全文获取类型
收费全文 | 4567篇 |
免费 | 101篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 51篇 |
化学工业 | 542篇 |
金属工艺 | 70篇 |
机械仪表 | 66篇 |
建筑科学 | 123篇 |
矿业工程 | 4篇 |
能源动力 | 92篇 |
轻工业 | 281篇 |
水利工程 | 21篇 |
石油天然气 | 3篇 |
无线电 | 358篇 |
一般工业技术 | 610篇 |
冶金工业 | 1806篇 |
原子能技术 | 47篇 |
自动化技术 | 597篇 |
出版年
2021年 | 26篇 |
2019年 | 34篇 |
2018年 | 44篇 |
2017年 | 48篇 |
2016年 | 34篇 |
2015年 | 40篇 |
2014年 | 75篇 |
2013年 | 182篇 |
2012年 | 78篇 |
2011年 | 120篇 |
2010年 | 105篇 |
2009年 | 104篇 |
2008年 | 110篇 |
2007年 | 124篇 |
2006年 | 92篇 |
2005年 | 82篇 |
2004年 | 82篇 |
2003年 | 95篇 |
2002年 | 86篇 |
2001年 | 91篇 |
2000年 | 85篇 |
1999年 | 114篇 |
1998年 | 532篇 |
1997年 | 303篇 |
1996年 | 220篇 |
1995年 | 149篇 |
1994年 | 129篇 |
1993年 | 141篇 |
1992年 | 61篇 |
1991年 | 63篇 |
1990年 | 55篇 |
1989年 | 65篇 |
1988年 | 62篇 |
1987年 | 57篇 |
1986年 | 41篇 |
1985年 | 50篇 |
1984年 | 61篇 |
1983年 | 55篇 |
1982年 | 46篇 |
1981年 | 54篇 |
1980年 | 54篇 |
1979年 | 56篇 |
1978年 | 44篇 |
1977年 | 72篇 |
1976年 | 133篇 |
1975年 | 41篇 |
1974年 | 33篇 |
1973年 | 21篇 |
1972年 | 25篇 |
1966年 | 22篇 |
排序方式: 共有4671条查询结果,搜索用时 15 毫秒
61.
Biologic data on benzene metabolite doses, cytotoxicity, and genotoxicity often show that these effects do not vary directly with cumulative benzene exposure (i.e., concentration times time, or c x t). To examine the effect of an alternate exposure metric, we analyzed cell-type specific leukemia mortality in Pliofilm workers. The work history of each Pliofilm worker was used to define each worker's maximally exposed job/department combination over time and the associated long-term average concentration associated with the maximally exposed job (LTA-MEJ). Using this measure, in conjunction with four job exposure estimates, we calculated SMRs for groups of workers with increasing LTA-MEJs. The analyses suggest that a critical concentration of benzene exposure must be reached in order for the risk of leukemia or, more specifically, AMML to be expressed. The minimum concentration is between 20 and 60 ppm depending on the exposure estimate and endpoint (all leukemias or AMMLs only). We believe these analyses are a useful adjunct to previous analyses of the Pliofilm data. They suggests that (a) AMML risk is shown only above a critical concentration of benzene exposure, measured as a long-term average and experienced for years, (b) the critical concentration is between 50 and 60 ppm when using a median exposure estimate derived from three previous exposure assessments, and is between 20 and 25 ppm using the lowest exposure estimates, and (c) risks for total leukemia are driven by risks for AMML, suggesting that AMML is the cell type related to benzene exposure. 相似文献
62.
63.
64.
65.
PN Hengen 《Canadian Metallurgical Quarterly》1996,21(6):224-225
One hundred and forty nine patients underwent thyroid and parathyroid surgery over a nine year period. The most common indications for surgery were the presence of a solitary thyroid nodule (56%) or the onset of pressure symptoms (30%). Carcinoma was found in 7.4% of cases. Wound complications occurred in 5%. The permanent nerve injury rate was 0.67%. The incidence of permanent hypothyroidism after surgery was 4%. No patients developed permanent hypoparathyroidism. 相似文献
66.
ZR Gan Y Li TM Connolly MK Sardana PK Tsai SD Lewis JA Shafer 《Canadian Metallurgical Quarterly》1993,301(2):228-236
Site-directed mutagenesis was employed to assess the importance of the Arg-Gly-Asp triplet that comprises residues 197 to 199 in the B-chain of thrombin. Properties of the R197E and the D199E variants were compared with those of zeta-thrombin and the inactive S205A variant wherein the active site Ser is replaced by Ala. Relative to zeta-thrombin, the R197E thrombin variant under the assay conditions used exhibits 26% activity toward a small chromogenic substrate, 13% activity in the activation of protein C in the presence of thrombomodulin, < 3% activity in processing fibrinogen, and 1% activity in inducing platelet activation. Thus, the substrate specificity of thrombin was altered by the R197-->E replacement. The D199E variant was essentially inactive. It exhibited only 0.02% of the activity of thrombin toward the chromogenic substrate and its reactivity toward the active site-directed alkylating agent D-Phe-Pro-Arg-CH2Cl was 10,000-fold lower than that of thrombin. Like the inactive S205A thrombin variant, the D199E variant antagonized the interactions of thrombin with hirudin and thrombomodulin, but was a less effective antagonist. The dependence of the antagonism of the thrombin-thrombomodulin interaction on the concentration of D199E thrombin variant provided evidence suggesting the presence of two or more domains in thrombin that independently interact with their counterparts in thrombomodulin. Although the S205A thrombin variant antagonized the action of thrombin on platelets no such activity could be demonstrated for the D199E variant in the concentration range studied (< 800 nm). Comparison of the circular dichroism spectra of zeta-thrombin, the D199E, R197E, and S205A variants indicated that subtle differences in conformation exist between the D199E variant and the other thrombins. These differences in conformation might well account for the altered behavior of the D199E variant with respect to its interactions toward thrombomodulin, hirudin, and platelets. 相似文献
67.
68.
A 20-year-old man presented with signs of thornapple intoxication: restlessness, disorientation, hallucinations, euphoria, and furthermore dry and red skin and symmetrical dilation of the pupils. Thornapple intoxication mimics atropine intoxication. Thorn apples (Datura stramonium) are seemingly becoming popular as a hallucinogenic drug. When the symptoms are mild gastric lavage leaving active charcoal in the stomach afterwards will suffice. In case of severe symptoms treatment with physostigmine is indicated. 相似文献
69.
ID Ireland DF Lewis XF Li A Renborg S Kwong M Chen NJ Dovichi 《Canadian Metallurgical Quarterly》1997,16(5):491-493
Capillary electrophoresis with laser-induced fluorescence detection (CE-LIF) is a promising new method for the analysis of protein sequencing products. It gives 10 zmol (1 zmol = 10(-21) mol) limits of detection (3 sigma) for fluorescein thiohydantoin (FTH) amino acids. We have developed a separation for the (FTH)-amino acid products generated from 18 of the 20 coded amino acids. The extremely low volume requirement associated with CE-LIF makes it incompatible with commercial sequencers. For this reason, we have also been developing a miniaturized sequencer that can be more easily coupled to our detection system. Both the CE-LIF system and the miniaturized sequencer are described. 相似文献
70.
Rheological Property and Stress Development during Drying of Tape-Cast Ceramic Layers 总被引:1,自引:0,他引:1
Jennifer A. Lewis Kimberly A. Blackman rea L. Ogden James A. Payne Lorraine F. Francis 《Journal of the American Ceramic Society》1996,79(12):3225-3234
Rheological property and stress development of tape-cast ceramic layers derived from nonaqueous alumina (A12 O3 )-poly(vinyl butyral) (PVB) suspensions were observed during drying. Casting suspensions exhibited strong shear-thinning behavior, with a low shear Newtonian plateau apparent viscosity >102 Pa. s. The apparent suspension viscosity displayed a power-law dependence on the A12 O3 volume fraction during the initial stage of drying (<30% solvent loss). Stress development, measured by a cantilever deflection method, and parallel weight loss measurements were performed during the drying of tape-cast layers and pure binder coatings. Maximum drying stresses (σmax ) of 1.37-0.77 MPa were observed for plasticized tapes cast at gap heights of 150-400 μm. In contrast, nonplasticized tapes of similar thickness displayed a more gradual stress increase, with σmax values approximately an order of magnitude higher than their plasticized counterparts. The stress histories of the corresponding binder coatings were quite similar to the tape-cast layers, albeit slightly lower σ max values were observed. Stresses decayed beyond σmax with a logarithmic time dependence to an almost constant value of 0.2-0.4 MPa for the plasticized tapes. Based on these observations, process methodologies have been offered to minimize stress development and retention in tape-cast ceramic layers 相似文献