全文获取类型
收费全文 | 23034篇 |
免费 | 2395篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 1451篇 |
综合类 | 865篇 |
化学工业 | 10067篇 |
金属工艺 | 373篇 |
机械仪表 | 482篇 |
建筑科学 | 891篇 |
矿业工程 | 204篇 |
能源动力 | 195篇 |
轻工业 | 2117篇 |
水利工程 | 151篇 |
石油天然气 | 86篇 |
武器工业 | 1篇 |
无线电 | 603篇 |
一般工业技术 | 3909篇 |
冶金工业 | 1253篇 |
原子能技术 | 80篇 |
自动化技术 | 2711篇 |
出版年
2023年 | 685篇 |
2022年 | 371篇 |
2021年 | 767篇 |
2020年 | 756篇 |
2019年 | 651篇 |
2018年 | 627篇 |
2017年 | 441篇 |
2016年 | 697篇 |
2015年 | 879篇 |
2014年 | 933篇 |
2013年 | 1744篇 |
2012年 | 707篇 |
2011年 | 600篇 |
2010年 | 993篇 |
2009年 | 1128篇 |
2008年 | 626篇 |
2007年 | 573篇 |
2006年 | 461篇 |
2005年 | 426篇 |
2004年 | 448篇 |
2003年 | 394篇 |
2002年 | 374篇 |
2001年 | 250篇 |
1999年 | 194篇 |
1998年 | 279篇 |
1997年 | 226篇 |
1996年 | 290篇 |
1995年 | 285篇 |
1994年 | 258篇 |
1993年 | 325篇 |
1992年 | 266篇 |
1990年 | 242篇 |
1989年 | 254篇 |
1988年 | 209篇 |
1987年 | 255篇 |
1986年 | 274篇 |
1985年 | 266篇 |
1984年 | 270篇 |
1983年 | 272篇 |
1982年 | 255篇 |
1981年 | 296篇 |
1980年 | 219篇 |
1979年 | 243篇 |
1977年 | 215篇 |
1976年 | 219篇 |
1975年 | 286篇 |
1974年 | 239篇 |
1973年 | 420篇 |
1972年 | 260篇 |
1971年 | 182篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Dr. Kazuo Ishihara 《Computing》1987,38(2):117-132
In this paper, we consider the successive overrelaxation method with projection for obtaining the finite element solutions under the nonlinear radiation boundary conditions. In particular we establish the convergence of the successive overrelaxation method with projection. Some numerical results are also given to illustrate the usefulness. 相似文献
82.
Dr. G. Bohlender 《Computing》1980,24(2-3):149-160
In numerical computations mainly real and complex numbers, intervals as well as matrices and vectors with such components occur. It is well known that the arithmetic operations with real numbers, complex numbers etc. can be carried over to real floating-point numbers, complex floating-point numbers etc. using roundings. This proceeding results in agreeable arithmetic-, order- and compatibility-properties for an abundance of numerical data types and the accompanying arithmetic operations. Most programming languages however only provide real floating-point numbers; all the other data types and operations have to be simulated, e. g. in the form of arrays and procedure calls, which often causes loss of accuracy and arithmetic properties. Furthermore the complicate notation makes programs difficult to read. Therefore in this article an extension of PASCAL is presented which serves as an example for the way these numerical data types can be embedded into the syntax of a programming language. 相似文献
83.
Treatment of exponentially growing cultures ofStreptococcus mutans BHT with growth-inhibitory concentrations (0.2 μg/ml) of benzylpenicillin stimulates the incorporation of [2-14C] acetate into lipids excreted by the cells by as much as 69-fold, but does not change the amount of14C incorporated into intracellular lipids. At this concentration of penicillin cellular lysis does not occur. The radioactive
label is incorporated exclusively into the fatty acid moieties of the glycerolipids. The increase in the radioactive content
of the extracellular lipids reflects an actual net increase in the total fatty acid content as determined by a chemical assay.
During a 4-hr incubation in the presence of penicillin, the extracellular fatty acid ester concentration (per mg cell dry
weight) increases 1.5 fold, even though there is no growth or cellular lysis. No change is observed in the intracellular fatty
acid ester content.
An indication of the relative rate of fatty acid synthesis was most readily obtained by placingS. mutans BHT in a buffer containing14C-acetate. Under these nongrowing conditions free fatty acids are the only lipids labeled, a factor which simplifies the assay.
The addition of glycerol to the buffer causes all of the nonesterified fatty acids to be incorporated into glycerolipid. The
cells excrete much of the lipid whether glycerol is present or not. Addition of penicillin to the nongrowth supporting buffer
system does not stimulate the incorporation of [14C]-acetate into fatty acids. However, if cells are exposed to penicillin in a growth-supporting medium and then are transferred
to the nongrowing buffer system containing no penicillin, the previously exposed cells retain the ability to incorporate [14C]-acetate into fatty acid at a higher rate than untreated cells over a prolonged period of time. The stimulation of [14C]-acetate into fatty acids in this system parallels but is not dependent on the stimulation by penicillin of the incorporation
of [14C]-glycerol into glycerolipid and lipoteichoic acid synthesis previously demonstrated by our laboratory.
The material of this paper is part of a thesis to be submitted by J.L.B. in partial fulfillment of the requirements for the
Ph.D. degree from the Department of Biochemistry, Temple University. 相似文献
84.
Prof. Dr. J. H. Ahrens 《Computing》1989,41(1-2):163-166
In many algorithms for sampling from non-uniform distributions the logarithm of a uniform deviate must be compared with some test quantity. It is shown that all these comparisons can be done efficiently without calling a logarithm subprogram: two procedures for this task are presented and compared. 相似文献
85.
86.
Prof. Dr.-Ing. M. Michel Dr.-Ing. Th. Schütze 《Electrical Engineering (Archiv fur Elektrotechnik)》1991,74(6):419-426
Übersicht Mit Hinblick auf die zunehmend Verbreitung findende Pulsmusterberechnung in Echtzeit werden in dem Aufsatz Gesichtspunkte diskutiert, die sich aus den Eigenschaften des leistungselektronischen Stellgliedes, des Pulswechselrichters, ergeben. Die bei Abtastregelungen für die Dauer einer Abtastperiode konstante Stellgröße muß bei ihm durch Pulsweitenmodulation in ein Pulsmuster mit konstanter Amplitude und Pulsen variabler Breite umgesetzt werden. Durch ein neues Verfahren mit versetzter Abtastung haben dabei Rechentotzeiten bis zur Dauer einer halben Abtastperiode keinen Einfluß mehr auf das Pulsmuster.
Herrn Prof. Dr.-Ing. Klemens Heumann zum 60. Geburtstag gewidmet 相似文献
Algorithms for pulswidth modulation of inverters with online calculated pulse patterns
Contents Online calculation of pulse patterns will be employed more intensively in the future. Aspects concerning the powereleotronic circuit, the pulsewidth-modulated inverter, are to be discussed. The set value being constant for the duration of a sampling interval, has to be converted by a modulation algorithm into a pulse pattern with constant amplitude and pulses of variable width. Calculation dead-times up to half of sampling interval have no influence on the pulse pattern when using a new algorthm with shifted sampling instants.
Herrn Prof. Dr.-Ing. Klemens Heumann zum 60. Geburtstag gewidmet 相似文献
87.
88.
Summary Plastic yielding of anisotropic metals can be either described by a macroscopic constitutive relation or assessed by means of a model which correlates single and polycrystal behaviors. The mathematical identification of the plastic work rate derived from the two approaches, for all strain rate tensors, leads to a fit of the polycrystal yield surface by an analytical function. When a quadratic from is assumed, the macroscopic anisotropy parameters become explicit functions of the texture coefficients. This identification method is applied to calculate yield surfaces andR-values of rolled and annealed steel sheets: theR-values and in general the flow rule, are more significantly modified by the fitting than the yield surface. Thus, it is worth extending the method to more general constitutive relations which may be given by the form of their work function: alternative forms of the work function for plastic materials are explored, especially in the bearing of convexity and homogeneity where quadratic forms have a distinct advantage. Finally, it is shown that the identification of the work function allows to express the phenomenological coefficients as analytical functions of the texture parameters for many forms of the work function; in the other cases, these coefficients may be obtained by linear or non-linear regression. 相似文献
89.
90.
Shmuel Yannai Ronald R. Marquardt 《Journal of the science of food and agriculture》1985,36(11):1161-1168
Rats were fed an adequate or a deficient diet and offered water or buthionine sulphoximine (BSO) solution for 2 weeks, and then the same diets with vicine for another week in experiment 1. BSO in combination with the deficient diet caused a marked decrease in blood glutathione (GSH) and growth retardation but failed to show any effects resulting from supplementation with vicine. In experiment 2 the rats were given an adequate diet and BSO as before, and injected intravenously with divicine (DV). Here again, BSO depressed rat growth, and so did DV. Each of the insults also caused haematological changes, especially a fall in GSH, but the most severe changes appeared in the group treated with both BSO and DV. A decrease in haematocrit and increases in adrenal and spleen weight were also noted. In experiment 3 the rats were injected with different doses of DV, without pretreatment with BSO. The main effect was a drop in blood GSH and haematocrit, and an increase in adrenal and spleen weights, all of which were dose-related. Administration of the higher doses of DV resulted in a severe cyanosis followed by death within a relatively short period of time. 相似文献