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   55503篇
  免费   5107篇
  国内免费   2658篇
电工技术   3500篇
技术理论   8篇
综合类   3633篇
化学工业   9418篇
金属工艺   2933篇
机械仪表   3277篇
建筑科学   3981篇
矿业工程   1507篇
能源动力   1754篇
轻工业   3487篇
水利工程   1096篇
石油天然气   2834篇
武器工业   648篇
无线电   6948篇
一般工业技术   6769篇
冶金工业   2905篇
原子能技术   698篇
自动化技术   7872篇
  2024年   255篇
  2023年   908篇
  2022年   1806篇
  2021年   2461篇
  2020年   1821篇
  2019年   1523篇
  2018年   1697篇
  2017年   1806篇
  2016年   1627篇
  2015年   2279篇
  2014年   2703篇
  2013年   3436篇
  2012年   3574篇
  2011年   3786篇
  2010年   3324篇
  2009年   3229篇
  2008年   3109篇
  2007年   2946篇
  2006年   2974篇
  2005年   2468篇
  2004年   1853篇
  2003年   1617篇
  2002年   1671篇
  2001年   1531篇
  2000年   1316篇
  1999年   1330篇
  1998年   1160篇
  1997年   990篇
  1996年   801篇
  1995年   672篇
  1994年   496篇
  1993年   429篇
  1992年   329篇
  1991年   266篇
  1990年   183篇
  1989年   179篇
  1988年   144篇
  1987年   86篇
  1986年   88篇
  1985年   77篇
  1984年   33篇
  1983年   27篇
  1982年   37篇
  1981年   34篇
  1980年   23篇
  1979年   21篇
  1977年   16篇
  1976年   19篇
  1974年   13篇
  1973年   14篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
The aim of this work was to identify which proteins in horse dander extracts are allergens and to characterise them. Two-dimensional PAGE showed that horse dander preparations are composed of up to 50 proteins, all having acidic isoelectric points in the pH range 3-4.5. Immunoblots of two-dimensional PAGE were used to compare the reactivity of the proteins with IgE from 23 allergic patients. Patient sera were divided into two main groups recognising either allergens of 18.5 kDa or proteins of 27-29 and 31 kDa. The proteins of 27-29 kDa and 31 kDa were all N-glycosylated and their glycan chains seem to play a role in the binding of IgE from allergic patients. The sugar composition of their carbohydrate moiety was determined and lectin-binding experiments indicated presence of terminal sialic acid linked alpha-(2-->6) to galactose, galactose linked beta-(1-->4) to N-acetylglucosamine, and possibly presence of sialic acid linked alpha-(2-->3) to galactose. The 27-29-kDa glycoproteins had heterogeneous isoelectric points, most probably due to different degrees of sialylation in their oligosaccharide chains. The two 18.5-kDa allergens exhibited slightly different isoelectric points and their N-terminal sequences were identical, showing that they most likely were isoforms of the same protein. Sequence analyses revealed that their N-terminal sequences are similar to proteins belonging to the lipocalin family. We named the two 18.5-kDa proteins Equ c 2.0101 and Equ c 2.0102, according to International Allergen Nomenclature recommendations [King, T. P., Hoffman, D., Lowenstein, H., Marsh, D. G., Platts-Mills, T. A. E. & Thomas, W. (1995) J. Allergy Clin. Immunol. 96, 5-14]. The N-terminal of the allergens of 27-29 kDa were blocked and their sequences were not determined. Their amino acid compositions were determined and comparison with acidic mammalian proteins in the Swiss-Prot database revealed high scores with lipocalin proteins. This suggests that the glycosylated horse dander allergens belong to the lipocalin family, like Equ c 2.0101 and Equ c 2.0102.  相似文献   
182.
研究了NCD-环上模M,在模半理想的条件下,可得到一些有趣的结果。  相似文献   
183.
The copolymer from D ,L -lactide and poly(tetramethyene ether glycol) (PTMG) was prepared in bulk with an isotributyl aluminum–water–phosphoric acid complex catalyst as the initiator and characterized by H-NMR, GPC, and DSC. The effects of the temperature and the amount of PTMG on the polymerization rate and the molecular weight of copolymers were studied. The behavior of the degradation and delivery rate of Levonorgestrel microspheres in vitro was observed. The results show that the degradation and the delivery rate can be controlled by adjusting the molar rate of hydrophilic and hydrophobic segments of the copolymer © 1995 John Wiley & Sons, Inc.  相似文献   
184.
聚乙烯接枝改性及其与铝的粘结性   总被引:8,自引:0,他引:8  
聚乙烯在过氧化二异丙苯存在下分别与丙烯酸,顺丁烯酸酐,顺丁烯二酸,顺丁烯二酸钠,丙烯酸羧丙酯,甲基丙烯酸环丙酯等单体熔融挤出,产物的红外光谱表明聚乙烯不同程度地接了各种极性基团。  相似文献   
185.
彭虹  程时端 《通信学报》1995,16(6):101-106
随着交换技术的飞速发展,程控交换软件的规模越来越大,改动也越来越频繁,如何使代码对数据的改动具有相对的稳定性成为程控软件设计的一个首要问题。本文以CCS7(7号公共信道信令)为例,从对象模型、动态模型、功能模型3个方面阐述了OO(面向对象)方法在CCS7软件设计中的应用。这一方法,也可应用于程控软件的设计。  相似文献   
186.
何国柱  蔡载熙 《核技术》1993,16(2):119-122
人体内微量元素含量平衡与否与人体健康状态有着密切关系已为大量实践所证实。人体血液中微量元素的正常值测定是研究人体健康与微量元素关系的一项基础性工作,本文提供了天津市正常人全血及血清中几种微量元素含量的数据。  相似文献   
187.
“双驱动足”回转式压电马达初步研究   总被引:7,自引:6,他引:1  
提出一种“双驱动足”回转式压电马达,分析了其工作原理,并根据工作原理,设计,研制了样机,进行了初步的试验研究,证明工作原理基本正确,为今后进一步研究提供了参考依据。  相似文献   
188.
A new class of potent, orally active phenyl piperazine-based GH secretagogues have been discovered from attempts to mimic the arrangement of the phenyl substituent in the spiroindanyl piperidine and spiroindoline sulfonamide privileged structures of 4 and 1, respectively. The best of these compounds, 18 (EC50 = 2.8 nM) is nearly as potent as MK-0677 for releasing GH from rat pituitary cells.  相似文献   
189.
High concentrations of Zn2+ are found in presynaptic terminals of excitatory neurons in the CNS. Zn2+ can be released during synaptic activity and modulate postsynaptic receptors, but little is known about the possibility that Zn2+ may enter postsynaptic cells and produce dynamic changes in the intracellular Zn2+ concentration ([Zn2+]i). We used fura-2 and magfura-2 to detect the consequences of Zn2+ influx in cultured neurons under conditions that restrict changes in intracellular Ca2+ and Mg2+ concentrations. The resulting ratio changes for both dyes were reversed completely by the Zn2+ chelator, N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine, indicating that these dyes are measuring changes in [Zn2+]i. We found that fura-2 was useful in measuring small increases in [Zn2+]i associated with exposure to Zn2+ alone that may be mediated by a Na+/Ca2+ exchanger. Magfura-2, which has a lower affinity for Zn2+, was more useful in measuring larger agonist-stimulated increases in [Zn2+]i. The coapplication of 300 microM Zn2+ and 100 microM glutamate/10 microM glycine resulted in a [Zn2+]i increase that was approximately 40-100 nM in magnitude and could be inhibited by the NMDA receptor antagonist, MK-801 (30 microM), or extracellular Na+. This suggests that Zn2+ influx can occur through at least two different pathways, leading to varying increases in [Zn2+]i. These findings demonstrate the feasibility of measuring changes in [Zn2+]i in neurons.  相似文献   
190.
Pre-bainitic Transformation in Fe-Ni Alloy   总被引:1,自引:0,他引:1  
Thepre-bainiticphenomenonisoneoftheim-portantsubjectsofbainitictransformationwhichisstilcontroversial.Oneviewisthatthesolutea...  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