全文获取类型
收费全文 | 485篇 |
免费 | 81篇 |
出版年
2021年 | 7篇 |
2020年 | 4篇 |
2019年 | 10篇 |
2018年 | 6篇 |
2017年 | 7篇 |
2016年 | 9篇 |
2015年 | 14篇 |
2014年 | 8篇 |
2013年 | 17篇 |
2012年 | 21篇 |
2011年 | 14篇 |
2010年 | 16篇 |
2009年 | 11篇 |
2008年 | 21篇 |
2007年 | 18篇 |
2006年 | 16篇 |
2005年 | 21篇 |
2004年 | 12篇 |
2003年 | 16篇 |
2002年 | 23篇 |
2001年 | 16篇 |
2000年 | 25篇 |
1999年 | 17篇 |
1998年 | 10篇 |
1997年 | 7篇 |
1995年 | 9篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 10篇 |
1991年 | 13篇 |
1990年 | 11篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 17篇 |
1986年 | 14篇 |
1985年 | 13篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1972年 | 9篇 |
1971年 | 6篇 |
1969年 | 6篇 |
1967年 | 3篇 |
1941年 | 3篇 |
1929年 | 3篇 |
排序方式: 共有566条查询结果,搜索用时 15 毫秒
521.
1. Static titrations reveal an exact stoicheiometry between various haem derivatives and apoperoxidase prepared from one isoenzyme of the horseradish enzyme. 2. Carbon monoxide-protohaem reacts rapidly with apoperoxidase and the kinetics can be accounted for by a mechanism already applied to the reaction of carbon monoxide-haem derivatives with apomyoglobin and apohaemoglobin. 3. According to this mechanism a complex is formed first whose combination and dissociation velocity constants are 5x10(8)m(-1)sec.(-1) and 10(3)sec.(-1) at pH9.1 and 20 degrees . The complex is converted into carbon monoxide-haemoprotein in a first-order process with a rate constant of 235sec.(-1) for peroxidase and 364sec.(-1) for myoglobin at pH9.1 and 20 degrees . 4. The effects of pH and temperature were examined. The activation energy for the process of complex-isomerization is about 13kcal./mole. 5. The similarity in the kinetics of the reactions of carbon monoxide-haem with apoperoxidase and with apomyoglobin suggests structural similarities at the haem-binding sites of the two proteins. 相似文献
522.
523.
524.
The sensitivity of female rats to the organizational effects of postnatal androgen was examined after néonatal manipulations known to affect the rate of brain development: thyroxine (T4) administration and handling at birth. Testosterone propionate (TP) was injected subcutaneously in oil on postnatal day 6 to littermates that (i) had been undisturbed at birth; (ii) had received saline injections (S) and associated handling (H) on the day of birth (postnatal day 1) and the following day; and (iii) had received T4 in saline (1 μg/g body wt) and H on postnatal days 1 and 2. Estrous cycles at 45 and 90 days of age, ovulation at Day 100 and sexual receptivity (lordosis score) at Days 115 and 125 were used to evaluate changes in TP effects. The majority of animals treated with 100 μg TP on postnatal day 6 exhibited persistent estrus (PE) at 45 and 90 days of age as expected. Neither T4 nor S pretreatment on postnatal days 1 and 2 changed the incidence of PE. A reduction in ovarian weights and incidence of ovulation at 100 days of age supported cycle data in that only one out of 25 androgenized rats showed ovulation, compared with 16 of 22 controls. At approximately 115 days of age 2 μg of estradiol benzoate were administered for 3 days and 0.5 mg progesterone given on the 4th day 4 hr prior to placing females with sexually vigorous males. T4-TP females exhibited higher (< .01) median lordosis scores than their S-TP littermates. The latter results were replicated in a second test conducted 10 days later (p = .002). In addition, the second test indicated that the S-TP group had lower (p = .005) lordosis scores than littermates given only TP neonatally. The results of these studies demonstrate that pretreatment with T4 and handling, which are known, respectively, to hasten and retard the chronology of brain maturation, can exert differential effects on behavioral manifestations of postnatal TP without modifying androgen-induced sterility. 相似文献
525.
526.
A new procedure is described for acquiring measurements of electrocardiographic parameters in unrestrained crocodilians. These measurements are difficult to obtain in freely moving animals; hence, electrocardiographic activity under natural conditions has not been previously quantified. In this investigation, twelve American alligators were equipped with subcutaneous electrodes. The lead wires were sutured to each animal's skin and the extracutaneous wires coiled and held in place against the animals' dorsal surfaces with waterproof elastic bandages. The electrodes were connected to an ECG analyzer only at the time of measurement. The presence of the leads and harness did not appear to interfere with the movements of the animals either in the animal room or during testing. This method allows for more precise measurements of cardiac activity under conditions which closely resemble those of crocodilians in their natural state. 相似文献
527.
A rapid purification of bovine testicular hyaluronidase by chromatography on dermatan sulphate-substituted 1,6-diaminohexane--sepharose 4B. 总被引:1,自引:1,他引:0
下载免费PDF全文
![点击此处可从《The Biochemical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dimensionless apparent ionization constants of charged low-molecular-weight species may be obtained from paper-electrophoretic data at 20-25 degrees C with buffers (I0.1-0.5) of measured pH (1.5-12.5) containing oxalate ions. Relative mobilities rather than absolute mobilities were measured by using glycerol and m-nitrobenzenesulphonate respectively as standards of zero and unit mobility. Application of the procedure to ionizations of adenine, adenosine, 2'-deoxyadenosine, 3'-deoxyadenosine, 3':5'-cyclic AMP, ADP, ADP-glucose-agrocin 84 and ATP is described. 相似文献
528.
529.
Abstract
Ferulic and syringic acids are methoxylated aromatic compounds that often serve as models of the subunits of lignin. Although
these compounds have important implications for global carbon cycles, there is limited information on their fate in anoxic
environments. Enrichment cultures were established on these two model compounds under methanogenic, sulfidogenic, and denitrifying
conditions, using a Raritan River (New Jersey) marsh sediment as the inoculum. All cultures completely degraded ∼1.5 mm of both substrates. Methane production in the methanogenic cultures corresponded to the stoichiometric values expected for
complete mineralization to CO2 and CH4. Sulfate and nitrate reduction in their respective cultures were both greater than 60% of the amounts predicted for complete
mineralization. Aromatic intermediates of ferulic and syringic acid metabolism were identified, and pathways of degradation
under sulfidogenic and denitrifying conditions are proposed. Syringic acid is sequentially O-demethylated to gallic acid under
both sulfate and nitrate-reducing conditions before ring cleavage occurs. Ferulic acid undergoes propenoate side chain reduction,
O-demethylation, removal of an acetate moiety from the side chain, and decarboxylation to form catechol. Catechol is further
degraded under sulfidogenic conditions. Under denitrifying conditions, ferulic acid undergoes loss of an acetate moiety, prior
to O-demethylation, to form protocatechuic acid, the last product detected before ring cleavage.
Received: 23 February 1996; Revised: 20 May 1996; Accepted: 24 May 1996 相似文献
530.