全文获取类型
收费全文 | 5154篇 |
免费 | 499篇 |
国内免费 | 537篇 |
专业分类
电工技术 | 321篇 |
综合类 | 437篇 |
化学工业 | 442篇 |
金属工艺 | 591篇 |
机械仪表 | 338篇 |
建筑科学 | 357篇 |
矿业工程 | 140篇 |
能源动力 | 83篇 |
轻工业 | 375篇 |
水利工程 | 106篇 |
石油天然气 | 105篇 |
武器工业 | 59篇 |
无线电 | 438篇 |
一般工业技术 | 435篇 |
冶金工业 | 1362篇 |
原子能技术 | 98篇 |
自动化技术 | 503篇 |
出版年
2024年 | 28篇 |
2023年 | 70篇 |
2022年 | 171篇 |
2021年 | 235篇 |
2020年 | 157篇 |
2019年 | 139篇 |
2018年 | 132篇 |
2017年 | 139篇 |
2016年 | 129篇 |
2015年 | 169篇 |
2014年 | 227篇 |
2013年 | 266篇 |
2012年 | 321篇 |
2011年 | 307篇 |
2010年 | 317篇 |
2009年 | 328篇 |
2008年 | 300篇 |
2007年 | 319篇 |
2006年 | 281篇 |
2005年 | 211篇 |
2004年 | 142篇 |
2003年 | 123篇 |
2002年 | 105篇 |
2001年 | 88篇 |
2000年 | 80篇 |
1999年 | 67篇 |
1998年 | 429篇 |
1997年 | 248篇 |
1996年 | 139篇 |
1995年 | 82篇 |
1994年 | 71篇 |
1993年 | 89篇 |
1992年 | 23篇 |
1991年 | 28篇 |
1990年 | 30篇 |
1989年 | 18篇 |
1988年 | 14篇 |
1987年 | 14篇 |
1986年 | 11篇 |
1985年 | 9篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 12篇 |
1977年 | 23篇 |
1976年 | 75篇 |
1975年 | 3篇 |
1959年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有6190条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
We have used proteolysis to examine the environment through which nascent secretory proteins are translocated across the membrane of the endoplasmic reticulum. After solubilization of rough microsomes with detergent, fragments comprised of the approximately 70 carboxyl-terminal amino acids of translocating nascent chains initiated and targeted in vivo were protected from digestion by added proteases. About 40 amino acids of nascent chains were protected from proteolysis by the ribosome; thus, membrane-derived components protect an additional 30 amino acids. Under conditions in which those 30 additional amino acids are protected, only a small set of integral membrane proteins remained associated with the ribosome. These proteins include the Sec61 complex previously identified as the core component of the membrane-bound protein translocation apparatus. These results support the concept of a translocation pore that makes intimate contact with the ribosome and thereby protects nascent chains from proteolytic digestion for an additional, constant length. 相似文献
5.
6.
7.
Neural crest cells are motile and mitotic, whereas their neuronal derivatives are terminally post-mitotic and consist of stationary cell body from which processes grow. The present study documents changes in the cytoskeleton that occur during neurogenesis in cultures of avain neural crest cells. The undifferentiated neural crest cells contain dense bundles of actin filaments throughout their cytoplasm, and a splayed array of microtubules attached to the centrosome. In newly differentiating neurons, the actin bundles are disrupted and most of the remaining actin filaments are reorganized into a cortical layer underlying the plasma membrane of the cell body and processes. Microtubules are more abundant in newly-differentiating neurons than in the undifferentiated cells, and individual microtubules can be seen dissociated from the centrosome. Neuron-specific beta-III tubulin appears in some crest cells prior to cessation of motility and cell division, and expression increases with total microtubule levels during neurogenesis. To investigate how these early cytoskeletal changes might contribute to alterations in morphology during neurogenesis, we have disrupted the cytoskeleton with pharmacologic agents. Microfilament disruption by cytochalasin immediately arrests the movement of neural crest cells and causes them to round-up, but does not significantly change the morphology of the immature neurons. Microtubule depolymerization by nocodazole slows the movement of undifferentiated cells and causes retraction of processes extended by the immature neurons. These results suggest that changes in the actin and microtubule arrays within neural crest cells govern distinct aspects of their morphogenesis into neurons. 相似文献
8.
TF Duffield D Sandals KE Leslie K Lissemore BW McBride JH Lumsden P Dick R Bagg 《Canadian Metallurgical Quarterly》1998,81(11):2866-2873
A total of 1010 dry cows and pregnant heifers was randomly selected from 25 dairy farms near Guelph, Ontario, Canada to receive either a controlled-release capsule of monensin or a placebo at 3 wk prior to expected calving. Serum samples were obtained at the time of treatment administration, and both serum and milk samples were collected at wk 1, 2, 3, 6, and 9 postcalving. The threshold used to define subclinical ketosis was selected a priori at a concentration of > or = 1200 mumol/L of beta-hydroxybutyrate. Using this threshold, the prevalence and incidence of subclinical ketosis were significantly reduced (50%) by monensin treatment. The duration of subclinical ketosis for cows that had been treated with monensin was also shorter than that for cows treated with the placebo. Monensin treatment significantly reduced the incidence of subclinical ketosis when the threshold was defined using higher concentrations of serum beta-hydroxybutyrate (1400 and 2000 mumol/L). In addition, monensin significantly reduced the prevalence of positive milk ketone tests. 相似文献
9.
10.