全文获取类型
收费全文 | 3538篇 |
免费 | 36篇 |
专业分类
电工技术 | 36篇 |
化学工业 | 347篇 |
金属工艺 | 33篇 |
机械仪表 | 24篇 |
建筑科学 | 122篇 |
矿业工程 | 1篇 |
能源动力 | 49篇 |
轻工业 | 183篇 |
水利工程 | 35篇 |
石油天然气 | 5篇 |
无线电 | 240篇 |
一般工业技术 | 363篇 |
冶金工业 | 1900篇 |
原子能技术 | 11篇 |
自动化技术 | 225篇 |
出版年
2021年 | 16篇 |
2020年 | 11篇 |
2018年 | 14篇 |
2017年 | 22篇 |
2016年 | 20篇 |
2015年 | 17篇 |
2014年 | 23篇 |
2013年 | 74篇 |
2012年 | 51篇 |
2011年 | 68篇 |
2010年 | 44篇 |
2009年 | 63篇 |
2008年 | 82篇 |
2007年 | 77篇 |
2006年 | 58篇 |
2005年 | 66篇 |
2004年 | 42篇 |
2003年 | 60篇 |
2002年 | 62篇 |
2001年 | 50篇 |
2000年 | 46篇 |
1999年 | 76篇 |
1998年 | 561篇 |
1997年 | 291篇 |
1996年 | 228篇 |
1995年 | 138篇 |
1994年 | 128篇 |
1993年 | 147篇 |
1992年 | 66篇 |
1991年 | 57篇 |
1990年 | 60篇 |
1989年 | 63篇 |
1988年 | 50篇 |
1987年 | 51篇 |
1986年 | 48篇 |
1985年 | 60篇 |
1984年 | 34篇 |
1983年 | 23篇 |
1982年 | 29篇 |
1981年 | 45篇 |
1980年 | 42篇 |
1979年 | 47篇 |
1978年 | 19篇 |
1977年 | 64篇 |
1976年 | 116篇 |
1975年 | 19篇 |
1974年 | 20篇 |
1973年 | 29篇 |
1971年 | 13篇 |
1967年 | 10篇 |
排序方式: 共有3574条查询结果,搜索用时 156 毫秒
51.
The effects of lipid peroxidation and the antioxidant vitamin E contained in LDL isolated from control plasma (LDL--) and from plasma preincubated with 0.5 mmol/ml alpha-tocopherol (LDL+) on the proliferation of estrogen-receptor positive (ER+ : ZR-75, T-47-D, MCF-7) and negative (ER--: HBL-100, MDA-MB-231) human breast cancer cells were studied. Human skin fibroblasts served as controls. Incubation of plasma with 0.5 mmol/ml alpha-tocopherol resulted in a 3-fold increase of its content and a significant reduction in lipid hydroperoxides and conjugated dienes in LDL. Incubation of fibroblasts or ER+ tumor cells with LDL- or LDL+ had an effect on neither cell proliferation nor on the cellular levels of peroxidation products as compared to control incubations in the absence of LDL. In ER- cells, however, LDL+ stimulated the proliferation, whereas LDL- yielded a cytotoxic effect. Moreover, LDL- supplementation resulted in an increase in the content of hydroperoxides and conjugated dienes. LDL+ supplemented cells exhibited hydroperoxide levels in these tumor cells comparable to the basal levels measured in the absence of LDL. Our data suggested that peroxidation products in LDL are cytotoxic to estrogen-receptor negative breast tumor cells and vitamin E counteracts this effect. 相似文献
52.
LF Cooper 《Canadian Metallurgical Quarterly》1997,18(3):271-6, 278, 280-1; quiz 282
Modern restorative dentistry is confronted with many challenges related to implant use in the craniofacial region, such as attempting to place implants in esthetically critical sites or anatomically limiting regions of the jaw. To assure a successful implant placement that is satisfactory to both the patient and the dentist, four key areas need to be improved: diagnostic procedures, surgical procedures and outcomes, esthetic results, and prosthetic complications. This article discusses how an integrated approach to these areas can improve clinical practice. 相似文献
53.
54.
55.
56.
57.
Ngoc-Anh T. Nguyen Mickey L. Wells David C. Cooper 《Drug development and industrial pharmacy》1995,21(14):1671-1682
To identify factors affecting the chemical stability and preservative efficacy of lamivudine oral liquid formulations, an optimization study using a central composite design was performed. In this design, five factors, each at three levels, were investigated: pH (4.5, 5.5, and 73, sucrose (5%, 20%. and 50% w/v), propylene glycol (0% 2%, and 5% w/v), glycerin (4% 8%, and 12% w/v). and EDTA (0.100. 0.175, and 0.250 mg/mL). All formulations contained a constant concentration of lamivudine, parabens, and artificial strawberry and banana flavors. All formulations were evaluated for preservative effectiveness against USP and BP standards and for chemical stability at 30°C and 40°C for three months. All formulations were effective against bacteria and yeasts, but indicated reduced preservative effectiveness against the mold Aspergillus niger. Preservative effectiveness improved with increasing pH (4.5 to 7.5) and to a lesser extent with increasing EDTA concentration (0.100 to 0.250 mg/mL). Increasing glycerin concentration (4% to 12% w/v) slightly decreased preservative effectiveness. Over the concentration ranges tested, no change in preservative effectiveness was noted with concentration changes in sucrose or propylene glycol. The pH was the main factor influencing the chemical stability of the drug and preservatives in this study. Lamivudine chemical stability increased with increasing pH from 4.5 to 7.5. Methyl and propylparaben showed extensive degradation at pH 7.5. 相似文献
58.
The Pao-Sah model for the long-channel MOSFET is generalized to include MOSFETs with resistive-gate electrodes (RG-MOSFETs). The RG-MOdSFETs current-voltage characteristics are studied using this extended Pao-Sah model. The steady-state operation of the RG-MOSFET can be divided into three regimes, separated by the uniform channel condition and the pinch-off condition, respectively. The regions of operation are discussed, and a simple analytical I -V expression is given for the device 相似文献
59.
60.
W Guo RS Lovell YH Zhang BL Huang TP Burris WJ Craigen ER McCabe 《Canadian Metallurgical Quarterly》1996,178(1-2):31-34
We cloned the murine full-length cDNA encoding Ahch, the mouse homologue of DAX1 (DSS-AHC Region on Human X Chromosome, Gene1) which is the gene responsible for human X-linked adrenal hypoplasia congenita (AHC) and hypogonadotropic hypogonadism (HH). Sequence analysis revealed that the murine and human cDNAs have 65% aa identity and 75% aa similarity overall. The cysteine residues in the putative DNA binding domain, which may interact with Zn2+ ions to form zinc fingers, are 100% conserved between the two species, indicating that the novel zinc-finger structures in DAX1 may be functional. In addition, mouse interspecific backcrosses show that the Ahch gene is closely linked to the glycerol kinase locus, GyK, on the mouse X chromosome, indicating that the order of the loci is conserved in this syntenic region between mouse and human. 相似文献