全文获取类型
收费全文 | 727篇 |
免费 | 0篇 |
专业分类
电工技术 | 3篇 |
化学工业 | 109篇 |
金属工艺 | 7篇 |
机械仪表 | 17篇 |
建筑科学 | 3篇 |
矿业工程 | 4篇 |
轻工业 | 1篇 |
水利工程 | 3篇 |
石油天然气 | 20篇 |
无线电 | 15篇 |
一般工业技术 | 46篇 |
冶金工业 | 484篇 |
原子能技术 | 14篇 |
自动化技术 | 1篇 |
出版年
2017年 | 3篇 |
2016年 | 8篇 |
2015年 | 2篇 |
2014年 | 4篇 |
2013年 | 3篇 |
2011年 | 5篇 |
2010年 | 5篇 |
2009年 | 4篇 |
2008年 | 7篇 |
2007年 | 7篇 |
2006年 | 6篇 |
2005年 | 3篇 |
2004年 | 2篇 |
2003年 | 9篇 |
2002年 | 9篇 |
2001年 | 4篇 |
2000年 | 6篇 |
1999年 | 28篇 |
1998年 | 143篇 |
1997年 | 82篇 |
1996年 | 65篇 |
1995年 | 32篇 |
1994年 | 36篇 |
1993年 | 35篇 |
1992年 | 5篇 |
1991年 | 8篇 |
1990年 | 8篇 |
1989年 | 14篇 |
1988年 | 13篇 |
1987年 | 3篇 |
1986年 | 7篇 |
1985年 | 10篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1977年 | 30篇 |
1976年 | 29篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 6篇 |
1972年 | 3篇 |
1971年 | 7篇 |
1970年 | 5篇 |
1969年 | 5篇 |
1968年 | 6篇 |
1966年 | 3篇 |
排序方式: 共有727条查询结果,搜索用时 756 毫秒
151.
A gene encoding a bifunctional homodimeric dihydrofolate reductase-
thymidylate synthase (DHFR-TS) was constructed by destroying the stop codon
of Escherichia coli dihydrofolate reductase (DHFR) and joining the coding
sequences of the monofunctional enzymes by a five amino acid linker. The
protein was designed to mimic features of active site proximity and
electrostatics in the protozoan DHFR-TSs which are believed to be important
in channeling of the DHFR substrate, H2folate, to TS. The genetically
engineered catalytically active homodimeric bifunctional DHFR-TS was
expressed, purified and characterized. The component activities of the
purified bifunctional enzyme had kinetic properties similar to those of the
monofunctional TS and DHFR, but unlike the authentic bifunctional enzymes
from protozoa this enzyme did not kinetically channel dihydrofolate from
DHFR to TS.
相似文献
152.
N. N. Zakharova I. D. Zenkov A. N. Sokira L. A. Volkov M. P. Zverev 《Fibre Chemistry》1989,20(3):164-166
Conclusions Special features of spinning a fibre by the wet method from a copolymer based on acrylonitrile and sodium methallylsulfonate which are connected with dissociation and solvation of the sulfonate groups have been examined.It has been found that, to obtain a fibre with satisfactory physico-mechanical properties which assure processing into textile articles from a sulfonate-containing copolymer, it is necessary to carry out the spinning either into nonaqueous baths or into aqueous baths which contain lyophilic salts.Translated from Khimicheskie Volokna, No. 3, pp. 10–12, May–June, 1988. 相似文献
153.
Margarita N. Shurupova Andrei A. Zverev 《The International journal of environmental studies》2017,74(5):724-731
AbstractThe criteria for assessing conservation categories of rare species are not identical in drafting the red lists of Russia and the IUCN. By the example of genus Saussurea (Compositae), we have shown that the conservation measures for some endangered species do not match their state. We conducted indicator analyses on two factors of more than 9000 relevés with Saussurea species with large ranges and determined their rarity types according to D. Rabinowitz. Only 2 Siberian Saussurea species are not characterised by any type of rarity. The other 54 taxa all feature a small range, low abundance or high habitat specificity. 相似文献
154.
By means of the proposed thermal model and corresponding software, the thermal characteristics of high-precision spindles may be quickly assessed in the initial stages of design. 相似文献
155.
Recent evidence suggests that conservative elites' claims of a liberal media are having an impact upon public perceptions of news coverage. With this in mind, we examined two related questions in the context of the 1988, 1992, and 1996 presidential elections. First, what factors may be prompting conservative elites to make allegations of liberal media bias? Second, what factors may influence when news media report these criticisms during presidential campaigns? Findings suggest that these criticisms of news media are at least partly strategic and reflect a dynamic relationship between political elites and journalists during a presidential campaign. 相似文献
156.
A. V. Zverev S. I. Romanov Ya. V. Titovskaya N. L. Shwartz Z. Sh. Yanovitskaya 《Optoelectronics, Instrumentation and Data Processing》2009,45(4):367-373
Monte Carlo simulations of atomic processes on the surface of silicon nanochannel membranes during molecular-beam epitaxy
and subsequent thermal oxidation are performed. It is demonstrated that silicon deposition on Si(001) wafers with 1–100 nm
cylindrical pores results in constriction of channel inlets. The rates of reduction of the nanochannel diameter are estimated
as functions of the wafer temperature, silicon deposition rate, and initial nanochannel diameter. Optimal conditions of silicon
deposition on nanochannel membranes are determined: the wafer temperature of 250–450°C and silicon flux intensity of 10−2 to 10 monolayers (ML) per second. Under these conditions, the rate of reduction of the nanochannel inlet diameter is 0.13–0.15
nm/ML, which allows membrane channel modifications over a wide range down to several nanometers. Simulations of nanochannel
membrane oxidation in an oxygen flux shows that precise reduction of nanochannel inlet diameters down to complete sealing
of the channel due to oxide growth is only possible for small diameters of the initial pores. For channels with large lateral
sizes, the effect of reduction of the channel inlet diameter due to oxidation is insignificant. Oxidation of pores enhances
their stability to subsequent high-temperature treatment. 相似文献
157.
158.
This study compared the effects of undiluted and 8% ethanol administered orally on gastrointestinal antioxidant components of male and female rats. Eight percent ethanol increased the activities of duodenal glutathione peroxide (29% in males, 14% in females) and superoxide dismutase in female gastric (24%) and male duodenal (15%) mucosa. This dose of ethanol also increased the glutathione content of gastric mucosa (12% in males, 13% in females). Undiluted ethanol decreased glutathione levels in gastric mucosa (22% in males, 11% in females) and increased glutathione peroxide activity in gastric mucosa (14% in males, 9% in females). Undiluted alcohol also produced decreases in the activity of glutathione reductase in stomach (14% in males, 9% in females) and duodenum (16% in males, 12% in females). Undiluted ethanol caused mucosal damage in the body of the stomach in both genders, accompanied by an increase in luminal pH and fluid accumulation in the stomach; these changes were absent in rats given 8% ethanol. The increase in gastrointestinal antioxidant capacity associated with the administration of 8% ethanol may be a factor in the reported cytoprotective effect of lower doses of ethanol. 相似文献
159.
160.
The present investigation was conducted to study the effect of selected processing and storage methods on the concentration of ascorbic acid and beta-carotene in Bathua and fenugreek leaves. Methods included storage of leaves with or without polythene bags for 24 and 48 h in a refrigerator at 5 degrees C; at 30 degrees C in polythene bags; drying (sun and oven); blanching (5, 10, 15 min); open pan and pressure cooking. Ascorbic acid content of fresh leaves was 220.97 to 377.65 mg and beta-carotene content was 19.00 to 24.64 mg/100 g, DW. The percent loss of ascorbic acid ranged from 2.03 to 8.77 and 45.15 to 66.9 while lower losses (0.0 to 1.75 and 1.63 to 2.84) of beta-carotene were observed in leaves stored in the refrigerator and at 30 degrees C, respectively. A markedly greater reduction in ascorbic acid and beta-carotene was observed in dried, blanched and cooked leaves. The study data suggest that storage of leaves in refrigeration, drying in oven, blanching for a short time and cooking in a pressure cooker results in better retention of these two vitamins. 相似文献