全文获取类型
收费全文 | 94291篇 |
免费 | 14621篇 |
国内免费 | 9819篇 |
专业分类
化学 | 50860篇 |
晶体学 | 657篇 |
力学 | 4739篇 |
综合类 | 310篇 |
数学 | 8197篇 |
物理学 | 28829篇 |
无线电 | 25139篇 |
出版年
2024年 | 415篇 |
2023年 | 2408篇 |
2022年 | 3019篇 |
2021年 | 3803篇 |
2020年 | 3792篇 |
2019年 | 3504篇 |
2018年 | 3019篇 |
2017年 | 2876篇 |
2016年 | 4154篇 |
2015年 | 4348篇 |
2014年 | 5176篇 |
2013年 | 6512篇 |
2012年 | 8108篇 |
2011年 | 8040篇 |
2010年 | 5724篇 |
2009年 | 5653篇 |
2008年 | 5957篇 |
2007年 | 5307篇 |
2006年 | 4973篇 |
2005年 | 4202篇 |
2004年 | 3111篇 |
2003年 | 2636篇 |
2002年 | 2338篇 |
2001年 | 1986篇 |
2000年 | 1926篇 |
1999年 | 2136篇 |
1998年 | 1840篇 |
1997年 | 1686篇 |
1996年 | 1683篇 |
1995年 | 1414篇 |
1994年 | 1230篇 |
1993年 | 1005篇 |
1992年 | 900篇 |
1991年 | 762篇 |
1990年 | 618篇 |
1989年 | 440篇 |
1988年 | 381篇 |
1987年 | 298篇 |
1986年 | 273篇 |
1985年 | 234篇 |
1984年 | 171篇 |
1983年 | 124篇 |
1982年 | 93篇 |
1981年 | 75篇 |
1980年 | 76篇 |
1979年 | 39篇 |
1978年 | 35篇 |
1977年 | 46篇 |
1976年 | 39篇 |
1973年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
The title compound, [Cd(SeCN)2(pyCN)2]∞, adopts an extended one‐dimensional chain structure in which the neighboring cadmium atoms are bridged by two selenocyanate ions. The central cadmium atom has a distorted octahedral geometry defined by two isonicotinonitrile and four selenocyanate ions in a 4N2Se fashion. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
112.
113.
In mononuclear HgI2[(C5H4N)3N], mercury is tetrahedrally coordinated by two nitrogen atoms of a tris(2‐pyridyl)amine ligand and two iodides. The coordination moieties are connected by weak intermolecular Hg(II)···I interactions to give a one‐dimensional structure. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
114.
115.
Jai-Ming Liu Ying-Chin Chen 《Quantum Electronics, IEEE Journal of》1985,21(4):298-306
The operations of a complete set of optical AND, NAND, OR, and NOR gates and clocked opticalS-R, D, J-K, andT flip-flops are demonstrated, based on direct polarization switching and polarization bistability, which we have recently observed in InGaAsP/InP semiconductor lasers. By operating the laser in the direct-polarization-switchable mode, the output of the laser can be directly switched between the TM00 and TE00 modes with high extinction ratios by changing the injection-current level, and optical logic gates are constructed with two optoelectronic switches or photodetectors. In the polarization-bistable mode, the laser exhibits controllable hysteresis loops in the polarization-resolved power versus current characteristics. When the laser is biased in the middle of hysteresis loop, the light output can be switched between the two polarization states by injection of short electrical or optical pulses, and clocked optical flip-flops are constructed with a few optoelectronic switches and/or photodetectors. The 1 and 0 states of these devices are defined through polarization changes of the laser and direct complement functions are obtainable from the TE and TM output signals from the same laser. Switching of the polarization-bistable lasers with fast-rising current pulses has an instrument-limited mode-switching time on the order of 1 ns. With fast optoelectronic switches and/or fast photodetectors, the overall switching speed of the logic gates and flip-flops is limited by the polarization-bistable laser to < 1 ns. We have demonstrated the operations of these devices using optical signals generated by semiconductor lasers. The proposed schemes of our devices are compatible with monolithic integration based on current fabrication technology and are applicable to other types of bistable semiconductor lasers. 相似文献
116.
The original article to which this Erratum refers was published in Journal of Graph Theory 47:129–146,2004 . 相似文献
117.
LiuYuqi LiZhigang YahYakun 《Acta Mechanica Solida Sinica》2004,17(1):58-64
By using the Finite Element Inverse Approach based on the Hill quadratic anisotrop-ically yield criterion and the quadrilateral element, a fast analyzing software-FASTAMP for the sheet metal forming is developed. The blank shapes of three typical stampings are simulated and compared with numerical results given by the AUTOFORM software and experimental results, respectively. The comparison shows that the FASTAMP can predict blank shape and strain distribution of the stamping more precisely and quickly than those given by the traditional methods and the AUTOFORM. 相似文献
118.
Jenn‐Long Liu 《国际流体数值方法杂志》2004,44(12):1299-1315
This paper presents a relaxation algorithm, which is based on the overset grid technology, an unsteady three‐dimensional Navier–Stokes flow solver, and an inner‐ and outer‐relaxation method, for simulation of the unsteady flows of moving high‐speed trains. The flow solutions on the overlapped grids can be accurately updated by introducing a grid tracking technique and the inner‐ and outer‐relaxation method. To evaluate the capability and solution accuracy of the present algorithm, the computational static pressure distribution of a single stationary TGV high‐speed train inside a long tunnel is investigated numerically, and is compared with the experimental data from low‐speed wind tunnel test. Further, the unsteady flows of two TGV high‐speed trains passing by each other inside a long tunnel and at the tunnel entrance are simulated. A series of time histories of pressure distributions and aerodynamic loads acting on the train and tunnel surfaces are depicted for detailed discussions. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
119.
120.
Fang‐Jung Huang Tzong‐Liu Wang 《Journal of polymer science. Part A, Polymer chemistry》2004,42(2):290-302
Liquid‐crystalline, segmented polyurethanes with methoxy–biphenyl mesogens pendant on the chain extender were synthesized by the conventional prepolymer technique and esterification reaction. Two, side‐chain, liquid‐crystalline (SCLC) polyurethanes with mesogens having spacers of six and eight methylene units were prepared. The structures of the mesogenic units and SCLC polyurethanes were confirmed by Fourier transform infrared spectroscopy and 1H NMR. Polymer properties were also examined by solubility tests, water uptakes, and inherent viscosity measurements. Differential scanning calorimetry studies indicated that the transition temperature of the isotropic to the liquid‐crystalline phase decreased with increasing spacer length. Wide‐angle X‐ray diffraction (WAXD) studies revealed the existence of liquid‐crystalline phases for both SCLC polyurethanes. Polarized optical microscopic investigations further confirmed the thermotropic liquid‐crystalline behaviors and nematic mesophases of both samples. Thermogravimetric analysis displayed better thermal stabilities for both SCLC polymers and indicated that the presence of mesogenic side chains may increase the thermal stability of segmented polyurethanes. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 290–302, 2004 相似文献