全文获取类型
收费全文 | 10405篇 |
免费 | 1963篇 |
国内免费 | 958篇 |
专业分类
化学 | 6936篇 |
晶体学 | 83篇 |
力学 | 664篇 |
综合类 | 85篇 |
数学 | 1197篇 |
物理学 | 4361篇 |
出版年
2024年 | 23篇 |
2023年 | 239篇 |
2022年 | 341篇 |
2021年 | 390篇 |
2020年 | 419篇 |
2019年 | 415篇 |
2018年 | 348篇 |
2017年 | 334篇 |
2016年 | 512篇 |
2015年 | 476篇 |
2014年 | 544篇 |
2013年 | 748篇 |
2012年 | 912篇 |
2011年 | 1018篇 |
2010年 | 638篇 |
2009年 | 667篇 |
2008年 | 663篇 |
2007年 | 570篇 |
2006年 | 525篇 |
2005年 | 437篇 |
2004年 | 342篇 |
2003年 | 281篇 |
2002年 | 256篇 |
2001年 | 208篇 |
2000年 | 218篇 |
1999年 | 204篇 |
1998年 | 212篇 |
1997年 | 191篇 |
1996年 | 149篇 |
1995年 | 195篇 |
1994年 | 166篇 |
1993年 | 125篇 |
1992年 | 101篇 |
1991年 | 85篇 |
1990年 | 90篇 |
1989年 | 64篇 |
1988年 | 43篇 |
1987年 | 33篇 |
1986年 | 35篇 |
1985年 | 21篇 |
1984年 | 18篇 |
1983年 | 21篇 |
1982年 | 12篇 |
1981年 | 6篇 |
1980年 | 10篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
911.
In this paper, a novel suspended droplet microextraction method was developed for the detection of trace of organic compounds in water samples. The process was executed in a rotating extraction vial without the use of a stir bar. A single drop of octan-1-ol placed on top of the water sample was used as the solvent. The droplet remained on top of the water sample as a thin layer with an expanding surface area during the extraction stage, while during the sampling stage, the droplet was collected and sampled by inserting a needle. The volume of the microdroplet used was 3 μL or less, to ensure high organic compound sensitivity. The microextraction experimental setup was simple, utilizing centrifugal forces and possesses the advantages of low cross-contaminant/interference and applicability to water samples apt to emulsification. Nitrobenzene was selected as a model organic compound, and samples were analyzed using gas chromatography (GC) or UV-vis spectrometry. Analysis of the microextraction method results showed a relative standard deviation (RSD) less than 3.82%. 相似文献
912.
Two new furostanol glycosides, torvosides O (1) and P (2), were isolated from leaves of Solanum torvum. Their structures were completely and unambiguously assigned by one‐ and two‐dimensional NMR techniques (1H NMR, 13C NMR, TOCSY, HSQC, ROESY and HMBC), ESI‐MS spectrometry and chemical methods. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
913.
Improvement of Steroid Biotransformation with Hydroxypropyl-β-Cyclodextrin Induced Complexation 总被引:1,自引:0,他引:1
Liting Zhang Min Wang Yanbing Shen Yinhu Ma Jianmei Luo 《Applied biochemistry and biotechnology》2009,159(3):642-654
The inclusion complexes induced by cyclodextrins and its derivates have been shown previously to enhance the biotransformation
of hydrophobic compounds. Using hydroxypropyl-β-cyclodextrin (HP-β-CD; 20% w/v), the water solubility of cortisone acetate increased from 0.039 to 7.382 g L−1 at 32 °C. The solubilization effect of HP-β-CD was far superior to dimethylformamide (DMF) and ethanol. The dissolution rate
also significantly increased in the presence of HP-β-CD. The enzymatic stability of Δ1-dehydrogenase from Arthrobacter simplex TCCC 11037 was not influenced by the increasing concentrations of HP-β-CD contrary to the organic cosolvents which negatively
influenced in the order DMF > ethanol. The activity inhibition effect caused by HP-β-CD was not so conspicuous as ethanol
and DMF. Inactivation constants of ethanol, DMF, and HP-β-CD were 5.832, 4.541, and 1.216, respectively. The inactivation
energy (E
a) was in the order of HP-β-CD (55.1 kJ mol−1) > ethanol (39.9 kJ mol−1) > DMF (37.1 kJ mol−1). 相似文献
914.
Feng Luo Saul Schleimer Stephan Tillmann 《Proceedings of the American Mathematical Society》2008,136(7):2625-2630
It is shown that every non-compact hyperbolic manifold of finite volume has a finite cover admitting a geodesic ideal triangulation. Also, every hyperbolic manifold of finite volume with non-empty, totally geodesic boundary has a finite regular cover which has a geodesic partially truncated triangulation. The proofs use an extension of a result due to Long and Niblo concerning the separability of peripheral subgroups.
915.
Ping Luo 《计算数学(英文版)》2001,(2)
1. IlltroductionA nonconforming domain decomposition method with Lagrangian multipliers was proposedin [13]. The basic idea of this method is to deal with the nonconforming of nonmatching gridsby illtroducing the Lagrangian multipliers on interfaces of subdomains and its advalltages arethat it allows not only the incompatibility of the internal variables on the interface betweensubdomains, but also the discolltinuity of the boundary variables on the common venices ofsubdomains. Thus one can c… 相似文献
916.
Continuous-wave operation of InAs/InP quantum dot tunable external-cavity laser grown by metal-organic chemical vapor deposition
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We demonstrate high-performance broadband tunable external-cavity lasers(ECLs) with the metal-organic chemical vapor deposition(MOCVD) grown In As/In P quantum dots(QDs) structures. Without cavity facet coatings, the 3-d B spectral bandwidth of the Fabry–Perot(FP) laser is approximately 10.8 nm, while the tuning bandwidth of ECLs is 45 nm.Combined with the anti-reflection(AR)/high-reflection(HR) facet coating, a 92 nm bandwidth tuning range has been obtained with the wavelength covering from 1414 nm to 1506 nm. In most of the tuning range, the threshold current density is lower than 1.5 k A/cm2. The maximum output power of 6.5 m W was achieved under a 500 m A injection current.All achievements mentioned above were obtained under continuous-wave(CW) mode at room temperature(RT). 相似文献
917.
The calculation results of the R-branch transition emission spectra of(0–0) band of the A21 → X21 transition system of Sb Na molecule are presented in this paper. These R-branch high-lying transitional emission spectral lines are predicted by using the difference converging method(DCM). Our results show excellent agreement between DCM spectral lines and the experimental values, and the deviations are controlled within 0.0224 cm-1. What is more, based on the principle of over-determined linear equations, the prediction error is quantified in this work, which provides reliable theoretical support for our predicted DCM calculations. This work provides a lot of useful information for understanding the microstructure of Sb Na molecule. 相似文献
918.
Ao Feng Hongxiang Li Zixi Liu Yuanjiang Luo Haibo Pu Bin Lin Tao Liu 《Entropy (Basel, Switzerland)》2021,23(6)
The thousand grain weight is an index of size, fullness and quality in crop seed detection and is an important basis for field yield prediction. To detect the thousand grain weight of rice requires the accurate counting of rice. We collected a total of 5670 images of three different types of rice seeds with different qualities to construct a model. Considering the different shapes of different types of rice, this study used an adaptive Gaussian kernel to convolve with the rice coordinate function to obtain a more accurate density map, which was used as an important basis for determining the results of subsequent experiments. A Multi-Column Convolutional Neural Network was used to extract the features of different sizes of rice, and the features were fused by the fusion network to learn the mapping relationship from the original map features to the density map features. An advanced prior step was added to the original algorithm to estimate the density level of the image, which weakened the effect of the rice adhesion condition on the counting results. Extensive comparison experiments show that the proposed method is more accurate than the original MCNN algorithm. 相似文献
919.
Dan Luo Yong Xiao Liam Hardwick Robert Snell Matthew Way Xavier Sanuy Morell Frances Livera Nicholas Ludford Chinnapat Panwisawas Hongbiao Dong Russell Goodall 《Entropy (Basel, Switzerland)》2021,23(1)
In the search for applications for alloys developed under the philosophy of the High Entropy Alloy (HEA)-type materials, the focus may be placed on applications where current alloys also use multiple components, albeit at lower levels than those found in HEAs. One such area, where alloys with complex compositions are already found, is in filler metals used for joining. In soldering (<450 °C) and brazing (>450 °C), filler metal alloys are taken above their liquidus temperature and used to form a metallic bond between two components, which remain both unmelted and largely unchanged throughout the process. These joining methods are widely used in applications from electronics to aerospace and energy, and filler metals are highly diverse, to allow compatibility with a broad range of base materials (including the capability to join ceramics to metals) and a large range of processing temperatures. Here, we review recent developments in filler metals relevant to High Entropy materials, and argue that such alloys merit further exploration to help overcome a number of current challenges that need to be solved for filler metal-based joining methods. 相似文献
920.
Jiangkuan Xing Kun Luo Haiou Wang Tai Jin Ruipeng Cai Jianren Fan 《Proceedings of the Combustion Institute》2021,38(3):4005-4012
Biomass co-firing within the existing pulverized coal boiler is thought as a practical near-term way of biomass utilization, while its detailed combustion characteristics and pollutant formation have not yet been fully understood. In the present study, we report a Carrier-phase Direct Numerical Simulation study coupled with detailed mechanism to provide a deep insight into the coal/biomass co-firing (CBCF) jet flames under different blending ratios. It is found that compared with the pure coal flame, the CBCF could (i) prompt the volatiles ignition, produce higher H2O and similar CO2 mass fractions at blending ratios of 20% and 40%, and obviously reduce the gas temperature and CO2 mass fraction at the blending ratio of 50%; (ii) prompt the coal devolatilization and char burnout at blending ratios of 20% and 40%, while the char burnout is reduced when blending ratio is 50% due to the local enrichment of large particles and lack of oxygen; (iii) reduce the thermal, prompt, NNH and N2O-intermediate routes of NO formation, but show limited effect on the NO-reburning route of NO destruction, therefore, resulting in an obvious NO reduction. 相似文献