全文获取类型
收费全文 | 3380篇 |
免费 | 70篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 190篇 |
综合类 | 8篇 |
化学工业 | 626篇 |
金属工艺 | 45篇 |
机械仪表 | 88篇 |
建筑科学 | 66篇 |
矿业工程 | 4篇 |
能源动力 | 100篇 |
轻工业 | 279篇 |
水利工程 | 9篇 |
石油天然气 | 13篇 |
无线电 | 438篇 |
一般工业技术 | 588篇 |
冶金工业 | 755篇 |
原子能技术 | 64篇 |
自动化技术 | 181篇 |
出版年
2023年 | 13篇 |
2022年 | 35篇 |
2021年 | 54篇 |
2020年 | 21篇 |
2019年 | 38篇 |
2018年 | 39篇 |
2017年 | 55篇 |
2016年 | 47篇 |
2015年 | 35篇 |
2014年 | 56篇 |
2013年 | 130篇 |
2012年 | 114篇 |
2011年 | 109篇 |
2010年 | 117篇 |
2009年 | 102篇 |
2008年 | 127篇 |
2007年 | 106篇 |
2006年 | 103篇 |
2005年 | 98篇 |
2004年 | 98篇 |
2003年 | 109篇 |
2002年 | 91篇 |
2001年 | 82篇 |
2000年 | 56篇 |
1999年 | 85篇 |
1998年 | 322篇 |
1997年 | 193篇 |
1996年 | 137篇 |
1995年 | 111篇 |
1994年 | 83篇 |
1993年 | 73篇 |
1992年 | 58篇 |
1991年 | 37篇 |
1990年 | 36篇 |
1989年 | 41篇 |
1988年 | 43篇 |
1987年 | 32篇 |
1986年 | 42篇 |
1985年 | 36篇 |
1984年 | 31篇 |
1983年 | 37篇 |
1982年 | 25篇 |
1981年 | 25篇 |
1980年 | 23篇 |
1979年 | 24篇 |
1978年 | 16篇 |
1977年 | 30篇 |
1976年 | 40篇 |
1975年 | 10篇 |
1971年 | 5篇 |
排序方式: 共有3454条查询结果,搜索用时 15 毫秒
101.
Takeshi Takahashi Kyosuke Kojima Wei Zhang Kanae Sasaki Masaru Ito Hironori Suzuki Masato Kawasaki Soichi Wakatsuki Terunao Takahara Hideki Shibata Masatoshi Maki 《International journal of molecular sciences》2015,16(2):3677-3699
ALG-2, a 22-kDa penta-EF-hand protein, is involved in cell death, signal transduction, membrane trafficking, etc., by interacting with various proteins in mammalian cells in a Ca2+-dependent manner. Most known ALG-2-interacting proteins contain proline-rich regions in which either PPYPXnYP (type 1 motif) or PXPGF (type 2 motif) is commonly found. Previous X-ray crystal structural analysis of the complex between ALG-2 and an ALIX peptide revealed that the peptide binds to the two hydrophobic pockets. In the present study, we resolved the crystal structure of the complex between ALG-2 and a peptide of Sec31A (outer shell component of coat complex II, COPII; containing the type 2 motif) and found that the peptide binds to the third hydrophobic pocket (Pocket 3). While amino acid substitution of Phe85, a Pocket 3 residue, with Ala abrogated the interaction with Sec31A, it did not affect the interaction with ALIX. On the other hand, amino acid substitution of Tyr180, a Pocket 1 residue, with Ala caused loss of binding to ALIX, but maintained binding to Sec31A. We conclude that ALG-2 recognizes two types of motifs at different hydrophobic surfaces. Furthermore, based on the results of serial mutational analysis of the ALG-2-binding sites in Sec31A, the type 2 motif was newly defined. 相似文献
102.
Kenta Takahashi Naru Shiraishi Risa Ishiko-Uzuka Takahisa Anada Osamu Suzuki Hiroshi Masumoto Keiichi Sasaki 《International journal of molecular sciences》2015,16(3):5779-5788
Dental implants are widely used and are a predictable treatment in various edentulous cases. Occlusal overload may be causally related to implant bone loss and a loss of integration. Stress concentrations may be diminished using a mechanobiologically integrated implant with bone tissue. The purpose of this study was to investigate the biomechanical behavior, biocompatibility and bioactivity of a Ti-Nb-Sn alloy as a dental implant material. It was compared with cpTi. Cell proliferation and alkaline phosphatase (ALP) activity were quantified. To assess the degree of osseointegration, a push-in test was carried out. Cell proliferation and ALP activity in the cells grown on prepared surfaces were similar for the Ti-Nb-Sn alloy and for cpTi in all the experiments. A comparison between the Ti-Nb-Sn alloy implant and the cpTi implant revealed that no significant difference was apparent for the push-in test values. These results suggest that implants fabricated using Ti-Nb-Sn have a similar biological potential as cpTi and are capable of excellent osseointegration. 相似文献
103.
Reaction kinetics and mechanisms of the decomposition of vanadyl etioporphyrin (VO-EP), the most common metal compounds present in heavy crude, were studied in a mixed solvent of supercritical water (SCW) and toluene without the addition of any catalyst, H2 or H2S to remove vanadium. The aim of this study was to remove vanadium an environmentally benign way from VO-EP at a high extent and in a short reaction time. The experiments were conducted in an 8.8 mL batch reactor fabricated from Hastelloy C-276. The capability of SCW to remove vanadium from VO-EP was discovered at temperatures of 410–490 °C and a water partial pressure (WPP) of 25 MPa. Experimental results revealed that the overall VO-EP conversion was 90.51% at a temperature of 490 °C, WPP of 25 MPa and reaction time of 180 min. Under the same reaction conditions, approximately 80.26% vanadium was removed by reaction with SCW. The global reaction followed first order kinetics, with Arrhenius parameters of activation energy 8.93 kcal/mol and a pre-exponential factor 5.66 s?1. A kinetic model of demetallation that well-fit the experimental results, was proposed. The reaction kinetics may be critically explained in terms of free radical mechanism. The obtained results suggest that SCW is capable of removing vanadium from VO-EP. 相似文献
104.
Pengzhan Sun Renzhi Ma Minoru Osada Takayoshi Sasaki Jinquan Wei Kunlin Wang Dehai Wu Yao Cheng Hongwei Zhu 《Carbon》2012,50(12):4518-4523
We report the fabrication of hybrid films of graphene and monolayer titania using a simple electrostatic self-assembly method. Ultraviolet (UV) responses of the hybrid films based on the graphene–titania structure were investigated. We observed that the resistance of the graphene–titania hybrid increased exponentially with UV irradiation time and decreased exponentially when UV was turned off. Time constants of the order of hundreds of seconds were identified and found to be sensitive to the gas environment of graphene. The UV response as well as the time constant is tunable by varying the number of titania layers. Our results confirmed that UV irradiation played a significant role in the resistance modulation of graphene as well as graphene–titania hybrid films. 相似文献
105.
Dr. Eita Sasaki Ryan M. Dragoman Dr. Shiksha Mantri Dr. Dmitry N. Dirin Prof. Dr. Maksym V. Kovalenko Prof. Dr. Donald Hilvert 《Chembiochem : a European journal of chemical biology》2020,21(1-2):74-79
The enzyme lumazine synthase (LS) has been engineered to self-assemble into hollow-shell structures that encapsulate unnatural cargo proteins through complementary electrostatic interactions. Herein, we show that a negatively supercharged LS variant can also form organic–inorganic hybrids with gold nanomaterials. Simple mixing of LS pentamers with positively charged gold nanocrystals in aqueous buffer spontaneously affords protein-shelled gold cores. The procedure works well with differently sized and shaped gold nanocrystals, and the resulting shelled complexes exhibit dramatically enhanced colloidal stability over a wide range of pH (4.0–10.0) and at high ionic strength (up to 1 m NaCl). They are even stable over days upon dilution in buffer. Self-assembly of engineered LS shells in this way offers an easy and attractive alternative to commonly used ligand-exchange methods for stabilizing inorganic nanomaterials. 相似文献
106.
Molecular mechanisms of epigenetic variation in plants 总被引:1,自引:0,他引:1
R Fujimoto T Sasaki R Ishikawa K Osabe T Kawanabe ES Dennis 《International journal of molecular sciences》2012,13(8):9900-9922
Natural variation is defined as the phenotypic variation caused by spontaneous mutations. In general, mutations are associated with changes of nucleotide sequence, and many mutations in genes that can cause changes in plant development have been identified. Epigenetic change, which does not involve alteration to the nucleotide sequence, can also cause changes in gene activity by changing the structure of chromatin through DNA methylation or histone modifications. Now there is evidence based on induced or spontaneous mutants that epigenetic changes can cause altering plant phenotypes. Epigenetic changes have occurred frequently in plants, and some are heritable or metastable causing variation in epigenetic status within or between species. Therefore, heritable epigenetic variation as well as genetic variation has the potential to drive natural variation. 相似文献
107.
Ogawa M Tohma Y Ohgushi H Takakura Y Tanaka Y 《International journal of molecular sciences》2012,13(5):5528-5541
To establish the methods of demonstrating early fixation of metal implants to bone, one side of a Cobalt-Chromium (CoCr) based alloy implant surface was seeded with rabbit marrow mesenchymal cells and the other side was left unseeded. The mesenchymal cells were further cultured in the presence of ascorbic acid, β-glycerophosphate and dexamethasone, resulting in the appearance of osteoblasts and bone matrix on the implant surface. Thus, we succeeded in generating tissue-engineered bone on one side of the CoCr implant. The CoCr implants were then implanted in rabbit bone defects. Three weeks after the implantation, evaluations of mechanical test, undecalcified histological section and electron microscope analysis were performed. Histological and electron microscope images of the tissue engineered surface exhibited abundant new bone formation. However, newly formed bone tissue was difficult to detect on the side without cell seeding. In the mechanical test, the mean values of pull-out forces were 77.15 N and 44.94 N for the tissue-engineered and non-cell-seeded surfaces, respectively. These findings indicate early bone fixation of the tissue-engineered CoCr surface just three weeks after implantation. 相似文献
108.
Versatile functionalization of metal clusters is a key step in understanding the reactivity of protective monolayers. We here demonstrate that reaction of the outermost amino groups on (S)-/(R)-penicillamine-protected gold clusters with ethyl isocyanate readily modifies the chiral surface structure through carbamoylation. Interestingly, the clusters are electrophoretically separated by the size of the surface ligand, not by the size of the gold core, which is revealed by UV-vis, IR, and energy dispersive X-ray (EDX) spectroscopy as well as SAXS measurements. The ligand size (or length) is extended through additional reactions of the carbamoylated amino groups with isocyanate, while the chemical similarity in ligand structures is realized by their IR spectral similarity. Optical and chiroptical responses of the separated cluster compounds are thus overall similar to each other, but a close inspection reveals that the ligand size has a small but distinct influence on the chiroptical response of the gold clusters. 相似文献
109.
Swelling degrees of poly(N-vinyl-2-pyrrolidone) (PVP) gel were measured in aqueous salt solutions and in water/organic solvent mixtures to find marked ion- and solvent-specificities. In order to investigate any correlation of those specificities with hydration or solvation of PVP, IR spectra band of the CO group was monitored by means of ATR method both for PVP gel and the relevant solution systems. Dependence of the peak frequency on the swelling ratio suggested that hydration of PVP carbonyl group in deswollen gel systems is different from that in the corresponding solution systems. In the solution systems, PVP carbonyl band showed a high-wavenumber shift for deswollen systems, which can be well correlated with changes in water proton charge through ionic hydration and with Gutmann's acceptor number of organic solvents. In the deswollen gel systems, the CO band showed a low-wavenumber shift, suggesting a strong hydration or doubly hydrated state. This unexpected behavior was interpreted by assuming an intermolecular hydrogen bond of two carbonyl groups intermediated by water molecules. 相似文献
110.
The recoverable shear strain (SR) for the liquid crystal‐forming hydroxypropyl cellulose solutions was determined by means of a concentric cylinder rotational apparatus as functions of shear stress prior to recovery and concentration of the solutions at 30°C. SR greatly depended on shear stress and concentration; the phase of the solution (the single phase or biphase) governed the dependences of SR on stress and concentration. SR increased with increasing stress for the single phase and decreased for the biphase. SR seemed to be related to the die swell (B): SR ∝ Bn. SR exhibited a maximum and a minimum with respect to concentration. SR for the cellulosic cholesteric liquid crystalline solutions was greater than that for the isotropic solutions. A model was proposed for explaining the greater SR. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 865–872, 2002 相似文献