全文获取类型
收费全文 | 151901篇 |
免费 | 1888篇 |
国内免费 | 656篇 |
专业分类
电工技术 | 3115篇 |
综合类 | 187篇 |
化学工业 | 24077篇 |
金属工艺 | 5781篇 |
机械仪表 | 4943篇 |
建筑科学 | 4420篇 |
矿业工程 | 377篇 |
能源动力 | 3927篇 |
轻工业 | 17308篇 |
水利工程 | 1140篇 |
石油天然气 | 618篇 |
武器工业 | 5篇 |
无线电 | 20493篇 |
一般工业技术 | 28848篇 |
冶金工业 | 23776篇 |
原子能技术 | 2341篇 |
自动化技术 | 13089篇 |
出版年
2019年 | 834篇 |
2018年 | 1081篇 |
2017年 | 1131篇 |
2016年 | 1268篇 |
2015年 | 1064篇 |
2014年 | 1796篇 |
2013年 | 6578篇 |
2012年 | 3196篇 |
2011年 | 4608篇 |
2010年 | 3597篇 |
2009年 | 4151篇 |
2008年 | 4647篇 |
2007年 | 4913篇 |
2006年 | 4351篇 |
2005年 | 4108篇 |
2004年 | 4002篇 |
2003年 | 3899篇 |
2002年 | 3929篇 |
2001年 | 3981篇 |
2000年 | 3741篇 |
1999年 | 3691篇 |
1998年 | 6634篇 |
1997年 | 5228篇 |
1996年 | 4461篇 |
1995年 | 3711篇 |
1994年 | 3359篇 |
1993年 | 3189篇 |
1992年 | 2783篇 |
1991年 | 2693篇 |
1990年 | 2632篇 |
1989年 | 2616篇 |
1988年 | 2460篇 |
1987年 | 2168篇 |
1986年 | 2115篇 |
1985年 | 2557篇 |
1984年 | 2316篇 |
1983年 | 2196篇 |
1982年 | 2068篇 |
1981年 | 1991篇 |
1980年 | 1860篇 |
1979年 | 1874篇 |
1978年 | 1770篇 |
1977年 | 2086篇 |
1976年 | 2562篇 |
1975年 | 1583篇 |
1974年 | 1431篇 |
1973年 | 1454篇 |
1972年 | 1196篇 |
1971年 | 1115篇 |
1970年 | 948篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
261.
Eight lactating Holstein dairy cows were fed corn silage-based diets with or without whole cottonseed at 18.5% of the dietary dry matter. At 42 days postpartum, a pulse injection of 100 mg glucose/kg body weight was given intravenously and plasma glucose concentration was monitored for 45 min. At 50 d postpartum, biopsies of adipose tissue and mammary tissue were taken and tissue slices were incubated in vitro with either uniform carbon-14 glucose or 1-carbon-14 palmitate. Basal concentration of plasma glucose was not affected by diet, although apparent distribution volume of glucose did seem to decrease due to feeding whole cottonseed. Feeding whole cottonseed decreased uptake of glucose and palmitate in both adipose tissue and mammary tissue and also decreased oxidation of glucose to carbon dioxide in both tissues. Palmitate oxidation was not affected by diet. Incorporation of carbon-14 from glucose into adipose tissue lipids was decreased in cows fed whole cottonseed. Results indicate that fat supplementation in the form of whole cottonseed may decrease palmitate incorporation and glucose utilization for glycerol and reducing equivalent synthesis in both adipose tissue and mammary tissue of lactating dairy cows. 相似文献
262.
Present-day worldwide water problems require new management tools and sustainable system innovations. At Delft University of Technology research is being carried out into water resources and management development aimed at forming such tools and innovations, focused on Integrated River Basin Management (IRBM). One of the case-studies deals with Dutch water management and technology in the context of European IRBM in the form of the 2000 Water Frame Directive. The Netherlands experience many water problems and European IRBM could bring help by offering a framework for both international cooperation and technological innovations. To work as an adequate management tool European IRBM should be tailored to the Dutch water tradition, which recently culminated in Integrated Water Management. Both approaches are in some respects contradicting. Europe pursues, for example, centralized control; while the Dutch have their strongly water boards based decentralized administration. The tensions between both approaches require mutual adaptation, for which the concept of subsidiarity might offer points of departure. This paper describes the first results of the case-research into Dutch water management and technology in the context of Europe as well as the backgrounds and the set-up of the research as a whole. 相似文献
263.
QRS feature extraction using linear prediction 总被引:10,自引:0,他引:10
This communication proposes a method called linear prediction (a high performant technique in digital speech processing) for analyzing digital ECG signals. There are several significant properties indicating that ECG signals have an important feature in the residual error signal obtained after processing by Durbin's linear prediction algorithm. This communication also indicates that the prediction order need not be more than two for fast arrhythmia detection. The ECG signal classification puts an emphasis on the residual error signal. For each ECG's QRS complex, the feature for recognition is obtained from a nonlinear transformation which transforms every residual error signal to a set of three states pulse-code train relative to the original ECG signal. The pulse-code train has the advantage of easy implementation in digital hardware circuits to achieve automated ECG diagnosis. The algorithm performs very well in feature extraction in arrhythmia detection. Using this method, our studies indicate that the PVC (premature ventricular contraction) detection has at least a 92 percent sensitivity for MIT/BIH arrhythmia database. 相似文献
264.
First available appraisals for 67,644 Jersey cows were used to estimate relative magnitudes of additive and selected sources of nonadditive genetic variance and covariance for 13 type traits scored linearly from 50 to 99 points. Covariances among four types of relatives were used to estimate components of genetic variance and covariance for each of the 13 traits. Direct additive, direct dominance, and additive maternal genetic variances and the direct-maternal additive genetic covariance were estimated using covariances among paternal half-sibs, full-sibs, daughters and dams, and maternal half-sibs. Estimates of additive genetic variance were 11 to 36% of variance within herd-appraiser subclasses with largest values for stature, strength, rump angle, rump width, and udder depth. Dominance components were two to four times the magnitude of additive components for dairy character, rump width, fore udder, rear udder height, rear udder width, and suspensory ligament but much smaller for other traits. Maternal effects and the direct-maternal additive genetic covariance appeared small for all linear type traits. 相似文献
265.
266.
Two techniques for the design and fast search of a vector quantiser codebook are proposed. These classify speech data vectors according to (i) the sign and (ii) the slope between successive samples. With both techniques the performance obtained is superior to that obtained from a conventional gain/shape vector quantiser and comparable to that of a full search vector quantiser. A major attraction of both approaches is that they significantly reduce the number of computations required for the codebook search. 相似文献
267.
Blair J.D. Correale A. Jr. Cranford H.C. Dombrowski D.A. Erdelyi C.K. Hoffman C.R. Lamphere J.L. Lang K.W. Lee J.K. Mullen J.M. Norman V.R. Oakland S.F. 《Solid-State Circuits, IEEE Journal of》1989,24(6):1647-1655
The authors describe a 9.02×9.02-mm chip built in 1-μm CMOS with two levels of metal and an additional mask level for fabricating capacitors. It contains both analog and digital circuits and has provisions for self-test. The function includes the transmitter, receiver, protocol handler, an microprocessor, as well as interfaces for RAM/ROM storage, IBM PC bus, IBM PS/2 bus, IBM 3174 bus, and Motorola 68000 bus. The physical design terrains are formed by 24K circuits of standard cell gates, a 10K-circuit equivalent hand-honed custom microprocessor, and an analog macro. The chip operates from a single 5-V supply, and the power consumption is 0.8 W nominal at 16 Mb/s. The chip can also be operated at 4 Mb/s 相似文献
268.
269.
Bilateral control of teleoperators with time delay 总被引:5,自引:0,他引:5
A control law for teleoperators is presented which overcomes the instability caused by time delay. By using passivity and scattering theory, a criterion is developed which shows why existing bilateral control systems are unstable for certain environments, and why the proposed bilateral control law is stable for any environment and any time delay. The control law has been implemented on a single-axis force-reflecting hand controller, and preliminary results are shown. To keep the presentation clear, a single-degree-of-freedom (DOF) linear time-invariant (LTI) teleoperator system is discussed. Nevertheless, results can be extended, without loss of generality, to an n -DOF nonlinear teleoperation system 相似文献
270.
Factors affecting the performance of antacids F-MA 11, dihydroxy aluminum aminoacetate, magaldrate and magnesium hydroxide were studied in vitro using Schaub's acid neutralization test, a modified Reheis reaction velocity test and the USP test. From the results obtained it was evident that type and combination of antacid, the adjuvants and formulation techniques used in preparation of antacids affect their performance. The USP preliminary antacid test and acid neutralization test are not optimal in vitro tests to evaluate in vitro onset and duration of action of antacids. 相似文献