全文获取类型
收费全文 | 4609篇 |
免费 | 117篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 124篇 |
综合类 | 8篇 |
化学工业 | 1071篇 |
金属工艺 | 90篇 |
机械仪表 | 96篇 |
建筑科学 | 285篇 |
矿业工程 | 20篇 |
能源动力 | 106篇 |
轻工业 | 478篇 |
水利工程 | 57篇 |
石油天然气 | 8篇 |
无线电 | 321篇 |
一般工业技术 | 597篇 |
冶金工业 | 878篇 |
原子能技术 | 77篇 |
自动化技术 | 516篇 |
出版年
2021年 | 72篇 |
2020年 | 44篇 |
2019年 | 58篇 |
2018年 | 45篇 |
2017年 | 55篇 |
2016年 | 68篇 |
2015年 | 72篇 |
2014年 | 106篇 |
2013年 | 197篇 |
2012年 | 136篇 |
2011年 | 208篇 |
2010年 | 135篇 |
2009年 | 137篇 |
2008年 | 170篇 |
2007年 | 146篇 |
2006年 | 150篇 |
2005年 | 124篇 |
2004年 | 105篇 |
2003年 | 100篇 |
2002年 | 103篇 |
2001年 | 71篇 |
2000年 | 68篇 |
1999年 | 81篇 |
1998年 | 159篇 |
1997年 | 123篇 |
1996年 | 91篇 |
1995年 | 87篇 |
1994年 | 75篇 |
1993年 | 68篇 |
1992年 | 53篇 |
1991年 | 52篇 |
1990年 | 64篇 |
1989年 | 60篇 |
1988年 | 52篇 |
1987年 | 60篇 |
1986年 | 52篇 |
1985年 | 65篇 |
1984年 | 61篇 |
1983年 | 64篇 |
1982年 | 53篇 |
1981年 | 44篇 |
1980年 | 43篇 |
1979年 | 48篇 |
1978年 | 60篇 |
1977年 | 62篇 |
1976年 | 69篇 |
1975年 | 55篇 |
1974年 | 53篇 |
1973年 | 59篇 |
1972年 | 43篇 |
排序方式: 共有4732条查询结果,搜索用时 359 毫秒
21.
We have used proteolysis to examine the environment through which nascent secretory proteins are translocated across the membrane of the endoplasmic reticulum. After solubilization of rough microsomes with detergent, fragments comprised of the approximately 70 carboxyl-terminal amino acids of translocating nascent chains initiated and targeted in vivo were protected from digestion by added proteases. About 40 amino acids of nascent chains were protected from proteolysis by the ribosome; thus, membrane-derived components protect an additional 30 amino acids. Under conditions in which those 30 additional amino acids are protected, only a small set of integral membrane proteins remained associated with the ribosome. These proteins include the Sec61 complex previously identified as the core component of the membrane-bound protein translocation apparatus. These results support the concept of a translocation pore that makes intimate contact with the ribosome and thereby protects nascent chains from proteolytic digestion for an additional, constant length. 相似文献
22.
23.
Structure-activity studies of human tumour necrosis factors 总被引:3,自引:0,他引:3
Van Ostade Xaveer; Tavernier Jan; Fiers Walter 《Protein engineering, design & selection : PEDS》1994,7(1):5-12
The mechanism by which tumour necrosis factors (TNF and lymphotoxin,also called TNFß and TNFß respectively) exerttheir cytotoxic activity on many malignant cells, remains largelyunknown. Furthermore, the broad array of differentiation (geneinduction) and mitogenic activities towards many primary cellsis still a subject of intensive investigation. TNF is an importantmediator in inflammation, immune responses and infection-relatedphenomena and these activities contribute to the severe toxidtyseen when TNF is used as an anticancer agent. The first stepin the mechanism of action is the specific binding of the ligandto its receptors and dissection of the molecular mechanism involvedin this interaction is the subject of this review. The reasonsfor the interest in this aspect are obvious: first, the developmentof strong antagonistic TNF analogues can be useful in dampeningthe potentially lethal or debilitating effects of an overproductionof the cytokine (as in septic shock or rheumatoid arthritis).Secondly, since two distinct TNF receptors exist, constructionof TNF muteins that distinguish between both types may leadto derivatives of this plekrtropic agent with a more restrictedbiological activity pattern. Ideally, one would like to developa TNF mutant that has retained its cytotoxic action on tumourcells without inducing the deleterious systemic toxteity. Suchan optimized TNF molecule could become a potent anticancer agent 相似文献
24.
25.
Johnson-Laird P. N.; Byrne Ruth M. J.; Schaeken Walter 《Canadian Metallurgical Quarterly》1994,101(4):734
D. P. O'Brien et al (see record 1995-08272-001) argue that the mental model theory of propositional reasoning is easy to refute, and they report 3 experiments that they believe falsify the theory. In contrast, L. Bonatti (see record 1995-08253-001) argues that the model theory is too flexible to be falsified. It is shown that the experiments by O'Brien et al do not refute the model theory and that Bonatti's claims are ill founded. Formal rule theories of propositional reasoning have 3 major weaknesses in comparison with the model theory: (1) They have no decision procedure; (2) they lack predictive power, providing no account of several robust phenomena (e.g., erroneous conclusions tend to be consistent with the premises); and (3) as a class of theories, they are difficult to refute experimentally. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
26.
27.
The modulation characteristics of DFB semiconductor lasers have been studied using a transfer matrix method combined with an appropriate rate equation analysis. The model takes into account longitudinal mode spatial hole burning, as well as the nonuniform current injection resulting from the axially varying Fermi voltage, and can be used for the efficient simulation of static, small-signal, and large-signal dynamic properties. The program is applied to the interpretation of experimental data from a strongly coupled InGaAsP/InP DFB laser. The experimental high-frequency properties of this device are well described by the simulations 相似文献
28.
SD Walter SE Birnie LD Marrett SM Taylor D Reynolds J Davies JJ Drake M Hayes 《Canadian Metallurgical Quarterly》1994,84(3):367-376
OBJECTIVES: Our objectives were (1) to describe an analysis of the spatial pattern of cancer incidence in Ontario and (2) to discuss the quality of data in the Ontario Cancer Registry with respect to the accuracy of local cancer rates. METHODS: Cancer incidence rates were calculated for 22 cancer sites in 49 counties of Ontario during 1976 to 1986. Capture-recapture methods were used to estimate completeness of case registration, and completeness of residence information was also assessed. Spatial autocorrelation was used in measuring the geographic pattern of incidence rates. Comparisons were also made between sexes and with earlier data from 1966 to 1975. RESULTS: The quality of the geographic data in the registry appeared good, and corrections for incomplete or inaccurate registration had little impact. About one third of the sex-site combinations showed some evidence of spatial patterning in the cancer rate. Particularly strong regional variation was noted for cancers of the stomach, lung, uterus, and prostate. CONCLUSIONS: The analysis revealed a number of cancers with significant spatial patterning of risk. Further work is needed to relate the cancer data to other information on potential life-style and environmental factors. 相似文献
29.
Arun Chandrasekhar Steven Brebels Serguei Stoukatch Eric Beyne Walter De Raedt Bart Nauwelaers 《Microelectronics Reliability》2003,43(3):351-357
At frequencies beyond 1 GHz, every component of the IC package contributes to the RF performance, whether required or not. In this work, we study the effects of packaging materials namely, the substrate and the globtop/underfill material on RF performance. We have measured interconnects on two area-array CSPs, the ball grid array and the polymer stud grid array using IMEC’s MCM-D technology. The measurements on the package interconnect show that the losses in the package substrate material account for about 50% of the total losses at 1.8 GHz and this drops to less than 20% at 5.2 GHz. The losses due to impedance mismatch dominate the losses especially below 10 GHz and considerable improvement in performance cannot be obtained by using an improved/expensive substrate. The other study is about the influence of globtop/underfill materials on wirebonds (through 3D EM simulations) as well as on standard 50 Ω MCM-D transmission lines (through experiments). While a higher value of dielectric constant of the globtop/underfill material is better on wirebonds, the influence of loss tangent is felt only above values of 0.1. The influence of seven different globtop/undefill materials on 50 Ω transmission lines has been used to extract their dielectric constant and loss tangent values at 30 GHz. These results are very valuable since one can hardly find the properties of globtop/underfill materials beyond 1 GHz. 相似文献
30.
Verbrugge Sara; Dieussaert Kristien; Schaeken Walter; Van Belle William 《Canadian Metallurgical Quarterly》2004,58(2):106
Evidence from reasoning tasks shows that promises and threats both tend to receive biconditional interpretations. They also both display high speaker control. On the face of it, the only difference seems to be the positive or negative signing of the consequent. In a promise, the speaker tries to persuade the hearer to do something by holding out the prospect of a particular reward; in a threat, the speaker tries to refrain the hearer from doing something by holding out the prospect of a particular punishment. This paper investigates the respects in which conditional promises and threats differ further by means of an inference task. The credibility of the consequent was manipulated in order to examine whether the acceptability ratings of inferences based on promises and on threats would be equally affected. The results of the inference task and an analysis of the reasons people give for their answers suggest that the credibility of promises is less affected by the use of excessive consequents than the credibility of threats. In other words, promise remains debt, whereas threat is another matter. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献