全文获取类型
收费全文 | 2741篇 |
免费 | 9篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 14篇 |
化学工业 | 131篇 |
金属工艺 | 30篇 |
机械仪表 | 30篇 |
建筑科学 | 61篇 |
矿业工程 | 1篇 |
能源动力 | 26篇 |
轻工业 | 132篇 |
水利工程 | 12篇 |
石油天然气 | 1篇 |
无线电 | 93篇 |
一般工业技术 | 214篇 |
冶金工业 | 1857篇 |
原子能技术 | 18篇 |
自动化技术 | 133篇 |
出版年
2021年 | 6篇 |
2018年 | 6篇 |
2016年 | 8篇 |
2015年 | 6篇 |
2014年 | 16篇 |
2013年 | 57篇 |
2012年 | 36篇 |
2011年 | 50篇 |
2010年 | 23篇 |
2009年 | 32篇 |
2008年 | 41篇 |
2007年 | 37篇 |
2006年 | 37篇 |
2005年 | 48篇 |
2004年 | 35篇 |
2003年 | 39篇 |
2002年 | 36篇 |
2001年 | 21篇 |
2000年 | 31篇 |
1999年 | 63篇 |
1998年 | 612篇 |
1997年 | 332篇 |
1996年 | 204篇 |
1995年 | 133篇 |
1994年 | 95篇 |
1993年 | 128篇 |
1992年 | 35篇 |
1991年 | 32篇 |
1990年 | 28篇 |
1989年 | 31篇 |
1988年 | 18篇 |
1987年 | 26篇 |
1986年 | 23篇 |
1985年 | 23篇 |
1984年 | 21篇 |
1983年 | 20篇 |
1982年 | 28篇 |
1981年 | 8篇 |
1980年 | 29篇 |
1979年 | 18篇 |
1978年 | 23篇 |
1977年 | 48篇 |
1976年 | 92篇 |
1975年 | 16篇 |
1974年 | 6篇 |
1973年 | 15篇 |
1971年 | 11篇 |
1970年 | 10篇 |
1965年 | 7篇 |
1955年 | 5篇 |
排序方式: 共有2753条查询结果,搜索用时 15 毫秒
41.
Starting with total RNA from spermatogenic cells of Mytilus trossulus and using random priming, we have cloned and sequenced the c-DNAs corresponding to two variants of the sperm-specific protein PLII* (phi 2B). DNA sequencing in conjunction with mass spectrometry and protein sequence data have allowed us to establish that of the three sperm-specific proteins present in the sperm of Mytilus (PL-II*(phi 2B), PL-III (phi 1), PL-IV (phi 3)), the first and the last one are the result of post-translational cleavage of a common precursor. This common precursor is a member of the histone H1 family, and it exhibits inter- and intraspecific microheterogeneity. 相似文献
42.
L Hunt 《Canadian Metallurgical Quarterly》1993,18(3):6-7, 18
The ocular aging process involves everyone. Misconceptions about visual changes from aging versus visual changes from a disease have resulted in needless vision loss for many in the older population. Lack of understanding and misinformation may cause a delay in seeking medical attention for diagnosis and treatment. 相似文献
43.
There were 2040 patients with temporomandibular joint (TMJ) diseases in the investigation including clinical, physiological, X-ray methods of research, contrast arthrotomography, computer arthrotomography and magnetic resonance tomography. The changes of structure in different lesions were estimated. The result of received data was elaboration of classification of TMJ internal derangements with estimation of clinical forms in according with structural changes and characteristics of syndromes. 相似文献
44.
Sleva M.Z. Hunt W.D. Connuck D.M. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1996,43(4):626-627
A novel ultrasound tissue characterization system is described which utilizes a network analyzer, S-parameter test set, 180° hybrid junction, and a mock transducer circuit to exploit the wide-band potential of a commercial piezoelectric polymer transducer. The relatively short round-trip pulselength achieved using the system (70 ns in water) is compared to that obtained using a high-frequency pulser/receiver and the same transducer (130 ns in water). Finally, the in vitro acoustic response of a section of neonate porcine carotid artery obtained using the network analyzer-based system is reported, along with histologic results for the same vessel 相似文献
45.
Hopko Derek R.; Hunt Melissa K.; Armento Maria E. A. 《Canadian Metallurgical Quarterly》2005,12(4):389
Anxious responding (trait, state, and test anxiety) has a negative impact on overt performance. Researchers have used a unidimensional method of assessing anxiety and performance, although a more informative approach would involve a comprehensive assessment battery and multiple performance tasks. Incorporating this strategy, the authors measured the impact of anxiety on 4 attentional processing tasks. Results revealed that "types" of anxiety symptoms were differentially related to attentional task performance; test anxiety accounted for the most variance in predicting performance on the Wechsler Adult Intelligence Scale-Third Edition (D. Wechsler, 1997) letter-number sequencing and digit-span subtests, trait anxiety and fear of negative evaluation were more significant in predicting Stroop performance, and math anxiety accounted for the largest variance toward understanding Paced Auditory Serial Addition Task (C. W. Lejuez, C. W. Kahler, & R. A. Brown, 2003) scores. Theoretical and clinical implications are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
46.
PG Tipping P Davenport M Gallicchio EL Filonzi J Apostolopoulos J Wojta 《Canadian Metallurgical Quarterly》1993,143(3):875-885
The capacity of macrophages to influence directly and indirectly fibrinolytic processes in atherosclerosis was studied using macrophages isolated from atherosclerotic plaques of patients undergoing surgical repair of distal aortic and femoral arteries. These cells were characterized by their morphology, adherence, esterase positivity, and expression of CD14 antigen. Production of plasminogen activator inhibitor type-1 (PAI-1) by plaque macrophages (6.7 +/- 2.7 ng/10(5) cells/24 hours [mean +/- SEM]) was significantly greater than PAI-1 production by blood monocytes isolated simultaneously from the same patients (1.8 +/- 1.5 ng/10(5) cells/24 hours). Production of tissue type plasminogen activator and urokinase type was not augmented compared to blood monocytes. Conditioned medium from cultured plaque macrophages significantly increased production of PAI-1 by endothelial cells (85 +/- 11% above basal) and vascular smooth muscle cells (25 +/- 10%) in vitro. This response was significantly greater than the response to monocyte-conditioned medium (endothelial cells 38 +/- 11%, vascular smooth muscle cells 2.5 +/- 2.0%). Stimulation of endothelial cell PAI-1 production by macrophage-conditioned medium was partially inhibitable by a monoclonal antibody to transforming growth factor-beta. Tissue type plasminogen activator production by endothelial cells and vascular smooth muscle cells was not affected by plaque macrophage- or monocyte-conditioned medium. Urokinase type plasminogen activator production by endothelial cells and vascular smooth muscle cells was undetectable in control medium and was augmented to similar levels in response to plaque macrophage- and monocyte-conditioned media. These results demonstrate upregulation of PAI-1 production by macrophages in atheromatous plaques and the capacity of soluble products from plaque macrophages to upregulate PAI-1 production by endothelial cells and vascular smooth muscle cells in vitro. These data suggest that macrophages in atherosclerotic plaques may inhibit thrombolysis both directly and indirectly by effects of their soluble products on endothelial cells and vascular smooth muscle cells. 相似文献
47.
NC Day PJ Shaw AL McCormack PJ Craig W Smith R Beattie TL Williams SB Ellis PG Ince MM Harpold D Lodge SG Volsen 《Canadian Metallurgical Quarterly》1996,71(4):1013-1024
The distribution of voltage-dependent calcium channel subunits in the central nervous system may provide information about the function of these channels. The present study examined the distribution of three alpha-1 subunits, alpha 1A, alpha 1B and alpha 1E, in the normal human hippocampal formation and parahippocampal gyrus using the techniques of in situ hybridization and immunocytochemistry. All three subunit mRNAs appeared to be similarly localized, with high levels of expression in the dentate granule and CA pyramidal layer. At the protein level, alpha 1A, alpha 1B and alpha 1E subunits were differentially localized. In general, alpha 1A-immunoreactivity was most intense in cell bodies and dendritic processes, including dentate granule cells, CA3 pyramidal cells and entorhinal cortex pre-alpha and pri-alpha cells. The alpha 1B antibody exhibited relatively weak staining of cell bodies but stronger staining of neuropil, especially in certain regions of high synaptic density such as the polymorphic layer of the dentate gyrus and the stratum lucidum and radiatum of the CA regions. The alpha 1E staining pattern shared features in common with both alpha 1A and alpha 1B, with strong immunoreactivity in dentate granule, CA3 pyramidal and entorhinal cortex pri-alpha cells, as well as staining of the CA3 stratum lucidum. These findings suggest regions in which particular subunits may be involved in synaptic communication. For example, comparison of alpha 1B and alpha 1E staining in the CA3 stratum lucidum with calbindin-immuno-reactivity suggested that these two calcium channels subunits may be localized presynaptically in mossy fibre terminals and therefore may be involved in neurotransmitter release from these terminals. 相似文献
48.
DE Sabatino AP Cline PG Gallagher LJ Garrett G Stamatoyannopoulos BG Forget DM Bodine 《Canadian Metallurgical Quarterly》1998,18(11):6634-6640
During development, changes occur in both the sites of erythropoiesis and the globin genes expressed at each developmental stage. Previous work has shown that high-level expression of human beta-like globin genes in transgenic mice requires the presence of the locus control region (LCR). Models of hemoglobin switching propose that the LCR and/or stage-specific elements interact with globin gene sequences to activate specific genes in erythroid cells. To test these models, we generated transgenic mice which contain the human Agamma-globin gene linked to a 576-bp fragment containing the human beta-spectrin promoter. In these mice, the beta-spectrin Agamma-globin (betasp/Agamma) transgene was expressed at high levels in erythroid cells throughout development. Transgenic mice containing a 40-kb cosmid construct with the micro-LCR, betasp/Agamma-, psibeta-, delta-, and beta-globin genes showed no developmental switching and expressed both human gamma- and beta-globin mRNAs in erythroid cells throughout development. Mice containing control cosmids with the Agamma-globin gene promoter showed developmental switching and expressed Agamma-globin mRNA in yolk sac and fetal liver erythroid cells and beta-globin mRNA in fetal liver and adult erythroid cells. Our results suggest that replacement of the gamma-globin promoter with the beta-spectrin promoter allows the expression of the beta-globin gene. We conclude that the gamma-globin promoter is necessary and sufficient to suppress the expression of the beta-globin gene in yolk sac erythroid cells. 相似文献
49.
50.