全文获取类型
收费全文 | 22997篇 |
免费 | 881篇 |
国内免费 | 2432篇 |
专业分类
化学 | 13638篇 |
晶体学 | 429篇 |
力学 | 216篇 |
综合类 | 266篇 |
数学 | 3178篇 |
物理学 | 4400篇 |
无线电 | 4183篇 |
出版年
2023年 | 232篇 |
2022年 | 423篇 |
2021年 | 350篇 |
2020年 | 354篇 |
2019年 | 469篇 |
2018年 | 468篇 |
2017年 | 397篇 |
2016年 | 459篇 |
2015年 | 447篇 |
2014年 | 773篇 |
2013年 | 1531篇 |
2012年 | 1115篇 |
2011年 | 1227篇 |
2010年 | 1100篇 |
2009年 | 1374篇 |
2008年 | 1432篇 |
2007年 | 1594篇 |
2006年 | 1376篇 |
2005年 | 1192篇 |
2004年 | 1096篇 |
2003年 | 850篇 |
2002年 | 1010篇 |
2001年 | 623篇 |
2000年 | 1402篇 |
1999年 | 1015篇 |
1998年 | 940篇 |
1997年 | 350篇 |
1996年 | 380篇 |
1995年 | 321篇 |
1994年 | 311篇 |
1993年 | 249篇 |
1992年 | 228篇 |
1991年 | 156篇 |
1990年 | 101篇 |
1989年 | 82篇 |
1988年 | 65篇 |
1987年 | 57篇 |
1986年 | 41篇 |
1985年 | 73篇 |
1984年 | 52篇 |
1983年 | 42篇 |
1982年 | 49篇 |
1981年 | 91篇 |
1980年 | 53篇 |
1979年 | 44篇 |
1978年 | 52篇 |
1977年 | 48篇 |
1976年 | 43篇 |
1974年 | 38篇 |
1973年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Kai Cheng Xiao-Shuai Zhang Jie An Cheng Li Ruo-Yun Zhang Run Ye Prof. Dr. Bang-Jiao Ye Prof. Dr. Bo Liu Prof. Dr. Yuan-Di Zhao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(31):7553-7560
Given their superior penetration depths, photosensitizers with longer absorption wavelengths present broader application prospects in photodynamic therapy (PDT). Herein, Ag2S quantum dots were discovered, for the first time, to be capable of killing tumor cells through the photodynamic route by near-infrared light irradiation, which means relatively less excitation of the probe compared with traditional photosensitizers absorbing short wavelengths. On modification with polydopamine (PDA), PDA-Ag2S was obtained, which showed outstanding capacity for inducing reactive oxygen species (increased by 1.69 times). With the addition of PDA, Ag2S had more opportunities to react with surrounding O2, which was demonstrated by typical triplet electron spin resonance (ESR) analysis. Furthermore, the PDT effects of Ag2S and PDA-Ag2S achieved at longer wavelengths were almost identical to the effects produced at 660 nm, which was proved by studies in vitro. PDA-Ag2S showed distinctly better therapeutic effects than Ag2S in experiments in vivo, which further validated the enhanced regulatory effect of PDA. Altogether, a new photosensitizer with longer absorption wavelength was developed by using the hitherto-unexplored photodynamic function of Ag2S quantum dots, which extended and enhanced the regulatory effect originating from PDA. 相似文献
2.
3.
4.
Ping Chen Yanhong Hao Xinxin Wang Prof. Dr. Dan Yuan Prof. Dr. Yingming Yao Prof. Dr. Lutz Ackermann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(30):7292-7297
Highly position selective alkylations of N-alkylindoles at C7-positions have been enabled by cationic zirconium complexes. The strategy provides a straightforward access to install alkyl groups at C7-positions of indoles without a complex directing group. Mechanistic studies provided support for the importance of Brønsted acids in the catalytic manifold. 相似文献
5.
高频结构仿真器(HFSS)是一种微波器件设计软件,该软件界面友好,通过仿真计算减小了调试工作量,使得微波器件的设计变得简单易行。本文利用HFSS对波导魔T进行了仿真分析,得到了该器件的S参数和动、静态场的分布情况,并对该器件进行了优化设计。 相似文献
6.
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
7.
光电设备电子机柜布线工艺研究 总被引:5,自引:0,他引:5
作为信号和电能载体的导线,同时也是噪声的载体和外来噪声侵入设备的媒体。描述了噪声通过导线侵入设备内部的方式,通过降低噪声的途径确定了机柜布线的原则,介绍了布线的要求和方法,最后提出了用布线槽布线的建议。 相似文献
8.
研究了红外频段非线性s偏振表面波在反铁磁晶体和电介质交界面上的频率特性,求出了非线性色散方程,揭示了非线性s偏振表面波存在一个临界频率,低于这个频率,非线性s偏振表面波的频率范围,发现功率不再是决定导波频率范围的唯一因素,两种材料的介电常数比在这里起了至关重要的作用。 相似文献
9.
M. Georgelin A. Pocheau 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(2):169-174
The polycrystalline perovskitelike manganese oxides La1-xAxMnO (A = Na, and K, ) have been fabricated by sol-gel technique. For all the compositions explored in this work, the average manganese oxidation
state is practically constant, at for A = Na, and for A = K, respectively. A close relationship is confirmed to hold between the Curie temperature (Tc) and the bond distance of Mn-O. Results of magnetic measurements show that these materials can be utilized as suitable candidates
for magnetic refrigerants with wide applied temperature span, for their significant entropy change and the easily tuned Curie
temperature.
Received: 12 September 1997 / Revised: 18 December 1997 / Accepted: 21 January 1998 相似文献
10.
C. Waldtmann H.-U. Everts B. Bernu C. Lhuillier P. Sindzingre P. Lecheminant L. Pierre 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(4):501-507
We study the exact low energy spectra of the spin 1/2 Heisenberg antiferromagnet on small samples of the kagomé lattice of up to N=36 sites. In agreement with the conclusions of previous authors, we find that these low energy spectra contradict the hypothesis
of Néel type long range order. Certainly, the ground state of this system is a spin liquid, but its properties are rather
unusual. The magnetic () excitations are separated from the ground state by a gap. However, this gap is filled with nonmagnetic () excitations. In the thermodynamic limit the spectrum of these nonmagnetic excitations will presumably develop into a gapless
continuum adjacent to the ground state. Surprisingly, the eigenstates of samples with an odd number of sites, i.e. samples with an unsaturated spin, exhibit symmetries which could support long range chiral order. We do not know if these
states will be true thermodynamic states or only metastable ones. In any case, the low energy properties of the spin 1/2 Heisenberg
antiferromagnet on the kagomé lattice clearly distinguish this system from either a short range RVB spin liquid or a standard chiral spin liquid. Presumably
they are facets of a generically new state of frustrated two-dimensional quantum antiferromagnets.
Received: 27 November 1997 / Accepted: 29 January 1998 相似文献