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131.
M.P. Berg H.A. Verhoef T. Bolger F. McCarthy J.M. Anderson P. Splatt T. Willison F. Beese M. Raubuch M.M. Couteaux H.A. Palka P. Ineson 《Biogeochemistry》1997,39(3):295-326
Increased emissions of nitrogen compounds have led to atmosphericdeposition to forest soils exceeding critical loads of N overlarge parts of Europe. To determine whether the chemistry offorest soils responds to changes in throughfall chemistry, intactsoil columns were reciprocally transplanted between sites, withdifferent physical conditions, across a gradient of N and Sdeposition in Europe.The transfer of a single soil to the various sites affected itsnet nitrification. This was not simply due to the nitrificationof different levels of N deposition but was explained bydifferences in physical climates which influenced mineralizationrates. Variation in the amount of net nitrification between soiltypes at a specific site were explained largely by soil pH.Within a site all soil types showed similar trends in netnitrification over time. Seasonal changes in net nitrificationcorresponds to oscillations in temperature but variable time lagshad to be introduced to explain the relationships. WithArrhenius law it was possible to approximate gross nitrificationas a function of temperature. Gross nitrification equalled netnitrification after adaptation of the microbial community oftransplanted soils to the new conditions. Time lags, andunderestimates of gross nitrification in autumn, were assumed tobe the result of increased NH
4
+
availability due either tochanges in the relative rates of gross and net N transformationsor to altered soil fauna-microbial interactions combined withimproved moisture conditions.Losses of NO
3
-
were associated with Ca2+and Mg2+ in non-acidified soil types and with losses ofAl3+ in the acidified soils. For single soils the ionequilibrium equation of Gaines-Thomas provided a useful approximationof Al3+ concentrations in the soil solution as a functionof the concentration of Ca2+. The between site deviationsfrom this predicted equilibrium, which existed for single soils, couldbe explained by differences in throughfall chemistry which affectedthe total ionic strength of the soil solution.The approach of reciprocally transferring soil columnshighlighted the importance of throughfall chemistry, interactingwith the effect of changes in physical climate on forest soilacidification through internal proton production, in determiningsoil solution chemistry. A framework outlining the etiology offorest die-back induced by nitrogen saturation is proposed. 相似文献
132.
1. Temperature- and time-dependent mortalities were studied and modelled in insects exposed in regimes with constant and alternating temperatures. In these experiments, freezing was not a cause of death.
2. Survival rates at a range of constant low temperatures (– 5 to + 1 °C) and for different exposure periods (1–14 days) were measured in the summer acclimated springtail Orchesella cincta .
3. Daily interruptions of the cold exposure with short intervals at high temperature reduced mortality or slowed the increase of mortality. This effect was stronger at higher temperature (19 vs 5 and 12 °C) and increased with the duration of the interruption (0·25–2 h).
4. The injury was reversible when the cold exposure was limited to 2 days.
5. Survival in desiccated animals (14% water loss) was reduced.
6. It is suggested that the mortality of summer acclimated springtails is caused by a complex metabolic disorder and membrane changes at low temperatures. 相似文献
2. Survival rates at a range of constant low temperatures (– 5 to + 1 °C) and for different exposure periods (1–14 days) were measured in the summer acclimated springtail Orchesella cincta .
3. Daily interruptions of the cold exposure with short intervals at high temperature reduced mortality or slowed the increase of mortality. This effect was stronger at higher temperature (19 vs 5 and 12 °C) and increased with the duration of the interruption (0·25–2 h).
4. The injury was reversible when the cold exposure was limited to 2 days.
5. Survival in desiccated animals (14% water loss) was reduced.
6. It is suggested that the mortality of summer acclimated springtails is caused by a complex metabolic disorder and membrane changes at low temperatures. 相似文献
133.
Transdermal peptide delivery 总被引:1,自引:0,他引:1
The transdermal delivery of peptide drugs, though ill-favoured by their hydrophilicity and high molecular mass, would seem very attractive from the pharmacotherapeutical and patient compliance point of view. In some cases, effective transdermal dosing has been achieved in vivo, especially with the aid of iontophoresis. This paper deals with a dodecapeptide, des-enkephalin-gamma-endorphin, of which the transepidermal permeation and the intra(epi-)dermal biotransformation were both studied in vitro. Small, though measurable, fluxes through human stratum corneum were obtained in vitro, which could be enhanced by using a skin lipid fluidizer. The half-life of the peptide, both in the epidermis and in the dermis, was surprisingly long as compared with that in human plasma. Hence, improvement of the transdermal bioavailability of the peptide will most likely be obtained chiefly by enhancing its flux (possibly through iontophoresis), intra(epi-)dermal degradation being a problem of only minor importance. 相似文献
134.
We carried out a study to determine the proportion of patients attending a university-based gastroenterology outpatient clinic who sought alternative medical care for the same health problem that had prompted them to see a gastroenterologist. After the patients completed a self-administered questionnaire, the gastroenterologist gave a diagnosis and assigned a functional rating. Of the 395 patients 287 (73%) had not used alternative medicine, and 36 (9%) had sought alternative medical care for the problem that had prompted them to see a gastroenterologist. There were no significant differences between alternative medicine users and nonusers in sociodemographic characteristics, use of health care services or general health status. Patients with a functional disease were more likely to seek alternative medical care than those with organic disease (33% v. 7%) (p less than 0.0001). Fewer alternative medicine users (54%) than nonusers (85%) were satisfied with conventional medicine (p less than 0.001), and more alternative medicine users (49%) than nonusers (13%) were very sceptical of conventional medicine (p less than 0.0001). 相似文献
135.
Alpha-endorphin, gamma-endorphin and their des-tyrosine fragments in rat pituitary and brain tissue 总被引:1,自引:0,他引:1
Enkephalins, endorphins and related peptides were determined in pituitary and brain tissue of rats which were killed by decapitation or microwave irradiation. The tissues were heated in 1M acetic acid prior to homogenization and the levels of the various peptides were measured by means of a combination of HPLC and radioimmunoassays. Enkephalin levels in pituitary and brain of irradiation-killed rats were much higher as compared to those in tissue of rats sacrificed by decapitation. Similar data were obtained with respect to pituitary levels of γ-endorphin, des-Tyr-γ-endorphin and des- Tyr-α-endorphin. However, brain levels of α- and γ-endorphin and their respective des-Tyr-fragments were not different with the two methods of sacrifice used. The concentrations of β-endorphin in the pituitary gland were similar in rats killed by microwave irradiation and decapitation, but irradiation showed higher β-endorphin levels in the brain than decapitation. These results suggest that β-endorphin fragments like α- and γ-endorphin and des-Tyr-α- and des-Tyr-γ-endorphin are endogenous peptides in the rat pituitary gland and the brain. 相似文献
136.
137.
押检测携带人肝细胞生长因子基因的重组腺病毒Ad-HGF在体外对成纤维细胞的感染效率以及感染细胞对目的蛋白的表达。以不同感染复数(m.o.i.)(25,50,100,200)的Ad-GFP感染NIH3T3细胞,48h时用流式细胞仪检测转染效率;以50m.o.i.感染NIH3T3细胞后48h,用ELISA和Western印迹杂交法分别检测感染上清中HGF的表达。分别以50m.o.i.的Ad-GFP和Ad-HGF感染原代培养人瘢痕成纤维细胞,以检测重组腺病毒对原代培养人瘢痕成纤维细胞的转染效率和其对HGF的表达。结果表明,当m.o.i.为50时,重组腺病毒对NIH3T3细胞的转染效率已达95%以上;HGF的表达量可达每2×106细胞249ng;并可检测到HGF蛋白的一特异杂交带。以50m.o.i.的Ad-GFP感染原代培养人瘢痕成纤维细胞,72h时GFP表达达高峰,此时转染效率可高达36.75%。Ad-HGF感染原代培养人瘢痕成纤维细胞后HGF的表达在72h时达高峰,表达量可达每3.3×105细胞66ng。初步认为重组腺病毒可有效地介导HGF基因转染正常或瘢痕成纤维细胞,且感染细胞可有效表达目的蛋白。 相似文献
138.
J B van Bree A G de Boer M Danhof J C Verhoef T B van Wimersma Greidanus D D Breimer 《Peptides》1988,9(3):555-559
The purpose of this investigation was to develop a sensitive and selective radioimmunoassay for Desglycinamide-Arginine Vasopressin (DGAVP). DGAVP was extracted from rat plasma after protein precipitation, using Sep-Pak C18 cartridges and 50 mM glycine buffer/methanol (10:90) solution. Extraction recovery was 73 +/- 14% (mean +/- S.D.; n = 11) and good linearity was achieved in the concentration range of 0.25-128 pg/tube. Instantaneous tracer addition resulted in a detection limit of 250 fg/tube, whereas 24 hours preincubation and delayed tracer addition resulted in a detection limit of 100 fg/tube. Intra-assay variation ranged between 7.4% and 10.0% depending on the peptide concentration and inter-assay variation was 13.2%. Using this procedure, plasma pharmacokinetics of DGAVP in the rat were determined after IV administration. DGAVP plasma concentration showed a rapid distribution phase (t1/2 = 1.0 +/- 0.2 min) and a somewhat slower elimination phase (t1/2 = 7.2 +/- 2.1 min). High clearance values (CLss = 97 +/- 30 ml.min-1) suggest rapid metabolism by amino- and carboxy-peptidases. 相似文献
139.
140.