全文获取类型
收费全文 | 19612篇 |
免费 | 741篇 |
国内免费 | 892篇 |
专业分类
化学 | 4483篇 |
晶体学 | 873篇 |
力学 | 465篇 |
综合类 | 76篇 |
数学 | 10805篇 |
物理学 | 2781篇 |
无线电 | 1762篇 |
出版年
2023年 | 93篇 |
2022年 | 186篇 |
2021年 | 199篇 |
2020年 | 196篇 |
2019年 | 431篇 |
2018年 | 450篇 |
2017年 | 370篇 |
2016年 | 381篇 |
2015年 | 394篇 |
2014年 | 790篇 |
2013年 | 1069篇 |
2012年 | 696篇 |
2011年 | 1306篇 |
2010年 | 1358篇 |
2009年 | 1498篇 |
2008年 | 1499篇 |
2007年 | 1514篇 |
2006年 | 1242篇 |
2005年 | 951篇 |
2004年 | 877篇 |
2003年 | 699篇 |
2002年 | 605篇 |
2001年 | 428篇 |
2000年 | 356篇 |
1999年 | 348篇 |
1998年 | 322篇 |
1997年 | 265篇 |
1996年 | 359篇 |
1995年 | 300篇 |
1994年 | 316篇 |
1993年 | 264篇 |
1992年 | 219篇 |
1991年 | 141篇 |
1990年 | 111篇 |
1989年 | 121篇 |
1988年 | 88篇 |
1987年 | 86篇 |
1986年 | 92篇 |
1985年 | 128篇 |
1984年 | 76篇 |
1983年 | 54篇 |
1982年 | 73篇 |
1981年 | 68篇 |
1980年 | 40篇 |
1979年 | 20篇 |
1978年 | 32篇 |
1977年 | 42篇 |
1976年 | 32篇 |
1974年 | 20篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 406 毫秒
1.
2.
This paper deals with the Cauchy–Dirichlet problem for the fractional Cahn–Hilliard equation. The main results consist of global (in time) existence of weak solutions, characterization of parabolic smoothing effects (implying under proper condition eventual boundedness of trajectories), and convergence of each solution to a (single) equilibrium. In particular, to prove the convergence result, a variant of the so-called ?ojasiewicz–Simon inequality is provided for the fractional Dirichlet Laplacian and (possibly) non-analytic (but ) nonlinearities. 相似文献
3.
4.
Qiang Wang Lei Shen Tong Xue Gao Cheng Cheng Zhi Huang Hong Jin Fan Yuan Ping Feng 《Advanced functional materials》2021,31(2):2002187
The {100} facet of single-crystalline TiO2(B) is an ideal platform for inserting Li ions, but it is hard to be obtained due to its high surface energy. Here, the single-crystalline TiO2(B) nanobelts from H2Ti3O7 with nearly 70% {100} facets exposed are synthesized, which significantly enhances Li-storage capacity. The first-principle calculations demonstrate an ab in-plane 2D diffusion through the exposed {100} facets. As a consequence, the nanobelts can significantly accommodate Li ions in LiTiO2 formula with specific capacity up to 335 mAh g−1, which is in good agreement with the electrochemical characterizations. Coating with conductive and protective poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), the cut-off discharge voltage is as low as 0.5 V, leading to a capacity of 160.7 mAh g−1 after 1500 cycles with a retention rate of 66% at 1C. This work provides a practical strategy to increase the Li-ion capacity and cycle stability by tailoring the crystal orientation and nanostructures. 相似文献
5.
It is believed that there are more fundamental gauge symmetries beyond those described by the Standard Model of particle physics. The scales of these new gauge symmetries are usually too high to be reachable by particle colliders. Considering that the phase transition (PT) relating to the spontaneous breaking of new gauge symmetries to the electroweak symmetry might be strongly first order, we propose considering the stochastic gravitational waves (GW) arising from this phase transition as an indirect way of detecting these new fundamental gauge symmetries. As an illustration, we explore the possibility of detecting the stochastic GW generated from the PT of \begin{document}$ {\bf{B}}-{\bf{L}}$\end{document} ![]()
![]()
in the space-based interferometer detectors. Our study demonstrates that the GW energy spectrum is reachable by the LISA, Tianqin, Taiji, BBO, and DECIGO experiments only for the case where the spontaneous breaking of \begin{document}$ {\bf{B}}-{\bf{L}}$\end{document} ![]()
![]()
is triggered by at least two electroweak singlet scalars. 相似文献
6.
1-read/1-write (1R1W) register file (RF) is a popular memory configuration in modern feature rich SoCs requiring significant amount of embedded memory. A memory compiler is constructed using the 8T RF bitcell spanning a range of instances from 32 b to 72 Kb. An 8T low-leakage bitcell of 0.106 μm2 is used in a 14 nm FinFET technology with a 70 nm contacted gate pitch for high-density (HD) two-port (TP) RF memory compiler which achieves 5.66 Mb/mm2 array density for a 72 Kb array which is the highest reported density in 14 nm FinFET technology. The density improvement is achieved by using techniques such as leaf-cell optimization (eliminating transistors), better architectural planning, top level connectivity through leaf-cell abutment and minimizing the number of unique leaf-cells. These techniques are fully compatible with memory compiler usage over the required span. Leakage power is minimized by using power-switches without degrading the density mentioned above. Self-induced supply voltage collapse technique is applied for write and a four stack static keeper is used for read Vmin improvement. Fabricated test chips using 14 nm process have demonstrated 2.33 GHz performance at 1.1 V/25 °C operation. Overall Vmin of 550 mV is achieved with this design at 25 °C. The inbuilt power-switch improves leakage power by 12x in simulation. Approximately 8% die area of a leading 14 nm SoC in commercialization is occupied by these compiled RF instances. 相似文献
7.
随着计算机网络技术的发展,远程教学系统的结构发生了重大的变化,逐步由原来的客户机/服务器(C/S)结构转变为基于Internet的浏览器/服务器(B/S)结构。本文提出了基于CORBA技术的B/S结构系统模型。分析了其运行过程,并与传统的结构进行了比较,指明了其优越性。在本文的结尾。指出了使用这种技术的一个具体例子。 相似文献
8.
9.
数字下变频器GC1012B原理及配置方法 总被引:1,自引:0,他引:1
数字下变频技术是软件无线电的一项核心技术,其性能的好坏直接影响数字接收机的精度。GC1012B是美国TI公司推出的新型数字下变频器。文中从GC1012B的结构特点和内部功能框图出发,分析其工作原理,并介绍GC1012B几个主要寄存器的配置方法,从而实现对频率、滤波模式、增益大小等参数的设置。最后给出了一个具体配置实例作为参考。 相似文献
10.
We prove that to most of the known hypercyclic operators A on separable Banach spaces there exist compact (compact convex, compact connected) subsets K of E such that each compact (compact convex, compact connected) subset of E can be approximated with respect to Hausdorff's distance by for suitable .
Received July 8, 1997, in final form October 17, 1997 相似文献