全文获取类型
收费全文 | 70223篇 |
免费 | 2171篇 |
国内免费 | 288篇 |
专业分类
电工技术 | 884篇 |
综合类 | 782篇 |
化学工业 | 9618篇 |
金属工艺 | 1213篇 |
机械仪表 | 1451篇 |
建筑科学 | 1802篇 |
矿业工程 | 473篇 |
能源动力 | 1365篇 |
轻工业 | 5877篇 |
水利工程 | 854篇 |
石油天然气 | 207篇 |
武器工业 | 10篇 |
无线电 | 4063篇 |
一般工业技术 | 7357篇 |
冶金工业 | 27174篇 |
原子能技术 | 422篇 |
自动化技术 | 9130篇 |
出版年
2024年 | 103篇 |
2023年 | 341篇 |
2022年 | 646篇 |
2021年 | 916篇 |
2020年 | 565篇 |
2019年 | 675篇 |
2018年 | 1104篇 |
2017年 | 1398篇 |
2016年 | 1757篇 |
2015年 | 1303篇 |
2014年 | 1278篇 |
2013年 | 1850篇 |
2012年 | 3341篇 |
2011年 | 4000篇 |
2010年 | 1836篇 |
2009年 | 1980篇 |
2008年 | 1708篇 |
2007年 | 1600篇 |
2006年 | 1331篇 |
2005年 | 4030篇 |
2004年 | 3321篇 |
2003年 | 2757篇 |
2002年 | 1627篇 |
2001年 | 1416篇 |
2000年 | 807篇 |
1999年 | 1131篇 |
1998年 | 8012篇 |
1997年 | 5039篇 |
1996年 | 3361篇 |
1995年 | 2017篇 |
1994年 | 1518篇 |
1993年 | 1605篇 |
1992年 | 458篇 |
1991年 | 580篇 |
1990年 | 521篇 |
1989年 | 454篇 |
1988年 | 484篇 |
1987年 | 374篇 |
1986年 | 358篇 |
1985年 | 344篇 |
1984年 | 197篇 |
1983年 | 167篇 |
1982年 | 241篇 |
1981年 | 293篇 |
1980年 | 303篇 |
1979年 | 149篇 |
1978年 | 171篇 |
1977年 | 739篇 |
1976年 | 1532篇 |
1975年 | 180篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
Quality of service has become today a major concern for operators of mobile communication networks. The massive development of networks and strong competition between operators has lead to the necessary and daily follow-up of network quality of service, a key factor for its subscriber’s fidelity. This article aims at presenting the optimization methodology and proposes its illustration with a case of RNO (Radio Network Optimisation) software usage, one of the Alcatel optimization toolchain component. After a short presentation of cellular network, the optimization basic principles are described. RNO software and its main functionnalities are then detailed before a last part dedicated to a real case of optimization done with RNO software. 相似文献
62.
63.
64.
65.
Characterisation of two biomass fuels (pelletised Miscanthus Giganteus and wood) was performed using thermogravimetric analysis with measurement of products by means of Fourier transform infrared spectroscopy (TG-FTIR). Three heating rate profiles were applied (10, 30 and 100 °C/min), with a final temperature of 900 °C. HCN and HNCO were found to be the major N-products, while the NH3 fraction was detected to a minor extent. Kinetic parameters were obtained from the TG-FTIR results using a model based on parallel first-order reactions with a Gaussian distribution of activation energies. On the basis of the above kinetic analysis and product yields, input files for the functional group-devolatilisation, vaporisation, cross-linking biomass-pyrolysis model were prepared. The fit of model parameters to TG-FTIR product-evolution data was found to be generally good, but the model-predicted yields for some species did not fit experimental data at all heating rates. Further improvements in the model are needed to resolve above difficulty. 相似文献
66.
Shanchieh Jay Yang Gustavo de Veciana 《Networking, IEEE/ACM Transactions on》2004,12(2):349-360
With a view on improving user-perceived performance on networks supporting best effort flows, e.g., multimedia/data file transfers, we propose a family of bandwidth allocation criteria that depends on the residual work of on-going transfers. Analysis and simulations show that allocating bandwidth in this fashion can significantly improve the user-perceived delay, bit transmission delay, and throughput over traditional approaches, e.g., by 58% on an 80% loaded linear network. A simple implementation based on TCP Reno, exemplifies how one might approach practically realizing such gains. We discuss several other advantages of incorporating such differentiation at the transport level. In particular we make the case that favoring small transfers combined with user impatience or peak rate constraints, both of which are natural mechanisms for users to express the utility of completing transfers, offers a lightweight approach to achieving good overall network goodput and/or utility for best effort networks. 相似文献
67.
The expression of cytokeratins (CK), involucrin, vimentin, CD34, and alpha-smooth-muscle actin was studied in fetal and adult hair follicles. The first stage of the developing hair follicle is characterized by palisaded, elongated epithelial cells budding from the epidermal basal layer. These cells express CK5/6, CK14, CK17, CK19, and vimentin. During the following weeks of gestation, different structures in the developing hair follicle can be identified and characterized. The matrical cells display only CK19. The keratinocytes of the outer root sheath express CK5/6, CK14, CK17, CK19, and involucrin; those of the inner root sheath, CK4, CK18, and involucrin; those of the isthmus, the same profile as the ORS. In the infundibulum, the basal-layer keratinocytes express CK5/6, CK14, CK17, and CK19, whereas in the suprabasal layers CK1, CK4, CK10, CK14, and CK17 are seen. The adult hair follicle in anagen fails to express CK19 in the matrical cells and isthmus and both CK17 and CK19 in the infundibulum. These profiles of intermediate filaments and other markers appear to be potentially useful in categorizing neoplasms with apparent follicular differentiation. 相似文献
68.
69.
Phospholamban (PLN) was expressed in Escherichia coli as a protein fusion with glutathione S-transferase (GST). GST-PLN was mostly present in the insoluble protein fraction and accounted for approximately 50% of total insoluble protein. Attempts to suppress inclusion body formation or to use GST as an affinity-purification tag failed. A successful purification method is based on preparative SDS/PAGE and electrodialysis. From 1 g cells we typically purified 13.5 mg fusion protein with a PLN content of 2.8 mg. We genetically inserted an enterokinase (EK) protease site just in front of the PLN sequence and demonstrated the proteolytical liberation of PLN from the carrier protein. The approach described represents a substantial advancement in PLN expression and purification. 相似文献
70.
We report a 20 month old female patient with diploid-triploid mixoploidy (46,XX/69,XXX) syndrome with hypothyroidism and precocious puberty. The triploid cell line was only expressed in the fibroblast culture and comprised the majority (95%) of the cells. Chromosome analysis of the fetal blood sample and peripheral blood sample were normal. The patient shows typical features of full triploidy (growth and severe mental retardation, cranial and facial dysmorphism, complete syndactyly of fingers 3/4, partial syndactyly of toes 2/3) and facial but no body asymmetry. At the age of 5 months central hypothyroidism and precocious puberty were diagnosed. Thin pigmented streaks were visible on the wrists and legs of the patient at the age of 16 months. This is the first patient reported so far with 46,XX/69,XXX mixoploidy suffering from hypothyroidism and precocious puberty. 相似文献