全文获取类型
收费全文 | 26520篇 |
免费 | 3607篇 |
国内免费 | 2027篇 |
专业分类
化学 | 13283篇 |
晶体学 | 188篇 |
力学 | 1059篇 |
综合类 | 76篇 |
数学 | 2050篇 |
物理学 | 7644篇 |
综合类 | 7854篇 |
出版年
2024年 | 129篇 |
2023年 | 536篇 |
2022年 | 880篇 |
2021年 | 908篇 |
2020年 | 850篇 |
2019年 | 805篇 |
2018年 | 812篇 |
2017年 | 672篇 |
2016年 | 1082篇 |
2015年 | 1076篇 |
2014年 | 1352篇 |
2013年 | 1667篇 |
2012年 | 1968篇 |
2011年 | 1998篇 |
2010年 | 1404篇 |
2009年 | 1351篇 |
2008年 | 1471篇 |
2007年 | 1319篇 |
2006年 | 1212篇 |
2005年 | 1039篇 |
2004年 | 788篇 |
2003年 | 585篇 |
2002年 | 604篇 |
2001年 | 520篇 |
2000年 | 519篇 |
1999年 | 831篇 |
1998年 | 701篇 |
1997年 | 726篇 |
1996年 | 653篇 |
1995年 | 549篇 |
1994年 | 523篇 |
1993年 | 468篇 |
1992年 | 337篇 |
1991年 | 375篇 |
1990年 | 291篇 |
1989年 | 247篇 |
1988年 | 219篇 |
1987年 | 157篇 |
1986年 | 98篇 |
1985年 | 65篇 |
1984年 | 60篇 |
1983年 | 31篇 |
1982年 | 32篇 |
1981年 | 23篇 |
1980年 | 26篇 |
1978年 | 13篇 |
1976年 | 16篇 |
1975年 | 15篇 |
1973年 | 15篇 |
1968年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
891.
Yingjie Zhang Ping Ning Xueqian Wang Langlang Wang Yixing Ma Qiang Ma Yibing Xie 《应用有机金属化学》2019,33(6)
Manganese‐ and cerium oxide‐modified titania catalysts were prepared by the deposition precipitation for the removal of elemental mercury (Hg0) from simulated yellow phosphorus off‐gas at low temperature. In addition, these catalysts were characterized by X‐ray diffraction, Brunauer–Emmett–Teller measurements, X‐ray photoelectron spectroscopy and field‐emission scanning electron microscope to determine the surface morphology of the obtained compounds and explore their formation mechanism. The results revealed that a Mn–Ce loading and reaction temperature of 10% and 150 °C, respectively, as well as a Mn/Ce molar ratio of 2:1, led to an optimal efficiency for the oxidation of elemental mercury. Furthermore, the effects of flue gas components were investigated. The presence of O2 clearly promoted the oxidation of Hg0. A CO atmosphere did not affect the Hg0 oxidation, when compared with N2, whereas the presence of H2S and water vapor inhibited the oxidation process. Furthermore, the X‐ray photoelectron spectroscopy spectra of Hg 4f revealed that the elemental mercury adsorbed by the catalyst is present as HgO. Finally, the Hg0 catalytic oxidation mechanism was discussed on the basis of the experimental results and characterization analysis. 相似文献
892.
Self‐assembly of a resorcin[4]arene‐based ligand (TMR4A) with metal salts and H3PMo12O40·xH2O offers two isostructural complexes, namely, [Ni2Cl(TMR4A)2(CH3CN)2]·[PMo12O40]·4CH3CN ( 1 ) and [Co2Cl(TMR4A)2(CH3CN)2]·[PMo12O40]·4CH3CN ( 2 ). In both 1 and 2 , one Cl? anion bridges two metal cations, and each metal cation is further chelated by four 2‐mercaptopyridine N‐oxide groups of one TMR4A, producing a [M2Cl(TMR4A)2]3+ dimer (M = Ni or Co). The negative [PMo12O40]3? as a counter‐anion balances the positive charge. Markedly, 1 and 2 exhibit high stability in aqueous solutions with different pH values and in organic solvents. Remarkably, the efficient heterogeneous catalytic capability for oxidative desulfurization was studied by suing 1 and 2 as recycled catalysts. Moreover, the electrochemical behaviors of the two compounds were discussed as well. 相似文献
893.
Positivity - Let F be a non-archimedean o-field and $$C=F(i)$$ be the field of generalized complex numbers over F. In Ma et al. (Order 35:461–466, 2018), all directed partial orders on C with... 相似文献
894.
895.
本文针对求矩阵方程AXB+CXD=F唯一解的参数迭代法,分析当矩阵A,B,C,D均是Hermite正(负)定矩阵时,迭代矩阵的特征值表达式,给出了最优参数的确定方法,并提出了相应的加速算法. 相似文献
896.
Numerical Algorithms - The present work proposes a finite iterative algorithm to find the least squares solutions of periodic matrix equations over symmetric ξ-periodic matrices. By this... 相似文献
897.
Three novel complexes, namely [Nd·L1·HCOO·(H2O)4] ( 1 ), [Pr·L1·HCOO·(H2O)4] ( 2 ) and [In·L2·Cl·(H2O)2] ( 3 ) (L1 = 1,1-bis(5-(pyrazin-2-yl)-1,2,4-triazol-3-yl)methane, L2 = 1,1-bis(5-(pyrazin-2-yl)-1,2,4-triazol-3-yl)ketone), were synthesized and characterized. The molecular structures of 1 – 3 were confirmed using single-crystal X-ray diffraction. All three obtained complexes are zero-dimensional and connected to each other by hydrogen bonds. In 1 and 2 the metal is surrounded by nine donors and 3 has seven coordination sites. The interaction of 1 – 3 with calf thymus DNA (CT-DNA) was explored using UV absorption spectra and fluorescence spectra. The intrinsic binding constants of 1 – 3 with CT-DNA are about 1.9 × 104, 1.4 × 104 and 1.1 × 104, respectively. Stern–Volmer quenching plots of 1 – 3 have slopes of 0.1508, 0.134 and 0.1205, respectively. The ability of these complexes to cleave pBR322 plasmid DNA was demonstrated using gel electrophoresis assay. Apoptosis studies of the three novel complexes showed a significant inhibitory effect on HeLa cells. Furthermore, MTT assays were used to evaluate the anticancer activity of the three complexes. The cytotoxicity study indicated that complex 1 possesses a higher inhibitory rate of HeLa cells than the other complexes. Especially, the efficacy of 1 was shown to be the highest for cisplatin at 24 h. A further molecular docking technique was introduced to understand the binding of the complexes toward the target DNA. 相似文献
898.
Dr. Jinghui Zhang Lei Gong Xiaoshuang Zhang Dr. Mengliang Zhu Chaorui Su Qing Ma Dr. Dongdong Qi Prof. Yongzhong Bian Prof. Hongwu Du Prof. Jianzhuang Jiang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(61):13842-13848
Two-photon excited fluorescent (TPEF) materials are highly desirable for bioimaging applications owing to their unique characteristics of deep-tissue penetration and high spatiotemporal resolution. Herein, by connecting one, two, or three electron-deficient zinc porphyrin units to an electron-rich triazatruxene core via ethynyl π-bridges, conjugated multipolar molecules TAT-(ZnP) n (n=1–3) were developed as TPEF materials for cell imaging. The three new dyes present high fluorescence quantum yields (0.40–0.47) and rationally improved two-photon absorption (TPA) properties. In particular, the peak TPA cross section of TAT-ZnP (436 GM) is significantly larger than that of the ZnP reference (59 GM). The δTPA values of TAT-(ZnP)2 and TAT-(ZnP)3 further increase to 1031 and up to 1496 GM, respectively, indicating the effect of incorporated ZnP units on the TPA properties. The substantial improvement of the TPEF properties is attributed to the formation of π-conjugated quadrapole/octupole molecules and the extension of D -π-A-D systems, which has been rationalized by density function theory (DFT) calculations. Moreover, all of the three new dyes display good biocompatibility and preferential targeting ability toward cytomembrane, thus can be superior candidates for TPEF imaging of living cells. Overall, this work demonstrated a promising strategy for the development of porphyrin-based TPEF materials by the construction and extension of D -π-A-D multipolar array. 相似文献
899.
Xiao Ma Chongying Xu Zhibiao Mao Peiyu Ji Chenggang Jin Dongsheng Xu Yuqiang Ding 《应用有机金属化学》2020,34(2):e5349
A series of chemical vapor deposition (CVD) precursors have been synthesized by a single-step reaction of 1,1,3,3-tetramethylguanidine and a variety of silicon chlorides. The structures of the 1,1,3,3-tetramethylguanidinate-based compounds were verified by 1H NMR, 13C NMR, XPS, EI-MS, and elemental analysis. The thermal stability, transport behavior, and vapor pressures of these compounds were evaluated by simultaneous thermal analyses (STA). These compounds are highly stable and those in liquid form are very volatile. Silicon carbonitride (SiCN) thin films were prepared by using bis (tetramethylguanidine)-dimethyl-silane as the precursor in helicon wave plasma chemical vapor deposition (HWP-CVD). The properties of the films were investigated by SEM, AFM, and XPS. The results showed that the films have good uniformities, low friction coefficient, and high hardness, enabling the films for fabrication of semiconductor devices. 相似文献
900.