14篇 |
1980年 | 13篇 |
1979年 | 14篇 |
1978年 | 19篇 |
1977年 | 12篇 |
1976年 | 12篇 |
1975年 | 9篇 |
1974年 | 9篇 |
1973年 | 11篇 |
排序方式: 共有1428条查询结果,搜索用时 15 毫秒
161.
162.
日本的教育体制大体上类似于其他国家,即小学6年,初中3年,高中3年,大学本科4年。大学本科毕业后另有2年硕士学位,再加3年博士学位的教育。当前在校学习的人数逐年增加,人均在校学习的时间也逐渐延长。到2000年已有将近一半的18岁同龄人进入大学学习。为适应上述教育情况的变化,日本政府目前开始了一个重整大学教育体制的计划。该计划将所有原来模式相同的649所大学划分为两大类,一类是研究和教学型的,另一类是教学型的。目前已有9所大学已被认定为第一类型的大学。本文介绍日本教育体制的变化以及上述重整计划的长远目标。 相似文献
163.
Numerical-Asymptotic Expansion Matching for Computing a Viscous Flow Around a Sharp Expansion Corner
A computational technique which is based on a numerical-asymptotic expansion matching for computing the local singular behavior
of a viscous flow around a sharp right-angle expansion corner is presented. Moffatt's (1964) asymptotic solution is extended
and a matching with a time-marching finite-difference scheme of the Navier--Stokes equations is formulated. Local mesh refinement
around the corner is required to meet the validity of the asymptotic solution. Flows in an expanding channel with expansion
ratio D/d=3 at various Reynolds numbers 1≤Re≤700 are simulated. The results are compared with those from a standard finite-difference scheme that uses second-order forward/backward
differences near the corner. It is found that the results of the standard scheme converge toward those of the present technique
as the level of local refinement near the corner is increased. The time-dependent parameters of the first two terms of the
asymptotic solution at the steady-state solution are also described for various cases of Re and D/d. It is demonstrated that the present method enhances the accuracy of the simulations and requires less refinements near the
corners to achieve converged numerical results.
Received 14 August 2000 and accepted 25 October 2001 相似文献
164.
Back Cover: CH Activation Generates Period‐Shortening Molecules That Target Cryptochrome in the Mammalian Circadian Clock (Angew. Chem. Int. Ed. 24/2015)
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Tsuyoshi Oshima Dr. Iori Yamanaka Dr. Anupriya Kumar Dr. Junichiro Yamaguchi Dr. Taeko Nishiwaki‐Ohkawa Kei Muto Rika Kawamura Dr. Tsuyoshi Hirota Prof. Dr. Kazuhiro Yagita Prof. Dr. Stephan Irle Prof. Dr. Steve A. Kay Prof. Dr. Takashi Yoshimura Prof. Dr. Kenichiro Itami 《Angewandte Chemie (International ed. in English)》2015,54(24):7200-7200
165.
166.
Dr. Aya Yoshimura Yuki Takamachi Prof. Dr. Li‐Biao Han Prof. Dr. Akiya Ogawa 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(40):13930-13933
An efficient metal‐free diboration of terminal alkynes is reported. In the presence of a catalytic amount of organosulfides under light, the addition of bis(pinacolato)diboron (B2pin2) to terminal alkynes takes place efficiently to produce the corresponding double borylation products in good yields. Mechanistic studies indicate that this metal‐free sulfide‐catalyzed diboration of alkynes likely occurs by generation of a boryl‐centered radical with the aid of light and a sulfide, since such a radical was detected in the reaction mixture by electron spin resonance (ESR) spectroscopy. The present form of catalysis (sulfide/light) is thought to be unprecedented and provides a new means of preparation for organoboranes without heavy metal contamination in the products, which is highly desired in the preparation of drugs and electronic materials. 相似文献
167.
Aya Yoshimura Akihiro Nomoto Mari Uchida Hiroki Kusano Tomokazu Saeki Akiya Ogawa 《Research on Chemical Intermediates》2017,43(6):3433-3443
The functionalization of polysilanes is an important subject in materials science because functionalized polysilanes are expected to exhibit potentially innovative properties. This research aims at the addition of a water-shedding property to polysilanes by introducing perfluoroalkyl groups into their skeleton. The photoinduced iodoperfluoroalkylation of various vinylsilanes takes place successfully upon irradiation with a xenon lamp: vinylmonosilanes undergo iodoperfluoroalkylation with perfluoroalkyl iodides (RfI) regioselectively, and the corresponding perfluoroalkylated silanes are obtained in moderate to high yields. Detailed optimization of the photoinduced iodoperfluoroalkylation has been investigated to apply this method to the functionalization of polysilanes. Polysilanes having vinyl groups can be synthesized by the reductive coupling of dichlorovinylsilanes with samarium diiodide (SmI2) and samarium metal (Sm) upon irradiation with visible light. The synthesized vinylpolysilanes and RfI (about 1.0 mM CHCl3 solution) are coated on a glass plate sequentially, and then the following photoirradiation with light of a wavelength over 300 nm successfully adds an excellent water-shedding property to the glass plate. 相似文献
168.
A method for the resolution of all stress components from the first invariant J1 measured by thermoelastic stress analyzer is described. This method may be used to determine, not only surface stress, but also internal stress and stress on the underside.The method is based on the following procedure:
- 1. (1) Pick an arbitrary domain Ω, within the structure, for which the stresses are required.
- 2. (2) Measure J1 on the surface of Ω.
- 3. (3) Determine the optimum traction along the boundary Γ, which is a part of Ω, by the least squares method such that the difference between the measured J1 and the calculated J1 is at a minimum. Either FEM or BEM may be used for this calculation.
169.
Response of an elastic Bingham fluid to oscillatory shear 总被引:1,自引:0,他引:1
The response of an elastic Bingham fluid to oscillatory strain has been modeled and compared with experiments on an oil-in-water emulsion. The newly developed model includes elastic solid deformation below the yield stress (or strain), and Newtonian flow above the yield stress. In sinusoidal oscillatory deformations at low strain amplitudes the stress response is sinusoidal and in phase with the strain. At large strain amplitudes, above the yield stress, the stress response is non-linear and is out of phase with strain because of the storage and release of elastic recoverable strain. In oscillatory deformation between parallel disks the non-uniform strain in the radial direction causes the location of the yield surface to move in-and-out during each oscillation. The radial location of the yield surface is calculated and the resulting torque on the stationary disk is determined. Torque waveforms are calculated for various strains and frequencies and compared to experiments on a model oil-in-water emulsion. Model parameters are evaluated independently: the elastic modulus of the emulsion is determined from data at low strains, the yield strain is determined from the phase shift between torque and strain, and the Bingham viscosity is determined from the frequency dependence of the torque at high strains. Using these parameters the torque waveforms are predicted quantitatively for all strains and frequencies. In accord with the model predictions the phase shift is found to depend on strain but to be independent of frequency.Notation
A
plate strain amplitude (parallel plates)
-
A
R
plate strain amplitude at disk edge (parallel disks)
-
G
elastic modulus
-
m
torque (parallel disks)
-
M
normalized torque (parallel disks) = 2m/R
30
-
N
ratio of viscous to elastic stresses (parallel plates) =µ A/
0 ratio of viscous to elastic stresses (parallel disks) =µ A
R/0
-
r
normalized radial position (parallel disks) =r/R
-
r
radial position (parallel disks)
-
R
disk radius (parallel disks)
-
t
normalized time = t — /2
-
t
time
-
E
elastic strain
-
P
plate strain (displacement of top plate or disk divided by distance between plates or disks)
-
PR
plate strain at disk edge (parallel disks)
-
0
yield strain
-
E
normalized elastic strain =
E/0
-
P
normalized plate strain =
P/0
-
PR
normalized plate strain at disk edge (parallel disks) =
PR/0
-
0
normalized plate strain amplitude (parallel plates) =A/
0 — normalized plate strain amplitude at disk edge (parallel disks) =A
R/0
-
phase shift between
P
andT (parallel plates) — phase shift between
PR
andM (parallel disks)
-
µ
Bingham viscosity
-
stress
-
0
yield stress
-
T
normalized stress =/
0
-
frequency 相似文献
170.
Thermal [2+2] cycloaddition of morpholinoenamines with C60 via a single electron transfer 总被引:1,自引:0,他引:1
The thermal reaction of C(60) with five- and six-membered morpholinocycloalkenes in refluxing toluene exclusively gave the [2+2] cycloadducts in high yields. However, a seven-membered homologue sluggishly reacted with C(60) because of the increasing steric hindrance. This cycloaddition reaction is likely to proceed via a single electron transfer (SET), a radical-coupling, and subsequent ion cyclization rather than the prior proton transfer between the radical ions. 相似文献