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991.
992.
This paper presents new demographic findings for a high altitude Himalayan population residing in Ladakh, India, and reviews problematic issues regarding the hypothesized relationship between fertility/fecundity and altitude in the Himalayas in light of these findings. It concludes that the low completed fertility ratio reported for the Sherpas of Khumbu, Nepal, is not caused by hypoxia-induced low fecundity, but is the product of cultural factors affecting the exposure of females to the risk of intercourse, a critical confounding factor that has not received adequate consideration in previous studies. Contrary to earlier reports, the present study demonstrates that all high altitude Himalayan populations for which published data exist exhibit moderately high fertility and fecundity, and do not differ significantly in their fertility levels. Furthermore, it argues that the claims for a statistically significant difference in fertility between high, moderate, and low altitude Himalayan populations are groundless, and suggests that a parallel reevaluation of Andean findings is required. [fertility, fecundity, hypoxia, Himalayas, Andes] 相似文献
993.
There are 10 unique dinucleotides of double-stranded DNA, but only 8 independent nearest-neighbor energies that occur in circular DNA, as shown by D. M. Gray and I. Tinoco [(1970) Biopolymers 9, 223-244]. We extend that analysis to include end effects, and show that the number of unique dinucleotide pairs (including ends) is 14, but there are only 12 independent energies. We discuss how these 12 energies (or spectra or any other pairwise additive property) can be measured and displayed, and how they should and should not be compared between experimenters. As an example, we analyzed the recently reported melting curves [M.J. Doktycz et al. (1992) Biopolymers, 32, 849-864.] of 16 DNA dumbbells in two different Na+ environments. This analysis reveals a new means for evaluating end effects and the emergence of longer than nearest-neighbor interactions at low salt concentration. 相似文献
994.
Thymopentin, a synthetic pentapeptide fragment of thymopoietin (residues 32–36, Arg-Lys-Asp-Val-Tyr) is biologically active but susceptible to proteolytic digestion. Analogs were synthesized and studied for biological activity and susceptibility to peptidases. Amino acid changes were incorporated at positions known to not affect activity adversely and N-terminal acetylation and C-terminal amidation were used to increase resistance to proteolytic degradation by exopeptidases. Ac-Pro2-TP5-NH2 and Aib2-TP5-NH2 retained activity and were shown to exhibit a high degree of stability when incubated in human serum. 相似文献
995.
996.
Summary Relative to the formation of an ordinary colorless plant of Blastocladiella emersonii (which does not require bicarbonate for its formation), the bicarbonate-induced genesis of a resistant-sporangial plant (R.S.) is associated with: (a), a two-fold increase in the rate of exponential, net synthesis of an endogenous, apparently highly branched, glycogen-like polysaccharide; and (b), a three-fold increase in the total pool of this polysaccharide built up within the plant.The polysaccharide accumulates during the early development of an R. S. plant in synchronous, single-generation culture when glucose is being consumed rapidly from the medium without detectable production of lactic acid.The accumulated polysaccharide pool disappears again during the maturation period of a resistant-sporangial plant, when glucose is no longer being consumed from the medium. During this time, (a), approximately one mole of lactic acid is liberated per mole of polysaccharideglucose consumed; and (b), the specific activity of glucose-6-phosphate dehydrogenase rises sharply. These observations are consistent with the possibility that the final maturation of the resistant sporangium is associated with an increase in glucose metabolism via the hexose monophosphate shunt. 相似文献
997.
V M Hirsch G A Dapolito S Goldstein H McClure P Emau P N Fultz M Isahakia R Lenroot G Myers P R Johnson 《Journal of virology》1993,67(3):1517-1528
Asymptomatic infection with simian immunodeficiency virus (SIV) has been demonstrated in African Sykes' monkeys (Cercopithecus mitis albogularis), and virus isolation confirmed infection with a novel SIV from Sykes' monkeys (SIVsyk). Macaques inoculated with SIVsyk became persistently infected but remained clinically healthy. We utilized polymerase chain reaction amplification to generate a full-length, infectious molecular clone of SIVsyk. The genome organization of SIVsyk is similar to that of the other primate lentiviruses, consisting of gag, pol, vif, vpr, tat, rev, env, and nef. A unique feature is the absence of the highly conserved NF-kappa B binding site in the long terminal repeat. SIVsyk is genetically equidistant from other primate lentiviruses. Thus, SIVsyk represents a new group that is distinct from the four previously recognized primate lentivirus groups: human immunodeficiency virus type 1 (HIV-1), SIV from sooty mangabeys (SIVsmm) and HIV-2, SIV from African green monkeys (SIVagm), and SIV from mandrills (SIVmnd). The genetic differences between SIVsyk and SIVagm, isolates derived from monkeys of the same genus, underscore the potential for other distinct SIVs which have yet to be isolated and characterized. 相似文献
998.
M. R. Hughes D. L. Goldstein L. Raveendran 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1993,163(6):524-531
The effects of dehydration and hemorrhage on plasma ionic, osmotic, and antidiuretic hormone (arginine vasotocin) concentrations and of hemorrhage on salt gland secretion and glomerular filtration rate were evaluated in glaucous-winged gulls, Larus glaucescens. Dehydration for 24 h did not affect plasma ionic, osmotic or arginine vasotocin concentrations; 72 h dehydration significantly elevated plasma osmolality, plasma sodium and chloride concentrations, and plasma arginine vasotocin concentration, but did not affect plasma potassium concentration. Constant infusion of 0.8 mol·l-1 NaCl increased plasma arginine vasotocin concentration and produced salt gland secretion in seven gulls; four secreted well, while three secreted less well. Removal of 20% blood volume during saline infusion immediately reduced (P<0.001) salt gland secretion rate in all gulls. After bleeding, good secretors maintained glomerular filtration rate and urine flow rate; the poorer secretors increased glomerular filtration rate and became diuretic. Blood replacement returned salt gland secretion rate to the prebleeding level (P<0.05) without affecting salt gland secretions sodium concentration in gulls which secreted well, but did not restimulate salt gland secretion in gulls which secreted poorly. Reinfusion of blood had no effect on glomerular filtration rate. Bleeding and blood replacement did not affect plasma arginine vasotocin concentration.Abbreviations AVT
arginine vasotocin
- ECF
extracellular fluid
- ECFV
extracellular fluid volume
- EDTA
ethylenediaminetetra-acetate
- EWL
evaporative water loss
- GFR
glomerular filtration rate
- Hct
hematocrit
- LB
large blood sample
- [Na+]pl
plasma sodium concentration
- Osmpl
plasma osmolality
- PEG
polyethylene glycol
- RH
relative humidity
- RIA
radioimmunoassay
- SB
small blood sample
- SGS
salt gland secretion
-
T
a
ambient temperature
- TFA
trifluoroacetic acid
- UFR
urine flow rate 相似文献
999.
Progression of heart failure: A role for interstitial fibrosis 总被引:8,自引:0,他引:8
Hani N. Sabbah Victor G. Sharov Michael Lesch Sidney Goldstein 《Molecular and cellular biochemistry》1995,147(1-2):29-34
Progressive deterioration of left ventricular (LV) function is a characteristic feature of the heart failure (HF) state. The mechanism or mechanisms responsible for this hemodynamic deterioration are not known but may be related to progressive intrinsic dysfunction, degeneration and loss of viable cardiocytes. In the present study, we tested the hypothesis that accumulation of collagen in the cardiac interstitium (reactive interstitial fibrosis, RIF), known to occur in HF, results in reduced capillary density (CD=capillary/fiber ratio) and increased oxygen diffusion distance (ODD) which can lead to hypoxia and dysfunction of the collagen encircled myocyte. Studies were performed in LV tissue obtained from 10 dogs with chronic HF (LV ejection fraction 26±1%) produced by multiple sequential intracoronary, microembolizations. In each dog, CD and ODD were evaluated in LV regions that manifested severe RIF (volume fraction 16±2%) and in LV regions of little or no RIF (volume fraction 4±1%). In regions of severe RIF, CD was significantly decreased compared to regions of no RIF (0.92±0.02 vs. 1.05±0.03) (P<0.03). Similarly, ODD was significantly increased in regions of severe RIF compared to regions of no RIF (15.3±0.4 vs. 12.2±0.3 m) (P<0.001). These data suggest that in dogs with chronic HF, constituent myocytes of LV regions which manifest severe RIF may be subjected to chronic hypoxia; a condition that can adversely impact the function and viability of the collagen encircled cardiocyte. 相似文献
1000.
Sidney Goldstein Victor G. Sharov Jane M. Cook Hani N. Sabbah 《Molecular and cellular biochemistry》1995,147(1-2):51-55
Structural remodeling of the left ventricular (LV) myocardium develops in a time-dependent fashion following acute myocardial infarction and may be an integral component in the transition toward overt heart failure. Globally, the remodeling process is characterized by progressive LV enlargement and increased chamber sphericity. At the cellular level, the remodeling process is associated with myocyte slippage, hypertrophy, and accumulation of collagen in the interstitial compartment. In the present study, we examined the effects of early, long-term monotherapy with the angiotensin converting enzyme (ACE) inhibitor, enalapril, on the progression of LV remodeling in dogs with LV dysfunction (ejection fractions 30–40%) produced by multiple sequential intracoronary microembolizations. Dogs were randomized to 3 months oral therapy with enalapril (n=7) or to no treatment (n=7). In untreated dogs, LV end-systolic volume index (ESVI), end-diastolic volume index (EDVI) and chamber sphericity increased significantly during the 3 months follow-up period. In contrast, in dogs treated with enalapril ESVI, EDVI and chamber sphericity remained essentially unchanged. Treatment with enalapril attenuated myocyte hypertrophy and the accumulation of interstitial collagen in comparison to untreated dogs. These data indicate that early treatment with ACE inhibitors can prevent the progression of LV remodeling in dogs with LV dysfunction. Afterload reduction, inhibition of direct action of angiotensin-II and possibly the decrease in bradykinin degradation elicited by ACE inhibition may act in concert in preventing the progression LV chamber remodeling. 相似文献