全文获取类型
收费全文 | 23170篇 |
免费 | 347篇 |
国内免费 | 122篇 |
专业分类
电工技术 | 497篇 |
综合类 | 64篇 |
化学工业 | 3165篇 |
金属工艺 | 939篇 |
机械仪表 | 657篇 |
建筑科学 | 548篇 |
矿业工程 | 67篇 |
能源动力 | 599篇 |
轻工业 | 1832篇 |
水利工程 | 212篇 |
石油天然气 | 179篇 |
武器工业 | 1篇 |
无线电 | 2586篇 |
一般工业技术 | 4069篇 |
冶金工业 | 6129篇 |
原子能技术 | 419篇 |
自动化技术 | 1676篇 |
出版年
2021年 | 149篇 |
2020年 | 114篇 |
2019年 | 157篇 |
2018年 | 229篇 |
2017年 | 229篇 |
2016年 | 255篇 |
2015年 | 177篇 |
2014年 | 296篇 |
2013年 | 819篇 |
2012年 | 507篇 |
2011年 | 776篇 |
2010年 | 559篇 |
2009年 | 621篇 |
2008年 | 715篇 |
2007年 | 747篇 |
2006年 | 629篇 |
2005年 | 718篇 |
2004年 | 587篇 |
2003年 | 634篇 |
2002年 | 675篇 |
2001年 | 670篇 |
2000年 | 599篇 |
1999年 | 614篇 |
1998年 | 2158篇 |
1997年 | 1402篇 |
1996年 | 1043篇 |
1995年 | 718篇 |
1994年 | 618篇 |
1993年 | 640篇 |
1992年 | 358篇 |
1991年 | 344篇 |
1990年 | 341篇 |
1989年 | 343篇 |
1988年 | 292篇 |
1987年 | 267篇 |
1986年 | 245篇 |
1985年 | 275篇 |
1984年 | 215篇 |
1983年 | 200篇 |
1982年 | 185篇 |
1981年 | 217篇 |
1980年 | 202篇 |
1979年 | 164篇 |
1978年 | 152篇 |
1977年 | 277篇 |
1976年 | 385篇 |
1975年 | 127篇 |
1974年 | 109篇 |
1973年 | 117篇 |
1972年 | 90篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
PAN共聚纤维的热氧化研究 总被引:8,自引:0,他引:8
本工作采用连续式实骏装置与方法,借助力学测试、X射线衍射、元素分析、红外光谱等技术,系统地研究了PAN共聚纤维在连续热氧化过程中化学、结构、性能间的联系,亦对PAN基碳纤维力学性能提高的途径进行了探讨。研究结累表明:在热氧化过程中,PAN共聚体系的热化学反应主要发生在250℃左右;其间纤维的序态结构变化剧烈,易使纤维产生结构缺陷,进而影响热氧化纤维力学性能的变化。 相似文献
172.
W Matthiessen N Sch?nfeld H Mauch U Wahn A Grassot 《Canadian Metallurgical Quarterly》1993,118(5):139-144
The chest radiograph of a 35-year-old man with fatigue, exertional dyspnoea and haemoptyses revealed a cavity in the left upper lobe and a shrunken left lung with radiolucency greater than that on the right. Acid-fast rods in sputum were identified as Mycobacterium kansasii on culture. Scintigraphy showed a 9% residual perfusion on the left and abnormal ventilation, compatible with Swyer-James syndrome. This had favoured the development of a mycobacterial infection. There was also a decrease in ciliary function (rate of 4-7 Hz, normal: 10-11). Treatment, begun when tuberculosis had been suspected, was after sensitivity tests changed to a combination of rifampicin (600 mg), ethambutol (1600 mg) and protionamide (500 mg) daily. There was marked regression of the findings within 4 weeks, but treatment was prematurely stopped after 11 months. Two years later there was a recurrence which again responded well to the same drug regimen with additional sulphamethoxazole (1600 mg/d). 相似文献
173.
J. excelsa , J. foetidissima and J. oxycedrus. Among the compounds the monoterpenes exist in minor amounts while the sesquiterpenes including their oxygenated members
as well as sesquiterpene alcohols consist of the majority of the whole substances. The existence of some compounds of the
oils might be attributes of the species and their sap- and heartwood. On the other side though notable differences, the essential
oils of Turkish juniper woods resemble the commercial cedar wood oils.
This work was supported by the research found of the Istanbul University. Project nr: 1335/280799. 相似文献
Die Zusammensetzung der flüchtigen Extraktstoffe im Holz von Juniperus foetidissima und Juniperus oxycedrus
J. excelsa , J. foetidissima und J. oxycedrus. Monoterpene bilden einen geringen Anteil der Extraktstoffe. Der Hauptteil besteht aus Sesquiterpenen mit deren Oxydationsprodukten. Das Vorkommen einiger der ?le k?nnte charakteristisch sein für die jeweilige Art bzw. deren Splint- und Kernholz Allerdings gleichen diese ?le, trotz geringer Unterschiede, den wesentlichen ?lbestandteilen von Kommerziellen Zedernh?lzern.
This work was supported by the research found of the Istanbul University. Project nr: 1335/280799. 相似文献
174.
Untextured bulk polycrystals usually possess macroscopically isotropic elastic properties whereas for most thin films transvers isotropy is expected,owing to the limited dimenionlity .The usually applied models for the calculation of elstic constants of polycrystals from single crystal elastic contants(so-called grain interaction models)erroneously predict macroscopic isotropy for an(untextured) thin film.This paper presents a summary of recent work where it has been demonstrated for the first time by X-ray diffraction analysis of stresses in thin films that elastic grain interaction can lead to macroscopically anisotropic behaviour (shown by non-linear sin^2φ plots).A new grain interaction model,predictin the macroscopically anisotropic behaviour of thin films,is proposed. 相似文献
175.
PF Tosi D Schwartz U Sharma Y Mouneimne J Hannig G Li G McKinley M Grieco CW Flexner J Lazarte D Norse C Nicolau DJ Volsky 《Canadian Metallurgical Quarterly》1996,87(11):4839-4844
Human erythrocytes bearing electroinserted full-length CD4 (RBC-CD4) can bind and fuse with a laboratory strain of human immunodeficiency virus type 1 (HIV-1) or with T cells infected by HIV-1. Here we show that RBC-CD4 neutralize primary HIV-1 strains in an assay of cocultivation of peripheral blood mononuclear cells (PBMC) from HIV-1-infected persons with uninfected PBMC. RBC-CD4 inhibited viral p24 core antigen accumulation in these cocultures up to 10,000-fold compared with RBC alone. Viral p24 accumulation was inhibited equally well when measured in culture supernatants or in call extracts. The inhibition was dose-dependent and long-lived. Two types of recombinant CD4 tested in parallel were largely ineffective. The neutralization of primary HIV-1 by RBC-CD4 in vitro was demonstrated in PBMC cultures from 21 of a total of 23 patients tested at two independent sites. RBC-CD4 may offer a route to blocking HIV-1 infection in vivo. 相似文献
176.
This paper describes the fabrication of NMOS-transistors with a geometric gate length of down to 50 nm using conventional optical lithography and a modified sidewall-etchback process. Based on measurements the transistors are characterised and their device parameters are compared to simulations. Finally the procedures for further optimisation of the process will be explained. 相似文献
177.
G. Staccioli R. Seraglia P. Traldi G. Menchi U. Matteoli 《Holz als Roh- und Werkstoff》1994,52(1):39-41
A specimen fromt he fossil forest of Dunarobba (Central Italy) attributed toTaxodioxylon gypsaceum was chemically analyzed particularly for its terpene content. Main chemical constituents show variations related to ageing and carbonization process, while terpene content exhibits a drop of mono- and sesquiterpenes in favour of diterpenes and higher MW compounds. All components are exclusively hydrocarbons and represent alicyclic or partially aromatic structures. The identified families include abietane, phyllocladane, norabietane and norpimarane among diterpenes and traces of cadinane and selinane among sesquiterpenes. 相似文献
178.
Zhi-Gong Wang Berroth M. Nowotny U. Hofmann P. Hulsmann A. Kohler K. Raynor B. Schneider J. 《Solid-State Circuits, IEEE Journal of》1994,29(8):995-997
A monolithically integrated clock recovery (CR) circuit making use of the phase-locked loop (PLL) circuit technique and enhancement/depletion AlGaAs/GaAs quantum well-high electron mobility transistors (QW-HEMT's) with gate lengths of 0.3 μm has been realized. A novel preprocessing circuit was used. In the PLL a fully-balanced varactorless VCO was applied. The VCO has a center oscillating frequency of about 7.7 GHz and a tuning range greater than 500 MHz. A satisfactory clock signal has been obtained at a bit rate of about 7.5 Gb/s. The power consumption is less than 200 mW at a supply voltage of -5 V 相似文献
179.
180.
A. N. Iyer U. Balachandran L. R. Motowidlo J. G. Hoehn P. Haldar 《Journal of Electronic Materials》1994,23(11):1087-1091
Pb0.4Bi1.8Sr2Ca2.2Cu3Ox (Bi-2223) precursor powder was prepared by a solid-state reaction of carbonates and oxides of lead, bismuth, strontium, calcium,
and copper, and the powder was then used to fabricate silver-clad tapes by the powder-in-tube technique. Transport critical
current density (Jc) values>4×104 A/cm2 at 77K and 2×105 A/cm2 at 4.2 and 27K have been achieved in short tape samples. Long lengths of tape were tested by winding them into pancake coils.
Recently, we fabricated a test magnet by stacking ten pancake coils, each containing three 16m lengths of rolled tape, and
tested it at 4.2, 27 and 77K. A maximum generated field of 2.6 T was measured in zero applied field at 4.2K and the test magnet
generated significant self-field in background fields up to 20 T. The results are discussed in this paper. 相似文献