全文获取类型
收费全文 | 26696篇 |
免费 | 4206篇 |
国内免费 | 2895篇 |
专业分类
化学 | 14795篇 |
晶体学 | 260篇 |
力学 | 1262篇 |
综合类 | 199篇 |
数学 | 2084篇 |
物理学 | 7941篇 |
无线电 | 7256篇 |
出版年
2024年 | 100篇 |
2023年 | 686篇 |
2022年 | 782篇 |
2021年 | 1027篇 |
2020年 | 989篇 |
2019年 | 951篇 |
2018年 | 823篇 |
2017年 | 801篇 |
2016年 | 1156篇 |
2015年 | 1246篇 |
2014年 | 1429篇 |
2013年 | 1824篇 |
2012年 | 2278篇 |
2011年 | 2275篇 |
2010年 | 1584篇 |
2009年 | 1523篇 |
2008年 | 1708篇 |
2007年 | 1639篇 |
2006年 | 1531篇 |
2005年 | 1294篇 |
2004年 | 899篇 |
2003年 | 829篇 |
2002年 | 725篇 |
2001年 | 606篇 |
2000年 | 575篇 |
1999年 | 625篇 |
1998年 | 492篇 |
1997年 | 496篇 |
1996年 | 439篇 |
1995年 | 416篇 |
1994年 | 400篇 |
1993年 | 310篇 |
1992年 | 260篇 |
1991年 | 242篇 |
1990年 | 217篇 |
1989年 | 137篇 |
1988年 | 105篇 |
1987年 | 98篇 |
1986年 | 75篇 |
1985年 | 53篇 |
1984年 | 50篇 |
1983年 | 28篇 |
1982年 | 29篇 |
1981年 | 21篇 |
1980年 | 15篇 |
1979年 | 1篇 |
1975年 | 3篇 |
1957年 | 4篇 |
1936年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
881.
Jing Zhou Shihua Song Feng Jiang Chunling Fu Prof. Shengming Ma 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(42):9948-9958
Herein, we report the total synthesis of traumatic lactone and rhizobialide by utilizing allenoic acid to construct the lactone ring. The key starting materials, allenoic acids, could be prepared by the ATA (allenation of terminal alkynes) of a terminal alkyne with an aldehyde that contained a protected hydroxyl group followed by hydrolysis. Importantly, the asymmetric synthesis could be realized just by replacing racemic diphenylprinol with (R)- or (S)-diphenylprinol to deliver the optically active allenoate. 相似文献
882.
Na-Na Jiang Shu-Zong Du Yan-Song Ye Hui Yan Xing-Wei Yang Jian Yang Yin Nian Gang Xu 《Tetrahedron letters》2019,60(45):151220
Hyphenone A (1), a new type of bicyclic polyprenylated acylphloroglucinols (BPAPs) featured with an unprecedented 3,3-diisoprenylated 1,3,5-trione core, were characterized from the roots of Hypericum henryi together with two new congeners (hyphenones B–C, 2–3) and five known biosynthetic related PPAPs. Biogenetically, 1 should be derived from a novel 3,3,5,5-tetraisoprenylated MPAPs precursor. Their structures were elucidated by comprehensive spectroscopic data and X-ray diffraction. Moreover, 1–3 were identified as the first PPAPs type Cav3.1 T-type calcium channel (TTCC) inhibitors, with IC50 values of 7.07, 6.19, and 5.47 μM, respectively. 相似文献
883.
Jiaguo Huang Yan Lyu Jingchao Li Penghui Cheng Yuyan Jiang Kanyi Pu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(49):17960-17968
Despite its high morbidity and mortality, contrast‐induced acute kidney injury (CIAKI) remains a diagnostic dilemma because it relies on in vitro detection of insensitive late‐stage blood and urinary biomarkers. We report the synthesis of an activatable duplex reporter (ADR) for real‐time in vivo imaging of CIAKI. ADR is equipped with chemiluminescence and near‐infrared fluorescence (NIRF) signaling channels that can be activated by oxidative stress (superoxide anion, O2.?) and lysosomal damage (N‐acetyl‐β‐d ‐glucosaminidase, NAG), respectively. By virtue of its high renal clearance efficiency (80 % injected doses after 24 h injection), ADR detects sequential upregulation of O2.? and NAG in the kidneys of living mice prior to a significant decrease in glomerular filtration rate (GFR) and tissue damage in the course of CIAKI. ADR outperforms the typical clinical assays and detects CIAKI at least 8 h (NIRF) and up to 16 h (chemiluminescence) earlier. 相似文献
884.
The spatial-temporal evolution of coherent structures(CS) is significant for turbulence control and drag reduction. Among the CS, low and high speed streak structures show typical burst phenomena. The analysis was based on a time series of three-dimensional and three-component(3D-3C) velocity fields of the flat plate turbulent boundary layer(TBL) measured by a Tomographic and Time-resolved PIV(Tomo TRPIV) system. Using multi-resolution wavelet transform and conditional sampling method, we extracted the intrinsic topologies and found that the streak structures appear in bar-like patterns. Furthermore, we seized locations and velocity information of transient CS, and then calculated the propagation velocity of CS based on spatial-temporal cross-correlation scanning. This laid a foundation for further studies on relevant dynamics properties. 相似文献
885.
Nan Jiang Xiao-Yu Yang Guo-Liang Ying Ling Shen Jing Liu Wei Geng Ling-Jun Dai Shao-Yin Liu Jian Cao Ge Tian Tao-Lei Sun Shi-Pu Li Bao-Lian Su 《Chemical science》2015,6(1):486-491
Self-repair is nature''s way of protecting living organisms. However, most single cells are inherently less capable of self-repairing, which greatly limits their wide applications. Here, we present a self-assembly approach to create a nanoshell around the cell surface using nanoporous biohybrid aggregates. The biohybrid shells present self-repairing behaviour, resulting in high activity and extended viability of the encapsulated cells (eukaryotic and prokaryotic cells) in harsh micro-environments, such as under UV radiation, natural toxin invasion, high-light radiation and abrupt pH-value changes. Furthermore, an interaction mechanism is proposed and studied, which is successful to guide design and synthesis of self-repairing biohybrid shells using different bioactive molecules. 相似文献
886.
887.
Yingying Ma Guangyan Zhang Lingjuan Li Huan Yu Jia Liu Chaoqun Wang Yanfeng Chu Renxi Zhuo Xulin Jiang 《Journal of polymer science. Part A, Polymer chemistry》2016,54(7):879-888
The pH‐sensitive tertiary amino groups were introduced to synthesize temperature and pH dual‐sensitive degradable polyaspartamide derivatives (phe/DEAE‐g‐PHPA) containing pendant aromatic structures and ionizable tertiary amino groups. The thermo/pH‐responsive behavior of phe/DEAE‐g‐PHPA polymer can be tuned by adjusting the graft copolymer composition. Due to the pH sensitivity of the phe/DEAE‐g‐PHPA‐g‐mPEG polymer with hydrophilic long PEG chain, the micelles and the anticancer drug‐loaded micelles were prepared by a quick pH‐changing method without using toxic organic solvent. The obtained polymeric micelles, paclitaxel‐loaded micelles and doxorubicin‐loaded micelles were stable under physiological conditions. Both the drug‐loaded micelles showed much faster release at pH 5 than at pH 7.4. The doxorubicin‐loaded micelles showed obvious and better anticancer activity against both HepG2 and HeLa cells than free doxorubicin. Thus these nontoxic, dual thermo‐ and pH‐sensitive phe/DEAE‐g‐PHPA‐g‐mPEG micelles may be a promising anticancer drug delivery system. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 879–888 相似文献
888.
889.
Fan Wang Zicheng Zuo Liang Li Kuo Li Feng He Zhongqing Jiang Yuliang Li 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(42):15152-15157
A two‐dimensional (2D) carbon nanofilm with uniform artificial nanopores is an ideal material to ultimately suppress the fuel permeation in the proton exchange membrane fuel cells. Graphdiyne has great mechanical strength, high dimensional stability, and controllable nanopores, and has good prospects to play this crucial role. It is found that graphdiyne nanofilm with amino groups and natural nanopores can be easily prepared with high integrity. The aminated graphdiyne has good compatibility with the Nafion matrix owing to the acid–base interaction between them. The excellent comprehensive properties of graphdiyne in selectivity, dimensional stability, and integrity effectively improve the power performance and stability of fuel cells at wide temperature. Our results can be developed into a universal method that can easily realize the selective separation of ions and small molecules, and open a new way for the emerging applications in green energy. 相似文献
890.
Tong Su Yafei Wang Yi Liu William G. Branton Eugene Asahchop Christopher Power Bei Jiang Linglong Kong Niansheng Tang 《Entropy (Basel, Switzerland)》2020,22(11)
Distance weighted discrimination (DWD) is an appealing classification method that is capable of overcoming data piling problems in high-dimensional settings. Especially when various sparsity structures are assumed in these settings, variable selection in multicategory classification poses great challenges. In this paper, we propose a multicategory generalized DWD (MgDWD) method that maintains intrinsic variable group structures during selection using a sparse group lasso penalty. Theoretically, we derive minimizer uniqueness for the penalized MgDWD loss function and consistency properties for the proposed classifier. We further develop an efficient algorithm based on the proximal operator to solve the optimization problem. The performance of MgDWD is evaluated using finite sample simulations and miRNA data from an HIV study. 相似文献