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991.
992.
George M. Helmkamp 《生物化学与生物物理学报:生物膜》1980,595(2):222-234
The major phospholipid exchange protein from bovine brain catalyzes the transfer of phosphatidylinositol and phosphatidylcholine between rat liver microsomes and sonicated liposomes. The effect of liposomal lipid composition on the transfer of these phospholipids has been investigated. Standard liposomes contained phosphatidylcholine-phosphatidic acid (98:2, mol%); in general, phosphatidylcholine was substituted by various positively charged, negatively charged, or zwitterionic lipids. The transfer of phosphatidylinositol was essentially unaffected by the incorporation into liposomes of phosphatidic acid, phosphatidylserine, or phosphatidylglycerol (5–20 mol%) but strongly depressed by the incorporation of stearylamine (10–40 mol%). Marked stimulation (2–4-fold) of transfer activity was observed into liposomes containing phosphatidylethanolamine (2–40 mol%). The inclusion of sphingomyelin in the acceptor liposomes gave mixed results: stimulation at low levels (2–10 mol%) and inhibition at higher levels (up to 40 mol%). Cholesterol slightly diminished transfer activity at a liposome cholesterol/phospholipid molar ratio of 0.81. Similar effects were noted for the transfer to phosphatidylcholine from microsomes to these various liposomes. Compared to standard liposomes, the magnitude of tended to increase for liposomes which depressed phospholipid transfer and to decrease for those which stimulated; little change was observed in the values of . Single phospholipid liposomes of phosphatidylinositol were inhibitory when added to standard liposomes. 相似文献
993.
Herman J.M. Kramer Rienk van Grondelle C.Neil Hunter Willem H.J. Westerhuis Jan Amesz 《BBA》1984,765(2):156-165
The B800–850 antenna complex of Rhodopseudomonas sphaeroides was studied by comparing the spectral properties of several different types of complexes, isolated from chromatophores by means of the detergents lithium dodecyl sulfate (LDS) or lauryl dimethylamine N-oxide (LDAO). Fluorescence polarization spectra of the BChl 800 emission at 4 K indicated that rapid energy transfer between at least two BChl 800 molecules occurs with a rate constant of energy transfer kET > 3 · 1012 s?1. The maximal dipole-dipole distance between the two BChl 800 molecules was calculated to be 18–19 Å. The porphyrin rings of the BChl 800 molecules are oriented parallel to each other, while their Qy transition moments are mutually perpendicular. The energy-transfer efficiency from carotenoid to bacteriochlorophyll measured in different complexes showed that two functionally different carotenoids are present associated with, respectively, BChl 800 and BChl 850. Fluorescence polarization and linear dichroism spectra revealed that these carotenoids have different absorption spectra and a different orientation with respect to the membrane. The carotenoid associated with BChl 800 absorbs some nanometers more to the red and its orientation is approximately parallel to the membrane, while the carotenoid associated with BChl 850 is oriented more or less perpendicular to the membrane. The fluorescence polarization of BChl 850 was the same for the different complexes. This indicates that the observed polarization of the fluorescence is determined by the smallest complex obtained which contains 8–10 BChl 850 molecules. The B800–850 complex isolated with LDAO thus must consist of a highly ordered array of smaller structures. On basis of these results a minimal model is proposed for the basic unit consisting of four BChl 850 and two BChl 800 and three carotenoid molecules. 相似文献
994.
Synthesis and in vitro bioactivity of human growth hormone-releasing factor analogs substituted at position-1 总被引:4,自引:0,他引:4
N Ling A Baird W B Wehrenberg N Ueno T Munegumi T C Chiang M Regno P Brazeau 《Biochemical and biophysical research communications》1984,122(1):304-310
Eight position-1 analogs of the 40-amino acid fragment and two position-1 analogs of human growth hormone-releasing factor were synthesized by solid phase methodology and their capacity to release growth hormone was determined using rat anterior pituitary cells in monolayer culture. Relative to hGRF(1-40)OH, which was arbitrarily assigned a potency value of 1, [D-Tyr1]hGRF(1-40)OH, [Phe1]hGRF(1-40)OH, [Trp1]hGRF(1-40)OH, [His1]hGRF(1-40)OH, [Ala1]hGRF(1-40)OH, [(-Ac)Tyr1]hGRF(1-40)OH, Arg0-hGRF(1-40)OH and Ala0-hGRF(1-40)OH have potencies of 0.022, 0.038, 0.003, 0.351, 0.010, 0.032, 0.002 and 0.007 respectively. Relative to hGRF(1-44)NH2 = 1, [(3-Me)His1]hGRF(1-44)NH2 and [(O-Me)Tyr1]hGRF(1-44)NH2 have potencies of 0.132 and 0.001 respectively. These results demonstrate the prerequisite for an aromatic residue at position-1 for potent biological activity and also suggest that the capacity for hydrogen bond formation with the first residue is required for full receptor-ligand interaction. 相似文献
995.
Synthetic bovine parathyroid hormone containing the NH2 terminal 34 amino acids [bPTH-(1-34)] was recently demonstrated to inhibit oxytocin stimulated uterine contraction in vitro. The parathyroid hormone analogues [Nle8, Nle18, Tyr34]bPTH-(3-34)amide [NTA-(3-34)] and [Tyr34]bPTH-(7-34)amide [NTA-(7-34)] have been reported to act as inhibitors of antagonists of parathyroid hormone (PTH) in numerous assays. In the present study the effects of these PTH analogues on uterine contraction and the ability of these analogues to act as antagonists to the uterine inhibitory action of bPTH-(1-34) in vitro were investigated. The NTA-(3-34) fragment had no effect on oxytocin stimulated uterine contractions. However, the NTA-(3-34) fragment was able to alter the ability of bPTH (1-34) to reduce oxytocin stimulated uterine contraction in a dose-related manner. Bovine PTH(1-34) (0.3 microgram/ml) reduced the contractile response obtained with oxytocin (0.5 mU/ml) by 20%. A dose of 15 micrograms/ml) of NTA-(3-34) abolished this inhibitory action of bPTH-(1-34) on oxytocin stimulated uterine contraction. In contrast the NTA-(7-34) caused a change in itself, stimulated contraction of resting uterine horns in a dose-related manner; 3.0 micrograms/ml of NTA-(7-34) caused a change in gram tension of + 1.5 grams. Bovine PTH-(1-34) was able to reduce the uterine contraction stimulated by NTA-(7-34) and 0.3 microgram/ml of bPTH-(1-34) reduced the contractile response obtained with 3.0 micrograms/ml of NTA-(7-34) by as much as 70%.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
996.
《Phytomedicine》2013,21(14):1247-1250
Green tea catechins have been shown to affect the activities of drug transporters in vitro, including P-glycoprotein and organic anion transporting polypeptides. However, it remains unclear whether catechins influence the in vivo disposition of substrate drugs for these transporters. In the present study, we investigated effects of green tea extract (GTE) and (−)-epigallocatechin-3-gallate (EGCG) on pharmacokinetics of a non-selective hydrophilic β-blocker nadolol, which is reported to be a substrate for several drug transporters and is not metabolized by cytochrome P450 enzymes. Male Sprague-Dawley rats received GTE (400 mg/kg), EGCG (150 mg/kg) or saline (control) by oral gavage, 30 min before a single intragastric administration of 10 mg/kg nadolol. Plasma and urinary concentrations of nadolol were determined using high performance liquid chromatography. Pharmacokinetic parameters were estimated by a noncompartmental analysis. Pretreatment with GTE resulted in marked reductions in the maximum concentration (Cmax) and area under the time–plasma concentration curve (AUC) of nadolol by 85% and 74%, respectively, as compared with control. In addition, EGCG alone significantly reduced Cmax and AUC of nadolol. Amounts of nadolol excreted into the urine were decreased by pretreatments with GTE and EGCG, while the terminal half-life of nadolol was not different among groups. These results suggest that the coadministration with green tea catechins, particularly EGCG, causes a significant alteration in the pharmacokinetics of nadolol, possibly through the inhibition of its intestinal absorption mediated by uptake transporters. 相似文献
997.
《Chronobiology international》2013,30(3):239-243
A new approach to the assessment of breast health was developed based upon continuous ambulatory recording of breast temperature for 24 hrs. A new data acquisition system consisting of a portable, multi-channel, microprocessor-based recorder worn on a belt was developed to record temperatures. Dramatic thermal fluctuations were noted during the recordings in response to multiple stimuli (physiological, behavioral, environmental). Specific algorithms and software programs were developed to process the thermobiologic and chronobiologic information. Data processing was fully automatic and included an examination report indicating a score and a chronothermodynamic class for each of the five areas examined on each breast. The preliminary clinical studies have concerned more than 450 patients with healthy or diseased breasts. 相似文献
998.
- The influence of predator cues on the behaviour of prey is well supported in the literature; however, a clear understanding of how predator cues affect prey in variable environmental conditions and over longer time scales is needed to better understand the underlying mechanisms. Here, we measure how predator odors affect herbivore colonization, abundance, oviposition, and plant damage across two growing seasons.
- The study system consisted of Leptinotarsa decemlineata (Colorado potato beetle) as prey, and the aggregation pheromone of live Podisus maculiventris (spined soldier bug) as the predator cue in a potato field.
- In 2016, the amount of feeding damage by early beetle colonists was lower in predator odor-treated plots, reducing plant damage by 22%. Larval abundance was also reduced in treated plots in 2016. Beetle abundance and damage in 2017 was similar in the treatment and control plots. Two mechanisms were investigated to better understand why prey response to the predator odor treatment weakened over the first season, including changes in predator odor cue strength and prey habituation. Predator odor cue strength emerged as a likely explanation, as dispensers, which released a synthetic predator pheromone over the entire season, reduced the probability of finding damage more consistently than the live predator treatment.
- These results suggest that temporal patterns of predator cue release and strength may drive prey response across the season, underscoring the importance of cue release-rate and consistency in both species interactions and for the future application of modifying insect behaviour using non-consumptive effects in agricultural systems.
999.
《Critical reviews in biochemistry and molecular biology》2013,48(3):233-242
Recent work has greatly contributed to the understanding of the biology and biochemistry of RecQ4. It plays an essential non-enzymatic role in the formation of the CMG complex, and thus replication initiation, by means of its Sld2 homologous domain. The helicase domain of RecQ4 has now been demonstrated to possess 3′–5′ DNA helicase activity, like the other members of the RecQ family. The biological purpose of this activity is still unclear, but helicase-dead mutants are unable to restore viability in the absence of wildtype RecQ4. This indicates that RecQ4 performs a second role, which requires helicase activity and is implicated in replication and DNA repair. Thus, it is clear that two helicases, RecQ4 and Mcm2-7, are integral to replication. The nature of the simultaneous involvement of these two helicases remains to be determined, and possible models will be proposed. 相似文献
1000.
1. Climate effects on plant defences, and subsequently insect herbivores, have received considerable attention. However, climate also directly affects the physiological condition of insects that may influence their ability to combat plant defences. 2. This study tested the effects of body fat and water content on the ability of mountain pine beetles, Dendroctonus ponderosae Hopkins, to tolerate monoterpenes, the primary defences of their host pine trees. To manipulate their physiological condition, we exposed beetles to one of three environmental treatments: cold (4 °C, 30% RH), humid (21 °C, 70% RH) or dry (21 °C, 30% RH). Beetles had the highest fat and water content in the cold treatment, followed by lower fat but the same water content in the humid treatment, and the lowest of both in the dry treatment. Following environmental treatments, beetles were exposed to 0, 312.5 or 625 ppm vapours of monoterpenes (−)-α-pinene or (R)-(+)-limonene. 3. Survival during both environmental and monoterpene treatments was highest for the cold treatment, less for the humid treatment, and lowest for the dry treatment. Fat and water content positively predicted survival. In response to increasing monoterpene concentration, survival, body condition and water content, but not fat, declined. 4. These results indicate that water content of insect herbivores was important for the realised toxicity of plant defences, presumably due to the process of excreting detoxified compounds. Energetic costs of detoxification were less evident. Dehydration of insects has not been widely considered in insect–plant interactions, but effects of climate change on humidity may become increasingly important for these interactions. 相似文献