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61.
62.
Summary Big Pod Ceanothus (Ceanothus megacarpus) is an obligate seeder after fire; Laurel Sumac (Rhus laurina) is primarily a resprouter after fire. Both species commonly occur together in mixed stands and are dominant members of the coastal chaparral of southern California. We compared the mean survival of post-fire seedlings of each species during the first summer drought after fire and found C. megacarpus to have a mean survival of 54% while R. laurina had a mean survival of only 0.1%. Rooting dephs were similar between species but predawn water potentials and leaf temperatures were higher for R. laurina seedlings. Leaf temperatures for R. laurina reached a mean value of 46.8° C on hot, summer days, about 5° C higher than seedlings of C. megacarpus. By the end of the first growing season, 92% of all C. megacarpus seedlings had suffered herbivory compared to only 17% of all R. laurina seedlings. Herbivory did not appear to be the immediate cause of seedling mortality. Transect data indicated that full recovery of prefire species composition and density at our study site was likely but the mode of recovery was different for the species examined. R. laurina recovered primarily by sprouting, C. megacarpus totally by seedling establishment and a third species, Adenostoma fasciculatum (chamise), by a combination of sprouting and seedling establishment. We attribute the higher mortality of R. laurina seedlings to the greater sensitivity of its tissue to water stress. It may be that differential survival of shrub seedlings and differential modes of reestablishment after fire play an important role in maintaining species diversity in the chaparral communities of coastal, southern California. 相似文献
63.
A human T cell-specific molecule is a member of a new gene family 总被引:40,自引:0,他引:40
T J Schall J Jongstra B J Dyer J Jorgensen C Clayberger M M Davis A M Krensky 《Journal of immunology (Baltimore, Md. : 1950)》1988,141(3):1018-1025
We have used a cDNA library enriched for T cell-specific sequences to isolate genes expressed by T cells but not by other cell types. We report here one such gene, designated RANTES, which encodes a novel T cell-specific molecule. The RANTES gene product is predicted to be 10 kDa and, after cleavage of the signal peptide, approximately 8 kDa. Of the 68 residues, 4 are cysteines, and there are no sites for N-linked glycosylation. RANTES is expressed by cultured T cell lines that are Ag specific and growth factor dependent. RANTES expression is inducible in PBL by Ag or mitogen. In CTL, expression of RANTES decreases after stimulation with Ag and growth factors. Interestingly, RANTES was not expressed by any T cell tumor line tested. There is significant homology between the RANTES sequence and several other T cell genes, suggesting that they comprise a previously undescribed family of small T cell molecules. 相似文献
64.
Examination of bile acid negative feedback regulation in rats 总被引:2,自引:0,他引:2
R A Davis C A Musso M Malone-McNeal G R Lattier P M Hyde J Archambault-Schexnayder M Straka 《Journal of lipid research》1988,29(2):202-211
Recent data obtained using cultured rat hepatocytes showed that bile acids do not inhibit bile acid synthesis, whereas cholesterol concentrations vary in parallel with bile acid synthesis (Davis et al. (1983. J. Biol. Chem. 258: 4079-4082). This led us to re-evaluate in vivo experiments upon which the consensus that bile acid synthesis is primarily regulated by bile acid "negative feedback" is based. Infusion of taurocholate into either the jugular vein or duodenum of bile-diverted rats stimulated biliary cholesterol secretion and bile flow, but it did not inhibit bile acid synthesis. The lack of an inhibitory effect was evident using several different infusion rates of taurocholate. Even at the greatest rate of taurocholate infusion (25 mumol/(100 g.hr] there was no significant inhibition of bile acid synthesis. In contrast, infusing mevinolin (1 mg/hr), a potent competitive inhibitor of HMG-CoA reductase, almost completely inhibited bile acid synthesis and biliary cholesterol secretion. Since mevinolin did not affect bile flow, these results cannot be ascribed to bile secretory failure. Thus, while these studies suggest that taurocholate may not regulate bile acid synthesis directly via negative feedback, cholesterol is likely to act as a positive effector of bile acid synthesis. 相似文献
65.
Relationships among airway reactivity, pupillary alpha-adrenergic and cholinergic responsiveness, and age 总被引:1,自引:0,他引:1
Healthy adult volunteers (n = 122), who denied personal history of lung disease or family history of cystic fibrosis or asthma, took no interfering medications, and had forced expiratory volume in 1 s greater than or equal to 80% predicted, underwent methacholine challenge and pupillary reactivity testing. Pupil diameter measured in dark and light test conditions declined with age (Pearson's r = -0.54 and -0.36). Pupillary alpha-adrenergic responsiveness (expressed as the concentration of phenylephrine required to dilate the pupil 1 mm) was significantly correlated with age. Older subjects required lower concentrations for dilation and therefore were more sensitive to phenylephrine. Pupillary cholinergic responsiveness (the concentration of carbachol required for 1-mm constriction) was not significantly correlated with age. Therefore the significantly smaller baseline pupil size in the elderly cannot be explained by failure of alpha-adrenergic receptor responses or by increased pupillary cholinergic responsiveness. We found no significant correlation of methacholine bronchial reactivity with age. In addition, there was no relation between airway reactivity and pupillary alpha-adrenergic or cholinergic responsiveness in this sample of healthy adults. These findings, taken with others in the literature, suggest that the contribution of alpha-adrenergic and cholinergic responsiveness to nonspecific airway reactivity in healthy persons is small, if it exists at all, and that there is no significant change in airway reactivity with age in healthy adults. 相似文献
66.
Sessler C. N.; Glauser F. L.; Davis D.; Fowler A. A. rd 《Journal of applied physiology》1988,65(6):2624-2631
We investigated whether platelet-activating factor (PAF) mediates endotoxin-induced systemic and pulmonary vascular derangements by studying the effects of a selective PAF receptor antagonist, SRI 63-441, during endotoxemia in sheep. Endotoxin infusion (1.3 micrograms/kg over 0.5 h) caused a rapid, transient rise in pulmonary arterial pressure (Ppa) from 16 +/- 3 to 36 +/- 10 mmHg (P less than 0.001) and pulmonary vascular resistance (PVR) from 187 +/- 84 to 682 +/- 340 dyn.s.cm-5 (P less than 0.05) at 0.5 h, followed by a persistent elevation in Ppa to 22 +/- 3 mmHg and in PVR to 522 +/- 285 dyn.s.cm-5 at 5 h in anesthetized sheep. Arterial PO2 (PaO2) decreased from 341 +/- 79 to 198 +/- 97 (P less than 0.01) and 202 +/- 161 Torr at 0.5 and 5 h, respectively (inspired O2 fraction = 1.0). SRI 63-441, 20 mg.kg-1.h-1 infused for 5 h, blocked the early rise in Ppa and PVR and fall in PaO2, but had no effect on the late phase pulmonary hypertension or hypoxemia. Endotoxin caused a gradual decrease in mean aortic pressure, which was unaffected by SRI 63-441. Infusion of SRI 63-441 alone caused no hemodynamic alterations. In follow-up studies, endotoxin caused an increase in lung lymph flow (QL) from 3.8 +/- 1.1 to 14.1 +/- 8.0 (P less than 0.05) and 12.7 +/- 8.6 ml/h at 1 and 4 h, respectively. SRI 63-441 abolished the early and attenuated the late increase in QL.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
67.
Davis G. M.; Coates A. L.; Papageorgiou A.; Bureau M. A. 《Journal of applied physiology》1988,65(3):1093-1098
The measurement of pulmonary mechanics has been developed extensively for adults, and these techniques have been applied directly to neonates and infants. However, the compliant chest wall of the infant frequently predisposes to chest wall distortion, especially when there is a low dynamic lung compliance (CL,dyn). We describe a technique of directly measuring the static chest wall compliance (Cw,st), developed initially in the newborn lamb and subsequently applied to the premature neonate with chest wall distortion. The mean CL,dyn in seven intubated newborn lambs in normoxia was 2.45 +/- 0.41 ml.cmH2O-1.kg-1, whereas Cw,st was 11.81 +/- 0.25 ml.cmH2O-1.kg-1. These values did not change significantly in seven animals breathing through a tight-fitting face mask or with hypercapnia-induced tachypnea. For the eight premature infants the mean CL,dyn was 1.35 +/- 0.36 ml.cmH2O-1.kg-1, whereas the mean Cw,st was 3.16 +/- 1.01 ml.cmH2O-1.kg-1. This study shows that, under relaxed conditions when measurements of static compliance are performed, the chest wall is more compliant than the lung. The measurement of Cw,st may thus be used to determine the contribution of the respiratory musculature in stabilizing the chest wall. 相似文献
68.
Cytoplasmic delivery of ribozymes leads to efficient reduction in alpha-lactalbumin mRNA levels in C127I mouse cells. 总被引:4,自引:0,他引:4
Ribozymes targeted to five sites along the alpha-lactalbumin (alpha-lac) mRNA were delivered to the cytoplasm of mouse C127I mammary cells using the T7-vaccinia virus delivery system and the amount of alpha-lac mRNA was monitored 24-48 h post-transfection. Three target sites were selected in the alpha-lac coding region (nucleotides 15, 145 and 361) and two were located in the 3' non-coding region (nucleotides 442 and 694). Acting in trans and at a target:ribozyme ratio of 1:1000, ribozymes targeting sites 361 and 694 reduced alpha-lac mRNA by > 80%; another two ribozymes (targeting nucleotides 442 and 145) reduced mRNA levels by 80 and 60% respectively; the fifth ribozyme (targeting nucleotide 15, near the AUG) was largely ineffective. The kinetic activity (kcat) of each ribozyme in vitro was somewhat predictive of the activity of the two ribozymes that targeted nucleotides 361 and 694, but was not predictive of the in vivo activity of the other three ribozymes. Down-regulation of the intracellular levels of alpha-lac paralleled the ribozyme-dependent reduction achieved for mRNA. For site 442, the reduction in both mRNA and protein was attributed to the catalytic activity of the ribozyme rather than to the antisense effects of the flanking arms, because delivery of an engineered (catalytically-inactive) variant had no effect on mRNA levels and a minimal effect on the level of alpha-lac present in the cell. 相似文献
69.
70.
A. A. Galoyan B. Ya. Gurvits L. A. Shuvalova Michael T. Davis John E. Shively Terry D. Lee 《Neurochemical research》1992,17(8):773-777
A new class of stimulators of basal activity of a number of calmodulin-dependent enzymes have been previously isolated from bovine hypothalamus. One of these stimulators, denoted as C3, has been purified to homogeneity by reverse phase HPLC and tentatively identified as thymosin 4 (1–39) by mass spectrometry and Edman microsequence analysis. The stimulating effect of C3 on rabbit skeletal muscle MLCK basal activity was compared with that of thymosin 1 and thymosin 4 (16–38). Evidence is presented that all the indicated compounds are Ca2+-independent high-affinity MLCK stimulators. The potency of the stimulators in activating the enzyme was: C3>4>(CaM+Ca2+>1.This revised version was published online in June 2005 with corrections to the author name Gurvits. 相似文献