全文获取类型
收费全文 | 121946篇 |
免费 | 16806篇 |
国内免费 | 9244篇 |
专业分类
化学 | 77721篇 |
晶体学 | 1519篇 |
力学 | 7156篇 |
综合类 | 514篇 |
数学 | 13544篇 |
物理学 | 47542篇 |
出版年
2023年 | 2040篇 |
2022年 | 2998篇 |
2021年 | 3487篇 |
2020年 | 4171篇 |
2019年 | 3741篇 |
2018年 | 3558篇 |
2017年 | 3163篇 |
2016年 | 5082篇 |
2015年 | 4495篇 |
2014年 | 5730篇 |
2013年 | 8018篇 |
2012年 | 9334篇 |
2011年 | 9997篇 |
2010年 | 6738篇 |
2009年 | 6530篇 |
2008年 | 7154篇 |
2007年 | 6423篇 |
2006年 | 6011篇 |
2005年 | 4898篇 |
2004年 | 3970篇 |
2003年 | 3196篇 |
2002年 | 2990篇 |
2001年 | 3036篇 |
2000年 | 2482篇 |
1999年 | 2534篇 |
1998年 | 2124篇 |
1997年 | 2104篇 |
1996年 | 2027篇 |
1995年 | 1765篇 |
1994年 | 1576篇 |
1993年 | 1368篇 |
1992年 | 1300篇 |
1991年 | 1236篇 |
1990年 | 1085篇 |
1989年 | 907篇 |
1988年 | 806篇 |
1987年 | 729篇 |
1986年 | 694篇 |
1985年 | 696篇 |
1984年 | 613篇 |
1983年 | 457篇 |
1982年 | 483篇 |
1981年 | 430篇 |
1980年 | 360篇 |
1979年 | 410篇 |
1978年 | 379篇 |
1977年 | 394篇 |
1976年 | 391篇 |
1975年 | 342篇 |
1973年 | 339篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A novel method of obtaining shearing interferogram by slightly moving the crystal in a photorefractive interferometer is proposed. This method can measure the phase of an object itself instead of its diffraction field, and it is easy to realize continuously changeable shearing distance in any lateral direction and introduce carrier fringes at the same time. Both the theoretical analysis and experimental verification are given. 相似文献
992.
Binyuan Liu Yang Li Boo‐Gyo Shin Do Yeung Yoon IL Kim Li Zhang Weidong Yan 《Journal of polymer science. Part A, Polymer chemistry》2007,45(15):3391-3399
Three novel functionalized polynorbornenes (PNB) with pendant dimethyl carboxylate group (carboxylates—acetate, propionate, and butyrate) are synthesized as a vinyl‐type with a palladium (II) catalyst in high yield. The effects of size of substitutents, molar ratio of monomer to catalyst, solvent polarity, reaction time, and temperature on the polymerization of exo‐norbornene dimethyl propionate were systematically investigated. The low molar ratio and temperature, as well as high polarity of solvent, and long reaction time, are favorable for the enhancement of the monomer conversion, especially, the solvent have an obvious effect on the catalyst activity. The resulting poly(cis‐norbornene‐exo‐2,3‐dimethyl carboxylates) (PNB‐dimethyl carboxylates) show good solubility in common organic solvent and high thermal stability up to 360 °C. The glass transition temperature was detected by DMA at 331, 324, and 318 °C for acetate, propionate, and butyrate, respectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3391–3399, 2007 相似文献
993.
We study Hamiltonians with singular spectra of Cantor type with a constant ratio of dissection. The decay properties of the states in such systems depend on the nature of the dissection rate that can be characterized in terms of the algebraic number theory. We show that in spite of simplicity of the considered model the computational modeling of nondecaying states is in general impossible. 相似文献
994.
The concept of crystallization dynamics method evaluating the miscibility of binary blend system including crystalline component
was proposed. Three characteristic rates, nucleation, crystal growth rates (N*, G*) and growth rate of conformation (G
c*) were used to evaluate the miscibility of PVDF/at-PMMA and PVDF/iso-PMMA by the simultaneous DSC-FTIR. N*, G* and G
c* depended remarkably on both temperature and blend fraction (ϕPMMA) for PVDF/at-PMMA system, which indicated the miscible system. PVDF/iso-PMMA showed small ϕPMMA dependency of N*, G* and G
c*, was estimated the immiscible system. The ΔT/T
m0 values, corresponding to Gibbs energy required to attend the constant G* and G
c*, evaluated from G* and G
c* showed the good linear relationships with different slope. The experimental results suggested that the concentration fluctuation
existed in PVDF/iso-PMMA system. 相似文献
995.
996.
Zhang Yinhuo 《数学年刊B辑(英文版)》1991,12(2):152-156
The author concludes that every commutative ring with ascending chain condition an annihilator ideals has a Kasch quotient ring, which generalizes the Theorem^{[1]} that
every commutative noetherian ring has a Kasch quosient ring. If follows that if R is a commutative ting with acc^{\perp},then that Q(R) is semiprimary is equivalent to that it is perfect, or to that R satisfies regular condition. Besides, that Q(R) is quasi-frobenius equals that Q(R) is FPF or PF, and that Q(R) is artinian equals that R/N, are of finite dimension, i=1,2,\ldots,n. N_{i}=J^{i}\cap R. 相似文献
997.
998.
999.
In this paper, by means of monotone iterative technique, a necessary and sufficient condition of the existence of positive solution for a class of nonlinear singular differential system is established, the results of the existence and uniqueness of the positive solution and the iterative sequence of solution are given. In the end, two classes extending boundary value differential systems are discussed and some further results are obtained. 相似文献
1000.
Measurement of small-signal and large-signal responses of packaged laser modules at high temperature
Ning Hua Zhu Ji Min Wen Hai Peng Song Shang Jian Zhang Liang Xie 《Optical and Quantum Electronics》2006,38(15):1245-1257
In this paper, the pulsed injection method is extended to measure the chip temperature of various packaged laser modules,
such as the DFB laser modules, the FP laser modules, and the EML laser modules. An optimal injection condition is obtained
by investigating the dependence of the lasing wavelength on the width and period of the injection pulse in a relatively wide
temperature range. The small-signal frequency responses and large-signal performances of packaged laser modules at different
chip temperature are measured. The adiabatic small-signal modulation characteristics of packaged LD are first extracted. In
the large-signal measurement, the effects of chip temperature, bias current and driving signal on the performances of the
laser modules are discussed. It has been found that the large-signal performances of the EML modules depend on the different
red-shift speeds of the DFB and EAM sections as chip temperature varying, and the optimal characteristics may be achieved
at higher temperature. 相似文献