全文获取类型
收费全文 | 26063篇 |
免费 | 850篇 |
国内免费 | 154篇 |
专业分类
化学 | 17300篇 |
晶体学 | 276篇 |
力学 | 817篇 |
数学 | 2521篇 |
物理学 | 6153篇 |
出版年
2023年 | 159篇 |
2022年 | 449篇 |
2021年 | 603篇 |
2020年 | 471篇 |
2019年 | 467篇 |
2018年 | 412篇 |
2017年 | 391篇 |
2016年 | 744篇 |
2015年 | 645篇 |
2014年 | 895篇 |
2013年 | 1522篇 |
2012年 | 1888篇 |
2011年 | 2096篇 |
2010年 | 1323篇 |
2009年 | 1159篇 |
2008年 | 1748篇 |
2007年 | 1541篇 |
2006年 | 1573篇 |
2005年 | 1336篇 |
2004年 | 1170篇 |
2003年 | 981篇 |
2002年 | 945篇 |
2001年 | 581篇 |
2000年 | 511篇 |
1999年 | 362篇 |
1998年 | 233篇 |
1997年 | 220篇 |
1996年 | 304篇 |
1995年 | 209篇 |
1994年 | 220篇 |
1993年 | 215篇 |
1992年 | 163篇 |
1991年 | 142篇 |
1990年 | 138篇 |
1989年 | 111篇 |
1988年 | 81篇 |
1987年 | 90篇 |
1986年 | 60篇 |
1985年 | 89篇 |
1984年 | 57篇 |
1983年 | 56篇 |
1982年 | 80篇 |
1981年 | 81篇 |
1980年 | 50篇 |
1979年 | 58篇 |
1978年 | 64篇 |
1977年 | 47篇 |
1976年 | 51篇 |
1975年 | 50篇 |
1974年 | 53篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
In this study, ultrasound-assisted extraction (UAE) was applied to extract bioactive substances with skin-whitening, anti-wrinkle, and antioxidant effects from safflower seeds, and the extraction conditions were optimized by a central composite design. The independent variables, including extraction time (5.0~55.0 min), extraction temperature (26.0~94.0 °C), and ethanol concentration (0.0~100%), were optimized to increase tyrosinase activity inhibitory (TAI), collagenase activity inhibitory (CAI), and radical scavenging activity (RSA), which are indicators of skin-whitening, anti-wrinkle, and antioxidant effects. An extraction time of 26.4 min, extraction temperature of 52.1 °C, and ethanol concentration of 50.7% were found to be optimum conditions of UAE, under which TAI, CAI, and RSA were 53.3%, 91.5%, and 27.7%, respectively. The extract produced by UAE was analyzed by LC-MS/MS, and maleic acid and levulinic acid were identified as the main substances. Therefore, UAE is evaluated as an effective process to extract skin-whitening, anti-wrinkle, and antioxidant substances from safflower seeds at lower temperatures and shorter extraction times compared to the conventional extraction methods. Overall, safflower seeds extract can be used as a material for value-added cosmetics, including maleic acid and levulinic acid, which have bioactive functions. 相似文献
993.
Real-time autodetachment dynamics of the loosely bound excess electron from the vibrational Feshbach resonances of the dipole-bound states (DBS) of 4-bromophonoxide (4-BrPhO−) and 4-chlorophenoxide (4-ClPhO−) anions have been thoroughly investigated. The state-specific autodetachment rate measurements obtained by the picosecond time-resolved pump-probe method on the cryogenically cooled anions exhibit an exceptionally long lifetime (τ) of ∼823 ± 156 ps for the 11′1 vibrational mode of the 4-BrPhO− DBS. Strong mode-dependency in the wide dynamic range has also been found, giving τ ∼ 5.3 ps for the 10′1 mode, for instance. Though it is nontrivial to get the state-specific rates for the 4-ClPhO− DBS, the average autodetachment lifetime of the 19′120′1/11′1 mode has been estimated to be ∼548 ± 108 ps. Observation of these exceptionally slow autodetachment rates of vibrational Feshbach resonances strongly indicates that the correlation effect may play a significant role in the DBS photodetachment dynamics. Fermi''s golden rule has been invoked so that the correlation effect is taken into account in the form of the interaction between the charge and the induced dipole where the latter is given by the polarizable counterparts of the electron-rich halogenated compound and the diffuse non-valence electron. This report suggests that one may measure, from the real-time autodetachment dynamics, the extent of the correlation effect contribution to the stabilization and/or dynamics of the excess non-valence electron among many different types of long-range interactions of the DBS.Exceptionally slow autodetachment dynamics of the vibrational Feshbach resonances found in the dipole-bound state of 4-bromophonoxide (4-BrPhO−) or 4-chlorophenoxide (4-ClPhO−) anions reveals the associated dynamic role of the correlation effect. 相似文献
994.
The surface-enhanced Raman scattering (SERS) of uracil, uridine, 2′-deoxyuridine and 5′-rUMP adsorbed on aqueous silver sol was investigated. Uracil was found to adsorb as the N-3 deprotonated form, which underwent a reorientation from the situation where the base was perpendicular to the surface to the situation where the base lay flat on the surface as the surface charge was made more negative. The N-3 deprotonated molecules of uridine, 2′-deoxyuridine and 5′-rUMP were found to lie flat on the silver surface regardless of the bulk concentration and the silver surface charge. 相似文献
995.
996.
ABSTRACTA novel BODIPY-based dye with highly emissive character was configured by Sonogashira coupling and routinely characterized by NMR and MS technology. The emission of dye was investigated in solution/film/solid and shows intensive emission. In solution, the emission peak appeared around 510 nm with little influence by the polar environment. The terthiophene plays an effective antenna effect, harvesting the light and transferring the energy to BODIPY. The pseudo Stoke's shift enlarged to ~170 nm in solution. In film, the emission peak shifted to 563 nm in polycarbonate matrix. And it shifted further to 585 nm in solid due to the highly twisted structure, which avoided closely regular-tight packing. The dye rendered an intense fluorescence, good optothermal stability, and high fluorescence quantum yield (0.55). The solid emission showed highly red emission with Commission Internationale de L'Eclairage (CIE) coordinates of (X = 0.69, Y = 0.31). Thus, the synthesized dye is idea candidate for emitting materials. 相似文献
997.
Jin Bai Kim 《数学研究及应用》1985,5(3):11-13
We give a characterization of a regular Boolean matrix and prove that AB = I Implies that BA = I, where A and B are Boolean matrices whose elements belong to a Boolean algebra of a set with more than two elements. 相似文献
998.
Yong Chan Kim 《Journal of Mathematical Analysis and Applications》2004,299(2):433-447
In this paper, nonlinear integral operators on normalized analytic functions in the unit disk are investigated in connection with the pre-Schwarzian derivative and the Hornich operation. In particular, several nontrivial relations between these operators and the class of strongly starlike functions will be deduced. 相似文献
999.
Jiyeon Park Dongmoung Kim Jin-Ok Lee Hyeon-Chun Park Brian Y. Ryu Ju Han Kim Sug Hyung Lee Yeun-Jun Chung 《Experimental & molecular medicine》2022,54(3):263
Despite growing evidence of the relevance of alternative splicing (AS) to cancer development and progression, the biological implications of AS for tumor behaviors, including papillary thyroid cancer (PTC), remain elusive. With the aim of further understanding the molecular and histological subtypes of PTC, we in this study explored whether AS events might act as new molecular determinants. For this purpose, AS profiles were analyzed in RNA-sequencing data from The Cancer Genome Atlas (TCGA) and from a Korean patient dataset. A total of 23 distinct exon-skipping (ES) events that correlated significantly with PTC oncogenic activity and differentiation scores were identified. The two top-ranked ES events, NUMA1_17515 in exon 18 of NUMA1 and TUBB3_38175 in exon 6 of TUBB3, showed high correlations with oncogenic activities and discriminated histological and molecular subtypes of PTC. Furthermore, two novel intron-retention (IR) events for TUBB3 were uncovered. All ES and IR events for the TUBB3 gene were predicted to induce nonsense-mediated mRNA decay. The relative abundances of intron reads in the PTC dataset from TCGA showed IR levels to differ significantly among PTC subtypes, possibly reflecting their different tumor behaviors. This study provides a landscape of AS changes among PTC subtypes and identified two significant AS events, NUMA1_17515 and TUBB3_38175, as potential AS biomarkers for PTC subclassification and characterization. The AS events identified in this study may be involved in the development of phenotypic differences underlying the functional characteristics and histological differentiation of PTCs.Subject terms: Cancer genomics, RNA splicing 相似文献
1000.
This investigation is dedicated to unlocking the hidden potential of discarded cosmetics towards building green sustainable road pavements in the future. It is particularly aiming at exploring waste lipstick (WLS) as a high-quality functional additive for advanced asphalt mix technologies. To fuel this novel innovation, the effect of various WLS doses (e.g., 5, 10, and 15 wt.%) on the performance of base AP-5 asphalt cement was studied in detail. A wide array of cutting-edge analytical lab techniques was employed to inspect in-depth the physicochemical, microstructural, thermo-morphological, and rheological properties of resultant admixtures including: elemental analysis, Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thin-layer chromatography-flame ionization detection (TLC-FID), scanning electron microscopy (SEM), atomic force microscopy (AFM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), needle penetration, ring and ball softening point, Brookfield viscometer, ductility, and dynamic shear rheometer (DSR) tests. Unlike the unstable response of asphaltenes, the additive/artificial aging treatments increased the fraction of resins the most, and decreased that of aromatics; however, asphaltenes did not impair the saturates portion, according to Iatroscan research. FT-IR scan divulged that the WLS-asphalt interaction was physical rather than chemical. XRD diagnosis not only revealed an obvious correlation between the asphaltenes content and the fresh-binder crystallinity but also revealed the presence of fillers in the WLS, which may generate outstanding technical qualities to bituminous mixes. According to AFM/SEM analyses, the stepwise incorporation of WLS grew the magnitude of the “bee-shaped” microstructures and extended the roughness rate of unaged/aged binders. The prolonged consumption of the high thermal-stable additive caused a remarkable drop in the onset degradation and glass transition temperature of mixtures, thus enhancing their workability and low-temperature performance, according to TGA/DTGA/DSC data. The DSR and empirical rheological experiments demonstrated that the WLS could effectively lower the manufacturing and compaction temperatures of asphalt mixes and impart them with valuable anti-aging/fatigue-cracking assets. In a nutshell, the use of waste lipstick as an asphalt modifier is viable and cost-effective and could attenuate the pollution arisen from the beauty sector, while improving the performance of hot/warm asphalt mixes (HAM/WAM) and extending the service life of roadways. 相似文献