全文获取类型
收费全文 | 3954篇 |
免费 | 295篇 |
国内免费 | 192篇 |
专业分类
电工技术 | 191篇 |
综合类 | 250篇 |
化学工业 | 395篇 |
金属工艺 | 216篇 |
机械仪表 | 185篇 |
建筑科学 | 295篇 |
矿业工程 | 114篇 |
能源动力 | 70篇 |
轻工业 | 390篇 |
水利工程 | 195篇 |
石油天然气 | 99篇 |
武器工业 | 74篇 |
无线电 | 317篇 |
一般工业技术 | 284篇 |
冶金工业 | 878篇 |
原子能技术 | 61篇 |
自动化技术 | 427篇 |
出版年
2024年 | 13篇 |
2023年 | 34篇 |
2022年 | 106篇 |
2021年 | 125篇 |
2020年 | 89篇 |
2019年 | 68篇 |
2018年 | 73篇 |
2017年 | 83篇 |
2016年 | 86篇 |
2015年 | 150篇 |
2014年 | 195篇 |
2013年 | 236篇 |
2012年 | 267篇 |
2011年 | 274篇 |
2010年 | 222篇 |
2009年 | 238篇 |
2008年 | 222篇 |
2007年 | 243篇 |
2006年 | 179篇 |
2005年 | 150篇 |
2004年 | 113篇 |
2003年 | 97篇 |
2002年 | 90篇 |
2001年 | 73篇 |
2000年 | 54篇 |
1999年 | 71篇 |
1998年 | 204篇 |
1997年 | 141篇 |
1996年 | 96篇 |
1995年 | 61篇 |
1994年 | 47篇 |
1993年 | 72篇 |
1992年 | 21篇 |
1991年 | 18篇 |
1990年 | 9篇 |
1989年 | 11篇 |
1988年 | 11篇 |
1987年 | 12篇 |
1986年 | 18篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 10篇 |
1982年 | 8篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1977年 | 27篇 |
1976年 | 49篇 |
1974年 | 8篇 |
排序方式: 共有4441条查询结果,搜索用时 31 毫秒
1.
2.
3.
D Averill D Blockus B Brabson J Brom C Jung H Ogren DR Rust M Derrick P Kooijman JS Loos B Musgrave LE Price J Repond K Sugano B Cork C Akerlof J Chapman D Errede MT Ken DI Meyer H Neal D Nitz R Thun R Tschirhart S Abachi P Baringer BG Bylsma R DeBonte D Koltick EH Low RL McIlwain DH Miller CR Ng EI Shibata 《Canadian Metallurgical Quarterly》1989,39(1):123-137
4.
5.
LA Knapp E Lehmann L Hennes ME Eberle DI Watkins 《Canadian Metallurgical Quarterly》1997,50(2):170-177
Skeletal development of transgenic mice with a type II collagen mutation was analyzed and compared with wild-type littermates. The single base substitution in Col2a1 resulted in a glycine to serine mutation within the helical domain and corresponded to one previously identified in a patient with the lethal human chondrodysplasia, hypochondrogenesis (Horton et al. [1992] Proc. Natl. Acad. Sci. U.S.A. 89:4583-4587). Skeletal staining of embryos from 14.5 through 18.5 days of gestation demonstrated a dwarf phenotype in the transgenic embryos, most notably short limb bones and vertebral column that was first detected at 15.5 days post-coitus. In addition to the reduced length, the extent of ossification was less in the transgenic mice. The architecture of the long bone growth plate was abnormal in the transgenic tissue, in particular there was no discernible proliferative zone. There were few stacks of characteristically flattened cells and the overall length of the growth plate in the mutant embryos was reduced. At the ultrastructural level, there were fewer collagen fibrils present in the transgenic mouse cartilage compared to that of wild-type littermates. Ultrastructural localization of collagen types II, IX and XI revealed a similar pattern between the transgenic and wild-type pups, suggesting that the collagen fibrils present in the matrix of littermates with both phenotypes had a similar composition. Skeletal analysis and cartilage histochemistry indicated that effect of the type II collagen mutation was to reduce the density of the collagen fibrils within the cartilage matrix which was associated with delayed bone formation and resulted in a short-limbed phenotype. 相似文献
6.
DI Rodenhiser JD Andrews DN Mancini JH Jung SM Singh 《Canadian Metallurgical Quarterly》1997,373(2):185-195
Glutamatergic synaptic potentials induced by micromolar concentrations of the potassium conductance blocker 4-aminopyridine (4-AP) were recorded intracellularly from rat neostriatal neurons in the presence of 10 microM bicuculline (BIC). These synaptic potentials originate from neostriatal cortical and thalamic afferents and were completely blocked by 10 microM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) plus 100 microM D-2-amino-5-phosphonovaleric acid (2-APV). Their inter-event time intervals could be fitted to exponential distributions, suggesting that they are induced randomly. Their amplitude distributions had most counts around 1 mV and fewer counts with values up to 5 mV. Since input resistance of the recorded neurons is about 40 M omega, the amplitudes agree to quantal size measurements in mammalian central neurons. The action of a D2 agonist, quinpirole, was studied on the frequency of these events. Mean amplitude of synaptic potentials was preserved in the presence of 2-10 microM quinpirole, but the frequency of 4-AP-induced glutamatergic synaptic potentials was reduced in 35% of cases. The effect was blocked by the D2 antagonist sulpiride (10 microM). Input resistance, membrane potential, or firing threshold did not change during quinpirole effect, suggesting a presynaptic site of action for quinpirole in some but not all glutamatergic afferents that make contact on a single cell. The present experiments show that dopaminergic presynaptic modulation of glutamatergic transmission in the neostriatum does not affect all stimulated afferents, suggesting that it is selective towards some of them. This may control the quality and quantity of afferent flow upon neostriatal neurons. 相似文献
7.
According to FDA regulations, a combination drug is not efficacious unless each component contributes to the claimed effects. For a univariate endpoint, this implies that the combination at specific doses must be superior to each of its components at the same doses. More demanding is the property of synergy, in which the effect of the combination must be superior to the effect expected based on those of its components. If it is equal to those effects, it is additive, and if it is inferior, it is antagonistic. We give regions in the combination dose plane where these concepts are well defined. If the effect of the combination is greater than the greatest effect achievable by any of its components it is therapeutically synergistic. A combination can be antagonistic, yet its components can still contribute to the claimed effects. If it is additive, synergistic or therapeutically synergistic, its components must contribute to the claimed effects. We relate these concepts and provide designs and sequential procedures for determining whether a combination is therapeutically synergistic, synergistic, additive, antagonistic and contributing or antagonistic and non-contributing. 相似文献
8.
DI Timokhin AV Istomin TS Shushkova TG Voronel' IG Mikha?lov 《Canadian Metallurgical Quarterly》1997,(2):19-21
Based on generalization and analysis of instructions and guidelines for therapeutical and prophylactic diets of workers, ways of its optimization were proposed, by using bifide-containing acid dairy products as a preventive agent against possible occupational diseases caused by occupational factors. 相似文献
9.
AK Rasmussen L Hilsted H Perrild E Christiansen K Siersbaek-Nielsen U Feldt-Rasmussen 《Canadian Metallurgical Quarterly》1997,259(1-2):117-128
A comparison of four different commercial immunometric thyrotropin (TSH) assays (Amerlite R TSH-30 Ultrasensitive assay from Kodak, BeriLux R hTSH from Behring Werke, Delfia R hTSH Ultra from Wallac and IMX R Ultrasensitive hTSH from Abbott) was made by measuring serum TSH in 81 consecutive patients referred to hospital for various reasons with a serum TSH less than 0.8 mlU/l in the IMX assay. The analytical and functional assay sensitivities of each of the assays were analysed. Even though three of the methods had a sensitivity corresponding to third generation assays, we could only demonstrate an overall agreement of serum TSH when comparing two of the kits. The measurements in Delfia Ultra and Berilux showed good agreement (P = 0.7, paired t-test and bias = 0.003 mIU/l), while the comparisons between the other assays showed different measurements (P < 0.00001, paired t-test and bias more than 0.07 mIU/l). Differences in the calibrators used in the assays might explain some of the discrepancy, although all methods were calibrated according to the same international standard. Also, differences in the specificity of the TSH monoclonal antibodies used in the assays might be an evident explanation and further studies of the specificity of the monoclonal antibodies are needed. An international collaborative study to clarify reasons for the differences between the TSH assays and to standardize the measurements is recommended. 相似文献
10.
This paper describes the implementation of a general and flexible method of formulating problems of mathematical programming in structural optimization systems. The method enables the formulation and solution of problems involving scalar, integral, min/max, max/min and possibly non-differentiable user defined functions in any conceivable mix. The mathematical formulation is based on the bound formulation, and the implementation specific details involve a parser capable of interpreting and performing symbolic differentiation of the user defined functions. 相似文献