全文获取类型
收费全文 | 6415篇 |
免费 | 363篇 |
国内免费 | 31篇 |
专业分类
化学 | 4344篇 |
晶体学 | 20篇 |
力学 | 140篇 |
数学 | 787篇 |
物理学 | 1000篇 |
无线电 | 518篇 |
出版年
2023年 | 67篇 |
2022年 | 60篇 |
2021年 | 106篇 |
2020年 | 132篇 |
2019年 | 136篇 |
2018年 | 95篇 |
2017年 | 82篇 |
2016年 | 253篇 |
2015年 | 225篇 |
2014年 | 230篇 |
2013年 | 357篇 |
2012年 | 422篇 |
2011年 | 441篇 |
2010年 | 290篇 |
2009年 | 254篇 |
2008年 | 352篇 |
2007年 | 331篇 |
2006年 | 329篇 |
2005年 | 325篇 |
2004年 | 289篇 |
2003年 | 196篇 |
2002年 | 229篇 |
2001年 | 116篇 |
2000年 | 111篇 |
1999年 | 100篇 |
1998年 | 74篇 |
1997年 | 110篇 |
1996年 | 90篇 |
1995年 | 94篇 |
1994年 | 75篇 |
1993年 | 82篇 |
1992年 | 67篇 |
1991年 | 41篇 |
1990年 | 50篇 |
1989年 | 46篇 |
1988年 | 30篇 |
1986年 | 22篇 |
1985年 | 23篇 |
1984年 | 27篇 |
1983年 | 22篇 |
1982年 | 30篇 |
1981年 | 29篇 |
1980年 | 25篇 |
1979年 | 30篇 |
1978年 | 23篇 |
1977年 | 30篇 |
1976年 | 21篇 |
1975年 | 27篇 |
1974年 | 28篇 |
1973年 | 37篇 |
排序方式: 共有6809条查询结果,搜索用时 15 毫秒
1.
Matteo Di Giosia Alice Soldà Markus Seeger Andrea Cantelli Fabio Arnesano Maria I. Nardella Vincenzo Mangini Francesco Valle Marco Montalti Francesco Zerbetto Stefania Rapino Matteo Calvaresi Vasilis Ntziachristos 《Advanced functional materials》2021,31(20):2101527
Fullerenes are candidates for theranostic applications because of their high photodynamic activity and intrinsic multimodal imaging contrast. However, fullerenes suffer from low solubility in aqueous media, poor biocompatibility, cell toxicity, and a tendency to aggregate. C70@lysozyme is introduced herein as a novel bioconjugate that is harmless to a cellular environment, yet is also photoactive and has excellent optical and optoacoustic contrast for tracking cellular uptake and intracellular localization. The formation, water-solubility, photoactivity, and unperturbed structure of C70@lysozyme are confirmed using UV-visible and 2D 1H, 15N NMR spectroscopy. The excellent imaging contrast of C70@lysozyme in optoacoustic and third harmonic generation microscopy is exploited to monitor its uptake in HeLa cells and lysosomal trafficking. Last, the photoactivity of C70@lysozyme and its ability to initiate cell death by means of singlet oxygen (1O2) production upon exposure to low levels of white light irradiation is demonstrated. This study introduces C70@lysozyme and other fullerene-protein conjugates as potential candidates for theranostic applications. 相似文献
2.
3.
4.
Markus Bödenler Ludovic de Rochefort P. James Ross Nicolas Chanet Geneviève Guillot Gareth R. Davies 《Molecular physics》2019,117(7-8):832-848
ABSTRACTFast field-cycling (FFC) nuclear magnetic resonance relaxometry is a well-established method to determine the relaxation rates as a function of magnetic field strength. This so-called nuclear magnetic relaxation dispersion gives insight into the underlying molecular dynamics of a wide range of complex systems and has gained interest especially in the characterisation of biological tissues and diseases. The combination of FFC techniques with magnetic resonance imaging (MRI) offers a high potential for new types of image contrast more specific to pathological molecular dynamics. This article reviews the progress in FFC-MRI over the last decade and gives an overview of the hardware systems currently in operation. We discuss limitations and error correction strategies specific to FFC-MRI such as field stability and homogeneity, signal-to-noise ratio, eddy currents and acquisition time. We also report potential applications with impact in biology and medicine. Finally, we discuss the challenges and future applications in transferring the underlying molecular dynamics into novel types of image contrast by exploiting the dispersive properties of biological tissue or MRI contrast agents. 相似文献
5.
电源设计者们仿佛正在目睹一个新的半导体技术的诞生。随之而来的新一代功率半导体器件远远优于现有的硅技术。SiC 材料可以让器件具有迄今为止设计工程师们梦寐以求却不能得到的出色特性。其最重要的优点包括以下几个方面::工作结温高达225 ℃,而相应的漏电流只有适度的增加。由于本质上不会出现热偏移thermal run-away),故可以在
很高的结温下可靠的工作。
没有正向或反向恢复,故即使在高温
下以高频工作时,也没有开关损耗。
甚至可以实现开关损耗极小、频率
高达1 M H z 的深度切换(h a rd
正向电阻具有… 相似文献
6.
A set of exact conditions is compiled for the purpose of developing and testing approximations for the exchange-correlation energy as a functional of the electron density. Special emphasis is placed upon recently developed density-scaling relationships. Commonly used generalized gradient approximations are compared against several of these conditions. A direct tabular comparison of these functionals (not of calculated properties) with one another is also made. © 1994 John Wiley & Sons, Inc. 相似文献
7.
Riikka Susitaival Ilmari Juva Markus Peuhkuri Samuli Aalto 《Telecommunication Systems》2006,33(1-3):67-88
In this paper we analyze measurements gathered from a 2.5~Gbps link in the Finnish university network (Funet) in 2004. The
traffic is broken down into origin-destination (OD) pair components based on source and destination IP address. We study the
traffic characteristics of these components, and identify four typical representative OD pairs. For these pairs we investigate
the validity of a moving IID Gaussian model. We find that the statistical properties of these OD pairs differ significantly
from each other, with only some of them close to Gaussian. The OD pairs are also found to have some cross-correlation between
each other, contradicting an often made assumption about OD pair independence. Furthermore, the existence of a mean-variance
relation between the OD pairs is studied. We find that there is a relation between mean and variance, but for some periods
of time it is rather weak. 相似文献
8.
9.
10.
We study the expected delay in cyclic polling models with general ‘branching-type’ service disciplines. For this class of
models, which contains models with exhaustive and gated service as special cases, we obtain closed-form expressions for the
expected delay under standard heavy-traffic scalings. We identify a single parameter associated with the service discipline
at each queue, which we call the ‘exhaustiveness’. We show that the scaled expected delay figures depend on the service policies
at the queues only through the exhaustiveness of each of the service disciplines. This implies that the influence of different
service disciplines, but with the same exhaustiveness, on the expected delays at the queues becomes the same when the system
reaches saturation. This observation leads to a new classification of the service disciplines. In addition, we show monotonicity
of the scaled expected delays with respect to the exhaustiveness of the service disciplines. This induces a complete ordering
in terms of efficiency of the service disciplines. The results also lead to new rules for optimization of the system performance
with respect to the service disciplines at the queues. Further, the exact asymptotic results suggest simple expected waiting-time
approximations for polling models in heavy traffic. Numerical experiments show that the accuracy of the approximations is
excellent for practical heavy-traffic scenarios.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献