全文获取类型
收费全文 | 11654篇 |
免费 | 1433篇 |
国内免费 | 502篇 |
专业分类
化学 | 1729篇 |
晶体学 | 21篇 |
力学 | 1311篇 |
综合类 | 178篇 |
数学 | 5149篇 |
物理学 | 5201篇 |
出版年
2024年 | 11篇 |
2023年 | 112篇 |
2022年 | 222篇 |
2021年 | 223篇 |
2020年 | 232篇 |
2019年 | 245篇 |
2018年 | 227篇 |
2017年 | 345篇 |
2016年 | 421篇 |
2015年 | 306篇 |
2014年 | 627篇 |
2013年 | 845篇 |
2012年 | 643篇 |
2011年 | 766篇 |
2010年 | 648篇 |
2009年 | 773篇 |
2008年 | 813篇 |
2007年 | 803篇 |
2006年 | 654篇 |
2005年 | 596篇 |
2004年 | 535篇 |
2003年 | 442篇 |
2002年 | 408篇 |
2001年 | 296篇 |
2000年 | 295篇 |
1999年 | 223篇 |
1998年 | 237篇 |
1997年 | 186篇 |
1996年 | 215篇 |
1995年 | 172篇 |
1994年 | 186篇 |
1993年 | 122篇 |
1992年 | 102篇 |
1991年 | 76篇 |
1990年 | 78篇 |
1989年 | 57篇 |
1988年 | 47篇 |
1987年 | 43篇 |
1986年 | 46篇 |
1985年 | 49篇 |
1984年 | 44篇 |
1983年 | 16篇 |
1982年 | 53篇 |
1981年 | 22篇 |
1980年 | 26篇 |
1979年 | 32篇 |
1978年 | 24篇 |
1977年 | 13篇 |
1976年 | 12篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
3.
4.
Clemens G. Raab Georg Regensburger Jamal Hossein Poor 《Journal of Pure and Applied Algebra》2021,225(5):106564
A formal computation proving a new operator identity from known ones is, in principle, restricted by domains and codomains of linear operators involved, since not any two operators can be added or composed. Algebraically, identities can be modelled by noncommutative polynomials and such a formal computation proves that the polynomial corresponding to the new identity lies in the ideal generated by the polynomials corresponding to the known identities. In order to prove an operator identity, however, just proving membership of the polynomial in the ideal is not enough, since the ring of noncommutative polynomials ignores domains and codomains. We show that it suffices to additionally verify compatibility of this polynomial and of the generators of the ideal with the labelled quiver that encodes which polynomials can be realized as linear operators. Then, for every consistent representation of such a quiver in a linear category, there exists a computation in the category that proves the corresponding instance of the identity. Moreover, by assigning the same label to several edges of the quiver, the algebraic framework developed allows to model different versions of an operator by the same indeterminate in the noncommutative polynomials. 相似文献
5.
The Electrostatic Discharge (ESD) phenomenon has been described through the IEC 61000-4-2. ESD current parameters' values, have been set in this Standard. The theoretical ESD current waveform defined in this standard, describing the conventional Contact discharge mode, needs to be re-evaluated on the basis of accurate experimental data. Even though the standard deals with commercial ESD generators, its goal is to simulate the natural phenomenon as good as possible. More and accurate data may contribute to the better simulation of the natural phenomenon. New values and better comprehension of the phenomenon demand new measurements based on high end measuring equipment. Such works and publications have been carried out the past years. Yet, the need to systematize and integrate this work remains. Larger and trust-worthy series of measurements need to be carried out and presented clearly.This paper deals with new ESD-current data, taken with broadband equipment. New and more detailed measurements like these, were never before taken at such a large number of individuals. The goal of this work is that the data acquired can serve as a basis for re-evaluating the conventional approach of the scientific community to the ESD event.In this paper, using a broadband measuring system, new parameters' values are measured and relations are presented, following standard statistical procedures. The results, which occur from measurements carried out on tenths of human individuals, are questioning the Standard in many points. A new way of approaching the standardization of the ESD current is proposed, as the excuse of the poor measuring equipment that sets barriers on the measuring accuracy, does not apply any more. The charging voltages of 500 V and 1000 V were also examined since such range of voltages are often met at ESD events and they are considered very harmful. 相似文献
6.
Chao Liu Liying Wang Lin Yang Famei Wang Chunhong Xu Jingwei Lv Guanglai Fu Xianli Li Qiang Liu Haiwei Mu Tao Sun Paul K. Chu 《Physics letters. A》2019,383(25):3200-3206
A single-polarization filter comprising a gold-coated photonic crystal fiber based on surface plasmon resonance is designed and investigated. The pattern matching and coupled polarization characteristics analyzed by the full-vector finite element method (FEM) and losses at 1,540 nm are achieved to 1,016.01739 dB/cm (x-pol core mode) and 33.81917 dB/cm (y-pol core mode). The crosstalk (CT) value of the 1,540 nm band is ?853.12653 dB for fiber length and the bandwidth is 850 nm. The working wavelength of the filter ranges from 1,280 nm to 1,540 nm by varying the diameter of outer air holes (), the diameter of inner air holes (), the metal film thickness (t), as well as the liquid refractive index (n). 相似文献
7.
8.
Tatiana Monaretto Andre Souza Tiago Bueno Moraes Victor Bertucci-Neto Corinne Rondeau-Mouro Luiz Alberto Colnago 《Magnetic resonance in chemistry : MRC》2019,57(9):616-625
The traditional way to enhance signal-to-noise ratio (SNR) of nuclear magnetic resonance (NMR) signals is to increase the number of scans. However, this procedure increases the measuring time that can be prohibitive for some applications. Therefore, we have tested the use of several post-acquisition digital filters to enhance SNR up to one order of magnitude in time domain NMR (TD-NMR) relaxation measurements. The procedures were studied using continuous wave free precession (CWFP-T1) signals, acquired with very low flip angles that contain six times more noise than the Carr–Purcell–Meiboom–Gill (CPMG) signal of the same sample and experimental time. Linear (LI) and logarithmic (LO) data compression, low-pass infinity impulse response (LP), Savitzky–Golay (SG), and wavelet transform (WA) post-acquisition filters enhanced the SNR of the CWFP-T1 signals by at least six times. The best filters were LO, SG, and WA that have high enhancement in SNR without significant distortions in the ILT relaxation distribution data. Therefore, it was demonstrated that these post-acquisition digital filters could be a useful way to denoise CWFP-T1, as well as CPMG noisy signals, and consequently reducing the experimental time. It was also demonstrated that filtered CWFP-T1 method has the potential to be a rapid and nondestructive method to measure fat content in beef and certainly in other meat samples. 相似文献
9.
In this paper, we consider a viscoelastic wave equation of variable coefficients in the presence of past history with nonlinear damping and delay in the internal feedback and dynamic boundary conditions. Under suitable assumptions, we establish an explicit and general decay rate result without imposing restrictive assumption on the behavior of the relaxation function at infinity by Riemannian geometry method and Lyapunov functional method. 相似文献
10.