全文获取类型
收费全文 | 4334篇 |
免费 | 211篇 |
国内免费 | 41篇 |
专业分类
化学 | 2881篇 |
晶体学 | 41篇 |
力学 | 132篇 |
数学 | 446篇 |
物理学 | 1086篇 |
出版年
2024年 | 19篇 |
2023年 | 44篇 |
2022年 | 236篇 |
2021年 | 221篇 |
2020年 | 171篇 |
2019年 | 166篇 |
2018年 | 168篇 |
2017年 | 135篇 |
2016年 | 202篇 |
2015年 | 144篇 |
2014年 | 214篇 |
2013年 | 378篇 |
2012年 | 308篇 |
2011年 | 303篇 |
2010年 | 238篇 |
2009年 | 191篇 |
2008年 | 215篇 |
2007年 | 183篇 |
2006年 | 148篇 |
2005年 | 90篇 |
2004年 | 104篇 |
2003年 | 55篇 |
2002年 | 56篇 |
2001年 | 34篇 |
2000年 | 28篇 |
1999年 | 31篇 |
1998年 | 21篇 |
1997年 | 31篇 |
1996年 | 26篇 |
1995年 | 16篇 |
1994年 | 30篇 |
1993年 | 21篇 |
1992年 | 19篇 |
1991年 | 14篇 |
1990年 | 19篇 |
1989年 | 13篇 |
1988年 | 15篇 |
1987年 | 17篇 |
1985年 | 24篇 |
1984年 | 23篇 |
1983年 | 16篇 |
1982年 | 20篇 |
1981年 | 13篇 |
1980年 | 38篇 |
1979年 | 11篇 |
1977年 | 16篇 |
1976年 | 11篇 |
1973年 | 11篇 |
1969年 | 10篇 |
1968年 | 8篇 |
排序方式: 共有4586条查询结果,搜索用时 15 毫秒
961.
M. Siddique I. H. Gul I. Ahmad N. M. Butt 《Journal of Radioanalytical and Nuclear Chemistry》2004,261(1):151-155
Fe-rich Nd-Fe-B permanent magnetic materials are of great technological interest because of their superior magnetic properties such as coercivity and large energy products. These properties can be further enhanced by the substitution of Nd or Fe. We are presenting the results of atomic replacement of iron by Ga, Dy, Nb and Si, in the base material N18Fe7 6B6, obtained by Mössbauer spectroscopy. It is observed that the net magnetization decreases for all compositions with the substitution of these elements. 相似文献
962.
Identifiability of finite mixtures using a new transform 总被引:2,自引:0,他引:2
Khalaf E. Ahmad 《Annals of the Institute of Statistical Mathematics》1988,40(2):261-265
Identifiability of finite mixtures of the following families of distributions are proved: Weibull, normal log, chi, pareto and power function. 相似文献
963.
A highly efficient gain-clamped L-band EDFA with improved noise figure characteristic is demonstrated by simply adding a broadband
C-band FBG in double-pass system. The combination of the FBG and optical circulator has created laser in the cavity for gain
clamping. By adjusting the power combination of pumps 1 and 2, the clamped gain level can be controlled. The amplifier gain
is clamped at 28.1 dB from −40 to −25 dBm with a gain variation of less than 0.5 dB by setting the pumps 1 and 2 at 59.5 and
50.6 mW, respectively. The gain is also flat from 1574 nm to 1604 nm with a gain variation of less than 3 dB. The corresponding
noise figure varies from 5.6 to 7.6 dB, which is 0.8 to 2.6 dB less than those of unclamped amplifier. 相似文献
964.
Hamdi M. Hassaneen Ahmed M. Farag Ahmad S. Shawali Mohamed S. Algharib 《Journal of heterocyclic chemistry》1987,24(3):577-580
The regioselectivity of the cycloadditions of α,β-unsaturated nitrilimine derived from N-phenylcinnamo-hydrazidoyl chloride 2 to C = Se, C = S and C = C double bonds of the resonance stabilized selenocyanate and thiocyanate anions, enol tautomer of dibenzoylmethane and benzalacetophenone was investigated. The results indicate that the reactions studied are dipole-LUMO-dipolarophile-HOMO controlled and that the larger orbital coefficient in the LUMO of N-phenylcinnamonitrilimine is on the carbon atom bearing the styryl group. The structures of the cycloadducts were assigned and confirmed on the basis of their elemental analyses and spectra. 相似文献
965.
Hafiz Ghulam Abbas Saeeda Asghar Maqbool Ahmad Shahid 《Journal of Radioanalytical and Nuclear Chemistry》1995,189(1):45-50
A method for labeling of anti-carcinoembryonic antigen (CEA) monoclonal antibody (MAb) BW 431/26 is described. For preparations of99mTc-anti-CEA complex, a solution (1 ml) of tetrasodium-1,1,3,3-propanetetetraphosphate dihydrate (2.7 mg), stannous chloride dihydrate (0.12 mg) and sodium chloride (0.2 mg) in 5 ml of 0.9% saline was added to a vial containing monoclonal antibody (2 mg) from mouse (MAb BW 431/26), D-glucitol (2 mg) and sodium sulfate (2 mg) to obtain a clear solution. A quantitative labeling yield of the MAb BW 431/26 was achieved by addition of 5 ml (40.5 mCi, 1.5 Gbq) technetium-99m-pertechnetate (99mTcO4) generator eluate at room temperature within 10 minutes. The radiochemical purity determined by ITLC (Gelman, SG) plates was >95%. 相似文献
966.
967.
968.
Anam Iqbal Syed Ali Raza Naqvi Rashid Rasheed Asim Mansha Matloob Ahmad Ameer Fawad Zahoor 《Applied biochemistry and biotechnology》2018,185(1):127-139
Bacterial infection poses life-threatening challenge to humanity and stimulates to the researchers for developing better diagnostic and therapeutic agents complying with existing theranostic techniques. Nuclear medicine technique helps to visualize hard-to-diagnose deep-seated bacterial infections using radionuclide-labeled tracer agents. Metronidazole is an antiprotozoal antibiotic that serves as a preeminent anaerobic chemotherapeutic agent. The aim of this study was to develop technetium-99m-labeled metronidazole radiotracer for the detection of deep-seated bacterial infections. Radiosynthesis of 99mTc-metronidazole was carried by reacting reduced technetium-99m and metronidazole at neutral pH for 30 min. The stannous chloride dihydrate was used as the reducing agent. At optimum radiolabeling conditions, ~ 94% radiochemical was obtained. Quality control analysis was carried out with a chromatographic paper and instant thin-layer chromatographic analysis. The biodistribution study of radiochemical was performed using Escherichia coli bacterial infection-induced rat model. The scintigraphic study was performed using E. coli bacterial infection-induced rabbit model. The results showed promising accumulation at the site of infection and its rapid clearance from the body. The tracer showed target-to-non-target ratio 5.57 ± 0.04 at 1 h post-injection. The results showed that 99mTc-MNZ has promising potential to accumulate at E. coli bacterial infection that can be used for E. coli infection imaging. 相似文献
969.
A supported nanoliquid membrane was developed to improve the separation of rare metal ion gadolinium (Gd) from nitrate solution medium. The nanoliquid membrane was prepared by dispersion of nanoparticles in organic phase and Aliquat 336 was applied as the carrier. TiO2 and SiO2 as hydrophobic and hydrophilic nanoparticles were effectively incorporated in the supported liquid membrane (SLM) system and the effect of size, concentration, and type of nanoparticle in the SLM were evaluated. A membrane phase of 0.015 M Aliquat-336 in kerosene and 0.04 wt% of SiO2 with the size of 15 nm was found to have the highest permeability coefficient of 12.57?×?10?5 m/s and enhanced the permeability coefficient by 28.2%. Hydrophobicity and hydrophilicity of the nanoparticles were observed to have remarkable effects on the permeation of the SLM system and concluded that the hydrophobic nanoparticle was more desirable. Results showed that the solid supported pore’s blockage and aggregation of nanoparticles could bring adverse effects at a high nanoparticle concentration at this SLM configuration. The stability tests were conducted over ten cycles of separation and the supported nanoliquid membrane had slight reduction of permeation during the test. 相似文献
970.
The nematic liquid crystals (LCs) are randomly dispersed material with random orientation order in polymer dispersed liquid crystal (PDLC) films. The LCs change their orientation from random to vertical as electric field is applied. This transformation of orientation order of nematic liquid crystals in the PDLC films is controlled by many factors operating simultaneously. For instance, some factors like the internal forces of attractions among the neighboring LC molecules, anchoring with polymeric matrix, ITO glass boundaries, and chemical structures of the materials are less studied. The learning of extent of vertical orientation of liquid crystal droplets in an electric field is essential to attain optimum electro optical properties of PDLCs. In this finding, bipolar and radial LCs droplets with random orientation have been observed in non-acrylic polymeric media. It is learned that with small increase of contents of external material, the extent of vertical orientation has been varied intensely. The extent of vertical orientation of LCs molecules increases as the contents of external non-acrylic polymeric material decreased. For this study, the orientations of LCs with respect to material type/contents, external applied force, and restoration of electric filed as hysteresis have been studied in details. 相似文献