全文获取类型
收费全文 | 15921篇 |
免费 | 2509篇 |
国内免费 | 1736篇 |
专业分类
化学 | 11691篇 |
晶体学 | 194篇 |
力学 | 840篇 |
综合类 | 72篇 |
数学 | 1545篇 |
物理学 | 5824篇 |
出版年
2024年 | 60篇 |
2023年 | 320篇 |
2022年 | 562篇 |
2021年 | 587篇 |
2020年 | 643篇 |
2019年 | 642篇 |
2018年 | 584篇 |
2017年 | 515篇 |
2016年 | 740篇 |
2015年 | 783篇 |
2014年 | 986篇 |
2013年 | 1210篇 |
2012年 | 1413篇 |
2011年 | 1495篇 |
2010年 | 1074篇 |
2009年 | 911篇 |
2008年 | 1055篇 |
2007年 | 959篇 |
2006年 | 845篇 |
2005年 | 730篇 |
2004年 | 547篇 |
2003年 | 462篇 |
2002年 | 428篇 |
2001年 | 307篇 |
2000年 | 309篇 |
1999年 | 254篇 |
1998年 | 225篇 |
1997年 | 197篇 |
1996年 | 184篇 |
1995年 | 144篇 |
1994年 | 185篇 |
1993年 | 129篇 |
1992年 | 128篇 |
1991年 | 97篇 |
1990年 | 90篇 |
1989年 | 85篇 |
1988年 | 46篇 |
1987年 | 31篇 |
1986年 | 34篇 |
1985年 | 29篇 |
1984年 | 22篇 |
1983年 | 11篇 |
1982年 | 15篇 |
1981年 | 7篇 |
1980年 | 17篇 |
1979年 | 7篇 |
1976年 | 10篇 |
1975年 | 7篇 |
1974年 | 8篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Kedong Song Dan Ge Shui Guan Chenggong Sun Xuehu Ma Tianqing Liu 《Applied biochemistry and biotechnology》2014,174(6):2114-2130
The aim of this study is to analyze the growth and substance metabolism of neural stem cells (NSCs) cultured in biological collagen-based scaffolds. Mass transfer and metabolism model of glucose, lactic acid, and dissolved oxygen (DO) were established and solved on MATLAB platform to obtain the concentration distributions of DO, glucose, and lactic acid in culture system, respectively. Calculation results showed that the DO influenced their normal growth and metabolism of NSCs mostly in the in vitro culture within collagen-based scaffolds. This study also confirmed that 2-mm thickness of collagen scaffold was capable of in vitro cultivation and growth of NSCs with an inoculating density of 1?×?106 cells/mL. 相似文献
92.
93.
Yu-Rong Chen Dr. Annavareddi Naresh Dr. Suh-Yuen Liang Dr. Chun-Hung Lin Dr. Rong-Jie Chein Dr. Hsiao-Ching Lin 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(32):13639-13643
The 1,3-enyne moiety is commonly found in cyclohexanoid natural products produced by endophytic and plant pathogenic fungi. Asperpentyn ( 1 ) is a 1,3-enyne-containing cyclohexanoid terpenoid isolated from Aspergillus and Pestalotiopsis. The genetic basis and biochemical mechanism of 1,3-enyne biosynthesis in 1 , and other natural products containing this motif, has remained enigmatic despite their potential ecological roles. Identified here is the biosynthetic gene cluster and characterization of two crucial enzymes in the biosynthesis of 1 . A P450 monooxygenase that has a dual function, to first catalyze dehydrogenation of the prenyl chain to generate a cis-diene intermediate and then serve as an acetylenase to yield an alkyne moiety, and thus the 1,3-enyne, was discovered. A UbiA prenyltransferase was also characterized and it is unusual in that it favors transferring a five-carbon prenyl chain, rather than a polyprenyl chain, to a p-hydroxybenzoic acid acceptor. 相似文献
94.
Guoyu Zhang Song Zhou Dr. Liang Fu Dr. Pinhong Chen Prof. Yibiao Li Prof. Dr. Jianping Zou Prof. Dr. Guosheng Liu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(46):20619-20624
The first copper-catalyzed asymmetric cyanation and etherification reactions of enamides have been established, where a carbon-centered radical adjacent to a nitrogen atom (CRAN) is enantioselectively trapped by a chiral copper(II) species. Moreover, the asymmetric cyanation of vinyl esters was disclosed as well. These reactions feature very mild reaction conditions and high functional group tolerance, and give a series of chiral α-cyano amides, α-cyano esters and α-hemiaminals in good yields with excellent enantioselectivity. The chiral α-cyano amides can be easily converted into enantioenriched 1,2-diamines and amino acids. 相似文献
95.
Wufeng Chen Haibin Song Jianfeng Li Chunming Cui 《Angewandte Chemie (International ed. in English)》2020,59(6):2365-2369
Hydrosilylation of alkynes generally yield vinylsilanes, which are inert to the further hydrosilylation because of the steric effects. Reported here is the first successful dihydrosilylation of aryl‐ and silyl‐substituted internal alkynes enabled by a rare‐earth ate complex to yield geminal bis‐ and tris(silanes), respectively. The lanthanum bis(amido) ate complex supported by an ene‐diamido ligand proved to be the ideal catalyst for this unprecedented transformation, while the same series of yttrium and samarium alkyl and samarium bis(amido) ate complexes exhibited poor activity and selectivity, indicating significant effects of the ionic size and ate structure of the rare‐earth catalysts. 相似文献
96.
Xuan Zhou Kai Li Yunxiang Lin Li Song Jincheng Liu Yu Liu Lingling Zhang Zhijian Wu Shuyan Song Jun Li Hongjie Zhang 《Angewandte Chemie (International ed. in English)》2020,59(32):13568-13574
Synthesis of well‐defined atomically mixed alloy nanoparticles on desired substrates is an ultimate goal for their practical application. Herein we report a general approach for preparing atomically mixed AuPt, AuPd, PtPd, AuPtPd NAs(nanoalloys) through single‐atom level manipulation. By utilizing the ubiquitous tendency of aggregation of single atoms into nanoparticles at elevated temperatures, we have synthesized nanoalloys on a solid solvent with CeO2 as a carrier and transition‐metal single atoms as an intermediate state. The supported nanoalloys/CeO2 with ultra‐low noble metal content (containing 0.2 wt % Au and 0.2 wt % Pt) exhibit enhanced catalytic performance towards complete CO oxidation at room temperature and remarkable thermostability. This work provides a general strategy for facile and rapid synthesis of well‐defined atomically mixed nanoalloys that can be applied for a range of emerging techniques. 相似文献
97.
Hualong Song Simon J. Allison Viktor Brabec Hannah E. Bridgewater Jana Kasparkova Hana Kostrhunova Vojtech Novohradsky Roger M. Phillips Jitka Pracharova Nicola J. Rogers Samantha L. Shepherd Peter Scott 《Angewandte Chemie (International ed. in English)》2020,59(34):14677-14685
Monosaccharides are added to the hydrophilic face of a self‐assembled asymmetric FeII metallohelix, using CuAAC chemistry. The sixteen resulting architectures are water‐stable and optically pure, and exhibit improved antiproliferative selectivity against colon cancer cells (HCT116 p53+/+) with respect to the non‐cancerous ARPE‐19 cell line. While the most selective compound is a glucose‐appended enantiomer, its cellular entry is not mainly glucose transporter‐mediated. Glucose conjugation nevertheless increases nuclear delivery ca 2.5‐fold, and a non‐destructive interaction with DNA is indicated. Addition of the glucose units affects the binding orientation of the metallohelix to naked DNA, but does not substantially alter the overall affinity. In a mouse model, the glucose conjugated compound was far better tolerated, and tumour growth delays for the parent compound (2.6 d) were improved to 4.3 d; performance as good as cisplatin but with the advantage of no weight loss in the subjects. 相似文献
98.
Yuan Haifeng Zhao Yan Yang Chan Zhang Cheng Yang Yue Meng Hongmin Huan Shuangyan Song Guosheng Zhang Xiaobing 《中国科学:化学(英文版)》2020,63(7):924-935
For chemotherapy, drug delivery systems often suffer from the inefficient drug loading capability, which usually cause systems toxicity and extra burden to excrete carrier itself. Moreover, the cancer therapeutic efficacy is also greatly limited by the specificity of tumor microenvironment for reactive oxygen species(ROS) based cancer therapeutic strategy(e.g., chemodynamic therapy). Herein, we have developed metal-drug coordination nanoplatform that can not only be responsive to tumor microenvironment but also modulate it, so as to achieve efficient treatment of cancer. Excitingly, by employing small molecule drug(6-thioguanine) as ligand copper ions, we achieve a high drug loading rate(60.1%) and 100% of utilization of metal-drug coordination nanoplatform(Cu-TG). Interestingly, Cu-TG possessed high-efficiently horseradish peroxidase-like, glutathione peroxidase-like and catalase-like activity. Under the tumor microenvironment, Cu-TG exhibited the self-reinforcing circular catalysis that is able to amplify the cellular oxidative stress, inducing notable cancer cellular apoptosis. Moreover, Cu-TG could be activated with glutathione(GSH) and facilitated for GSH triggered 6-TG release, higher selective therapeutic effect toward cancer cells, and GSH activated T_1 weight-magnetic resonance imaging. Based on the above properties, Cu-TG exhibited magnetic resonance imaging(MRI) guiding, efficient and synergistic combination of chemodynamic and chemotherapy with self-reinforcing therapeutic outcomes in vivo. 相似文献
99.
Nonlinear Dynamics - During the process of spacecraft launch, the extreme vibration environment is the major influence factor that induces the failure of the mission. Inspired by the smooth motions... 相似文献
100.
Wei Song Marvin D. Rausch James C. W. Chien 《Journal of polymer science. Part A, Polymer chemistry》1996,34(14):2945-2953
The effect of reaction conditions, including catalyst concentration, temperature, and immobilization on support, have been investigated for syndioselective propylene polymerization by the “bare” zirconocenium ion generated from 1,1-diphenyl-methylidene(1-η5-cyclopentadienyl)(9-η5-fluorenyl)zirconium-dichloride precursor (2). Neither variation of the catalyst concentration nor immobilization of 2 on silica support affect the syndiospecificity of polymerization. The stereoregularity of the syndiotactic polypropylene, as judged from the melting transition temperature and homosteric r-pentad population by 13C-NMR, were found to be proportional to polymer molecular weight. These behaviors are compared with a typical isoselective catalyst ethylenebis(4,5,6,7-tetrahydroindenyl) Zr precursor (4). They are in close resemblance in the case of the S-enantiomeric complex of 4, but the racemic mixture of 4 is markedly inferior. The origins of stereo- and regio-errors are discussed. © 1996 John Wiley & Sons, Inc. 相似文献