全文获取类型
收费全文 | 2598篇 |
免费 | 77篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 167篇 |
综合类 | 2篇 |
化学工业 | 501篇 |
金属工艺 | 60篇 |
机械仪表 | 45篇 |
建筑科学 | 49篇 |
矿业工程 | 2篇 |
能源动力 | 64篇 |
轻工业 | 254篇 |
水利工程 | 14篇 |
无线电 | 289篇 |
一般工业技术 | 408篇 |
冶金工业 | 561篇 |
原子能技术 | 60篇 |
自动化技术 | 207篇 |
出版年
2023年 | 17篇 |
2022年 | 44篇 |
2021年 | 62篇 |
2020年 | 35篇 |
2019年 | 28篇 |
2018年 | 49篇 |
2017年 | 36篇 |
2016年 | 52篇 |
2015年 | 38篇 |
2014年 | 77篇 |
2013年 | 108篇 |
2012年 | 90篇 |
2011年 | 132篇 |
2010年 | 80篇 |
2009年 | 110篇 |
2008年 | 105篇 |
2007年 | 88篇 |
2006年 | 81篇 |
2005年 | 89篇 |
2004年 | 71篇 |
2003年 | 49篇 |
2002年 | 71篇 |
2001年 | 35篇 |
2000年 | 53篇 |
1999年 | 53篇 |
1998年 | 207篇 |
1997年 | 134篇 |
1996年 | 98篇 |
1995年 | 68篇 |
1994年 | 64篇 |
1993年 | 73篇 |
1992年 | 42篇 |
1991年 | 30篇 |
1990年 | 22篇 |
1989年 | 28篇 |
1988年 | 28篇 |
1987年 | 14篇 |
1986年 | 14篇 |
1985年 | 24篇 |
1984年 | 22篇 |
1983年 | 15篇 |
1982年 | 19篇 |
1981年 | 17篇 |
1980年 | 12篇 |
1979年 | 16篇 |
1978年 | 8篇 |
1977年 | 21篇 |
1976年 | 18篇 |
1975年 | 9篇 |
1967年 | 7篇 |
排序方式: 共有2683条查询结果,搜索用时 15 毫秒
31.
T Hatanaka K Fujita K Ohsumi R Nakagawa Y Fukuda Y Nihei Y Suga Y Akiyama T Tsuji 《Canadian Metallurgical Quarterly》1998,8(23):3371-3374
A series of B-ring modified combretastatin analogues were synthesized and their inhibitory activity against microtubule assembly, cytotoxic activity against Colon 26 adenocarcinoma cancer cell line were evaluated. Among these, pyridone derivative (19) showed strong antimitotic activity and cytotoxicity, along with excellent water-solubility. 相似文献
32.
The microstructure of InxGa1−xAs/GaAs (5 nm/5 nm, x < 0 to 1.0), as grown by a metalorganic chemical vapor deposition two-step growth technique on Si(100)
at 450‡C, and subsequently annealed at 750‡C, is investigated using plan-view and cross-sectional transmission electron microscopy.
The variations in resultant island morphology and strain as a function of the In content were examined through the comparison
of the misfit dislocation arrays and moirés observed. The results are discussed in relation to the ways in which the island
relaxation process changes for high In content. 相似文献
33.
MQ Fujita N Hashida M Shin H Nakanishi W Yoshihara K Aozasa 《Canadian Metallurgical Quarterly》1998,55(6):600-606
Poly(A)+ mRNA was isolated from leaves of potato plants (Solanum tuberosum L. cv. Desiree) according to standard protocols. This poly(A)+ mRNA was injected via glass microcapillaries into oocytes that were surgically removed from the African clawed toad Xenopus laevis. As a control, oocytes were either injected with H2O or remained untreated. Three days after injection the oocytes were analyzed by two electrode voltage clamping. Current voltage analysis revealed that a K+ channel from potato was functionally expressed in injected oocytes. The identity of this K+ channel was confirmed by its substrate specificity and a shift in the reversal potential. In particular, when the outside K+ concentration was increased the reversal potential of poly(A)+ injected oocytes shifted to more positive values. Furthermore, K+ outward currents declined when the outside K+ concentration was raised from 0.1 to 100 mM. Inward currents increased with an elevation of the K+ concentration. Several pharmaceuticals were tested for their potential to block this K+ channel. As a result, the channel was completely blocked by BaCl2. A three state reaction kinetic model was used to simulate the currents through the K+ transport protein as function of the extracellular K+ concentration. In particular, the simulation revealed current voltage relations that exactly matched the measured ones. Saturation of current voltage curves emerged from the simulation as a consequence of high extracellular potassium concentration. 相似文献
34.
OBJECTIVE: To characterize the existence and role of transforming growth factor-beta (TGF-beta) in otitis media with effusion (OME). STUDY DESIGN: Retrospective. METHODS: The levels of two major TGF-beta isoforms, TGF-beta1 and TGF-beta2, in the middle ear effusions (MEEs) of 44 children were evaluated using enzyme-linked immunospecific assays (ELISAs). Forty-eight MEEs were separated into three clinically relevant groups (i.e., serous, mucoid, and purulent), and TGF-beta levels were correlated with clinical parameters of disease for these MEEs. RESULTS: Both TGF-beta1 and TGF-beta2 were present in the samples. Mean levels of TGF-beta1 (920.36 +/- 437.75 pg/mg total protein) were generally 100-fold greater than those of TGF-beta2 (9.65 +/- 11.19 pg/mg total protein). TGF-beta1 levels were elevated in association with a history of previous tympanostomy tube placements (TTPs) (P = .029) and mucoid effusions (P = .042). TGF-beta2 levels were elevated in association with a history of previous TTPs (P = .100) and chronic (i.e., serous or mucoid) effusions (P = .003). CONCLUSIONS: TGF-beta1 is present in the MEEs of children with OME. Furthermore, TGF-beta1 and TGF-beta2 levels were elevated differentially in the presence of chronic disease indicators in OME, suggesting that these isoforms may have differing roles in the inflammatory processes that characterize OME. 相似文献
35.
Eri Chatani Keisuke Yuzu Yumiko Ohhashi Yuji Goto 《International journal of molecular sciences》2021,22(9)
Amyloid fibrils are supramolecular protein assemblies represented by a cross-β structure and fibrous morphology, whose structural architecture has been previously investigated. While amyloid fibrils are basically a main-chain-dominated structure consisting of a backbone of hydrogen bonds, side-chain interactions also play an important role in determining their detailed structures and physicochemical properties. In amyloid fibrils comprising short peptide segments, a steric zipper where a pair of β-sheets with side chains interdigitate tightly is found as a fundamental motif. In amyloid fibrils comprising longer polypeptides, each polypeptide chain folds into a planar structure composed of several β-strands linked by turns or loops, and the steric zippers are formed locally to stabilize the structure. Multiple segments capable of forming steric zippers are contained within a single protein molecule in many cases, and polymorphism appears as a result of the diverse regions and counterparts of the steric zippers. Furthermore, the β-solenoid structure, where the polypeptide chain folds in a solenoid shape with side chains packed inside, is recognized as another important amyloid motif. While side-chain interactions are primarily achieved by non-polar residues in disease-related amyloid fibrils, the participation of hydrophilic and charged residues is prominent in functional amyloids, which often leads to spatiotemporally controlled fibrillation, high reversibility, and the formation of labile amyloids with kinked backbone topology. Achieving precise control of the side-chain interactions within amyloid structures will open up a new horizon for designing useful amyloid-based nanomaterials. 相似文献
36.
Shoji Watanabe Kyoichi Suga Tsutomu Fujita Nobuo Takasaka 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1974,24(11):639-643
Various terpene alcohols were prepared from isoprene oligomers via two steps: epoxidation with peracetic acid and isomerisation with aluminium triisopropoxide. For example, 2-methylene-6-methyl-7-octene-1-o1 was prepared from 2,6-dimethyl-1,7-octadiene. From 2,6-dimethyl-2,7-octadiene, 3,3,6-trimethyl-1,5-heptadiene, 2,7-dimethyl-2,6-octadiene, 2,6-dimethyl-1,3,6-octatriene, 1-methyl-4-isopropenyl-1-cyclohexene, and 1,5-dimethyl-1,5-cyclooctadiene, the corresponding alcohols were obtained, respectively. 相似文献
37.
S. Watanabe T. Fujita M. Sakamoto H. Endo T. Kitazume 《Journal of the American Oil Chemists' Society》1987,64(6):874-875
Monofluoro esters were prepared by the reaction of hydroxy esters with N,N-diethyl-1,1,2,3,3,3-hexafluoro propylamine (PPDA).
Saponification of these monofluoroesters with enzyme (lipase MY) was attempted to give their corresponding monofluorocarboxylic
acids in moderate yields. 相似文献
38.
Selective modification by ozonation for the surface of polyvinyl chloride (PVC) was evaluated to separate PVC from the other plastics, polyethylene terephthalate (PET), polycarbonate (PC) and polymethyl methacrylate (PMMA), with almost the same density as PVC by the froth flotation process. Ozonation could selectively decrease the contact angles of flexible PVC from 87.5 degrees to 68.4 degrees and rigid PVC from 90.3 degrees to 66.9 degrees, whereas little decreases in the contact angle were observed for other plastics. This would be due to the replacement of the chloride group on the surface of PVC, into hydrophilic functional groups; carbonyl, carboxyl and ester group. The PVC was successfully separated from the other plastics by the froth flotation process after the selective surface modification by ozonation. 相似文献
39.
Lithium naphthalene reacts with acetic acid to give α-anion of lithium acetate. The reaction of this anion with various ketones gives the corresponding β-hydroxy-acids in good yield. 相似文献
40.
Prediction of the biologically active sites in eclosion hormone from the silkworm, Bombyx mori 总被引:1,自引:0,他引:1
Kikuchi T; Okamoto M; Geiser M; Schmitz A; Gohda K; Takai M; Morita T; Horii K; Fujita N 《Protein engineering, design & selection : PEDS》1997,10(3):217-222
The structure-activity relationship of eclosion hormone from the silkworm,
Bombyx mori, was analyzed. First, the probable active residues in silkworm
eclosion hormone and also tobacco hornworm eclosion hormone were predicted
by the average distance map method. To examine the contributions of those
residues to the activity of silkworm eclosion hormone, Gly-substituted
mutants for those predicted residues were produced by site-directed
mutagenesis and their activities were evaluated by a bioassay. Finally,
Glu12, Met24 and Phe25 were estimated to be the crucial residues for the
eclosion hormone activity. The possibility of the development of a blocker
of an eclosion hormone receptor on the basis of the present work is also
discussed.
相似文献