全文获取类型
收费全文 | 1745篇 |
免费 | 69篇 |
国内免费 | 16篇 |
专业分类
化学 | 908篇 |
晶体学 | 17篇 |
力学 | 35篇 |
数学 | 379篇 |
物理学 | 288篇 |
无线电 | 203篇 |
出版年
2024年 | 4篇 |
2023年 | 22篇 |
2022年 | 42篇 |
2021年 | 53篇 |
2020年 | 46篇 |
2019年 | 53篇 |
2018年 | 49篇 |
2017年 | 54篇 |
2016年 | 71篇 |
2015年 | 45篇 |
2014年 | 105篇 |
2013年 | 158篇 |
2012年 | 112篇 |
2011年 | 100篇 |
2010年 | 89篇 |
2009年 | 70篇 |
2008年 | 107篇 |
2007年 | 94篇 |
2006年 | 89篇 |
2005年 | 55篇 |
2004年 | 65篇 |
2003年 | 54篇 |
2002年 | 46篇 |
2001年 | 25篇 |
2000年 | 21篇 |
1999年 | 21篇 |
1998年 | 10篇 |
1997年 | 11篇 |
1996年 | 11篇 |
1995年 | 11篇 |
1994年 | 12篇 |
1993年 | 13篇 |
1992年 | 14篇 |
1991年 | 10篇 |
1990年 | 5篇 |
1989年 | 11篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 15篇 |
1981年 | 1篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有1830条查询结果,搜索用时 15 毫秒
51.
Characterization and application of an electrode modified by mechanically immobilized copper hexacyanoferrate 总被引:1,自引:0,他引:1
A newly modified electrode was prepared by mechanical immobilization of copper hexacyanoferrate (CuHCF) on a graphite electrode.
The modified electrode was characterized by cyclic voltammetric experiments. The effect of different background electrolytes,
pHs and scan rates on the electrochemical behaviour of the electrode has been evaluated. In NH4Cl two reversible redox peaks were observed. The first redox peak corresponding to Cu+/Cu2+ is observed only in this medium. The second redox peak corresponds to the Fe(CN)6
4–/Fe(CN)6
3– couple. Both anodic peaks were used for catalytic oxidation of ascorbic acid. As the anodic current for catalytic oxidation
was proportional to the amount of ascorbic acid, an analytical method was developed for the determination of ascorbic acid
in commercial samples.
Received: 26 May 1998 / Revised: 15 March 1999 / Accepted: 20 March 1999 相似文献
52.
Srinivas G. Ravi Kumar V. Laxma Reddy K. Praveen Kumar Y. Satyanarayana S. 《Russian Journal of General Chemistry》2018,88(12):2621-2627
Russian Journal of General Chemistry - A thiophene contained imidazo phenanthroline ligand TIP {TIP = 2-(thiophen-2-yl)-1H-imidazo-[4,5-f][1,10]phenanthroline{ and its mononuclear Ru(II)... 相似文献
53.
Sakram B. Madhu P. Sonyanaik B. Rambabu S. Ravi D. Kurumanna A. 《Russian Journal of General Chemistry》2018,88(6):1224-1227
Russian Journal of General Chemistry - A new methodology has been developed for the synthesis of novel 2-oxo-1,2-dihydro-1,8-naphthyridine-3-carboxylates from 2-aminonicotinaldehyde,... 相似文献
54.
Nagaraju Chirra Varshitha Shanigarapu Naga Pranathi Abburi Ekaterina O. Sinegubova Ravi Kumar Pedapati Yana L. Esaulkova Vladimir V. Zarubaev Srinivas Kantevari 《Journal of heterocyclic chemistry》2024,61(3):496-505
Herein described the synthesis and antiviral evaluation of a novel series of morpholine and thio-morpholine coupled imidazo[2,1-b]thiazoles. The three-step reaction sequence involving the condensation of 1,3-dichloroacetone with thiourea followed by coupling with morpholine and thiomorpholine and finally cyclization with substituted α-bromoacetophenones yielded the desired imidazothiazoles 7(a–l) . Screening of all the new compounds for their in vitro antiviral activity against influenza virus A/Puerto Rico/8/34 (H1N1) in MDCK cells, resulted in two potent analogs, 7d (IC50: 1.1 μM, C50: >300 μM, SI = 273) and 7e (IC50: 2.0 μM, C50: >300 μM, SI = 150), with a favorable toxicity profile and are the best anti-influenza hit analogs for further structural optimization. 相似文献
55.
Sagar Suman Panda Khusbu Sharma Bijeta Mohanty Ravi Kumar Venkata Varaha Bera Sasmita Kumari Acharjya Sarwar Beg 《液相色谱法及相关技术杂志》2017,40(19):951-958
An ultrafast liquid chromatographic bioanalytical method was developed and validated for the determination of telaprevir in Wistar albino rat serum. Principles of quality by design (QbD) were implemented for enhancing the bioanalytical liquid–liquid extraction of telaprevir from rat serum. A Box–Behnken design was utilized in the studies by selecting extraction time, centrifugation speed, and vortex time as the critical method variables for evaluating their effect on the critical analytical attribute, i.e., %recovery of telaprevir. Chromatographic separation was achieved within a run time of 10?min using a C-18 column and mobile phase comprising of methanol:borate buffer of pH 9 (90:10 v/v) flowing at 1.2?mL/min. Photodiode array detection was performed at 270?nm. Results of validation studies were satisfactory. The method was linear over a concentration of 25–10,000?ng/mL. Limit of detection for the developed method was 10?ng/mL. Further, design of experiments (DoE) used for inter-day accuracy and precision study suggested superior method reliability. This integrated QbD- and DoE-based approach ensured the development of a validated and reliable analytical method for optimum bioanalysis of telaprevir in biological matrix. 相似文献
56.
Ravi Madhukar Mawale Mayuri Vilas Ausekar Lubomír Prokeš Virginie Nazabal Emeline Baudet Tomáš Halenkovič Marek Bouška Milan Alberti Petr Němec Josef Havel 《Journal of the American Society for Mass Spectrometry》2017,28(12):2569-2579
Laser desorption ionization using time-of-flight mass spectrometer afforded with quadrupole ion trap was used to study As2Ch3 (Ch = S, Se, and Te) bulk chalcogenide materials. The main goal of the study is the identification of species present in the plasma originating from the interaction of laser pulses with solid state material. The generated clusters in both positive and negative ion mode are identified as 10 unary (S p +/– and As m +/– ) and 34 binary (As m S p +/– ) species for As2S3 glass, 2 unary (Se q +/– ) and 26 binary (As m Se q +/– ) species for As2Se3 glass, 7 unary (Te r +/– ) and 23 binary (As m Te r +/– ) species for As2Te3 material. The fragmentation of chalcogenide materials was diminished using some polymers and in this way 45 new, higher mass clusters have been detected. This novel approach opens a new possibility for laser desorption ionization mass spectrometry analysis of chalcogenides as well as other materials. 相似文献
57.
R. Parthasarathy Ravi V. Prasad P. R. Sarode K. J. Rao 《Journal of Chemical Sciences》1982,91(3):201-205
The exafs of Co2+ has been studied in rare earth cobaltites and in sulphate and borate glasses. It has been found that the environment of Co2+ ions is very similar in these cases. It appears feasible to study local structures in glasses using probe ion exafs.
Communication No. 151 from the Solid State and Structural Chemistry Unit. 相似文献
58.
Ravi P. Agarwal 《Journal of Computational and Applied Mathematics》1983,9(4):315-325
The paper deals with some general iterative methods in n-metric spaces. The obtained results are more explicit than those known in the literature and provides error estimates when the sequence obtained on a floating-point system starts oscillating. A stopping criteria and error estimates at that stage are provided. An application to multi-point boundary value problems is also given. 相似文献
59.
Fredholm boundary value problems for perturbed systems of dynamic equations on time scales 下载免费PDF全文
Ravi P. Agarwal Martin Bohner Alexandr Boı̆chuk Olexandr Strakh 《Mathematical Methods in the Applied Sciences》2015,38(17):4178-4186
This paper offers conditions ensuring the existence of solutions of linear boundary value problems for systems of dynamic equations on time scales. Utilizing a method of Moore–Penrose pseudo‐inverse matrices leads to an analytical form of a criterion for the existence of solutions in a relevant space and, moreover, to the construction of a family of linearly independent solutions of such problems in a general case with the number of boundary conditions (defined by a linear vector functional) not coinciding with the number of unknowns of a system of dynamic equations. As an example of an application of the presented results, the problem of bifurcation of solutions of boundary value problems for systems of dynamic equations on time scales with a small parameter is considered. 相似文献
60.
Ravi P. Agarwal Alexander Domoshnitsky Abraham Maghakyan 《Czechoslovak Mathematical Journal》2015,65(4):1047-1068
We propose a new method for studying stability of second order delay differential equations. Results we obtained are of the form: the exponential stability of ordinary differential equation implies the exponential stability of the corresponding delay differential equation if the delays are small enough. We estimate this smallness through the coefficients of this delay equation. Examples demonstrate that our tests of the exponential stability are essentially better than the known ones. This method works not only for autonomous equations but also for equations with variable coefficients and delays. 相似文献