全文获取类型
收费全文 | 873篇 |
免费 | 35篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 5篇 |
综合类 | 2篇 |
化学工业 | 137篇 |
金属工艺 | 33篇 |
机械仪表 | 34篇 |
建筑科学 | 33篇 |
矿业工程 | 3篇 |
能源动力 | 22篇 |
轻工业 | 73篇 |
水利工程 | 7篇 |
石油天然气 | 7篇 |
无线电 | 62篇 |
一般工业技术 | 135篇 |
冶金工业 | 267篇 |
原子能技术 | 26篇 |
自动化技术 | 67篇 |
出版年
2022年 | 14篇 |
2021年 | 7篇 |
2020年 | 9篇 |
2019年 | 10篇 |
2018年 | 17篇 |
2017年 | 19篇 |
2016年 | 12篇 |
2015年 | 15篇 |
2014年 | 21篇 |
2013年 | 59篇 |
2012年 | 26篇 |
2011年 | 31篇 |
2010年 | 21篇 |
2009年 | 27篇 |
2008年 | 35篇 |
2007年 | 27篇 |
2006年 | 32篇 |
2005年 | 21篇 |
2004年 | 23篇 |
2003年 | 20篇 |
2002年 | 20篇 |
2001年 | 16篇 |
2000年 | 17篇 |
1999年 | 16篇 |
1998年 | 35篇 |
1997年 | 21篇 |
1996年 | 17篇 |
1995年 | 15篇 |
1992年 | 7篇 |
1990年 | 7篇 |
1989年 | 14篇 |
1988年 | 10篇 |
1987年 | 13篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1984年 | 15篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 12篇 |
1979年 | 12篇 |
1977年 | 12篇 |
1976年 | 11篇 |
1975年 | 9篇 |
1974年 | 14篇 |
1973年 | 10篇 |
1972年 | 10篇 |
1971年 | 8篇 |
1964年 | 8篇 |
1956年 | 6篇 |
1955年 | 7篇 |
排序方式: 共有913条查询结果,搜索用时 15 毫秒
91.
过去两年来,消费品市场的供应链出现一系列深刻的结构调整.无线芯片供应商面临一个关键问题:哪些公司将成为蠢笨的巨人,哪些公司能够灵巧地适应新环境并生存下来? 相似文献
92.
Presents an obituary for Joseph B. Margolin. In the 1940s, Margolin was in the U.S. Army Signal Corps. During that period, he was stationed at an Army hospital in California, and it was there that he developed an interest in clinical psychology. After being discharged, he returned to New York, where he received his doctorate in clinical and social psychology from New York University in 1954. He was always interested in combining his clinical activities with professional and political involvement, and held several positions including president of the District of Columbia Psychological Association, chair of the Maryland Board of Examiners for Psychologists, and staff member of the 1960 White House Conference on Children and Youth. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
93.
We have constructed a human osteogenic sarcoma cell line, U-2 OS/GFP-Gu, that expresses nucleolar RNA helicase RH-II/Gu tagged with green fluorescent protein (GFP). The presence of a GFP tag does not inhibit RNA helicase, RNA folding and ATPase activities of RH-II/Gu protein. The derived cell line responds to cytotoxic agents like the parental cell line U-2 OS. In the presence of either actinomycin D or toyocamycin, the GFP-RH-II/Gu fusion protein translocates from the nucleolus to the nucleoplasm in the same way as the translocation of endogenous RH-II/Gu. The drug-induced translocation of GFP-RH-II/Gu is easily monitored by direct observation of live cells in vivo. This cell line can be used to screen cytotoxic drugs and to study the mechanisms of drug-induced translocation of RH-II/Gu. The cellular localization of RH-II/Gu during the cell cycle-dependent formation of the nucleolus is readily monitored. Real-time results are obtained more quickly without the disadvantages associated with cell fixation and immunofluorescence-based staining. 相似文献
94.
The NIb protein of tobacco etch potyvirus (TEV) possesses several functions, including RNA-dependent RNA polymerase and nuclear translocation activities. Using a reporter protein fusion strategy, NIb was shown to contain two independent nuclear localization signals (NLS I and NLS II). NLS I was mapped to a sequence within amino acid residues 1 to 17, and NLS II was identified between residues 292 and 316. Clustered point mutations resulting in substitutions of basic residues within the NLSs were shown previously to disrupt nuclear translocation activity. These mutations also abolished TEV RNA amplification when introduced into the viral genome. The amplification defects caused by each NLS mutation were complemented in trans within transgenic cells expressing functional NIb, although the level of complementation detected for each mutant differed significantly. Combined with previous results (X. H. Li and J. C. Carrington, Proc. Natl. Acad. Sci. USA 92:457-461, 1995), these data suggest that the NLSs overlap with essential regions necessary for NIb trans-active function(s). The fact that NIb functions in trans implies that it must interact with one or more other components of the genome replication apparatus. A yeast two-hybrid system was used to investigate physical interactions between NIb and several other TEV replication proteins, including the multifunctional VPg/proteinase NIa and the RNA helicase CI. A specific interaction was detected between NIa and NIb. Deletion of any of five regions spanning the NIb sequence resulted in NIb variants that were unable to interact with NIa. Clustered point mutations affecting the conserved GDD motif or NLS II within the central region of NIb, but not mutations affecting NLS I near the N terminus, reduced or eliminated the interaction. The C-terminal proteinase (Pro) domain of NIa, but not the N-terminal VPg domain, interacted with NIb. The effects of NIb mutations within NLS I, NLS II, and the GDD motif on the interaction between the Pro domain and NIb were identical to the effects of these mutations on the interaction between full-length NIa and NIb. These data are compatible with a model in which NIb is directed to replication complexes through an interaction with the Pro domain of NIa. 相似文献
95.
An adaptive nulling algorithm for adjusting the array weights under the soft constraint of the weight norm being very much less than 1 or equal to 1, based on the measured correlations between the array and element outputs, is described. The algorithm can be regarded as an extension of the constrained least-mean-square algorithm. It is derived from the same concept of signal and noise subspaces defined in the multiple signal classification (MUSIC) algorithm. One of the unique features of the present algorithm is that the number of the iterations required to adapt the array weights to form nulls is exactly equal to the number of interferers 相似文献
96.
1 . INTRODUCTIONHigh speedliquidjetsareoftenseeninrainerosionsimulationofaircraftandmissiles ,JilbertandField[1] and jetcuttingofmaterials ,Kob ayashi[2 ] .Inthegenerationofjets ,itistechnicallyinterestingtoknowhowtooperatetheexperimen talfacilityattheoptimumconditiontoobtainthejetvelocitymostefficiently .ThisisdescribedbyShiandTakayama[3] ,ShiandItoh[4 ] ,ShiandIt oh[5] .Intheearlieststudyofa pulsedhigh speedliquidjet ,BowdenandBrunton[6 ] puttheliquidinanozzleandthenusedaslugimpact… 相似文献
97.
Replicated R. E. Carlson's (see record 1971-21928-001) study of the effects of favorability, order, and type of information on interviewers' decisions. Raters were 80 psychology students in introductory and upper-level courses. Results showed that unfavorable information was more important to interviewers' ratings than favorable information. However, this effect was moderated by the expected typical applicant-an applicant of high caliber leading to a more favorable 1st impression of unfavorable information. Unfavorable information showed contrast effects moderated by the type of information. Interviewers' confidence in evaluations was greater for favorable than for unfavorable information. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
98.
A hybrid-mode model is developed which allows analytical calculation of the leaky-mode loss coefficient in Ti-diffused LiNbO3 waveguides. Field representations correspond to the approximation of geometrical optics. Hybrid-mode effective indexes are approximated utilizing the known anisotropy of LiNbO3 . ForX - orY -cut waveguides the leaky mode is shown to be an extraordinary-like hybrid mode with a small ordinary field component which arises from extraordinary to ordinary power conversion at the abrupt index boundary. This ordinary index component is not bound by the graded index boundary, giving rise to the power loss. The theoretical dependence of the loss coefficient on propagation direction is in agreement with experiment. 相似文献
99.
100.
JL You SC Milton RC Milton NS Rangaraju RB Harris 《Canadian Metallurgical Quarterly》1993,12(2):133-141
Homogeneous pre-pro-GnRH/GAP protein was recently synthesized in 100 mg quantities by solid-phase methods and surprisingly, the synthetic pre-pro-protein, which normally does not escape the endoplasmic reticulum, was found to inhibit the release of prolactin from cultured pituitary cells. This is the first demonstration of significant biological activity associated with a precursor protein and provides the rationale for its further study. We now report the results of our initial examination of the conformational properties of pre-pro-GnRH/GAP protein as a prelude to solving its solution phase conformation by homonuclear 1H-NMR protocols. Thermal and pH titration fluorescence and circular dichroism spectroscopies reveal that the protein is resistant to thermal-induced conformational changes but is particularly sensitive to pH-induced conformational changes; while Asp/Glu and Arg residues may contribute to structural stability, His and Lys residues predominate. Pre-pro-GnRH/GAP is about 30% helix in the range of 2-40 degrees C; however, even at 90 degrees C, the peptide retains nearly 50% of its helix character. There is no evidence for a cooperative transition; for this reason, differential scanning calorimetry failed to yield a defined transition thermogram. Pre-pro-GnRH/GAP apparently does not pass through a transition state as a function of temperature but appears to flex and retain a high percentage of helix structure, resulting in subtle changes in secondary structure. There is no discernible isodichroic point. On either side of the neutral pH range, however, there are dramatic changes in structure that result in nonreversible denaturation of the protein.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献