全文获取类型
收费全文 | 23952篇 |
免费 | 591篇 |
国内免费 | 477篇 |
专业分类
化学 | 4101篇 |
晶体学 | 936篇 |
力学 | 417篇 |
综合类 | 50篇 |
数学 | 15393篇 |
物理学 | 4123篇 |
出版年
2023年 | 61篇 |
2022年 | 160篇 |
2021年 | 174篇 |
2020年 | 178篇 |
2019年 | 469篇 |
2018年 | 495篇 |
2017年 | 345篇 |
2016年 | 374篇 |
2015年 | 387篇 |
2014年 | 708篇 |
2013年 | 1505篇 |
2012年 | 676篇 |
2011年 | 1856篇 |
2010年 | 1632篇 |
2009年 | 1598篇 |
2008年 | 1714篇 |
2007年 | 1711篇 |
2006年 | 1267篇 |
2005年 | 1061篇 |
2004年 | 928篇 |
2003年 | 738篇 |
2002年 | 710篇 |
2001年 | 505篇 |
2000年 | 476篇 |
1999年 | 462篇 |
1998年 | 461篇 |
1997年 | 332篇 |
1996年 | 422篇 |
1995年 | 432篇 |
1994年 | 405篇 |
1993年 | 310篇 |
1992年 | 291篇 |
1991年 | 197篇 |
1990年 | 204篇 |
1989年 | 186篇 |
1988年 | 115篇 |
1987年 | 131篇 |
1986年 | 100篇 |
1985年 | 176篇 |
1984年 | 125篇 |
1983年 | 75篇 |
1982年 | 106篇 |
1981年 | 131篇 |
1980年 | 116篇 |
1979年 | 65篇 |
1978年 | 115篇 |
1977年 | 103篇 |
1976年 | 98篇 |
1975年 | 40篇 |
1974年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Havva Esma OKUR KUTAY 《Turkish Journal of Chemistry》2020,44(6):1463
The existence of cation-vacancy sites in fullerides might lead to long-range ordering and generate a new vacancy-ordered superstructure. The purpose of this work is to search whether or not long-range ordering of vacant tetrahedral sites, namely superstructure emerges in nonstoichiometric K 1.5 Ba 0.25 CsC 60 fulleride. Therefore, K 1.5 Ba 0.25 CsC 60 with cation-vacancy sites is synthesized using a precursor method to avoid inadequate stoichiometry control and formation of impurity phases within the target composition. For this purpose, first, phase-pure K 6 C 60 , Ba 6 C 60 and Cs 6 C 60 precursors are synthesized. Stoichiometric quantities of these precursors are used for further reaction with C 60 to afford K 1.5 Ba 0.25 CsC 60 . Rietveld analysis of the high-resolution synchrotron X-ray powder diffraction data of the precursors and K 1.5 Ba 0.25 CsC 60 confirms that K 6 C 60 , Ba 6 C 60 and Cs 6 C 60 are single-phase and they crystallize in a body-centered-cubic structure ( Im 3) as reported in the literature. The analysis also shows that K 1.5 Ba 0.25 CsC 60 phase can be perfectly modeled using a face-centered cubic structure. No new peaks appear which could have implied the appearance of a superstructure. This suggests that there is no long-range ordered arrangement of vacant tetrahedral sites in K 1.5 Ba 0.25 CsC 60 . 相似文献
992.
Ionic liquid A327H+Cl− was generated by reaction of tertiary amine A327 and HCl, and the liquid-liquid extraction of indium(III) from the HCl medium by this ionic liquid dissolved in Solvesso 100 was investigated. The extraction reaction is exothermic. The numerical analysis of indium distribution data suggests the formation of A327H+InCl4− in the organic phase. The results derived from indium(III) extraction have been implemented in a supported liquid membrane system. The influence of the stirring speed (600–1200 min−1), carrier concentration (2.5–20% v/v) in the membrane phase, and indium concentration (0.01–0.2 g/L) in the feed phase on metal transport have been investigated. 相似文献
993.
Hui Sun Yun-Feng Zhang Hui-Xia Huo Peng-Wei Guan Chao-Chao Wang Hui-Na Yao 《Natural product research》2020,34(14):2030-2036
AbstractTwo new benzophenone glycosides, aquilarisides A (1) and B (2), together with six known analogues (3-8) were isolated from the pericarps of Aquilaria yunnanensis S. C. Huang. Their structures were elucidated on the basis of 1D and 2D NMR and mass spectroscopic analyses, and the absolute configuration of compound 1 was determined by experimental and calculated electronic circular dichroism (ECD) spectra. Anti-inflammatory activities of all compounds 1–8 were evaluated for their inhibitory activities against lipopolysaccharide (LPS)-stimulated induced nitric oxide (NO) production in RAW 264.7 cells using the Griess assay. Compound 2 indicated a weak inhibition of NO production. 相似文献
994.
BackgroundThyroid carcinoma (THCA) is one of the most frequent endocrine cancers and has increasing morbidity. Annexin A2 (ANXA2) has been found to be highly expressed in various cancers; however, its expression level and potential mechanism in THCA remain unknown. This study investigated the clinicopathological value and primary molecular machinery of ANXA2 in THCA.Material and MethodsPublic RNA-sequencing and microarray data were obtained and analyzed with ANXA2 expression in THCA and corresponding non-cancerous thyroid tissue. A Pearson correlation coefficient calculation was used for the acquisition of ANXA2 coexpressed genes, while edgR, limma, and Robust Rank Aggregation were employed for differentially expressed gene (DEG) in THCA. The probable mechanism of ANXA2 in THCA was predicted by gene ontology and pathway enrichment. A dual-luciferase reporter assay was employed to confirm the targeting relationships between ANXA2 and its predicted microRNA (miRNA).ResultsExpression of ANXA2 was significantly upregulated in THCA tissues with a summarized standardized mean difference of 1.09 (P < 0.0001) based on 992 THCA cases and 589 cases of normal thyroid tissue. Expression of ANXA2 was related to pathologic stage. Subsequently, 1442 genes were obtained when overlapping 4542 ANXA2 coexpressed genes with 2248 DEGs in THCA; these genes were mostly enriched in pathways of extracellular matrix-receptor interaction, cell adhesion molecules, and complement and coagulation cascades. MiR-23b-3p was confirmed to target ANXA2 by dual-luciferase reporter assay.ConclusionsUpregulated expression of ANXA2 may promote the malignant biological behavior of THCA by affecting the involving pathways or being targeted by miR-23b-3p. 相似文献
995.
AbstractThe phytochemical investigation on the twigs and leaves of Archidendron clypearia (Jack) I.C.N. led to the isolation of three pairs of furolactone-type lignans enantiomers, including a pair of new compounds (1R,5S,6S)-Kachiranol (1a) and (1S,5R,6R)-Kachiranol (1b) and four known compounds (2a/2b and 3a/3b). Separation of the furolactone-type lignans enantiomeric mixtures was achieved using chiral HPLC for the first time. Their structures were determined by spectroscopic analysis and comparison between the experimental and calculated electronic circular dichroism (ECD) spectra. All optical pure compounds were evaluated for their inhibitory effects on β-amyloid aggregation by ThT assay. Among them, the inhibitory activity of the compound 1b (71.1%) was higher than the positive control (61.0%) and other compounds. In addition, molecular dynamics and molecular docking were employed to explore the binding relationship between the ligand and the receptor. 相似文献
996.
To explain the mechanism underlying the adsorption of stevia's polar component rebaudioside A in hydrophilic interaction liquid chromatography mode, the characteristics of rebaudioside A adsorption on various resins in an organic‐solvent‐rich system were studied. Among the tested resins, the strongly acidic cation resin FPC11 showed the best adsorption behavior for rebaudioside A. The factors affecting the adsorption kinetics of the resin for rebaudioside A are discussed. The results showed that the pseudo‐second‐order reaction model and intra‐particle diffusion model best described the adsorption kinetics of rebaudioside A on the resin. The adsorption rate was controlled by physical sorption, mainly via electron sharing or electron transfer between the adsorbent and the adsorbate. The adsorption process with multiple stages involved weak initial adsorption behavior. Thermodynamic studies showed that the adsorption of rebaudioside A on the resin was not an ideal monolayer adsorption, but mutual adsorption effects between the adsorbates. The adsorption was a spontaneous, entropy‐increasing endothermic process. The synergistic effect of hydrogen bonding and ion–dipole was a possible driving force. 相似文献
997.
998.
基于Hill动力学与Michaelis-Menten方程,建立理论模型研究发状分裂相关增强子1(hairy and enhancer of split 1,Hes1)调控蛋白激酶B (Protein Kinase B,AKT)-鼠双微体2 (Murine Double Minute2,MDM2)-抗癌基因p53(p53)-第10号染色体缺失的磷酸酶及张力蛋白同源的基因(Phosphatase and tensin homolog deleted on chromosome ten,PTEN)通路的一种物理机制.研究发现,Hes1通过与PTEN结合抑制PTEN表达,并调控AKT信号.表明了Hes1蛋白的合成,以及Hes1与PTEN相互作用调控AKTMDM2-p53-PTEN通路信号,将会有效地控制细胞结果 . Hes1作为AKT-MDM2-p53-PTEN信号通路中上游调节的重要因素,还可以在一定程度上通过影响p53蛋白功能,改变p53对肿瘤的抑制性.理论结果可用于预测Notch通路信号异常诱导的致癌性,并进一步揭示了Notch信号通路影响细胞AKT-MDM2-p53-PTEN通路的激活... 相似文献
999.
1000.