全文获取类型
收费全文 | 149340篇 |
免费 | 2981篇 |
国内免费 | 2215篇 |
专业分类
电工技术 | 3410篇 |
技术理论 | 2篇 |
综合类 | 1033篇 |
化学工业 | 17737篇 |
金属工艺 | 8182篇 |
机械仪表 | 4945篇 |
建筑科学 | 3593篇 |
矿业工程 | 636篇 |
能源动力 | 4497篇 |
轻工业 | 9035篇 |
水利工程 | 1251篇 |
石油天然气 | 2424篇 |
武器工业 | 143篇 |
无线电 | 20638篇 |
一般工业技术 | 31240篇 |
冶金工业 | 32344篇 |
原子能技术 | 2148篇 |
自动化技术 | 11278篇 |
出版年
2022年 | 1061篇 |
2021年 | 1489篇 |
2020年 | 1155篇 |
2019年 | 1289篇 |
2018年 | 1995篇 |
2017年 | 2047篇 |
2016年 | 2169篇 |
2015年 | 1810篇 |
2014年 | 2718篇 |
2013年 | 7225篇 |
2012年 | 4401篇 |
2011年 | 6010篇 |
2010年 | 4985篇 |
2009年 | 5767篇 |
2008年 | 5732篇 |
2007年 | 6013篇 |
2006年 | 5268篇 |
2005年 | 4717篇 |
2004年 | 4478篇 |
2003年 | 4218篇 |
2002年 | 3965篇 |
2001年 | 4236篇 |
2000年 | 3752篇 |
1999年 | 4106篇 |
1998年 | 11425篇 |
1997年 | 7685篇 |
1996年 | 6089篇 |
1995年 | 4102篇 |
1994年 | 3520篇 |
1993年 | 3463篇 |
1992年 | 2191篇 |
1991年 | 2136篇 |
1990年 | 2019篇 |
1989年 | 1788篇 |
1988年 | 1532篇 |
1987年 | 1259篇 |
1986年 | 1239篇 |
1985年 | 1276篇 |
1984年 | 1097篇 |
1983年 | 986篇 |
1982年 | 995篇 |
1981年 | 972篇 |
1980年 | 914篇 |
1979年 | 810篇 |
1978年 | 701篇 |
1977年 | 940篇 |
1976年 | 1578篇 |
1975年 | 607篇 |
1974年 | 562篇 |
1973年 | 567篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
51.
A survey of the state of SQA in Japan finds that the situation is much like, but slightly different than, that in the US. 相似文献
52.
We introduce a new probabilistic approach to dealing with uncertainty, based on the observation that probability theory does not require that every event be assigned a probability. For a nonmeasurable event (one to which we do not assign a probability), we can talk about only the inner measure and outer measure of the event. In addition to removing the requirement that every event be assigned a probability, our approach circumvents other criticisms of probability-based approaches to uncertainty. For example, the measure of belief in an event turns out to be represented by an interval (defined by the inner and outer measures), rather than by a single number. Further, this approach allows us to assign a belief (inner measure) to an event E without committing to a belief about its negation -E (since the inner measure of an event plus the inner measure of its negation is not necessarily one). Interestingly enough, inner measures induced by probability measures turn out to correspond in a precise sense to Dempster-Shafer belief functions. Hence, in addition to providing promising new conceptual tools for dealing with uncertainty, our approach shows that a key part of the important Dempster-Shafer theory of evidence is firmly rooted in classical probability theory. Cet article présente une nouvelle approche probabiliste en ce qui concerne le traitement de l'incertitude; celle-ci est basée sur l'observation que la théorie des probabilityés n'exige pas qu'une probabilityé soit assignée à chaque événement. Dans le cas d'un événement non mesurable (un événement pour lequel on n'assigne aucune probabilityé), nous ne pouvons discuter que de la mesure intérieure et de la mesure extérieure de l'évenément. En plus d'éliminer la nécessité d'assigner une probabilityéà l'événement, cette nouvelle approche apporte une réponse aux autres critiques des approches à l'incertitude basées sur des probabilityés. Par exemple, la mesure de croyance dans un événement est représentée par un intervalle (défini par la mesure intérieure et extérieure) plutǒt que par un nombre unique. De plus, cette approche nous permet d'assigner une croyance (mesure intérieure) à un événement E sans se compromettre vers une croyance à propos de sa négation -E (puisque la mesure intérieure d'un événement et la mesure intérieure de sa négation ne sont pas nécessairement une seule et unique mesure). II est intéressant de noter que les mesures intérieures qui résultent des mesures de probabilityé correspondent d'une manière précise aux fonctions de croyance de Dempster-Shafer. En plus de constituer un nouvel outil conceptuel prometteur dans le traitement de l'incertitude, cette approche démontre qu'une partie importante de la théorie de l'évidence de Dempster-Shafer est fermement ancrée dans la theorie classique des probabilityés. 相似文献
53.
Sverak J.G. Wang W. Gervais Y. Do X.-D. Mukhedkar D. 《Power Delivery, IEEE Transactions on》1992,7(3):1196-1206
An improved multivariable, probabilistic method for the safety analysis of power grounding systems is presented. The application of this method is demonstrated in four examples. The first three examples illustrate the practical evaluation of one new and two existing substation grounding grids when the substation is connected to an overhead distribution system. The fourth example ascertains the relative impact of a difference between the S curve of IEC Publication 479 and Dalziel's equation for the allowable body current used in ANSI/IEEE Std 80-1986 on the validity of an exposure model based on the requirements of Std 80. In this example, the statistical data on ground faults have been taken from actual system records. Further possible refinements of the exposure model are discussed 相似文献
54.
55.
Time variation of drinking is substantial and has an effect on aggregate estimates of consumption. In this article it is shown that because of a considerable seasonal variation in consumption (+/- 20%) a serious bias in annual consumption estimates can be expected in surveys with a limited time frame. The present study analyzes drinking data collected in the general population of the Netherlands from March 1985 through December 1985 (including Christmas and New Year's Eve). Since it was expected that sensitivity to temporal fluctuations might not be equal for different methods of measurement, several indices of consumption were compared. Although the assessed seasonal effect varies indeed across types of measurement, across male and female subsample and across types of alcoholic beverage, the general tendency is for consumption to be highest in the spring season and lowest in the autumn. Sales figures fluctuate accordingly. It is evident that the risk of biased estimates is larger the shorter the time frame of the survey. Seasonal variation was highest in the frequency domain. Furthermore, exclusion from the time frame of collective holidays, during which people drink more often and more per occasion (viz., Christmas), increases the risk of biased estimates. Even estimates of abstention, but also regular heavy drinking among women, appear to vary considerably over the three seasons in this study. The main conclusion is that results of comparisons of survey data on drinking, particularly those over time, are more or less invalid if the respective time frames of the surveys do not correspond. 相似文献
56.
Mastrapasqua M. Luryi S. Belenky G.L. Garbinski P.A. Cho A.Y. Sivco D.L. 《Electron Devices, IEEE Transactions on》1993,40(8):1371-1377
A monolithic multiterminal logic device that functions both optically and electrically as an ORNAND gate, is demonstrated for the first time. The device, based on the real-space transfer of hot electrons into a complementary collector layer, has been implemented in an InGaAs/InAlAs/InGaAs heterostructure grown by molecular beam epitaxy. Excellent performance is obtained at room temperature. The collector current and the optical output power both exhibit the OR and the NAND functions of any two of the three input terminals, these functions being interchangeable by the voltage on the third terminal 相似文献
57.
In this study, an aluminum based metallic matrix (Al-2wt.% Cu) was reinforced with SiC particulates using a conventional casting technique and a new disintegrated melt deposition technique. Microstructural characterization studies conducted on the samples taken from disintegrated melt deposition technique revealed a more uniform distribution of SiC particulates and good interfacial integrity between SiC particulates and metallic matrix when compared to the conventionally cast composite samples. Results of ambient temperature mechanical tests demonstrate an increase in 0.2% YS and ultimate tensile strength of samples taken from disintegrated melt deposition technique when compared with the unreinforced and conventionally cast composite samples. The results of microstructural characterization and mechanical testing were finally rationalized in terms of the nature of processing technique employed to reinforce Al-2wt.% Cu metallic matrix with SiC particulates. 相似文献
58.
Pharmacodynamic Comparison of a Nasal Formulation of Verapamil and Intravenous and Oral Dosage Forms
The nasal route has been shown to be effective for the administration of numerous drugs in order to improve drug bioavailability. A nasal gel of verapamil hydrochloride was formulated and evaluated pharmacodynamically in humans, using electrocardiographic results, with comparison to oral and IV routes. Seven volunteers were involved in the study and the pharmacodynamic parameters were evaluated statistically. Experimental nasal gel showed similar pharmacodynamic results with the intravenous route, which is a hint to the reduction in verapamilinduced first-pass metabolism. However, oral route of administration showed a tendency of less efficacy. No reasonable effect of verapamil could be obtained with the placebo group. 相似文献
59.
Tsukude M. Arimoto K. Hidaka H. Konishi Y. Hayashikoshi M. Suma K. Fujishima K. 《Design & Test of Computers, IEEE》1993,10(2):6-12
Two testing techniques for ultra-large-scale integrated (ULSI) memories containing on-chip voltage downconverters (VDCs) are described. The first in an on-chip VDC tuning technique that adjusts internal VCC to compensate for the monitored characteristics of the process parameters during repair analysis testing. The second is an operating-voltage margin test, performed at various internal VCC levels during the water sort test (WT) and the final shipping test (FT) 相似文献
60.
The normal prostate is, structurally and functionally, a highly complex glandular tissue in which populations of epithelial and stromal cells interact, one with the other, and are under a constant state of proliferation, differentiation, elimination and selective secondary replenishment so that functional integrity of the tissue is maintained. The ability of normal prostatic tissue to maintain its structure and function is dependent upon retention of cells, generally regarded as 'stem cells', which are able to respond by proliferation and selective differentiation within a wide range of phenotypic alternatives. With respect to cells in the epithelial compartment, replenishment is possible at several levels from within distinct pathways of normal cellular differentiation. It is now appreciated that fully differentiated prostatic epithelial cells retain a far greater degree of phenotypic 'plasticity' than was earlier apparent from morphological examination of the intact tissue. This inherent plasticity, coupled with the ability of the intact tissue to respond to diverse environmental (particularly humoral) stimuli by regenerating a wide and divergent spectrum of functional prostatic epithelial phenotypes is its strength--but also its weakness. Disturbance and distortion of the homeostatic regulatory mechanisms, whether physical or humoral, which control the normal sequence of epithelial proliferation, differentiation and elimination exposes these cells, particularly multipotent 'stem cells', to an increased probability of genetic change, thus resulting in either transient, or permanent, neoplastic transformation. 相似文献