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961.
Allan H. Fawcett Avril E. Surgenor
Zahir Bashir
Robert E. Litchfield Norman G. Todd 《Polymer》1992,33(24):5282-5293Copolymers of acrylonitrile with a furfuryl alcohol resin have been prepared by a free radical reaction, and have been characterized by n.m.r. and i.r. spectroscopy. Their t.g.a. has been performed in air and in a nitrogen atmosphere, to permit the recognition of a number of stages in the weight loss process. D.s.c., also in air and in nitrogen, has identified a number of exothermic and one endothermic process in the copolymers. Solid state cross-polarization/magic angle spinning 13C n.m.r. spectroscopy and i.r. spectroscopy has been used to obtain some insight into the chemistry of the various chemical changes, which in air are completed by combustion and in nitrogen leave a carbon. 相似文献
962.
In the absence of a bulk diffusion effect, it is shown for the first time that the impedance spectra for the chlorine evolution reaction on a rotating thin ring electrode comprise three consecutive semicircles in the capacitive half of the complex plane. The first (highest frequency) semicircle is due to the charge-transfer resistance for chloride discharge and the simultaneous chlorine adsorption coupled to the double-layer capacitance. The second semicircle (around 5 Hz) is due to the adsorption and desorption of a chlorine intermediate. The third (lowest frequency, around 0.5 Hz) semicircle is due to the relaxation of surface oxygen species. The impedance data allow the steps of the overall reaction to be examined individually. On a Pt surface the rate of chloride discharge and simultaneous chlorine adsorption (the admittance of the first semicircle) is first order with respect to chloride concentration and has a potential-dependence close to 58 mV/decade. The rate of the adsorption and desorption process (the admittance of the second semicircle) is second order with respect to chloride concentration, and has a potential dependence close to 30 mV/decade. The time constant for the adsorption/desorption processes is ca 20 ms, independent of electrode potential in the range studied. These features are consistent with a mechanism in which a faster discharge reaction (Cl− Clad + e) is followed by a slower surface combination reaction (2Clad → Cl2), but inconsistent with mechanisms in which ion + atom desorption is predominant, the initial chloride discharge is slow, or a unipositively charged chlorine species is involved. 相似文献
963.
Robin A. Henderson Robert G. Jensen Carol J. Lammi-Keefe Ann M. Ferris Kenneth R. Dardick 《Lipids》1992,27(11):863-869
To examine the effect of fish oil supplementation on the fatty acid (FA) composition of human milk and maternal and infant
erythrocytes, five lactating women were supplemented with 6 g of fish oil daily for 21d. Usual maternal diets contained 1,147
mg of total n−3 FA, with 120 mg from very long-chain (>C18) n−3 FA. Supplementation increased dietary levels to 3,092 mg of total n−3 FA and 2,006 mg of very long-chain n−3 FA. Milk
samples were collected daily, prior to fish oil ingestion, and at 4-h intervals on days 1, 7, 14 and 21. Milk n−3 FA content
increased within 8 h and reached steady state levels within one week. The n−6 fatty acid content decreased. Erythrocyte eicosapentaenoic
acid content increased from 0.24% to 1.4% (P<0.01) in mothers and from 0.11% to 0.70% (P<0.05) in infants. Docosapentaenoic acid increased from 1.4% to 2.2% (P<0.05) in mothers and from 0.30% to 0.78% (P<0.01) in infants. There was no significant change in docosahexaenoic acid or n−6 fatty acid content. Maternal platelet aggregation
responses were variable. No differences in milk or plasma tocopherol levels were noted.
Based on a paper presented at the Symposium on Milk Lipids held at the AOCS Annual Meeting, Baltimore, MD, April 1990. 相似文献
964.
A cytosolic protein, that is inhibitory to neutral cholesteryl ester hydrolase, has been investigated in the livers of female
rats using microsomes isolated from the mammary gland of lactating rats as an enzyme source. To facilitate comparisons, inhibitory
activity is expressed in terms of the amount (μg) of cytosolic protein required to reduce esterase activity by 50% and is
compared to the hepatic content of both cholesterol and cholesteryl esters. The experiments revealed a sexual difference in
the level of inhibitory activity, with the livers of both suckling and mature male animals containing less of the material
than the corresponding females. Alterations in the physiological status of the females, such as pregnancy and lactation, led
to a decrease in the activity of the protein. This was reversed by blocking lactation with a combination of an antiserum to
rat growth hormone and the anti-prolactin drug, bromcoriptine, but not by premature weaning of the animals. Food withdrawal
for 24 hr also had the effect of increasing inhibitory activity. In general the cholesteryl ester content of the livers correlated
with the level of inhibitory activity. Thus the activity of the cytosolic inhibitor of neutral cholesteryl ester hydrolase
responded to changes in both the hormonal and the nutritional status of the female animal. It is suggested that the presence
of the greater cholesteryl ester hydrolase inhibitory activity in the female liver may help to explain the lower risk of coronary
heart disease in premenopausal females by facilitating increased hepatic storage of the sterol in the form of the ester. 相似文献
965.
The fatty acid composition of 16 brands of evening primrose oil (EPO) capsules was determined by capillary gas chromatography.
Fourteen of these EPO brands contained γ-linolenic acid (GLA) levels between 7% and 10% (mean, 8.7; range, 1.9–10.5%) and
there was generally good agreement between the level of GLA claimed by the manufacturer and the level determined by analysis.
Low levels of the monoenes 22∶1 and 24∶1 found in some brands may indicate contamination of EPO with borage oil. 相似文献
966.
Sjofn Sigurgisladottir Santosh P. Lall Christopher C. Parrish Robert G. Ackman 《Lipids》1992,27(6):418-424
Salmonid fish require long-chain n−3 fatty acids in their diet. The digestibility of different chemical forms of fish oil
fatty acids, fed as triacylglycerols, free fatty acids or ethyl esters, was examined in 300 g farmed Atlantic salmon (Salmo salar) using cholestane as an indicator of fat absorptionin lieu of the chromium oxide (Cr2O3) which is commonly used as a marker in digestibility studies. It was established that the two digestibility markers gave
similar results. Conveniently, cholestane does not require a separate analysis if fatty acids are to be determined by appropriate
gas-liquid chromatography. The long-chain polyunsaturated fatty acids were particularly well absorbed, the apparent digestibility
being 90–98% when feeding triacylglycerols or free fatty acids. However, the digestibility of monounsaturated fatty acids
(75–94%) was lower, and lower still for saturated fatty acids (50–80%). Ethyl esters of fatty acids were significantly less
well absorbed (P<0.05) than were the corresponding fatty acids in free acid or triacylglycerol form. Irrespective of dietary fat type, only
free fatty acids were identified in feces, indicating total hydrolysis of triacylglycerols and ethyl esters.
Presented in part at the World Aquaculture Society meeting, June 10–14, 1990, Halifax, Canada. 相似文献
967.
Robert A. Gibson Mark A. Neumann Sharon L. Burnard Josephine A. Rinaldi Glen S. Patten Edward J. McMurchie 《Lipids》1992,27(3):169-176
Adult male marmoset monkeys were fed eicosapentaenoic acid (20∶5n−3) as the ethyl ester in diets containing either 32% (reference
diet, no added cholesterol) or 7% (atherogenic diet with 0.2% added cholesterol) linoleic acid (18∶2n−6) for 30 wk. No changes
were seen in the level of phosphatidylcholine (PC) or phosphatidylethanolamine (PE) but minor changes were observed in both
the sphingomyelin (SPM) and phosphatidylinositol plus phosphatidylserine (PI+PS) fractions of erythrocyte lipids. The extent
of total n−3 fatty acid incorporation into membrane lipids was higher in atherogenic diets (polyunsaturated/monounsaturated/saturated
(P/M/S) ratio 0.2∶0.6∶1.0) than reference diets (P/M/S ratio 1∶1∶1) and this was true for both PE (33.4±1.0%vs 24.3±1.1%) and PC (9.3±0.5%vs 4.9±0.3%). Although suitable controls for cholesterol effects were not included in the study, earlier results obtained with
marmosets lead us to believe such effects were probably small. Regardless of basic diet (atherogenic, reference), 20∶5n−3
was preferentially incorporated into PE (10.8±0.2%, 6.0±0.02%) while smaller amounts were incorporated into PC (6.9±0.4%,
3.2±0.2%). The major n−3 polyunsaturated fatty acid found in PE in response to dietary 20∶5n−3 was the elongation metabolite
22∶5n−3 in both the atherogenic (17.7±0.7%) and reference (14.3±1.0%) dietary groups; 22∶6n−3 levels were less affected by
diet (4.7±0.3% and 3.9±0.2%, respectively). The results can be interpreted to indicate an inverse relationship between the
amount of dietary 18∶2n−6 and incorporation of 20∶5n−3 into erythrocyte membrane phospholipids regardless of whether the major
dietary n−3 fatty acid was α-linolenate (18∶3n−3) or 20∶5n−3. This interpretation is supported by theoretical calculations. 相似文献
968.
Greenwood M.Jeffrey; Ong Edgar; Gilkes R.Neil; Warren R.Antony J.; Miller C.Robert Jr; Kilburn G.Douglas 《Protein engineering, design & selection : PEDS》1992,5(4):361-365
The endoglucanase CenA and the exoglucanase Cex from Cellulomonasfimi each contain a discrete cellulose-binding domain (CBD),at the amino-terminus or carboxyl-terminus respectively. Thegene fragment encoding the CBD can be fused to the gene of aprotein of interest. Using this approach hybrid proteins canbe engineered which bind reversibly to cellulose and exhibitthe biological activity of the protein partner. Alkaline phosphatase(PhoA) from Escherichia coli, and a ß-glucosidase(Abg) from an Agrobacterium sp. are dimeric proteins. The fusionpolypeptides CenA-PhoA and Abg-CBCcex are sensitive to proteolysisat the junctions between the fusion partners. Proteolysis resultsin a mixture of homo- and heterodimers; these bind to celluloseif one or both of the monomers carry a CBD, e.g. CenA-PhoA/CenA-PhoAand CenA-PhoA/PhoA. CBD fusion polypeptides could be used inthis way to purify polypeptides which associate with the fusionpartner. 相似文献
969.
Poly(ethylene ether carbonate) polyols can be modified by chemical reactions with polyglycol modifiers under conditions of elevated temperatures and reduced pressures. The modifier becomes chemically incorporated into the modified polyol and is used to control properties such as moisture sensitivity, CO2 content, Tg, density, etc. in the resultant polyol. However, glycerol cannot be used as a modifier for poly(ethylene ether carbonate) polyols under the same conditions since it reacts with poly(ethylene ether carbonate) polyols by a transesterification reaction sequence to form glyceryl carbonate. As the temperature is increased, the glyceryl carbonate decomposes to yield glycidol and carbon dioxide. These reactions are conveniently followed by 13C-NMR. The preparation of glyceryl carbonate by this process has not been previously reported. 相似文献
970.
Basavaraj V. Hiremath Robert E. Newnham Leslie E. Cross 《Journal of the American Ceramic Society》1992,75(11):2953-2958
A new type of barrier layer capacitor is described utilizing thin glass layers on highly conducting ceramics of barium plumbate and barium bismuth plumbate. The frequency dispersion of the apparent dielectric constant has been explained using a modified version of the Maxwell–Wagner model. These capacitors have a low temperature coefficient of capacitance and a high dispersion frequency in the megahertz range. Simple processing conditions together with low firing temperature make it possible to produce the barrier layer capacitors inexpensively. 相似文献