全文获取类型
收费全文 | 77593篇 |
免费 | 13342篇 |
国内免费 | 8435篇 |
专业分类
化学 | 54991篇 |
晶体学 | 944篇 |
力学 | 4636篇 |
综合类 | 459篇 |
数学 | 8784篇 |
物理学 | 29556篇 |
出版年
2024年 | 193篇 |
2023年 | 1602篇 |
2022年 | 2291篇 |
2021年 | 2889篇 |
2020年 | 3343篇 |
2019年 | 3211篇 |
2018年 | 2692篇 |
2017年 | 2556篇 |
2016年 | 3817篇 |
2015年 | 3713篇 |
2014年 | 4593篇 |
2013年 | 5809篇 |
2012年 | 7142篇 |
2011年 | 7303篇 |
2010年 | 4956篇 |
2009年 | 4670篇 |
2008年 | 5080篇 |
2007年 | 4497篇 |
2006年 | 4100篇 |
2005年 | 3403篇 |
2004年 | 2605篇 |
2003年 | 2058篇 |
2002年 | 1954篇 |
2001年 | 1564篇 |
2000年 | 1310篇 |
1999年 | 1581篇 |
1998年 | 1319篇 |
1997年 | 1257篇 |
1996年 | 1255篇 |
1995年 | 1119篇 |
1994年 | 937篇 |
1993年 | 776篇 |
1992年 | 694篇 |
1991年 | 602篇 |
1990年 | 513篇 |
1989年 | 375篇 |
1988年 | 263篇 |
1987年 | 228篇 |
1986年 | 253篇 |
1985年 | 206篇 |
1984年 | 120篇 |
1983年 | 135篇 |
1982年 | 81篇 |
1981年 | 60篇 |
1980年 | 36篇 |
1979年 | 20篇 |
1976年 | 21篇 |
1975年 | 22篇 |
1972年 | 19篇 |
1957年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
151.
Fiber-optic reflex sensor for in-line production measurement 总被引:1,自引:0,他引:1
The paper describes experiments concerning distance measurement with fiber-optic sensor and improvement of the measurement principle. The sensor probe was well-designed with a small structure and multi-function. The novel optical fiber probe arrangement as well as the possibilities of use for complex measurement problems are explained using the measurement of an internal screw thread as an example. The experimental results show that the measurement uncertainty of the thread minor diameter can reach ±10 μm, and the stability of the measurement system is better than 0.07%. 相似文献
152.
153.
154.
Propagation of the Hermite–Gaussian beams through misaligned optical system with a circular aperture
By means of expanding a hard-edged aperture into a finite sum of complex Gaussian functions, the approximate analytical formula of one kind of higher-order Gaussian beams called the Hermite–Gaussian beams (HGBs) passing through circular apertured and misaligned optical system is obtained in this paper. The result provides more convenience for studying its propagation than the usual way by using diffraction integral directly. Some numerical simulations are also given for illustrating the propagation properties of the HGBs through the circular apertured optical systems. 相似文献
155.
Zhao Hanzhong 《Acta Mechanica Solida Sinica》2002,15(2):156-162
A finite difference/boundary integral procedure to determine the acoustic reflected pressure from a fluid-loaded bi-laminated
plate is described. The bi-laminate is composed of a piezoelectric layer and an elastic layer in contact with the fluid, and
is held by an acoustically hard baffle. In the numerical model, the fluid pressure at fluid/solid interface is replaced by
a continuum of point sources weighted by the normal acceleration of the elastic plate, and the governing equation system is
solved in the solid domain. With the normal acceleration found, the reflected pressure in the fluid is determined by an integral
expression involving the Green's function. It is demonstrated that an appropriate applied voltage potential across the piezoelectric
layer has the effect of cancelling either the reflected or scattered pressure of the plate at any chosen field points in the
fluid.
Project supported by the National Natural Science Foundation of China (No. 10172039). 相似文献
156.
157.
158.
Hongbo Zhang Rui Wang Kaixin Chen Han Yang Daming Zhang Maobin Yi Guoquan Wang Zhenchang Ma 《Optics & Laser Technology》2002,34(4):283-286
A new method, based on zero point of longitudinal electric field, was used to determine the spatial resolution of external electro-optic (EO) probing equipment. Considering the diffraction of Gauss beam, the result of external EO probing was simulated which was in accordance with the experiment. A spatial resolution <1 μm was demonstrated initially in our equipment using 650 nm laser diode as probe beam and semi-insulating GaP as probe tip. 相似文献
159.
Liyue Liu Yingge Yang Yafei Zhang 《Physica E: Low-dimensional Systems and Nanostructures》2004,24(3-4):343-348
The electrical conductivity was investigated for multi-walled carbon nanotubes (MWNTs) dissolved in chloroform and toluene, respectively. The electrical conductivity remarkably increased with increase in the content of MWNTs, which is in accordance with Archie's equation . Furthermore, a hypothesis of the electronic transport process was proposed to explain the difference between the solution and the solid compound. In addition, the temperature dependence of the electrical conductivity shows that log σ vs. 1/T exist in a good linear relationship. The activation energy of the electrical conductivity decreased with increase in concentration and an inflexion was observed at 60 °C in MWNT/toluene solution. 相似文献
160.
A series of low density polyethylene systems has been studied with respect to structural evolution and short-term dielectric breakdown behaviour. All materials were based upon a single polymer, that is commonly used in high voltage applications, but with different additives. In all three of these systems, multiple melting transitions were observed, as a result of molecular fractionation effects during crystallization. In the virgin polymer, a space-filling banded spherulitic morphology was found to develop at low temperatures (102 °C and below) whereas, at higher temperatures, only a few isolated axialites were observed. Inclusion of the antioxidant resulted in greatly increased nucleation densities, such that, at low temperatures, no evidence of spherulitic organisation remained. At higher temperatures, sheaf-like lamellar aggregates developed, which were much smaller and much more numerous than in the case of the virgin polymer. Further addition of dicumyl peroxide (DCP) resulted in the rapid formation of a crosslinked network at 200 °C. Some crosslinking also occurred at 150 °C, but over a much longer timescale. Where extensive crosslinking occurred prior to crystallization, the resulting gel inhibited structural development, such that only a few small, isolated sheaves were able to form at 102 °C. In view of the principal application area of this material, the breakdown strength of each of the above systems was then measured and the whole data set was analysed statistically. When structural factors were considered alongside the statistics, no clear trends emerged to indicate that either the compositional or morphological variations were reflected in the short-term electrical failure processes. 相似文献