全文获取类型
收费全文 | 434477篇 |
免费 | 44446篇 |
国内免费 | 26983篇 |
专业分类
电工技术 | 31955篇 |
技术理论 | 20篇 |
综合类 | 38928篇 |
化学工业 | 76494篇 |
金属工艺 | 24265篇 |
机械仪表 | 23117篇 |
建筑科学 | 33649篇 |
矿业工程 | 10342篇 |
能源动力 | 14129篇 |
轻工业 | 26384篇 |
水利工程 | 7931篇 |
石油天然气 | 17072篇 |
武器工业 | 3861篇 |
无线电 | 47613篇 |
一般工业技术 | 48373篇 |
冶金工业 | 13221篇 |
原子能技术 | 5226篇 |
自动化技术 | 83326篇 |
出版年
2024年 | 872篇 |
2023年 | 6515篇 |
2022年 | 10990篇 |
2021年 | 14707篇 |
2020年 | 13255篇 |
2019年 | 11235篇 |
2018年 | 10795篇 |
2017年 | 12909篇 |
2016年 | 14834篇 |
2015年 | 16704篇 |
2014年 | 25367篇 |
2013年 | 25533篇 |
2012年 | 27124篇 |
2011年 | 29270篇 |
2010年 | 23483篇 |
2009年 | 26501篇 |
2008年 | 25603篇 |
2007年 | 29638篇 |
2006年 | 27482篇 |
2005年 | 23284篇 |
2004年 | 19254篇 |
2003年 | 17787篇 |
2002年 | 14878篇 |
2001年 | 11829篇 |
2000年 | 10517篇 |
1999年 | 8902篇 |
1998年 | 6848篇 |
1997年 | 5979篇 |
1996年 | 5668篇 |
1995年 | 5425篇 |
1994年 | 4795篇 |
1993年 | 3260篇 |
1992年 | 2957篇 |
1991年 | 2042篇 |
1990年 | 1610篇 |
1989年 | 1368篇 |
1988年 | 1068篇 |
1987年 | 665篇 |
1986年 | 485篇 |
1985年 | 620篇 |
1984年 | 627篇 |
1983年 | 590篇 |
1982年 | 507篇 |
1981年 | 510篇 |
1980年 | 389篇 |
1979年 | 172篇 |
1978年 | 156篇 |
1977年 | 101篇 |
1976年 | 81篇 |
1975年 | 87篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Wan-Li Tan Dr. Chun Zhang Yang Li Dr. Kai Guo Dr. Xiao-Wei Gao Dr. Jun Wei Dr. Dong Yi Prof. Lin Pu Prof. Dr. Qin Wang 《ChemMedChem》2021,16(23):3569-3575
Forty samples of optically active falcarindiol analogues are synthesized by using the easily available C2 symmetric (R)- and (S)-1,1’-binaphth-2-ol (BINOL) in combination with Ti(OiPr)4, Zn powder and EtI. Their anticancer activities on Hccc-9810, HepG2, MDA-MB-231, Hela, MG-63 and H460 cells are assayed to elucidate their structure-activity relationships. These results showed that the falcarindiol analogue (3R,8S)- 2 i with the terminal double bond has the most potent anti-proliferation effect on Hccc-9810 cells with IC50 value of 0.46 μM. The falcarindiol analogue (3R,8S)- 2 i can induce obvious Hccc-9810 cell apoptosis in a concentration-dependent manner by Hoechst staining and flow cytometry analysis. The proposed mechanism suggests that the falcarindiol analogue (3R,8S)- 2 i increases LDH release and MDA content, and reduces the levels of SOD activity, which lead to the accumulation of oxidative stress and induce apoptosis in Hccc-9810 cells. 相似文献
42.
Tomoki Murata Toru Asaka Sakyo Hirose 《Journal of the American Ceramic Society》2021,104(11):5794-5802
Dielectric tunability has been extensively investigated in ferroelectric materials, which exhibit a negative tunability of dielectric permittivity in an external electric field. In contrast, positive tunability is rare and has been reported only in a few antiferroelectric materials. We present positive (and negative) tunability in the titanite, CaTiSiO5. The dielectric property of CaTiSiO5 was measured up to an extraordinarily high electric field of 40 MV/m. A nonlinear polarization field loop with no hysteresis was obtained. The dielectric permittivity of εr ~ 25 increases up to εr ~ 40 at 20 MV/m and room temperature. Although titanite has an antipolar structure and is expected to be “antiferroelectric,” its dielectric response in high electric fields up to ~40 MV/m differs from that of conventional antiferroelectrics. We demonstrate that the phase-transition temperature and dielectric tunability could be modulated through the chemical substitution of Ca1−xLaxTiSi1−xAlxO5, in which the destabilization of the long-range antipolar order is revealed by transmission electron microscopy analysis. These results indicate that the observed dielectric response to an electric field may originate from the unique features of the antipolar and domain structures in CaTiSiO5. 相似文献
43.
Sawao Honda Kento Nakashima Taketo Yoshida Yusuke Daiko Shinobu Hashimoto Yuji Iwamoto 《Journal of the American Ceramic Society》2021,104(2):1178-1187
To quantitatively investigate the initial crystallization of zeolite beta synthesized by direct heating, the extent of the reaction was precisely evaluated by X-ray diffraction measurements and Rietveld structural refinement, and a kinetic analysis of crystallization was performed using the Avrami-Erofe'ev equation. The activation energy for crystallization was lower than that for hydrothermal synthesis. Reaction and synthesis time curves revealed that the initial zeolite beta crystallization consisted of three stages. The first was an induction period with nucleation by the generation of building units and the formation of an initial coordinated structure. The second stage was crystal growth by a diffusion-controlled reaction, and the third stage involved slowing down of crystallization by the limitation of dehydrocondensation. These stages could be analyzed by calculation of the rate constant and Avrami exponent for each stage. 相似文献
44.
Chaozhong Sun Xiaoying Guo Rui Ji Changzheng Hu Laijun Liu Liang Fang Zhenxiang Cheng Nengneng Luo 《Ceramics International》2021,47(4):5038-5043
The triboelectric effect has recently demonstrated its great potential in environmental remediation and even new energy applications for triggering a number of catalytic reactions by utilizing trivial mechanical energy. In this study, Ba4Nd2Fe2Nb8O30 (BNFN) submicron powders were used to degrade organic dyes via the tribocatalytic effect. Under the frictional excitation of three PTFE stirring rods in a 5 mg/L RhB dye solution, BNFN demonstrates a high tribocatalytic degradation efficiency of 97% in 2 h. Hydroxyl radicals (?OH) and superoxide radicals (?O2-) were also detected during the catalysis process, which proves that triboelectric energy stimulates BNFN to generate electron-hole pairs. The tribocatalysis of tungsten bronze BNFN submicron powders provides a novel and efficient method for the degradation of wastewater dye by utilizing trivial mechanical energy. 相似文献
45.
Stephanie Weiss Regina Seidl Waltraud Kessler Rudolf W. Kessler Edith M. Zikulnig-Rusch Andreas Kandelbauer 《应用聚合物科学杂志》2021,138(27):50635
During curing of thermosetting resins the technologically relevant properties of binders and coatings develop. However, curing is difficult to monitor due to the multitude of chemical and physical processes taking place. Precise prediction of specific technological properties based on molecular properties is very difficult. In this study, the potential of principal component analysis (PCA) and principal component regression (PCR) in the analysis of Fourier transform infrared (FTIR) spectra is demonstrated using the example of melamine-formaldehyde (MF) resin curing in solid state. FTIR/PCA-based reaction trajectories are used to visualize the influence of temperature on isothermal cure. An FTIR/PCR model for predicting the hydrolysis resistance of cured MF resin from their spectral fingerprints is presented which illustrates the advantages of FTIR/PCR compared to the combination differential scanning calorimetry/isoconversional kinetic analysis. The presented methodology is transferable to the curing reactions of any thermosetting resin and can be applied to model other technologically relevant final properties as well. 相似文献
46.
Ewa Olewnik-Kruszkowska Magdalena Gierszewska Sylwia Grabska-Zieliska Joanna Skopiska-Winiewska Ewelina Jakubowska 《International journal of molecular sciences》2021,22(7)
Hydrogels based on chitosan are very versatile materials which can be used for tissue engineering as well as in controlled drug delivery systems. One of the methods for obtaining a chitosan-based hydrogel is crosslinking by applying different components. The objective of the present study was to obtain a series of new crosslinked chitosan-based films by means of solvent casting method. Squaric acid—3,4-dihydroxy-3-cyclobutene-1,2-dione—was used as a safe crosslinking agent. The effect of the squaric acid on the structural, mechanical, thermal, and swelling properties of the formed films was determined. It was established that the addition of the squaric acid significantly improved Young’s modulus, tensile strength, and thermal stability of the obtained materials. Moreover, it should be stressed that the samples consisting of chitosan and squaric acid were characterized by a higher swelling than pure chitosan. The detailed characterization proved that squaric acid could be used as a new effective crosslinking agent. 相似文献
47.
Deoxyribonucleic acid (DNA) replication can be divided into three major steps: initiation, elongation and termination. Each time a human cell divides, these steps must be reiteratively carried out. Disruption of DNA replication can lead to genomic instability, with the accumulation of point mutations or larger chromosomal anomalies such as rearrangements. While cancer is the most common class of disease associated with genomic instability, several congenital diseases with dysfunctional DNA replication give rise to similar DNA alterations. In this review, we discuss all congenital diseases that arise from pathogenic variants in essential replication genes across the spectrum of aberrant replisome assembly, origin activation and DNA synthesis. For each of these conditions, we describe their clinical phenotypes as well as molecular studies aimed at determining the functional mechanisms of disease, including the assessment of genomic stability. By comparing and contrasting these diseases, we hope to illuminate how the disruption of DNA replication at distinct steps affects human health in a surprisingly cell-type-specific manner. 相似文献
48.
Nowadays, oil pollution has become more serious, which causes great threats both to the ecological environment and human life. In this study, a novel type of multifunctional deacetylated cellulose acetate/polyurethane (d-MCA:MTPU) composite nanofiber membranes for oil/water separation are successfully fabricated by electrospinning, which show super-amphiphilicity in air, super-hydrophilicity in oil, and oleophobicity in water. All the d-MCA:MTPU composite nanofiber membranes with different mass ratios can be used as water-removing, oil-removing, and emulsion separation substance only by gravity driving force. The highest separation flux for water and oil reaches up to 37 000 and 74 000 L m−2 h−1, respectively, and all the separation efficiencies are more than 99%. They have outstanding comprehensive mechanics performance, which can be controlled by simply adjusting the mass ratios. They show excellent antifouling and self-cleaning ability, endowing powerful cyclic stability and reusability. Those results show that d-MCA:MTPU composite nanofiber membranes have great application prospects in oil/water separation. 相似文献
49.
Jiatong Zhu Xuanyu Meng Ping Zhang Zhuolun Li Jie Xu Michael J. Reece Feng Gao 《Journal of the European Ceramic Society》2021,41(4):2861-2869
A series of rare earth zirconates (RE2Zr2O7) high-entropy ceramics with single- and dual-phase structure were prepared. Compared with La2Zr2O7 and Yb2Zr2O7, the smaller “rattling” ions (Yb3+, Er3+, Y3+) have been incorporated into pyrochlore lattice in (La0.2Nd0.2Y0.2Er0.2Yb0.2)2Zr2O7 (LNYEY) while larger ions (La3+, Nd3+, Sm3+, Eu3+) incorporated into fluorite lattice in (La0.2Nd0.2Sm0.2Gd0.2Yb0.2)2Zr2O7 (LNSGY). Due to high-entropy lattice distortion and resonant scattering derived from smaller ions Yb3+, Er3+, and Y3+, LNYEY shows a lower glass-like thermal conductivity (1.62-1.59 W m-1 K-1, 100-600℃) than LNSGY (1.74-1.75 W m-1 K-1, 100-600℃). Moreover, LNYEY and LNSGY exhibit enhanced Vickers’ hardness (LNYEY, Hv = 11.47 ± 0.41 GPa; LNSGY, Hv = 10.96 ± 0.26 GPa) and thermal expansion coefficients (LNYEY, 10.45 × 10-6 K-1, 1000℃; LNSGY, 11.02 × 10-6 K-1, 1000℃). These results indicate that dual-phase rare-earth-zirconate high-entropy ceramics could be desirable for thermal barrier coatings. 相似文献
50.