全文获取类型
收费全文 | 21221篇 |
免费 | 1496篇 |
国内免费 | 11篇 |
出版年
2023年 | 54篇 |
2022年 | 159篇 |
2021年 | 412篇 |
2020年 | 247篇 |
2019年 | 310篇 |
2018年 | 531篇 |
2017年 | 393篇 |
2016年 | 680篇 |
2015年 | 1126篇 |
2014年 | 1223篇 |
2013年 | 1393篇 |
2012年 | 1825篇 |
2011年 | 1706篇 |
2010年 | 1098篇 |
2009年 | 912篇 |
2008年 | 1344篇 |
2007年 | 1184篇 |
2006年 | 1052篇 |
2005年 | 971篇 |
2004年 | 958篇 |
2003年 | 777篇 |
2002年 | 784篇 |
2001年 | 627篇 |
2000年 | 632篇 |
1999年 | 422篇 |
1998年 | 166篇 |
1997年 | 129篇 |
1996年 | 119篇 |
1995年 | 87篇 |
1994年 | 82篇 |
1993年 | 69篇 |
1992年 | 157篇 |
1991年 | 125篇 |
1990年 | 88篇 |
1989年 | 103篇 |
1988年 | 70篇 |
1987年 | 65篇 |
1986年 | 69篇 |
1985年 | 53篇 |
1984年 | 47篇 |
1983年 | 37篇 |
1982年 | 27篇 |
1981年 | 24篇 |
1978年 | 28篇 |
1977年 | 23篇 |
1976年 | 32篇 |
1975年 | 29篇 |
1973年 | 33篇 |
1971年 | 23篇 |
1969年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
941.
Bioconversion of waste office paper to L(+)-lactic acid by the filamentous fungus Rhizopus oryzae 总被引:4,自引:0,他引:4
L(+)-lactic acid production was investigated using an enzymatic hydrolysate of waste office automation (OA) paper in a culture of the filamentous fungus Rhizopus oryzae. In 4 d culture, 82.8 g/l glucose, 7 g/l xylose, and 3.4 g/l cellobiose contained in the hydrolysate were consumed to produce 49.1 g/l of lactic acid. The lactic acid yield and production rate were only 0.59 g/g and 16.3 g/l/d, respectively, only 75% and 61% of the results from the glucose medium. The low production rate from waste OA hydrolysate was elucidated by trials using xylose as the sole carbon source; in those trials, the lactic acid production rate was 7.3 g/l/d, only 28% that of glucose or cellobiose. The low lactic acid yield from waste OA hydrolysate was clarified by trials using artificial hydrolysates comprised of 7:2:1 or 7:1:2 ratios of glucose:cellobiose:xylose. For both, the lactic acid production rate of 17.4 g/l/d matched that of waste OA paper, while the lactic acid yield was similar to that of the glucose medium. This indicates that the production rate may be inhibited by xylose derived from hemicellulose, and the yield may be inhibited by unknown compounds derived from paper pulp. 相似文献
942.
Lee SK Park EJ Lee E Min HY Kim EY Lee T Kim S 《Bioorganic & medicinal chemistry letters》2004,14(9):2105-2108
The inhibitory effects of a series of styrylheterocycles on the production of cyclooxygenase-2-mediated prostaglandin E(2) (PGE(2)) were evaluated in lipopolysaccharide-stimulated RAW264.7 murine macrophages. A new series of potential inhibitors, including 3-[2-(4-methoxy-phenyl)-vinyl]-thiophene, have been identified, thus providing novel chemical leads for the further development of potential inhibitors in this capacity. The suppression of COX-2 mRNA expression by the active styrylheterocycles, in part, was involved in the inhibitory activity against the overproduction of PGE(2). 相似文献
943.
Stearns BA Anker N Arruda JM Campbell BT Chen C Cramer M Hu T Jiang X Park K Ren KK Sablad M Santini A Schaffhauser H Urban MO Munoz B 《Bioorganic & medicinal chemistry letters》2004,14(5):1295-1298
A novel class of 6-aryl-6H-pyrrolo[3,4-d]pyridazine ligands for the alpha2delta subunit of voltage-gated calcium channels has been described. Substitutions in the aryl ring of the molecule were generally not tolerated, and resulted in diminished binding to the alpha2delta subunit. Modifications to the pyridazine ring revealed numerous permissive substitutions, and detailed SAR studies were carried out in this portion of the molecule. Replacement of the pyridazine ring methyl group with an aminomethyl functionality provided greatly improved potency over the initial lead. The initial lead compound displayed good rat pharmacokinetic properties, and was shown to be efficacious in the Chung model for neuropathic pain in rats. 相似文献
944.
Lee WS Lee DW Baek YI An S An SJ Cho KH Choi YK Kim HC Park HY Bae KH Jeong TS 《Bioorganic & medicinal chemistry letters》2004,14(12):3109-3112
The sesquineolignan, saucerneol B (1), and dineolignans, manassantin A (2), and manassantin B (3), were isolated from the methanol extracts of Saururus chinensis root and elucidated by their spectroscopic data analysis. Compounds 1-3 inhibited hACAT-1 and hACAT-2 with IC(50) values of 43.0 and 124.0 microM for 1, of 39.0 and 8.0 microM for 2, of 82.0 microM and only 32% inhibition at 1mM for 3, respectively. The EtOAc-soluble fraction, which contained compounds 1-3, of methanol extracts of S. chinensis exhibited strong cholesterol-lowering effect in high cholesterol-fed mice. 相似文献
945.
Park HG Choi JY Choi SH Park MK Lee J Suh YG Cho H Oh U Kim HD Joo YH Kim SY Park YH Jeong YS Choi JK Kim JK Jew SS 《Bioorganic & medicinal chemistry letters》2004,14(7):1693-1696
A series of N-4-methansulfonamidobenzyl-N'-2-substituted-4-tert-butylbenzyl thioureas were prepared for the study of their agonistic/antagonistic activities to the vanilloid receptor in rat DRG neurons. Their structure-activity relationship reveals that there is a space for another hydrophobic binding interaction around 2-position in 4-tert-butylbenzyl region. Among the prepared derivatives, 6n show the highest antagonistic activity against the vanilloid receptor (IC(50)=15 nM). 相似文献
946.
Synthesis and biological activity of new quinoxaline antibiotics of echinomycin analogues 总被引:5,自引:0,他引:5
Novel quinoxaline antibiotics having the methylenedithioether bridge as an analogue of echinomycin have been synthesized by insertion of methylene moiety between -S-S- bond. The compound 1a shows remarkable cytotoxicities against human tumor various cell lines, and is active VRE (vancomycin-resistant enterococci) within MIC range 0.5-8 microg/mL. According to the eukaryotic or prokaryotic data, 1a might be a first analogue to replace echinomycin. 相似文献
947.
Induction of G2/M cell cycle arrest and apoptosis by a benz[f]indole-4,9-dione analog in cultured human lung (A549) cancer cells 总被引:1,自引:0,他引:1
Lee EJ Lee HJ Park HJ Min HY Suh ME Chung HJ Lee SK 《Bioorganic & medicinal chemistry letters》2004,14(20):5175-5178
A synthetic benz[f]indole-4,9-dione analog, 2-amino-3-ethoxycarbonyl-N-methylbenz[f]indole-4,9-dione (SME-6), showed a potent growth inhibition of a panel of human cancer cell lines. The mechanism of action study revealed that the growth inhibitory effect of SME-6 was highly related to the induction of G2/M cell cycle arrest and apoptosis in human lung cancer cells (A549). These data may provide new information for understanding the mechanisms by benz[f]indole-4,9-diones-mediated antitumor activity. 相似文献
948.
Homolasonolide A and 10-desmethyllasonolide A are biologically less active than lasonolide A. The ethyl ester analogue of lasonolide A exhibited higher activity than the parent compound in some biological test. 相似文献
949.
Park HG Choi JY Choi SH Park MK Lee J Suh YG Cho H Oh U Lee J Kang SU Lee J Kim HD Park YH Su Jeong Y Kyu Choi J Jew SS 《Bioorganic & medicinal chemistry letters》2004,14(3):787-791
A series of N-4-substituted-benzyl-N'-tert-butylbenzyl thioureas were prepared for the study of their agonistic/antagonistic activities to the vanilloid receptor in rat DRG neurons. Their structure-activity relationship reveals that not only the two oxygens and amide hydrogen of sulfonamido group, but also the optimal size of methyl in methanesulfonamido group play an integral role for the antagonistic activity on vanilloid receptor. 相似文献
950.
Oh M Im I Lee YJ Kim YH Yoon JH Park HG Higashiyama S Kim YC Park WJ 《Bioorganic & medicinal chemistry letters》2004,14(24):6071-6074
We describe a series of potent and selective inhibitors of ADAM12 that were discovered using computational screening of a focused virtual library. The initial structure-based virtual screening selected 64 compounds from a 3D database of 67,062 molecules. Being evaluated by a cell-based ADAM12 activity assay, compounds 5, 11, 14, 16 were further identified as the potent and selective inhibitors of ADAM12 with low nanomolar IC50 values. The mechanism underlying the potency and selectivity of a representative compound, 5, was investigated through molecular docking studies. 相似文献