全文获取类型
收费全文 | 892篇 |
免费 | 80篇 |
专业分类
972篇 |
出版年
2024年 | 3篇 |
2023年 | 8篇 |
2022年 | 12篇 |
2021年 | 28篇 |
2020年 | 6篇 |
2019年 | 7篇 |
2018年 | 14篇 |
2017年 | 13篇 |
2016年 | 22篇 |
2015年 | 53篇 |
2014年 | 43篇 |
2013年 | 60篇 |
2012年 | 76篇 |
2011年 | 61篇 |
2010年 | 55篇 |
2009年 | 32篇 |
2008年 | 51篇 |
2007年 | 55篇 |
2006年 | 43篇 |
2005年 | 49篇 |
2004年 | 34篇 |
2003年 | 34篇 |
2002年 | 31篇 |
2001年 | 12篇 |
2000年 | 9篇 |
1999年 | 10篇 |
1998年 | 11篇 |
1997年 | 7篇 |
1996年 | 5篇 |
1995年 | 8篇 |
1994年 | 3篇 |
1993年 | 7篇 |
1992年 | 9篇 |
1991年 | 4篇 |
1990年 | 10篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 7篇 |
1982年 | 4篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1971年 | 3篇 |
1968年 | 4篇 |
排序方式: 共有972条查询结果,搜索用时 15 毫秒
1.
Bertin N.; Guichard S.; Leonardi C.; Longuenesse J. J.; Langlois D.; Navez B. 《Annals of botany》2000,85(6):741-750
Changes in yield and quality of fresh tomatoes in response toair vapour pressure deficit (VPD) and plant fruit load werestudied under Mediterranean summer conditions. Plants thinnedto three or six fruits per truss were grown in two compartments,one at a VPD below 1.5 kPa, the other without VPD control. Theseasonal trend in fruit yield and quality was assessed fromApril to September by weekly measurement of number, fresh weightand dry matter content of harvested fruits, together with theoccurrence of blossom-end-rot (BER) and cracking. On two occasions,in July and September, sugar and acid content was measured atthree ripening stages. The seasonal decrease in fresh yieldwas attenuated at low VPD, because of higher individual fruitfresh weight, especially at low fruit load. Low VPD decreasedoccurrence of BER but like low fruit load, it increased fruitcracking. Fruit dry matter content was lower at low VPD, butwas unaffected by fruit load. Sugar content and the ratio ofsugars:acids was increased at high VPD and low fruit load, withinteractive effects depending on season and ripening stage.The influence of VPD on acid content differed with fruit loadand also changed during ripening and between seasons. Resultsshowed that water was the main limiting factor for growth offruits picked in July; at this time, reducing fruit load topromote mean fruit size had negative effects on BER and cracking.Reducing VPD reduced BER but had a negative effect on crackingand diluted both the dry matter and sugar content. For fruitsharvested later in summer, these negative effects were attenuatedbecause fruit growth was also carbon limited. Copyright 2000Annals of Botany Company Lycopersicon esculentum Mill., tomato, water and carbon stress, yield, quality, dry matter, sugar, acid, BER, volatile composition 相似文献
2.
Tissue and Cellular Distribution of Glutamine Synthetase in Roots of Pea (Pisum sativum) Seedlings 总被引:6,自引:3,他引:3 下载免费PDF全文
The effect of nitrate application on glutamine synthetase activity in roots of pea (Pisum sativum L.) seedlings (2 weeks old) was studied. Separation of organelles from root fragments by sucrose density-gradient centrifugation revealed that both nitrite reductase and glutamine synthetase activities increased in root plastids as a response to nitrate application and that no such response was induced by ammonium application. Glutamine synthetase activity was also found to increase in plastids with distance from apex in nitrate-treated plants, the highest specific activity being located in the fourth 1-centimeter segment. Separation by SDS-PAGE and characterization by Western blotting showed that cytosolic glutamine synthetase contains one subunit polypeptide (28 kilodaltons) and that plastid glutamine synthetase contains both the 38-kilodalton subunit and a heavier subunit. When nitrate was present in the nutrient solution, the heavier subunit increased in abundance in protein fractions obtained from purified root plastids. 相似文献
3.
Valérie Toulon Hervé Sentenac Jean-Baptiste Thibaud André Soler David Clarkson Claude Grignon 《Planta》1989,179(2):235-241
The effect of HCO
3
-
on ion absorption by young corn roots was studied in conditions allowing the independent control of both the pH of uptake solution and the CO2 partial pressure in air bubbled through the solution. The surface pH shift in the vicinity of the outer surface of the plasmalemma induced by active H+ excretion was estimated using the initial uptake rate of acetic acid as a pH probe (Sentenac and Grignon (1987) Plant Physiol. 84, 1367). Acetic acid and orthophosphate uptake rates and NO
3
-
accumulation were slowed down, while 86Rb+ uptake and K+ accumulation rates were increased by HCO
3
-
. These effects were similar to those induced by 4-(2-hydroxyethyl)-1-piperazineethane sulfonic acid/2-amino-2-(hydroxymethyl)-1,3-propanediol (Hepes-Tris). They were more pronounced when the H+ excretion was strong, were rapidly reversible and were not additive to those of Hepes-Tris. The hypothesis is advanced that the buffering system CO2/H2CO3/HCO
3
-
accelerated the diffusion of equivalent H+ inside the cell wall towards the medium. This attenuated the surface pH shift in the vicinity the plasma membrane and affected the coupling between the proton pump and cotransport systems.Abbreviations FW
fresh weight
- Hepes
4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid
- Jaa
acetic acid influx
- JK
+
K+ influx
- JPi
orthophosphate influx
- Mes
2-(N-morpholino)ethanesulfonic acid
- pCO2
CO2 partial pressure
- Tris
2-amino-2-(hydroxymethyl)-1,3-propanediol 相似文献
4.
The molecular structure of a 4'-epiadriamycin complex with d(TGATCA) at 1.7A resolution: comparison with the structure of 4'-epiadriamycin d(TGTACA) and d(CGATCG) complexes. 下载免费PDF全文
The structure of the complex between d(TGATCA) and the anthracycline 4'-epiadriamycin has been determined by crystallographic methods. The crystals are tetragonal, space group P4(1)2(1)2 with unit cell dimensions of a = 28.01, c = 52.95A. The asymmetric unit consists of one strand of hexanucleotide, one molecule of 4'-epiadriamycin and 34 waters. The R-factor is 20.2% for 1694 reflections with F greater than or equal to 2 sigma F to 1.7A. Two asymmetric units associate to generate a duplex complexed with two drug molecules at the d(TpG) steps of the duplex. The chromophore intercalates between these base pairs with the anthracycline amino-sugar positioned in the minor groove. The double helix is a distorted B-DNA type structure. Our structure determination of d(TGATCA) complexed to 4'-epiadriamycin allows for comparison with the previously reported structures of 4'-epiadriamycin bound to d(TGTACA) and to d(CGATCG). The three complexes are similar in gross features and the intercalation geometry is the same irrespective of whether a d(CpG) or d(TpG) sequence is involved. However, the orientation of the amino-sugar displays a dependence on the sequence adjacent to the intercalation site. The flexibility of this amino-sugar may help explain why this class of antibiotics displays a relative insensitivity to base sequence when they bind to DNA. 相似文献
5.
C Fardeau M Langlois D Ingrand C Asselot H Moret F Nugier 《Comptes rendus de l'Académie des sciences. Série III, Sciences de la vie》1992,314(10):443-449
During 7 serial passages of Herpes Simplex Virus (HSV1) in rabbit cornea treated with idoxuridine (IUdR) (P1 to P7), the emergence of resistance had been obtained from P3. The reversion towards IUdR sensitivity has been investigated from either viral population P3 or P6 by 6 serial passages in rabbit cornea treated by Vaseline (V1 to V6). From viral population P3, the reversion to IUdR sensitivity has been obtained at V4. In contrast, from viral population P6, the IUdR resistance was conserved from V1 to V6. In vitro, on Vero cells, the effective doses 50% (ED50) and 90% (ED90), determined by dye uptake assay and plaque reduction assay, confirmed the reversibility towards IUdR sensitivity obtained from P3 and the stability of IUdR resistance from P6. 相似文献
6.
Laetitia Mathon Virginie Marques Stéphanie Manel Camille Albouy Marco Andrello Emilie Boulanger Julie Deter Régis Hocdé Fabien Leprieur Tom B. Letessier Nicolas Loiseau Eva Maire Alice Valentini Laurent Vigliola Florian Baletaud Sandra Bessudo Tony Dejean Nadia Faure Pierre-Edouard Guerin Meret Jucker Jean-Baptiste Juhel Kadarusman Andrea Polanco F. Laurent Pouyaud Dario Schwörer Kirsten F. Thompson Marc Troussellier Hagi Yulia Sugeha Laure Velez Xiaowei Zhang Wenjun Zhong Loïc Pellissier David Mouillot 《Global Ecology and Biogeography》2023,32(8):1336-1352
Aim
Coastal fishes have a fundamental role in marine ecosystem functioning and contributions to people, but face increasing threats due to climate change, habitat degradation and overexploitation. The extent to which human pressures are impacting coastal fish biodiversity in comparison with geographic and environmental factors at large spatial scale is still under scrutiny. Here, we took advantage of environmental DNA (eDNA) metabarcoding to investigate the relationship between fish biodiversity, including taxonomic and genetic components, and environmental but also socio-economic factors.Location
Tropical, temperate and polar coastal areas.Time period
Present day.Major taxa studied
Marine fishes.Methods
We analysed fish eDNA in 263 stations (samples) in 68 sites distributed across polar, temperate and tropical regions. We modelled the effect of environmental, geographic and socio-economic factors on α- and β-diversity. We then computed the partial effect of each factor on several fish biodiversity components using taxonomic molecular units (MOTU) and genetic sequences. We also investigated the relationship between fish genetic α- and β-diversity measured from our barcodes, and phylogenetic but also functional diversity.Results
We show that fish eDNA MOTU and sequence α- and β-diversity have the strongest correlation with environmental factors on coastal ecosystems worldwide. However, our models also reveal a negative correlation between biodiversity and human dependence on marine ecosystems. In areas with high dependence, diversity of all fish, cryptobenthic fish and large fish MOTUs declined steeply. Finally, we show that a sequence diversity index, accounting for genetic distance between pairs of MOTUs, within and between communities, is a reliable proxy of phylogenetic and functional diversity.Main conclusions
Together, our results demonstrate that short eDNA sequences can be used to assess climate and direct human impacts on marine biodiversity at large scale in the Anthropocene and can further be extended to investigate biodiversity in its phylogenetic and functional dimensions. 相似文献7.
8.
Some characteristics and antibiotic resistance of anaerobic bacteria from the ceca and colons of pigs fed chlortetracycline-containing and unmedicated diets. 总被引:2,自引:1,他引:1 下载免费PDF全文
Morphology and end product patterns were used to group 112 bacterial isolates from the ceca and colons of pigs fed unmedicated and chlortetracycline-containing diets. Most of the isolates (68%) were resistant to chlortetracycline (greater than 4 micrograms/ml). Chlortetracycline resistance was associated with all groups of anaerobic and facultative bacteria. 相似文献
9.
10.
Forty-two patients were followed up after 44 renal transplantations in an effort to evaluate possible benefits from the following protocol: systematic microbiologic and clinical surveillance, early and aggressive research for the cause of suspected infections, refusal to use prophylactic antibiotherapy, and selection of treatment according to the established cause of the infection. During 18,030 days of follow-up 124 infections were recorded, of which 110 were bacterial, 11 viral and 3 protozoal. Eighty originated in the urinary tract, 17 in skin wounds and 10 in the lower respiratory tract. Septicemia occurred three times, and one death due to infection was recorded. In the treatment of bacterial infections patients received antibiotics for 2486 days. Ampicillin (given for 816 days) and "minor" drugs such as sulfonamides and urinary antiseptics (given for 1036 days) were used 74.5% of the time, whereas gentamicin was used only 2.6% of the time (64 days). Combined antibacterial therapy was needed 1.2% of the time (29 days). A restrictive policy regarding anti-biotherapy seems to be beneficial to renal transplant recipients. 相似文献