全文获取类型
收费全文 | 9814篇 |
免费 | 596篇 |
国内免费 | 4篇 |
出版年
2023年 | 93篇 |
2022年 | 127篇 |
2021年 | 260篇 |
2020年 | 199篇 |
2019年 | 217篇 |
2018年 | 279篇 |
2017年 | 255篇 |
2016年 | 400篇 |
2015年 | 515篇 |
2014年 | 555篇 |
2013年 | 701篇 |
2012年 | 845篇 |
2011年 | 740篇 |
2010年 | 523篇 |
2009年 | 447篇 |
2008年 | 575篇 |
2007年 | 567篇 |
2006年 | 504篇 |
2005年 | 426篇 |
2004年 | 400篇 |
2003年 | 349篇 |
2002年 | 293篇 |
2001年 | 83篇 |
2000年 | 64篇 |
1999年 | 72篇 |
1998年 | 84篇 |
1997年 | 61篇 |
1996年 | 62篇 |
1995年 | 64篇 |
1994年 | 54篇 |
1993年 | 48篇 |
1992年 | 45篇 |
1991年 | 39篇 |
1990年 | 21篇 |
1989年 | 30篇 |
1988年 | 31篇 |
1987年 | 18篇 |
1986年 | 23篇 |
1985年 | 25篇 |
1984年 | 36篇 |
1983年 | 24篇 |
1982年 | 20篇 |
1981年 | 30篇 |
1980年 | 27篇 |
1979年 | 23篇 |
1978年 | 19篇 |
1976年 | 15篇 |
1975年 | 12篇 |
1974年 | 19篇 |
1973年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
41.
Fernando Pliego-Alfaro Mary Joy R. Monsalud Richard E. Litz Dennis J. Gray Pamela A. Moon 《Plant Cell, Tissue and Organ Culture》1996,44(1):63-70
Inhibition of mango somatic embryo growth was inducedin vitro by treatments for 4 or more weeks with abscisic acid (0–100 M ABA) with and without high osmolarity provided by mannitol (0–10%). High osmolarity and ABA significantly affected somatic embryo length, precocious germination and the production of good quality secondary somatic embryos. High osmolarity also affected root elongation. Abscisic acid was more effective in suppressing growth and development of 0.5 cm-length somatic embryos than smaller somatic embryos. Development beyond the heart stage was significantly inhibited by both ABA and mannitol treatments. The recovery of good quality somatic embryos was enhanced by high levels of ABA (100 M) with and without mannitol (0–5%). Somatic embryos that had been pulsed with ABA were partially desiccated at different relative humidities. Weight loss was affected only by relative humidity; and ABA did not enhance desiccation tolerance.Abbreviations ABA
Abscisic acid
- 2,4-D
2,4-Dichlorophenoxyacetic acid
- MM1
Mango maturation medium
- RH
Relative humidity 相似文献
42.
Jose Pontón Fernando L. Hernando Maria Dolores Moragues Pedro L. Barea Mara Gerloni Stefania Conti Paola Fisicaro Cristina Cantelli Luciano Polonelli 《Mycopathologia》1996,133(2):89-94
The presence of heat shock mannoproteins (HSMPs) reactive with sIgA was demonstrated in several C. albicans strains. The subculture of the C. albicans isolated from mucosal surfaces on Sabouraud's dextrose agar at 25 °C switched off the HSMP expression. A re-expression of the HSMPs was obtained in the same medium by shifting the temperature of incubation to 37 °C. However, expression of HSMPs in two strains isolated from deep infections was maintained during several subcultures on Sabouraud's dextrose agar at 25 °C. A glycoprotein of 200 kDa seemed to be the main HSMP reacting with vaginal sIgA. The data presented in this study suggest that factors other than temperature can influence the expression of C. albicans HSMPs and therefore these antigens should be referred as stress mannoproteins.Abbreviations HSMPs
heat shock mannoproteins
- MAb
monoclonal antibody
- sIgA
secretory IgA 相似文献
43.
Effects of plant size on photosynthesis and water relations in the desert shrub Prosopis glandulosa (Fabaceae) 总被引:1,自引:0,他引:1
Amrita G. de Soyza Augusto C. Franco Ross A. Virginia James F. Reynolds Walter G. Whitford 《American journal of botany》1996,83(1):99-105
The Jornada del Muerto basin of the Chihuahuan Desert of southern New Mexico, USA, has undergone a marked transition of plant communities. Shrubs such as mesquite (Prosopis glandulosa) have greatly increased or now dominate in areas that were previously dominated by perennial grasses. The replacement of grasses by shrubs requires an establishment phase where small shrubs must compete directly with similar-sized grass plants. This is followed by a phase in which large, established shrubs sequester nutrients and water within their biomass and alter soil resources directly under their canopy, creating “islands” of fertility. We hypothesized that these two phases were associated with shrubs having different physiological response capacities related to their age or size and the resource structure of the environment. As a corollary, we hypothesized that responses of small shrubs would be more tightly coupled to variation in soil moisture availability compared to large shrubs. To test these hypotheses, we studied gas exchange and water relations of small (establishing) and large (established) shrubs growing in the Jornada del Muerto as a function of varying soil moisture during the season. The small shrubs had greater net assimilation, stomatal conductance, transpiration, and xylem water potential than large shrubs following high summer rainfall in July, and highest seasonal soil moisture at 0.3 m. High rates of carbon assimilation and water use would be an advantage for small shrubs competing with grasses when shallow soil moisture was plentiful. Large shrubs had greater net assimilation and water-use efficiency, and lower xylem water potential than small shrubs following a dry period in September, when soil moisture at 0.3 m was lowest. Low xylem water potentials and high water-use efficiency would allow large shrubs to continue acquiring and conserving water as soil moisture is depleted. Although the study provides evidence of differences in physiological responses of different-sized shrubs, there was not support for the hypothesis that small shrubs are more closely coupled to variation in soil moisture availability than large shrubs. Small shrubs may actually be less coupled to soil moisture than large shrubs, and thus avoid conditions when continued transpiration could not be matched by equivalent water uptake. 相似文献
44.
45.
Antonio Balas Felix Garcia-Sanchez Fernando Gomez-Reino Jose L. Vicario 《Immunogenetics》1994,39(6):452-452
Correspondence to: J. L. Vicario. 相似文献
46.
R. F. M. van Steveninck A. Babare D. R. Fernando M. E. van Steveninck 《Plant and Soil》1994,167(1):157-164
Plant species adapted to soils enriched with heavy metals often accumulate these metals in their above or below ground organs. In this study, electron probe microanalysis of fractured, quench-frozen root specimens of common crop species shows that an appreciable quantity of Zn can be bound as Zn phytate (myo-inositolkis-hexaphosphate) within small vacuoles of cells in the root elongation zone of lucerne, soybean, lupins, tomato, rapeseed, cabbage, radish, maize and wheat exposed to high levels of Zn (80–300 M). Globular deposits of Zn phytate are most frequently observed in the endodermis of dicotyledonous species and in the pericycle of monocotyledonous species, but may also occur in the stele and inner cortex after prolonged exposure to toxic levels of Zn. The deposits could not be found in Zn-treated sunflower, field peas and Italian ryegrass. In three crop species, lucerne, soybean and maize, Zn-induced phytate globules were frequent, but exposure of roots to 30 M Cd did not induce the formation of Cd-containing globular deposits as observed inLemna minor (Van Steveninck et al., 1990a, 1992). Simultaneous Zn and Cd treatment induced the formation of Zn phytate globules as effectively as Zn alone, and Cd was not detected in the deposits. 相似文献
47.
Iman Abdelmoty Fernando Albericio Louis A. Carpino Bruce M. Foxman Steven A. Kates 《Letters in Peptide Science》1994,1(2):57-67
Summary X-ray structure determinations of HBTU and HATU, well-known reagents for peptide bond formation, show that the solid-state structures of these compounds differ markedly from those commonly presented in the literature. The solid-state structures are isomers of the N,N,N',N'-tetramethyluronium salt formulation commonly written for HBTU and HATU. HBTU and HATU, obtained either directly from synthesis or from CH3CN solution, crystallize as the guanidinium N-oxide isomers. Both compounds crystallize in nearly identical conformations, despite marked differences in crystal packing. 相似文献
48.
The presence of an adenylate translocator in the envelope membranesof proplastids isolated from the cultured cells of tobacco (Nicotianatabacum L. cv. BY2) was examined by means of transport experimentsusing the silicone oil filtering centrifugation technique. Itwas observed that proplastids can import [3H]ATP, [3H]ADP, [3H]AMPand less specifically ADP-[14C]Glc which can eventually be usedfor starch biosynthesis. The effects of specific inhibitorsof the mitochondrial adenylate translocator, i.e. atractyloside,bongkrekic acid and carboxyatractyloside were tested. Similarto the case of amyloplasts isolated from the cultured cellsof sycamore and chloroplasts isolated from spinach leaves, onlyATP and ADP-Glc uptake were shown to be partially inhibitedby carboxyatractyloside. On the other hand, neither atractylosidenor bongkrekic acid exerted a significant inhibitory effecton adenylate uptake. (Received August 8, 1992; Accepted November 26, 1992) 相似文献
49.
Russell B. Lingham Keith C. Silverman Gerald F. Bills Carmen Cascales Manual Sanchez Rosalind G. Jenkins Suzanne E. Gartner Isabel Martin Maria T. Diez Fernando Peláez Sagrario Mochales Yu-Lin Kong Richard W. Burg Maria S. Meinz Leeyuan Huang Mary Nallin-Omstead Scott D. Mosser Michael D. Schaber Charles A. Omer David L. Pompliano Jackson B. Gibbs Sheo B. Singh 《Applied microbiology and biotechnology》1993,40(2-3):370-374
Chaetomellic acids A and B, isolated from Chaetomella acutiseta, are specific inhibitors of farnesyl-protein transferase that do not inhibit geranylgeranyl transferase type 1 or squalene synthase. Chaetomellic acids A and B are reversible inhibitors, resemble farnesyl diphosphate and probably inhibit FPTase by substituting for farnesyl diphosphate. Chaetomellic acid production appears to be widespread within the genus Chaetomella.
Correspondence to: R. B. Lingham 相似文献
50.
Fernando Hiraldo Borja Heredia Juan Carlos Alonso 《Ethology : formerly Zeitschrift fur Tierpsychologie》1993,93(2):117-124
Social feeding strategies of wintering red kites are analyzed in relation to age, food, roost-sites and differences from kite residents. Whereas young and adult wintering kites gathered at roost sites almost daily, adult residents did not, and immature residents only occasionally. Kites using roost sites feed more often on prey prelocated by others, while lone roosters also forage and discover food alone. After finding food, kites tend to shift to a new roost site and foraging area. Two details of the ‘information centre’ hypothesis are confirmed in our study: carcasses are unpredictably found patches, divisible between several individuals. But carcasses disappeared fast in the study area, and no increase with time in the number of birds consuming a carcass was observed, so that information transmission was unconfirmed. When kites leave the roost in groups no leader is detectable. It seems that other types of social foraging are operating, and the model best matching our results is network foraging. 相似文献