全文获取类型
收费全文 | 221632篇 |
免费 | 3740篇 |
国内免费 | 1847篇 |
专业分类
化学 | 123381篇 |
晶体学 | 2657篇 |
力学 | 9139篇 |
综合类 | 85篇 |
数学 | 24827篇 |
物理学 | 67130篇 |
出版年
2020年 | 1946篇 |
2019年 | 2079篇 |
2018年 | 2646篇 |
2017年 | 2661篇 |
2016年 | 3911篇 |
2015年 | 2633篇 |
2014年 | 3779篇 |
2013年 | 9219篇 |
2012年 | 8120篇 |
2011年 | 9823篇 |
2010年 | 6942篇 |
2009年 | 6725篇 |
2008年 | 9080篇 |
2007年 | 9128篇 |
2006年 | 8602篇 |
2005年 | 7902篇 |
2004年 | 7045篇 |
2003年 | 6125篇 |
2002年 | 5662篇 |
2001年 | 6590篇 |
2000年 | 4862篇 |
1999年 | 3477篇 |
1998年 | 2861篇 |
1997年 | 2878篇 |
1996年 | 2857篇 |
1995年 | 2623篇 |
1994年 | 2706篇 |
1993年 | 2567篇 |
1992年 | 2792篇 |
1991年 | 2877篇 |
1990年 | 2669篇 |
1989年 | 2572篇 |
1988年 | 2527篇 |
1987年 | 2462篇 |
1986年 | 2479篇 |
1985年 | 3274篇 |
1984年 | 3319篇 |
1983年 | 2774篇 |
1982年 | 3012篇 |
1981年 | 2769篇 |
1980年 | 2576篇 |
1979年 | 2751篇 |
1978年 | 2972篇 |
1977年 | 3009篇 |
1976年 | 3029篇 |
1975年 | 2777篇 |
1974年 | 2888篇 |
1973年 | 2939篇 |
1972年 | 2301篇 |
1971年 | 1826篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
Russian Journal of Organic Chemistry - A rapid and efficient catalytic approach has been proposed for the synthesis of dimethyl 2-[2-(aryl-amino)but-3-en-1-yl]- and... 相似文献
102.
Prof. James S. M. Anderson Prof. Juan I. Rodríguez Prof. Paul W. Ayers Daniel E. Trujillo-González Dr. Andreas W. Götz Prof. Jochen Autschbach Prof. Fray L. Castillo-Alvarado Prof. Koichi Yamashita 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(10):2538-2544
The topology of the molecular electron density of benzene dithiol gold cluster complex Au4−S−C6H4−S′−Au′4 changed when relativistic corrections were made and the structure was close to a minimum of the Born–Oppenheimer energy surface. Specifically, new bond paths between hydrogen atoms on the benzene ring and gold atoms appeared, indicating that there is a favorable interaction between these atoms at the relativistic level. This is consistent with the observation that gold becomes a better electron acceptor when relativistic corrections are applied. In addition to relativistic effects, here, we establish the sensitivity of molecular topology to basis sets and convergence thresholds for geometry optimization. 相似文献
103.
Zhilitskaya L. V. Yarosh N. O. Shagun L. G. Dorofeev I. A. 《Russian Journal of General Chemistry》2019,89(8):1625-1629
Russian Journal of General Chemistry - The earlier unknown organosilicon polyiodides of 2-thiobenzimidazolium have been synthesized basing on the three-component reaction of 2-thiobenzimidazole,... 相似文献
104.
Mycophenolic acid (MPA), a frequently used immunosuppressant, exhibits large inter‐patient pharmacokinetic variability. This study (a) developed and validated a sensitive liquid chromatography–tandem mass spectrometry (LC–MS/MS) assay for MPA and metabolites [MPA glucuronide (MPAG) and acyl‐glucuronide (AcMPAG)] in the culture medium of HepaRG cells; and (b) characterized the metabolism interaction between MPA and p‐cresol (a common uremic toxin) in this in vitro model as a potential mechanism of pharmacokinetic variability. Chromatographic separation was achieved with a C18 column (4.6 × 250 mm,5 μm) using a gradient elution with water and methanol (with 0.1% formic acid and 2 mm ammonium acetate). A dual ion source ionization mode with positive multiple reaction monitoring was utilized. Multiple reaction monitoring mass transitions (m/z) were: MPA (320.95 → 207.05), MPAG (514.10 → 303.20) and AcMPAG (514.10 → 207.05). MPA‐d3 (323.95 → 210.15) and MPAG‐d3 (517.00 → 306.10) were utilized as internal standards. The calibration curves were linear from 0.00467 to 3.2 μg/mL for MPA/MPAG and from 0.00467 to 0.1 μg/mL for AcMPAG. The assay was validated based on industry standards. p‐Cresol inhibited MPA glucuronidation (IC50 ≈ 55 μm ) and increased MPA concentration (up to >2‐fold) at physiologically relevant substrate‐inhibitor concentrations (n = 3). Our findings suggested that fluctuations in p‐cresol concentrations might be in part responsible for the large pharmacokinetic variability observed for MPA in the clinic. 相似文献
105.
Crystallography Reports - A novel hydrated cesium hydroxypentaborate is synthesized from boric acid flux at 180°С, and its crystal structure is determined by X-ray diffraction. The... 相似文献
106.
Kaminskii A. A. Manomenova V. L. Rudneva E. B. Sorokina N. I. Grebenev V. V. Kozlova N. N. Angeluts A. A. Ozheredov I. A. Solyankin P. M. Denisyuk I. Yu. Fokina M. I. Zulina N. A. Shkurinov A. P. Voloshin A. E. 《Crystallography Reports》2019,64(4):669-677
Crystallography Reports - Aqueous solutions of guanylurea hydrogen phosphite (GUHP) have been synthesized. The temperature dependence of equilibrium GUHP concentration in water was obtained. The... 相似文献
107.
Russian Journal of General Chemistry - Reactions of 2-and 3-furoyl chlorides having chloromethyl or butylthiomethyl group in the adjacent position of the furan ring as well as of analogous... 相似文献
108.
Ian Drake Gregoire Cardoen Andrew Hughes Kebede Beshah Kenneth L. Kearns Tianlan Zhang John Reffner Casey Wolf Ralph Even 《Journal of polymer science. Part A, Polymer chemistry》2019,57(13):1373-1388
A polyurea macromer (PUM) was synthesized and dispersed in basic conditions to form self‐assembled nanoparticles (<20 nm dispersions, up to 30 wt % aq. soln.). These nanoparticles enabled surfactant‐free emulsion polymerization to form hybrid polyurea‐acrylic particles despite the absence of a measureable water‐soluble fraction. The Tg of the starting PUM material was a strong function of the PUM's extent of neutralization and hydration (varying between 100 °C and >175 °C) due to changes in hydrogen and ionic bonding. Two separate hybrid polyurea‐acrylic emulsion systems were prepared: one by direct polymerization of (meth)acrylic monomers in the presence of the nanodispersion and a second by a physical blend of PUM nanodispersion with an acrylic latex control. The direct polymerization method resulted in a hybrid emulsion particle size that developed by a mechanism resembling conventional emulsion polymerization and was unlike that described for seeded polyurethane dispersion systems. Film hardness was shown to increase with increasing coating thickness for the hybrid film prepared by direct polymerization. The resulting mechanical properties could be explained by applying mechanical models for a composite foam structure. These results were unprecedented for normal elastomer films. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1373–1388 相似文献
109.
Thomas Marmin Prof. Yves L. Dory 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(27):6707-6711
Cyclohexane and cyclotri-β-alanyl have been used as scaffolds for the design of new C3-symmetric rings incorporating conjugated alkenes and dienes. All three C3-symmetric lactams share the same triangular shape and their crystal system is trigonal. They all belong to the R3 space group, R3m, R3 and R3c, for the increasingly large 12-, 18- and 24-membered rigid rings, respectively. All lactams stack on top of each other, through H-bonds and van der Waals noncovalent interactions, leading to endless supramolecular cylinders and tubes. The largest member of the family leads to tubes, the central pores of which is wide enough to let water in. A common feature of all the lactams is their very large dipole, of around 9 D, according to DFT calculations. Surprisingly, all the resulting cylinders and tubes pack side by side in the crystals, with all the dipoles pointing to the same direction. As a result, all three crystals are anisotropic and appear to be the first members of a new kind of highly polar crystals. 相似文献
110.