全文获取类型
收费全文 | 2544篇 |
免费 | 129篇 |
国内免费 | 55篇 |
专业分类
化学 | 1562篇 |
晶体学 | 37篇 |
力学 | 88篇 |
综合类 | 1篇 |
数学 | 434篇 |
物理学 | 606篇 |
出版年
2023年 | 16篇 |
2022年 | 18篇 |
2021年 | 38篇 |
2020年 | 46篇 |
2019年 | 42篇 |
2018年 | 37篇 |
2017年 | 31篇 |
2016年 | 79篇 |
2015年 | 52篇 |
2014年 | 67篇 |
2013年 | 148篇 |
2012年 | 167篇 |
2011年 | 172篇 |
2010年 | 129篇 |
2009年 | 89篇 |
2008年 | 137篇 |
2007年 | 122篇 |
2006年 | 132篇 |
2005年 | 111篇 |
2004年 | 103篇 |
2003年 | 95篇 |
2002年 | 73篇 |
2001年 | 59篇 |
2000年 | 61篇 |
1999年 | 55篇 |
1998年 | 29篇 |
1997年 | 42篇 |
1996年 | 23篇 |
1995年 | 36篇 |
1994年 | 31篇 |
1993年 | 40篇 |
1992年 | 50篇 |
1991年 | 39篇 |
1990年 | 34篇 |
1989年 | 32篇 |
1988年 | 17篇 |
1987年 | 23篇 |
1986年 | 21篇 |
1985年 | 30篇 |
1984年 | 26篇 |
1982年 | 15篇 |
1981年 | 17篇 |
1980年 | 13篇 |
1979年 | 20篇 |
1978年 | 23篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1975年 | 10篇 |
1974年 | 12篇 |
1973年 | 13篇 |
排序方式: 共有2728条查询结果,搜索用时 15 毫秒
1.
miRNA (miR)-155 is a potential biomarker for breast cancers. We aimed at developing a nanosensor for miR-155 detection by integrating hybridization chain reaction (HCR) and silver nanoclusters (AgNCs). HCR serves as an enzyme-free and isothermal amplification method, whereas AgNCs provide a built-in fluorogenic detection probe that could simplify the downstream analysis. The two components were integrated by adding a nucleation sequence of AgNCs to the hairpin of HCR. The working principle was based on the influence of microenvironment towards the hosted AgNCs, whereby unfolding of hairpin upon HCR has manipulated the distance between the hosted AgNCs and cytosine-rich toehold region of hairpin. As such, the dominant emission of AgNCs changed from red to yellow in the absence and presence of miR-155, enabling a ratiometric measurement of miR with high sensitivity. The limit of detection (LOD) of our HCR-AgNCs nanosensor is 1.13 fM in buffered solution. We have also tested the assay in diluted serum samples, with comparable LOD of 1.58 fM obtained. This shows the great promise of our HCR-AgNCs nanosensor for clinical application. 相似文献
2.
3.
The natural modes of a discrete linear system are orthogonal with respect to the mass and stiffness matrices in a generalized sense. However, these modes are usually not orthogonal to each other in the ordinary sense. The purpose of this paper is to document a number of conditions under which the modes are also orthogonal in an ordinary fashion. 相似文献
4.
Siaw-Lynn Ng 《Order》2004,21(1):1-5
We present a characterisation of posets of size n with linear discrepancy n − 2. These are the posets that are “furthest” from a linear order without being an antichain.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
5.
We will prove a result concerning the inclusion of non-trivial invariant ideals inside non-trivial ideals of a twisted crossed
product. We will also give results concerning the primeness and simplicity of crossed products of twisted actions of locally
compact groups on -algebras.
Received: 25 January 2002; in final form: 22 May 2002/Published online: 2 December 2002
This work is partially supported by Hong Kong RGC Direct Grant. 相似文献
6.
7.
Zhong‐Zhen Yu Mingshu Yang Qingxin Zhang Chungui Zhao Yiu‐Wing Mai 《Journal of Polymer Science.Polymer Physics》2003,41(11):1234-1243
Nylon‐66 nanocomposites were prepared by melt‐compounding nylon‐66 with an alkyl ammonium surfactant pretreated montmorillonite (MMT). The thermal stability of the organic MMT powders was measured by thermogravimetric analysis. The decomposition of the surfactant on the MMT occurred from 200 to 500 °C. The low onset decomposition temperature of the organic MMT is one shortcoming when it is used to prepare polymer nanocomposites at high melt‐compounding temperatures. To provide greater property enhancement and better thermal stability of the polymer/MMT nanocomposites, it is necessary to develop MMT modified with more thermally stable surfactants. The dispersion and spatial distribution of the organic MMT layers in the nylon‐66 matrix were characterized by X‐ray diffraction. The organic MMT layers were exfoliated but not randomly dispersed in the nylon‐66 matrix. A model was proposed to describe the spatial distribution of the organic MMT layers in an injection‐molded rectangular bar of nylon‐66/organic MMT nanocomposites. Most organic MMT layers were oriented in the injection‐molding direction. Layers near the four surfaces of the bar were parallel to their corresponding surfaces; whereas those in the bulk differed from the near‐surface layers and rotated themselves about the injection‐molding direction. The influence of the spatial distribution of the organic MMT on crystallization of nylon‐66 was also investigated. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1234–1243, 2003 相似文献
8.
Discrete global descent method for discrete global optimization and nonlinear integer programming 总被引:2,自引:0,他引:2
A novel method, entitled the discrete global descent method, is developed in this paper to solve discrete global optimization
problems and nonlinear integer programming problems. This method moves from one discrete minimizer of the objective function
f to another better one at each iteration with the help of an auxiliary function, entitled the discrete global descent function.
The discrete global descent function guarantees that its discrete minimizers coincide with the better discrete minimizers
of f under some standard assumptions. This property also ensures that a better discrete minimizer of f can be found by some classical local search methods. Numerical experiments on several test problems with up to 100 integer
variables and up to 1.38 × 10104 feasible points have demonstrated the applicability and efficiency of the proposed method. 相似文献
9.
The purpose of the present study was to describe the effects ofacute laryngitis on some aerodynamic, acoustic, and perceptual measures. Eleven subjects with diagnosed acute laryngitis due to upper respiratory infection were recorded during a laryngitic episode and 1 week to 10 days after amelioration of the laryngitic condition. Fundamental frequency values, collapsed across the five vowels, were significantly reduced in the laryngitic compared with the normal speaking condition. The decrease in fundamental frequency associated with acute laryngitis suggests an increase in the mass of the vocal folds. In addition, aerodynamic values differed significantly for the laryngitic condition compared with the normal speaking condition, suggesting the presence of laryngeal hypofunction. Perceptual data indicated that speakers in the laryngitic condition were judged to have a hoarse voice when compared with the normal speaking condition. 相似文献
10.
The use of phase-Doppler anemometry (PDA) to characterize the detail in-flight plasma sprayed particle behavior has been demonstrated
previously [Ma et al. Plasma Chem Plasma Process 24(1):85; 25(1):56] The present articles shows further that a direct relationship
may exist between the PDA measured particle volume flux and the coating microstructure and deposition efficiency (DE). In
the situation when the precise particle temperature information is not available, the PDA measured particle volume flux may
provide an alternative to predict quantitatively the variation of the coating microstructure and the DE. By monitoring the
in-flight particle volume flux variations, instead of the particle velocity, size and temperature individually and simultaneously,
the optimal settings of the plasma spraying parameters may also be determined conveniently. However, it is noted that the
effective applications of such approach depend largely on the particle surface morphology and the pre-determination of the
particle size range. 相似文献