全文获取类型
收费全文 | 321篇 |
免费 | 13篇 |
出版年
2021年 | 4篇 |
2020年 | 1篇 |
2018年 | 1篇 |
2017年 | 5篇 |
2016年 | 6篇 |
2015年 | 11篇 |
2014年 | 14篇 |
2013年 | 11篇 |
2012年 | 24篇 |
2011年 | 22篇 |
2010年 | 16篇 |
2009年 | 18篇 |
2008年 | 21篇 |
2007年 | 23篇 |
2006年 | 17篇 |
2005年 | 24篇 |
2004年 | 22篇 |
2003年 | 15篇 |
2002年 | 21篇 |
2001年 | 12篇 |
2000年 | 9篇 |
1999年 | 7篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有334条查询结果,搜索用时 15 毫秒
71.
James S. Farris Mari Källersjö Victor A. Albert Marc Allard Arne Anderberg Brunella Bowditch Carol Bult James M. Carpenter Timothy M. Crowe Jan De Laet Kirk Fitzhugh Darryl Frost Pablo Goloboff Christopher J. Humphries Ulf Jondelius Darlene Judd Per Ola Karis Diana Lipscomb Melissa Luckow David Mindell Jyrki Muona Kevin Nixon William Presch Ole Seberg Mark E. Siddall Lena Struwe ers Tehler John Wenzel Quentin Wheeler Ward Wheeler 《Cladistics : the international journal of the Willi Hennig Society》1995,11(2):211-218
72.
Sarita Keski-Saari Jyrki Pusenius Riitta Julkunen-Tiitto 《Global Change Biology》2005,11(7):1180-1194
We studied the ability of tree seedlings to respond to two environmental factors, elevated ultraviolet B (UVB) radiation and availability of nitrogen (N), at the beginning of their development. Seeds of two birch species, Betula pubescens Ehrh. (common white birch) and B. pendula Roth (silver birch), were germinated and the seedlings grown in an experimental field in eastern Finland. The experimental design consisted of a constant 50% increase in UVB radiation (including a slight increase in UVA), a UVA control (a slight increase in UVA) and a control. The seedlings were fertilized with three levels of N. The experiment lasted for 2 months; aboveground biomass was measured and the most mature leaf of each seedling was taken for the analyses of phenolics. Growth of the seedlings was not significantly affected by enhanced UVB, but was increased by increasing N. Elevated UVB induced significant changes in phenolic compounds. Quercetin glycosides were accumulated in the leaves of both species in response to UVB; this is considered to be a protective response. However, the direction of the responses of individual phenolics to different N regimens differed. In addition, concentration of soluble condensed tannins was lower at moderate N than that at lower levels of N in both species; on the contrary, in B. pubescens the concentration of insoluble condensed tannins was highest at moderate N. No significant interaction between UV and N was detected, and the responses of the two species were highly similar to UVB, while the responses to N regimens varied slightly more between species. 相似文献
73.
The highest specific activity of beta-N-acetylglucosaminidase (beta-NAG) was found in the different parts of the epididymis, where the activity seemed to be partly in secretory and partly in non-secretory, tissue-bound form. Epididymal spermatozoa also contained moderate beta-NAG activity. The beta-NAG was separated by chromatofocussing and anion exchange chromatography with HPLC into multiple forms with distinct pI values (8.0-4.0). The cauda epididymidis, ampulla and the seminal vesicles formed the major secretory sources of the high beta-NAG activity in bull seminal plasma. The major secretory forms of beta-NAG in caput and cauda epididymidis showed distinct elution profiles. In the fractionation with gel filtration on Sepharose 6B, the beta-NAG activities derived from bull testis and caput epididymidis had smaller molecular weights than did the secretory enzymes in seminal plasma, seminal vesicle secretion and cauda epididymidis. Maximum activity of all beta-NAG isoenzymes was observed at pH 5.0. They were almost totally inactivated at 60 degrees C and about 75-80% of the activity was lost at 55 degrees C. All the isoenzymes were strongly inhibited by thiol reagents but not with other metal ions and chelating agents. Histochemical studies showed a strong granular (lysosomal) reaction for beta-NAG in basal cells and basal parts of the principal cells in all but the initial segment of the epididymis. An apical (secretory) reaction was prominent in the distal caput and corpus as well as in distal cauda. After the distal caput the luminal sperm mass became increasingly mixed with a beta-NAG-positive material. The epithelial cells of the ampulla and seminal vesicle displayed a moderate apical (secretory) reaction. 相似文献
74.
alpha-L-Fucosidase (EC 3.2.1.51) activity was studied in different reproductive organs, seminal plasma and spermatozoa of the bull. The highest specific activity of alpha-L-fucosidase was found in the epididymis. Gel filtration at pH 7.0 revealed two alpha-L-fucosidases (alpha-L-fucosidase I and alpha-L-fucosidase II) in most reproductive tissues, but seminal plasma, spermatozoa and epididymal cauda contained only form I. Fractionation at basic pH (pH 8.5) resulted in the elution of alpha-L-fucosidase as form II. Some differences were encountered in pH profiles and thermal stabilities of the two enzyme forms and they showed additional polymorphism after chromatofocusing. The comparison of enzyme profiles after fractionations suggests that cauda epididymidis is the main source of the seminal plasma activity in the bull. 相似文献
75.
The biochemical distribution of beta-glucuronidase activity was studied in different reproductive organs, seminal plasma and spermatozoa of the bull. The highest specific activity was found in the epididymis, where the activity seemed to be mostly in nonsecretory and only partly in secretory form. A molecular weight of 340 X 10(3) to 360 X 10(3) was recorded for beta-glucuronidase in the bull seminal plasma and different reproductive organs with gel filtration on Sepharose 6B. In chromatofocusing four activity areas (CF-1 to CF-4) were usually obtained for beta-glucuronidase in the bull seminal plasma. The major peak CF-2 (also in the different reproductive organs) had a pI value of 5.6-5.3 and the two minor activity areas CF-1 and CF-3 had pI values of 6.0-5.8 and 5.2-4.5, respectively. Peak CF-4 eluted with a NaCl gradient after the Polybuffer elution and possibly represents an enzyme form incompletely detached from negatively charged cellular material. Isoelectric focusing on polyacrylamide gel confirmed the heterogeneity of beta-glucuronidase, since several activity bands were detected in the secretion of the different parts of the epididymis. beta-Glucuronidase activities CF-1, CF-2 and CF-3 had similar pH activity profiles (pH optimum around pH 3.0-4.0) and response to thermal inactivation at 50 degrees C. The multiple beta-glucuronidase activities of the bull seminal plasma are proposed to derive mainly from the secretion of the cauda epididymidis. 相似文献
76.
Human plasma lecithin-cholesterol acyltransferase. An elucidation of the catalytic mechanism 总被引:6,自引:0,他引:6
Human plasma lecithin-cholesterol acyltransferase (LCAT) transacylates the sn-2 fatty acid of lecithin to cholesterol forming cholesteryl ester and lysolecithin. Measurement of the phospholipase A2 and transacylase activities of the enzyme using proteoliposome substrates and following selective chemical modification of serine, histidine, and cysteine residues of pure homogeneous LCAT indicated the following catalytic mechanism: HS-Cys-E-Ser-OH + lecithin in equilibrium HS-Cys-E-Ser-O-FA + lysolecithin, HS-Cys-E-Ser-O-FA in equilibrium FA-S-Cys-E-Ser-OH, FA-S-Cys-E-Ser-OH + cholesterol-OH in equilibrium HS-Cys-E-Ser-OH + cholesterol-O-FA, where FA denotes fatty acid. Modification of 2 LCAT cysteine residues with 5,5'-dithiobis-(2-nitrobenzoic acid) or treatment with ferricyanide inactivated the transacylase but not the phospholipase A2 activity. Modification of 1 serine residue with phenylmethanesulfonyl fluoride or 1 histidine residue with diethyl pyrocarbonate inhibited cholesteryl ester formation and phospholipase A2 activity. Proteoliposome substrates protected both activities against chemical inactivation. Lecithin alone protected the phospholipase A2 activity against phenylmethanesulfonyl fluoride inactivation but not the transacylase against 5,5'-dithiobis-(2-nitrobenzoic acid) inactivation. Incubation of native LCAT with arachidonyl-CoA or the lecithin-apo-A-I proteoliposome resulted in acylation of three enzyme sites, only one of which was stable to neutral hydroxylamine after denaturation. Fatty acylenzyme oxy- and thioesters were demonstrable in both cases. No transfer of arachidonic acid from iodoacetamide-modified LCAT to cholesterol occurred, indicating that the fatty-acylated serine residue cannot directly esterify cholesterol. Cholesterol arachidonate was formed upon incubation of phenylmethanesulfonyl fluoride-modified LCAT with arachidonyl-CoA. 相似文献
77.
Anne I. Nissinen Juha-Matti Pihlava Satu Latvala Lauri Jauhiainen 《The Annals of applied biology》2020,177(2):166-177
The control of carrot psyllid Trioza apicalis Förster largely relies on chemical measures, and the current integrated pest management (IPM) strategy is based on pest scouting. The number of active ingredients available for psyllid control will further decline in the coming years. The need for alternative control measures is therefore urgent. In this work the efficiency of different control programs including a kaolin particle film and plant-derived, crude saponin extract, chemical control, insect net and IPM (kaolin in combination with insecticides) programs to reduce psyllid feeding damage, reproduction and the spread of “Candidatus Liberibacter solanacearum” (CLso) in carrots was studied. Each year in 2016–2018, four replicates of each treatment were randomised in a row-column design on a commercial carrot farm. After the treatments were executed, the psyllid nymphs and eggs were counted. At the harvest, the carrot roots and shoots were weighed, damages assessed, and samples were taken for CLso detection from 50 plants at each replicate. Kaolin treatment alone and in combination with insecticides effectively reduced the number of psyllid nymphs and eggs in all the years studied. Saponin was applied only on the first year, since it significantly increased the number of T. apicalis eggs compared to other treatments. The insect net was superior to other treatments in all the studied aspects in all the years. Under normal weather conditions, the highest root weight was harvested under the insect net, followed by the chemical control program consisting of pyrethroids, kaolin treatment, untreated control and saponin treatment. During extreme weather conditions, chemical control programs were not effective at protecting the carrots from psyllid feeding, which was reflected as low root yield. In all years, the carrot leaf damage percent negatively correlated with the root weight. Similarly, the shoot:root ratio increased as the leaf-curling percentage rose, which was even pronounced under drought stress. The effect of climatic stress should be considered when developing IPM strategies. 相似文献
78.
Geraldine Cilpa-Karhu Matti Jauhiainen Marja-Liisa Riekkola 《Journal of lipid research》2015,56(1):98-108
Inhibition of cholesterol ester transfer protein (CETP), a protein mediating transfer of neutral lipids between lipoproteins, has been proposed as a means to elevate atheroprotective HDL subpopulations and thereby reduce atherosclerosis. However, off-target and adverse effects of the inhibition have raised doubts about the molecular mechanism of CETP-HDL interaction. Recent experimental findings have demonstrated the penetration of CETP into HDL. However, atomic level resolution of CETP penetration into HDL, a prerequisite for a better understanding of CETP functionality and HDL atheroprotection, is missing. We constructed an HDL particle that mimics the actual human HDL mass composition and investigated for the first time, by large-scale atomistic molecular dynamics, the interaction of an upright CETP with a human HDL-mimicking model. The results demonstrated how CETP can penetrate the HDL particle surface, with the formation of an opening in the N barrel domain end of CETP, put in evidence the major anchoring role of a tryptophan-rich region of this domain, and unveiled the presence of a phenylalanine barrier controlling further access of HDL-derived lipids to the tunnel of CETP. The findings reveal novel atomistic details of the CETP-HDL interaction mechanism and can provide new insight into therapeutic strategies. 相似文献
79.
Jyrki Rasku Martti Juhola Esko Toppila Ilmari Pyykk 《Biomedical signal processing and control》2007,2(1):1-8
The objective of the present research was to investigate whether hidden Markov models can be used to recognise and classify balance signals extracted from two subject groups, the healthy and patients suffering from otoneurological vertiginous diseases. Two different testing protocols were applied: arising from a chair and standing on the force platform. Signals recorded according to these protocols were trained for models with different numbers of states to find the best choices as model structures. We found that these models with 7–15 states were able to recognise the healthy subjects from the patients with the accuracy between 70 and 90% although their balance measurements were visually very similar and difficult to separate between two groups. 相似文献
80.
Annina Lyly Carina von Schantz Tarja Salonen Outi Kopra Jani Saarela Matti Jauhiainen Aija Kyttälä Anu Jalanko 《BMC cell biology》2007,8(1):1-14