全文获取类型
收费全文 | 3528篇 |
免费 | 777篇 |
国内免费 | 292篇 |
专业分类
化学 | 2771篇 |
晶体学 | 4篇 |
力学 | 66篇 |
综合类 | 49篇 |
数学 | 659篇 |
物理学 | 1048篇 |
出版年
2024年 | 3篇 |
2023年 | 38篇 |
2022年 | 65篇 |
2021年 | 106篇 |
2020年 | 166篇 |
2019年 | 109篇 |
2018年 | 120篇 |
2017年 | 128篇 |
2016年 | 222篇 |
2015年 | 206篇 |
2014年 | 278篇 |
2013年 | 394篇 |
2012年 | 258篇 |
2011年 | 257篇 |
2010年 | 184篇 |
2009年 | 226篇 |
2008年 | 222篇 |
2007年 | 271篇 |
2006年 | 201篇 |
2005年 | 195篇 |
2004年 | 166篇 |
2003年 | 156篇 |
2002年 | 95篇 |
2001年 | 77篇 |
2000年 | 71篇 |
1999年 | 55篇 |
1998年 | 58篇 |
1997年 | 53篇 |
1996年 | 39篇 |
1995年 | 33篇 |
1994年 | 18篇 |
1993年 | 30篇 |
1992年 | 8篇 |
1991年 | 17篇 |
1990年 | 8篇 |
1989年 | 4篇 |
1988年 | 11篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1973年 | 2篇 |
排序方式: 共有4597条查询结果,搜索用时 62 毫秒
91.
以1-甲基吡咯为原料,通过酰化、硝化、酯化、还原、成盐等五步反应,合 成得到1-甲基-2-甲氧羰基-4-氨基吡咯盐酸盐,总产率20%左右。该法具有 原料便宜易得、操作简单、产物易于分离提纯等优点,有利于该化合物的大量制备 和应用。 相似文献
92.
The fully substituted cyclopentenedione core of madindoline A (1) and B (2) as potent and selective inhibitor of IL-6 has been synthesized efficiently. The quaternary carbon center C-2' was constructed on the basis of a newly developed AIEt3-promoted tandem reductive rearrangement of α-hydroxy epoxides. 相似文献
93.
94.
95.
96.
N.C. Dafader M.E. Haque F. Akhtar 《高分子科学》2007,(5):519-523
Natural rubber latex(NRL)and methyl methacrylate(MMA)grafted rubber latex were blended in different ratios and irradiated at various absorbed doses by gamma rays from Co-60 source at room temperature.The tensile properties, swelling ratio and permanent set were measured.The maximum tensile strength and modulus at 500% elongation were obtained at an absorbed dose of 8 kGy.Modulus increases from 6.99 MPa to 9.87 MPa for an increase in proportion of MMA grafted rubber from 40% to 60% in the blend at similar absorbed dose.Elongation at break and swelling ratio decrease with increasing absorbed dose as well as the MMA grafted rubber content in the blends.The decreasing trend of permanent set is high up to 5 kGy absorbed dose,and beyond that dose,it becomes almost flat. 相似文献
97.
Radiation formation of polymeric nanogels 总被引:4,自引:0,他引:4
An alternative method of synthesis of polymeric nanogels is proposed, based not on polymerization, but on intramolecular crosslinking of polymer chains, initiated by pulse irradiation in dilute aqueous solutions. Kinetic data show that for many water-soluble polymers irradiation under these conditions result in intramolecular crosslinking. Preliminary product studies on poly(vinyl alcohol) indicate that in fact internally crosslinked macromolecules can be obtained by this technique. 相似文献
98.
《Arabian Journal of Chemistry》2022,15(7):103933
In this study, a fingerprint-activity relationship modeling between chemical fingerprints and antirheumatic activity was established, and multivariate statistical analysis was used to evaluate the quality of Taxilli Herba (TH) from different hosts. Characteristic fingerprints of 20 batches of TH samples were generated by high-performance liquid chromatography coupled with triple quadrupole-time of flight tandem mass spectrometry (HPLC-Triple TOF-MS/MS), and the similarity analysis was calculated based on thirteen common characteristic peaks by hierarchical clustering analysis (HCA). Subsequently, nine efficacy markers were discovered by combining fingerprints and antirheumatic activity through grey correlation analysis (GCA) and bivariate correlation analysis (BCA). Meanwhile, the content of 5 constituents in 9 markers was determined by high-performance liquid chromatography coupled with triple quadrupole-linear ion trap tandem mass spectrometry (HPLC-QTRAP-MS/MS). The comprehensive quality of TH was assessed using multivariate statistical analysis, including principal components analysis (PCA) and technique for order preference by similarity to ideal solution (TOPSIS). The results showed that a high dose of TH extract could markedly ameliorate arthritis damage compared to other doses, with flavonoids playing an important role in the antirheumatic activity. The comprehensive quality of samples from Morus alba L. (SS) was superior to those from Liquidambar formosana Hance (FXS). The present study will demonstrate the markers associated with efficacy, and provide an applicable strategy for more comprehensive quality control and evaluation of TH. 相似文献
99.
《Arabian Journal of Chemistry》2022,15(12):104368
Protein hydrolysates have the potential to be natural and safer sources of bioactive peptides. In this study, two proteases were used to hydrolyze Chinese sturgeon (Acipenser sinensis) protein, and the hydrolysates were then purified to yield antioxidant peptides. The degree of hydrolysis of 23.56 % and 18.14 % was obtained using papain and alcalase 2.4L, respectivly, and hydrolysates had 96.80 % and 87.24 % total amino acid content, respectivly. The papain hydrolysate (PH) and alcalase 2.4L hydrolysate (AH) showed good antioxidant activity against DPPH? (IC50 of 3.64 and 3.15 mg/mL) and ABTS?+ (IC50 of 1.92 and 1.58 mg/mL), respectively. The low-molecular-weight (<1000 Da) fraction of both hydrolysates demonstrated the highest antiradical activity (IC50 of 2.59 and 2.31 mg/mL, DPPH) and (IC50 of 1.54 and 1.36 mg/mL, ABTS), respectively. Nine peptides were separated from both hydrolysates using reverse phase high performance liquid chromatography (RP-HPLC). The IC50 for ABTS?+ scavenging activity of peptide P5 with valine, glycine and asparagine (MW of 282.13 Da) from PH, and peptide P3 with histidine, glycine and alanine (MW of 302.74 Da) from AH was 0.89 and 0.72 mg/mL, respectively. The fractions and purified peptides obtained from Chinese sturgeon hydrolysates could be utilized as natural antioxidant substitutes in pharmaceuticals and food products. 相似文献
100.
The title Schiff base compound,C19H19N3O3,a derivative of antipyrine,has been synthesized and characterized by elemental analysis,IR,and single-crystal X-ray diffraction.The crystal belongs to the monoclinic system,space group C2/c,with α = 27.935(5),b = 7.553(1),c =16.692(3) (A),β = 105.810(3)°,Z= 8,V= 3388.7(10) (A)3,Dc = 1.323 g/cm3,Mr = 337.37,λ(MoKα) =0.71073 (A),μ = 0.091 mm-1,F(000) = 1424,R = 0.0630 and wR = 0.1273.A total of 3513 unique reflections were collected,of which 2112 with I > 2σ(I) were observed.The molecular structure adopts a trans configuration about the C=N double bond.The pyrazoline and C(1)~C(6) pheny1 ring are approximately coplanar (mean deviation from the combined plane is 0.069(3) (A)),with the dihedral angle of 9.7(2)°.The preliminary biological tests show that the compound has high antibacterial activities. 相似文献