全文获取类型
收费全文 | 2129篇 |
免费 | 47篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 91篇 |
综合类 | 5篇 |
化学工业 | 430篇 |
金属工艺 | 58篇 |
机械仪表 | 36篇 |
建筑科学 | 25篇 |
能源动力 | 72篇 |
轻工业 | 199篇 |
水利工程 | 7篇 |
石油天然气 | 12篇 |
无线电 | 218篇 |
一般工业技术 | 373篇 |
冶金工业 | 468篇 |
原子能技术 | 58篇 |
自动化技术 | 126篇 |
出版年
2023年 | 10篇 |
2022年 | 39篇 |
2021年 | 45篇 |
2020年 | 19篇 |
2019年 | 28篇 |
2018年 | 28篇 |
2017年 | 31篇 |
2016年 | 49篇 |
2015年 | 31篇 |
2014年 | 38篇 |
2013年 | 85篇 |
2012年 | 63篇 |
2011年 | 121篇 |
2010年 | 75篇 |
2009年 | 83篇 |
2008年 | 91篇 |
2007年 | 94篇 |
2006年 | 40篇 |
2005年 | 48篇 |
2004年 | 55篇 |
2003年 | 47篇 |
2002年 | 39篇 |
2001年 | 37篇 |
2000年 | 43篇 |
1999年 | 38篇 |
1998年 | 152篇 |
1997年 | 124篇 |
1996年 | 97篇 |
1995年 | 49篇 |
1994年 | 50篇 |
1993年 | 44篇 |
1992年 | 28篇 |
1991年 | 27篇 |
1990年 | 21篇 |
1989年 | 31篇 |
1988年 | 12篇 |
1987年 | 24篇 |
1986年 | 27篇 |
1985年 | 15篇 |
1984年 | 26篇 |
1983年 | 21篇 |
1982年 | 18篇 |
1981年 | 14篇 |
1980年 | 18篇 |
1979年 | 20篇 |
1978年 | 11篇 |
1977年 | 26篇 |
1976年 | 26篇 |
1975年 | 5篇 |
1974年 | 6篇 |
排序方式: 共有2178条查询结果,搜索用时 15 毫秒
91.
The extraction equilibria of In3+, Ga3, and Zn2+ with bis(4‐ethylcyclohexyl)phosphoric acid (D4ECHPA), bis(4‐cyclohexylcyclohexyl)phosphoric acid (D4DCHPA), and bis(2‐ethylhexyl)phosphoric acid (D2EHPA) were investigated in acidic aqueous sulfate media. The order of extractability of metal ions is D4DCHPA > D2EHPA > D4ECHPA, which corresponds to the lipophilicity (log P) of the extractants. The separation factors, β(In/Ga) and β(Ga/Zn), of D4ECHPA and D4DCHPA are greater or comparable than that of D2EHPA, because of the steric hindrance of the bulky cyclohexyl groups. In3+ can be therefore separated from simulated liquor containing a high concentration of Zn2+ by D4DCHPA. 相似文献
92.
93.
Angiogenesis is an important process for tumor growth and progression of various solid tumors including urological cancers. Thrombospondins (TSPs), especially TSP-1, are representative “anti”-angiogenic molecules and many studies have clarified their pathological role and clinical significance in vivo and in vitro. In fact, TSP-1 expression is associated with clinicopathological features and prognosis in many types of cancers. However, TSP-1 is a multi-functional protein and its biological activities vary according to the specific tumor environments. Consequently, there is no general agreement on its cancer-related function in urological cancers, and detailed information regarding regulative mechanisms is essential for a better understanding of its therapeutic effects and prognostic values. Various “suppressor genes” and “oncogenes” are known to be regulators and TSP-1-related factors under physiological and pathological conditions. In addition, various types of fragments derived from TSP-1 exist in a given tissue microenvironment and TSP-1 derived-peptides have specific activities. However, a detailed pathological function in human cancer tissues is not still understood. This review will focus on the pathological roles and clinical significance of TSP-1 in urological cancers, including prostate cancer, renal cell carcinoma, and urothelial cancer. In addition, special attention is paid to TSP-1-derived peptide and TSP-1-based therapy for malignancies. 相似文献
94.
Isao Kagomiya Shinji Matsumoto Ken-ichi Kakimoto Hitoshi Ohsato Hiroshi Sakai Yukinori Maeda 《Journal of the European Ceramic Society》2013,33(5):985-990
We investigated annealing effects of La1?xSrxMnO3 (x = 0–0.6) on electrical resistivity and the temperature coefficient of resistivity (TCR). The annealed samples’ resistivity was lower than those of non-annealed samples. For example, annealing changed the resistivity of x = 0.3 at 25 °C from 4.50 × 10?5 to 3.71 × 10?5 Ω m. Remarkable difference in TCR was observed after annealing, for x = 0.3, 0.45, and 0.5. For x = 0.3, the TCR after annealing was 4000 ppm/°C, which was 1250 ppm/°C greater than that before annealing. We investigated (1) crystal phase, (2) Mn average valence, (3) Mott insulator–metal transition temperature, and (4) microstructure. The microstructure was remarkably varied for annealed x = 0.3 and 0.5. The average grain size of the x = 0.3 increased from 1.60 up to 2.38 μm. Results show that annealing affects resistivity and TCR because of grain growth during annealing. 相似文献
95.
Production of hyaluronic‐acid‐based cell‐enclosing microparticles and microcapsules via enzymatic reaction using a microfluidic system 下载免费PDF全文
This article describes the preparation of cell‐enclosing hyaluronic acid (HA) microparticles with solid core and microcapsules with liquid core through cell‐friendly horseradish peroxidase (HRP)‐catalyzed hydrogelation. The spherical vehicles were made from HA derivative possessing phenolic hydroxyl moieties (HA‐Ph) cross‐linkable through the enzymatic reaction by extruding cell‐suspending HA‐Ph aqueous solution containing HRP from a needle of 180 μm in inner diameter into the ambient coaxial flow of liquid paraffin containing H2O2 in a microtubule of 600 μm in diameter. By altering the flow rate of liquid paraffin, the diameters of gelatin and HA‐Ph microparticles were varied in the range of 120–220 μm and 100–300 μm, respectively. The viability of the enclosed human hepatoma HepG2 cells in the HA‐Ph microparticles of 180 μm in diameter was 94.2 ± 2.3%. The growth of the enclosed HepG2 cells was enhanced by decreasing the HRP concentration. The microcapsules of 200 μm in diameter were obtained by extruding HA‐Ph aqueous solution containing thermally liquefiable cell‐enclosing gelatin microparticles of 150 μm in diameter using the same microfluidic system. The enclosed cells grew and filled the cavity within 10 days. Spherical tissues covered with a heterogeneous cell layer were obtained by degrading the microcapsule membrane using hyaluronidase after covering the surface with a heterogeneous cell layer. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43107. 相似文献
96.
Yosuke Sumida Sachio Iwai Yoshiaki Nishiya Shinya Kumagai Toshihide Yamada Masayuki Azuma 《Advanced Synthesis \u0026amp; Catalysis》2016,358(13):2041-2046
Chiral amino acids are important intermediates for the pharmaceutical industry. We have developed a novel one‐pot enzymatic method for D ‐amino acid synthesis by the dynamic kinetic resolution of N‐succinyl‐dl ‐amino acids using D ‐succinylase (DSA) and N‐succinylamino acid racemase (NSAR, EC 4.2.1.113). The DSA from Cupriavidus sp. P4‐10‐C, which hydrolyzes N‐succinyl‐D ‐amino acids enantioselectively to their corresponding D ‐amino acids, was identified for the first time by screening soil microorganisms. Subsequently, the DSA gene was cloned and overexpressed in Escherichia coli. DSA was shown to comprise two subunits with molecular masses of 26 kDa and 60 kDa. Additionally, the NSAR gene from Geobacillus stearothermphilus NCA1503, which racemizes N‐succinylamino acids, was also cloned and overexpressed in E. coli. The highly purified DSA and NSAR prepared from each recombinant E. coli were characterized and used for D ‐amino acid synthesis. A one‐pot enzymatic method converted 100 mM N‐succinyl‐dl ‐phenylalanine to D ‐phenylalanine in 91.1% conversion with 86.7% ee. This novel enzymatic method may be useful for the industrial production of many D ‐amino acids.
97.
Phenolic resin‐crosslinked natural rubber/clay nanocomposites: Influence of clay loading and interfacial adhesion on strain‐induced crystallization behavior 下载免费PDF全文
Abdulhakim Masa Ryota Saito Hiromu Saito Tadamoto Sakai Azizon Kaesaman Natinee Lopattananon 《应用聚合物科学杂志》2016,133(12)
Nanocomposites of natural rubber (NR) and pristine clay (clay) were prepared by latex mixing, then crosslinked with phenolic resin (PhOH). For comparative study, the PhOH‐crosslinked neat NR was also prepared. Influence of clay loading (i.e., 1, 3, 5, and 10 phr) on mechanical properties and structural change of PhOH‐crosslinked NR/clay nanocomposites was studied through X‐ray diffraction (XRD), transmission electron microscopic (TEM), wide‐angle X‐ray diffraction (WAXD), tensile property measurement, and Fourier transform infrared spectroscopy (FTIR). XRD and TEM showed that the clay was partly intercalated and aggregated, and that the dispersion state of clay was non‐uniform at higher clay loading (>5 phr). From tensile test measurement, it was found that the pronounced upturn of tensile stress was observed when the clay loading was increased and a maximum tensile strength of the PhOH‐crosslinked NR/clay nanocomposites was obtained at 5 phr clay. WAXD observations showed that an increased addition of clay induced more orientation and alignment of NR chains, thereby lowering onset strain of strain‐induced crystallization and promoting crystallinity of the NR matrix during tensile deformation. FTIR investigation indicated a strong interfacial adhesion between NR matrix and clay filler through a phenolic resin bridge. This suggested that the PhOH did not only act as curative agent for crosslinking of NR, but it also worked as coupling agent for promoting interfacial reaction between NR and clay. The presence of strong interfacial adhesion was found to play an important role in the crystallization process, leading to promotion of mechanical properties of the PhOH‐crosslinked NR/clay nanocomposites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43214. 相似文献
98.
Numerical Evaluation of Toughening by Crack-Face Grain Interlocking in Self-Reinforced Ceramics 总被引:1,自引:0,他引:1
Serguei Kovalev Tatsuya Miyajima Yukihiko Yamauchi Mototsugu Sakai 《Journal of the American Ceramic Society》2000,83(4):817-824
Crack bridging associated with the pull-out process of interlocking grains in self-reinforced ceramic materials is studied through a micromechanical simulation. The pullout of a single inclined grain is modeled via the numerical solution of a general contact problem. The bridging-force versus crack-opening-distance curve indicates a nonlinear, springlike response for the pullout of interlocking grains. The sliding friction along the debonded interface, induced by highly localized contact stresses, dominates the total bridging force. The bridging force increases with grain inclination until eventual bridge failure. The pullout of misaligned grains mainly affects short-crack toughening, with a rising R -curve, whereas aligned grains contribute to long-crack toughening. The residual stresses of the thermal expansion anisotropy play a minor role in the pull-out process of grain interlocking and the resultant toughening. The proposed mechanism is operative in both single-phase and composite ceramics in which pullout of elongated grains/reinforcements occurs. 相似文献
99.
The sorption behavior of CO2 gas in photocrosslinked poly(vinyl cinnamate) film was examined under atmospheric pressure. The sorption isotherm was well described by the Langmuir equation, suggesting that sorption of CO2 is mainly governed by adsorption in the microvoids. The amount of sorbed CO2 was significantly affected by the degree of crosslinking. The CO2 sorption was enhanced at a lower degree of crosslinking but was decreased at a higher degree of crosslinking. The unexpected increase in the amount of adsorbed CO2 correlated with the increase in the number of microvoids that occurred as a result of the crosslinking reaction. However, further crosslinking led to a decrease in the mean size of the microvoids. The smaller microvoids, in comparison to CO2 molecules, did not act as adsorption sites, so that the amount of sorbed CO2 decreased. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1744–1750, 2000 相似文献
100.
Tsutomu Osawa Masashi Ando Saori Sakai Tadao Harada Osamu Takayasu 《Catalysis Letters》2005,105(1-2):41-45
The role of acetic acid added to the reaction media for the enantio-differentiating hydrogenation of methyl acetoacetate over
a (R,R)-tartaric acid-in-situ-modified nickel catalyst was studied from the viewpoint of the hydrogenation rate during repeated
runs. The hydrogenation of methyl acetoacetate on the “enantio-differentiating sites” of a tartaric acid-modified nickel catalyst
was specifically accelerated by the acetic acid added to the reaction media to increase the enantio-differentiating ability
of the catalyst. In order to increase the enantio-differentiating ability, the addition of acetic acid to the reaction media
was required in each run during the repeated use of the catalyst. 相似文献