全文获取类型
收费全文 | 2973篇 |
免费 | 153篇 |
国内免费 | 1篇 |
专业分类
3127篇 |
出版年
2022年 | 20篇 |
2021年 | 33篇 |
2020年 | 14篇 |
2019年 | 15篇 |
2018年 | 36篇 |
2017年 | 31篇 |
2016年 | 55篇 |
2015年 | 85篇 |
2014年 | 89篇 |
2013年 | 137篇 |
2012年 | 185篇 |
2011年 | 189篇 |
2010年 | 126篇 |
2009年 | 133篇 |
2008年 | 162篇 |
2007年 | 195篇 |
2006年 | 183篇 |
2005年 | 174篇 |
2004年 | 164篇 |
2003年 | 170篇 |
2002年 | 146篇 |
2001年 | 58篇 |
2000年 | 74篇 |
1999年 | 55篇 |
1998年 | 46篇 |
1997年 | 48篇 |
1996年 | 25篇 |
1995年 | 31篇 |
1994年 | 20篇 |
1993年 | 21篇 |
1992年 | 39篇 |
1991年 | 31篇 |
1990年 | 33篇 |
1989年 | 34篇 |
1988年 | 34篇 |
1987年 | 23篇 |
1986年 | 18篇 |
1985年 | 31篇 |
1984年 | 10篇 |
1983年 | 20篇 |
1982年 | 20篇 |
1981年 | 14篇 |
1980年 | 14篇 |
1979年 | 19篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1976年 | 6篇 |
1975年 | 7篇 |
1974年 | 8篇 |
1969年 | 4篇 |
排序方式: 共有3127条查询结果,搜索用时 10 毫秒
21.
Gomez-Godinez V Wu T Sherman AJ Lee CS Liaw LH Zhongsheng Y Yokomori K Berns MW 《Nucleic acids research》2010,38(22):e202
In this study the femtosecond near-IR and nanosecond green lasers are used to induce alterations in mitotic chromosomes. The subsequent double-strand break responses are studied. We show that both lasers are capable of creating comparable chromosomal alterations and that a phase paling observed within 1-2 s of laser exposure is associated with an alteration of chromatin as confirmed by serial section electron microscopy, DAPI, γH2AX and phospho-H3 staining. Additionally, the accumulation of dark material observed using phase contrast light microscopy (indicative of a change in refractive index of the chromatin) ~ 34 s post-laser exposure corresponds spatially to the accumulation of Nbs1, Ku and ubiquitin. This study demonstrates that chromosomes selectively altered in mitosis initiate the DNA damage response within 30 s and that the accumulation of proteins are visually represented by phase-dark material at the irradiation site, allowing us to determine the fate of the damage as cells enter G1. These results occur with two widely different laser systems, making this approach to study DNA damage responses in the mitotic phase generally available to many different labs. Additionally, we present a summary of most of the published laser studies on chromosomes in order to provide a general guide of the lasers and operating parameters used by other laboratories. 相似文献
22.
Sakurai N Nakagawa-Goto K Ito J Sakurai Y Nakanishi Y Bastow KF Cragg G Lee KH 《Phytochemistry》2006,67(9):894-897
Seven alkaloids (1-7) were isolated from the stem bark of Alangium longiflorum. Compound 1, (-)-10-O-demethylisocephaeline, was isolated for the first time as a naturally occurring product from a plant source. All structures were elucidated by detailed spectroscopic analysis. Biological evaluation showed that 2, 10-O-demethylcephaeline, exhibited potent cytotoxic activity against human lung carcinoma (A549) and breast adenocarcinoma (MCF-7) with ED(50) values of 0.013 and 0.062 microM, respectively. The stereoisomer 1 was less potent than 2, and related compounds with different hydroxy/methoxy substitution patterns were also less potent or inactive. Thus, compound 2 merits attention as a cytotoxic lead for further study. 相似文献
23.
24.
We obtained monoclonal antibodies against N(1),N(12)-diacetylspermine (DiAcSpm) and N(1),N(8)-diacetylspermidine (DiAcSpd), and developed two systems of competitive ELISA that utilize the antibodies and a common enzyme-labeled antigen to measure these di-acetylpolyamines. Cross-reactions with N(1)-acetylspermidine in the assay of DiAcSpm and with N8-acetylspermidine in the assay of DiAcSpd were as low as 0.26 and 0.6%, respectively, and were judged to be insignificant in clinical use for measuring urinary diacetylpolyamines. These assays were used to assess diurnal variations in diacetylpolyamine excretion in urine to show that the excretion of diacetylpolyamines after normalization for the concentration of creatinine is stable over a day with only minimal diurnal variation. 相似文献
25.
Keiko Tadano-Aritomi Harumi Kubo Philip Ireland Takeshi Kasama Shizuo Handa Ineo Ishizuka 《Glycoconjugate journal》1996,13(2):285-293
A novel mono-sulfated glycosphingolipid based on the gangliotriaose core structure was isolated from rat kidney. The isolation procedure involved extraction of lipids with chloroform/methanol, mild alkaline methanolysis, column chromatographies with anion exchangers and silica beads. The structure was characterized by compositional analysis, FTIR spectroscopy, methylation analysis,1H-NMR spectroscopy and negative-ion liquid secondary ion mass spectrometry (LSIMS) using the intact glycolipid and its desulfation product. The two dimensional chemical shift correlated spectroscopy provided information on the sugar sequence as well as anomeric configurations, and indicated the presence of a 3-O-sulfatedN-acetylgalactosamine within the molecule. Negative-ion LSIMS with high- and low-energy collision-induced dissociation defined the sugar sequence and ceramide composition, confirming the presence of a sulfatedN-acetylgalactosamine at the non-reducing terminus. From these results, the complete structure was proposed to be HSO3-3GalNAc1-4Gal1-4Glc1-1Cer (Gg3Cer III3-sulfate, SM2b).
Abbreviations: Abbreviations for sulfated glycolipids [17] follow the modifications of the nomenclature system of Svennerholm for gangliosides [37], and the designation of the other glycosphingolipids follows the IUPAC-IUB recommendations [38]. Cer, ceramide; LacCer, lactosylceramide, Gal1-4Glc1-1Cer; Gg3Cer, gangliotriaosylceramide, GalNAc1-4Gal1-4Glc1-1Cer; Gg4Cer, gangliotetraosylceramide, Gal1-3GalNAc1-4Gal1-4Glc1-1Cer; iGb4Cer, isoglobotetraosylceramide, GalNAc1-3Gal1-3Gal1-4Glc1-1Cer; Gb4Cer, globotetraosylceramide, GalNAc1-3Gal1-4Gal1-4Glc1-1Cer; SM4s, galactosylceramide sulfate, GalCer I3-sulfate; SM3, lactosylceramide sulfate, LacCer II3-sulfate; SM2a, Gg3Cer II3-sulfate; SM2b, Gg3Cer III3-sulfate; SB2, Gg3Cer II3,III3-bis-sulfate; SM1a, Gg4Cer II3-sulfate; SM1b, Gg4Cer IV3-sulfate; SB1a, Gg4Cer II3,IV3-bissulfate; GLC, gas-liquid chromatography; GC-MS, gas chromatography-mass spectrometry; DQF, double quantum filtered; COSY, chemical-shift-correlated spectroscopy; LSIMS, liquid secondary ion mass spectrometry; CID, collision-induced dissociation; MS/MS, tandem mass spectrometry. 相似文献
26.
Suzuki R Nagata K Yumoto F Kawakami M Nemoto N Furutani M Adachi K Maruyama T Tanokura M 《Journal of molecular biology》2003,328(5):1149-1160
Here we report the solution structure of an archaeal FK506-binding protein (FKBP) from a thermophilic archaeum, Methanococcus thermolithotrophicus (MtFKBP17), which has peptidyl prolyl cis-trans isomerase (PPIase) and chaperone-like activities, to reveal the structural basis for the dual function. In addition to a typical PPIase domain, a newly identified domain is formed in the flap loop by a 48-residue insert that is required for the chaperone-like activity. The new domain, called IF domain (the Insert in the Flap), is a novel-folding motif and exposes a hydrophobic surface, which we consider to play an important role in the chaperone-like activity. 相似文献
27.
28.
Yoshie Maitani Sae Yano Yoshiyuki Hattori Masahiko Furuhata Kyoko Hayashi 《Journal of liposome research》2013,23(4):359-372
For injectable-sized liposome complexed with DNA (lipoplexes) with high transfection efficiency of genes, we initially prepared small-sized liposomes by addition of biosurfactant. For selectivity of gene expression, the thymidine kinase (MK-tk) gene controlled by midkine was used for herpes simplex virus thymidine kinase (HSV-tk) gene therapy. Liposomes composed of 3([N-(N′,N′–dimethylaminoethane)-carbamoyl] cholesterol (DC-Chol), L-dioleoylphosphatidylethanolamine (DOPE), and a biosurfactant, such as β-sitosterol β-D-glucoside (Sit-G) for Sit-G-liposomes and mannosylerythrytol lipid A (MEL) for MEL-liposomes, produced about 300-nm-sized lipoplexes. Sit-G- and MEL-liposomes showed higher transfection efficiency of the luciferase marker gene and thymidine kinase activity in the presence of serum in the cells. The treatment with transfection of MK-tk gene by Sit-G-liposome and injection of ganciclovir significantly reduced tumor growth in a solid tumor model, compared with that by Sit-G-liposome alone. This finding suggested that Sit-G-liposome is a potential vector for HSV-tk gene therapy. 相似文献
29.
Kumiko Ogawa Kyoko Nabae Jianqing Wang Kanako Wake So‐ichi Watanabe Mayumi Kawabe Osamu Fujiwara Satoru Takahashi Toshio Ichihara Seiko Tamano Tomoyuki Shirai 《Bioelectromagnetics》2009,30(3):205-212
The present study was designed to evaluate whether gestational exposure to an EMF targeting the head region, similar to that from cellular phones, might affect embryogenesis in rats. A 1.95‐GHz wide‐band code division multiple access (W‐CDMA) signal, which is one applied for the International Mobile Telecommunication 2000 (IMT‐2000) system and used for the freedom of mobile multimedia access (FOMA), was employed for exposure to the heads of four groups of pregnant CD(SD) IGS rats (20 per group) for gestational days 7–17. The exposure was performed for 90 min/day in the morning. The spatial average specific absorption rate (SAR) for individual brains was designed to be 0.67 and 2.0 W/kg with peak brain SARs of 3.1 and 7.0 W/kg for low (group 3) and high (group 4) exposures, respectively, and a whole‐body average SAR less than 0.4 W/kg so as not to cause thermal effects due to temperature elevation. Control and sham exposure groups were also included. At gestational day 20, all dams were killed and fetuses were taken out by cesarean section. There were no differences in maternal body weight gain. No adverse effects of EMF exposure were observed on any reproductive and embryotoxic parameters such as number of live (243–271 fetuses), dead or resorbed embryos, placental weights, sex ratios, weights or external, visceral or skeletal abnormalities of live fetuses. Bioelectromagnetics 30:205–212, 2009. © 2008 Wiley‐Liss, Inc. 相似文献
30.