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151.
John T. Crosman Robert J. Pinchuk David G. Cooper 《Journal of the American Oil Chemists' Society》2002,79(5):467-472
Enhanced biosurfactant production by Corynebacterium alkanolyticum ATCC 21511 was accomplished in a self-cycling fermenter (SCF) on a hexadecane substrate. The phospholipid biosurfactant produced
during each cycle could be monitored rapidly using fluorescence spectroscopy. By optimizing the cycling pattern of the SCF,
significantly better yields of biosurfactant were obtained than previously reported for this microorganism. It was also possible
to virtually eliminate the hydrocarbon residue in the product. Harvest concentrations of 1.9 g L−1 were obtained by using a two-stage fermentation. The first step was the growth of C. alkanolyticum in an SCF to yield a harvest of synchronous cells. These cells were transferred to a second vessel for the production stage.
The concentration of biosurfactant could be further increased to 2.7 g L−1 by the addition of more hexadecane at the beginning of the second stage. 相似文献
152.
Mechanical activation before carbothermic reduction can substantially enhance the formation of SiC from SiO2 and carbon mixtures. However, the morphology (e.g., particles or whiskers) of SiC formed from mechanically activated SiO2 and carbon mixtures is dependent of the degree of mechanical activation and the condition of the subsequent carbothermic reduction. These phenomena are investigated and rationalized based on the increased reactivity of the reactants and SiC formation mechanisms. 相似文献
153.
W. A. Van Sickle M. R. Angelastro P. Wilson J. R. Cooper A. Marquart M. A. Flanagan 《Lipids》1992,27(3):157-160
Two squalene derivatives, trisnorsqualene cyclopropylamine and trisnorsqualeneN-methylcyclopropylamine, were synthesized and tested for inhibition of lanosterol and squalene epoxide formation from squalene
in rat hepatic microsomes, and for the inhibition of cholesterol syntheses in human cultured hepatoblastoma (HepG2) cells.
Trisnorsqualene cyclopropylamine inhibited [3H]-squalene conversion to [3H]squalene epoxide in microsomes (IC50=5.0 μM), indicating that this derivative inhibited squalene mono-oxygenase. Trisnorsqualenen-methylcyclopropylamine inhibited [3H]squalene conversion to [3H]lanosterol (IC50=12.0 μM) and caused [3H]-squalene epoxide to accumulate in microsomes, indicating that this derivative inhibited 2,3-oxidosqualene cyclase. Cholesterol
biosynthesis from [14C]acetate in HepG2 cells was inhibited by both derivatives (IC50=1.0 μM for trisnorsqualene cyclopropylamine; IC50=0.5 μM for trisnorsqualeneN-methylcyclopropylamine). Cells incubated with trisnorsqualene cyclopropylamine accumulated [14C]squalene, while cells incubated with trisnorsqualeneN-methylcyclopropylamine accumulated [14C]squalene epoxide and [14C]squalene diepoxide. The concentration range of inhibitor which caused these intermediates to accumulate coincided with that
which inhibited cholesterol synthesis. The results indicate that cyclopropylamine derivatives of squalene are effective inhibitors
of cholesterol synthesis, and that substitutions at the nitrogen affect enzyme selectivity and thus the mechanism of action
of the compounds. 相似文献
154.
Casimir C. Akoh Carolyn Cooper Chigozie V. Nwosu 《Journal of the American Oil Chemists' Society》1992,69(3):257-260
Monoglycerides were synthesized with Lipase G fromPenicillium sp. as biocatalyst. This enzyme successfully catalyzed the esterification of glycerol with oleic acid (18:1 n-9) or eicosapentaenoic
acid, EPA (20:5 n-3) in hexane. Esterification at 40°C for 24 hr resulted in 86.3 mol% and 64.3 mol% incorporation of 18:1
n-9 and 20:5 n-3, respectively. Lipase GC fromGeotrichum candidum was not effective in esterifying the fatty acids under the present experimental conditions. Lipase G was able to incorporate
98.5 mol% and 98.1 mol% of 18:1 n-9 onto glycerol in 24 hr or less at 25°C and 37°C, respectively, in the absence of molecular
sieve 4A. The product formed was analyzed by high performance liquid chromatography (HPLC) with a combined evaporative light
scattering mass detector (ELSD) and ultraviolet detection at 206 nm. The result of this study demonstrates that Lipase G is
capable of incorporating long-chain fatty acids of potential health benefit onto glycerol. 相似文献
155.
An experimental procedure was developed to study directly the process by which liquid bridges between small particles in a granule form and solidify. The evolution of saturated solutions of such pharmaceutical excipients as lactose and mannitol in a liquid bridge was studied on a system situated on a microscope slide. Solidification and crystallization kinetics and phase composition during and immediately following bridge formation were observed directly. It was shown that bridges on the microscope slide and in the granule behave very much the same regardless of the different length and diffusion-scales of the two systems.We found that solid bridge formation takes place in several consecutive but distinct steps. In the case of lactose, considerable shrinkage of the initial liquid bridge takes place prior to the onset of crystallization. Further bridge solidification at ambient conditions occurs via simultaneous crystallization and vitrification within minutes. As a result, a “solid” bridge usually contains both a crystalline and a non-crystalline phase, the crystalline phase being predominately α-lactose monohydrate. Most of the non-crystalline phase eventually converts to crystalline β-lactose but the process may take many hours or even days. Results for this process are compared for samples obtained from different manufacturers of commercially available lactose. In the case of mannitol, different polymorphic forms crystallize as the drying/crystallization process progresses. A formed “solid” bridge usually contains several polymorphs of mannitol. The relevance of the behavior of the two model systems (pure lactose and pure mannitol) to a real granulation and tabletting process is discussed. 相似文献
156.
The physical properties of 5 wt% poly(NIPAM) (Mv=3.22×105) semi-dilute solutions in H2O, D2O, and THF (tetrahydrofuran) solvents were studied using dynamic light scattering (DLS) and dynamic shear viscosity (DSV) measurements. The DLS data showed that there were poly(NIPAM) slow mode inter-polymer chains associations in H2O and D2O solvents. However, no DLS slow mode was observed in poly(NIPAM)/THF solutions. The DSV data showed that there are shear thickening behavior in these three poly(NIPAM) solutions, resulting in a maximum shear viscosity ηpeak in the viscosity η′(ω) versus shear frequency ω curve. The slow mode hydrodynamic radius 〈Rhs〉 of DLS measurements and the zero shear rate viscosity η0 and maximum viscosity ηpeak data of DSV measurements from poly(NIPAM)/H2O and poly(NIPAM)/D2O solutions show two critical transition temperatures with Tcr1=30-32 °C and Tcr2=32-34 °C. Poly(NIPASM)/D2O has higher Tcr1 and Tcr2 than poly(NIPASM)/H2O. However, no transition temperatures of poly(NIPAM)/THF solution were observed. The different temperature dependencies of these three solutions were attributed to the ‘solubility’ and ‘hydrogen bonding’ effects between poly(NIPAM) with H2O, D2O, and THF solvents. Without considering the polymer-solvent hydrogen bonding, the solubility of poly(NIPAM) in solvents decreases in the following sequence: THF>H2O>D2O and the degree of polymer-solvent hydrogen bonding increases in the following sequence: THF<H2O<D2O. The effects of the degree of ‘hydrogen bonding’ and the ‘solubility’ of polymer in solvents on the physical properties of poly(NIPAM) solutions are discussed. 相似文献
157.
Ming Zhou Hidetaka Hara Yifan Dai Lisha Mou David K. C. Cooper Changyou Wu Zhiming Cai 《International journal of molecular sciences》2016,17(8)
Different cell types possess different miRNA expression profiles, and cell/tissue/organ-specific miRNAs (or profiles) indicate different diseases. Circulating miRNA is either actively secreted by living cells or passively released during cell death. Circulating cell/tissue/organ-specific miRNA may serve as a non-invasive biomarker for allo- or xeno-transplantation to monitor organ survival and immune rejection. In this review, we summarize the proof of concept that circulating organ-specific miRNAs serve as non-invasive biomarkers for a wide spectrum of clinical organ-specific manifestations such as liver-related disease, heart-related disease, kidney-related disease, and lung-related disease. Furthermore, we summarize how circulating organ-specific miRNAs may have advantages over conventional methods for monitoring immune rejection in organ transplantation. Finally, we discuss the implications and challenges of applying miRNA to monitor organ survival and immune rejection in allo- or xeno-transplantation. 相似文献
158.
Kun-San Chen T. Leon Yu Yung-Sin Chen Tsang-Lang Lin Wen-Jiun Liu 《Journal of Polymer Research》2001,8(2):99-109
Polyester based polyurethanes were synthesized from 4,4′-methylene bis(phenyl isocyanate) (MDI) with butanediol as a chain
extender and low molecular weight polyester-diol as a soft segment. Three polyesters were used in the synthesis of polyurethanes.
Two of the polyesters, with molecular weight Mn = 2,660 and 2,155, were synthesized from adipic acid and 1,6-hexanediol, which had an even number of carbon atoms (polyester-6-6-1
and polyester-6-6-2). The other polyester with Mn = 2,770 was synthesized from pimelic acid and 1,5-pentanediol, which had an odd number of carbon atoms (polyester-7-5). Polyester-6-6-1
and polyester-6-6-2 consisting of even carbon monomers, had a higher degree of crystallinity at room temperature than polyester-7-5,
which consists of an odd number of carbon monomers. The effect of polyester molecular weight and soft and hard-segmental geometric
structure on the soft-and hard-segmental phase segregation was studied using differential scanning calorimetry (DSC), Fourier
transform infrared spectroscopy (FTIR), and small angle X-ray scattering (SAXS). 相似文献
159.
Comparison of the bligh and dyer and folch methods for total lipid determination in a broad range of marine tissue 总被引:10,自引:1,他引:10
For many studies, it is important to measure the total lipid content of biological samples accurately. The Bligh and Dyer method of extraction was developed as a rapid but effective method for determining total lipid content in fish muscle. However, it is also widely used in studies measuring total lipid content of whole fish and other tissues. Although some investigators may have used modified Bligh and Dyer procedures, rarely have modifications been specified nor has their effectiveness been quantitatively evaluated. Thus, we compared this method with that of the classic Folch extraction in determining total lipid content of fish samples ranging from 0.5 to 26.6% lipid. We performed both methods as originally specified, i.e., using the chloroform/methanol/water ratios of 1:2:0.8 and 2:2:1.8 (before and after dilution, respectively) for Bligh and Dyer and of 8:4:3 for Folch, and with the initial solvent/sample ratios of (3+1):1 (Bligh and Dyer) and 20:1 (Folch). We also compared these with several other solvent/sample ratios. In samples containing <2% lipid, the results of the two methods did not differ. However, for samples containing >2% lipid, the Bligh and Dyer method produced significantly lower estimates of lipid content, and this underestimation increased significantly with increasing lipid content of the sample. In the highest lipid samples, lipid content was underestimated by up to 50% using the Bligh and Dyer method. However, we found a highly significant linear relationship between the two methods, which will permit the correction of reported lipid levels in samples previously analyzed using an unmodified Bligh and Dyer extraction. In the future, modifications to procedures and solvent/sample ratios should be described. 相似文献
160.
Rei‐Mei Chou Chi‐Chin Chang T Leon Yu Yu‐Hsien Tseng Mo‐Jyi Wu 《Polymer International》2001,50(2):213-221
The crystallization kinetics of poly(butylene terephthalate) (PBT), poly(ethylene terephthalate) (PET), and their copolymers poly(1,4‐butylene‐co‐ethylene terephthalate) (PBET) containing 70/30, 65/35 and 60/40 molar ratios of 1,4‐butanediol/ethylene glycol were investigated using differential scanning calorimetry (DSC) at crystallization temperatures (Tc) which were 35–90 °C below equilibrium melting temperature . Although these copolymers contain both monomers in high proportion, DSC data revealed for copolymer crystallization behaviour. The reason for such copolymers being able to crystallize could be due to the similar chemical structures of 1,4‐butanediol and ethylene glycol. DSC results for isothermal crystallization revealed that random copolymers had a lower degree of crystallinity and lower crystallite growth rate than those of homopolymers. DSC heating scans, after completion of isothermal crystallization, showed triple melting endotherms for all these polyesters, similar to those of other polymers as reported in the literature. The crystallization isotherms followed the Avrami equation with an exponent n of 2–2.5 for PET and 2.5–3.0 for PBT and PBETs. Analyses of the Lauritzen–Hoffman equation for DSC isothermal crystallization data revealed that PBT and PET had higher growth rate constant Go, and nucleation constant Kg than those of PBET copolymers. © 2001 Society of Chemical Industry 相似文献