全文获取类型
收费全文 | 4783篇 |
免费 | 29篇 |
专业分类
电工技术 | 10篇 |
综合类 | 3篇 |
化学工业 | 300篇 |
金属工艺 | 27篇 |
机械仪表 | 25篇 |
建筑科学 | 80篇 |
矿业工程 | 2篇 |
能源动力 | 18篇 |
轻工业 | 113篇 |
水利工程 | 8篇 |
石油天然气 | 1篇 |
无线电 | 73篇 |
一般工业技术 | 171篇 |
冶金工业 | 3881篇 |
原子能技术 | 9篇 |
自动化技术 | 91篇 |
出版年
2022年 | 16篇 |
2021年 | 21篇 |
2016年 | 17篇 |
2015年 | 20篇 |
2014年 | 17篇 |
2013年 | 42篇 |
2012年 | 31篇 |
2011年 | 35篇 |
2010年 | 41篇 |
2009年 | 32篇 |
2008年 | 32篇 |
2007年 | 34篇 |
2006年 | 39篇 |
2005年 | 24篇 |
2004年 | 26篇 |
2003年 | 27篇 |
2002年 | 32篇 |
2001年 | 28篇 |
2000年 | 15篇 |
1999年 | 123篇 |
1998年 | 1061篇 |
1997年 | 653篇 |
1996年 | 410篇 |
1995年 | 244篇 |
1994年 | 234篇 |
1993年 | 254篇 |
1992年 | 54篇 |
1991年 | 70篇 |
1990年 | 66篇 |
1989年 | 78篇 |
1988年 | 72篇 |
1987年 | 80篇 |
1986年 | 72篇 |
1985年 | 73篇 |
1984年 | 23篇 |
1983年 | 26篇 |
1982年 | 31篇 |
1981年 | 39篇 |
1980年 | 49篇 |
1979年 | 13篇 |
1978年 | 21篇 |
1977年 | 122篇 |
1976年 | 251篇 |
1975年 | 29篇 |
1974年 | 8篇 |
1973年 | 10篇 |
1972年 | 9篇 |
1971年 | 11篇 |
1970年 | 20篇 |
1968年 | 8篇 |
排序方式: 共有4812条查询结果,搜索用时 15 毫秒
41.
42.
43.
The paper describes a program of experiments for speed reduction on 28 through roads in Nordrhein-Westfalen. In the process, different measures of construction, design, and traffic control were examined to determine their usefulness to reduce speed and to improve road safety. The need for systematic evaluation of a catalogue of measures partly resulted in unsatisfactory design conceptions for the through roads. The evaluation of the effects of the program has been carried out by use of before-and-after-studies of large extent. The speed measurements show that a distinct speed reduction can be obtained only from selected physical improvements. Measures based on optical effects and traffic signs were found to have very little effect on vehicle speeds. Furthermore, in light of the relatively small number of accidents that occur on the selected facilities, it was not possible to establish the beneficial impact of each specific control measure with statistical certainty. However, the results of the experiment have had an influence on the current definition of new design standards for main urban streets in Germany. 相似文献
44.
45.
RL Prestidge PM Grandison DW Chuk RJ Booth JD Watson 《Canadian Metallurgical Quarterly》1995,164(1):129-132
The 19-kDa antigen (19Ag) of Mycobacterium tuberculosis (Mt) is a lipoprotein which is released from the organism during growth. In order to study the possible involvement of this antigen in the host protective response against Mt infection, it would be helpful to obtain high-level production of 19Ag from a recombinant organism. We have found that overexpression of the native 19Ag gene in Escherichia coli or yeast leads to products which are aggregated and insoluble. By site-directed mutagenesis of the 19Ag lipoprotein leader sequence, we have generated a mutant gene which directs the production of 19Ag into the periplasmic space of E. coli, from where it can be easily purified in high yield. 19Ag obtained from this mutant construct lacks the lipid-modified N-terminal Cys residue found in the native 19Ag, and is not glycosylated, but is otherwise indistinguishable from 19Ag isolated from Mt culture supernatant. 相似文献
46.
47.
Marcela Brugnach Andrew Tagg Florian Keil Wim J. de Lange 《Water Resources Management》2007,21(7):1075-1090
The use of computer models offers a general and flexible framework that can help to deal with some of the complexities and
difficulties associated with the development of water management plans as prescribed by the Water Framework Directive. However,
despite the advantages modelling presents, the integration of information derived from models into policy is far away from
being trivial or the norm. Part of the difficulties of this integration is rooted in the lack of confidence policy makers
have on the incorporation of modelling information into policy formulation. In this paper we examine the reasons for this
apparent lack of confidence and explore how some tools, presently in use, address this problem. We conclude that public confidence
in models is highly dependent on the way uncertainties are addressed and suggest possible directions of action to improve
the current situation. Four real case studies illustrate how computer models have been used in The Netherlands for carrying
out management plans at regional and national scale. We suggest that the solution to integrate modelling information into
policy formulation lies on both the modelling and the policy-making communities. 相似文献
48.
49.
50.
Evaluation of humoral immune responses in cattle grazing endophyte-infected or endophyte-free fescue
RL Rice DJ Blodgett GG Schurig WS Swecker JP Fontenot VG Allen RM Akers 《Canadian Metallurgical Quarterly》1997,59(3-4):285-291
Anecdotal reports suggest cattle with fescue toxicosis may not respond to vaccination and thus, experience increased incidence of Bovine Respiratory Disease Complex (BRDC) when shipped to feedlots. Fescue toxicosis causes hypoprolactemia in cattle. Hypoprolactemia decreases humoral immune responses in mice. Therefore, a study was conducted to compare the magnitude of primary and secondary humoral immune responses against specific antigens in cattle grazing endophyte-infected or endophyte-free fescue. Angus steers were blocked by weight and allocated into four groups. Two groups grazed endophyte-infected (EI) fescue and the other two groups grazed endophyte-free (EF) fescue. All steers were injected IM on d 0 and 21 with lysozyme without adjuvant and concanavalin. A (Con A) with sheep red blood cells (SRBC) in incomplete adjuvant of Freund. Steers were bled on days 0, 21 and 35 post-vaccination. Average daily gains (ADG), alkaline phosphatase (ALP) activity, cholesterol concentrations, rectal temperatures, and serum prolactin concentrations were measured to confirm fescue toxicosis in steers grazing EI fescue. Antibodies to Con A and SRBC were determined by ELISA and hemagglutination assay, respectively. The ADG were decreased for the EI group during the first month. Rectal temperature were elevated and serum prolactin concentrations were decreased in the EI group. Cholesterol and ALP concentrations also were decreased in the EI group. Primary and secondary immune responses against Con A tended to be increased and were increased against SRBC in the EI group. Antibodies against lysozyme were not induced in either group. In conclusion, cattle grazing EI fescue mounted similar humoral immune responses to vaccination, despite hypoprolactemia, as cattle grazing EF fescue. Increases in bovine respiratory disease in cattle maintained on EI fescue probably is not associated with lack of humoral immune response to vaccination protocols as a result of fescue toxicosis. 相似文献