全文获取类型
收费全文 | 23238篇 |
免费 | 335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 | 3187篇 |
金属工艺 | 939篇 |
机械仪表 | 658篇 |
建筑科学 | 552篇 |
矿业工程 | 67篇 |
能源动力 | 603篇 |
轻工业 | 1835篇 |
水利工程 | 213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 | 4068篇 |
冶金工业 | 6145篇 |
原子能技术 | 419篇 |
自动化技术 | 1682篇 |
出版年
2021年 | 150篇 |
2020年 | 114篇 |
2019年 | 163篇 |
2018年 | 232篇 |
2017年 | 232篇 |
2016年 | 255篇 |
2015年 | 177篇 |
2014年 | 298篇 |
2013年 | 824篇 |
2012年 | 511篇 |
2011年 | 778篇 |
2010年 | 560篇 |
2009年 | 622篇 |
2008年 | 715篇 |
2007年 | 748篇 |
2006年 | 632篇 |
2005年 | 718篇 |
2004年 | 587篇 |
2003年 | 634篇 |
2002年 | 675篇 |
2001年 | 672篇 |
2000年 | 599篇 |
1999年 | 615篇 |
1998年 | 2165篇 |
1997年 | 1407篇 |
1996年 | 1045篇 |
1995年 | 720篇 |
1994年 | 618篇 |
1993年 | 640篇 |
1992年 | 358篇 |
1991年 | 346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 | 216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 102 毫秒
101.
Microstructure-composition relationships and Ms temperatures have been determined in high purity nitrided Fe-Cr-Mn alloys, as part of a program to develop improved corrosion-abrasion
resistant steels with unstable austenitic microstructures. Compositions in the range 8 to 12 pct Cr, 0 to 10 pct Mn, and 0
to 0.6 pct N were investigated by a resistivity technique to determine Ms temperatures and by X-ray diffraction and metallography to determine constitution. Hardness measurements were also made.
At the low alloy end of the range, microstructures after annealing and air cooling are fully martensitic while at the high
alloy end they are fully austenitic. At intermediate compositions, mixed martensite-austenite microstructures (with epsilon
present as a minor phase in some cases) and unstable austenitic microstructures are obtained. The austenitic alloys contain
a high density of stacking faults and the unstable austenitic alloys transform to martensite on deformation. At low N contents
(up to at least 0.25 pct N) the Ms-composition relationship is linear and described by: Ms = 555 - 9(Cr - 8) - 40Mn - 450N [1] where Ms is in °C and Cr, Mn, and N are the weight percentages of these elements. At higher N contents, the Ms generally falls more rapidly with increasing nitrogen content. Nitrogen solubility at 1050 °C exceeds about 0.3 pct in all
alloys and increases with increasing Cr and Mn content. In commercial purity steels, unstable austenitic microstructures are
expected to be obtained in compositions around 10 to 14 pct Cr, 8 to 12 pct Mn, and 0.1 to 0.3 pct N when the total level
of these elements is selected to ensure the Ms is below room temperature. 相似文献
102.
T Bartfai U Langel K Bedecs S Andell T Land S Gregersen B Ahrén P Girotti S Consolo R Corwin 《Canadian Metallurgical Quarterly》1993,90(23):11287-11291
The galanin-receptor ligand M40 [galanin-(1-12)-Pro3-(Ala-Leu)2-Ala amide] binds with high affinity to [mono[125I]iodo-Tyr26]galanin-binding sites in hippocampal, hypothalamic, and spinal cord membranes and in membranes from Rin m5F rat insulinoma cells (IC50 = 3-15 nM). Receptor autoradiographic studies show that M40 (1 microM) displaces [mono[125I]iodo-Tyr26]galanin from binding sites in the hippocampus, hypothalamus, and spinal cord. In the brain, M40 acts as a potent galanin-receptor antagonist: M40, in doses comparable to that of galanin, antagonizes the stimulatory effects of galanin on feeding, and it blocks the galaninergic inhibition of the scopolamine-induced acetylcholine release in the ventral hippocampus in vivo. In contrast, M40 completely fails to antagonize both the galanin-mediated inhibition of the glucose-induced insulin release in isolated mouse pancreatic islets and the inhibitory effects of galanin on the forskolin-stimulated accumulation of 3',5'-cAMP in Rin m5F cells; instead M40 is a weak agonist at the galanin receptors in these two systems. M40 acts as a weak antagonist of galanin in the spinal flexor reflex model. These results suggest that at least two subtypes of the galanin receptor may exist. Hypothalamic and hippocampal galanin receptors represent a putative central galanin-receptor subtype (GL-1-receptor) that is blocked by M40. The pancreatic galanin receptor may represent another subtype (GL-2-receptor) that recognizes M40, but as a weak agonist. The galanin receptors in the spinal cord occupy an intermediate position between these two putative subtypes. 相似文献
103.
H Teschler G Hoheisel M Fischer KM Müller N Konietzko U Costabel 《Canadian Metallurgical Quarterly》1993,118(48):1749-1754
Pulmonary asbestos burdens are usually determined by quantitative pulmonary dust analysis. The aim of this study was to investigate the value of bronchoalveolar lavage (BAL) for this purpose. First, the upper limit of normal for asbestos bodies (AB) in BAL fluid was established using a reference group of 371 patients with no evidence of increased exposure to asbestos. 99% of these patients had less than 0.5 AB/ml. In order to see whether BAL fluid AB concentration reflected pulmonary tissue content, BAL fluid and lung tissue from a further 64 patients with diverse histories of asbestos exposure were investigated. There was a positive association between AB concentration in BAL fluid and lung tissue only for the overall group of 64 patients (r = 0.86; P < 0.001). Twelve of 13 patients with more than 1 AB/ml and ten patients with more than 5 AB/ml had more than 1000 AB/cm3 lung tissue, a value that is usually exceeded in asbestosis. When the upper concentration limit was set at 0.5 AB/ml for BAL fluid and 50 AB/cm3 for lung tissue, only two out of 64 patients had a false positive value (specificity 95%), but eleven patients had false negative results (sensitivity 58%). These investigations establish that concentrations of > or = 0.5 AB/ml are a reliable indicator of increased asbestos exposure and concentrations > 1 AB/ml are associated with a higher probability of having more than 1000 AB/cm3 lung tissue. However, exclusion of increased asbestos exposure is not possible on the basis of negative BAL findings, since the sensitivity of the method is too low. 相似文献
104.
HH Henneicke-von Zepelin U Mrowietz L F?rber K Bruck-Borchers C Schober J Huber G Lutz R Kohnen E Christophers D Welzel 《Canadian Metallurgical Quarterly》1993,129(6):713-717
We report the results of a multicentre, double-blind, placebo-controlled study of topical therapy with omega-3-polyunsaturated fatty acids (omega-3-PUFA) in 52 patients suffering from moderate plaque-type psoriasis. In each patient, two similar stable psoriatic plaques served as indicator lesions for the study. One indicator lesion was randomly assigned to treatment with topical preparations of highly purified omega-3-PUFA in one of two concentrations (1 or 10%), and the other was treated with placebo. Efficacy assessment was based on changes in local psoriasis severity index, area involved, erythema, desquamation, induration and pruritus. After 8 weeks of treatment, all indicator lesions had improved significantly, compared with baseline. However, no statistically or clinically relevant differences between the omega-3-PUFA-treated and the placebo-treated lesions were found. Therapy was well tolerated and, apart from one patient who developed perilesional eczema, no clinically relevant adverse events occurred. In conclusion, topical omega-3-PUFA were not effective in a randomized, placebo-controlled, double-blind setting. Results of non-blind trials should be (re-)considered with caution. 相似文献
105.
U B?ssler 《Canadian Metallurgical Quarterly》1993,18(2):207-226
In a form of top-down analysis, the femur-tibia control system of stick insects is investigated. Open-loop experiments show that it is mainly velocity-sensitive with an extremely low velocity-threshold, that it possesses a very high gain and that it has only a very small phase reserve and thus works close to instability. The closed-loop system generates catalepsy. The system consists of a single sense organ with approximately 80 sense cells with known characteristics, a small number of interneurones (mainly non-spiking ones) and a small number of motor neurones. The characteristics of the whole system can quantitatively be attributed to the characteristics of its elements. The gain of the loop is state-dependent and the system is 'switched off' during active movements and replaced by a control system with different attributes. It is discussed that most of the characteristics of this system are, at least qualitatively, similar to joint control systems in other animals. Because the described system can be more easily investigated than other systems (especially in vertebrates) it can serve as a model against which more complicated joint control loops may be compared. 相似文献
106.
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
107.
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
108.
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
109.
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
110.
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