全文获取类型
收费全文 | 2663篇 |
免费 | 94篇 |
国内免费 | 28篇 |
专业分类
化学 | 1483篇 |
晶体学 | 13篇 |
力学 | 124篇 |
数学 | 665篇 |
物理学 | 500篇 |
出版年
2023年 | 25篇 |
2022年 | 74篇 |
2021年 | 109篇 |
2020年 | 115篇 |
2019年 | 107篇 |
2018年 | 86篇 |
2017年 | 82篇 |
2016年 | 134篇 |
2015年 | 79篇 |
2014年 | 117篇 |
2013年 | 185篇 |
2012年 | 177篇 |
2011年 | 168篇 |
2010年 | 99篇 |
2009年 | 88篇 |
2008年 | 118篇 |
2007年 | 106篇 |
2006年 | 74篇 |
2005年 | 76篇 |
2004年 | 73篇 |
2003年 | 50篇 |
2002年 | 60篇 |
2001年 | 28篇 |
2000年 | 36篇 |
1999年 | 25篇 |
1998年 | 28篇 |
1997年 | 20篇 |
1996年 | 25篇 |
1995年 | 20篇 |
1994年 | 20篇 |
1993年 | 21篇 |
1992年 | 18篇 |
1991年 | 13篇 |
1990年 | 17篇 |
1989年 | 17篇 |
1988年 | 15篇 |
1987年 | 19篇 |
1986年 | 11篇 |
1985年 | 23篇 |
1984年 | 26篇 |
1982年 | 33篇 |
1981年 | 22篇 |
1980年 | 21篇 |
1979年 | 25篇 |
1978年 | 12篇 |
1977年 | 19篇 |
1976年 | 16篇 |
1975年 | 15篇 |
1974年 | 9篇 |
1973年 | 6篇 |
排序方式: 共有2785条查询结果,搜索用时 15 毫秒
161.
162.
The Alperin Weight Conjecture was stated by J. Alperin in 1986 and constitutes one of the main problems in the representation
theory of finite groups. In this paper, we provide a reduction to simple groups and as an application we prove the conjecture
in several cases. 相似文献
163.
Tran Van Hung 《Journal of Radioanalytical and Nuclear Chemistry》2011,287(1):103-106
The neutron temperature is a characteristic parameter in irradiation channels of reactor. For nuclides which have resonances
in the thermal neutron energy range, their Westcott g-factors are different from unity. The values of g-factors and cross-sections
of (n, γ) reaction of these nuclides are temperature dependence. The standard energy for tabulation of thermal neutron cross-section
(σ0) is that of room temperature (293.59 K or 20.43 °C), corresponding to a neutron energy 0.0253 eV or to a neutron velocity
of 2200 m/s. However, in the irradiation channels of reactor, the temperature is not exact at 20.43 °C. Thus, the temperature
at the irradiation position must be known to convert σ0 to σ(T). A method for determination of the neutron temperature in irradiation channels of Dalat reactor is presented by fitting
the thermal neutron spectrum obtained from the calculation using MCNP code. 相似文献
164.
Globally solving a nonlinear UAV task assignment problem by stochastic and deterministic optimization approaches 总被引:1,自引:0,他引:1
In this paper, we consider a task allocation model that consists of assigning a set of m unmanned aerial vehicles (UAVs) to a set of n tasks in an optimal way. The optimality is quantified by target scores. The mission is to maximize the target score while
satisfying capacity constraints of both the UAVs and the tasks. This problem is known to be NP-hard. Existing algorithms are
not suitable for the large scale setting. Scalability and robustness are recognized as two main issues. We deal with these
issues by two optimization approaches. The first approach is the Cross-Entropy (CE) method, a generic and practical tool of
stochastic optimization for solving NP-hard problem. The second one is Branch and Bound algorithm, an efficient classical
tool of global deterministic optimization. The numerical results show the efficiency of our approaches, in particular the
CE method for very large scale setting. 相似文献
165.
Regular conjugated terpolymers comprising two different acceptors and bithiophene donor in repeating group: Effect of strong and weak acceptors on semiconducting properties
下载免费PDF全文
![点击此处可从《Journal of polymer science. Part A, Polymer chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Duc Nghia Nguyen Trinh Tung Ngo Dae Hee Lee Min Ju Cho Dong Hoon Choi 《Journal of polymer science. Part A, Polymer chemistry》2016,54(10):1339-1347
Diketopyrrolopyrrole (DPP)‐based terpolymers—P(DPP‐TPyT) and P(DPP‐T3MTT)—bearing bithiophene donating groups and weak accepting units such as pyridine (Py) or methyl thiophene‐3‐carboxylate (3MT), in the polymer backbone, were successfully synthesized. Although the two polymers had similar physical and electrochemical properties, grazing incidence X‐ray diffraction patterns of P(DPP‐TPyT) and P(DPP‐T3MTT) showed mixed and edge‐on orientations, respectively, in thermally annealed films. Accordingly, the P(DPP‐T3MTT) showed twice the hole mobility of P(DPP‐TPyT) in a thin‐film transistor, and a blended film of P(DPP‐T3MTT) and [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM) showed better power conversion efficiency in a polymer solar cell. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1339‐1347 相似文献
166.
S. M. Arakelian A. V. Osipov I. O. Skryabin Tran Dinh Phong Nguyen Tran Thuath 《Bulletin of the Russian Academy of Sciences: Physics》2017,81(12):1416-1419
The current-voltage relationships of deposited structures are measured for cluster structures consisting of nanoparticles of lead telluride. Variation in the value of the tunnel current is shown. Optimum conditions for the possible emergence of quantum-hopping conductivity due to carrier tunneling (the characteristic sizes of the nanoclusters and the distances between them) are determined. 相似文献
167.
Nguyen Van Hieu Nguyen Van Duy Pham Thanh Huy Nguyen Duc Chien 《Physica E: Low-dimensional Systems and Nanostructures》2008,40(9):2950-2958
Nb-Pt co-doped TiO2 and the hybrid SWCNTs/Nb-Pt co-doped TiO2 thin films have been prepared by the sol–gel spin-coating process for gas-sensor fabrication. Field emission scanning electron microscope (FE-SEM, TEM and X-ray diffraction (XRD) characterizations indicated that the SWCNTs inclusion did not affect the morphology of the TiO2 thin film and the particle size. Additionally, the SWCNTs were well embedded in the TiO2 matrix. The gas-sensing properties of Nb–Pt co-doped TiO2 thin films with and without SWCNTs inclusion were investigated. The hybrid sensors with the inclusion of different SWCNTs contents are examined to elucidate the effect of SWCNTs content on the gas-sensing properties. Experimental results revealed that the responses to ethanol of Nb–Pt co-doped TiO2 sensors with SWNCTs inclusion increase by factors of 2–5 depending on the operating temperature and the ethanol concentration, compared to that of the sensor without SWCNTs inclusion. Moreover, all hybrid sensors can operate with high sensitivity and stability at a relatively low operating temperature (<335 °C). The responses of the hybrid sensors are greatly affected by SWCNTs content inclusion. The optimized SWCNTs content of 0.01% by weight was obtained for our experiment. The improved gas-sensing performance should be attributed to the additional formation of the p/n junction between SWCNTs (p-type) and TiO2 (n-type). 相似文献
168.
Pham Anh Minh 《Proceedings of the American Mathematical Society》2002,130(2):307-310
The purpose of this note is to provide a -group whose mod-3 cohomology ring has a nilpotent element satisfying .
169.
Our research involves the development of new cationic materials for anion-based applications. We report the solvothermal synthesis and characterization of Pb(3)F(5)NO(3), a new layered lead fluoride material that, unlike the majority of layered and open-framework materials, is cationic in charge. The structure consists of polyhedral lead centers connected by doubly and triply bridging fluoride groups. We quantitatively exchanged the interlamellar nitrate groups of Pb(3)F(5)NO(3) for dichromate, under ambient aqueous conditions. Nuclear magnetic resonance and UV-vis spectroscopy show the reaction proceeds to 61.0% completion in several days. The material is also stable to 450 degrees C, which is vastly superior to organic resins that are still the standard for anion-exchange. The presence of extraframework anions also opens up other potentially unique anion-based properties, such as new catalytic reactions, anion intercalation, or growth of anionic clusters within the void spaces of the cationic material. 相似文献
170.
Tezuka Y Stampoulis P Banskota AH Awale S Tran KQ Saiki I Kadota S 《Chemical & pharmaceutical bulletin》2000,48(11):1711-1719
From the MeOH extract of the aerial part of Vietnamese Orthosiphon stamineus, five new isopimarane-type diterpenes [orthosiphols F-J (1-5)] and two new diterpenes [staminols A (6) and B (7)] with a novel carbon-framework, to which we proposed the name "staminane", and three new highly-oxygenated staminane-type diterpenes [staminolactones A (8) and B (9) and norstaminol A (10)1 were isolated. Moreover, staminolactone A (8) is 8,14-secostaminane-type and staminolactone B (9) is 13,14-secostaminane-type, while norstaminol A (10) is 14-norstaminen-type. Together with these new diterpenes, sixteen known compounds were also isolated and identified to be: 7,3',4'-tri-O-methylluteolin (11), eupatorin (12), sinensetin (13), 5-hydroxy-6,7,3',4'-tetramethoxyflavone (14), salvigenin (15), ladanein (16), tetramethylscutellarein (17), 6-hydroxy-5,7,4'-trimethoxyflavone (18), vomifoliol (19), aurantiamide acetate (20), rosmarinic acid (21), caffeic acid (22), oleanolic acid (23), ursolic acid (24), betulinic acid (25), and beta-sitosterol (26). All the isolated compounds were tested for their cytotoxicity towards highly liver metastatic murine colon 26-L5 carcinoma cells, and the new diterpenes, except for 4, and flavonoids (11, 12, 16, 18) showed cytotoxicity with an ED50 value between 10 and 90 microg/ml. 相似文献