全文获取类型
收费全文 | 927篇 |
免费 | 7篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 4篇 |
化学工业 | 60篇 |
金属工艺 | 2篇 |
机械仪表 | 32篇 |
建筑科学 | 13篇 |
矿业工程 | 2篇 |
能源动力 | 15篇 |
轻工业 | 24篇 |
水利工程 | 1篇 |
无线电 | 49篇 |
一般工业技术 | 66篇 |
冶金工业 | 612篇 |
原子能技术 | 12篇 |
自动化技术 | 44篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 4篇 |
2018年 | 8篇 |
2017年 | 10篇 |
2016年 | 7篇 |
2015年 | 5篇 |
2014年 | 15篇 |
2013年 | 25篇 |
2012年 | 7篇 |
2011年 | 14篇 |
2010年 | 12篇 |
2009年 | 18篇 |
2008年 | 11篇 |
2007年 | 16篇 |
2006年 | 11篇 |
2005年 | 7篇 |
2004年 | 8篇 |
2003年 | 7篇 |
2002年 | 7篇 |
2001年 | 5篇 |
2000年 | 8篇 |
1999年 | 11篇 |
1998年 | 162篇 |
1997年 | 115篇 |
1996年 | 61篇 |
1995年 | 53篇 |
1994年 | 38篇 |
1993年 | 49篇 |
1992年 | 10篇 |
1991年 | 13篇 |
1990年 | 12篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 11篇 |
1986年 | 15篇 |
1985年 | 15篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 21篇 |
1976年 | 61篇 |
1975年 | 3篇 |
1964年 | 2篇 |
排序方式: 共有936条查询结果,搜索用时 15 毫秒
71.
72.
Dimethyl sulfonium 2-pyridyl carbonyl methylide (Ypy-s) initiated radical polymerization of styrene in dimethyl sulfoxide at 85±0.1°C for 6 h under a nitrogen blanket using dilatometric techniques has been studied. The initiator and monomer exponent values were calculated to be 0.5 and 1.2, respectively. The system follows ideal radical kinetics with bimolecular termination. The higher monomer exponent value is ascribed to significant solvent effects on the initiation rate. The overall activation energy and average value of k2p/kt are 52.0 kJ mol?1 and 1.0 × 10?3 litre mol?1 s?1, respectively. The polymerization was retarded in the presence of hydroquinone or benzene; dimethylformamide, however, enhanced the rate of polymerization. Kinetic data and ESR studies indicate that the overall polymerization takes place via triplet carbene formation which acts as a source of free radicals. 相似文献
73.
Chronic action of different xenobiotics which form a part of condensed hydrogen sulphide-containing gas causes substantial changes in the activity of xenobiotic metabolic enzymes, which is suggestive of the damaged hepatic microsomal monooxygenase system. As the rate of biotransformation becomes higher, there are increases in the activity of microsomal monooxygenases and in the generation of active oxygen forms and hydrogen peroxide, by impairing antiradical and antiperoxide mechanisms. The experimentally used concentration of substances as constituents of condensed gas corresponds to the maximum acceptable air concentration of in the working area of gas-refining plants, but the functional features of the body's detoxifying system--the hepatic monooxygenase system should be taken into account while developing preventive measures of occupational diseases. 相似文献
74.
BC Bonning VK Ward MM van Meer TF Booth BD Hammock 《Canadian Metallurgical Quarterly》1997,94(12):6007-6012
Juvenile hormone esterase (JHE; EC 3.1.1.1), which is intrinsically involved in regulation of development of some insect larvae, is rapidly removed from the hemolymph by the pericardial cells. Lys-29 and Lys-524, which are implicated in the degradation of JHE, were mutated to Arg. Neither the half-life of the modified JHE in the hemolymph nor the catalytic parameters were changed significantly, but when combined, these mutations resulted in apparent failure of lysosomal targeting in the pericardial cell complex. A hypothesis for the mechanism of reduced efficiency of lysosomal targeting is presented. Infection of larvae with a recombinant baculovirus expressing the modified JHE resulted in a 50% reduction in feeding damage compared with larvae infected with the wild-type virus, thus demonstrating improved properties as a biological insecticide. These data demonstrate that alteration of specific residues of JHE that disrupted lysosomal targeting, dramatically increased the insecticidal activity of this protein. 相似文献
75.
Cyclins are essential proteins in cell cycle control, and their deranged expression has been reported to be associated with malignant transformation. Involvement of cyclins in the development of endometrioid carcinomas of the endometrium was studied immunohistochemically using antibodies against both cyclin A and tumor suppressor gene product p53, and their expression was compared with that of Ki-67 antigen. Sixty-two cases of endometrial endometrioid carcinoma and 20 cases of normal endometrium (10 proliferative and 10 secretory phase) were examined. Of the 62 endometrioid carcinomas, atrophic endometrium and hyperplasia were found adjacent to the cancers in 30 and 19 cases respectively. Cyclin A was expressed in < 1% of the glandular cells of normal endometrium in the proliferative phase and in hyperplasia, but was negligible in normal secretory phase and atrophic endometrium. p53 was almost always negative in normal endometrium and hyperplasia. Of the 62 endometrioid carcinomas, 12 tumors (19.4%) overexpressed cyclin A and 21 tumors (33.8%) overexpressed p53 (positive cells > 1%). Cyclin A and p53 were more frequently expressed in poorly differentiated tumors than in well differentiated tumors (cyclin A, p = 0.002; p53, p = 0.016). In addition, cyclin A-positive cells were topographically related to those cells positive for p53 as well as Ki-67. In conclusion, the abnormal expression of cyclin A and p53 is associated with high-grade endometrial endometrioid carcinomas. 相似文献
76.
77.
78.
Acid Mine Drainage (AMD) originates from the oxidation and leaching of sulphide minerals present in coal and metalliferrous ore bodies and gives rise to several environmental degradation problems. An investigation has been carried out to combat the acidic water problems. Results of this investigation indicate that application of anionic surfactant (sodium lauryl sulphate) and food preservatives (sodium benzoate and potassium sorbate) effectively abate the acid formation at low concentration levels (15–40 ppm) as tested in laboratory as well as at pilot-scale levels. Acidity, sulphate and iron concentrations are found to reduce by over 70 percent and remained low for more than three months after treatment. Thus this investigation demonstrates the management of these problems in an environmentally safe manner by controlling acid formation at its source. 相似文献
79.
P H?llsberg C Scholz DE Anderson EA Greenfield VK Kuchroo GJ Freeman DA Hafler 《Canadian Metallurgical Quarterly》1997,159(10):4799-4805
CD80 (B7-1) and CD86 (B7-2) on APC provide a major costimulatory signal through interactions with CD28 on T cells. Absent from resting human T cells, CD86 is up-regulated early upon T cell activation, whereas CD80 expression appears later. Whereas T cell expression of CD80 has been implicated in costimulation, the functional significance of CD86 expression on T cells is unclear. We now demonstrate that CD86 expressed on human CD4+ T cell clones does not provide a costimulatory signal for other CD4+ T cell clones. Binding studies using CD28-Ig and CTLA-4-Ig fusion proteins demonstrate that CD86 expressed on T cells has significantly reduced binding affinity for CTLA-4 and no detectable binding to CD28. Biochemical analysis demonstrates that post-translational modifications of CD86 in human T cells are different from those of CD86-transfected Chinese hamster ovary cells or EBV-transformed B cells, in that T cells express a hypoglycosylated form of CD86 on the surface membrane. Thus, our results suggest that while CD86 is expressed on a number of different cell types, its costimulatory function and affinity for its ligands may be regulated by cell type-specific post-translational modifications. 相似文献
80.