全文获取类型
收费全文 | 3234篇 |
免费 | 162篇 |
国内免费 | 200篇 |
专业分类
化学 | 1518篇 |
晶体学 | 21篇 |
力学 | 650篇 |
综合类 | 34篇 |
数学 | 331篇 |
物理学 | 1042篇 |
出版年
2024年 | 5篇 |
2023年 | 33篇 |
2022年 | 55篇 |
2021年 | 61篇 |
2020年 | 105篇 |
2019年 | 165篇 |
2018年 | 88篇 |
2017年 | 119篇 |
2016年 | 119篇 |
2015年 | 107篇 |
2014年 | 114篇 |
2013年 | 324篇 |
2012年 | 151篇 |
2011年 | 186篇 |
2010年 | 125篇 |
2009年 | 166篇 |
2008年 | 148篇 |
2007年 | 218篇 |
2006年 | 180篇 |
2005年 | 206篇 |
2004年 | 138篇 |
2003年 | 107篇 |
2002年 | 91篇 |
2001年 | 64篇 |
2000年 | 77篇 |
1999年 | 94篇 |
1998年 | 50篇 |
1997年 | 53篇 |
1996年 | 39篇 |
1995年 | 39篇 |
1994年 | 25篇 |
1993年 | 16篇 |
1992年 | 22篇 |
1991年 | 29篇 |
1990年 | 14篇 |
1989年 | 14篇 |
1988年 | 13篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1973年 | 2篇 |
1957年 | 3篇 |
排序方式: 共有3596条查询结果,搜索用时 250 毫秒
211.
利用火焰原子吸收光谱法(FAAS),测定了硫酸铜、硫酸锌、膨润土、米糠、氧化锌、菜渣、盐等7种肉牛饲料添加剂中铅(Pb)元素的含量.各添加剂的加标回收率在98%-108%之间,相对标准偏差(RSD)小于1.3%,具有良好的准确度和精确度.结果表明,试验中所测的硫酸铜、硫酸锌、氧化锌添加剂中铅含量严重超出国家标准. 相似文献
212.
Ching Hsuan Lin Hung Tse Lin Yu Wei Tian Shenghong A. Dai Wen Chiung Su 《Journal of polymer science. Part A, Polymer chemistry》2011,49(22):4851-4860
We reveal a route for the preparation of phosphinated bisphenol, 1,1‐bis(4‐hydroxyphenyl)‐1‐(6‐oxido‐6H‐dibenz <c,e> <1,2> oxaphosphorin‐6‐yl)ethane (2) , via a one‐pot reaction of 1,1,1‐tris(4‐hydroxyphenyl)ethane and 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene 10‐oxide (DOPO) in the catalysis of p‐toluenesulfonic acid. A two‐step reaction mechanism, acid‐fragmentation of 1,1,1‐tris(4‐hydroxyphenyl)ethane followed by nucleophilic addition of DOPO, is proposed for the synthesis. Based on (2) , a dicyanate ester derivative, 1,1‐bis(4‐cyanatophenyl)‐1‐(6‐oxido‐6H‐dibenz <c,e> <1,2> oxaphosphorin‐6‐yl)ethane (3) was prepared and co‐cured with a commercially available dicyanate ester, the dicyanate ester of bisphenol A (BACY). Experimental data show that incorporating (3) into BACY enhances the flame retardancy and dielectric properties with little penalty to the thermal properties. A thermoset with Tg 274 °C, coefficient of thermal expansion (CTE) 49 ppm/°C, Dk 3.04 (1 GHz), Td (5%,) N2: 435 °C, air: 424 °C, and UL‐94 V‐0 rating can be achieved via this approach. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011. 相似文献
213.
214.
Hirokazu Sato Shusaku Hamada Roberto M. Sertkawa Tatsuya Nishimura Takashi Usui Hideo Sekino 《高压研究》2013,33(1-6):403-413
Abstract Continuous flames have been observed in Supercritical water oxidation (scWO) of isopropyl alcohol (IPA), using a vertical continuous reactor with sapphire windows and a mixing nozzle. Two types of continuous flame were confirmed: the one was long pale blue colored and the other was red short cone shaped, changing blue to red at around air ratio 2.0. The flame was strongly influenced by IPA concentration, air ratio and design of the mixing nozzle. Results for decomposition of PA are presented for IPA concentrations ranging from 600 up to 28260 ppm as TOC and initial reactor temperatures, were mostly around 490°C, at 25 MPa. Decomposition rate at steady state was over 99.9%. Experimentally measured CO2 and O2 concentrations at the flue gas were in good agreement with theoretically calculated values. Even for low air ratio as 1.1, high decomposition rate without CO, NO, NO2 was achieved. 相似文献
215.
Alejandro R. Diaz Noboru Klkuchl Panos Papalambros John E. Taylor 《基于设计的结构力学与机械力学》2013,41(2):215-230
ABSTRACT Finite element solutions of improved quality are obtained by optimizing the location of nodes of the finite element grid, while keeping the number of degrees of freedom fixed. The formulation of the grid optimization problem is based on the reduction of error associated with interpolation of the exact solution, using functions from the finite element space. Element sizes are selected as design variables: length in R1 and area in R2. Analytically derived optimality conditions are presented and an approximation to these conditions is introduced to obtain a set of operationally useful equations that can be used as guidelines for construction of improved grids. Example problems are given for illustration. 相似文献
216.
P. V. S. MARQUES P. J. MOREIRA D. ALEXANDRE M. MELO T. E. A. SCHMIDT R. MUENZNER 《Fiber and Integrated Optics》2013,32(3-4):149-169
Abstract This article presents results of device fabrication using UV processing of materials and integrated optic components produced by flame hydrolysis deposition and hybrid sol-gel technology. Photosensitive materials were employed in the fabrication of channel waveguides and channel photo-imprinted waveguides incorporating Bragg gratings through single and double-step exposure. 相似文献
217.
In this article, we obtain some results about the mean curvature integrals of the parallel body of a convex set in R^n. These mean curvature integrals are generalizations of the Santalo's results. 相似文献
218.
α-Fetoprotein (AFP) is a prospective biopharmaceutical candidate currently undergoing advanced-stage clinical trials for autoimmune indications. The high AFP expression yields in the form of inclusion bodies in Escherichia coli renders the inclusion body route potentially advantageous for process scale commercial manufacture, if high-throughput refolding can be achieved. This study reports the successful development of an ‘anion-exchange chromatography’-based refolding process for recombinant human AFP (rhAFP), which carries the challenges of contaminant spectrum and molecule complexity. rhAFP was readily refolded on-column at rhAFP concentrations unachievable with dilution refolding due to viscosity and solubility constraints. DEAE-FF functioned as a refolding enhancer to achieve rhAFP refolding yield of 28% and product purity of 95% in 3 h, at 1 mg/ml protein refolding concentration. Optimization of both refolding and chromatography column operation parameters (i.e. resin chemistry, column geometry, redox potential and feed conditioning) significantly improved rhAFP refolding efficiency. Compared to dilution refolding, on-column rhAFP refolding productivity was 9-fold higher, while that of off-column refolding was more than an order of magnitude higher. Successful demonstration that a simple anion-exchange column can, in a single step, readily refold and purify semi-crude rhAFP comprising 16 disulfide bonds, will certainly extend the application of column refolding to a myriad of complex industrial inclusion body proteins. 相似文献
219.
Periodic orbits belonging to the stromgren families A, B and C around the collinear libration points in the restricted three
body problem have been studied when the smaller primary is a triaxial rigid body and more massive body is a source of radiation
pressure. These families are determined in three different cases: (i) classical case, (ii) when bigger primary is a source
of radiation pressure, (iii) when smaller primary is a triaxial rigid body and bigger primary is a source of radiation pressure.
The Liapunov stability of each periodic solution has also been examined.
相似文献
220.
AimNeutron-activated holmium-166 (166Ho) is an excellent radionuclide for internal radiation therapy (Eβmax = 1.84 MeV) with an appropriate half-life (26.8 h), which emits photons (81 keV, 6.2%) suitable to be detected by gamma cameras. Preparing and injecting radiopharmaceuticals containing beta/gamma emitting holmium-166 implies a risk of exceeding the upper limit for skin and hand radiation equivalent doses (500 mSv/an). This study was aimed to estimate the whole body and finger exposure for staff responsible for dose preparation, dose dispensing, and dose injection of holmium-166 therapy.MethodsTo measure the finger dose from external exposure, all staff members wore TLD dosimeters. Personal dose equivalents Hp(10) were measured using electronic personal dosimeters (EPD MK2, Thermo Fischer Scientific) placed on the left side of the chest. During our study, staff members administered more than 40 166Ho-based therapies for preclinical trial. Appropriate radiation safety procedures and shielding were applied at each stage.ResultsIn this study, the whole body doses were 2.80 ± 1.56 nSv MBq−1 for one 166Ho-therapy preparation/formulation, and 2.68 ± 1.70 nSv MBq−1 for one intravenous injection. Maximum finger doses were 2.9 ± 0.2 μSv MBq−1 and 2.5 ± 0.3 μSv MBq−1 for preparation and injection, respectively (activities injected: 72 ± 3 MBq).ConclusionExtrapolated annual doses from 300 166Ho radionuclide therapies were lower than the annual limit doses for skin and the whole body, 500 mSv and 20 mSv, respectively, reported in the European Directive EURATOM 96/29 when applying appropriate radiation protection standards. However, these doses have to be added to other diagnostic or therapeutic protocols, performed in preclinical facilities. 相似文献