全文获取类型
收费全文 | 85106篇 |
免费 | 16208篇 |
国内免费 | 22042篇 |
学科分类
数理化 | 123356篇 |
出版年
2024年 | 272篇 |
2023年 | 1259篇 |
2022年 | 3088篇 |
2021年 | 3074篇 |
2020年 | 3127篇 |
2019年 | 3008篇 |
2018年 | 2732篇 |
2017年 | 3538篇 |
2016年 | 3355篇 |
2015年 | 4203篇 |
2014年 | 5095篇 |
2013年 | 6638篇 |
2012年 | 7068篇 |
2011年 | 7406篇 |
2010年 | 6544篇 |
2009年 | 6661篇 |
2008年 | 7463篇 |
2007年 | 6590篇 |
2006年 | 6468篇 |
2005年 | 5433篇 |
2004年 | 4202篇 |
2003年 | 3182篇 |
2002年 | 3082篇 |
2001年 | 2940篇 |
2000年 | 3068篇 |
1999年 | 2059篇 |
1998年 | 1389篇 |
1997年 | 1210篇 |
1996年 | 1176篇 |
1995年 | 1046篇 |
1994年 | 1052篇 |
1993年 | 904篇 |
1992年 | 827篇 |
1991年 | 607篇 |
1990年 | 585篇 |
1989年 | 554篇 |
1988年 | 461篇 |
1987年 | 378篇 |
1986年 | 312篇 |
1985年 | 276篇 |
1984年 | 224篇 |
1983年 | 205篇 |
1982年 | 173篇 |
1981年 | 133篇 |
1980年 | 86篇 |
1979年 | 72篇 |
1978年 | 24篇 |
1977年 | 18篇 |
1971年 | 16篇 |
1959年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
The Monte Carlo ray-tracing method (MCRT) based on the concept of radiation distribution factor is extended to solve radiative heat transfer problem in turbulent fluctuating media under the optically thin fluctuation approximation. A one-dimensional non-scattering turbulent fluctuating media is considered, in which the mean temperature and absorption coefficient distribution are assumed and the shape of probability density function is given. The distribution of the time-averaged volume radiation heat source is solved by MCRT and direct integration method. It is shown that the results of MCRT based on the concept of radiation distribution factor agree with these of integration solution very well, but results of MCRT based on the concept of radiative transfer coefficient do not agree with these of integration solution. The solution of time-averaged radiative transfer equation by the concept of radiative transfer coefficient should be treated with caution. 相似文献
104.
Huimin Xie Biao Li Robert Geer Bai Xu James Castracane 《Optics and Lasers in Engineering》2003,40(3):163-177
A focused ion beam (FIB) Moiré method is proposed to measure the in-plane deformation of object in a micrometer scale. The FIB Moiré is generated by the interference between a prepared specimen grating and FIB raster scan lines. The principle of the FIB Moiré is described. The sensitivity and accuracy of deformation measurement are discussed in detail. Several specimen gratings with 0.14 and 0.20 μm spacing are used to generate FIB Moiré patterns. The FIB Moiré method is successfully used to measure the residual deformation in a micro-electro-mechanical system structure after removing the SiO2 sacrificial layer with a 5000 lines/mm grating. The results demonstrate the feasibility of this method. 相似文献
105.
A facile, rapid and regioselective method for the 1-O-deacylation of peracylated glycopyranoses is described which occurs under mild conditions by absorption onto alumina using microwave irradiation. 相似文献
106.
Under dielectric continuum approximation, interface optical (IO) phonon modes and the Frohlich electron-IO phonon interaction Hamiltonian in a multi-shell spherical nanoheterosystem were derived and studied. Numericalcalculations on three-layer and four-layer CdS/HgS spherical nanoheterosystems have been performed. Results revealthat there are four IO phonon modes for the three-layer system and six IO phonon modes for the four-layer system.On each interface, there are two IO phonon modes, the frequency of one is between WTO,CdS and WLO,CdS, and that ofthe other is between WTO,HgS and WLO,HgS. With the increasing of quantum number l, the frequency of each IO modeapproaches one of the two frequency values of the single CdS/HgS heterostructure, and the potential for each IO modeis more and more localized at a certain interface, furthermore, the coupling between the electron-lO phonons becomes weaker. 相似文献
107.
Comment on “A Hierarchy of Integrable Nonlinear Lattice Equations and New Integrable Symplectic Map“
Comment on a recent paper on Commun. Theor. Phys. (Beijing, China) 38 (2002) pp. 523-528. 相似文献
108.
109.
A convenient and large-scale preparation of retinoic acid 1 from β-ionone in five steps with 38% overall yield is described.The key steps are the epoxidization of 2 with a new methylated agent and the condensation 4 with tetraethyl methylenediphophonate in one-pot procedure to prepare 6. 相似文献
110.
Bi12TiO20纳米粉体的制备及其光吸收特性研究 总被引:3,自引:0,他引:3
以钛酸四丁酯和硝酸铋为原料 ,利用化学溶液分解法制备了Bi12 TiO2 0 纳米多晶粉体 .采用XRD和TEM对其结构和形貌进行了表征 .结合热重 差热 (TG DTA)分析 ,探讨了Bi12 TiO2 0 晶相的形成机理 .通过UV Vis漫反射谱的测定 ,研究了Bi12 TiO2 0 纳米晶粉体的光吸收特性 .结果显示 ,从组成为化学计量比的前驱液中可以很容易制得纯Bi12 TiO2 0 纳米晶粉体 ,该Bi12 TiO2 0 纳米晶粉体呈现了在很宽的波长范围内 (5 6 0~ 385nm )对光的吸收的特性 . 相似文献