全文获取类型
收费全文 | 4508篇 |
免费 | 26篇 |
专业分类
电工技术 | 18篇 |
综合类 | 2篇 |
化学工业 | 310篇 |
金属工艺 | 21篇 |
机械仪表 | 36篇 |
建筑科学 | 71篇 |
矿业工程 | 12篇 |
能源动力 | 56篇 |
轻工业 | 173篇 |
水利工程 | 12篇 |
石油天然气 | 9篇 |
无线电 | 71篇 |
一般工业技术 | 251篇 |
冶金工业 | 3369篇 |
原子能技术 | 13篇 |
自动化技术 | 110篇 |
出版年
2022年 | 10篇 |
2020年 | 14篇 |
2019年 | 13篇 |
2018年 | 15篇 |
2017年 | 16篇 |
2016年 | 11篇 |
2015年 | 14篇 |
2014年 | 21篇 |
2013年 | 84篇 |
2012年 | 25篇 |
2011年 | 44篇 |
2010年 | 36篇 |
2009年 | 41篇 |
2008年 | 50篇 |
2007年 | 47篇 |
2006年 | 54篇 |
2005年 | 39篇 |
2004年 | 36篇 |
2003年 | 36篇 |
2002年 | 44篇 |
2001年 | 19篇 |
2000年 | 24篇 |
1999年 | 124篇 |
1998年 | 915篇 |
1997年 | 508篇 |
1996年 | 335篇 |
1995年 | 211篇 |
1994年 | 152篇 |
1993年 | 227篇 |
1992年 | 52篇 |
1991年 | 48篇 |
1990年 | 60篇 |
1989年 | 77篇 |
1988年 | 69篇 |
1987年 | 75篇 |
1986年 | 67篇 |
1985年 | 72篇 |
1984年 | 35篇 |
1983年 | 27篇 |
1982年 | 36篇 |
1981年 | 60篇 |
1980年 | 62篇 |
1979年 | 24篇 |
1978年 | 27篇 |
1977年 | 128篇 |
1976年 | 272篇 |
1975年 | 32篇 |
1974年 | 14篇 |
1973年 | 19篇 |
1972年 | 12篇 |
排序方式: 共有4534条查询结果,搜索用时 15 毫秒
951.
952.
953.
954.
955.
Certain properties of the highly specialized synaptic transmitter vesicles are shared by constitutively occurring vesicles. We and others have thus identified a cDNA in various nonneuroendocrine cell types of rat and human that is related to synaptophysin, one of the major synaptic vesicle membrane proteins, which we termed pantophysin. Here we characterize the gene structure, mRNA and protein expression, and intracellular distribution of pantophysin. Its mRNA is detected in murine cell types of nonneuroendocrine as well as of neuroendocrine origin. The intron/exon structure of the murine pantophysin gene is identical to that of synaptophysin except for the last intron that is absent in pantophysin. The encoded polypeptide of calculated mol wt 28,926 shares many sequence features with synaptophysin, most notably the four hydrophobic putative transmembrane domains, although the cytoplasmic end domains are completely different. Using antibodies against the unique carboxy terminus pantophysin can be detected by immunofluorescence microscopy in both exocrine and endocrine cells of human pancreas, and in cultured cells, colocalizing with constitutive secretory and endocytotic vesicle markers in nonneuroendocrine cells and with synaptophysin in cDNA-transfected epithelial cells. By immunoelectron microscopy, the majority of pantophysin reactivity is detected at vesicles with a diameter of < 100 nm that have a smooth surface and an electron-translucent interior. Using cell fractionation in combination with immunoisolation, these vesicles are enriched in a light fraction and shown to contain the cellular vSNARE cellubrevin and the ubiquitous SCAMPs in epithelial cells and synaptophysin in neuroendocrine or cDNA-transfected nonneuroendocrine cells and neuroendocrine tissues. Pantophysin is therefore a broadly distributed marker of small cytoplasmic transport vesicles independent of their content. 相似文献
956.
957.
958.
LM Salamone NW Glynn DM Black RE Ferrell L Palermo RS Epstein LH Kuller JA Cauley 《Canadian Metallurgical Quarterly》1996,11(10):1557-1565
Bone mineral density (BMD) is a reflection of both genetic and lifestyle factors. The interplay of genetic (vitamin D receptor [VDR] gene polymorphisms) and lifestyle factors on BMD at the lumbar spine and proximal femur was examined in 470 healthy premenopausal women, aged 44-50 years, using a Hologic QDR 2000 densitometer. The objective of this study was to examine the genetic and lifestyle determinants of premenopausal BMD. Each participant was genotyped for BsmI polymorphism at the VDR gene locus. The presence of a restriction site within VDR, specified as bb (189, 40.2%) (n, %) was associated with reduced spinal BMD, whereas absence of this site in BB (97, 20.6%) conferred greater spinal BMD, as did the genotype Bb (184, 39.1%). Associations between smoking, alcohol use, oral contraceptives, education level, multivitamins, number of children, degree of obesity, body weight, physical activity, dietary calcium intake, and VDR genotype to BMDs were examined. VDR genotype, body weight, degree of obesity, physical activity, and dietary calcium intake were all significant determinants of BMD. The association of VDR genotype with BMD at the femoral neck appeared to be modified by calcium intake (BB and Bb: 0.797 +/- 0.11 g/cm2 vs. 0.844 +/- 0.11 g/cm2, interaction term, p = 0.06) for low (< 1036 mg/day) and high (> or = 1036 mg/day; upper quartile) calcium intakes, respectively. A similar trend was demonstrated for physical activity. These findings suggest that prophylactic interventions aimed at achieving and maintaining optimal BMD, such as greater calcium intake or physical activity, may be important in maximizing one's genetic potential for BMD. 相似文献
959.
960.