全文获取类型
收费全文 | 1897篇 |
免费 | 58篇 |
国内免费 | 13篇 |
专业分类
化学 | 1428篇 |
晶体学 | 12篇 |
力学 | 27篇 |
数学 | 273篇 |
物理学 | 228篇 |
出版年
2023年 | 12篇 |
2022年 | 25篇 |
2021年 | 31篇 |
2020年 | 29篇 |
2019年 | 20篇 |
2018年 | 26篇 |
2017年 | 22篇 |
2016年 | 45篇 |
2015年 | 46篇 |
2014年 | 66篇 |
2013年 | 99篇 |
2012年 | 121篇 |
2011年 | 137篇 |
2010年 | 77篇 |
2009年 | 55篇 |
2008年 | 122篇 |
2007年 | 164篇 |
2006年 | 107篇 |
2005年 | 129篇 |
2004年 | 102篇 |
2003年 | 102篇 |
2002年 | 75篇 |
2001年 | 28篇 |
2000年 | 22篇 |
1999年 | 26篇 |
1998年 | 13篇 |
1997年 | 29篇 |
1996年 | 32篇 |
1995年 | 15篇 |
1994年 | 18篇 |
1993年 | 13篇 |
1992年 | 15篇 |
1991年 | 12篇 |
1990年 | 13篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1987年 | 8篇 |
1986年 | 9篇 |
1985年 | 16篇 |
1984年 | 8篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 4篇 |
1980年 | 9篇 |
1979年 | 10篇 |
1976年 | 7篇 |
1975年 | 2篇 |
1970年 | 2篇 |
1969年 | 2篇 |
1962年 | 1篇 |
排序方式: 共有1968条查询结果,搜索用时 15 毫秒
91.
Sharpless KE Lindstrom RM Nelson BC Phinney KW Rimmer CA Sander LC Schantz MM Spatz RO Thomas JB Turk GC Wise SA Wood LJ Yen JH 《Journal of AOAC International》2010,93(4):1262-1274
Standard Reference Material (SRM) 1849 Infant/Adult Nutritional Formula has been issued by the National Institute of Standards and Technology (NIST) as a replacement for SRM 1846 Infant Formula, issued in 1996. Extraction characteristics of SRM 1846 have changed over time, as have NIST's analytical capabilities. While certified mass fraction values were provided for five constituents in SRM 1846 (four vitamins plus iodine), certified mass fraction values for 43 constituents are provided in SRM 1849 (fatty acids, elements, and vitamins) and reference mass fraction values are provided for an additional 43 constituents including amino acids and nucleotides, making it the most extensively characterized food-matrix SRM available from NIST. 相似文献
92.
Karen A. Wulfeck-Kleier Michael D. Ybarra Thomas F. Speth Matthew L. Magnuson 《Journal of chromatography. A》2010,1217(5):676-682
Although the herbicide atrazine has been reported to not react measurably with free chlorine during drinking water treatment, this work demonstrates that at contact times consistent with drinking water distribution system residence times, a transformation of atrazine can be observed. Some transformation products detected through the use of high performance liquid chromatography–electrospray mass spectrometry are consistent with the formation of N-chloro atrazine. The effects of applied chlorine, pH, and reaction time on the transformation reaction were studied to help understand the practical implications of the transformation on the accurate determination of atrazine in drinking waters. The errors in the determination of atrazine are a function of the type of dechlorinating agent applied during sample preparation and the analytical instrumentation utilized. When a reductive dechlorinating agent, such as sodium sulfite or ascorbic acid is used, the quantification of the atrazine can be inaccurate, ranging from 2-fold at pH 7.5 to 30-fold at pH 6.0. The results suggest HPLC/UV and ammonium chloride quenching may be best for accurate quantification. Hence, the results also appear to have implications for both compliance monitoring and health effects studies that utilize gas chromatography analysis with sodium sulfite or ascorbic acid as the quenching agent. 相似文献
93.
The processes of lactic acid production include two key stages, which are (a) fermentation and (b) product recovery. In this
study, free cell of Bifidobacterium longum was used to produce lactic acid from cheese whey. The produced lactic acid was then separated and purified from the fermentation
broth using combination of nanofiltration and reverse osmosis membranes. Nanofiltration membrane with a molecular weight cutoff
of 100–400 Da was used to separate lactic acid from lactose and cells in the cheese whey fermentation broth in the first step.
The obtained permeate from the above nanofiltration is mainly composed of lactic acid and water, which was then concentrated
with a reverse osmosis membrane in the second step. Among the tested nanofiltration membranes, HL membrane from GE Osmonics
has the highest lactose retention (97 ± 1%). In the reverse osmosis process, the ADF membrane could retain 100% of lactic
acid to obtain permeate with water only. The effect of membrane and pressure on permeate flux and retention of lactose/lactic
acid was also reported in this paper. 相似文献
94.
L. Renee Ruhaak Sandra L. Taylor Suzanne Miyamoto Karen Kelly Gary S. Leiserowitz David Gandara Carlito B. Lebrilla Kyoungmi Kim 《Analytical and bioanalytical chemistry》2013,405(14):4953-4958
Many studies focused on the discovery of novel biomarkers for the diagnosis and treatment of disease states are facilitated by mass spectrometry-based technology. HPLC coupled to mass spectrometry is widely used; miniaturization of this technique using nano-liquid chromatography (LC)-mass spectrometry (MS) usually results in better sensitivity, but is associated with limited repeatability. The recent introduction of chip-based technology has significantly improved the stability of nano-LC-MS, but no substantial studies to verify this have been performed. To evaluate the temporal repeatability of chip-based nano-LC-MS analyses, N-glycans released from a serum sample were repeatedly analyzed using nLC-PGC-chip-TOF-MS on three non-consecutive days. With an average inter-day coefficient of variation of 4 %, determined on log10-transformed integrals, the repeatability of the system is very high. Overall, chip-based nano-LC-MS appears to be a highly stable technology, which is suitable for the profiling of large numbers of clinical samples for biomarker discovery. 相似文献
95.
Laurens van Gelderen Gadi Rothenberg V. Roberto Calderone Karen Wilson N. Raveendran Shiju 《应用有机金属化学》2013,27(1):23-27
Copper immobilized on a functionalized silica support is a good catalyst for the homocoupling of terminal alkynes. The so‐called Glaser–Hay coupling reaction can be run in air with catalytic amounts of base. The copper catalyst is active for multiple substituted alkynes, in both polar and non‐polar solvents, with good to excellent yields (75–95%). Depending on the alkyne, full conversion can be achieved within 3–24 h. The catalyst was characterized by TGA, inductively coupled plasma and X‐ray photoelectron spectroscopy. Leaching tests confirm that the catalyst is and remains heterogeneous. Importantly, the overall reaction requires only alkyne and oxygen (in this case, air) as reagents, making this a clean catalytic oxidative coupling reaction. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
96.
97.
98.
99.
Jose Castro‐Perez Nathan Hatcher Nana Kofi Karikari Sheng‐Ping Wang Vivienne Mendoza Henry Shion Alan Millar John Shockcor Mark Towers David McLaren Vinit Shah Stephen Previs Karen Akinsanya Michele Cleary Thomas P. Roddy Douglas G. Johns 《Rapid communications in mass spectrometry : RCM》2014,28(22):2471-2479
100.
Abstract: Abstract. 1-Alkyl- and 2-alkylnaphthalenes are conveniently brominated in the 4-and 1-positions respectively using N-bromosuccinimide (NBS) in acetonitrile. The reactions are easy to perform and give higher chemical yields and better regioselectivity compared to brominations employing bromine/dichloromethane. 相似文献