全文获取类型
收费全文 | 2188篇 |
免费 | 68篇 |
国内免费 | 6篇 |
专业分类
化学 | 1581篇 |
晶体学 | 112篇 |
力学 | 55篇 |
数学 | 93篇 |
物理学 | 421篇 |
出版年
2023年 | 16篇 |
2022年 | 50篇 |
2021年 | 43篇 |
2020年 | 39篇 |
2019年 | 47篇 |
2018年 | 35篇 |
2017年 | 60篇 |
2016年 | 84篇 |
2015年 | 41篇 |
2014年 | 58篇 |
2013年 | 198篇 |
2012年 | 116篇 |
2011年 | 138篇 |
2010年 | 90篇 |
2009年 | 72篇 |
2008年 | 117篇 |
2007年 | 99篇 |
2006年 | 98篇 |
2005年 | 73篇 |
2004年 | 59篇 |
2003年 | 51篇 |
2002年 | 52篇 |
2001年 | 28篇 |
2000年 | 31篇 |
1999年 | 24篇 |
1998年 | 14篇 |
1997年 | 15篇 |
1996年 | 19篇 |
1995年 | 21篇 |
1994年 | 24篇 |
1993年 | 19篇 |
1992年 | 23篇 |
1991年 | 24篇 |
1990年 | 15篇 |
1989年 | 17篇 |
1988年 | 15篇 |
1987年 | 19篇 |
1986年 | 23篇 |
1985年 | 17篇 |
1984年 | 27篇 |
1983年 | 23篇 |
1982年 | 28篇 |
1981年 | 30篇 |
1980年 | 22篇 |
1979年 | 23篇 |
1978年 | 20篇 |
1977年 | 11篇 |
1976年 | 13篇 |
1975年 | 18篇 |
1973年 | 16篇 |
排序方式: 共有2262条查询结果,搜索用时 0 毫秒
21.
Chirag Patel Vishwanada Sastry Datta Madamwar 《Applied biochemistry and biotechnology》1996,56(1):89-94
To obtain enriched methane content and improve the anaerobic digestion of a mixture of cattle dung, poultry waste, and cheese
whey, the effect of various doses of Tegoprens: T-3012, T-3022, T-5842, T-5843, T-5851, T-5852 has been studied, in bench-scale
digesters. Among them, Tegoprens 3022 showed more than a 45% increase in gas production with higher methane content. 相似文献
22.
Mogon Patel Anthony C. Swain Robert S. Maxwell 《Polymer Degradation and Stability》2006,91(3):548-554
Poly(m-carboranyl-siloxane) elastomers containing a mixture of di-methyl- and methylphenyl-silyl units were synthesised using the ferric chloride catalysed condensation reaction between di-chloro-diorganosilane and bis(di-methylmethoxysilyl)-m-carborane. These elastomeric materials were originally developed to have greater stability to extreme thermal environments and retain tailorable physical and chemical properties relative to comparable non-carborane containing elastomers. Prepared samples were aged either by heating in air at elevated temperatures or by gamma irradiation from a 60Co source. Multinuclear (1H, 13C and 11B) solid and solution state nuclear magnetic resonance (NMR) was used to assess degradation. This included measurements of segmental chain dynamics using a solid-echo pulse sequence reflecting changes in crosslink density and assessing changes to the carborane fragment by 11B and 1H Magic Angle Spinning (MAS) methods. Thermogravimetric measurements were also performed to assess thermal stability. Gamma radiation (to a dose of 1 MGy) was found to induce only a small degree of elastomer hardening as evidenced by a reduction in segmental chain dynamics. The carborane cage however, remained intact at these dose levels. Thermal degradation was observed to lead to oxidative crosslinking, the degree of which is dependent on temperature. At temperatures below 350 °C, only small changes in segmental dynamics were observed commensurate with only minor weight loss at this temperature. At temperatures above 350 °C, the degradation of the elastomer increased dramatically with decreased segmental dynamics and presumed partial oxidation of the carborane cage. The integrity of the m-carborane cage and the segmental dynamics were found to be significantly reduced at temperatures above 580 °C, in line with the known cage rearrangement temperature for icosahedral carboranes. 相似文献
23.
Edwards KW Ogg M Bellerive A Britton DI Hyatt ER MacFarlane DB Patel PM Spaan B Sadoff AJ Ammar R Baringer P Bean A Besson D Coppage D Copty N Davis R Hancock N Kelly M Kotov S Kravchenko I Kwak N Lam H Kubota Y Lattery M Momayezi M Nelson JK Patton S Poling R Savinov V Schrenk S Wang R Alam MS Kim IJ Ling Z Mahmood AH O'Neill JJ Severini H Sun CR Wappler F Crawford G Daubenmier CM Fulton R Fujino D Gan KK Honscheid K Kagan H Kass R Lee J Sung M White C Wolf A Zoeller MM Butler F Fu X Nemati B 《Physical review letters》1995,74(17):3331-3335
24.
Battle M Ernst J Kwon Y Roberts S Thorndike EH Wang CH Dominick J Lambrecht M Sanghera S Shelkov V Skwarnicki T Stroynowski R Volobouev I Wei G Zadorozhny P Artuso M Goldberg M He D Horwitz N Kennett R Mountain R Moneti GC Muheim F Mukhin Y Playfer S Rozen Y Stone S Thulasidas M Vasseur G Zhu G Bartelt J Csorna SE Egyed Z Jain V Kinoshita K Edwards KW Ogg M Britton DI Hyatt ER MacFarlane DB Patel PM Akerib DS Barish B Chadha M Chan S Cowen DF Eigen G Miller JS O'Grady C Urheim J Weinstein AJ 《Physical review letters》1994,73(8):1079-1083
25.
26.
27.
28.
Validation of LC/MS electrospray ionisation method for the estimation of ursodiol in human plasma and its application in bioequivalence study 总被引:1,自引:0,他引:1
Sundd Singh S Shah H Gupta S Jain M Sharma K Patel H Shah B Thakkar P Patel N Shah R Bhushan Lohary B 《Annali di chimica》2004,94(12):951-959
A novel High Performance Liquid Chromatography-electrospray mass spectrometric method has been developed for the estimation of Ursodiol (Ursodeoxycholic acid)--a bile acid, in human plasma using Ornidazole as internal standard. The methodology involved solid phase extraction of the analyte from human plasma matrix. The chromatographic separation was achieved within seven minutes by an isocratic mobile phase containing 1.0 mM ammonium acetate and Acetonitrile (65:35, v/v), flowing through XTerra MS C18, 100 x 2.1, 3.5 microm analytical column, at a flow rate of 0.2 ml/min. Ion signals were measured in negative mode for Ursodiol and internal standard at m/z 391.3 and 278.1, respectively. A detailed validation of the method was performed as per USFDA guidelines and the standard curves were found to be linear in the range 50.0 ng/ml to 3000.0 ng/ml with the mean correlation coefficient more than 0.99. The absolute recovery was more than 54.90% for Ursodiol and 76.51% for internal standard. Ursodiol was stable for sixty-nine days at -70 degrees C and for eight hours at ambient temperature. After extraction from plasma, the reconstituted samples of Ursodiol were stable in autosampler at 10 degrees C for forty-eight hours. Upon subjecting to three freeze thaw cycles, there was no change in the recovery of the analyte. The integrity of the plasma samples remained unaffected even upon four-fold dilution with drug free human plasma. The method was simple, specific, sensitive, precise, accurate and suitable for bioequivalence and pharmacokinetic studies. It was successfully applied to the pilot bioequivalence study of Ursodiol in male human subjects. 相似文献
29.
Patel RN Singh N Shukla KK Gundla VL Chauhan UK 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(11-12):2603-2610
X-band electron spin resonance (ESR) and UV-vis spectra of a homobinuclear [(Bipy)2Cu-E-Im-Cu(Bipy)2](BF4)3 and a heterobinuclear [(Bipy)2Cu-E-Im-Zn(Bipy)2](BF4)3 complexes, E-Im=2-ethylimidazolate ion have been described as possible models for superoxide dismutase (SOD). Magnetic moment and ESR spectral measurements of the homobinuclear complex have shown an antiferromagnetic exchange interaction. From pH-dependent ESR and UV-vis spectral measurements studies, these complexes have been found to be stable over 8.5-10.5 pH range. These complexes catalyze the dismutation of superoxide (O2-) at biological pH. All the observations indicate that these complexes act as good possible models for superoxide dismutase. 相似文献
30.
Gabapentin is an anticonvulsant drug used for the treatment of epilepsy. It is not bound to plasma protein and is not metabolized. A high performance liquid chromatography–mass spectrometric micro method is described in this report for its determination from human plasma. Chromatography was performed on a 50 × 4.6 mm, 4 μm nitrile column and the parent ion detected in the positive ionization mode on single quadrupole analyzer (Q1MI) with atmospheric pressure ionization source. Extraction was carried out on C18, 100 mg/3cc cartridge using 10 μL sample volume. The mean extraction recovery was 97% and within batch and between batch coefficients of variation were <9%. Lack of interference from endogenous substances helped in achieving a highly sensitive method without the need for monitoring fragment ions. The lowest concentration injected on column for calibration curve was 195 pg (range 0.5–64 ng). The method was applied for analysis of samples from a cross-over bio-equivalence study comparing two formulations. 相似文献