首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   3538篇
  免费   36篇
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
  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.
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.
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   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号