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91.
Fibric acid derivatives are used to treat hyperlipidemia and have wide ranging effects on lipid metabolism. The action of
these compounds on cholesterol esterification, catalyzed by acyl-coenzyme A:cholesterol acyltransferase (ACAT), has been quite
widely studied, but their effect on cholesteryl ester hydrolysis and the enzyme neutral cholesteryl ester hydrolase (nCEH)
has been largely ignored. Male rats were therefore fed for 10 d on a standard chow diet supplemented with either clofibrate
or bezafibrate, to study their effects on plasma lipid levels and hepatic cholesterol metabolism. Plasma triacyglycerols were
not significantly altered by these diets, but bezafibrate significantly lowered plasma cholesterol levels (29.7%,P<0.01). When expressed per unit weight of DNA, both fibrates reduced the hepatic content of triacylglycerol, cholesterol and
cholesteryl esters (40, 18.7, 16.5 and 66.7, 28.6, 34.2% for clofibrate and bezafibrate, respectively). ACAT activity was
significantly reduced by both drugs, but clofibrate (65% inhibition) was more effective than bezafibrate (35% inhibition).
The most dramatic effect of the diets was a marked increase in the activity of both the microsomal and the cytosolic nCEH.
When expressed on a whole liver basis, the effect of bezafibrate on the cytosolic enzyme (13.6-fold increase in activity)
was much greater than that of clofibrate (4.8-fold increase). Increases in the activity of a cytosolic protein that inhibits
the activity of nCEH were also noted, but these changes were relatively small. The results suggest that the activation of
nCEH, in combination with the inhibition in ACAT activity, contributes to a decrease in the cholesteryl ester content of the
liver which may influence the secretion of very low density lipoprotein. 相似文献
92.
The influence of dietary simvastatin, cholestyramine, and the combination of simvastatin plus cholestyramine on hepatic cholesterol
metabolism has been investigated in male rats. Recovery from the effects of the drugs was also investigated by refeeding normal
chow for 24 h. Both drugs, alone and in combination, increased 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase activityin vitro, but activity returned toward control values, after drug withdrawal. Acyl-CoA:cholesterol acyltransferase (ACAT) was significantly
reduced (P<0.001) by simvastatin (−75%), cholestyramine (−71%), and by the drug combination (−81%), due both to a decrease in microsomal
cholesterol and to nonsubstrate-dependent modulation of enzyme activity. Refeeding control diet increased ACAT activity but
not to control levels. The enhanced activity arose partly from higher microsomal cholesterol and partly from increases in
total enzyme activity. Cytosolic neutral cholesteryl ester hydrolase (CEH) activity was substantially elevated by simvastatin
(3-fold) and by the drug combination (6-fold), whereas the effect of cholestyramine was smaller (1.5-fold). Normal chow for
24 h only partially returned cytosolic CEH activity to control values. Microsomal CEH activity was increased by simvastatin,
alone and in combination with cholestyramine (1.4 to 1.7-fold), and was also enhanced, in the cholestyramine-treated animals,
following drug withdrawal. Removal of simvastatin did not allow recovery of this enzyme activity, while withdrawal of the
drug combination led to values 29% below controls. The results indicate that in the rat, simvastatin and cholestyramine alter
both ACAT and CEH activity, as well as inhibiting HMG-CoA reductase activity. 相似文献
93.
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
94.
G. Oladunni Taylor John J. Albers G. Russell Warnick Janet L. Adolphson H. McFariane D. R. Sullivan C. E. West V. Sri-Hari R. Edwards 《Lipids》1987,22(3):173-177
The high mortality rate from coronary heart disease (CHD) among Indians compared to Negroes in Trinidad led us to test plasma
lipid profiles to see whether dietary or genetic factors might be involved. There were no interracial differences in the composition
of plasma cholesterol ester fatty acids of the tested women and neonates. This finding suggests that dietary fat does not
account for the interracial difference in CHD, nor does the cause appear to be due to genetic differences in lipid profiles,
as there was no significant difference between values for plasma triglycerides, total cholesterol, high density lipoprotein
(HDL) cholesterol, apo-I, apo-II, apo B or cholesterol ester fatty acids in the cord blood of each racial group.
Blood samples were collected from 69 nonpregnant and 71 postpartum, fasted Negro and Indian women. Also taken were 71 umbilical
cord blood samples. The mean triglyceride level was significantly lower in the Negro nonpregnant and postpartum women than
in the Indians. HDL cholesterol and apo-I values were lower in the Indian women. There were no significant differences in
the total cholesterol and apo B measurements. The triglyceride values for postpartum women were higher than those of the nonpregnant
Negroes and Indians (75% and 47%, respectively), whereas the total cholesterol and HDL cholesterol, apo A-I and apo A-II ranged
from 9% to 29% higher in the postpartum women. Apo B was about 40% higher postpartum in both ethnic groups.
The high CHD rate of Indians in Trinidad cannot be explained by dietary factors, plasma total cholesterol or fatty acid composition.
However, the lower level of HDL cholesterol and plasma A-I could play a role in the higher CHD rate in Indians. 相似文献
95.
R. D. Armstrong A. D. Sperrin F. L. Tye G. D. West 《Journal of Applied Electrochemistry》1972,2(4):265-273
Sintered plate Cd electrodes have been studied in alkaline solutions using potentiostatic and galvanostatic techniques. The behaviour is, in many ways, similar to that of a flat Cd electrode. A pseudo steady-state current is found due to the dissolution of Cd as Cd(OH)2–4. At more anodic potentials passivation occurs due to the solid state formation of Cd(OH)2. This model can account for the results obtained on galvanostatic discharge. 相似文献
96.
Ritesh Rawal Antonio Feteira Alberto Arenas Flores Neil C. Hyatt Anthony R. West Derek C. Sinclair Kumaravinothan Sarma Neil McN. Alford 《Journal of the American Ceramic Society》2006,89(1):336-339
The dielectric properties of dense ceramics of the "twinned" 8H-hexagonal perovskite Ba8 Nb4 Ti3 O24 are reported. Single-phase powders were obtained from the mixed-oxide route at 1325°C and ceramics (>92% of the theoretical X-ray density) by sintering in air or flowing O2 at 1400°–1450°C. The ceramics are dc insulators with a band gap >3.4 eV that resonate at microwave frequencies with relative permittivity, ɛr ∼44–48, quality factor, Q × f r ∼21 000–23 500 GHz (at f r ∼5.5 GHz) and temperature coefficient of resonant frequency, TC f ,∼+115 ppm/K. 相似文献
97.
Samkharadze N Kumar A Manfra MJ Pfeiffer LN West KW Csáthy GA 《The Review of scientific instruments》2011,82(5):053902
We fabricated a He-3 immersion cell for transport measurements of semiconductor nanostructures at ultra low temperatures and in strong magnetic fields. We have a new scheme of field-independent thermometry based on quartz tuning fork Helium-3 viscometry which monitors the local temperature of the sample's environment in real time. The operation and measurement circuitry of the quartz viscometer is described in detail. We provide evidence that the temperature of two-dimensional electron gas confined to a GaAs quantum well follows the temperature of the quartz viscometer down to 4 mK. 相似文献
98.
Smith JD West AA 《Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine》2008,222(6):947-958
The rehabilitation of the range of individuals covering medical patients to elite athletes is a costly and time-consuming process involving the knowledge of experienced physical therapists, medical practitioners, coaches, and dedicated training facilities. In order to improve the effectiveness and efficiency of the rehabilitation process, a modular variable-resistance rehabilitation device has been developed. The mechanical, electromechanical, and software systems identified during this research have been shown to provide a step change in exercise functionality, real-time patient monitoring, performance feedback, and safety. Using distributed network concepts, the physical therapist will be able to design and implement training regimes remotely, which can subsequently be downloaded to the localized resistance devices. The patient and/or athlete is able to complete the required exercises without personal supervision. The data from these sessions can be saved and accessed for assessment at a convenient time, thereby maximizing therapist productivity and optimizing the utilization of medical resources. 相似文献
99.
The canonical monomers (approximately 170 bp) of an abundant (1.9 x 10(6) copies per diploid genome) satellite DNA sequence family in the genome of Cyprinodon variegatus, a "pupfish" that ranges along the Atlantic coast from Cape Cod to central Mexico, are divergent in base sequence in 10 of 12 samples collected from natural populations. The divergence involves substitutions, deletions, and insertions, is marked in scope (mean pairwise sequence similarity = 61.6%; range = 35-95.9%), is largely confined to the 3' half of the monomer, and is not correlated with the distance among collecting sites. Repetitive cloning and direct genomic sequencing experiments failed to detect intrapopulation and intraindividual variation, suggesting high levels of sequence homogeneity within populations. The satellite sequence has therefore undergone "concerted evolution," at the level of the local population. Concerted evolution has previously almost always been discussed in terms of the divergence of species or higher taxa; its intraspecific occurrence apparently has not been reported previously. The generality of the observation is difficult to evaluate, for although satellite DNAs from a large number of organisms have been studied in detail, there appear to be little or no other data on their sequence variation in natural populations. The relationship (if any) between concerted, population level, satellite DNA divergence and the extent of gene flow/genetic isolation among conspecific natural populations remains to be established. 相似文献
100.