全文获取类型
收费全文 | 275282篇 |
免费 | 7170篇 |
国内免费 | 7566篇 |
专业分类
化学 | 153969篇 |
晶体学 | 3348篇 |
力学 | 11818篇 |
综合类 | 423篇 |
数学 | 36934篇 |
物理学 | 83526篇 |
出版年
2021年 | 2208篇 |
2020年 | 2611篇 |
2019年 | 2848篇 |
2018年 | 4385篇 |
2017年 | 4672篇 |
2016年 | 5418篇 |
2015年 | 4212篇 |
2014年 | 5398篇 |
2013年 | 11398篇 |
2012年 | 12699篇 |
2011年 | 14877篇 |
2010年 | 10501篇 |
2009年 | 9981篇 |
2008年 | 11124篇 |
2007年 | 11067篇 |
2006年 | 10434篇 |
2005年 | 13393篇 |
2004年 | 12743篇 |
2003年 | 9784篇 |
2002年 | 7992篇 |
2001年 | 8235篇 |
2000年 | 5922篇 |
1999年 | 4498篇 |
1998年 | 3747篇 |
1997年 | 3468篇 |
1996年 | 3177篇 |
1995年 | 2946篇 |
1994年 | 2974篇 |
1993年 | 3127篇 |
1992年 | 3496篇 |
1991年 | 3373篇 |
1990年 | 3151篇 |
1989年 | 2985篇 |
1988年 | 2705篇 |
1987年 | 2541篇 |
1986年 | 2561篇 |
1985年 | 3336篇 |
1984年 | 3380篇 |
1983年 | 2823篇 |
1982年 | 3043篇 |
1981年 | 2798篇 |
1980年 | 2598篇 |
1979年 | 2789篇 |
1978年 | 2997篇 |
1977年 | 3030篇 |
1976年 | 3105篇 |
1975年 | 2804篇 |
1974年 | 2924篇 |
1973年 | 2982篇 |
1972年 | 2330篇 |
排序方式: 共有10000条查询结果,搜索用时 358 毫秒
91.
J. Conrad J. Cohen-Tanugi L. E. Strigari 《Journal of Experimental and Theoretical Physics》2015,121(6):1104-1135
The launch of the gamma-ray telescope Fermi Large Area Telescope (Fermi-LAT) started a pivotal period in indirect detection of dark matter. By outperforming expectations, for the first time a robust and stringent test of the paradigm of weakly interacting massive particles (WIMPs) is within reach. In this paper, we discuss astrophysical targets for WIMP detection and the challenges they present, review the analysis tools which have been employed to tackle these challenges, and summarize the status of constraints on and the claimed detections in the WIMP parameter space. Methods and results will be discussed in comparison to Imaging Air Cherenkov Telescopes. We also provide an outlook on short term and longer term developments. 相似文献
92.
Kondakov N. N. Mel´nikova T. M. Chekryzhova T. V. Mel´nikova M. V. Zinin A. I. Torgov V. I. Chizhov A. O. Kononov L. O. 《Russian Chemical Bulletin》2015,64(5):1142-1148
Russian Chemical Bulletin - Terminal disaccharide fragment of phenolic glycolipid from Mycobacterium leprae (PGL-I) was synthesized as a glycoside with 4-(2-aminoethoxy)phenyl aglycon. The obtained... 相似文献
93.
Claudia Poloni Marc C. A. Stuart Pieter van der Meulen Wiktor Szymanski Ben L. Feringa 《Chemical science》2015,6(12):7311-7318
The external photocontrol over peptide folding, by the incorporation of molecular photoswitches into their structure, provides a powerful tool to study biological processes. However, it is limited so far to switches that exhibit only a rather limited geometrical change upon photoisomerization and that show thermal instability of the photoisomer. Here we describe the use of an overcrowded alkene photoswitch to control a model β-hairpin peptide. This photoresponsive unit undergoes a large conformational change and has two thermally stable isomers which has major influence on the secondary structure and the aggregation of the peptide, permitting the phototriggered formation of amyloid-like fibrils. 相似文献
94.
Briana L. Simms Nan Ji Indika Chandrasiri Mohammad Farid Zia Chinwe S. Udemgba Ravinder Kaur Jared H. Delcamp Alex Flynt Chalet Tan Davita L. Watkins 《Journal of polymer science. Part A, Polymer chemistry》2021,59(19):2177-2192
Here, we demonstrate the applicability of self-assembling linear-dendritic block copolymers (LDBCs) and their nanoaggregates possessing varied surfaces as therapeutic nanocarriers. These LDBCs are comprised of a hydrophobic, linear polyester chemically coupled to a hydrophilic dendron polyamidoamine (PAMAM)—the latter of which acts as the surface of the self-assembled nanoaggregate in aqueous media. To better understand how surface charge density affects the overall operability of these nanomaterials, we modified the nanoaggregate surface to yield cationic (NH3+), neutral (OH), and anionic (COO−) surfaces. The effect of these modifications on the physicochemical properties (i.e., size, morphology, and surface charge density), colloidal stability, and cellular uptake mechanism of the polymeric nanocarrier were investigated. This comparative study demonstrates the viability of nanoaggregates formed from PDLLA-PAMAM LDBCs to serve as nanocarriers for applications in drug delivery. 相似文献
95.
以典型的双稳态系统——屈曲梁结构为例,基于等效模型,结合解析、数值和实验手段,研究了双稳态结构中的1/2次谐波共振特性、演化过程、参数调节规律及其对隔振特性的影响.研究发现,当非线性刚度系数或激励幅值增加到一定程度时,系统会在一定带宽下产生显著的1/2次谐波共振;随着激励幅值增加,阻尼系统的1/2次谐波遵循“产生-增强-衰退-消失”的过程,该过程对峰值频率和峰值传递率有重要影响;适当提高非线性强度能有效改善双稳态结构隔振特性.针对双稳态屈曲梁结构开展的实验验证了1/2次谐波特性和隔振特性变化规律. 相似文献
96.
97.
98.
99.
100.
Natalia L. Calvo Sebastian O. SimonettiRubén M. Maggio Teodoro S. Kaufman 《Analytica chimica acta》2015
Exposure of cimetidine (CIM) to dry heat (160–180 °C) afforded, upon cooling, a glassy solid containing new and hitherto unknown products. The kinetics of this process was studied by a second order chemometrics-assisted multi-spectroscopic approach. Proton and carbon-13 nuclear magnetic resonance (NMR), as well as ultraviolet and infrared spectroscopic data were jointly used, whereas multivariate curve resolution with alternating least squares (MCR-ALS) was employed as the chemometrics method to extract process information. It was established that drug degradation follows a first order kinetics. 相似文献