全文获取类型
收费全文 | 304篇 |
免费 | 21篇 |
国内免费 | 6篇 |
出版年
2023年 | 3篇 |
2022年 | 3篇 |
2021年 | 3篇 |
2020年 | 14篇 |
2019年 | 7篇 |
2018年 | 10篇 |
2017年 | 9篇 |
2016年 | 9篇 |
2015年 | 6篇 |
2014年 | 12篇 |
2013年 | 16篇 |
2012年 | 9篇 |
2011年 | 9篇 |
2010年 | 7篇 |
2009年 | 13篇 |
2008年 | 14篇 |
2007年 | 7篇 |
2006年 | 7篇 |
2005年 | 10篇 |
2004年 | 8篇 |
2003年 | 15篇 |
2002年 | 10篇 |
2001年 | 7篇 |
2000年 | 7篇 |
1999年 | 3篇 |
1998年 | 11篇 |
1997年 | 7篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 14篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有331条查询结果,搜索用时 15 毫秒
1.
2.
Over the past two decades, the dendroclimate community has produced various annually resolved, warm season temperature reconstructions for the extratropical Northern Hemisphere. Here we compare these tree-ring based reconstructions back to 831 CE and present a set of basic metrics to provide guidance for non-specialists on their interpretation and use. We specifically draw attention to (i) the imbalance between (numerous) short and (few) long site chronologies incorporated into the hemispheric means, (ii) the beneficial effects of including maximum latewood density chronologies in the recently published reconstructions, (iii) a decrease in reconstruction covariance prior to 1400 CE, and (iv) the varying amplitudes and trends of reconstructed temperatures over the past 1100 years. Whereas the reconstructions agree on several important features, such as warmth during medieval times and cooler temperatures in the 17th and 19th centuries, they still exhibit substantial differences during 13th and 14th centuries. We caution users who might consider combining the reconstructions through simple averaging that all reconstructions share some of the same underlying tree-ring data, and provide four recommendations to guide future efforts to better understand past millennium temperature variability. 相似文献
3.
THE COMBINED EFFECTS OF LOW TEMPERATURE AND SO2 +NO2 POLLUTION ON THE NEW SEASON'S GROWTH AND WATER RELATIONS OF PICEA SITCHENSIS 总被引:6,自引:5,他引:1
Picea sitchensis (Bong.) Carr. seedlings were exposed to SO2 , NO2 and SO2 + NO2 during dormancy in controlled environments, and were taken to night temperatures of 4, 0, −5, −10 and −15 °C in a freezer. Conditions in the freezer were carefully monitored during the low–temperature treatments. In two experiments, different photoenvironments and temperature regimes were imposed prior to the cold treatments, and different effects were observed. In the first, only limited frost hardiness was achieved and night temperatures of −15 °C were lethal. Temperatures of −5 and − 10 °C led to poor survival of lateral buds, particularly in plants exposed to 45 ppb SO2 . The poor bud break in plants exposed to SO2 and to − 5 °C resulted in a loss of the effectiveness of this temperature as a chill requirement. Pressure-volume analysis showed that the shoots of plants exposed to NO2 had greater elasticity (lower elastic moduli, e), so that loss of turgor occurred at lower relative water contents. In contrast, a hardening period (2 weeks in night/day temperatures of 3/10 °C and 8 h days at 50 μmol m−2 s−1 PAR) gave decreased elasticity and lower solute potentials of spruce shoots. In the second experiment, exposure to 30 ppb SO2 and SO2 + NO2 led to slight, but consistent, increases in frost injury to the needles of plants frozen to − 5 and − 10 °C. The results suggest that the main interaction of low temperatures and winter pollutants may be on bud survival rather than on needle damage, but that effects are subtle, only occurring with certain combinations of pollutant dose and cold treatment. 相似文献
4.
Abstract The diversity of bacterial communities isolated from Antarctic lake sediment in chemostats under constant low temperature (8°C) or diurnally fluctuating temperature (1°C to 16°C) was examined. The median optimum temperature for growth of the freshwater bacteria isolated from the fluctuation chemostat was significantly lower ( P < 1%) than that for those from the constant temperature chemostat. The diversity of the enriched bacterial community isolated in the chemostat culture subjected to short-term temperature fluctuations was greater than that enriched under constant temperature. At least 4 different groups of bacteria, that occupied separate 'temperature niches', were isolated from the fluctuating chemostat compared to only one group isolated from the stable chemostat. Furthermore, a pseudomonad from the fluctuating chemostat was shown to out-compete another pseudomonad from the stable chemostat when both were subjected to the fluctuating temperature regime. However, the pseudomonad of constant (8°C) temperature origin out-competed that isolated under fluctuating conditions when subjected to a stable temperature regime. 相似文献
5.
Seasonal changes in circadian rhythms of body temperatures in humans living in a dry tropical climate 总被引:1,自引:0,他引:1
A. Buguet R. Gati G. Soubiran J. P. Straboni A. M. Hanniquet G. Livecchi-Gonnot J. Bittel 《European journal of applied physiology and occupational physiology》1988,58(3):334-339
Seven volunteers (3 females and 4 males; 3 Caucasians and 4 Africans) participated in two 24 h sessions during the cool dry (CD) and the hot dry (HD) seasons of the sahelian tropical climate. Body temperatures were taken on portable cassette recorders for 24 h. Rectal (Tre) and mean skin (Tsk) temperatures decreased in the HD compared to the CD conditions, meeting one of the criteria for adaptation to heat. No ethnic differences in thermal responses were found. Males and females differed in their body temperature rhythms and in their reactions to heat. Body temperatures were higher in females than in males. Males reacted to heat with a decrease in Tre, without change in the Tre-Tsk gradient. Females showed a decrease in both Tre and Tsk, more marked for Tsk, with an increase in the Tre-Tsk gradient. It was concluded that males showed seasonal acclimatization to heat via a decrease in metabolism confirmed by a decrease in plasma levels of thyroid stimulating hormone (TSH) in the HD condition. Females showed a mixed metabolic and thermolytic type of acclimatization, with an absence of variation in plasma TSH levels. In conclusion, the steady rise in temperature between the CD and HD conditions was sufficient to trigger an acclimatization to heat similar in Caucasian and African subjects, although exposure to the external climate differed widely. 相似文献
6.
J. P. Libert C. Amoros J. Di Nisi A. Muzet H. Fukuda J. Ehrhart 《European journal of applied physiology and occupational physiology》1988,57(4):499-506
Body temperature regulation was studied in 6 male subjects during an acclimation procedure involving uninterrupted heat exposure for 5 successive days and nights in a hot dry environment (ambient temperature = 35 degrees C, dew-point temperature = 7 degrees C; air velocity = 0.2 m.s-1). Data were obtained at rest and during exercise (relative mechanical workload = 35% VO2max). At rest, hourly measurements were made of oesophageal and 4 local skin temperatures, to allow the calculation of mean skin temperature, and of body motility and heart rate. During the working periods these measurements were made at 5 min intervals. Hourly whole-body weight loss was measured at rest on a sensitive platform scale while in the working condition just before starting and immediately after completing the bicycle exercise. The results show that, in both exercise and at rest, the successive heat exposures increased the sweat gland output during the first 3 days. Afterwards, sweat rate decreased without any corresponding change in body temperature. For the fixed workload, the sweat rate decline was associated with a decrease in circulatory strain. Adjustments in both sweating and circulatory mechanisms occur in the first 3 days of continuous heat exposure. The overall sweat rate decline could involve a redistribution of the regional sweating rates which enhances the sweat gland activities of skin areas with maximal evaporative efficiencies. 相似文献
7.
ABSTRACT.
- 1 The mean supercooling points of first instar and adult Myzus persicae (Sulzer) maintained at 20°C and cooled at 1°C min?1 were ?26.6 and ?25.0°C respectively.
- 2 The LT50 (temperature) of the same age groups drawn from the same population and cooled at the same rate were ?8.1 and ?6.9°C, indicating extensive pre-freeze mortality in M.persicae under laboratory conditions.
- 3 Acclimation at 10 and 5°C did not affect supercooling but depressed the LT50 of both first instars and adult aphids.
- 4 Freezing of leaves during feeding did not increase mortality above that expected from the direct effects of low temperature.
- 5 The level of cold in different winters can be expressed in terms of the total number of frost days, and the frequency of abnormally cold days. Winter temperatures differ markedly in a vertical profile from the soil to the soil or grass surface, and then to the air (and foliage) above.
- 6 The time of the first record of M.persicae in suction trap samples is correlated with January and February temperatures except in the west of England and Wales. Further north December and January temperatures are relatively more important.
- 7 Winter temperatures and the resultant aphid mortality is a primary determinant of the timing of the spring migration.
8.
Summary The sum of effective temperatures (SET) and lower development threshold (LDT) were established for eggs and/or pupae of central European populations of 20 species of chrysopid, coccinellid, hemerobiid, and syrphid predators of aphids. LDT ranged between 5.6° and 12.2°C, SET between 38.3 and 140.9 day degrees (dd), with broad overlap among stages and taxa. When LDT was plotted against SET, the data for both eggs and pupae were scattered along a single regression line which predicted a 0.47°C decrease in LDT per 10 dd increase in SET (r=-0.77, p<0.001). A regression calculated from published data from all over the world predicted a 0.24°C/10 dd decrease in LDT, and the data were more scattered (r=-0.38, p<0.01). This is perhaps the first report on the functional relationship between LDT and SET at the interspecific level. The species and stages differed in typical development length (VDL) and in the extent of its deceleration by low temperatures (DD). DD increased with increasing VDL, but the relative effect of low temperature on development length (DD/VDL ratio) reflected thermal adaptations consistent with the life history of the species. Polyvoltine species were less affected by low temperatures than monovoltine species, particularly the thermophilic ones. 相似文献
9.
10.
Toshinobu Yaginuma Michihiro Kobayashi Okitsugu Yamashita 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1990,160(3):277-285
Summary Diapause eggs of the silkworm, Bombyx mori, exposed to 5°C and 0.5°C from 2 or 30 days after oviposition, were examined for changes in contents of glycogen, sorbitol and glycerol. Cold acclimation did not alter the profile of accumulation of sorbitol from that in eggs kept continuously at 25°C. However, acclimation at 5°C resulted in conversion of sorbitol to glycogen, while acclimation at 0.5°C was not accompanied by the utilization of sorbitol. NAD-sorbitol dehydrogenase (NAD-SDH; EC 1.1.1.14) activity was examined in the cold-acclimated eggs. The activity was induced by acclimation at 5°C but not at 0.5°C. Incubation at 0.5°C suppressed any further increase in the activity that had been induced. Temperature-directed changes in NAD-SDH activity paralleled those in sorbitol content. Hatching of the diapause eggs was monitored after cold acclimation for various periods of time and subsequent transfer to 25°C. Incubation at 0.5°C was less effective than 5°C at breaking diapause. The time required for the eggs to hatch in synchrony after acclimation at 5°C coincided with that required for the induction of NAD-SDH activity. These results show that different effects result from acclimation at 5°C and near 0°C with respect to the control of NAD-SDH activity, that utilization of sorbitol is controlled by NAD-SDH activity, and that induction of this activity is temperature-dependent. Furthermore, induction of NAD-SDH activity is involved in the termination of diapause in B. mori.Abbreviations
DH
diapause hormone
-
NAD
nicotinamide-adenine-dinucleotide
-
NAD-SDH
NAD-sorbitol-dehydrogenase 相似文献