全文获取类型
收费全文 | 14995篇 |
免费 | 1781篇 |
国内免费 | 1602篇 |
专业分类
化学 | 1129篇 |
晶体学 | 20篇 |
力学 | 729篇 |
综合类 | 312篇 |
数学 | 9408篇 |
物理学 | 2666篇 |
无线电 | 4114篇 |
出版年
2024年 | 88篇 |
2023年 | 298篇 |
2022年 | 523篇 |
2021年 | 551篇 |
2020年 | 549篇 |
2019年 | 477篇 |
2018年 | 413篇 |
2017年 | 477篇 |
2016年 | 480篇 |
2015年 | 458篇 |
2014年 | 745篇 |
2013年 | 958篇 |
2012年 | 694篇 |
2011年 | 916篇 |
2010年 | 786篇 |
2009年 | 954篇 |
2008年 | 1009篇 |
2007年 | 1090篇 |
2006年 | 907篇 |
2005年 | 833篇 |
2004年 | 627篇 |
2003年 | 684篇 |
2002年 | 555篇 |
2001年 | 480篇 |
2000年 | 531篇 |
1999年 | 444篇 |
1998年 | 400篇 |
1997年 | 322篇 |
1996年 | 238篇 |
1995年 | 137篇 |
1994年 | 139篇 |
1993年 | 89篇 |
1992年 | 68篇 |
1991年 | 59篇 |
1990年 | 48篇 |
1989年 | 35篇 |
1988年 | 35篇 |
1987年 | 16篇 |
1986年 | 16篇 |
1985年 | 39篇 |
1984年 | 38篇 |
1983年 | 15篇 |
1982年 | 28篇 |
1981年 | 18篇 |
1980年 | 21篇 |
1979年 | 21篇 |
1978年 | 15篇 |
1977年 | 11篇 |
1976年 | 8篇 |
1975年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
151.
Thissa N. Siriwardena Alice Capecchi Bee‐Ha Gan Dr. Xian Jin Dr. Runze He Dr. Dengwen Wei Lan Ma Dr. Thilo Köhler Prof. Dr. Christian van Delden Dr. Sacha Javor Prof. Dr. Jean‐Louis Reymond 《Angewandte Chemie (International ed. in English)》2018,57(28):8483-8487
We used nearest‐neighbor searches in chemical space to improve the activity of the antimicrobial peptide dendrimer (AMPD) G3KL and identified dendrimer T7 , which has an expanded activity range against Gram‐negative pathogenic bacteria including Klebsiellae pneumoniae, increased serum stability, and promising activity in an in vivo infection model against a multidrug‐resistant strain of Acinetobacter baumannii. Imaging, spectroscopic studies, and a structural model from molecular dynamics simulations suggest that T7 acts through membrane disruption. These experiments provide the first example of using virtual screening in the field of dendrimers and show that dendrimer size does not limit the activity of AMPDs. 相似文献
152.
Çiğdem Arpa Sarah Albayati Maha Yahya 《International journal of environmental analytical chemistry》2018,98(10):938-953
A new effervescence-assisted dispersive liquid-liquid microextraction, EA-DLLME, technique was developed for preconcentration and flame atomic absorption spectrometric determination of copper in aqueous samples. Effervescence assistance and DES combination for metal ion extraction was used for the first time. In the presented study, six different effervescence powders were examined to achieve maximum extraction efficiency. In addition, 1,5 diphenyl carbazide was used as complexing agent and DES prepared by mixing choline chloride and phenol was used as extraction solvent. The effect of several parameters such as pH, concentration of complexing agent, composition and volume of DES, amount of THF, composition and amount of effervescent agent were examined. Performed experiments showed that optimum pH was 6.0, the best effervesce powder composition was NaH2PO4:Na2CO3 with 2 × 10?3:1 × 10?3 molar ratio and the amount of effervesce powder was 0.4 g. Under optimum conditions enhancement factor, limit of detection and limit of quantification were calculated as 78, 2.9 and 9.7 μg L?1, respectively. In addition, to prove precision of the method intra-day relative standard deviations were calculated for 10 and 50 μg L?1 Cu2+ concentrations and found as 2.1% and 1.3%, respectively. The proposed method showed good linearity within the range of 10.0–100 μg L?1. Finally, proposed method was successfully applied to determination of copper traces in aqueous samples. 相似文献
153.
采用溶胶-凝胶法和光还原沉积法制备出Ag改性的纳米BiFeO3粒子,对复合材料进行了FESEM、XRD、XPS、FTIR、UV-Vis/DRS等分析和表征。考察了波长365nm以上的光照下,铁磁性材料的空间选择性光化学反应对复合材料的结构、形貌以及光谱性质的影响。以罗丹明B为模拟污染物,考察了纳米Ag-BiFeO3粒子的可见光光催化活性以及稳定性。结果表明:通过光化学沉积,不仅增强了BiFeO3在200~800nm光照下的响应,而且抑制了光腐蚀现象,提高了BiFeO3的稳定性。在波长大于400nm的光照射12h后单纯纳米BiFeO3粒子对罗丹明B脱色率约为74%,而Ag-BiFeO3复合材料6h后约为90%,并且重复使用3次后光催化效果基本不变。 相似文献
154.
Martin Gruebele 《Theoretical chemistry accounts》2003,109(2):53-63
Vibrational energy flow in organic molecules occurs by a multiple-time-scale mechanism that can be modeled by a single exponential
only in its initial stages. The mechanism is a consequence of the hierarchical structure of the vibrational Hamiltonian, which
leads to diffusion of vibrational wavepackets on a manifold with far fewer than the 3N−6 dimensions of the full vibrational state space. The dynamics are controlled by a local density of states, which does not
keep increasing with molecular size. In addition, the number of vibrational coordinates severely perturbed during chemical
reaction is small, leading to preservation of the hierarchical structure at chemically interesting energies. This regularity
opens up the possibility of controlling chemical reactions by controlling the vibrational energy flow. Computationally, laser
control of intramolecular vibrational energy redistribution can be modeled by quantum-classical, or by purely quantum-mechanical
models of the molecule and control field.
Received: 26 July 2002 / Accepted: 30 September 2002 / Published online: 2 December 2002
Electronic Supplementary Material to this paper can be obtained by using the Springer Link server located at http://dx.doi.org/10.1007/s00214-002-0394-2.
Acknowledgements. This work was supported by NSF grant CHE 9986670.
Correspondence to: M. Gruebele e-mail: gruebele@scs.uiuc.edu 相似文献
155.
156.
《Green Chemistry Letters and Reviews》2013,6(4):487-533
Abstract Deep eutectic solvents (DES) and glycerol have been successfully employed as efficient catalysts/reaction media in the synthesis of N-aryl phthalimide derivatives from phthalic anhydride and primary aromatic amines. The DES prepared from choline chloride and malonic acid proved to be an efficient catalyst whereas glycerol and the DES of choline chloride and urea played a dual role of catalyst and solvent. These mixtures are biodegradable, nontoxic, and cost-effective thereby providing a good industrial alternative to conventional methods. These methods gave products in moderate to high yields with good recyclability of catalyst/solvent at least up to five consecutive runs. 相似文献
157.
Prof. Dr. Pekka Pyykkö 《Chemphyschem》2019,20(1):123-127
A simple formula is derived for the eutectic point of an A–B system in terms of the monomer melting points and melting enthalpies. This estimate is tested on several non-ionic or ionic systems, with or without common ions, including choline chloride/urea mixtures. The results are compared with the Schröder-van Laar equation. 相似文献
158.
Mohammadali Torbati Mir Ali Farajzadeh Mohammad Reza Afshar Mogaddam Mostafa Torbati 《Journal of separation science》2019,42(9):1768-1776
A homogeneous liquid‐liquid extraction performed in narrow tube coupled to in–syringe‐dispersive liquid‐liquid microextraction based on deep eutectic solvent has been developed for the extraction of six herbicides from tea samples. In this method, sodium chloride as a separation agent is filled into the narrow tube and the tea sample is placed on top of the salt. Then a mixture of deionized water and deep eutectic solvent (water miscible) is passed through the tube. In this procedure, the deep eutectic solvent is realized as tiny droplets in contact with salt. By passing the droplets from the tea layer placed on the salt layer, the analytes are extracted into them. After collecting the solvent as separated layer, it is mixed with another deep eutectic solvent (choline chloride/butyric acid) and the mixture is dispersed into deionized water placed in a syringe. After adding acetonitrile to break up the cloudy state, the collected organic phase is injected into gas chromatography‐mass spectrometry. Under optimal conditions, limits of detection and quantification in the ranges of 2.6–8.4 and 9.7–29 ng/kg, respectively, were obtained. The extraction recoveries and enrichment factors in the ranges of 70–89% and 350–445 were obtained, respectively. 相似文献
159.
160.
基于Aerolysin生物膜通道蛋白的纳米孔道电化学分析技术,因其高的电化学空间限域能力可实现超灵敏DNA单分子检测。本文利用单个Aerolysin纳米孔道在无需标记、无需扩增的条件下直接分辨3种具有单个碱基差异的单链DNA。实验结果显示,具有单个炔基侧链基团修饰的单个ss DNA在限域空间内与Aerol-ysin纳米孔道的相互作用时间较未修饰的ss DNA增长近7倍,电流阻断程度增大7%,且高斯峰半峰宽减小了44%,增强了Aerolysin纳米孔道对单个DNA分子的分辨能力。研究成果有望推动Aerolysin纳米孔在DNA直接测序及表观遗传修饰检测中的应用。 相似文献