全文获取类型
收费全文 | 260315篇 |
免费 | 4712篇 |
国内免费 | 1817篇 |
专业分类
电工技术 | 5412篇 |
技术理论 | 5篇 |
综合类 | 1164篇 |
化学工业 | 42036篇 |
金属工艺 | 11020篇 |
机械仪表 | 7741篇 |
建筑科学 | 6590篇 |
矿业工程 | 1660篇 |
能源动力 | 5591篇 |
轻工业 | 25795篇 |
水利工程 | 2889篇 |
石油天然气 | 5997篇 |
武器工业 | 243篇 |
无线电 | 27783篇 |
一般工业技术 | 49181篇 |
冶金工业 | 47215篇 |
原子能技术 | 5616篇 |
自动化技术 | 20906篇 |
出版年
2021年 | 2474篇 |
2019年 | 2118篇 |
2018年 | 3385篇 |
2017年 | 3357篇 |
2016年 | 3683篇 |
2015年 | 2797篇 |
2014年 | 4578篇 |
2013年 | 11351篇 |
2012年 | 7685篇 |
2011年 | 10190篇 |
2010年 | 8113篇 |
2009年 | 8666篇 |
2008年 | 9471篇 |
2007年 | 9585篇 |
2006年 | 8431篇 |
2005年 | 7385篇 |
2004年 | 6654篇 |
2003年 | 6200篇 |
2002年 | 6208篇 |
2001年 | 6318篇 |
2000年 | 5906篇 |
1999年 | 5875篇 |
1998年 | 12856篇 |
1997年 | 9535篇 |
1996年 | 7277篇 |
1995年 | 5526篇 |
1994年 | 5083篇 |
1993年 | 4948篇 |
1992年 | 3943篇 |
1991年 | 3751篇 |
1990年 | 3823篇 |
1989年 | 3770篇 |
1988年 | 3530篇 |
1987年 | 3021篇 |
1986年 | 3050篇 |
1985年 | 3408篇 |
1984年 | 3321篇 |
1983年 | 3074篇 |
1982年 | 2698篇 |
1981年 | 2902篇 |
1980年 | 2643篇 |
1979年 | 2839篇 |
1978年 | 2736篇 |
1977年 | 2842篇 |
1976年 | 3694篇 |
1975年 | 2457篇 |
1974年 | 2290篇 |
1973年 | 2320篇 |
1972年 | 1981篇 |
1971年 | 1785篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
Cell division in higher eukaryotes is mainly controlled by p34cdc2 or related kinases and by other components of these kinase complexes. We present evidence that cdc2-like kinases also occur in Paramecium. Two polypeptides reacted with an antibody directed against the perfectly conserved PSTAIR region found in cdc2 kinases in other eukaryotes. Only the less abundant peptide bound to p13suc1 from Schizosaccharomyces pombe. Using centrifugal elutriation to select cells on the basis of size, we isolated highly synchronous Paramecium G1 cells. With this procedure, we demonstrated that the p13suc1-associated cdc2-like histone H1 kinase was activated before cell division at the point of commitment to division in Paramecium. Further, we show that Paramecium cdc2-like proteins occurred principally as monomers and that these monomers were active as histone H1 kinases in vitro. 相似文献
942.
This paper looks into a new area for knowledge-based system application, that of manufacturing modelling. Manual generation of IDEF0 models of manufacturing systems is time-consuming and inconsistent. However, the process can be automated to improve timeliness and consistency. In this paper, a knowledge-based manufacturing modelling system for the automatic generation of IDEF0 models is proposed. The system will not only greatly reduce the IDEF0 modelling time but will also eliminate the inconsistency problem of conventional IDEF0 modelling systems. The paper explains the knowledge-based approach and identifies the kinds of domain knowledge that are required for the construction of the knowledge-based manufacturing modelling system. 相似文献
943.
944.
Rotational and functional motor behavioral changes were studied in five MPTP lesioned chronic hemiparkinsonian Macaca nemestrina monkeys after i.m. pramipexole, a predominant D2 subfamily agonist. Pramipexole induced contraversive rotations in a dose-dependent manner with an optimal dose of 56 microg/kg for approximately 2 to 4 hr after injection. Three different rating scales were used to determine drug-induced functional improvement. They included a monkey parkinsonism rating scale, volitional responses to fruit presentations, and number of hand movements that appeared volitional. A dose of 56 microg/kg of pramipexole produced functional improvements on hand disability, and on a parkinsonian rating scale for monkeys in a dose-dependent manner from 32 to 100 microg/kg. These doses produced an increase in significant hand movements in the affected (contralateral) as well as in the normal (ipsilateral) hand to the side of the brain lesion compared with 5% dextrose in water vehicle control. With a dose of 100 microg/kg, the therapeutic effects of pramipexole on hand movements were less than with 56 microg/kg, due to side effects such as scratching. 相似文献
945.
Researchers have recently called for the development of primary prevention of eating disorders programs aimed at elementary school students. The present study reports on the development of a curriculum for fifth graders designed to encourage healthy eating, exercise, and body image while discouraging calorie-restrictive dieting, exercising for weight loss, and the development of body dissatisfaction. The program consisted of ten lessons taught by the classroom teachers. The influence of the curriculum on (1) knowledge about nutrition, body fat, and dieting; (2) attitudes about fat people and own body (body esteem); and (3) behaviors, including attempts at weight reduction, consumption of fruits and vegetables, and exercising, were evaluated in a pre-post controlled experimental design. There were 222 white public school children who participated in both the pre- and posttesting, 167 of whom were in the classrooms receiving the curriculum. Results indicated that knowledge was broadly improved by the curriculum. There were information improvements in terms of nutrition, effects of dieting, and causes of body fat. Attitudinal changes were less pronounced, although the curriculum did positively affect attitudes about fat people. Behavior, including eating patterns, exercise patterns, weight reduction attempts, and teasing of fat children, was not changed by participation in the curriculum. 相似文献
946.
A cross-sectional study was conducted, between June and November 1993, to determine the prevalence of Salmonella excretion in a representative sample (n = 300) of adult cattle, chosen by strict random sampling of the isolated bovine population in Gozo. Salmonellae were found in 41.3% of the cattle investigated, and seven animals yielded multiple Salmonella serovars. The total number of Salmonella isolates was 131. These included Salmonella Croft (55 isolates), S. Telaviv (29), S. Montevideo (17), S. Kpeme (7), S. Infantis (2) and S. Abadina (1). A seventh serovar (14 isolates) was found to have a novel antigenic structure: the name S. Gozo was proposed, and was accepted by the World Health Organisation Salmonella Reference Centre. All isolates were sensitive to four antibiotics, while 43% of the Salmonella strains were sensitive to nine antibiotics. No resistance was detected to cefuroxime, ciprofloxacin and gentamicin. 相似文献
947.
S Cohrs G Herrendorf J Wiltfang A Rodenbeck J Kinkelbur L Adler G Hajak 《Canadian Metallurgical Quarterly》1996,146(13-14):366-368
10 patients with obstructive sleep apnea syndrome (OSAS) have been treated with the new surgical procedure functional palatoraphy and modified genioplasty. 5 months after surgery 7 patients with an apnea hypopnea index under 10 were cured. Three therapy refractory patients were all overweight with a body mass index of more than 29 kg/m2. Excessively overweight patients should therefore not be operated. Following the selection criteria we introduced an effective new treatment method for OSAS. 相似文献
948.
L. D. Pilipchatin V. V. Peschanskaya V. D. Troyan G. A. Belokrys N. G. Aleinikov 《Refractories and Industrial Ceramics》1996,37(8):281-284
Basic parameters of a resource-saving technology for manufacturing unfired articles for bottom steel casting that was developed under laboratory conditions are presented. Industrial tests of an experimental batch of unfired bottom tubes produced by the suggested technology have shown high performance properties for them and applicability of them for bottom casting of steel.Translated from Ogneupory i Tekhnicheskaya Keramika, No. 8, pp. 27–29, August, 1996. 相似文献
949.
L. V. Uzberg A. A. Malyutin G. V. Efimova A. F. Edneral N. N. Teplyakov 《Refractories and Industrial Ceramics》1996,37(11):396-398
Results of a laboratory study of the properties of corundum concrete with metallic fibers of five compositions are presented. It is shown that some of the fibers affect favorably the strength and heat resistance of the concrete. Industrial tests of parts made of the suggested reinforced concrete have proved these conclusions.Translated from Ogneupory i Tekhnicheskaya Keramika, No. 11, pp. 22–24, November, 1996. 相似文献
950.
The high-temperature crystallization of poly(p-phenylene terephthalamide) (PPTA) from dilute organic solutions was achieved through the introduction of a non-solvent, or precipitating agent, at the desired crystallization temperature. The morphology and crystal structure were examined for crystals produced from PPTA polymer with two different molecular weights (Mw = 46000 and 3430 g mol−1), using transmission electron microscopy. For the high-molecular-weight polymer, ribbon-like crystals were produced, while the low-molecular-weight polymer yielded small needles or platelets. In both cases, electron diffraction showed that the Northolt allomorph was obtained. For the high-molecular-weight polymer, the molecular axes were parallel to the ribbon axes in a chain-extended type structure. A hypothesis for the orientation of the low-molecular-weight PPTA in the small platelets, is also given. 相似文献