全文获取类型
收费全文 | 2171篇 |
免费 | 82篇 |
国内免费 | 33篇 |
专业分类
化学 | 1289篇 |
晶体学 | 7篇 |
力学 | 82篇 |
数学 | 551篇 |
物理学 | 357篇 |
出版年
2023年 | 18篇 |
2022年 | 58篇 |
2021年 | 73篇 |
2020年 | 81篇 |
2019年 | 75篇 |
2018年 | 81篇 |
2017年 | 65篇 |
2016年 | 92篇 |
2015年 | 57篇 |
2014年 | 75篇 |
2013年 | 156篇 |
2012年 | 121篇 |
2011年 | 131篇 |
2010年 | 100篇 |
2009年 | 75篇 |
2008年 | 131篇 |
2007年 | 101篇 |
2006年 | 74篇 |
2005年 | 66篇 |
2004年 | 54篇 |
2003年 | 39篇 |
2002年 | 41篇 |
2001年 | 19篇 |
2000年 | 16篇 |
1999年 | 19篇 |
1998年 | 17篇 |
1997年 | 19篇 |
1996年 | 23篇 |
1995年 | 29篇 |
1994年 | 21篇 |
1993年 | 19篇 |
1992年 | 23篇 |
1991年 | 15篇 |
1990年 | 13篇 |
1989年 | 21篇 |
1988年 | 11篇 |
1987年 | 17篇 |
1986年 | 13篇 |
1985年 | 23篇 |
1984年 | 18篇 |
1982年 | 21篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 18篇 |
1978年 | 12篇 |
1977年 | 20篇 |
1976年 | 15篇 |
1975年 | 26篇 |
1974年 | 8篇 |
1973年 | 12篇 |
排序方式: 共有2286条查询结果,搜索用时 15 毫秒
91.
Pham Duy Khanh Tran Hong Mo Trinh T. T. Tran 《Numerical Functional Analysis & Optimization》2019,40(8):924-943
Necessary and sufficient conditions for qualitative properties of infinite dimensional linear programing problems such as solvability, duality, and complementary slackness conditions are studied in this article. As illustrations for the results, we investigate the parametric version of Gale’s example. 相似文献
92.
Bui Dac Dung Trinh Van Giap Tibor Kovacs Tran Ngoc Toan Le Dinh Cuong Tran Khanh Minh Nguyen Huu Quyet Nguyen Van Khanh 《Journal of Radioanalytical and Nuclear Chemistry》2014,299(3):1943-1948
Mineral sands are mined in several countries to supply to the titanium and zircon producing industries. Coastal black mineral sands usually contain, besides ilmenite (FeTiO3) and rutile (TiO2), radioactive minerals such as zircon (ZrSiO4) and monazite (RePO4). Radon and thoron activity concentration originated from natural radioactive contents of the black mineral sand was monitored at the extraction and processing for black minerals in the coastal areas of Ha Tinh Province, one of the around 40 coastal mineral sand deposits in Vietnam. The survey was carried out with the Raduet chambers made by Radosys Ltd—Hungary. The obtained results for 25 investigated points show that the measured values are not high in the residential houses and in case of the sand extraction site as well. At the titanium processing plant the measured values were higher than outside the facility (Radon: 18–55 Bq/m3 with average of 34 Bq/3 and Thoron 33–118 Bq/m3 with average of 58 Bq/m3) but still comparable to the average concentration of the world published by UNSCEAR. The typical outdoor levels of radon and thoron gas are each of the order of 10 Bq/m3. Although the radon concentrations were low in the zircon and titanium processing plants, the thoron concentrations in the houses for separating rutile and zircon were very high. At zircon processing factory, the thoron concentration could reach 2,931 Bq/m3 and the estimated annual effective dose would be 21.4 mSv/a. Intervention has to be taken in order to reduce the thoron level in this factory since the level of thoron and its progenies corresponding to an annual occupational effective dose is beyond the action level of 6 mSv/a. 相似文献
93.
A solid state-based method using a hot reaction chamber is applied to the synthesis of Y2O3:Eu particles containing Eu from 0 to 5 mol%. The produced powders are studied using X-ray diffraction (XRD), scanning electron microscopy and transmission electron microscopy (TEM), as well as photoluminescence (PL) and radioluminescence tests. TEM and XRD results revealed the powder to be mono-disperse and in the form of a solid solution. The PL of Y2O3:Eu powder depends on both the concentration quenching effect (due to an excess of Eu concentration) and the surface luminescence effect (depicted by a higher surface area induced by the large phosphor concentration in the solution or smaller particle sizes). A 22Na gamma source is used to compare the recorded count rates for four Y2O3:Eu scintillator materials with different concentrations of Eu. Each scintillator composition is examined in four forms: solid pellets with a high volume porosity and three aqueous solutions of Y2O3:Eu particles of the different scintillator materials at concentrations of 25, 50 and 100 mg/mL. The radioluminescence results indicated that increasing the transparency and/or the amount of Eu mol% of the scintillators increases the net average counts. 相似文献
94.
Thanh Duc Mai Benjamin Bomastyk Hong Anh Duong Hung Viet Pham Peter C. Hauser 《Analytica chimica acta》2012
An extension of a capillary electrophoresis instrument coupled to a sequential injection analysis manifold was developed for automated measurements with on-line solid-phase extraction preconcentration. An in-house built capacitively coupled contactless conductivity detector was employed for sensitive detection with narrow capillaries of 25 μm internal diameter. The system was assembled into standardized 19 in. frames and racks for easy transport and mobile deployment. The system can be left running unattendedly without manual intervention with good operation stability. To demonstrate the application of the system, a method for the determination of four drugs, namely ibuprofen, diclofenac, naproxen and bezafibrate, was developed with enrichment factors of up to several hundreds. Detection of the drug residues down to the nM-scale was found possible and the method was found suitable for the detection of ibuprofen in the waste water of a hospital in Hanoi. 相似文献
95.
96.
97.
Harish Holla Ian D. Jenkins Juliette E. Neve Rebecca H. Pouwer Ngoc Pham Simon J. Teague Ronald J. Quinn 《Tetrahedron letters》2012,53(52):7101-7103
A synthesis of the unusual cyclobutane-quinolinone alkaloids melicodenines C, D and E by intermolecular [2+2] cycloaddition is described. 相似文献
98.
99.
This paper deals with ultrasound medical image processing, particularly to filter the noise while preserving the edges and
structures of information. The mathematical processing consists in solving by a numerical way a nonlinear evolutive boundary
value problem. Several numerical semi-implicit time marching schemes are considered and analyzed. At each time step, parallel
synchronous or asynchronous Schwarz alternating methods are used to solve the linear system and its convergence is studied.
Lastly, the results of sequential and parallel simulations are presented.
相似文献
100.
E. Herrmann Nguyen Thi Thu Chau O. Navratil G. Ohms L. Beyer 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4)
Abstract The new 1,1-disubstituted 3-diphenoxy(thio)phosphoryl-(thio)ureas, R1R2NC(X)NHP(0Ph)2, HA, with X,Y = O,S, were synthesized by addition of secondary mines to the corresponding P-iso(thio)cyanates. This reaction is reversible if X,Y = S. (PhO)2P(Y)Cl reacts with H2NC(X)NR2 in the presence of an HCl acceptor only if X,Y a 0. Side reactions are observed. Phosphorylated derivatives of biuret were isolated from such a reaction mixture. 相似文献