全文获取类型
收费全文 | 3260篇 |
免费 | 116篇 |
国内免费 | 19篇 |
学科分类
数理化 | 3395篇 |
出版年
2023年 | 13篇 |
2022年 | 20篇 |
2021年 | 32篇 |
2020年 | 51篇 |
2019年 | 58篇 |
2018年 | 44篇 |
2017年 | 27篇 |
2016年 | 85篇 |
2015年 | 78篇 |
2014年 | 77篇 |
2013年 | 134篇 |
2012年 | 154篇 |
2011年 | 243篇 |
2010年 | 105篇 |
2009年 | 122篇 |
2008年 | 228篇 |
2007年 | 204篇 |
2006年 | 204篇 |
2005年 | 174篇 |
2004年 | 185篇 |
2003年 | 145篇 |
2002年 | 125篇 |
2001年 | 68篇 |
2000年 | 57篇 |
1999年 | 59篇 |
1998年 | 42篇 |
1997年 | 36篇 |
1996年 | 43篇 |
1995年 | 23篇 |
1994年 | 26篇 |
1993年 | 26篇 |
1992年 | 25篇 |
1991年 | 24篇 |
1990年 | 28篇 |
1989年 | 20篇 |
1988年 | 23篇 |
1987年 | 33篇 |
1986年 | 20篇 |
1985年 | 41篇 |
1984年 | 39篇 |
1983年 | 27篇 |
1982年 | 31篇 |
1981年 | 27篇 |
1980年 | 17篇 |
1979年 | 24篇 |
1978年 | 12篇 |
1977年 | 13篇 |
1976年 | 16篇 |
1975年 | 18篇 |
1973年 | 19篇 |
排序方式: 共有3395条查询结果,搜索用时 0 毫秒
1.
Surface texturing has been recognized as an effective means to improve the tribological performances of sliding surfaces. Usually, generation additional hydrodynamic pressure to increase the load carrying capacity is regarded as the most significant effect of surface texture. In the case of silicon carbide sliding against identical material in water, the experimental results indicate that surface texture is also helpful to improve the running-in progress to smooth the contact surfaces, showing another reason to result in low friction. Based on the consideration of enhancing the generation of hydrodynamic pressure and improving running-in progress, a surface texture pattern, which was combined with large (circle, 350 μm in diameter) and small (rectangular, 40 μm in length) dimples, was designed to maximize the texture effect on the load carrying capacity of SiC surfaces sliding in water. The friction coefficient of such textured surface was evaluated and compared with that of untextured and those only with large or small dimples only. The friction reduction mechanisms of the patterns with different dimples in size are discussed. 相似文献
2.
We study the relation between the cohomology of general linear and symmetric groups and their respective quantizations, using Schur algebras and standard homological techniques to build appropriate spectral sequences. As our methods fit inside a much more general context within the theory of finite-dimensional algebras, we develop our results first in that general setting, and then specialize to the above situations. From this we obtain new proofs of several known results in modular representation theory of symmetric groups. Moreover, we reduce certain questions about computing extensions for symmetric groups and Hecke algebras to questions about extensions for general linear groups and their quantizations. 相似文献
3.
R. Bairava Ganesh Hitoshi Matsuo Takahiro Kawamura Yoshihiro Kangawa Koji Arafune Yoshio Ohshita Masafumi Yamaguchi Koichi Kakimoto 《Journal of Crystal Growth》2008,310(11):2697-2701
Multicrystalline silicon was grown by unidirectional solidification method using the accelerated crucible rotation technique. The application of the accelerated crucible rotation technique in unidirectional solidification method induced growth striations across the axial direction of the grown crystal. This striation pattern was observed from carbon concentration distribution, obtained by using Fourier transform infrared spectroscopy. The generated striation pattern was found to be weak and discontinuous. Some striations were absent, probably due to back melting, caused during each crucible rotation. From the growth striations and applied time period in crucible rotation, the growth rate was estimated by using Fourier transformation analysis. 相似文献
4.
Yoshio Suzuki Noriyuki Tanji Chikako Ikeda Aki Honda Kenji Ookubo Daniel Citterio Suzuki Koji 《Analytical sciences》2004,20(3):475-482
Novel labeling reagents, called MS probes, which possess a positively charged quaternary amine moiety and can transform a neutral analyte into a charged compound by simply mixing with the analyte and allowing the mixture to stand from several minutes to 30 min at room temperature or while heating to 50 degrees C, were designed and synthesized for the highly sensitive detection of carbonyl, alcohol, carboxylic acid and primary amine samples by electrospray ionization mass spectrometry (ESI-MS). The positively charged products can be detected with high sensitivity in an ESI-MS system, which is the most popular liquid MS instrument. All of the labeled products showed a remarkably large increase in the molecular-ion peak abundance detection sensitivity of over 500-fold at picomolar concentration levels compared to that of unlabeled analytes in an ESI-MS system. These MS probes, used together with liquid MS detection, are widely applicable as a convenient method for the highly sensitive detection of less than picomolar levels of analytes, and therefore greatly enhance the power of ESI-MS analysis. 相似文献
5.
In order to change the ion-exchange selectivity of anion-exchange resin, the surface of a gel-type anion exchange resin was modified with anionic polyelectrolyte, polystyrenesulfonic acid. Using this modified resin, the ion-exchange rate of nitrate was little decreased, but that of sulfate was evidently decreased. It is considered that the ion-exchange reaction of the multivalent anion is suppressed by the greater electrostatic repulsive force against the modification layer than that against the monovalent anion. Thus, this modified resin may be suitable for the selective separation of monovalent anions. The influence of the modified condition on the ion-exchange rate was examined. Furthermore, this modified resin was used to separate nitrate ions from sulfate ions in the aqueous solution. 相似文献
6.
7.
8.
Koji Hasegawa 《Communications in Mathematical Physics》1997,187(2):289-325
For Belavin's elliptic quantum R-matrix, we construct an L-operator as a set of difference operators acting on functions on
the type A weight space. According to the fundamental relation RLL=LLR, taking the trace of the L-operator gives a set of commuting difference operators. We show that for the above mentioned L-operator
this approach gives Macdonald type operators with elliptic theta function coefficient, actually equivalent to Ruijsenaars'
operators. The relationship between the difference L-operator and Krichever's Lax matrix is given, and an explicit formula
for elliptic commuting differential operators is derived. We also study the invariant subspace for the system which is spanned
by symmetric theta functions on the weight space.
Received: 27 December 1995 / Accepted: 11 November 1996 相似文献
9.
S. Nakano Y. Kuwano M. Ohnishi 《Applied Physics A: Materials Science & Processing》1986,41(4):267-274
The super chamber, a separated UHV reaction-chamber system has been developed. A conversion efficiency of 11.7% was obtained for an a-Si solar cell using a high-quality i-layer deposited by the super chamber, and a p-layer fabricated by a photo-CVD method.As a new material, amorphous superlattice-structure films were fabricated by the photo-CVD method for the first time. Superlattice structure p-layer a-Si solar cells were fabricated, and a conversion efficiency of 10.5% was obtained.For the fabrication of integrated type a-Si solar cell modules, a laser pattering method was investigated. A thermal analysis of the multilayer structure was done. It was confirmed that selective scribing for a-Si, TCO and metal film is possible by controlling the laser power density. Recently developed a-Si solar power generation systems and a-Si solar cell roofing tiles are also described. 相似文献
10.
This paper presents a simple chaotic circuit consisting of two capacitors, one linear two-port VCCS and one time-state-controlled
impulsive switch. The impulsive switch causes rich chaotic and periodic behavior. The circuit dynamics can be simplified into
a one-dimensional return map that is piecewise linear and piecewise monotone. Using the return map, we clarify parameter conditions
for existence of chaotic and periodic attractors and coexistence state of attractors. 相似文献