全文获取类型
收费全文 | 4006篇 |
免费 | 63篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 14篇 |
综合类 | 4篇 |
化学工业 | 416篇 |
金属工艺 | 52篇 |
机械仪表 | 36篇 |
建筑科学 | 71篇 |
矿业工程 | 5篇 |
能源动力 | 49篇 |
轻工业 | 140篇 |
水利工程 | 19篇 |
石油天然气 | 9篇 |
无线电 | 203篇 |
一般工业技术 | 260篇 |
冶金工业 | 2596篇 |
原子能技术 | 9篇 |
自动化技术 | 187篇 |
出版年
2022年 | 21篇 |
2021年 | 19篇 |
2020年 | 16篇 |
2019年 | 16篇 |
2018年 | 29篇 |
2017年 | 25篇 |
2016年 | 30篇 |
2015年 | 24篇 |
2014年 | 38篇 |
2013年 | 82篇 |
2012年 | 43篇 |
2011年 | 69篇 |
2010年 | 34篇 |
2009年 | 51篇 |
2008年 | 54篇 |
2007年 | 69篇 |
2006年 | 37篇 |
2005年 | 40篇 |
2004年 | 32篇 |
2003年 | 33篇 |
2002年 | 38篇 |
2001年 | 37篇 |
2000年 | 25篇 |
1999年 | 115篇 |
1998年 | 911篇 |
1997年 | 522篇 |
1996年 | 311篇 |
1995年 | 185篇 |
1994年 | 157篇 |
1993年 | 161篇 |
1992年 | 47篇 |
1991年 | 38篇 |
1990年 | 33篇 |
1989年 | 39篇 |
1988年 | 43篇 |
1987年 | 64篇 |
1986年 | 33篇 |
1985年 | 40篇 |
1984年 | 31篇 |
1983年 | 26篇 |
1982年 | 37篇 |
1981年 | 34篇 |
1980年 | 40篇 |
1979年 | 19篇 |
1978年 | 19篇 |
1977年 | 53篇 |
1976年 | 106篇 |
1975年 | 16篇 |
1973年 | 16篇 |
1969年 | 15篇 |
排序方式: 共有4070条查询结果,搜索用时 31 毫秒
1.
Robert Creutznacher Eric Schulze Georg Wallmann Prof. Dr. Thomas Peters Dr. Matthias Stein Dr. Alvaro Mallagaray 《Chembiochem : a European journal of chemical biology》2020,21(7):1007-1021
Bile acids have been reported as important cofactors promoting human and murine norovirus (NoV) infections in cell culture. The underlying mechanisms are not resolved. Through the use of chemical shift perturbation (CSP) NMR experiments, we identified a low-affinity bile acid binding site of a human GII.4 NoV strain. Long-timescale MD simulations reveal the formation of a ligand-accessible binding pocket of flexible shape, allowing the formation of stable viral coat protein–bile acid complexes in agreement with experimental CSP data. CSP NMR experiments also show that this mode of bile acid binding has a minor influence on the binding of histo-blood group antigens and vice versa. STD NMR experiments probing the binding of bile acids to virus-like particles of seven different strains suggest that low-affinity bile acid binding is a common feature of human NoV and should therefore be important for understanding the role of bile acids as cofactors in NoV infection. 相似文献
2.
3.
Development of the new drugs often involves the screening of compound libraries for biological activity. Currently, the biologically active component can only be identified if either a pure compound is being tested or if the components of a mixture are spatially separated, for example, on beads. Here, we present an NMR technique based on the transferred nuclear Overhauser effect (transfer NOE) that allows identification and structural characterization of biologically active molecules from a mixture. As an example we demonstrate that from mixtures of oligosaccharides only alpha-L-Fuc-(1-->6)-beta-D-GlcNAc-OMe binds to Aleuria aurantia agglutinin. The sign of transferred NOEs is opposite to NOEs of small molecules that do not bind to the protein and, thus, an unequivocal identification of molecules with binding activity is possible. Normally, the selection of bound ligands is further facilitated in that the absolute intensity of transfer NOEs is much greater than that of NOEs of non-binding molecules. In addition, transfer NOEs provide information on the three-dimensional structure of the ligands in the bound state. Therefore, measuring transfer NOEs of mixtures of small molecules in the presence of large molecules, like proteins, should significantly enhance the options for screening mixtures of compounds for biological activity. 相似文献
4.
Shamansky H.T. Dominek A.K. Peters L. Jr. 《Antennas and Propagation, IEEE Transactions on》1989,37(8):1019-1025
The traveling-wave energy, which multiply diffracts on a straight thin wire, is represented as a sum of terms, each with a distinct physical meaning, that can be individually examined in the time domain. Expressions for each scattering mechanism on a straight thin wire are cast in the form of four basic electromagnetic wave concepts: diffraction, attachment, launch, and reflection. Using the basic mechanisms from P.Ya. Ufimtsev (1962), each of the scattering mechanisms is included into the total scattered field for the straight thin wire. Scattering as a function of angle and frequency is then compared to the moment-method solution. These analytic expressions are then extended to a lossy wire with a simple approximate modification using the propagation velocity on the wire as derived from the Sommerfeld wave on a straight lossy wire. Both the perfectly conducting and lossy wire solutions are compared to moment-method results, and excellent agreement is found. As is common with asymptotic solutions, when the electrical length of wire is smaller than 0.2 λ the results lose accuracy. The expressions modified to approximate the scattering for the lossy thin wire yield excellent agreement even for lossy wires where the wire radius is on the order of skin depth 相似文献
5.
6.
Self-control is demonstrated when a less desirable immediate outcome is chosen to ensure a substantially better future. In a novel animal analogue of this situation, primary reinforcement was delivered in both the initial and terminal links of a concurrent chain schedule. Rats made initial link choices between equal amounts of ethanol-free or ethanol-containing milk. Choosing the ethanol-free reinforcer resulted in delivery of the larger terminal link reinforcer and was thus analogous to self-control. Self-control decreased as the delay between initial and terminal links increased. The results have implications for human choice situations where decisions are made between two immediately available reinforcement alternatives each associated with a different delayed outcome. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
7.
IMP dehydrogenase (IMPDH) catalyzes the oxidation of IMP to XMP with the concomitant reduction of NAD+; the enzyme is activated by K+. This reaction is the rate-limiting step in de novo guanine nucleotide biosynthesis. In order to identify functionally important residues in IMPDH, including those involved in substrate and K+ binding, we have mutated 11 conserved Asp and Glu residues to Ala in Escherichia coli IMPDH. The values of kcat, Km, and Ki for GMP, XMP, mizoribine 5'-monophosphate (MMP), and beta-methylene-tiazofurin adenine dinucleotide (TAD) were determined. Five of these mutations caused a significant change (>/=10-fold) in one of these parameters. The Asp248 --> Ala mutation caused 100-fold decrease in the value of kcat and a 25-fold increase in the value of Kii for TAD; these observations suggest that Asp248 is in the NAD+ binding site. The Asp338 --> Ala mutation caused a 600-fold decrease in the value of kcat, but only a 5-10-fold increase in the values of Km for IMP and Kis for IMP analogs, suggesting that Asp338 may be involved in acid-base catalysis as well as IMP binding. The remaining three residues, Asp13, Asp50, and Glu469, appear to be involved in K+ activation; these residues may be ligands at one or more K+ binding sites. Interestingly, changes in the values of Ki for MMP correlate with changes in kcat/KmKm of IMPDH, while no such correlation is observed for GMP, XMP, and TAD. This observation indicates that MMP is a transition state analog for the IMPDH reaction. 相似文献
8.
DL Ellies DW Stock G Hatch G Giroux KM Weiss M Ekker 《Canadian Metallurgical Quarterly》1997,45(3):580-590
To understand the relationship between the expression and the genomic organization of the zebrafish dlx genes, we have determined the genomic structure of the dlx2 and dlx4 loci. This led to the identification of the zebrafish dlx1 and dlx6 genes, which are closely linked to dlx2 and dlx4, respectively. Therefore, the inverted convergent configuration of Dlx genes is conserved among vertebrates. Analysis of the expression patterns of dlx1 and dlx6 showed striking similarities to those of dlx2 and dlx4, respectively, the genes to which they are linked. Furthermore, the expression patterns of dlx3 and dlx7, which likely constitute a third pair of convergently transcribed genes, are indistinguishable. Thus, the overlapping expression patterns of linked Dlx genes during embryonic development suggest that they share cis-acting sequences that control their spatiotemporal expression. The evolutionary conservation of the genomic organization and combinatorial expression of Dlx genes in distantly related vertebrates suggest tight control mechanisms that are essential for their function during development. 相似文献
9.
Paraquat (1,1'-dimethyl-4,4'-dipyridylium) is an herbicide associated with both accidental and intentional ingestion, leading to severe and often fatal toxicity. Prognosis is largely dependent on the amount of paraquat absorbed. Rapid identification of the symptoms of paraquat toxicity (burns or ulceration at the site of ingestion or injection, acute respiratory distress, and renal failure) can facilitate early treatment intervention to limit absorption. We report a case of a 71-year-old man with a suicidal ingestion of paraquat 2 days prior to presentation. Serum paraquat levels, time elapsed since ingestion, and clinical symptoms all indicated poor prognosis. The patient developed severe respiratory distress and progressive renal failure, and died 6 days after admission to the hospital. 相似文献
10.
KM Shokat 《Canadian Metallurgical Quarterly》1995,2(8):509-514
Cytoplasmic tyrosine kinases are composed of modular domains; one (SH1) has catalytic activity, the other two (SH2 and SH3) do not. Kinase specificity is largely determined by the binding preferences of the SH2 domain. Attaching the SH1 domain to a new SH2 domain, via protein-protein association or mutation, can thus dramatically change kinase function. 相似文献