全文获取类型
收费全文 | 93044篇 |
免费 | 10413篇 |
国内免费 | 6524篇 |
专业分类
电工技术 | 8050篇 |
综合类 | 9406篇 |
化学工业 | 10814篇 |
金属工艺 | 5960篇 |
机械仪表 | 5787篇 |
建筑科学 | 6061篇 |
矿业工程 | 3848篇 |
能源动力 | 2483篇 |
轻工业 | 10751篇 |
水利工程 | 3030篇 |
石油天然气 | 3055篇 |
武器工业 | 1570篇 |
无线电 | 8009篇 |
一般工业技术 | 6952篇 |
冶金工业 | 11081篇 |
原子能技术 | 1427篇 |
自动化技术 | 11697篇 |
出版年
2024年 | 627篇 |
2023年 | 1581篇 |
2022年 | 3627篇 |
2021年 | 4597篇 |
2020年 | 3304篇 |
2019年 | 2252篇 |
2018年 | 2430篇 |
2017年 | 2765篇 |
2016年 | 2537篇 |
2015年 | 4019篇 |
2014年 | 4909篇 |
2013年 | 5826篇 |
2012年 | 7288篇 |
2011年 | 7529篇 |
2010年 | 7227篇 |
2009年 | 6600篇 |
2008年 | 6713篇 |
2007年 | 6514篇 |
2006年 | 5589篇 |
2005年 | 4324篇 |
2004年 | 3201篇 |
2003年 | 2183篇 |
2002年 | 1935篇 |
2001年 | 1781篇 |
2000年 | 1450篇 |
1999年 | 750篇 |
1998年 | 2729篇 |
1997年 | 1568篇 |
1996年 | 1011篇 |
1995年 | 588篇 |
1994年 | 493篇 |
1993年 | 542篇 |
1992年 | 113篇 |
1991年 | 116篇 |
1990年 | 119篇 |
1989年 | 121篇 |
1988年 | 93篇 |
1987年 | 82篇 |
1986年 | 75篇 |
1985年 | 53篇 |
1983年 | 17篇 |
1982年 | 39篇 |
1981年 | 41篇 |
1980年 | 72篇 |
1979年 | 17篇 |
1977年 | 158篇 |
1976年 | 283篇 |
1975年 | 13篇 |
1959年 | 36篇 |
1951年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
Spontaneous mutation for a quantitative trait in Drosophila melanogaster. II. Distribution of mutant effects on the trait and fitness 总被引:7,自引:0,他引:7
Exposure of the Chinese hamster ovarian AuxB1 cell line in vitro to fractionated X-irradiation generated sublines designated DXR-10, which proved resistant to multiple drugs and overexpressed P-glycoprotein (Pgp), as judged by Western blotting using the C219 monoclonal antibody. Further characterization of these irradiated DXR-10 sublines has provided evidence for: (i) the expression of cross-resistance to gramacidin D, taxol, puromycin and Navelbine, but not to daunomycin or mitoxantrone; (ii) overexpression of the class I Pgp, as judged by Western blotting using the C494 monoclonal antibody; (iii) decreased accumulation of 3H-vincristine, which could be enhanced by verapamil addition; (iv) unaltered accumulation and subcellular distribution of adriamycin; (v) significantly increased rhodamine 123 accumulation in the presence of verapamil; (vi) plasma-membrane ultrastructural modifications resulting in a significantly increased surface area; (vii) numerous clonal karyotypic alterations, with abnormalities involving the long arm of chromosome 1 being consistently identified; (viii) a lack of overexpression of sorcin; (ix) increased total glutathione levels and overexpression of glutathione S-transferase pi. The fact that only certain of these features are considered characteristic of the 'classic' multidrug-resistant CHRC5 cell line supports our earlier proposal that exposure to fractionated X-irradiation results in the expression of a unique drug-resistance phenotype. 相似文献
73.
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
74.
75.
76.
凿岩钎具存在的问题及改进措施 总被引:1,自引:0,他引:1
分析叙述了凿岩钎具损坏的形式和原因。并从设计、制造、选材和操作技术等方面提出了相应的改进措施。从而有效地提高了凿岩钎具的制造质量,延长了使用寿命。 相似文献
77.
78.
79.
在10 ̄(-5)_eV-20MeV中子能量范围内对天然汞的中子核数据进行评价。评价内容包括总的、弹性、去弹、总非弹、30条分立能级、连续非弹、(n,2n)、(n,3n,)、(n,n'P)、(n,n'α)、(n,P)、(n,α)、(n,d)、(n,t)和(n,γ)截面;次级中子角分布;双微分截面(DDCS);γ射线产生数据等。评价根据有效实验数据(至1993年)和UNF-92 ̄[1]理论计算。评价数据以ENDF/B6格式录入中国评价核数据库CENDL-2.1版(MAT=1800),并提供核工程有关部门使用。 相似文献
80.
MA Heneghan B Cleary M Murray TA O'Gorman CF McCarthy 《Canadian Metallurgical Quarterly》1998,43(6):1356-1361
Thromboembolic events frequently complicate the clinical course of patients with inflammatory bowel disease (IBD). Hereditary thrombophilia may contribute to this tendency. Resistance to activated protein C is the most recently described thrombophilic state and may account for up to 40% of patients with thrombophilia. Thirty-seven patients with IBD were studied (mean age 44 years, range 18-82 years). Three patients had a history of thrombotic episodes. The 37 controls included 23 men and 17 women (mean age 48 years, range 16-89 years). Disease activity was assessed using the Harvey Bradshaw index for patients with Crohn's disease and the Truelove and Witts grading system for patients with ulcerative colitis. Levels of fibrinogen, antithrombin III (ATIII), protein C, protein S, activated protein C resistance (APCR), and the presence of a lupus anticoagulant (LA) were determined. Median ATIII levels in patients with IBD were significantly lower than controls (98% vs 106%, P = 0.007), while fibrinogen was elevated (4.2 vs 3.3 g/liter, P = 0.026) despite quiescent disease activity. LA was detected in 7/37 patients in the IBD group compared to 0/37 controls. (chi2 = 5.68, P = 0.017). No significant difference was observed in levels of inherited thrombophilic factors and in particular APCR between IBD patients and controls. In conclusion, the presence of inherited thrombophilic defects, in particular APCR, is uncommon in patients with IBD and does not merit routine screening. 相似文献