全文获取类型
收费全文 | 5918篇 |
免费 | 536篇 |
国内免费 | 289篇 |
专业分类
电工技术 | 440篇 |
综合类 | 484篇 |
化学工业 | 577篇 |
金属工艺 | 323篇 |
机械仪表 | 292篇 |
建筑科学 | 313篇 |
矿业工程 | 243篇 |
能源动力 | 183篇 |
轻工业 | 491篇 |
水利工程 | 157篇 |
石油天然气 | 148篇 |
武器工业 | 103篇 |
无线电 | 581篇 |
一般工业技术 | 495篇 |
冶金工业 | 1218篇 |
原子能技术 | 52篇 |
自动化技术 | 643篇 |
出版年
2024年 | 37篇 |
2023年 | 97篇 |
2022年 | 199篇 |
2021年 | 279篇 |
2020年 | 169篇 |
2019年 | 114篇 |
2018年 | 146篇 |
2017年 | 156篇 |
2016年 | 122篇 |
2015年 | 181篇 |
2014年 | 235篇 |
2013年 | 319篇 |
2012年 | 372篇 |
2011年 | 442篇 |
2010年 | 364篇 |
2009年 | 368篇 |
2008年 | 356篇 |
2007年 | 352篇 |
2006年 | 308篇 |
2005年 | 229篇 |
2004年 | 189篇 |
2003年 | 115篇 |
2002年 | 110篇 |
2001年 | 91篇 |
2000年 | 87篇 |
1999年 | 59篇 |
1998年 | 293篇 |
1997年 | 168篇 |
1996年 | 122篇 |
1995年 | 92篇 |
1994年 | 75篇 |
1993年 | 78篇 |
1992年 | 26篇 |
1991年 | 20篇 |
1990年 | 20篇 |
1989年 | 18篇 |
1988年 | 21篇 |
1987年 | 15篇 |
1986年 | 14篇 |
1985年 | 15篇 |
1983年 | 12篇 |
1982年 | 17篇 |
1981年 | 20篇 |
1980年 | 18篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1977年 | 37篇 |
1976年 | 76篇 |
1975年 | 11篇 |
1974年 | 9篇 |
排序方式: 共有6743条查询结果,搜索用时 15 毫秒
1.
有机-无机压电材料是一种分子铁电体,具有柔性、结构灵活、易成膜、全液相合成及环保节能等优点,可满足新一代薄膜器件及可穿戴设备的需求。该文以三甲基卤代甲基铵(TMXM, X=F, Cl, Br)为有机部分,MnCl2为无机部分,通过溶液蒸发法制备了具有钙钛矿分子结构的有机-无机压电材料三甲基氯三氯化锰(TMCM-MnCl3),并对其分子结构组成、压电、热学、声学及铁电性进行表征。结果表明,TMCM-MnCl3的压电常数为106 pC/N,居里温度为130 ℃,声阻抗值约为16.5 MRayl,低于压电陶瓷PZT-4(大于33 MRayl),具有广阔的应用前景。 相似文献
2.
3.
Emily S. Patterson David D. Woods Richard I. Cook Marta L. Render 《Cognition, Technology & Work》2007,9(3):155-162
Resilience, the ability to adapt or absorb disturbance, disruption, and change, may be increased by team processes in a complex,
socio-technical system. In particular, collaborative cross-checking is a strategy where at least two individuals or groups
with different perspectives examine the others’ assumptions and/or actions to assess validity or accuracy. With this strategy,
erroneous assessments or actions can be detected quickly enough to mitigate or eliminate negative consequences. In this paper,
we seek to add to the understanding of the elements that are needed in effective cross-checking and the limitations of the
strategy. We define collaborative cross-checking, describe in detail three healthcare incidents where collaborative cross-checks
played a key role, and discuss the implications of emerging patterns. 相似文献
4.
Insulin receptor substrate (IRS) proteins are key regulators of basic functions such as cellular growth and metabolism. They provide an interface between multiple receptors and a complex network of intracellular signaling molecules. Two members of this family (IRS-1 and IRS-2) have been identified previously. In this investigation, we analyzed a mouse expressed sequence tag clone that proved to be a new member of the IRS family. Sequence analysis of this clone and comparison with the sequences deposited in GenBank demonstrates this protein may be the murine homolog of rat IRS-3, recently purified and cloned from rat adipocytes. Accordingly, we have named our protein mouse IRS-3. The expressed sequence tag clone contains the complete coding sequence of 1485 bp, encoding a protein of 495 amino acids. Sequence alignment with the other members of the IRS family shows that this protein contains pleckstrin homology and phosphotyrosine-binding domains that are highly conserved. In addition, there is conservation of many tyrosine phosphorylation motifs responsible for interactions with downstream signaling molecules containing SH2 domains. The murine IRS-3 messenger RNA (2.4 kilobases in length) is expressed in many tissues, with highest levels in liver and lung. Mouse IRS-3 is highly expressed in the first part of the embryonic life, when IRS-1 messenger RNA is barely detectable. Unlike the genes encoding IRS-1 and IRS-2, the IRS-3 gene contains an intron (344 bp in length) in the region between the pleckstrin homology and the phosphotyrosine-binding domains. Fluorescent in situ hybridization localized the mouse IRS-3 gene on the telomeric region of chromosome 5G2. Cloning of the murine IRS-3 gene will make it possible to apply genetic approaches to elucidate the physiological role of this new member of the IRS family of proteins. 相似文献
5.
HG Morrison EJ Weil SI Karchner ML Sogin JJ Stegeman 《Canadian Metallurgical Quarterly》1998,121(1-3):231-240
Since we published a phylogenetic analysis of the CYP1A subfamily in 1995, several additional full-length sequences have been reported, including three members of an entirely new subfamily, CYP1B. Two avian sequences were recently published, so that CYP1A sequence data are now available from three of the five major vertebrate lineages. The two new branches that have been added to the CYP1 family tree significantly add to our understanding of P450 evolution. The inclusion of the CYP1Bs to the phylogenetic analysis allows us to root inferred trees. Addition of the avian CYP1As indicates that the CYP1A1/CYP1A2 duplication present in the mammalian lineage may have occurred after the divergence of birds and mammals. The number of fish species from which full-length coding regions of CYP1A genes have been sequenced has increased from four (trout, plaice, toadfish, and scup) to nine. These include CYP1A sequences from tomcod, butterflyfish, sea bream, sea bass, and the full-length sequence of CYP1A from the killifish Fundulus heteroclitus that is reported here. Phylogenetic analyses incorporating the new fish CYP1A sequences support our original conclusion that the fish CYP1As are monophyletic and indicate that the genes are evolving at very different rates in different species. 相似文献
6.
双乙醛草酰二肼直接快速光度法测定食品中痕量铜 总被引:1,自引:0,他引:1
研究了双乙醛草酸二肼与铜的显色反应,建立了分光光度法直接测定铜的新方法。试验结果表明,在pH8.0-10.0范围内,Cu2 与双乙醛草酸二肼形成稳定的紫红色配合物。该配合物在540nm处有一最大吸收峰,其表明摩尔吸光系数为2.4×104,铜量在0-12mg/50ml范围内符合比尔定律。共存离子干扰,误差仅 2.00%。用于食品中痕量钢测定.结果准确、可靠。 相似文献
7.
8.
当线路末端故障时,行波在线路末端的反射情况比较复杂,反向电流行波的极性有可能与正向电流行波的极性相反,而此时测距结果又与线路无故障时相同。因此,会造成行波测距式与行波极性比较式合闸保护的不正确动作。根据行波的折、反射理论,分析出当线路无故障时正向电流行波仅在线路末端发生反射,且电流行波的反射系数为-1,而当线路存在故障时,正向电流行波将在故障点发生反射,无论故障是否在线路末端,电流行波的反射系数都不会是-1。根据这一特征,提出了一种新的行波合闸保护方法。从原理上保证了在各种情况下保护都可以正确动作,大量的电磁暂态仿真结果也证明了这一点。 相似文献
9.
10.
可膨胀尾管悬挂器技术及其应用 总被引:8,自引:2,他引:6
可膨胀管悬挂器(ELH)作为尾管固井、完井工艺中一项革新型工具,可以成功地解决常规悬挂器因其原理和结构特点带来的固井施工难题及重叠段固井质量差等问题,成为下一代悬挂器研究的重点。文中以实体膨胀悬挂器系统为例,介绍了其结构原理及应用情况。 相似文献