全文获取类型
收费全文 | 450篇 |
免费 | 29篇 |
国内免费 | 9篇 |
出版年
2021年 | 10篇 |
2020年 | 6篇 |
2019年 | 7篇 |
2018年 | 4篇 |
2016年 | 9篇 |
2015年 | 15篇 |
2014年 | 14篇 |
2013年 | 17篇 |
2012年 | 18篇 |
2011年 | 30篇 |
2010年 | 14篇 |
2009年 | 12篇 |
2008年 | 17篇 |
2007年 | 20篇 |
2006年 | 20篇 |
2005年 | 16篇 |
2004年 | 20篇 |
2003年 | 17篇 |
2002年 | 14篇 |
2001年 | 11篇 |
2000年 | 15篇 |
1999年 | 6篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1993年 | 4篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1989年 | 10篇 |
1988年 | 5篇 |
1987年 | 12篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 6篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1972年 | 5篇 |
1971年 | 18篇 |
1970年 | 10篇 |
1969年 | 3篇 |
1968年 | 7篇 |
1967年 | 5篇 |
1966年 | 3篇 |
1964年 | 3篇 |
排序方式: 共有488条查询结果,搜索用时 125 毫秒
1.
激光光漂恢复技术测定了异硫氰基荧光素标记的林蛀卵表面分子在第一次卵裂前的运动。发现固着在玻片上的剥离“细胞膜”的分子运动形式为扩散。扩散系数为(4.6±1.3)×10~(-12)cm~2/s,可动部份为15%。完整卵子上的分子运动形式为流动。细胞膜在不停地流动着。它可能起着协助细胞质运动的作用。细胞膜流动的速度随时间而异,卵裂前不久,在大多数的卵子上,出现两个流动较慢的谷,少数细胞只测到一个谷。这可能与光漂起始时间,光斑与未来分裂沟的距离,和卵子间的差异有关。也讨论了这种速度变化与表面收缩波的关系。 相似文献
2.
3.
A more accurate method for measurement of tuberculocidal activity of disinfectants. 总被引:7,自引:3,他引:4 下载免费PDF全文
The current Association of Official Analytical Chemists method for testing tuberculocidal activity of disinfectants has been shown to be inaccurate and to have a high degree of variability. An alternate test method is proposed which is more accurate, more precise, and quantitative. A suspension of Mycobacterium bovis BCG was exposed to a variety of disinfectant chemicals and a kill curve was constructed from quantitative data. Data are presented that show the discrepancy between current claims, determined by the Association of Official Analytical Chemists method, of selected commercially available products and claims generated by the proposed method. The effects of different recovery media were examined. The data indicated that Mycobacteria 7H11 and Middlebrook 7H10 agars were equal in recovery of the different chemically treated cells, with Lowenstein-Jensen agar having approximately the same recovery rate but requiring incubation for up to 3 weeks longer for countability. The kill curves generated for several different chemicals were reproducible, as indicated by the standard deviations of the slopes and intercepts of the linear regression curves. 相似文献
4.
电刺激大鼠延髓头端腹外侧区对交感节前神经元单位放电的影响 总被引:1,自引:0,他引:1
本实验用氨基甲酸乙酯麻醉和箭毒化的雄性大鼠,细胞外记录脊髓胸2节段的交感节前神经元(SPN)单位放电,电刺激同侧颈交感干,逆向激活 SPN,以确定所记录的神经元为交感节前神经元。共分析了80个 SPN 单位放电,其中有自发活动和无自发活动的单位各40个。SPN 轴突传导速度为0.59—3.75m/s。实验观察到电刺激同侧延髓头端腹外侧区(Rostralventrolateral medulla:RVL)可兴奋多数有自发活动的 SPN(19/25),并可使少数静止SPN 产生诱发反应(4/23),潜伏期为6—115ms。电刺激对侧 RVL 结果类似:多数自发活动的 SPN(6/9)呈兴奋反应,及少数静止 SPN(3/17)产生诱发反应,潜伏期为11—105ms。表明 RVL 对双侧 SPN 有兴奋性影响。 相似文献
5.
Abstract Photosynthetic metabolism was investigated in leaves of five species of Flaveria (Asteraceac), all previously considered to be C4 plants. Leaves were exposed to 14CO2 for different intervals up to 16s. Extrapolation of 14C-product curves to zero time indicated that only F. trinervia and F.bidentis assimilated atmospheric CO2 exclusively through phosphoenolpyruvate carboxylase. The proportion of direct fixation of 14CO2 by ribulose-I, 5-bisphosphate carboxylase/oxygenase (Rubisco) ranged from 5 to 10% in leaves of F. australasica. F. palmeri and F. vaginata. Protoplasts of leaf mesophyll and bundle sheath cells were utilized to examine the intercellular compartmentation of principal photosynthetic enzymes. Leaves of F. australasica, F. palmeri and F. vaginata contained 5 to 7% of the leaf's Rubisco activity in the mesophyll cells, while leaves of F. trinervia and F. bidentis contained at most 0.2 to 0.8% of such activity in their mesophyll cells. Thus, F. trinervia and F. bidentis have the complete C4 syndrome, while F. australasica, F. palmeri and F. vaginata are less advanced, C4-like species. 相似文献
6.
7.
Effect of amino acid substitutions and deletions on the thermal stability, the pH stability and unfolding by urea of bovine calbindin D9k 总被引:3,自引:0,他引:3
B Wendt T Hofmann S R Martin P Bayley P Brodin T Grundstr?m E Thulin S Linse S Forsén 《European journal of biochemistry》1988,175(3):439-445
The influence of amino acid substitutions and deletions on the stability of bovine calbindin D9k, the smallest protein known with a pair of EF-hand calcium-binding sites, has been studied using circular dichroism and ultraviolet absorption spectroscopy. The five modifications are confined to one of the two Ca2+ -binding sites. The Ca2+-loaded forms of the wild-type and mutant calbindins are too stable to be significantly denatured by heating at 90 degrees C or by adding 8 M urea. For the Ca2+-free (apo) forms thermal unfolding appears to be only half complete at 90 degrees C, while denaturation is complete in 7-8 M urea. Four of the mutant proteins show reduced resistance towards unfolding by urea, but one of the modified proteins (Glu-17----Gln) shows an increased stability, presumably because of a reduced electrostatic repulsion in the native state. According to X-ray crystallographic data the OH group of the single tyrosine of calbindin (Tyr-13) is hydrogen-bonded to the carboxyl group of Glu-35, thus linking the two alpha helices flanking the N-terminal Ca2+ site. The pK of ionization of the Tyr-13 hydroxyl group was over 13 for calcium forms of the wild-type protein, between 12.3 and 12.8 for the calcium form of three mutants and between 11.5 and 11.7 for the apoproteins. Significant differences in pH stability between wild type and mutants were observed in the calcium forms, but were not apparent in the apo forms. 相似文献
8.
Saturation transfer EPR spectroscopy on spin-labeled muscle fibers using a loop-gap resonator. 下载免费PDF全文
Previously, saturation transfer (ST-EPR) studies of biomolecular dynamics have involved the use of a resonant cavity and the V'2 display (absorption, second harmonic, out of phase). In the present study, we replaced the resonant cavity with a loop-gap resonator and used the U'1 display (dispersion, first harmonic, out of phase) to study spin-labeled muscle fibers. The new resonator and display showed several advantages over those previously used. It produced virtually noiseless U'1 spectra on a 0.4 microliter sample using a 4 min scan; previous U'1 experiments on spin-labeled muscle, using a conventional rectangular cavity, resulted in an unacceptably low signal-to-noise ratio. The high filling factor of the resonator facilitated the study of these extremely small fiber bundles and permitted high microwave field intensities to be achieved at much lower incident microwave power levels, thus greatly enhancing the signal-to-noise ratio in U'1 experiments. This reduction in the noise level made it possible to benefit from the other advantages of U'1 over V'2, such as stronger signals, simpler line shapes, and simpler data analysis. For these muscle fiber samples, the resulting sensitivity (signal/noise/sample volume) of the U'1 signals was greater than 100 times that of V'2 signals obtained in a conventional cavity. Another advantage of the U'1 display is that signals from weakly immobilized probes, i.e., probes that have nanosecond rotational mobility relative to the labeled protein (myosin), are greatly suppressed relative to strongly immobilized probes. This reduces the ambiguity of spectral analysis, and eliminates the need for chemical treatments [e.g., using K3Fe(CN)6] that were previously required in muscle fibers and other systems. Further suppression of this weakly immobilized component was achieved in U'1 spectra by increasing the microwave power and decreasing the field modulation frequency. 相似文献
9.
Zusammenfassung Die NADH-Diaphorase wurde an 725 gesunden Probanden mit Hilfe der Stärkegelelektrophorese untersucht. Zwei verschiedene Varianten wurden beobachtet: eine heterozygot schnelle (DIA 2-1) und eine heterozygot langsame (DIA 3-1). Die Genhäufigkeiten sind: DIA2=0,0021; DIA3=0,0007.
Mit Unterstützung durch die Deutsche Forschungsgemeinschaft. 相似文献
Genetically determined variants of NADH-diaphorase
Summary By means of starchgel-electrophoresis a screening for variants of NADH-Diaphorase was carried out within a sample of 725 healthy probands. Two kinds of genetically determined variants have been observed: a heterozygous phenotype with greater mobility (DIA 2-1) and a heterozygous phenotype with slower mobility (DIA 3-1). The gene-frequencies are estimated so far as 0.0021 (DIA2) and 0.0007 (DIA3).
Mit Unterstützung durch die Deutsche Forschungsgemeinschaft. 相似文献
10.
Summary In 214 healthy young Germans the activity of Pyruvatekinase from red blood cells has been determined. Three persons had values in the heterozygote range between 10.0 and 20.0 U. Suggesting a 2-allele-model the frequency of the three phenotypes in the German population can be calculated as followed: PK(A)=98.6%, PK(AB)=1.4%, PK(B)=0.005%.No correlation could be found between the distribution of blood-and serum-groups and the enzyme-activity.
Direktor: Prof. Dr. med. G. W. Löhr
Direktor: Prof. Dr. med. G. G. Wendt
Mit dankenswerter Unterstützung durch die Deutsche Volkswagen-Stiftung.
Herrn Professor Dr.H. E. Bock, Tübingen, zum 65. Geburtstag gewidmet. Wesentliche Teile dieser Arbeit werden von Olaf Praetsch der Medizinischen Fakultät als Dissertation vorgelegt. 相似文献
Direktor: Prof. Dr. med. G. W. Löhr
Direktor: Prof. Dr. med. G. G. Wendt
Mit dankenswerter Unterstützung durch die Deutsche Volkswagen-Stiftung.
Herrn Professor Dr.H. E. Bock, Tübingen, zum 65. Geburtstag gewidmet. Wesentliche Teile dieser Arbeit werden von Olaf Praetsch der Medizinischen Fakultät als Dissertation vorgelegt. 相似文献