全文获取类型
收费全文 | 8975篇 |
免费 | 478篇 |
国内免费 | 18篇 |
专业分类
电工技术 | 127篇 |
综合类 | 9篇 |
化学工业 | 1465篇 |
金属工艺 | 245篇 |
机械仪表 | 409篇 |
建筑科学 | 127篇 |
矿业工程 | 2篇 |
能源动力 | 234篇 |
轻工业 | 622篇 |
水利工程 | 22篇 |
石油天然气 | 6篇 |
无线电 | 1152篇 |
一般工业技术 | 1408篇 |
冶金工业 | 2763篇 |
原子能技术 | 71篇 |
自动化技术 | 809篇 |
出版年
2024年 | 7篇 |
2023年 | 84篇 |
2022年 | 124篇 |
2021年 | 217篇 |
2020年 | 153篇 |
2019年 | 177篇 |
2018年 | 219篇 |
2017年 | 218篇 |
2016年 | 246篇 |
2015年 | 225篇 |
2014年 | 320篇 |
2013年 | 435篇 |
2012年 | 447篇 |
2011年 | 527篇 |
2010年 | 347篇 |
2009年 | 394篇 |
2008年 | 347篇 |
2007年 | 264篇 |
2006年 | 279篇 |
2005年 | 226篇 |
2004年 | 212篇 |
2003年 | 187篇 |
2002年 | 177篇 |
2001年 | 145篇 |
2000年 | 123篇 |
1999年 | 208篇 |
1998年 | 1005篇 |
1997年 | 613篇 |
1996年 | 326篇 |
1995年 | 239篇 |
1994年 | 191篇 |
1993年 | 196篇 |
1992年 | 58篇 |
1991年 | 52篇 |
1990年 | 51篇 |
1989年 | 48篇 |
1988年 | 31篇 |
1987年 | 39篇 |
1986年 | 28篇 |
1985年 | 21篇 |
1984年 | 15篇 |
1983年 | 13篇 |
1982年 | 8篇 |
1981年 | 18篇 |
1980年 | 15篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 49篇 |
1976年 | 116篇 |
1975年 | 8篇 |
排序方式: 共有9471条查询结果,搜索用时 7 毫秒
81.
The base station (BS) in the CDMA Mobile System (CMS) connects calls through the radio interface and is designed to provide mobile subscribers with high quality service in spite of mobile subscribers’ motions. The BS consists of multiple base station transceiver subsystems (BTSs), a base station controller (BSC) and a base station manager (BSM). This paper is concerned with the BSC and the BSM. The BSC is located between the BTSs and the mobile switching center (MSC) connected with the public network, and is responsible for controlling mobile calls from and to mobile subscribers via the BTSs. The BSM provides operator-interfaces per the BS and takes responsibility of operation and maintenance (OAM) of the BS. Design of the BSC is based on two module types: functional module and unit module. The functional module is used to support new services easily and the unit module to increase the system capacity economically. Both modular types are easily achieved by inserting the corresponding modules to the system. Particularly, in order to efficiently support the soft handover which is one of CDMA superior advantages, the BSC adopts a large high-speed packet switch connecting up to 512 BTSs, and thus mobile subscribers can be provided with soft handover in high probability. The BSM is based on a commercial workstation to support OAM functions efficiently and guarantee high reliability of the functions. The BSM uses graphical user interface (GUI) for efficient OAM functions of the BS. 相似文献
82.
We generated plasmid expression vectors encoding ubiquitin and beta-galactosidase (beta-gal) with different intervening amino acids, allowing for the production of processed protein products that have either stabilizing or destabilizing residues at their N-termini. P815 cells transfected with plasmids encoding beta-gal with a destabilizing N-terminus did not have detectable expression beta-gal unless they were treated with inhibitors specific for the proteasome. Inhibitors of other proteolysis pathways had no such effect. Nevertheless, transfectants expressing beta-gal with different amino acid residues were equally sensitive to cytolysis by a CTL clone specific for a beta-gal peptide presented in the context of H-2Ld. In contrast to vectors encoding native beta-gal, plasmid vectors encoding beta-gal with a destabilizing residue did not induce detectable anti-beta-gal Abs when injected into skeletal muscle of BALB/c mice. However, such vectors were significantly more effective than vectors encoding native beta-gal or beta-gal with a stabilizing residue in stimulating CTL specific for P13.2, a lacZ transfectant of P815. We conclude that incorporation of strategies that enhance proteasome-dependent degradation may generate DNA vaccines that are more effective in inducing cellular immunity against targeted Ags. 相似文献
83.
AJ van Winkelhoff TJ van Steenbergen J de Graaff 《Canadian Metallurgical Quarterly》1992,18(9):431-434
Porphyromonas endodontalis (formerly Bacteroides endodontalis) is a black-pigmented anaerobic Gram-negative rod which is associated with endodontal infections. It has been isolated from infected dental root canals and submucous abscesses of endodontal origin. The presence of P. endodontalis in infected dental root canals has been correlated with symptoms of an acute infection. It is occasionally found on oral mucous membranes and periodontal pockets. P. endodontalis has shown relatively low virulence in experimental monoinfections. In anaerobic mixed infections it can play an essential role. Differences in virulence between strains have been related to capsular material. On the basis of different types of capsules, three serotypes have been described. P. endodontalis is sensitive to a wide range of antibiotics, including the penicillins, the tetracyclines, and metronidazole. 相似文献
84.
DA Carter A Burt JW Taylor GL Koenig BM Dechairo TJ White 《Canadian Metallurgical Quarterly》1997,18(7):1047-1053
A set of eleven biallelic and three multiallelic molecular markers have been developed to analyze populations of Histoplasma capsulatum. All markers are amplified by polymerase chain reaction (PCR) and can be readily scored using minimal amounts of template DNA. The 11 biallelic loci have polymorphic restriction endonuclease sites or small insertions or deletions which may be assessed by agarose gel electrophoresis. These markers are inherited in an unambiguous manner and are ideal for assessing structure and gene flow within US populations of H. capsulatum, but are monomorphic in non-US populations. Both length and sequence variation are present in the multiallelic loci, which can be scored by direct sequencing, polyacrylamide gel electrophoresis, or single-strand conformation polymorphism (SSCP): As they are hypervariable, the multiallelic loci can be used to type isolates and to assess the level of genetic variation within populations. Preliminary results indicate that the three multiallelic markers presented are sufficient to distinguish isolates at the individual level and are polymorphic in both US and non-US populations. This collection of molecular markers will be a useful tool in population and epidemiology studies of H. capsulatum. 相似文献
85.
86.
This study has explored the potential energy surface on the chemical reaction of CH2OH with NO by using ab initio calculation. We have found the new reaction pathway producing N-hydroxy formamide, which can further decompose to generate isocyanic acid as a reducing agent of hydrocarbons selective catalytic reduction. 相似文献
87.
88.
The authors propose and test an exemplar-based random walk model for predicting response times in tasks of speeded, multidimensional perceptual classification. The model combines elements of R. M. Nosofsky's (1986) generalized context model of categorization and G. D. Logan's (1988) instance-based model of automaticity. In the model, exemplars race among one another to be retrieved from memory, with rates determined by their similarity to test items. The retrieved exemplars provide incremental information that enters into a random walk process for making classification decisions. The model predicts correctly effects of within- and between-categories similarity, individual-object familiarity, and extended practice on classification response times. It also builds bridges between the domains of categorization and automaticity. 相似文献
89.
MS Oitzl ER de Kloet M Jo?ls W Schmid TJ Cole 《Canadian Metallurgical Quarterly》1997,9(11):2284-2296
Previous studies in rats using the Morris water maze suggested that the processing of spatial information is modulated by corticosteroid hormones through mineralocorticoid and glucocorticoid receptors in the hippocampus. Mineralocorticoid receptors appear to be involved in the modulation of explorative behaviour, while additional activation of glucocorticoid receptors facilitates the storage of information. In the present study we used the water maze task to examine spatial learning and memory in mice homozygous and heterozygous for a targeted disruption of the glucocorticoid receptor gene. Compared with wild-type controls, homozygous and heterozygous mice were impaired in the processing of spatial but not visual information. Homozygous mutants performed variably during training, without specific platform-directed search strategies. The spatial learning disability was partly compensated for by increased motor activity. The deficits were indicative of a dysfunction of glucocorticoid receptors as well as of mineralocorticoid receptors. Although the heterozygous mice performed similarly to wild-type mice with respect to latency to find the platform, their strategy was more similar to that of the homozygous mice. Glucocorticoid receptor-related long-term spatial memory was impaired. The increased behavioural reactivity of the heterozygous mice in the open field points to a more prominent mineralocorticoid receptor-mediated function. The findings indicate that (i) the glucocorticoid receptor is of critical importance for the control of spatial behavioural functions, and (ii) mineralocorticoid receptor-mediated effects on this behaviour require interaction with functional glucocorticoid receptors. Until the development of site-specific, inducible glucocorticoid receptor mutants, glucocorticoid receptor-knockout mice present the only animal model for the study of corticosteroid-mediated effects in the complete absence of a functional receptor. 相似文献
90.